This document discusses radiological imaging of anterior knee pain. It notes that knee MRI is the gold standard for evaluating damage to anatomical structures like ligaments, tendons, meniscus and cartilage. Common causes of anterior knee pain discussed include patellar fractures, osteoarthritis, tendinitis, dislocations and cartilage defects. Specific conditions like osteochondritis dissecans, fat pad syndromes, and bipartite/multipartite patella are described. MRI features of various pathologies are shown through images to aid radiologists in diagnosis.

1. Radiological Imaging of Anterior knee pain.
Dr/ ABD ALLAH NAZEER. MD.

2. Anterior knee pain that originates at the front of the
knee joint is a common complaint. This disorder has
a profound economic and social impact as it affects
approximately 15-33% of young and active people.
The role of physical examination in making
differential diagnosis is rather limited since different
conditions cause similar symptoms. Knee MRI is
considered the gold standard in evaluating the
damage to the anatomical structures of the knee,
such as ligament or tendon rupture, meniscus or
cartilage injury. It is often the case that MRI findings
determine the therapy, therefore radiologists have to
know what to look for in knee MRI images.

3. Anterior knee pain is common with a variety
of causes including:
Patella fracture.
Osteoarthritis.
Inflammatory and depositional arthritis
Bursitis around the knee.
Patellofemoral maltracking.
Excessive lateral pressure syndrome (ELPS).
Patellar cartilage defect.
Patellofemoral chondromalacia.
Patellar tendinitis.
Medial plica.
Hoffa's disease.
iliotibial band friction syndrome.

4. Patellar fracture
A direct blow or increased tension in a quadriceps and patellar tendon can cause patellar
fracture. In most cases, a fracture line is transverse and passes between the middle and
inferior third. Usually, the diagnosis is made on x-ray images. An MRI scan is useful in
excluding ligamentous injury or in cases of suspected stress fracture. On MRI images stress
fracture appears as low intensity line surrounded by bone marrow edema.
Inferior third of patella fracture without dislocation.

5. On MRI image the fracture line (arrows) extends across patella
with bone edema in the surrounding marrow.

6. Osteochondral sleeve fracture in a pediatric patient. (A) Lateral plain film of a
patellar avulsion fracture of the inferior pole of the patella demonstrating a
superiorly displaced patella and a small bone fragment (arrow). Sagittal T1-
weighted (B) and sagittal gradient recalled echo (C) MR images demonstrating an
osteochondral fracture of high signal intensity with a small bone fragment (arrow).

7. Patellar dislocation
It is one of the most common causes of anterior knee pain in young
people. A high-riding patella and femoral trochlear dysplasia are the
major predisposing factors. It is often the case that a dislocated
patella reduces spontaneously without patient's awareness of the
fact. The following MRI features of patellar dislocation are noted:
Medial retinaculum and medial capsule injury/tear
Lateral femoral condyle contusion and osteochondral damage
Medial patellar facet contusion with or without cartilaginous lesion
Medial retinaculum tears occur at the attachment site to the femur
or along the medial margin of the patella and subsequently may
cause avulsion injuries. Cartilaginous lesions can result in the
formation of loose bodies in the joint space.

8. An axial T2-weighted fast-spin-echo magnetic resonance imaging scan illustrates a
eighteen year-old female sustaining a primary traumatic lateral dislocation of the
patella while jumping. Complete avulsion of the medial patellofemoral ligament from
its femoral insertion can be seen (arrow) (Figure 2A). The bone contusions (stars)
(Figure 2B) of the lateral femoral condyle and the medial patellar facet are noted.

9. Axial (a) PD FS and sagittal (b) T2 shows medial retinaculum avulsion fracture
with patellar edge fragment (asterisk), medial patellar facet contusion
and cartilaginous lesion (black arrows), lateral femoral condyle contusion
(open arrow), loose cartilaginous body in anterolateral joint space.

10. Lateral patellar tilt and subluxation(red arrow)
and acute chondral defect(yellow arrow).

11. X-ray and MRI after luxation of the patella. There is a fragment and bone bruise
at the medial surface of the patella and in the corresponding surface of the
lateral condyle of the femur. The medial retinaculum of the patella is disrupted.

12. Coronal PD FS (a, b) shows lateral femoral condyle contusion and osteochondral damage
(white arrow), loose cartilaginous body (black arrows) in antero-lateral joint space.

13. Chondromalacia is defined as softening and
degeneration of the articular hyaline cartilage. Overuse
and trauma cause damage to the cartilage which over
time leads to fissuring and partial loss of cartilage
thickness. Subsequently, patients with high grade
osteoarthritis sustain cartilage destruction with underlying
bone changes. Cartilaginous lesions are graded according
to the Outer bridge classification which is based on a
correlation between MRI and arthroscopic findings.
Although arthroscopy is a gold standard for the evaluation
of the severity of cartilage defects, new MRI sequences
(T2 mapping, DW, dGEMRIC, T1rho,) allow early diagnosis,
contribute to preoperative planning and postoperative
follow-up.

