Summary
This study aimed to identify correlations between pre-operative anatomic characteristics and lower-extremity kinematics at sports clearance in adolescents following MPFL reconstruction for PFI.
Abstract
Introduction
Patellofemoral instability (PFI) is highly correlated with patello-trochlear dysplasia. The relationship between these dysplastic features and biomechanics during sport-related tasks like the drop vertical jump (DVJ) has not been investigated. This study aimed to identify correlations between pre-operative anatomic characteristics and lower-extremity kinematics at sports clearance in adolescents following MPFL reconstruction for PFI. We hypothesized that PFI-associated dysplasia would correlate strongly with pelvis, hip, and knee kinematics during dynamic movements.
Methods
This IRB-approved prospective cohort study recruited adolescent patients aged 10-18 who underwent MPFL reconstruction for PFI between 2019 and 2023. Motion capture data was collected following the patient’s sports clearance visit. Protocol included landing from a 31cm plyo-box, with subsequent maximal vertical jump. Joint angles and internal moments of the hip and knee were assessed during descent phase of the DVJ. Preoperative radiographs and MRI were utilized to record tibial tubercle to trochlear groove distance (TT-TG), tibial tubercle-posterior cruciate ligament (TT-PCL) trochlear width (TW), trochlear sulcus depth (TSD), lateral inclination angle (LIA), patellar tilt angle (PTA) and femorotibial angle (FTA). Spearman correlations were used to explore relationships between preoperative anatomy and DVJ kinematics.
Results
A total of 17 participants were tested (8 male, 15.5 ± 1.4 years, 15 unilateral, 166.3 ± 11.4 cm, 65.1 ± 19.4 kg). TT-PCL, TT-TG, and TSD were not found to significantly correlate with any kinematic variable. Greater pelvic obliquity (r=0.672, p=0.004), which quantifies pelvic drop on the ipsilateral side, and hip internal rotation (r=0.508, p=0.044) were positively correlated with FTA, an indicator of genu valgum. Greater severity of patella-trochlear dysplasia (decreased TW (r=-0.486, p=0.048) and increased PTA (r=0.689, p=0.002)) were associated with the knee joint moving further away from the midline, causing greater hip abduction across the descent phase. TW was also positively correlated with internal hip rotation (r=0.503, p=0.040), indicating that patients with a wider femoral trochlea exhibited greater internal rotation throughout descent. For the knee joint, greater flexion during landing was negatively correlated with PTA (r=-0.547, p=0.023), indicating patients with more severe PTAs exhibited stiffer landings. Furthermore, greater knee valgus was positively correlated with TW (r=0.483, p=0.049), and greater internal knee rotation was positively correlated with LIA (r=0.513, p=0.035).
Discussion
These results highlighted that more severe patella-trochlear dysplasia—measured by factors such as TW, LIA, and PTA—was significantly linked to distinct biomechanical patterns during dynamic movements. Increasing and cumulative dysplasia correlated with knee valgus and decreased flexion at landing, as well as increased pelvic obliquity and hip internal rotation. The finding of persistent knee extension, valgus and internal rotation at landing even after patellar stabilization may assist in patient counseling regarding expectation of outcomes regarding knee performance upon return to sport.