[Cartilage regeneration after high tibial osteotomy. Results of an arthroscopic study].

AIM: High tibial osteotomy (HTO) has been established as an effective method for the treatment of unicondylar knee osteoarthritis. This study was undertaken to quantify the potential for restoration of cartilage lesions or defects after HTO in relation to different cartilage treatment modalities. Control arthroscopy was undertaken to identify the cartilage lesions within the knee joint 1.5 years after medial opening wedge osteotomy.

MATERIAL AND METHOD: A total of 135 patients (72 male and 63 female) had undergone medial-opening high tibial osteotomy and arthroscopy. The mean age at operation was 48.8 (36 to 65) years. All HTO were fixed with an angle-stable, mobile spacer-containing plate (HTO-Platte, Königsee, Deutschland). All HTO were combined with a simultaneous arthroscopy. Grade III cartilage lesions had undergone either shaving or temperature-controlled chondroplasty (Paragon ArthroW Austin, TX, USA). In some case these cartilage lesions had remained untreated. Control arthroscopy and removal of the implants was performed 1.5 years after HTO. The cartilage lesions were graded accordingly to the ICRS guidelines (International Cartilage Repair Society).

RESULTS: The KOOS at HTO was 49.9 (SD 10.6) points. We observed at follow-up a mean increase from 66.1 (SD 28.8, 95 % CI: 61.2-71.1) points. The KOOS at follow-up was 16.1 (SD 29.8) points. There was no delayed union of the HTO space. Before HTO the varus angle was 10.4° (SD 3.9 range 5 to 20°). The correction angle was 13.6° (SD 4.4, 95 % CI: 12.9-14.4°). Finally we determined a valgus angle of -3.2° (SD 1.8 minimum 0° varus, maximum -6° valgus. The clinical outcome (KOOS) significantly (p < 0.001) correlated (R = 0.605) with the extension of valgisation. Patients with a valgus angle of 3° and more had the best outcome. Of the grade III lesions 40.4 % in the medial femoral condyle and 62.3 % in the medial tibial plateau increased to grade II or I lesions. In 13.1 % of the medial femoral condyle and 8.5 % of medial tibial plateau cases we found complete (grade IV) defects at control arthroscopy. The highest rate of regenerations was detected after temperature-controlled chondroplasty. The worst results were produced after mechanical debridement. Microfracturing of complete defects produced regeneration in about ⅔ in the medial femoral condyle and about ⅓ in the medial tibial plateau. No increase was observed within the lateral or patello-femoral compartment. No correlation was seen between cartilage regeneration and outcome. The extension of valgisation did not influence the cartilage regeneration.

CONCLUSIONS: The main effect of the HTO is the shift of the weight-bearing line from the arthritic compartment to the opposite femorotibial healthy one. In addition, HTO also produces a partial restoration of cartilage lesions. Deep cartilage lesions (grade III) restore in about 60 % of the cases after HTO. The worst restoration is found after mechanical shaving. This method should be avoided in the future. The best restoration was found in deep lesions after thermochondroplasty. Furthermore, in about half of the patients with complete (grade IV) defects, microfracturing caused the formation of fibrocartilaginous regenerates. This procedure should always be performed if possible.