Clinical classification and surgical treatment of habitual dislocation of the patella in adult

Objective To explore the efficacy of the 3 types classification and the surgical technique included intensive lateral release, vastus lateralis oblique (VLO) tendon lengthening, tibial tubercle proximalization combined with MPFL reconstruction for habitual patellar dislocations in adults. Methods Date of 36 patients with habitual dislocation of patella who were operated between January 2011 and January 2016 were retrospectively analyzed. There were 12 males and 24 females, with an average age of 24 years old (range, 15-44 years). All the cases were followed-up for more than 2 years, and 26 of which was primary surgery, while the other 10 was revision surgery. According to the flexion angle when the patella dislocation occurred and difficulty to reduce the patella, the patients were divided into 3 types. The mild type means patellar dislocation angle was more than 90°, and the treatment was lateral release (LR) combined with MPFL reconstruction. The moderate type means the patellar dislocation angle was about 60° to 90°, and the treatment was LR combined with VLO lengthening and MPFL reconstruction. The severe type means the patellar dislocation angle was less than 60°, and the treatment was LR+VLO combined with proximalization of tibial tubercle. Based on this surgical algorithm, all the patients reveived the surgical treatment. Results All 36 patients had been sucessfully followed up. The mean follow-up period was 38.6 (range, 23-78) months. All the patients gained stable patella with no recurrence of dislocation. There was 1 patient in the mild group, 6 patients in the moderate group and 29 patients in the severe group. The patient in the mild group showed that the congruence angle of was improved from 72° preoperatively to 5° postoperatively, with 0.82 of Caton-Deschamps index, and 28mm of tibial tubercle-trochlear Groove, and the sulcus angle was 150°. The 6 patients in the moderate group showed that the congruence angle of was improved from mean 82.2°±11.7° preoperatively to 6.9°±26.4° postoperatively. The changes of Caton-Deschamps index, TT-TG and the sulcus angle were not significantly. The 29 patients in the severe group showed that the congruence angle of was improved from mean 75.0°±27.3° preoperatively to 0.0°±21.0° postoperatively. The Caton-Deschamps index was improved from mean 0.76±0.24 preoperatively to 1.06±0.24 postoperatively. TT-TG was decreased form mean 22.9±5.1 mm preoperatively to 6.0±4.9 mm. The change of sulcus angle was not significantly. The Lysholm score was improved from 59 preoperatively to 100 postoperatively in the mild group, 61 to 93 in the moderate group, and 66.0±8.0 to 93.7±3.0 in the severe group. The Kujala score was improved from 55 preoperatively to 83 postoperatively in the mild group, 55.0±4.1 to 83.8±1.9 in the moderate group, and 66.0±8.0 to 93.7±3.0 in the severe group. There was no flexion limited in the mild and moderate groups. The average flexion loss was 17.5°±7.6° in 6 patients postoperatively in the severe group. No extension limited. The consistency of the 3 types classification method by two observers was good (Kappa=0.918, P=0.000). Conclusion These results suggest that the 3 types classification provides an efficient method for habitual patellar dislocation. The surgical techniques included intensive lateral release, VLO lengthening, tibial tubercle proximalization combined with MPFL reconstruction are effective for treatment of habitual patellar dislocation in adults. In our opinion, lateral release and proximalization of tibial tubercle play an important role in the surgical treatment. Key words: Patellar dislocation; Adult; Treatment outcome