Knee Injuries

Gross Anatomy of the Knee Joint and Common Acute Injuries Andrew Bonett University of South Florida M.S.M.S. Anatomy July 16, 2009

2 No joint in the body endures as much constant force and mechanical stress as the knee joint. And despite the strength required to support most of the weight of the body, the knee is still one of the most flexible of joints. However, the skeletal framework involved provides for a rather unstable joint and the knee is thus reliable on strong support from several ligaments and muscles. Consequently, the knee joint is one of the most common sites of orthopedic maladies, and is an especially vulnerable target for sports-related injuries. There are many, many different variations of knee-related injuries, but this paper will only discuss the acute and most common. These include patellar dislocation, meniscal tears, and sprains of the four major ligaments. Finally, current research in the orthopedic field, focusing on cruciate ligament reconstruction, will be discussed briefly. In order to understand the mechanisms of these injuries, though, the normal anatomy of the knee must first be appreciated. Gross Anatomy The knee is the largest synovial joint in the body and although it seems to act like a simple hinge joint, it is actually a little more complex. The knee can be thought of as two separate joints: the articulation that comprises the tibiofemoral condyloid joint and that of the patellofemoral interaction. As can be inferred from the names of the participating joints, the only bones included in the knee joint are the distal end of the femur, the proximal end of the tibia, and the patella. The femur and tibia are long bones that provide most of the structural support for the thigh and leg, respectively. The distal end of the femur has a medial and a lateral condyle separated by the intercondylar fossa posteriorly, and displays the patellar surface, sometimes called the trochlea, between the condyles anteriorly. The palpable medial condyle is the larger of the two, having a

3 greater area of articulation with the tibia. The lateral condyle is shorter when viewed anteriorly and has a long axis that runs nearly parallel to the sagittal plane, whereas the long axis of the medial condyle points about 22° anterolaterally from the sagittal plane. The posterior surfaces of the condyles, which articulate with the tibia when the knee is flexed, are round and allow smooth movement for varying degrees of flexion or extension. The inferior surface of the distal femur, on the other hand, is rather flat and contributes to the locking mechanism that alleviates some of the weight-bearing work required from thigh muscles to keep the joint fully extended when standing. Hyaline cartilage covers the patellar surface of the femur and continues inferiorly and posteriorly to cover most of the femoral condyles for articulation with the patella and tibia. The proximal end of the tibia is expanded as a “tibial plateau” that includes a medial and lateral condyle and an intercondylar eminence. The medial tibial condyle is larger and flatter than the lateral condyle, although both are slightly concave. Each condyle is covered superiorly by a fibrocartilaginous C-shaped structure called the meniscus that helps contour the rather incompatible joint structures. Both menisci have their attachments in the intercondylar region of the tibia and a ligament connects their anterior horns – the transverse ligament. The menisci are thicker around their peripheral borders, giving them a triangular appearance in cross-section, such as seen in MRI. A clinically significant characteristic of the menisci is that they only receive direct vascular nourishment from the inferior geniculate arteries in their peripheral 2-3 mm. This becomes considerably important when addressing tears of the meniscus and the approach to treatment because the avascular central meniscus will not heal on its own. The medial meniscus is more oval-shaped, whereas the lateral meniscus is more circular. Although

4 the medial skeletal structures are larger, it is actually the lateral meniscus that covers a larger portion of the articular surfaces. The lateral meniscus is also more mobile because it is not attached to the fibrous capsule of the joint, unlike the medial meniscus. The intercondylar eminence of the tibia has two tubercles that project superiorly between the femoral condyles and simply help prevent side-to-side movement of the joint when it is extended. The anterior face of the proximal tibia has a large protuberance called the tibial tuberosity, which provides attachment for the patellar ligament. In reality, the patellar ligament is simply an extension of the quadriceps femoris tendon in which a sesamoid bone called the patella develops. The patella is a small, round bone with a somewhat triangular shape that points inferiorly. Comprising half of the patellofemoral joint, the patella is located anterior to the distal end of the femur and is covered with hyaline cartilage on its posterior surface. Its posterior surface has a smaller medial facet and a larger lateral facet that make for a fitting articulation with the patellar surface of the femur. The patella changes the angle of the quadriceps tendon as it spans the knee joint in such a way that the distance between the tendon and the center of rotation of the joint is maximized. This allows for greater efficiency of the extensor muscles by the same principles that govern the simple pulley system. It also decreases friction and prolongs the effects of wear and tear on the tendon. Like all synovial joints, the knee has a highly vascular synovial membrane, which harbors synovial fluid that lubricates and nourishes the articulating surfaces. The synovial membrane attaches to the borders of the articular surfaces and menisci, has a posterior reflection to exclude the cruciate ligaments, and also has two extensions that act as bursae beneath two associated tendons. The suprapatellar bursa is a superior

5 expansion of the synovial cavity between the anterior surface of the distal femur and the tendon of the quadriceps femoris. The subpopliteal recess is a small, lateral expansion of the synovial cavity between the lateral meniscus and the intracapsular tendon of the popliteus muscle. Other bursae that do not communicate with the synovial cavity include the prepatellar bursa and the subcutaneous and deep infrapatellar bursae. The fibrous capsule encompasses the synovial membrane and the intercondylar region of the femur. It receives contributions from several muscles and ligaments, but it is outside the scope of this discussion to explore its individual components. The knee joint contains many strong ligaments that compensate for the lack of stability provided by the bony framework. Because of the joint’s dependence on these ligaments, they are commonly injured in athletes as a result of over-exertion or sudden trauma. The most essential ligaments of the knee are the patellar ligament, the two collateral ligaments and the two cruciate ligaments. The functional importance of the patellar ligament was previously discussed, but it also provides anterior support as it spans the joint and inserts on the tibial tuberosity. As in most hinge joints, collateral ligaments provide lateral stabilization and are the most external of the ligaments. The fibular (lateral) collateral ligament, or LCL, is attached to the lateral epicondyle of the femur, runs inferiorly outside of the fibrous capsule, and attaches just below the head of the fibula on its lateral surface. This ligament protects against adduction and hyperextension injuries. The tibial (medial) collateral ligament, or MCL, is attached to the medial epicondyle of the femur just inferior to the adductor tubercle, runs anteroinferiorly, and attaches to the medial condyle of the tibia just superior and posterior to the insertion of the pes anserinus. Because of its orientation, when the knee is

