Jumping patella is associated with inferior clinical outcomes after MPFL reconstruction for recurrent patellar dislocation: a retrospective cohort study

BACKGROUND: To date, two studies have established the correlation between jumping sign and multiple bony abnormalities. However, no studies have yet reported the association between the jumping sign and clinical outcomes. PURPOSE: (1) To determine the bony risk factors of jumping patella and (2) to compare clinical outcomes between jumping and gliding patellae following medial patellofemoral ligament (MPFL) reconstruction. PATIENTS AND METHODS: Between 2018 and 2022, 85 patients with recurrent patellar dislocation (RPD) who underwent MPFL reconstruction were retrospectively reviewed. Patients were stratified into two groups based on the presence or absence of the preoperative patellar jumping sign. Standard hip-knee-ankle computed tomography (CT) scans were obtained for all patients, through which lower limb torsional deformities and bony morphology were evaluated. Bony risk factors for preoperative jumping patella were identified using logistic regression analysis. Clinical outcomes were compared between groups at final follow-up. Subgroup analyses were conducted to examine outcome differences between surgical procedures within each patellar tracking group. RESULTS: This study included a total of 85 patients, with 36 cases in the jumping group. Multivariate regression analysis identified knee torsion (odds ratio [OR] = 7.16, 95% confidence interval [CI] = 1.64-31.33, P = 0.009) and supratrochlear bump (OR = 30.5, 95% CI = 6.95-133.77, P < 0.001) as significant factors associated with jumping patella. At the final follow-up, the jumping group demonstrated significantly lower Lysholm (75.7 versus 86.1, P = 0.002) and Kujala (80.8 versus 89.9, P = 0.003) scores compared with the gliding group. The jumping group showed significantly greater patellar medial laxity index (38% versus 22%, P = 0.001), and higher rates of residual maltracking (55.6% versus 16.3%, P < 0.001), jumping patella (27.8% versus 2%, P < 0.001), MPFL graft laxity (22.2% versus 4.1%, P = 0.01), and patellar redislocation (13.9% versus 2%, P = 0.035), compared with the gliding group. The subgroup analysis revealed that in cases of MPFL reconstruction combined with tibial tubercle transfer, the jumping patella had a much higher incidence of residual patellar maltracking (54.5% versus 15.6%, P = 0.005) and positive jumping sign (27.3% versus 0%, P = 0.002), compared with the gliding group, while no significant differences were found between the two groups in patient-reported outcome measures (PROMs), MPFL graft laxity, and patellar redislocation (all P > 0.05). CONCLUSIONS: Compared with the gliding patella, the jumping patella undergoing isolated MPFL reconstruction exhibited worse clinical outcomes. Although the combined procedure improved knee function and reduced redislocation rates to some extent, it could not significantly correct the persistent maltracking or jumping sign postoperatively.