First-Time Patellofemoral Dislocation: Risk Factors for Recurrent Instability

Abstract

Patellofemoral instability is a complex problem, which can be difficult to manage. The purpose of this study was to describe the demographics of patients with a first-time patellofemoral dislocation, and identify risk factors for recurrent instability. This was a single institution, institutional review board-approved, retrospective review of >2,000 patients with a patellar dislocation between 1998 and 2010. Inclusion criteria are as follows: (1) no prior history of patellofemoral subluxation or dislocation of the affected knee; (2) X-rays within 4 weeks of the initial instability episode; and (3) a dislocated patella requiring reduction, or history/findings suggestive of acute patellar dislocation (effusion/hemarthrosis, tenderness along the medial parapatellar structures, and apprehension with lateral patellar translation). Clinical records and radiographs were reviewed. The Caton-Deschamps and Insall-Salvati indices were used to evaluate patella alta. Trochlear dysplasia was assessed using the Dejour classification system. Skeletal maturity was graded based on the distal femoral and proximal tibial physes, using one of the following categories: open, closing, or closed. Three hundred twenty-six knees (312 patients) met the aforementioned criteria. There were 145 females (46.5%) and 167 males (53.5%), with an average age of 19.6 years (range, 9-62 years). Thirty-five patients (10.7%) were treated with surgery after the initial dislocation. All others were initially managed nonoperatively. Of the 291 patients managed nonoperatively, 89 (30.6%) had recurrent instability, 44 (49.4%) of which eventually required surgery. Several risk factors for recurrent instability were identified, including younger age (p < 0.01), immature physes (p < 0.01), sports-related injuries (p < 0.01), patella alta (p = 0.02), and trochlear dysplasia (p < 0.01). Sixty-nine percent of patients with a first-time patellofemoral dislocation will stabilize with conservative treatment. However, patients younger than 25 years with trochlear dysplasia have a 60 to 70% risk of recurrence by 5 years. This information is helpful when counseling patients on their risk for recurrent instability and determining the most appropriate treatment plan. The clinical tool shown in Fig. 4 may be especially useful.

Anteromedializing Tibial Tubercle Osteotomy for Patellofemoral Instability: Occupational and Functional Outcomes in U.S. Military Service Members

“…large-scale population studies have identified prior patellar dislocation, 3 younger age, [2][3][4][5][6] female sex, 5 participation in athletic activities, [2][3][4]6 soft-tissue laxity/disruption, 6 and anthropometric measures 6 as risk factors for patellar dislocation. Additional anatomic and radiographic risk factors associated with patellofemoral joint instability include abnormal bony anatomy 2,7 (e.g., patella alta, trochlear dysplasia, increased tibial tubercle-trochlear groove distance, and patellar tilt) and soft-tissue factors 6 (e.g., medial retinaculum laxity, medial patellofemoral ligament disruption, and weakened vastus medialis).…”

Operative Management of Patellar Instability in the United States

“…25,28 However, some authors have noted that sex is not a significant risk factor for patellar dislocation, and that in the case of acute, traumatic patellar dislocation, males actually have a greater incidence of injury. 21,47 …”

I.S.Mu.L.T. first-time patellar dislocation guidelines

“…The post-traumatic marrow edema is usually seen in the femoral condyle in 80-100% of patients, while in 41-61% of patients it is detectable even at the level of the inferior-medial aspect of the patella. Osteochondral lesions are more common on the patellar (70%) rather than in femoral (40%) articular surface, and can result in intra-articular loose bodies in 1/3 of patients [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] .…”