6 extended the anterior fibers are relaxed while the posterior fibers are stretched. As the knee flexes, the anterior fibers are stretched while the posterior fibers relax. A notable characteristic of the MCL that is of clinical importance is its attachment to the fibrous membrane and to the medial meniscus, which prevents posterior sliding of the medial meniscus during flexion. This ligament also protects against abduction and hyperextension injuries. The cruciate ligaments are intracapsular, yet extrasynovial, and provide both anteroposterior and rotational stability. The anterior cruciate ligament, commonly known as the ACL, runs posterolaterally from an anterior facet of the intercondylar area of the tibia to the posterior medial aspect of the lateral femoral condyle. It also shares some attachment with the medial meniscus, which is another important clinical characteristic. The ACL prevents posterior displacement of the femur relative to the tibia, excessive medial rotation of the tibia, and hyperextension. The posterior cruciate ligament, or PCL, is a thicker and stronger ligament and crosses the ACL medially. It attaches to the posterior part of the intercondylar area of the tibia and runs anteromedially to attach to the lateral aspect of the medial femoral condyle. The exact function of the PCL has long been debated, but it primarily prevents anterior displacement of the femur relative to the tibia, especially when the knee is flexed. It also checks excessive lateral rotation of the tibia and both hyperextension and hyperflexion of the knee. Numerous muscles cross the knee joint. These include most muscles from the anterior compartment of the thigh, all from the posterior thigh, one from the medial compartment of the thigh, three muscles from the posterior compartment of the leg, and even one tendon from the gluteal region. These muscles are mainly involved in flexion

7 and extension of the leg at the knee, while also providing stability and some rotational function. The quadriceps femoris muscles (vastus medialis, vastus lateralis, vastus intermedius, and rectus femoris) converge into the quadriceps femoris tendon that inserts on the patella and becomes the patellar ligament. They are the main extensors of the knee. The sartorius muscle crosses the knee medially, inserts just inferomedial to the tibial tuberosity, and aids in flexion. The gracilis muscle is the only muscle from the medial compartment of the thigh that is associated with the knee joint. It inserts into the tibia immediately posterior to the sartorius tendon and also aids in flexion. The hamstring muscles (biceps femoris, semimembranosus, and semitendinosus) are the main flexors of the leg at the knee. Both heads of the biceps femoris converge into one tendon that crosses the knee laterally, inserts into the head of the fibula, and contributes to the LCL and other ligaments. The biceps femoris also laterally rotates the leg at the knee when the knee is partly flexed. The other two hamstring muscles pass medially and thus medially rotate the leg at the partly flexed knee joint. The semimembranosus contributes greatly to the fibrous capsule and other ligaments, while the semitendinosus inserts into the tibia just posterior to the insertion of the gracilis. The tendons of the sartorius, gracilis, and semitendinosus muscles actually conjoin to form a common insertion known as the pes anserinus. From the gluteal region, part of the gluteus maximus and tensor fascia latae converge to form the iliotibial tract, which inserts into the lateral condyle of the tibia, contributes to the fibrous capsule, and provides lateral stabilization for the extended knee. The gastrocnemius and plantaris muscles are mainly involved in plantar flexion of the foot, but because they have origins just superior to the femoral condyles, they are also considered weak knee flexors. A deep muscle of the posterior leg, the

8 popliteus is unique both anatomically and functionally. The popliteus muscle is one of few in the entire body to penetrate the joint capsule. Inside the capsule, the tendon of the popliteus originates from the lateral femoral condyle and separates the lateral meniscus from the fibrous membrane before exiting and inserting into the tibia just superior to the soleal line. Contraction of this muscle laterally rotates the femur on the tibia, “unlocking” the knee and initiating flexion. The posterior, diamond-shaped area formed by the hamstring tendons and by each head of the gastrocnemius muscle is called the popliteal fossa. Its main contents are essential to communication between the thigh and leg and are clinically relevant regarding knee injuries. It contains the popliteal artery and vein and the primary branches of the sciatic nerve – the tibial nerve and the common fibular (peroneal) nerve. These structures give rise to the sural nerves, as well as the genicular, circumflex, and tibial arteries and are of considerable importance when treating an injury to the knee. One artery of particular significance is the middle genicular artery. Branching from the popliteal artery, it descends anterolaterally before piercing the posterior fibers of the joint capsule. Intra-articularly, it courses between the cruciate ligaments, running closely to the distal end of the posterior cruciate, as it gives off multiple branches that supply these two ligaments. Damage to these genicular and circumflex arteries, and especially to the popliteal artery, during surgery can be devastating. Fortunately, vascular injuries overall occur in less than 1% of arthroscopic procedures.

9 The Injured Knee The demanding forces exerted on the knee throughout life often lead to overuse injuries such as stress fractures, arthritis (synovitis), tendinitis and bursitis. However, acute injuries of the knee joint arising from sports or from an accident are often much more painful and severe. These types of injuries include dislocations or subluxations, sprains, strains, and fractures. A dislocation is complete displacement of the two articular surfaces of a joint, whereas subluxation is a partial displacement. As far as the knee is concerned, this type of injury is exclusive to the patellofemoral joint. The tearing of a ligament is known as a sprain, while damage to a muscle or its tendon is called a strain. Sprains and strains are both classified according to the severity of the injury. A minor tear of only a few fibers constitutes a 1st degree injury, whereas 3rd degree sprains or strains are characterized by a complete rupture. (These types of injuries can also be called Grade I, II, or III). As if the knee isn’t under enough stress during daily activities, participating in rigorous sports (especially football and soccer) is not the best way to maintain a healthy knee. Of all the clinical visits from patients claiming to have incurred a sports-related injury, almost 50% of them turn out to be related to the knee. Furthermore, when taking into account all injuries from all sports, either acute or chronic, both minor and severe, knee injuries represent 15%. Part of the reason for this high incidence is the wide range of injuries that a joint as complex as the knee can sustain. Patellar Dislocation Patellar dislocation refers to the complete displacement of the patella from the femoral trochlea to the lateral surface of the lateral femoral condyle. Individuals with

