Recent studies suggest the use of computer navigation during TKA can reduce intraoperative blood loss. The purpose of this study was to assess if navigation affected blood loss after TKA in the morbidly obese patient (BMI> 40).

Total body blood loss was calculated from body weight, height and haemotocrit change, using a model which accurately assess true blood loss.

The computer navigated group comprised of 60 patients, 30 with BMI > 40 and 30 with BMI< 30. The matched conventional knee arthroplasty group consisted of 62 consecutive patients, 31 with BMI> 40 and 31 with BMI< 30 The groups were matched for age, gender, diagnosis and operative technique.

Following TKA, the mean total loss was 1014mls (521-1942, SD 312) in the computer assisted group and 1287mls (687-2356, SD 330) in the conventional group. This difference was statistically different (p< 0.001). The mean calculated loss of haemoglobin was 19 g/dl in the navigated group versus 25 g/dl in the conventional group; this was also significant at p< 0.01. The mean total loss was 1105mls in patients with a BMI> 40 in the navigated group compared to 1300mls in the conventional group (p< 0.01). A significant correlation was found between total blood loss and BMI (r=0.2, p< 0.05).

This study confirms a highly significant reduction in total body blood loss and calculated Hb loss between computer assisted and conventional TKA in obese patients. Therefore navigation-assisted TKA could present an effective and safe method for reducing blood loss and preventing blood transfusion in obese patients undergoing TKA.

Computer navigated total knee arthroplasty (TKA) has several proposed benefits including reduced post operative blood loss. We compared the total blood volume loss in a cohort of morbidly obese (BMI> 40) patients undergoing computer navigated (n=30) or standard intramedullary techniques (n=30) with a cohort of matched patients with a BMI< 30 also undergoing navigated (n=31) or standard TKA (n=31). Total body blood loss was calculated from body weight, height and haemotocrit change, using a model which accurately assesses true blood loss as was maximum allowable blood loss. The groups were matched for age, gender, diagnosis and operative technique.

The mean true blood volume loss was significantly (p< 0.001) less in the computer assisted group (1014±312mls) compared to the conventional group (1287±330mls). Patients with a BMI > 40 and a computer navigated procedure (1105 ±321mls) had a significantly lower (p< 0.001) blood volume loss compared to those who underwent a conventional TKA (1399±330mls). There was no significant difference in the transfusion rate or those reaching the maximum allowable blood loss between groups.

This study confirms a significant reduction in total body blood loss between computer assisted and conventional TKA in morbidly obese patients. However computer navigation did not affect the transfusion rate or those reaching the transfusion trigger in the morbidly obese group. Therefore computer navigation may reduce blood loss in the morbidly obese patient but this may not be clinically relevant to transfusion requirements as previously suggested.

The influence of BMI on outcomes from TKA remains unclear. The purpose of this study was to evaluate if navigation affected the outcomes of TKA in obese patients.

Sixty-four (mean age 65 yrs±7) consecutive computer navigated TKA’s were compared with a matched group of 64 (65yrs±8) conventional TKA’s in patients with a BMI > 35. The groups were matched for age, gender, diagnosis and operative technique. Patients were reviewed pre-operatively and 6 weeks and 1 year post-operatively. All patients had clinical and radiological assessment and were scored using the Oxford knee score.

There were significant improvements (p< 0.001) in all clinical outcomes at 6 weeks and 1 year post-operatively in both groups. No significant differences were found between groups 6 weeks post surgery. The computer navigated group performed significantly better in post operative knee flexion (Nav 99° ± 10, Conv 94° ±12, p< 0.05) and Oxford scores (Nav 20 ± 10, Conv 25±12, p< 0.01) at 1 year compared to the conventional group. There were significantly (p< 0.05) more flexion contractures one year post-operatively in the conventional group which correlated significantly (p< 0.001) with decreased maximal knee flexion at one year.

This study suggests that navigated TKA produces better early clinical outcomes than conventional TKA in the obese patients possibly due to improved sagittal alignment as evidenced by the lack of flexion contractures 1 year post-operatively.