Knee biomechanics


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Knee joint biomechanics

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Knee biomechanics

  2. 2. Sreeraj S R KNEE JOINT
  3. 3. Sreeraj S R INTRODUCTION FUNCTIONS OF KNEE ARE: 1. Provide mobility 2. Support body during Dynamic & Static activities. 3. In closed K chain it works with hip & ankle joints to support body wt. in static erect posture. 4. Dynamically, support during sitting & squatting activities and transferring body wt. during locomotor activities. 5. In open K chain knee provides mobility for foot in space.
  4. 4. Sreeraj S R ARTICULATIONS Knee complex composed of 2 articulations within a single capsule: 1. The tibiofemoral joint 2. The patellofemoral joint
  5. 5. Sreeraj S R TIBIOFEMORAL JOINT 1. Is a double condyloid joint with medial & lateral articular surfaces. 2. Flexion and Extension occur in sagittal plane around a coronal axis. 3. Medial & Lateral rotation occur in transverse plane & vertical axis.
  6. 6. Sreeraj S R FEMORAL ARTICULAR SURFACE Medial & Lateral femoral condyles forms proximal articular surface. Patellar groove.
  7. 7. Sreeraj S R TIBIAL ARTICULAR SURFACE This corresponds to femoral articular surface. They are 2 concave medial and lateral asymmetrical plateaus. Medial condyle is 50% larger than lateral condyle.
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  9. 9. Sreeraj S R MENISCI Two asymmetrical fibro cartilaginous joint disks called MENISCI are located on tibial condyles that enhances the congruence of knee joint. Med.Men. is semi circle. Lat.Men. is 4/5 of a ring. Both men. open towards intercondylar area. They are thick peripherally & thin centrally forming concavities.
  10. 10. Sreeraj S R MENISCI USES. 1. Increases joint congruence. 2. Distribute weight bearing forces. 3. Reduces friction between joints. 4. Serve as shock absorbers.
  11. 11. Sreeraj S R MENISCI ATTATCHMENTS: 1.Both Men. are attached to, Intercondylar tubercles of tibia. Tibial condyle via coronary lig. Patella via patellomeniscal & patellofemoral ligs. Transverse lig. ACL. 2.Med. Men. attached to, MCL. Semitendinous muscle. 3.Lat. Men. attached to, Ant. & Post. menisco femoral ligs. PCL. Popliteus muscle.
  12. 12. Sreeraj S R MENISCI OTHER FACTS Meniscal complex is well established in 8 weeks old embryo. Well vascularised in 1st yr. of life. Vascularity gradually reduces from 18 months to 18 yrs. Over age 50 only periphery is vascularised. The horns remain vascularised throughout life. Whole meniscal complex is well innervated. Innervation is denser in post. horns. May be due to greater load on post. horns. The meniscal innervation is a source of information about: 1. Joint position. 2. Movt. Direction. 3. Movt. Velocity. 4. Tissue formation.
  13. 13. Sreeraj S R TF ALLIGNMENT & WEIGHT BEARING FORCES Anatomical or Longitudinal axis of femur is oblique falling medially & inferiorly. Anatomical axis of tibia is almost vertical. These 2 lines forms an angle of 185-190° medially at the knee i.e. physiologic valgus angle. Mechanical axis of lower extremity falls from head of femur to sup. Surface of head of talus. This line passes through the knee joint in bilateral static stance giving equal forces to both the condyles. If the med.TF angle is more than 195˚(>165˚lat.) it is Genu Valgum or Knock Knee. If the med.TF angle is less than 180˚(<180˚ lat.) it is Genu Varum or Bow Legs.
  14. 14. Sreeraj S R TIBIOFEMORAL JOINT REACTION FORCE JRF reach 2-3 times body weight in normal gait. JRF reach 5-6 times B W in running, stair climbing etc. This time menisci assume 40-60% of imposed load. In the absence of menisci JRF doubles on femur & increase 6-7 times on tibial condyle.
  15. 15. Sreeraj S R KNEE JOINT CAPSULE Restrict various movts. To maintain joint integrity and normal joint function. ATTATCHMENTS Postly. :proximally to post. margins of femoral condyles and inter condylar notch. Distally to post.tibial condyle. Med. & Lat. :Prox. above femoral condyle & dist. margins of tibial condyle. Collateral ligs. reinforce sides of capsule. Antly. : Patella,Q’ceps muscle superiorly and patellar lig. inferiorly. Anterolaterally & anteromedially expansions from vastus med. & vastus lat. From patella to collateral ligs. And tibial condyles
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  17. 17. Sreeraj S R EXTENSOR RETINACULUM Anteromedial & anterolateral portions of capsule are known as Extensor retinaculum or medial & lateral patellar retinacula. Have 2 layers. Deeper and Superficial. Deeper longitudinal fibers connects capsule anteriorly to menisci and tibia via coronary ligs.This is known as patellomeniscal bands. Superficial transverse fibers blend with fibers of vastus medialis & lateralis and to post. tibial condyles. The transverse fibers connecting patella and femoral condyle are known as patellofemoral ligs.
