To report the clinical outcomes of recurrent patellar dislocation (RPD) patients after medial patellofemoral ligament reconstruction (MPFLR) combined with tibial tubercle osteotomy (TTO), to evaluate the impact of preoperative J sign severity on postoperative residual graft laxity correction, and to identify the predisposing factors of high grade J sign.

A total of 165 adult consecutive RPD patients who underwent MPFL reconstruction and TTO at the Orthopedic Department of Peking University Shougang Hospital and were followed for more than 2 years were analyzed retrospectively in this study. All the patients were classified into three groups based on the severity of pre-operative knee J sign: grade 1+, grade 2+, and grade 3+. Computed tomography (CT) examination was performed in all patients at 0° extension of the knee, and true lateral X-ray films of the knee were obtained at 20° flexion. The patellar laxity index measured by patellar glide test (PGT) under anesthesia and the radiographic parameters (tibial tuberosity-trochlear groove distance, patellar height, trochlear groove classification, patella trochlear-groove distance, femoral anteversion angle, tibial external angle, and knee rotational angle), as well as the pre/postoperative knee functional scores including International Knee Documentation Committee (IKDC) score, Kujala score, and Lysholm score, were assessed. Furthermore, the postoperative residual J sign and surgical failure rate were compared among the three groups at the final follow-up.

Totally, 138 (83.6%, 138/165) patients participated in the final follow up. The average follow-up duration was (38.2±5.9) months (range, 36~45 months), and most of the patients (97.1%, 134/138) did not suffer from RPD during the follow-up period except for 4 patients in the grade 3+ group. Seventeen patients had grade 3+ J sign, 24 had grade 2+, and 97 had grade1+ preoperatively. There was no significant difference among the three groups in age, gender, injury side, time from injury to surgery, follow-up duration, and preoperative knee function scores (P＞0.05). At the final follow-up, the patellar laxity index was (36.4±19.6) % in the grade 3+ J sign group, (23.5±8.1)% in the grade 2+ group, and (22.9±9.8)% in the grade 1+ group; there was a significant difference in the patellar laxity index among the three groups (P＜0.05). The patella trochlear-groove distance in the grade 3+, grade 2+, and grade 1+ groups was (-1.7±8.2) mm, (-6.6±8.0) mm, and (9.4±7.4) mm, respectively; there was a significant difference among three groups (P＜0.05). The femoral anteversion angle in the grade 3+, grade 2+, and grade 1+ groups was (28.2±11.6)°, (20.4±12.6)°, and (19.6±10.7)°, respectively; there was a significant difference in the femoral anteversion angle among the three groups (P＜0.05). The tibial external angle in the grade 3+, grade 2+, and grade 1+ groups was (30.4±20.0)°, (16.5±17.5)°, and (19.8±16.2)°, respectively; there was a significant difference in the tibial external angle among the three groups (P＜0.05). The knee rotational angle in the grade 3+, grade 2+, and grade 1+ groups was (14.6±5.4)°, (8.3±3.9)°, and (9.2±5.2)°, respectively; there was a significant difference in the knee rotational angle among the three groups (P＜0.05). The three groups had no significant difference in patellar height or trochlear groove classification (P＞0.05). The IKDC, Kujala, and Lysholm scores were (77.2±6.1), (76.1±3.3), and (84.7±5.6) in the grade 3+group, (87.3±8.7), (84.4±4.8), and (91.6±8.0) in the grade 2+group, and (86.4±6.5), (85.3±1.2), and (93.1±4.3) in the grade 1+group, respectively; all were significantly improved compared with the preoperative scores (P＜0.05).The failure rate in the grade 3+ group was 23.5%, which was significantly higher compared with those in the grade 2+ (0%) group and grade 1+ group (0%) (P＜0.05). The odds ratio of high grade J sign (3+) with patella trochlear-groove distance was 1.44, that with femoral anteversion angle was 1.37, and that with knee rotational angle was 1.24 (P＜0.05).

MPFL reconstruction combined with TTO is effective for most of RPD patients during the 2-year follow-up period except for patients with preoperative high grade J sign (grade 3+). However, the morbidity of postoperative positive residual patellar J sign was 26% and the positive J sign might increase the laxity of the patella. Preoperative high grade patellar J sign may lead to postoperative residual graft laxity and even failure, and high grade J sign appears to be associated with increased patella trochlear-groove distance, femoral anteversion angle, and tibial external angle.