Total knee arthroplasty after varus distal femoral osteotomy vs native knee: similar results in a case control study. 
The aim of this study was to investigate the results of total knee arthroplasty (TKA) performed after varus distal femoral osteotomy (VrDFO), in comparison to a control group of TKAs performed as the primary intervention for arthrosis.  Main hypothesis was that the medium term results for the two groups would be similar.  All TKAs performed after VrDFO were extracted from a single centre, prospective database of 4046 arthroplasties.  A case-control study was performed with a control group comprising two TKAs performed as the primary intervention for each TKA after VrDFO, and matched for sex, age at intervention, body mass index, the type of arthrosis and the type of implant.  All prostheses used a system of posterior stabilisation by a third median condyle (Laboritoire Tornier-Wright).  The primary outcome measure was the post-operative Knee Society Score (KSS).  Fourteen TKAs after VrDFO were identified, with a median follow-up of 42 months (12-102 months).  The control group comprised 28 patients.  There were no significant differences between groups in terms of the matching criteria.  Pre-operatively, there were no differences between groups in terms of KSS (knee and function scores), range of motion (fixed-flexion and maximum flexion), and mechanical axes on long leg films.  Operative duration was identical for the two groups.  In the VrDFO group there was more lateral intra-operative laxity (p = 0.006), more intra-operative complications (patella tendon injuries, p = 0.0008), and more frequent need for screw support for the tibial component due to more severe lower limb deformity (p < 0.0001).  No significant difference was found between groups with regards to the post-operative KSS; median knee score was 91.7 in the VrDFO group compared to 82.3 in the control group, and function score 70.6 compared to 77.8.  Range of motion was comparable between groups with median maximum flexion in the VrDFO group of 115.7° and 110.9° in the control group.  TKAs after VrDFO is uncommon and can carry an increased risk of intra-operative complications.  Despite this, the medium term results are comparable to arthroplasty performed as a primary intervention.  TKA should not be denied to patients with previous femoral osteotomy, but care must be taken with gap balancing and axis correction.  3.