Comparison of mid-term results between conversion total knee arthroplasties following closed wedge high tibial osteotomy and primary total knee arthroplasties: A matched pair study including patellar symptom and position.

Background: The purpose of this study was to compare mid-term clinical and radiographic results of conversion total knee arthroplasties (TKA) following a closed-wedge high tibial osteotomy (HTO) and primary TKAs.

Methods: A total of 32 conversion TKAs (29 patients) were compared with a matched control group of patients who had undergone primary TKA. The clinical results were evaluated using the Knee Society Knee and Function score, the Western Ontario and McMaster Universities score, patella score, and range of motion (ROM). The radiographic results were evaluated using femorotibial angle, mechanical axis (MA), the method employed by the American Knee Society, joint line height (JLH), the amount of tibial bone resection, and the Insall-Salvati ratio. The clinical and radiographic results of conversion TKAs were compared with primary TKAs. The thickness of the polyethylene insert was also compared.

Results: No significant differences were observed in the clinical scores or ROM between two groups. No significant differences were detected in femorotibial angle, MA, and position of the components between two groups. The amount of tibial bone resection and pre-operative JLH both were significantly lower in the conversion group than those in the control group, although postoperative JLH and pre and postoperative Insall-Salvati ratio did not differ between two groups. No significant difference in the thickness of the polyethylene insert was identified between two groups.

Conclusions: The previous closed-wedge HTO itself had no detrimental effect on the mid-term outcome of the subsequent TKA, including patellar symptom and position. No significant differences in the postoperative joint line and patella height were detected between the conversion and primary TKA groups.