Abstract
Introduction
Total knee arthroplasty is traditionally performed using bone anatomy to dictate femoral implant rotation and soft tissue release to balance any resulting deficiencies. A force sensing device has been developed that reverses this conventional order. It measures the forces in the medial and lateral compartments and dictates the femoral rotation cuts when these are equal. The purpose of this study was to compare the traditional methods of femoral rotation (TEA, AP axis, and posterior referenced) to this novel approach using computer navigation with the force sensor to determine a balanced flexion gap.
Methods
This was a prospective cohort study of 50 consecutive primary TKA's. Inclusion criteria were diagnosis of OA and primary TKA. Exclusion criteria were inability to use force sensing device. The cohort consisted of 29 females and 19 males with an average age of 70.8 years (50.2-90.3) and BMI of 32.0 (19.8 – 56.1). Intra-operative data was collected using computer navigation. Post operative CT scans were obtained on 31 of the 50 knees to assess femoral implant rotation to the patients' true TEA. CT measurements were made by two different observers. Simple descriptive statistics and t-tests were used for analysis.
Results
The novel approach, which is assumed to be a well-balanced/symmetric flexion gap, had an average rotation within 1.8 degrees to the TEA as evidenced by the CT measurements. The navigation data showed that the posterior referenced, TEA, and AP method would have resulted in an asymmetric flexion gap (greater than 3° from CT observed TEA) in 52%, 52%, and 44% respectively as opposed to the novel approach at 23%.
Conclusion
This study showed that this novel device when accompanied with computer navigation can result in a balanced flexion gap and femoral implant rotation within 3° of the TEA 77% of the time.
