Knee Replacement Using a Modern Bluetooth Navigation System in Obese Patients

Introduction: The combination of aging population with growing rate of obesity in the western world will lead to an increased incidence of knee osteoarthritis in obese patients. Long-term survival of knee replacement is related to correct prosthesis and knee alignment. Correct alignment may be more difficult to achieve in obese patients, where some of the anatomic landmarks are obscured by fatty soft tissue. The use of navigation systems in knee replacement surgery proved to improve alignment and significantly reduce outliers.

Hypothesis: Knee replacement in obese patients performed with a Bluetooth navigation system (iAssist, Zimmer) will result in improved alignment compared to conventional technique.

Patients and methods: This was a prospective randomized study. Sixty patients with knee osteoarthritis and BMI>30 were allocated to one of two surgical techniques (30 patients operated with iAssist navigation and 30 patients operated with conventional technique). Using long standing radiographs, we measured hip knee ankle angle (HKA) as well as femoral and tibial component alignment before and after surgery.

Results: Out of 60 surgeries performed, full data was available form 55 operations. On HKA measurements the average distance from neutral improved from 12.2° preoperatively to 3.5° postoperatively in the control group. In the study group, HKA improved from 8.9° to 2.8° respectively.

Femoral component coronal alignment (compared to the mechanical femoral axis) was 89.3° in the control group compared with 89.8° in the study group.

Tibial component coronal alignment was 90.8° in the control group compared with 90.9° in the study group.

Our study did not show a preference with a statistically significant difference on T-test.

There was no significant difference in the number of outliers between the groups – outliers considered component alignment that deviated more than 3 degrees from desired alignment.

Conclusion: In obese patients undergoing knee arthroplasty good coronal alignment can be achieved both in conventional technique and navigation assisted surgery. The use of navigation did not decrease the number of outliers. This may be related to the small sample size.