  18. 18. Sreeraj S R SYNOVIAL LINING Most extensive and involved in the body. Anteriorly synovium adheres to inner wall of the joint. Posteriorly synovium invaginate anteriorly following the contour of femoral intercondylar notch & adheres to the ant. aspect and sides of ACL & PCL. Embryonically synovial lining is divided by septa into 3 compartments. • Superior PF compartment. • Medial TF compartment. • Lateral TF compartment.
  19. 19. Sreeraj S R SYNOVIUM (cont ) By 12 weeks of gestation synovial septa resorbed resulting in a single joint cavity. The superior compartment remain as a superior recess of capsule known as Suprapatellar bursa. Posteriorly the synovial lining may invaginate : • Laterally between popliteus muscle and lat. Femoral condyle. • Medially invaginate between semimembranosus tendon, med. head of gastrocnemius tendon and med. femoral condyle.
  20. 20. Sreeraj S R SYNOVIUM (cont ) PLICAE Synovial septa which are not resorbed into adulthood exist as folds or pleats of synovial tissue known as Plicae. They are composed of loose, pliant and elastic fibrous connective tissue. They easily passes back and forth over femoral condyles as the knee flexes and extends. Observed in 20 to 60% of population. Commonly known plicae are: 1. Inferior/Infrapatellar plica extends from ant. portion of intercondylar notch to infrapatellar fat pad. 2. Superior/Suprapatellar plica is located between suprapatellar bursa and knee joint. 3. Medial/ Mediopatellar plica arises from medial wall of retinaculum to infrapatellar fat pad. Plica can become irritated and inflamed, leads to pain, effusion and changes in joint structure and function.
  21. 21. Sreeraj S R KNEE JOINT LIGAMENTS The knee ligaments are credited with restricting and controlling: 1. Excessive knee motion 2. Varus and valgus stresses at knee 3. Anterior and posterior displacement of tibia beneath femur 4. Medial and lateral rotation of tibia beneath femur 5. Stabilization in anteroposterior displacements and rotations of tibia known as rotary stabilization.
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  25. 25. Sreeraj S R CRUCIATE LIGAMENTS
  26. 26. Sreeraj S R Anatomy of the ACL 3 strands Anterior medial tibia to posterior lateral femur Prevent anterior tibial displacement on femur Secondarily, prevents hyperextension, varus & valgus stresses
  27. 27. Sreeraj S R Biomechanics of the ACL Most injuries occur in Closed Kinetic Chain Least stress on ACL between 30-60 degrees of flexion Anteromedial bundle tight in flexion & extension Posterior lateral bundle tight only in extension
  28. 28. Sreeraj S R Posterior Cruciate Ligament Two bundles • Anteromedial, taut in flexion • Posterolateral, taut in extension Orientation prevents posterior motion of tibia PCL larger & stronger than ACL
  29. 29. Sreeraj S R PCL Biomechanics Functions: • Primary stabilizer of the knee against posterior movement of the tibia on the femur • Prevents flexion, extension, and hyperextension Taut at 30 degrees of flexion • posterior lateral fibers loose in early flexion
  30. 30. Sreeraj S R PCL Biomechanics PCL • Primary restraint to post. Displacement - 90% • relaxed in extension, tense in flexion • reinforced by Humphreys/ant. MF lig. or Wrisberg/post.MF lig. • restraint to varus /valgus force • resists rotation, especially int. rotn. of tibia on femur
  31. 31. Sreeraj S R KNEE JOINT MOTION Flexion/Extension The axis for these movements lies medially oblique through the joint This causes the tibia to move from a position slightly lateral to the femur in full extension to a position medial to the femur in full flexion Passive ROM 0-130˚ Normal gait on level ground needs 60˚ of flexion 80° for stair climbing 90° for sitting down on a chair Excessive knee hyper extension is termed as Genu recurvatum
  32. 32. Sreeraj S R ARTHROKINEMATICS flexion/extension Femur rolling & gliding at 25° Anterior glide is due to 1. Tension of ACL 2. The menisci Extension is reverse roll, spin and glide 1. Tension of PCL 2. menisci
  33. 33. Sreeraj S R LOCKING AND UNLOCKING DURING KNEE EXTENSION The tibia glides anteriorly on the femur. During the last 20 degrees of knee extension, anterior tibial glide persists on the tibia's medial condyle because its articular surface is longer in that dimension than the lateral condyle's. Prolonged anterior glide on the medial side produces external tibial rotation, the "screw- home" mechanism.