10 genu valgum (knock knees), weak quadriceps femoris muscles, or patellar hypermobility are predisposed to this injury. It commonly occurs in overweight individuals with genu valgum, as well as in athletes as a result of direct contact to the medial side or from external rotation of the tibia with forceful contraction of the quadriceps femoris, as in cutting off of a planted foot. Normally, extension does in fact move the patella laterally, but it is restrained by the lateral femoral condyle, the pull of the vastus medialis muscle, the medial patellar retinaculum, and fibers of other nearby ligaments. Consequently, patellar dislocations are almost always associated with a vastus medialis strain and rupture of the medial patellar retinaculum. When this injury occurs, a distinctive popping sound may be audible to other participants and the athlete is immediately disabled. The dislocation can often be reduced simply by extending the knee, but hemarthrosis causes major swelling within minutes. Diagnosis is obviously unmistakable if the patient presents with a persistent dislocation, but that is rarely the case. The patellar hypermobility/apprehension test is used to determine if a dislocated patella has been reduced. Sitting on the examination table, the physician places the patient’s knee over his thigh in a flexed position before placing both thumbs on the medial aspect of the patella. He then applies a lateral force to the patella and notes the degree of laxity. If the patient senses an impending subluxation of the patella, he or she shows extreme apprehension to the maneuver, which is why the test was aptly named. It is important to note that when performing specific tests such as this one, along with those yet to be discussed, they should first be conducted on the unaffected knee so as to provide a reference for comparison. After testing, X-rays may be taken to rule out an intra-articular fracture, as that is the only associated complication in which surgery is indicated. Aspiration of the

11 knee may temporarily relieve pain, but treatment is usually limited to ice, focal compression, immobilization, and rest. Surgery is only necessary to repair intra-articular fractures or tears of the medial patellar restraints. Rehabilitation exercises aimed at strengthening the vastus medialis muscle help prevent recurrent subluxations. Meniscus Injuries Meniscal injuries are extremely common because the menisci are responsible for much of the weight-bearing function of the knee and are regularly exposed to a great deal of shear force. Because of the magnitude of stress placed on the menisci, and their semi- vascular nature, the cartilage becomes increasingly brittle with age and the cause of injury may be acute, degenerative, or a combination of both. Thus, the high incidence of meniscal tears is widespread between athletes, overweight individuals, and the elderly. Regardless of the health of the meniscus, the only motions that can cause a tear are squatting or twisting of the knee joint. In acute injuries, especially in athletes, the flexed knee is suddenly twisted (internal tibial rotation for a medial meniscus tear) while the foot is fixed, and a multitude of injuries can occur. The “unhappy triad” is a term used to refer to simultaneous injury to the medial meniscus, medial collateral ligament, and anterior cruciate ligament as a result of sudden abduction and internal rotation of the knee. Therefore, when diagnosing an injury to one of these three structures, the clinician should be suspicious of the integrity of the other two. Tears of the menisci come in three main varieties – longitudinal, horizontal, and radial. A horizontal tear is the most common and is usually considered degenerative in nature, often being associated with osteoarthritis. It can be thought of as a tear in the transverse plane of the meniscus. In most cases, a horizontal tear is initially within the substance of the meniscus, not causing

12 any mechanical disturbance, and is not apparent on the surface. However, it can easily progress to reach the surface, more often forming an inferior flap that may move into the intercondylar area and cause locking of the knee. Longitudinal and radial tears are more associated with acute, traumatic injuries and are much more urgent and disabling. Because of the twisting shear force applied by the femoral condyle during rotation of the knee, longitudinal tears are vertically oriented but divide the meniscus obliquely downwards and centrally in cross section. Initially, they are usually restricted to the posterior horn of the meniscus as a partial tear. A complete longitudinal tear is one that progresses to the anterior horn of the meniscus more anteriorly than the cruciate ligament. If the inner segment of the torn meniscus becomes permanently displaced toward the center of the joint, the condition is colloquially referred to as the bucket handle tear. This type of tear is much more likely to cause locking and full extension can only be achieved at the expense of the ACL. Radial tears are also vertical and trauma-related, but are oriented in the coronal plane of the meniscus and arise from the internal, concave surface. This type of injury immediately creates a free-moving flap that can fold upon itself and cause locking and discomfort. Medial Meniscus As previously mentioned the medial meniscus is attached to the fibrous capsule and MCL, is less mobile due to its further-apart attachments, and is slightly thinner in its periphery as the lateral meniscus. All of these traits account for the higher incidence of medial meniscus tears. Acute injury to the medial meniscus is caused by internal rotation of the tibia while the knee is in the flexed position. In the clinic, there are many different methods that can be utilized to produce an accurate diagnosis. Generally, if the patient

13 presents with tenderness among the medial joint line upon palpation, it is more likely due to a chronic lesion because of effusion. However, palpation is seldom sufficient for diagnosing knee injuries. Specific tests provide the physician with valuable information before imaging is necessary. The most popular test conducted to rule out meniscal tears is called McMurray’s test. This test requires the patient to be lying down in the supine position with the troublesome knee flexed but relaxed. With the knee maximally flexed, the physician externally rotates the foot and extends the knee toward full extension while palpating the medial joint line. A positive McMurray’s test is a painful clicking sound produced during extension as the medial femoral condyle passes over the lesion. A similar test is Apley’s compression test, or the Apley grind test, which can be helpful in differentiating between meniscal tears and other internal knee injuries. Here, the patient lies in a prone position with the knee flexed at 90 degrees. The physician again externally rotates the tibia, but now applies axial pressure to the sole of the foot while flexing and extending the knee. A positive Apley test produces the same results as McMurray’s test. Although the physician can usually make a correct diagnosis with these tests, an MRI can almost always confirm the lesion. A healthy meniscus shows up as a solid black triangle in MRI imaging and any white interruption in that triangle depicts a meniscal tear. In fact, MRI has a sensitivity of at least 94% in respect to medial meniscus tears. If for any reason there is still doubt concerning the nature of the injury, diagnostic arthroscopy is the definitive method of identifying a tear. Small tears eliciting only minor pain and effusion may be treated with the basic “PRICES” regimen (Protection, Rest, Ice, Compression, Elevation, and Support) followed by rehabilitation, but only if there is no ligamentous instability. However,

