The orthopaedic unit at the Golden Jubilee National Hospital consists of eight consultant orthopaedic surgeons who have a varied practice with regard to navigated TKA with some surgeons using navigation for all cases, some for what are deemed difficult cases and others using it rarely or not at all. One mechanical jig-based system and two different navigation systems are in routine use. The results from the two navigated (nav 1 and nav 2) and non-navigated (non-nav) systems were audited and compared with published studies to determine whether the reported results from randomised controlled trials were reproduced in our routine practice. The primary outcome measure was the mechanical femorotibial (MFT) angle as measured by Hip-Knee-Ankle (HKA) radiographs. This is a standard outcome measure that allowed ready comparison with other studies.

Demographic data and post-operative MFT angles were collected retrospectively for each patient. The HKA digital radiographs (stored on a Picture Archive and Communication system) were taken six to twelve weeks post-operatively. The MFT angle was measured using a standardised protocol, which used the method of Mose to find the centre of the femoral head, the highest point in the femoral notch as the centre of the knee and the middle of the talus for the centre of the ankle. Repeated measurements were taken to identify intra- and inter-observer error.

There were 86 patients in the nav 1 series, 95 in nav 2 and 95 in non-nav. Mean age was nav 1 = 70, nav 2 = 69 and non-nav = 71. Mean BMI was nav 1 = 34, nav 2 = 31.5 and non-nav = 30. Male to female ratio was nav 1 = 51:35, nav 2 = 44:51 and non-nav = 30:65. Intra- and inter- observer comparison showed a maximum difference of 1° for the measurement of MFT angle. For series nav 1 74% of TKAs had a MFT angle in the range ±3°, for series nav 2 this was 85% and for the non-nav series it was 68%.

Much of the literature on RCTs for navigation vs. non navigation outcomes in TKA indicates that over 93 % of patients undergoing navigated TKA have a mechanical axis alignment within the ±3° range, with non-navigated techniques having 73–87% within this range [1,2]. Our audit shows lower percentages for both navigated and non-navigated techniques. Our results are however similar to those obtained by Chauhan et al. [3] with 85% and 66% respectively. The lower numbers of patients falling into the ±3° range may be due to our audit covering a number of surgeons and trainees. The nav 1 series had five consultants and six trainees, nav 2 had two consultants and the non-nav series had four consultant and six trainees. It may also relate to the extent of pre-operative deformities, which were not quantified. In conclusion the high levels of TKA coronal alignment within ±3° seen in many RCTs may not be readily reproducible in a general setting.