ABSTRACT: Background:Habitual patellar dislocation in extension (HPD-E) is a distinctive subtype of recurrent patellar dislocation (RPD); HPD-E represents the most severe type of patellar maltracking in RPD. It has been reported that the presence of preoperative patellar maltracking is associated with a worse clinical outcome after medial patellofemoral ligament (MPFL) reconstruction (MPFL-R). Purpose:To describe the radiological characteristics of HPD-E and to compare clinical outcomes after MPFL-R among patients with and without preoperative HPD-E. Study Design:Cohort study; Level of evidence, 3. Methods:From January 2012 to December 2015, a total of 230 consecutive patients (246 knees) with RPD were treated with MPFL-R alone or combined with tibial tubercle osteotomy. Among them, 28 patients diagnosed with HPD-E by preoperative 3-dimensional computed tomography (CT; HPD-E group) were matched in a 1:1 fashion to 28 control participants who did not show HPD-E (control group). Routine radiography and CT were performed to evaluate patellar height, trochlear dysplasia, tibial tubercle-trochlear groove distance, and torsional deformities. The mean patellar laxity index and lateral patellar translation assessed with stress radiography were measured preoperatively and postoperatively to quantify MPFL laxity. At minimum 2-year follow-up, patient-reported outcomes (Kujala, Lysholm, and Tegner scores), patellar maltracking, and redislocation rates were compared between the HPD-E and control groups. Results:The radiological characteristics of the HPD-E group were as follows: 89% (25/28) of patients had severe trochlear dysplasia (Dejour type B or D), and the mean femoral anteversion angle was 35.5° ± 4.7°. At the final follow-up, the HPD-E group had a significantly lower Kujala score (76.2 vs 84.5, respectively; P = .001), Lysholm score (75.4 vs 86.6, respectively; P < .001), and Tegner score (4.1 vs 5.8, respectively; P = .021) compared with the control group. The postoperative patellar laxity index (43% vs 19%, respectively; P < .001) and redislocation rate (25% vs 0%, respectively; P = .01) were significantly higher in the HPD-E group than in the control group. Conclusion:Preoperative 3-dimensional CT is a reliable method of identfying patients with HPD-E. Treatment of HPD-E by MPFL-R alone or combined with tibial tubercle osteotomy resulted in a higher redislocation rate, more severe MPFL residual laxity, and lower patient-reported outcome scores compared with patients without HPD-E who underwent MPFL-R.