14 treatment usually includes an arthroscopic partial meniscectomy and is the preferred approach. Longitudinal tears involving the peripheral vascular part of the meniscus used to mean a complete excision of the meniscus, but are now treated with arthroscopic meniscal repair. In fact, before modern imaging technology, total excision was the preferred treatment for all meniscal tears because the menisci were thought of as mere space fillers and diagnosis of multiple tears was nearly impossible. Partial meniscectomy is most successfully performed on bucket handle tears and radial tears, with the goal in both cases being to remove the locking agent that may also cause degeneration of the articular surfaces if left untreated. For a bucket handle tear, the centrally displaced portion of the meniscus is simply excised and what is left of the peripheral meniscus remains. When treating a radial tear, the flaps are eliminated by shaving off a smooth, rounded curve that includes the lesion. The post-operative meniscus should look similar in shape, but maybe with a more pronounced recess on the concave surface. Lateral Meniscus Injury to the lateral meniscus has a lower incidence due to its greater mobility, thicker and more uniform composition, and lack of attachment to the fibrous capsule. The lateral meniscus is vulnerable to the same types of tears as those suffered by the medial meniscus, but some conditions more typically involve the former and can sometimes be more painful. Because the anterior horn of the lateral meniscus is more posterior than that of the medial meniscus, it is not as rare for a tear to be limited to the anterior horn. Also, the lateral meniscus is more prone to a rare, congenital variation known as a discoid meniscus, in which the meniscus is a full disc of cartilage rather than semilunar and there is no articulation between the lateral femoral condyle and the tibia.

15 Because of its congenital nature, the discoid meniscus is present during childhood, but is often asymptomatic until well into adulthood. Discoid lateral menisci only affect 1.5 – 3% of the population, while discoid medial menisci only develop in 0.1 – 0.3% of the general population. A discoid meniscus is much more vulnerable to lesions and cystic degeneration even despite the normal mechanism of a meniscal tear. Finally, the lateral meniscus is more likely to incur a vertical radial, or parrot beak tear. This type of tear can actually start out as two separate horizontal cleavages that connect and eventually incorporate the superior and inferior surfaces of the meniscus. Therefore, it is essentially a compound vertical/horizontal tear with a curved inner portion. The greater thickness of the lateral meniscus facilitates this mechanism of rupture. The same diagnostic procedures are used with the lateral meniscus as are with the medial. The patient may experience tenderness along the lateral joint line upon palpation, and the same two tests are used. However, when conducting McMurray’s test and Apley’s compression test, this time the physician internally rotates the tibia during flexion and extension. Unfortunately, MRI imaging is considerably less effective in detecting lateral meniscus tears, with sensitivity being as low as 78%. There is no major difference in the preferred treatment approach for an acute tear of the lateral meniscus, with the exception of a discoid lateral meniscus. A discoid meniscus may be sculpted to resemble a normal lateral meniscus or a complete meniscectomy may be indicated for a hypermobile lateral meniscus. This subtype of discoid meniscus, also known as the Wrisberg type, lacks a posterior attachment to the tibia (only to the Wrisberg ligament), and is thus not effectively treated with a partial meniscectomy.

16 Ligament Injuries A simple balance of equilibrium between external and internal forces determines the integrity of the knee joint. Integrity is maintained when internal forces prevail, while exceeding external forces cause injury. Internal stabilizing forces of the knee joint come from three sources: active stabilization from muscles that cross the joint; and passive stabilization from the ligaments and the geometrical congruity of the joint itself. For example, a posteriorly directed external force applied to the anterior aspect of the joint would be countered by the flexors of the knee (along with the ligaments). Obviously the passive forces are biologically and anatomically limited, but fitness and muscle strength can contribute to a more stable joint. Nevertheless, sudden and unexpected external forces, often encountered in sports such as football, skiing, soccer, or rugby, eliminate the active component of stabilization. Since geometrical congruity of the joint is naturally lacking, most of the burden is placed on the ligaments and they often succumb, leaving the joint even more vulnerable to further injury. Diagnostic techniques are similar for evaluating all ligaments of the knee. The first step is one of the most important. Understanding the patient’s history and learning as much about the injury as can be recalled can already give the physician an idea of where to direct his focus. This is why it is crucial to have a strong appreciation for the mechanisms of these injuries. Specific laxity tests also provide valuable information and are usually done next. The most efficient imaging technique is MRI, but X-rays can sometimes supplement and help rule out associated fractures. If all else fails, the definitive diagnostic technique is arthroscopy, which is always the last resort.

17 Medial Collateral Ligament The medial collateral ligament, or MCL, is directly attached to the fibrous capsule and medial meniscus and provides the most vital support against valgus stresses. Thus, not only is it one of the most commonly sprained ligaments in athletics, but it also rarely presents as an isolated injury. As previously mentioned, MCL sprains constitute one- third of the “unhappy triad” seen by many a team physician. They can occur as a result of a noncontact, external rotation of the tibia (skiing), but it is usually a direct valgus, or abduction, force to the lateral knee that is the cause. Because of this, most injuries to the MCL are suffered by football players. These sprains, along with those of the succeeding ligaments, are classified as Grade I, Grade II, or Grade III according to their severity. Pain associated with the injury is well localized to the medial joint line, but often quickly subsides with a Grade III complete tear of the ligament. This is particularly dangerous in athletics because it encourages the participant to continue with a poorly stabilized knee. Often the most notable complaint by the patient is simply valgus laxity. Specific tests to be performed by the physician include the abduction stress test, performed with 30° of flexion and again with full extension, and the anterior drawer test with external rotation of the tibia. The abduction stress test is performed with the patient lying in the supine position and the physician supporting the thigh and knee so as to create some flexion (about 30°) while keeping all of the muscles relaxed. This is sometimes easier when the thigh is supported by the examination table and the leg slightly hangs over the edge. With his elbow on the medial side of the patient’s foot, he applies a valgus force to the knee with his opposite hand and palpates the medial joint line for abnormal instability. Excessive flexibility or elicited pain are positive signs and

