Patellar tendon length following opening wedge high tibial osteotomy using an external fixator with particular reference to later total knee replacement.

The aim of this retrospective study was to examine a cohort of patients who had undergone high tibial osteotomy (HTO) using the method of opening wedge hemicallotasis, and who later required conversion to total knee replacement (TKR). The incidence of patella infra and any technical difficulties encountered during TKR operation were examined. A consecutive series of 76 valgus osteotomies in 65 patients were carried out by one surgeon using a dynamic axial fixator (DAF). Later conversion to TKR, required for the progression of symptoms, was carried out in nine knees (seven patients) at a mean time from the initial osteotomy of 7 years (1.5-11). All of those patients who underwent HTO and subsequently required conversion to TKR were followed up. The patellar height was assessed by one observer in all knees pre- and post-HTO using the Insall and Salvati and Blackburne and Peel ratios. Using these criteria, only one case of patella infra occurred. There were no added technical difficulties in performing TKR as a result of the previous osteotomy and clinical outcomes using the Oxford knee score were satisfactory (34 where 48 is maximum).