14. Cartilage lesions on T2 images: a- focal area of hyperintensity with normal
contour; b- fragmentation of cartilage; c- partial thickness cartilage loss with focal
ulceration; d- full thickness cartilage loss with underlying bone reactive changes.

15. Chondromalacia patellae grades II–IV in various patients. (A) Axial fast spin echo
proton density fat saturated (FSE PD FS) MR image of chondromalacia patellae
grade II in a 46-year-old male. High signal is seen in the patellar cartilage in the
lateral patellar facet (arrows). (B) Axial FSE PD FS MR image of chondromalacia
patellae grade III in a 51-year-old female. There is full thickness focal signal intensity
change, contour irregularity and thinning of the cartilage (arrows). (C) Axial PD

16. Cartilage T2 mapping allows to evaluate the articular
cartilage of the knee joint. Red color shows cartilage lesion.

17. Patellar Abnormality.
-Bipartite patella.
-Multipartite patella.

18. Types of
bipartite
patella: type I-
inferior pole
(a,b); type II-
lateral margin
(c, d); type III-
superolateral
portion (e, f).

20. Osteochondritis dissecans of the patellofemoral joint is an
uncommon condition that may be the cause of anterior
knee pain or crepitus. The osteochondral lesions involve
the convex articular surfaces. The trochlear groove is the
rarest location for osteochondritis dissecans. MR is the
test of choice since it detects an osteochondral fragment
and evaluates its stability. A high signal line demarcating
the fragment from bone usually indicates an unstable
lesion. Cartilaginous lesions can be classified into three
main groups:
Subchondral- intact cartilage surface
Osteochondral fractures- disrupted articular surface with a
fragment of cortical bone
Chondral injury- underlying bone is intact

21. Bilateral osteochondritis dissecans of the knee.

22. Osteochondritis dissecans

23. Extensor mechanism of the knee pathology.
-Traumatic.
-Tendinosis.
-Patellar tendon tear.
-Quadriceps tendon tear.
.Intrinsic patellar tendon lesions. e.g. gout.
.Patellar enthesopathy.
.Osteochondrosis, e.g. Osgood-Schlatter disease.

24. Patellar tendinosis.
.Pain in the infrapatellar region.
.Commonly seen in athletes.
.MRI demonstrate thickening of the
patellar tendon with intermediate T1
and increased signal at T2 especially
with fat suppression sequences.
.Ultrasound show thickening, low
echogenicity and increase blood flow
at the Doppler study.

25. Chronic patellar tendinosis.

26. Patellar tendinopathy and Partial patellar tendon tear.

27. On sagittal (a) and axial (b) PD FS proximal end of patellar tendon is seen high intensity,
enlarged (white arrow) surrounding by inflammatory changes (black arrow).

28. Sagittal T2 (a) and PD SPIR (b) shows tibial tuberosity bony hypertrophy (black
arrow), fragmentation and inflammatory changes of overlying tissues.

29. Coronal (a) and sagittal (b) PD FS shows changes involving the inferior pole of the
patella which is characteristic for Sinding–Larsen–Johansson disease.

30. Complete Patellar tendon tear. Images show no continuity
between fibers and patella. The tendon is thickened.
Complete Patellar tendon tear. Image on the right shows
hemorrhagic bursitis ( low signal in bursa).

31. Quadriceps tendon tear.
Tear may be partial or complete.
Partial quadriceps tendon tear: T2W-images.LEFT: Abnormal attachment of tendon. Right :
Most of tendon is retracted (red arrow) deep part (vastus intermedius) is still intact.

32. Complete quadriceps tear. Sag T2W-images.
No continuity. Hematoma in between.

33. Sagittal PD FS (a) and T2 (b) shows quadriceps tendon full
thickness rupture as a gap filled with hyperintense fluid.

34. Intrinsic patellar tendon lesions : Gout
MRI show low T1 and mildly high T2 signal.

37. Fat pad syndromes
The infrapatellar (Hoffa's) fat pad is an intraarticular and yet
an extrasynovial structure which has an abundant vasculature
and innervation. Pathological changes are often associated
with other conditions, such as patellar tendinopathy, ligament
reconstruction or meniscal tear. Acute injury usually occurs in
the dorsal part of the fat pad and presents as edema or tears.
In chronic injury hemosiderin deposits or scarring are
observed. Lateral patellofemoral impingement involves of
edema of the superolateral part of the fat pat, a shallow
femoral trochlea, patellar malalignment and chondromalacia.
The inflammation of a quadriceps fat pad is rare and features
are similar to that of Hoffa’s fat pad.
Also, benign or malignant masses can be the cause of anterior
knee pain

38. Sagittal (a) and axial (b) IR shows high signal intensity at infrapatellar
fat pad (arrows). Sagittal image demonstrates patella alta.