18 indicate an MCL sprain. The test is then performed with the knee in full extension to rule out an associated sprain of the posterior cruciate ligament. The anterior drawer test is primarily used to check the integrity of the anterior cruciate ligament and will be discussed in detail later with the corresponding injury. A variation of this test, however, can help diagnose a tear of the medial collateral ligament when it is performed with the tibia externally rotated 30°. Excessive anterior rotation of the medial tibial condyle constitutes a positive sign for this test. X-rays are not too practical for diagnosing a ligament tear, although they may be taken in the abduction stress position if the patient is of young age to rule out an epiphyseal fracture. If the MCL is compromised, the X-ray will show an enlarged medial joint cavity with excessive distance between the medial condyles of the femur and tibia. An anteroposterior MRI taken in the coronal plane is the best way to view the collateral ligaments. A normal MCL is depicted as a thin, taut, low- signal (black) structure that is tightly adhered to the medial femoral epicondyle and medial tibial metaphysis. Grade I tears show a less than well-defined MCL caused by some surrounding intermediate signaling, which is indicative of edema. Grade II tears show a seemingly thicker ligament with even more intermediate signaling, also due to edema, but with possible accompanying hemorrhage. The ligament also appears “looser” and is not as tightly bound to the bones. Grade III tears are quite remarkable with severe edema and are difficult to misdiagnose. Treatment of a torn medial collateral ligament is completely dependent on the severity of the injury and whether it is isolated. Isolated injuries rarely call for surgical intervention, except for some grade III tears, whereas compound injuries usually require surgery. Isolated grade I and II tears are treated with the basic “PRICES” remedy that is

19 also used for minor meniscal tears, along with the use of crutches for the first ten days. Grade III tears are often repaired surgically, although immobilization with a knee brace has proven to be sufficient in isolated cases. Unfortunately, a full recovery from a grade III MCL sprain can sometimes take three to four months. Rehabilitation is a vital component of the treatment plan for any ligament tear. Lateral Collateral Ligament Of the four major ligaments in the knee, the lateral collateral ligament (LCL) is sprained least frequently, and even less so as an isolated incident. There are two reasons for the rarity of this injury. First, the mechanism of injury is mainly adduction due to contact to the medial knee joint while it is flexed. Needless to say, it is rare for a force great enough to cause injury to be oriented in this direction. Other possible sources of varus stress include noncontact incidences such as landing from a jump off balance or unexpectedly stepping into a hole. Secondly, the tendons of the biceps femoris, popliteus muscle, and iliotibial tract all aid the LCL in providing lateral stabilization. This accounts for the greater resistance of the knee against varus stress than against valgus stress, and is also why isolated LCL tears occur in the flexed knee. A violent blow to the medial aspect of the extended knee would most likely affect all of the aforementioned structures and, more devastatingly, may damage the common peroneal nerve. This nerve gives branches that innervate the lateral and anterior compartments of the leg, as well as some of the intrinsic muscles of the foot. Damage to it could result in permanent disabilities such as foot drop and loss of sensation from parts of the leg and foot. More commonly, the knee receives a violent blow from the anteromedial aspect, resulting in a posterolateral corner injury.

20 Patients may actually hear a popping sound during an acute injury and pain is well localized over the lateral joint line. A feeling of varus laxity or general instability may also be present, but not as apparently so as compared to a compromised MCL. The LCL is more easily palpated in a flexed knee than the MCL, but similar tests are still carried out during diagnosis. The adduction stress test parallels the abduction stress test that was discussed earlier, but is performed in the opposite manner. The external rotation recurvatum test is a rather simple test used to rule out a posterolateral corner injury. With the patient lying relaxed and in a supine position, the physician lifts both legs by holding on to only the great toes. Apparent recurvatum (hyperextension), external tibial rotation, and an assumed varus of the knee constitute a positive sign. These features may even be apparent upon standing when the tear is significant. The posterolateral drawer test is similar to the corresponding test for the MCL. The tibia is still externally rotated 30° on the knee while flexed at 90°, but this time posterior force is applied to the proximal tibia. Excessive posterior rotation of the lateral tibial condyle is a positive sign and also suggests a posterolateral corner injury. The fourth test, called the reverse pivot shift test, involves temporary subluxation of the lateral tibial condyle and is preferably performed under anesthesia for the sake of the patient. With the knee flexed to 90°, the tibia externally rotated, and a slight valgus force applied by the physician, the leg is slowly extended. For a positive test, the lateral tibial condyle subluxates posteriorly at around 30° of flexion and then forcibly reduces with further extension. MRI for diagnosing LCL tears has an accuracy rate of 90%, but is a little more difficult than with the MCL. The LCL courses slightly posterior on its way to the head of the fibula, making it impossible to view in its entirety on a truly coronal scan. A coronal oblique scan may reveal the

