Patellar Dislocation

Traumatic Patellar dislocation is more common in women owing to physiological laxity and in patients with connective tissue disorders (e.g. Ehlers– Danlos or Marfan syndrome).

Mechanism of Injury

Patellar dislocations can be categorized based on their direction, which is determined by the injury’s mechanism. These categories include lateral, medial, intraarticular, and superior dislocations. Among these, lateral patellar dislocation is the most prevalent, while the occurrence of other types is quite rare.

Lateral patellar dislocation arises when there’s a forced internal rotation of the femur on an externally rotated and planted tibia, while the knee is flexed. On the other hand, instances of medial instability are infrequent and usually result from iatrogenic, congenital, traumatic causes, or are linked to quadriceps musculature atrophy.

See Also: Patellar Instability

Superior dislocation primarily affects elderly individuals, resulting from hyperextension injuries to the knee, often with the patella locked onto an anterior femoral osteophyte.

Regarding intra-articular dislocations, they fall into two categories. The more common one involves a horizontal intra-articular dislocation of the patella with detachment of the quadriceps tendon. This leads to the patellar articular surface facing the tibial articular surface. The other type also presents a horizontal patellar dislocation, but here, the patella’s inferior pole becomes detached from the patellar tendon, causing the articular surface to face upward.

See Also: Patellar Tendinitis (Jumper’s knee)

Clinical Evaluation

Patients usually experience difficulty in bearing weight and are incapable of flexing the knee. Haemarthrosis is observed alongside a noticeable displacement of the patella during palpation.

In the case of lateral patellar dislocations, there is tenderness along the medial joint due to tears in the medial retinaculum at the point where the medial patellofemoral ligament attaches to the femur.

Radiology

Radiographic assessment involves capturing anteroposterior and lateral perspectives of the knee. Studies have indicated a prevalence of 39–71 % for osteochondral or chondral injuries following an acute patellar dislocation. To detect these particular injuries and potential accompanying damage to the medial soft tissues, a knee MRI proves to be a valuable diagnostic tool.

Patellar Dislocation Treatment

Closed methods are typically used to manage acute patella dislocations. In the case of lateral dislocations, the patella can be repositioned by extending the flexed knee while applying pressure to its lateral edge.

Following reduction, the patient can walk with a cylindrical cast that keeps the knee extended for about 3 weeks. Subsequently, a gradual increase in knee flexion can be initiated through physical therapy aimed at strengthening the quadriceps.

While surgical intervention for acute dislocations is uncommon, it may be necessary to address displaced osteochondral fragments. Additionally, any disrupted medial tissues, including the vastus medialis muscle, should be repaired. Surgical reduction becomes essential in cases of intra-articular dislocations to restore the extensor mechanism.

The primary complication frequently encountered is the recurrent patellar dislocation. Individuals who are younger and those with a natural looseness in their ligaments are more prone to experiencing this recurrent dislocation. Prolonged periods of immobilization can lead to a reduction in the range of motion of the knee, underscoring the significance of initiating early range of motion exercises. Additionally, there’s a possibility of experiencing patellofemoral pain due to damage to the cartilage (chondral injury).

References & More

1. Mercer’s Textbook of Orthopaedics and Trauma, Tenth edition.
2. Sallay PI, Poggi J, Speer KP, et al. Acute dislocation of the patella: a correlative pathoanatomic study. American Journal of Sports Medicine 1996;24:52. PubMed
3. Nsouli AZ, Nahabedian AM. Intraarticular dislocation of the patella. Journal of Trauma 1988;28:256. PubMed
4. Cash JD, Hughston JC. Treatment of acute patellar dislocation. American Journal of Sports Medicine 1988;16:244. PubMed