Medial patellofemoral ligament injury
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Medial patellofemoral ligament injuries comprise sprains, tears and ruptures as well as avulsion fractures of the medial patellofemoral ligament (MPFL). They occur regularly in the association with acute traumatic lateral patellar dislocations and are also found in the setting of multi-ligament knee injuries.
The medial patellofemoral ligament is almost always injured in acute first-time lateral patellar dislocations 1-3, less often in recurrent dislocations and may be injured in multi-ligament injuries of the knee 4, especially in those involving the medial collateral ligament.
Risk factors for a medial patellofemoral ligament injury include 1:
- trochlear dysplasia
- patella alta
- lateralization of the tibial tuberosity
- patellofemoral instability
- young age
In addition, the following activities increase the likelihood of developing a medial patellofemoral ligament injury:
- rugby / American football
- football (soccer)
Conditions associated with a medial patellofemoral ligament injury include 1,5:
- acute traumatic lateral patellar dislocation
- chondral injury
- osteochondral injury
- intra-articular fragments
- medial collateral ligament injury
Typical symptoms include swelling, pain and tenderness along the medial joint line in particular at the medial border of the patella or the site of the origin between the medial epicondyle and the adductor tubercle. History might reveal a patellar dislocation. The clinical examination might show patellar lateralization and no firm endpoint on lateral patellar translation 1.
Additional symptoms might include locking indicating associated chondral or osteochondral injury.
Medial patellofemoral ligament injury can lead to the following conditions 1,2,6:
- recurrent lateral patellar dislocations (especially femoral sided or combined MPFL tears)
- chondral injury
- patellofemoral osteoarthritis
Medial patellofemoral ligament injuries include sprains, partial and complete tears as well as pure bony or osteochondral avulsion injuries.
A common mechanism of medial patellofemoral injury is mal-tracking of the patella during knee flexion with the tibia in a valgus position. In addition, a patellar dislocation can occur due to direct impact and high energy trauma 2.
Medial patellofemoral ligament injuries can occur at their patellar or femoral insertion sites, midsubstance or in more than one location 1,5.
Medial patellofemoral ligament injuries can be classified based on the type and/or location 1,6-8. A further subclassification can be made based on the type of injury at the patellar insertion site: ligamentous, bony avulsion or osteochondral injury 1.
Plain radiographs might detect bony avulsion injuries and possibly lipohemarthrosis. Beyond that, they might show a sliver sign indicating a recent lateral patellar dislocation.
Like plain radiographs, CT can detect a bony avulsion injury as well as knee joint effusion and possibly concomitant osteochondral injuries. In addition, CT is required in the preoperative workup of predisposing factors for lateral patellar dislocation 2.
MRI can directly depict the medial patellofemoral ligament (MPFL) is best visualized in axial views distal to the vastus medialis oblique (VMO) and can categorize the exact location and extent of the injury 9. It can show additional chondral and osteochondral injuries, intra-articular fragments or other ligamentous and concomitant meniscal injuries and is therefore recommended for the workup of patellar dislocation 1. Like other ligament injuries, the extent or type of the injury can be graded based on fiber discontinuity in a sprain (signal alteration and surrounding fluid), partial tears and complete disruption.
The radiological report should include a description of the following 1:
- location and grade of the injury (sprain, partial tear, disruption)
- associated avulsion injuries (bony, osteochondral)
- etiology (lateral patellar dislocation, multi-ligament injury)
- associated chondral injuries and location (patellar, trochlear, lateral femoral condyle)
- associated ligament injuries or meniscal tears
- presence of intra-articular fragments
Treatment and prognosis
Treatment options include non-surgical and surgical approaches and will mainly depend on the presence of associated injuries and the grade of the injury and patient activity 1.
First time isolated, uncomplicated medial patellofemoral ligament sprains and partial tears are usually treated conservatively with initial immobilization and other conservative measures followed up by early mobilization, range of motion exercises and functional rehabilitation 1,2.
Conservative treatment failure or recurrent medial patellofemoral ligament injuries are rather treated surgically as well as bony avulsions or osteochondral injuries suitable for direct repair 1,6. Chronic ligament injuries at the insertion points not suitable for suture might need reconstruction (e.g. semitendinosus tendon graft) 1,10,11.
Conditions that can mimic the presentation and/or the appearance of a medial patellofemoral ligament injury include:
- medial collateral ligament injury
- anterior cruciate ligament injury
- posteromedial corner injury
- fat pad impingement syndromes
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