21 entire LCL, but lateral scans in the sagittal plane are necessary to accurately diagnose a tear. A sagittal scan is also vital because it shows the fibular head and the common insertion of the tendon of the biceps femoris. It is important not to neglect these structures because fibular fractures and avulsions of the associated tendons frequently occur in conjunction with LCL injuries. When examining the images, a torn LCL has different characteristics than a torn MCL because of its completely extracapsular nature. Never appearing to be enlarged, an acutely torn LCL appears to be less taut and often discontinuous. Chronic tears do have a thickened appearance with more low weight signaling. Although the lateral collateral ligament does not heal as easily as the medial, there are no remarkable differences in the treatment of grade I or II tears. Grade III sprains almost always require surgery, especially because they are almost never isolated. In severe cases, when tendons need to be reconstructed by using a graft from either the quadriceps femoris or hamstring tendons, an open-knee procedure is necessary. Full recovery time for a grade III repair can be up to eight weeks. Anterior Cruciate Ligament The anterior cruciate ligament, or ACL, is the smallest and shortest ligament in the knee. However, what the ACL lacks in size it makes up for in function. It is the most crucial stabilizer of the knee, checking hyperextension, medial rotation of the tibia, posterior dislocation of the femur, and even hyperflexion in association with the PCL. It is able to provide all of this stability because of its composition and helical orientation - the anteromedial fibers are taut during flexion and mainly check anterior displacement,

22 while the posterolateral fibers are taut during extension and mainly control rotational stability. A sprain of the ACL may involve either or both of these fiber groups. Because of its imperative and diverse function, it is the most frequently injured ligament for athletes competing in basketball, football, soccer, skiing, gymnastics, etc. Another reason that most athletes are so vulnerable to ACL injuries is that an isolated sprain is seldom the result of contact. More commonly, sudden twisting movements, abrupt deceleration, or landing awkwardly from a jump causes problems for the ACL. Collision injuries usually affect the ACL in the event of an “unhappy triad” injury. An abduction injury cannot tear the ACL unaccompanied by a tear of the MCL. External rotation of the femur on a fixed tibia is the easiest way to cause an isolated tear. Posterior displacement of the femur when the knee is flexed can also single out the ACL because the collateral ligaments are more relaxed. Hyperextension is a threat to the posterolateral fibers of the ACL, but would also bring the collateral ligaments back into consideration. Depending on the mechanism of injury, a complete tear can occur at the tibial attachment (3-10%), at the femoral attachment (7-20%), or in the middle of the ligament (70%). In younger patients, the tibial spine may even be avulsed. The location of the lesion is significant because the middle portion of the ACL is relatively avascular, while the femoral end receives a branch from the middle geniculate artery, as does the synovial membrane. Although the common superior lesion causes more complications, any type of lesion is followed by relatively ineffective healing due to the extrasynovial nature of the ACL. When an ACL tear occurs, the individual can usually hear it pop or snap before the knee buckles and gives out. Swelling will likely follow along with possible dizziness,

23 sweating, or nausea. The intensity and duration of pain varies widely but is somewhat localized to the anterior knee. Next to MRI, specific physical tests are the most effective method for diagnosing ACL injuries. The classic ACL test is the anterior drawer test. With the knee flexed at 90° and no tibial rotation, and the hamstrings relaxed by the support of the physician, the proximal end of the tibia is gently pulled anteriorly. If there is excessive anterior displacement or no definite end point when compared to the uninjured knee, that is considered a positive test. However, severe ACL sprains associated with a negative anterior drawer test have been well documented because this technique does not eliminate the influence of other structures. Therefore, this test can be contributory, but is not sufficient. The most accurate of physical tests for an ACL injury is called the Lachman test. It is simply a variation of the anterior drawer test; the only difference being that the knee is flexed no more than 30°. Similarly to with the LCL, the pivot shift test or the jerk test may be conducted to supplement the Lachman test. The pivot shift test is performed with the patient supine and relaxed, the tibia internally rotated with the knee in full extension, and a slight valgus applied by abduction of the foot. As the knee is gradually flexed, the physician feels for an anterior subluxation of the lateral tibial condyle at around 30°. Upon further flexion, the subluxated tibia should suddenly reduce. The jerk test is basically the same test but performed backwards. The knee starts flexed at 90°, and the anterior subluxation and subsequent reduction should occur with gradual extension. MRI provides an accurate diagnosis in as many as 95% of ACL cases, but is not always necessary if the physician feels strongly enough about the results of the Lachman test. Although the ACL is ideally evaluated in slight flexion, imaging is done in full extension so as to include an accurate depiction of the menisci.

24 Because the course of the ACL is in three dimensions (from its attachment to the tibia it runs posteriorly, laterally, and superiorly), it is imaged in the coronal, sagittal, and axial planes. Axial imaging is especially helpful for examining the proximal ACL, where it normally shows up as a dark, low-signal eclipse on the medial side of the lateral femoral condyle. One primary sign of an acute ACL tear is actually not being able to see the ACL at all. In its place between the femoral condyles is a blurry, intermediate-signal mass of edema and hemorrhage. Other primary indications of a tear include a high-signal interruption, a nonlinear appearance, or an abnormal axis of the ligament in relation to the bony structures. Secondary indications, including osteochondral fractures, anterior displacement of the tibia, and Segond fractures, are not nearly as reliable. A Segond fracture is a vertical, elliptical avulsion fracture of the lateral tibial condyle caused by a combined varus force and internal tibial rotation. Segond fractures are accompanied by an ACL tear 75-100% of the time. Once again, arthroscopy eliminates any doubt but is preferably avoided. The treatment approach heavily depends on the presence of compound injuries, the patient’s activity level and age, and his willingness to pursue the proper physical therapy if surgery is indicated. Regardless of the severity of the sprain, the patient should use crutches and avoid all weight-bearing activities for the first week. For isolated partial tears, the “PRICES” regimen, along with functional rehabilitation and bracing of the slightly flexed knee, is often sufficient. Still, the ACL is extrasynovial and does not heal as efficiently as other ligaments. A full recovery could take as long as six months. Most acute tears suffered by active athletes cannot be repaired and require complete excision of the ligament followed by reconstructive surgery. It is now recommended that the surgery