39. Hoffa's Disease.

40. Sagittal T2 (a) and PD FS (b) shows heterointensive mass (arrows) at quadriceps fat pad
which was confirmed histologically as a metastasis of renocellular carcinoma

41. Sagittal MRI scans of the knee show an intermediate signal lesion in the apex of Hoffa's fat pad
between the inferior pole of the patella and the adjacent femoral condyle. The lesion's surface
retains the shape of the adjoining femoral condyle, indicating chronic wedging that reflects the
chronic nature of the lesion. The lesion was surgically excised. Histology showed adipose and
synovial tissue with inflammation and fibrosis, supporting a diagnosis of Hoffa's disease.

42. Pigmented villonodular synovitis is rare benign neoplastic synovial
proliferation with villous and nodular projections and hemosiderin deposition.
It mainly affects knee joint. On MRI images it appears as mass like lesion with
well- defined low signal intensity nodule. On both T1 and T2 images it is seen
low signal intensity with variable postcontrast enhancement.
A synovial nodular lesion is seen (arrows), with heterogenous signal characteristics.

43. Pigmented villonodular synovitis.

44. Localized Nodular Synovitis.

45. Intra-articular Chondroma.
A rare lesion occur around the knee typically at the infrapatellar fat pad.
May be calcified or erode the lower pole of patella.
Intra-articular Chondroma.

46. Infrapatellar Plica injury.
A thin fold of synovial tissue, extending from the inferior pole of the patella through
Hoffa's fat to the intercondylar notch anterior to the anterior cruciate ligament.
.High signal along the course of the plica indicates injury to the plica.
.Thickening of the plica even in the absence of edema or fluid suggestive of chronic injury.
Infrapatellar Plica injury.

47. Sagittal T2 (a) and axial PD FS (b) shows thickening of medial patellar place
(arrows) and insignificant Chondromalacia of femoral trochlear groove.

48. Iliotibial band syndrome, also known as Runner’s knee, is caused by an
excessive friction between the iliotibial band and the lateral femoral epicondyle. MRI
findings include the thickening of the iliotibial band and a deep bursa located over the
lateral epicondyle. Also, there is an inflammation of the surrounding soft tissues. MRI
is reserved to exclude other etiologies of pain such as lateral meniscal tear.
Coronal (a) and axial (b) PD FS shows thickened and edematous iliotibial band (white
arrow) and bursa (black arrow) between the band and lateral epicondyle of the femur.

49. Bursitis
There are four bursae anterior to the knee joint: a suprapatellar, a
subcutaneous prepatellar, a subcutaneous infrapatellar and a deep
infrapatellar bursa. Inflammation can be caused by acute or chronic trauma
and systemic diseases such as rheumatoid arthritis or metabolic disorders.
Axial PD FS (a) and sagittal GRE (b) shows hyperintense fluid in prepatellar region (black
arrows) and suprapatellar bursae (white arrows) - characteristic for prepatellar and suprapatellar bursitis

50. Prepatellar Bursitis.

51. Prepatellar Bursitis.

52. Ligament injury
Cruciate ligaments stabilize the knee joint. Once they rupture, a shift in ligament
balance forces occurs and may lead to cartilage damage. An ACL rupture causes
rotational instability and secondary changes, such as medial compartment and
patellofemoral joint overload.
A PCL rupture causes posterior instability. When the tibia slips dorsally,
mechanical load to the patella increases and speeds up wear and tear. Following
an anterior cruciate ligament reconstruction, pain can be caused by postoperative
complications, such as:
Arthrofibrosis is a contracture of a infrapatellar fat pad and patellar tendon. A ill-
defined low signal area on T1 and T2 weighted images, similar to fibrous tissue.
Cyclops lesion is defined as a nodule located anteriorly to the distal end of an ACL
graft.
Two histologic types: “hard”- composed of bone or cartilage, more often acts as
obstacle and “soft”- only composed of fibrous tissue, rarely causes
impingement. A low signal intensity nodule on T1WI images, anteriorly to the
graft. It could show similar intensity to synovial fluid. The nodule is heterogeneous
on T2WI, usually hypointense and well differentiated from fluid. Differential
diagnosis should include focal pigmented villonodular synovitis, synovial
chondromatosis and loose bodies.

53. Coronal (frontal) IR FSE (a) and sagittal T2 FSE (b) shows unevenly thinning
of medial knee joint and femur trochlear groove cartilage (arrows)
caused by chronic rupture of anterior cruciate ligament.

54. Axial PDW SPIR (a) and sagittal PDW (b) shows fibrous nodule
(arrows) at distal part of anterior cruciate ligament transplant.

55. Thank You.