Effect of Trochlear Dysplasia on Outcomes After Isolated Soft Tissue Stabilization for Patellar Instability.

BACKGROUND: Trochlear dysplasia is a well-described risk factor for patellofemoral instability. Despite its clear association with the incidence of patellar instability, it is unclear whether the presence of high-grade trochlear dysplasia influences clinical outcome after patellofemoral stabilization.

PURPOSE: To determine whether isolated proximal soft tissue stabilization for patellofemoral instability is as successful in patients with high-grade dysplasia compared with low-grade or no dysplasia, as measured by disease-specific quality-of-life and pain scores.

STUDY DESIGN: Case series; Level of evidence, 4.

METHODS: A total of 277 patellofemoral stabilization procedures were performed during the study period. An isolated stabilization was performed in 233 patients, and 203 of these patients (87%) had adequate lateral radiographs and complete Banff Patella Instability Instrument (BPII) scores available for assessment. Of these, 152 patients underwent a medial patellofemoral ligament reconstruction (MPFL-R) and 51 patients received a medial patellofemoral ligament imbrication (MPFL-I). There were 21 patients with no trochlear dysplasia, 89 patients with low-grade dysplasia (Dejour type A), and 93 patients with high-grade dysplasia (Dejour types B-D). An independent-samples t test was used to determine the difference between the pre- and postoperative BPII scores. A Spearman rho correlation was calculated between 3 trochlear dysplasia groups and the BPII scores at a mean 24 months after patellofemoral stabilization. An independent-samples t test was used to assess the influence of trochlear bump size on outcomes by stratifying data and assessing for a relationship to BPII scores.

RESULTS: The independent-samples t test demonstrated statistically significant improvements in pre- to postoperative BPII scores for both groups. The MPFL-R group improved from a mean BPII score of 24.36 to 65.16 (P < .001), and the MPFL-I group improved from a mean of 28.92 to 73.45 (P < .01). For the MPFL-R patient cohort, the Spearman rho correlation demonstrated a significant relationship between postoperative BPII scores and presence of a trochlear bump and degree of dysplasia (P ≤ .05). Overall, a trochlear bump of ≥5 mm was associated with lower postoperative BPII scores (t(193) = 2.65, η(2) = 0.04).

CONCLUSION: This research has established a statistically significant correlation between trochlear dysplasia and disease-specific outcomes after MPFL-R surgery. Overall, there was evidence of significant improvement in disease-specific quality-of-life scores after patellofemoral stabilization surgery. This study is the largest cohort reported to date and therefore adds substantially to the evidence that trochlear dysplasia is a significant risk factor for and predictor of outcome among patients with patellofemoral instability.