25 be delayed about three weeks after the injury to allow the swelling to subside and a wider range of motion to return. Studies have shown that late reconstruction is associated with less post-operative stiffness and more favorable outcomes. A more in-depth look at cruciate ligament reconstruction will be discussed later. Posterior Cruciate Ligament The posterior cruciate ligament is broader and much stronger than the ACL, and is thus another one of the most important stabilizers of the knee joint. However, its precise mechanism of stabilization carries a history of uncertainty with it due to its unique structure. It has been demonstrated that the posterior fibers of the PCL are taut at both full extension and deep flexion, while the anterior fibers are most stressed during mid- flexion. While it is widely agreed upon that its primary function is to prevent posterior displacement of the tibia, its secondary functions include prevention of hyperextension and to a lesser extent lateral rotation and hyperflexion. Meniscofemoral ligaments (MFL) originate at the same site as the proximal PCL and are thoroughly integrated with it. They run parallel to the PCL and attach to the posterior horn of the lateral meniscus, countering the action of the popliteus muscle. The MFL are the last restraint against posterior displacement of the tibia when the PCL is completely ruptured. Injury to the PCL occurs much less frequently than to the ACL, and rarely so in isolation. The primary cause of an isolated PCL tear is a direct blow to the anterior face of the proximal tibia when the knee is flexed. This commonly occurs in automobile collisions when the knees strike the dashboard. In sports, hyperextension is the main source of PCL injury (especially in combination with valgus/varus forces), although this mechanism also renders other structures of the knee vulnerable. Another typical mechanism of injury

26 involves falling on the knee with the foot in plantar flexion so that the tibia strikes the ground first. Because PCL tears are so frequently associated with other injuries, minor tears are often overlooked and the incidence is probably much higher than that observed (anywhere between 3% and 20% of all knee injuries). Like the ACL, the proximal PCL receives vasculature from the medial genicular artery and is extrasynovial, hindering the natural healing process. However, the PCL does receive a better blood supply than the ACL and minor tears can heal without surgical intervention. Severe tears can lead to other associated injuries if not treated immediately. A grade III PCL tear may lead to a posterior tibial dislocation, which could endanger the tibial and peroneal nerves, although a posterolateral corner injury is more likely to damage the peroneal nerve. On occasion, thrombosis or transection of the popliteal artery may also occur. Symptoms associated with injury to the PCL parallel those for ACL injuries, except, of course, pain is localized posteriorly. Rupture of the PCL usually elicits a popping sound that is audible to the patient, followed by swelling, possible effusion or hemarthrosis, and a sense of posterior instability. An accurate diagnosis is critical for treating PCL tears because it is not uncommon for the patient to present with minimal pain and full range of motion. An easy clue during initial observation is a contusion on the anterior proximal tibia, suggesting the “dashboard injury” mechanism. The specific physical tests for PCL assessment are simple and straightforward. The posterior drawer test is much like the anterior drawer test, except that a posterior force is applied to the proximal tibia. The physician still looks for abnormal posterior excursion and a sharp endpoint to the displacement. It is crucial that the starting point of the tibia prior to applying the posterior force is in fact the neutral position. Otherwise, returning the tibia

27 to a neutral position from a posterior displacement may be misdiagnosed as a positive anterior drawer test. This exemplifies the importance in assessing the healthy knee first. Another simple test is called the posterior tibial sag test. With the patient in the same position (supine, hips flexed at 45°, knees flexed at 90°), the physician simply observes, from a lateral view, any posterior displacement of one tibial tuberosity in relation to the other. This test is often repeated with the hips flexed to 90° while the physician supports the legs by holding the ankles or feet. Positive signs for these tests are usually associated with the primary mechanism of injury previously discussed. A positive sag test in full extension indicates a compound injury. If the injury was sustained from a valgus or varus force to the completely extended knee, a positive sign may be seen when conducting the abduction or adduction stress test at full extension. Lateral view X-rays may reinforce the sag test results or reveal an avulsion of the tibial attachment in a severe sprain. Once again, the most effective method for diagnosing a PCL tear is MRI. Scans should be taken on all three axes, but the most sensitive plane is a sagittal oblique one that parallels the ligament. The PCL can be viewed in its entirety with one or two sagittal scans, but a coronal scan will only show a portion of it. The intact PCL also shows lower-signal intensity than the intact ACL because its fibers are more parallel and regularly organized. Indications of a tear are the same as with the ACL and are characterized by high-signal intensity interruptions. Treatment of PCL tears is an issue of much debate. It is generally agreed that isolated, partial tears can be treated with PRICES and rehabilitation, while avulsion fractures and compound sprains require surgical reconstruction. However, controversy exists for treating tears that fall within these two extremes. Surgery is avoided when at

28 all possible because the position of the PCL makes it difficult to access and there are additional risk factors associated with reconstruction, such as avascular necrosis of the medial femoral condyle. It is seldom recommended for a tear that is less severe than grade III. Regardless of the treatment approach taken, proper rehabilitation is crucial. Exercises are usually aimed at strengthening the quadriceps muscles because they provide an anterior drawer to the tibia and essentially compensate for a PCL of poor integrity. Prognosis is rather favorable for isolated tears because the inferior genicular arteries allow for successful revascularization. Cruciate Ligament Reconstruction Reconstruction of the cruciate ligaments involves complete excision of the injured ligament followed by replacement with a graft. The graft is normally taken from a tendon and inserted into holes drilled in the bones at the original insertion sites of the ligament before being anchored with screws. Amazingly, this can all be carried out arthroscopically. The ideal graft would have identical structural characteristics as the ligament, heal and incorporate itself with the insertion sites quickly, and be simple to harvest. However, the ideal graft does not exist and the source is therefore up to the surgeon. The patellar tendon, quadriceps tendon, and calcaneus tendon are commonly shaved to provide the graft for cruciate ligament reconstruction. There are also several advantages and disadvantages to using an allograft versus an autograft. An allograft is a tissue donated by another individual of the same species (usually a cadaver in this instance); while an autograft is tissue taken from another part of the same individual’s body. Allografts benefit the patient by requiring less operation time and causing less stiffness since the harvest is performed on another specimen. This also equates to

