Introduction: High tibial osteotomy is considered as alternative treatment for the unicompartmental arthritis of the varus knee. Low tibial osteotomy due to delayed union is avoided. Corticotomy and the use of external fixation system for stabilization and progressive correction of the axis offers all the osteotomie’s advantages, and, furthermore, reduces the bone healing time.

Material and Method: Fifty-seven patients, aged 49–76 y. (mean age 63.2 y.) with unicompartmental arthritis of the knee were treated, using the above technique. In all the cases arthroscopy was firstly performed to examine the knee joint. The mean time of external fixation presevation was six weeks. Folllow-up examination ranged from 6 months to ten years (mean time 6 y.). Since, the second postoperative day partial weight bearing was permitted. Patient’s hospitalization was 3 days. Postoperative correction of the axis was 1° per day, for 12–15 days.

Results: Regarding the pain and the range of motion the results are excellent in 49/57 patients. Loss of full knee extension was presented in one patient. Lateral knee instability and pain were presented in 3 patients. One patient was submitted in total knee arthroplasty two years after the osteotomy. Delayed-union of the osteotomy was presented in 4 patients that were fully healed, while non-union was presented in one patient. Two patients presented peroneal nerve neurapraxia, that were fully healed.

Conclusion: Conclusively, knee osteotomy with the use of external fixation system and progressive correction of the axis is a reliable method for the treatment of the unicompartmental arthritis of the knee. It permits the early weight bearing of the limb and offers very good results regarding pain and range of motion.