Introduction
Patellar dislocations are responsible for 2-3% of knee injuries and primarily affect younger, active individuals, with the highest occurrence in the second and third decades of life. Among these demographics, adolescent females show the highest incidence rates. If left untreated, patellar dislocations can lead to chronic issues such as patella instability, recurring dislocations or subluxations, persistent pain, and a decrease in athletic performance. Typically, acute patellar dislocations result from traumatic incidents, such as non-contact twisting injuries or direct blows to the patella. This article will delve into the management and rehabilitation of acute first-time or primary patellar dislocations.
Patellofemoral Joint Anatomy
The stability of the patellofemoral joint relies on a complex interplay of active and dynamic stabilizers. Recent research has emphasized the significant role of the medial patellofemoral ligament (MPFL) as the primary passive stabilizer of the patella. Other surrounding soft tissues, including the patellomeniscal and patellotibial ligaments, as well as the medial retinaculum, also contribute to stability.
Predisposing Factors
Primary factors contributing to patellar dislocations include trochlear dysplasia, elevated TT-TG distance, patella alta, and patellar tilt. Secondary factors encompass elevated Q angle with tibial tubercle lateralization and genu valgum, elevated femoral anteversion with compensatory lateral tibial torsion, vastus medialis hypoplasia, ligament laxity, and patellar dysplasia.
Patellar dislocations can also occur in individuals with hypermobility or generalized ligament laxity under less traumatic conditions. However, these cases tend to result in recurrent subluxation episodes rather than complete dislocations.
Mechanism of Injury
Patellar dislocation occurs when the patella fully disengages from its normal position in the trochlear groove, while subluxations involve only partial movement of the patella. Lateral patellar dislocations, where the patella moves outward, are the most common, while medial dislocations (inward) are typically iatrogenic. Although intra-articular dislocations are possible, they are rare.
Approximately 90% of lateral patellar dislocations stem from non-contact twisting injuries, such as sudden lateral cuts. The most frequent dislocation pattern occurs with the knee nearly straight at the onset of flexion, dislocating as a rotational or valgus force is applied during further flexion. Less common mechanisms involve dislocation from a greater range of knee flexion, either during deceleration from a squatting position or during acceleration from a bent knee position.
Patients often report pain, knee deformity, a popping sensation, and a feeling of instability post-dislocation. Swelling, joint effusion, and hemarthrosis (bleeding into the joint) are common in primary dislocations but less so in recurrent episodes.
Early Management
Reduction of patellar dislocations typically occurs spontaneously or with simple manipulation in the emergency department. If needed, the reduction process involves flexing the hip, applying gentle medially directed pressure to the lateral patella, and slowly extending the knee.
Imaging
X-ray imaging, including weight-bearing AP view in extension, Merchant view (weight-bearing in 45˚ flexion), and lateral view in 30˚ flexion, should be conducted. CT imaging helps assess osseous predisposing factors, while MRI precisely determines injured structures for treatment guidance.
Dislocation Sequelae
Patellar dislocation can lead to damage in surrounding bony surfaces and soft tissues. MRI findings may include hemarthrosis, bone edema, osteochondral lesions, inferomedial patellar deformity, capsulo-ligamentous tears, and osteochondral fractures.
Conservative vs Surgical Management
Systematic reviews and meta-analyses comparing conservative versus surgical management have shown no significant difference in outcomes except for re-dislocation rates. Surgical intervention is typically indicated for osteochondral fractures, intra-articular joint disorders, major tears of the MPFL, failed conservative management, or recurrent dislocations.
Physiotherapy Rehabilitation
Both surgical and conservative approaches require rehabilitation focusing on muscle strengthening, proprioception, and neuromuscular control. Exercises target muscles crossing the knee joint and the wider kinetic chain. While vastus medialis strengthening was historically emphasized, it's now part of a comprehensive quadriceps strengthening regime.
Return to Sport
Return to sport involves a criteria-based progression rather than time-based, ensuring patients meet individualized criteria for safe return. Criteria include radiographic healing, full range of motion, absence of knee effusion or pain, satisfactory core strength, completed neuromuscular training, acceptable limb symmetry index, and psychological readiness.
Strength Testing and Dynamic Stability
Isokinetic strength testing assesses knee flexion and extension strength, with a limb symmetry index of at least 90% required before return to sport. Dynamic stability tests, such as balance excursions and single-leg squats, also play a crucial role, with qualitative video analysis aiding in assessment.
Psychological Readiness
Psychological readiness, including confidence and fear of re-injury, is integral to the return to sport process. Open communication and education are essential to address psychological barriers.
Conclusion
Patellar dislocations predominantly affect young, active individuals and involve complex anatomical factors. Effective management involves early reduction, imaging for accurate diagnosis, and tailored rehabilitation focusing on strength, stability, and psychological readiness. Both conservative and surgical approaches have their merits, with rehabilitation playing a pivotal role in facilitating a safe return to sport.
