Long term outcomes of computer navigated lateral opening wedge distal femoral osteotomy for lateral compartment knee arthrosis

INTRODUCTION: Osteotomy of the distal femur (DFO) to address symptomatic degeneration in the knee is a well-established procedure with good results reported in the literature . Broadly the osteotomy is based on either an opening or a closing wedge alignment technique. Several patient related parameters including age, gender, body mass index (BMI) and surgical factors such as osteotomy site, gap, and fixation technique amongst others have been demonstrated to influence the outcome of DFO. Preoperative planning based on imaging is vital to assess the type and extent of deformity correction to be undertaken in order to achieve optimal alignment. Computer-assisted surgery (CAS) has been extensively used as dynamic intraoperative alignment aid in knee arthroplasty providing good outcomes. Several investigators in the current literature have utilised computer navigation in proximal tibial osteotomy and reported improved accuracy in realising the planned alignment. However there is paucity of studies reporting the long-term outcomes of distal femur lateral opening-wedge (DFLOWO) using computer navigation. Through our study we aim to report on the long-term outcomes and survivorship of computer navigated DFLOWO. HYPOTHESES: We hypothesize that use of computer navigation will improve the survivorship of distal femoral osteotomy. METHODS: Ethics committee approval was obtained for this study. Due consent was taken for the use of data from all the patients for this study. A retrospective analysis of prospectively collected data for patients with lateral compartment arthritis who underwent navigated lateral opening wedge distal femoral osteotomy from December 2006 to November 2012 was performed. Consecutive patients of lateral compartment knee arthrosis aged less than 55 years who failed to respond to conservative management were included in the study. Patients who had end stage arthritis with fixed flexion deformity of > 15 degrees, < 90 degrees of knee flexion or who did not consent for the procedure were excluded. Included patients were operated by one of the three senior surgeons attached to our research institute. The included patients were followed up with clinical and radiological evaluation at regular intervals (6 weeks / 6 months / 1 year / 5years). The final follow-up for the included patients was done using email questionnaire of the patient reported outcomes measures. Conversion to either UKA or TKA during the follow-up was the end point. Additionally, this information was verified from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) database RESULTS: 19 DFLOWO with mean age of 46.6 ± 6.5 years formed the study cohort. The coronal alignment was corrected from a mean of 7.1º (2-11º) valgus to mean 2.1º (0.5º - 3º) varus. IKDC scores improved from mean of 39 pre-op to 53 at the mean long-term follow-up of 9.1 years. KOOS scores at the long-term follow-up were pain-71, symptoms-56, activities of daily living-82, sports and recreation-59, quality of life-43. Survivorship of DFLOWO was 78.9% at a follow-up of 9.1 years. Presence of ≥ grade 2 ICRS cartilage degeneration in the medial compartment of knee and >7⁰ pre-operative valgus deformity strongly correlated with conversion to TKA at the long-term follow-up (r - 0.66). CONCLUSION: Computer navigated DFLOWO has satisfactory clinical outcomes and 79% survivorship in long-term follow-up. Presence of more than ICRS ≥ grade 2 degenerative changes in the medial compartment of knee with > 7 degrees pre-operative valgus deformity negatively affects the survivorship of DFLOWO in the long-term follow-up.