Summary

This study assessed whether medial patellofemoral distance (MPFD) measured by dynamic ultrasound could predict postoperative knee function after patellar stabilization surgery, finding no significant correlation between MPFD measurements and functional outcomes, suggesting the need for further research with larger cohorts.

Abstract

Dynamic portable ultrasound has been shown to accurately identify patellar instability, with prior studies demonstrating a medial patellofemoral distance (MPFD) > 2 mm indicating medial patellofemoral complex (MPFC) insufficiency. Currently, no method exists to predict knee function after medial patellofemoral ligament (MPFL) and medial quadriceps tendon femoral ligament (MQTFL) reconstruction. The purpose of this study was to determine whether MPFD measured on dynamic ultrasound images can predict postoperative function after patellar stabilization surgery. A retrospective cohort of patients was followed from the initial encounter up to one year post-surgery. Dynamic portable ultrasound images and MPFD measurements were obtained as previously described, demonstrating the space between the medial patella and trochlea with and without lateralizing load. Patients completed Kujala questionnaires at standard postoperative intervals; the questionnaires were scored out of 100, with higher scores indicating better knee function. Pre and postoperative measurements and functional scores were compared. Previously established thresholds of MPFD were used to determine their relationship to outcome scores. Linear regression analysis was performed to assess a relationship between ultrasound-based measurements and postoperative Kujala scores. Sex-specific comparisons were performed. 40 patients were included in this study (mean age: 23 ± 9.1, 17 males, 23 females). 10 patients underwent MPFL reconstruction, and 30 patients underwent MQTFL reconstruction. No patients had a re-dislocation in this timeframe. The mean MPFD-delta preoperatively was 3.6 ± 1.3 and postoperatively was 1.1 ± 1.2. The mean Kujala score preoperatively was 51.9 ± 24.2 and postoperatively improved to 84.3 ± 14.1 at 6 months. No significant relationship was found between postoperative ultrasound measurements and Kujala scores (R² = 0.018, p = 0.320). Sex-based analysis demonstrated showed no significant relationship in males (R² = 0.051, p = 0.337) or females (R² = 0.003, p = 0.761). Using the known MPFD threshold of 2 mm, patients with MPFD < 2 mm had a Kujala score of 82.9 ± 14.9, compared to 89.8 ± 7.5 for those with MPFD ≥ 2 mm (p = 0.229), indicating no significant difference. While dynamic portable ultrasound measurements have been shown to effectively assess patellar instability, the application to this surgical cohort did not demonstrate a relationship with short-term functional outcomes. Longer-term studies with larger patient populations are needed to determine the relationship between MPFD measurements of patellar stability and functional knee outcomes after patellar stabilization surgery.