29 aesthetic advantages and no donor-site morbidity. On the other hand, using an allograft always carries the risk of disease transmission and an unfavorable immune response to the foreign tissue. An autograft might incorporate faster, but multiple studies indicate that allografts have the potential to become more “ligament-like” and can be nearly identical histologically after one year of incorporation. Once installed, the graft undergoes major biological modifications for at least one month before it is fully functional. At first the graft actually becomes inflamed and partially necrotic before undergoing revascularization. It then becomes repopulated with extrinsic fibroblasts while its collagenous structure is modified, and original donor fibroblasts are absent by about six weeks post-op. The type of graft with the most favorable long-term effects is a topic of many studies still today. Reconstruction of the anterior cruciate ligament may be achieved with several different types of grafts. Two widely used grafts that are commonly autogenic are the quadruple hamstrings tendon graft and the B-PT-B (bone- patellar tendon-bone) graft. The B-PT-B graft includes surgically avulsed fragments of the tibia and femur from the donor, keeping the insertion sites of the patellar tendon intact. This allows for bone-to- bone healing in contrast to tendon-to-bone healing and leads to a faster recovery. The quadruple hamstrings graft is two parts semitendinosus tendon and two parts gracilis tendon. Both of these reconstructive methods, however, utilize a “single-bundle” approach and involve replacing two fiber bundles (anteromedial and posterolateral) with only one (the tendinous graft essentially replaces only the AM bundle). Consequently, anterior cruciate ligaments reconstructed with a single bundle do not provide sufficient rotational stability to the knee joint and, in this aspect, are virtually ineffectual.

30 Currently, double-bundle reconstructions are more frequently performed and are better suited for full restoration of knee stability. In the double-bundle method, a combination of the former two procedures, a B-T-B graft serves to function as the anteromedial bundle and a semitendinosus graft (ST) mimics the posterolateral fibers of the ACL. The grafts share a common tibial insertion at the isometric point, the B-T-B is inserted at the femoral isometric point, and the ST is fed posteriorly and superiorly through the intercondylar region to the posterior face of the lateral femoral condyle. It is vital to note that in order to recreate the most physiologically accurate ACL, the B-T-B graft is fixed with the knee at 20° of flexion, while the ST graft is fixed at 90° of flexion. A retrospective study by Kubo et al. observed long-term integrity following full recovery of this procedure. Their findings showed no signs of resulting pain, limited range of motion, or instability in 14 out of 14 patients. Posterior cruciate ligament reconstruction is less common because, as previously mentioned, partial tears can heal without surgical intervention. When PCL reconstruction is indicated, allografts are more useful, especially since isolated ruptures are rare and there may be multiple ligaments to harvest. Also, because the PCL is a longer ligament than the ACL, common autografts (B-T-B and ST) are sometimes too short to reach the isometric points of PCL insertion. One major difference between ACL and PCL reconstructions is that, as far as current studies suggest, full PCL function and stability can actually be achieved by reconstructing only the anterolateral bundle. Lack of the posteromedial fibers causes no observed deficiencies in stability, but our poor understanding of the PCL’s exact functions might contribute to this conclusion. As with the ACL, a chief area of concern and recent study is the long-term efficacy of these

31 reconstructions and whether allografts or autografts should be the graft of choice. A study published just this year by Miyamoto et al. is the first to report a long-term, in vivo histological analysis of a PCL reconstruction 11 years after a calcaneus tendon allograft was used. Their results show hypervascularity and increased cellularity at the periphery of the graft, with hypovascularity and high collagen density in the core of the graft, nearly indistinguishable from a normal cruciate ligament. They conclude that an allograft used for PCL reconstruction has the ability to fully incorporate and withstand both degeneration and host rejection over extended periods of time. The future of knee ligament surgery surprisingly relies on advancements at the cellular and molecular levels of biology, with the primary objective being to improve healing and remodeling. There are several different methods for achieving this goal that are being researched today. Gene therapy involves either a viral or non-viral vector delivering a specific gene that encodes growth factors or antibiotics to a target tissue. One advantage of this method is that, depending on which gene is delivered, it can be used to target ligaments, cartilage, or bone. Another approach, called tissue engineering, aims at using cells such as mesenchymal stem cells to deliver the therapeutic genes and increase the production of growth factors. Regardless of which method is found to be the best, the general idea is to improve healing time, remodeling of the ligament insertion sites, and nerve and vasculature restoration via biological manufacture of growth factors, antibiotics, other cytokines, etc.

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33 Insall, John N., M.D., ed. Surgery of the Knee. New York: Churchill Livingstone, 1984. Kubo, Toshikazu, et al. “Anterior Cruciate Ligament Reconstruction Using the Double Bundle Method.” JOS 8.2 (Dec. 2000). 3 July 2009. 59-63. <http://www.josonline.org/PDF/v8i2p59.pdf>. Maquet, Paul G.J. Biomechanics of the Knee. 2nd ed. Berlin: Springer-Verlag, 1984. Miyamoto, Ryan G., et al. “Histologic Presentation of Achilles Allograft 11 Years After Its Use in Posterior Cruciate Ligament Reconstruction.” AJO 38.1 (Jan. 2009). 3 July 2009. E25-E27. <http://www.amjorthopedics.com/pdfs/038010025e.pdf>. Salaria, H., and R. Atkinson. “Anatomic Study of the Middle Genicular Artery.” JOS 16.1 (2008). 3 July 2009. 47-49. <http://www.josonline.org/pdf/v16i1p47.pdf>. Smillie, Ian S. Injuries of the Knee Joint. 5th ed. Constable, Edinburgh: Longman, 1978. Teitz, Carol C., M.D., ed. “UW Medicine Orthopaedics and Sports Medicine: Torn Meniscus – Torn Knee Cartilage Not Limited to Athletes or Sports.” 12 January 2005. 30 May 2009 <http://www.orthop.washington.edu/uw/tornmeniscustorn/tabID_3376/ItemID_16 1/Articles/Default.aspx>. Walsh, W. Michael, M.D., ed. “Knee Injuries.” The Team Physician’s Handbook. 2nd ed. Philadelphia: Hanley, 1997. 554-578. Williams, Arnold, F.R.C.R., F.R.C.S., and Roger Evans, F.R.C.P., and Paul D. Shirley, M.D., P.A. “The Knee.” Imaging of Sports Injuries. London: Saunders, 1989. 101-124.

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Knee Injuries Document Transcript