Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.

OBJECTIVE: High tibial osteotomy (HTO) for the treatment of unicompartmental knee osteoarthritis in the presence of axial malalignment is recognized as an effective treatment for young and active patients. The aim of this study was to identify HTO prognostic factors.
METHODS: A total of 94 patients who had undergone HTO with additive arthroscopy were scored using the "knee injury and osteoarthritis outcome score" (KOOS). A KOOS of less than 114 points was judged as a poor outcome.
RESULTS: A total of 84 patients were available for follow-up after a time-interval of 45.9+/-7.6 (range 34-60) months. The KOOS increased from 46.1+/-11.1 to 120.3+/-40.8. The preoperative varus angle in all patients was 7.5 degrees +/-1.9 (range 5-14 degrees ). In follow-up the patients had a mean valgus angle of 3.7 degrees +/-2.5. Twenty-three patients (27.4%) had suffered a loss of correction (0.8 degrees , range 0-2 degrees ). A loss of correction correlated with a minor result in tendency. A total of 25 patients (29.8%) had a poor KOOS. Factors associated with a poor HTO outcome were a patient history of more than 24 months, a preoperative KOOS>50 points, obesity, and smoking. However, the results were also influenced by radiological findings, such as medial tibial exophyte, a medial joint space width of less than 5mm, and intraarticular damage, such as a degree IV cartilage defect of the tibia. Gender was also a minor prognostic factor. Patient's age and the event of prior surgery did not influence the outcome.
CONCLUSION: This study identified relevant factors that significantly influenced HTO results. It was possible to create a "predictive score" for HTO patients. Patients with more than 4 of the poor prognostic factors should chose primary arthroplasty.