Background

Patient specific instrumentation (PSI) proponents have suggested improved component alignment and reduced outliers. We attempted to assess the advantage of using PSI over conventional intermedullary (IM) guides for primary TKA in patients with bilateral severe femoral bowing (> 5°). We hypothesize that PSI would support more accurate alignment of components and the lower-limb axis during TKA with severe femoral bowing in comparison with IM guides.

Methods

Among 336 patients undergoing bilateral TKA with osteoarthritis (OA), 29 patients with bilateral lateral femoral bowing = 5° were enrolled. Each was randomized to PSI on one side and conventional instrumentation with lateralization of the entry point of the femoral IM
guide on the other side. The hip–knee–ankle (HKA) angle on preoperative and postoperative long film standing radiographs was measured and other parameters on weight-bearing radiographs. CT of the rotational alignment of the femoral component was done.

Results

The postoperative mean ± SD HKA angle was varus 4.00° (± 2.74°) for conventional side and varus 4.08° (± 3.12°) for PSI (p = 0.459). The component orientation showed no significant differences except the sagittal alignment of the femoral component (p = 0.001), with a PSI mean ± SD flexion of 5.83° (± 3.67°) and a conventional method flexion of 3.17° (± 2.46°), due to the intentional 3° flexion in the sagittal plane to prevent femoral notching for the former. Transepicondylar axis on CT showed no difference between the two groups (p = 0.485).

Conclusion

PSI showed no advantage over IM guidance in patients with lateral femoral bowing.