  34. 34. Sreeraj S R LOCKING AND UNLOCKING DURING KNEE FLEXION When the knee begins to flex from a position of full extension, posterior tibial glide begins first on the longer medial condyle. Between 0 deg. extension and 20 deg. of flexion, posterior glide on the medial side produces relative tibial internal rotation, a reversal of the screw-home mechanism. popliteus is the muscle that ‘unlocks’ the knee at the beginning of flexion of the fully extended knee. As the extended and locked knee prepares to flex (when beginning to descend into a squat position), the popliteus provides an external rotation torque to the femur that mechanically unlocks the knee. Since the knee is mechanically locked by a combo of extension and slight IR of the femur on a fixed tibia, unlocking the knee requires that the femur ER on the fixed tibia.
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  36. 36. Sreeraj S R KNEE JOINT MOTION Rotation: in 2 different ways Axial rotation : occurs around a longitudinal axis. Med. and lat. rotn. are possible. This occur in flexed position. Approximately 60-70° of active or passive ROM is possible Terminal or automatic rotation : associated with locking mechanism
  37. 37. Sreeraj S R ARTHROKINEMATICS Axial rotation Longitudinal axis for axis rotation lies at medial intercondylar tubercle i.e. med. Condyle act as pivot point while the lat. condyle move through a greater arc of motion When lat. and med. rotation of tibia occurs at knee joint When lat. and med. rotation of femur occurs at knee joint
  38. 38. Sreeraj S R Knee Muscles Knee Extension • Rectus Femoris • Vastus Medialis • Vastus Lateralis • Vastus Intermedius
  39. 39. Sreeraj S R Rectus Femoris Two-jointed, bipennate ACTIONS May contribute to lateral rotation and abduction of hip Extends knee and flexes hip EFFECTS OF WEAKNESS Decreases knee extension strength EFFECTS OF TIGHTNESS Limits knee flexion range of motion (ROM) with hip extended Hip abduction reduces stretch of rectus femoris.
  40. 40. Sreeraj S R Vastus Medialis Consists of longitudinal (vastus medialis longus [VML]) and oblique (vastus medialis oblique [VMO]) portions ACTIONS Knee extension Patellar stabilization Active with other heads throughout knee extension EFFECTS OF WEAKNESS Decreased knee extension strength Few data support the belief that specific vastus medialis weakness contributes to patellar tracking abnormalities. And, the VMO has been refuted to contribute to the last 15 deg of knee extension. EFFECTS OF TIGHTNESS With rest of quadriceps, limits knee flexion ROM
  41. 41. Sreeraj S R Vastus Lateralis Largest head of quadriceps in many individuals ACTIONS Knee extension EFFECTS OF WEAKNESS Significant weakness in knee extension EFFECTS OF TIGHTNESS Decreased knee flexion ROM May contribute to patellofemoral dysfunction
  42. 42. Sreeraj S R Vastus Intermedius Unipennate and deep ACTIONS Extends knee and pulls capsule proximally EFFECTS OF WEAKNESS Significant loss of knee extension strength 15- 40% of PCSA EFFECTS OF TIGHTNESS Decreased knee flexion ROM regardless of hip position
  43. 43. Sreeraj S R Knee Muscles Knee Flexion— •Biceps Femoris •Semitendinosous •Semimembranosus •Gastrocnemius •Plantaris
  44. 44. Sreeraj S R Hamstrings ACTIONS Knee flexion Active knee flexion without rotation requires simultaneous contraction of medial and lateral hamstrings. Contribute to knee joint stability Hip extension throughout ROM of hip May also adduct and rotate hip EFFECTS OF WEAKNESS Knee flexion weakness Larger impairment may be weakness of hip extension. EFFECTS OF TIGHTNESS Decreased knee extension ROM with the hip flexed May contribute to knee flexion contractures and posterior rotation of pelvis Considerable evidence from cadaver studies indicating that the hamstings muscles decrease the stress/strain on the ACL
  45. 45. Sreeraj S R Hamstring and Gait
  46. 46. Sreeraj S R Rotation of the Knee and hamstrings
  47. 47. Sreeraj S R Tightness of hamstrings can pull the pelvis into a posterior pelvic tilt, flattening the lumbar spine
  48. 48. Sreeraj S R Popliteus ACTIONS Small muscle Increased activity with combined knee flexion and medial rotation of tibia Medially rotates knee Adds stability to tibiofemoral joint EFFECTS OF WEAKNESS Difficult to determine Injured with extensive posterolateral ligamentous structures EFFECTS OF TIGHTNESS Difficult to discern but would contribute to knee flexion contractures
