Abstract
Introduction
Conventional total knee instrumentation is used for most total knee replacements. Computer-assisted total knee arthroplasty (CA-TKA) including custom guides has gained popularity due to its reported accuracy in restoring optimal alignment. CA-TKA has demonstrated increased surgical time and cost, with know risks of pin-site infection and fracture. We assessed the radiographic alignment of conventional TKA by one surgeon and determined whether preoperative alignment has an effect on postoperative alignment.
Methods
A prospective series of 100 primary total knee arthroplasties (in 95 patients) from 1/2012-3/2013 were performed by the senior author, using a single conventional instrument system and a consistent methodology of 5° valgus distal femoral cut, intramedullary femoral entry-point, and minor cement balancing. Mechanical axis and component alignment were measured digitally on preoperative and postoperative lower extremity scanograms. Target alignment was set at neutral ± 3°. Knees with preoperative deformity within 0 ± 5° (non-deformed group) and those with >5° varus/valgus (deformed group) were compared using chi-square test.
Results
Target mechanical axis alignment (0 ± 3°) was achieved in 79% cases, while 21% remained in varus alignment (Fig 1). The non-deformed group achieved target alignment in 93.2% cases versus 62.2% in the deformed group (p = 0.0006). The femoral component fell within target alignment (90 ± 3°) 80% of the time and most often was in 1° of varus. The tibial component achieved target alignment (90 ± 3°) 96% cases and was most often in neutral (Fig 2).
Conclusion
Our results were consistent with those reported in the literature for conventional TKA, with a trend towards under-correction of varus deformity. The majority of the variability stemmed from the femoral component position and careful adjustments should be made to accommodate the individual differences of each patient. Given the significant difference in achieving target alignment between the deformed and non-deformed groups, perhaps CA-TKA could be useful in patients with preoperative deformity > ± 5°.
