Association Between Preoperative Patellar Jumping Sign and Graft Failure After Medial Patellofemoral Ligament Reconstruction for Recurrent Patellar Dislocation

Background: Two recent studies have shown that patients with jumping sign exhibit more pronounced lower limb torsional abnormalities and trochlear bump in recurrent patellar dislocation (RPD), suggesting that medial patellofemoral ligament (MPFL) reconstruction may not fully correct the patellofemoral relationship in patients with a jumping sign. Purpose: To determine whether there was an association between the preoperative jumping sign and MPFL graft failure. Study Design: Case-control study; Level of evidence, 3. Methods: Patients who underwent primary surgery and follow-up evaluation due to RPD at our institution from 2012 to 2022 were eligible. Those who received initial combined derotational osteotomy were excluded. Patients with graft failure (postoperative patellar redislocation) were matched in a 1:2 ratio with patients who did not experience failure. Preoperative lower limb bony structural abnormalities were evaluated and combined with the jumping sign to analyze independent factors associated with graft failure. A graft failure nomogram was constructed, and model performance was examined. Results: A total of 129 patients (129 knees) were included, with 43 in the graft failure group. The 2 groups were comparable in terms of age, sex, number of dislocations, duration of symptoms, and primary procedures. The incidence of preoperative jumping signs in the graft failure group was significantly higher than that in the control group (69.8% vs 18.6%, P < .001). Multivariable regression analysis identified 3 independent factors associated with graft failure: jumping sign (odds ratio [OR], 4.44; 95% CI, 1.63-12.12; P = .004), increased femoral anteversion (OR, 6.23; 95% CI, 2.18-17.77; P = .001), and excessive knee torsion (OR, 3.02; 95% CI, 1.51-11.58; P = .006). After including these factors in a nomogram, the C-index of the model was 0.832, indicating reliable performance. Good concordance between the predicted risk and the actual graft failure rate was also observed. Conclusion: A preoperative jumping sign was present in almost 70% of patients with MPFL graft failure. This sign, combined with excessive lower limb rotational abnormalities, was identified as associated with graft failure after primary MPFL reconstruction in patients with RPD.