  49. 49. Sreeraj S R MEDIAL ROTATORS OF THE KNEE Sartorius and Gracilis, in addition to medial hamstrings and popliteus
  50. 50. Sreeraj S R Sartorius Strap muscle with very long muscle fibers ACTIONS Hip flexion with large moment arms to also abduct and laterally rotate hip Knee flexion Inactive with isolated medial rotation of knee EFFECTS OF WEAKNESS Isolated weakness may have little effect EFFECTS OF TIGHTNESS Small effect but may contribute to flexion contracture
  51. 51. Sreeraj S R Gracilis ACTIONS Medial rotation and flexion of knee Adduction of hip EFFECTS OF WEAKNESS No reports but may affect hip adduction and knee flexion and medial rotation strengths
  52. 52. Sreeraj S R Pes Anserinus Semitendinosus, sartorius, and gracilis attach to tibia by a common tendon on the anteromedial aspect of the tibia. They effectively stabilize the medial aspect of the knee.
  53. 53. Sreeraj S R LATERAL ROTATORS OF THE KNEE Tensor fasciae latae with lateral hamstrings
  54. 54. Sreeraj S R Tensor Fasciae Latae ACTIONS Flexes, abducts, and medially rotates hip Extends and laterally rotates knee Participates in gait with other abductors, perhaps to stabilize pelvis or progress pelvis over stance limb EFFECTS OF WEAKNESS Effects small, but reduced hip abduction, flexion, and medial rotation strength and decreased knee extension strength EFFECTS OF TIGHTNESS Decreased hip adduction and lateral rotation ROM Associated with knee and patellofemoral pain and dysfunction
  55. 55. Sreeraj S R Patellofemoral Joint Patella is a true sesamoid bone Posterior surface of the patella is covered with thick hyaline cartilage The patella slides within the trochlear groove Function of the patella • 1) Aids knee extension by producing anterior displacement of quadriceps tendon and lengthening the lever arm of the quad muscle force • 2) Allows wider distribution of compressive stress on the femur by increasing area of contact between patellar tendon and femur
  56. 56. Sreeraj S R PATELLAR MOVEMENTS In full extension the patella sits on ant. Surface of femur In flexion , the patella slides distally on the femoral condyles In full flexion the patella sinks into the intercondylar notch The patella in extended knee has little contact with femoral sulcus beneath it First contact made at 10-20° of flexion on inferior margin of patella By 90° flexion all patella got some contact except odd facet Above 90° odd facet gain contact At 125° flexion contact is on lateral facet
  57. 57. Sreeraj S R PMJ STABILITY PFJ is under control of two restricting mechanisms that cross each other at right angles 1. Transverse group of stabilizers 2. Longitudinal group of stabilizers In a so called patellar tracking both the transverse and Longitudinal structures will influence the medial and lateral positioning of the patella within the femoral sulcus Medial – lateral forces 1. Pull of VL is 12-15° lateral on long axis of femur 2. Pull of VM is 15-18° medial with 50-55° pulling of VMO
  58. 58. Sreeraj S R Q-Angle The Q-angle is the angle formed by a line from the anterior superior spine of the ilium to the middle of the patella and a line from the middle of the patella to the tibial tuberosity. Males typically have Q- angles between 10 to 14° Females between 15-17° A Q- angle of more than 20° or more is considered to be abnormal creating excessive lateral forces on the patella.
  59. 59. Sreeraj S R PF joint reaction forces The patella is pulled simultaneously by the quadriceps tendon superiorly and by the patella tendon inferiorly In normal full extension the patella is suspended between them Even a strong contraction of quadriceps produce no PF compression – Minimal quad forces are required during upright and relaxed standing (center of gravity almost directly above knee)
  60. 60. Sreeraj S R PF joint reaction forces As knee flexion increases, the center of gravity shifts posterior, increasing flexion moments required Knee flexion affects angle between patellar tendon force and quadriceps tendon force The total joint reaction force depends on 1. Magnitude of active or passive pull of quadriceps 2. Angle of knee flexion 10-15deg flexion: 50% of BW Increase flexion, increased muscle activity up to 3.3xBW Mechanical advantage is the biggest between 30-70deg flexion