Correlation between femorotibial pressure and joint gap in osteoarthritis patients with varus deformity: an intraoperative measurement using sensor device in primary posterior-stabilized total knee arthroplasty

BACKGROUND: The normal femorotibial pressure and its variation under different gap values remain unknown. Thus, for the purpose of improving soft-tissue balancing in total knee arthroplasty (TKA), a load-sensor device was used to measure femorotibial pressures. More specifically, the aim of this study was to analyze the trend in pressure changes. METHODS: Twenty TKAs were first balanced by conventional techniques, and then femorotibial pressure was measured using the sensor. After this, the difference in pressure among different joint gaps was calculated to analyze the trend. A repeated measure of analysis of variance and a Tukey’s honestly significant difference (HSD) test were used to analyze the data. RESULTS: The medial gap pressure was significantly increased at extension and flexion as the thickness of the sensor increased in most patients, while the lateral gap pressure changed without a specific trend. The average medial gap pressure was significantly larger than the average lateral gap pressure at both the full extension and 90° flexion positions. The average extension gap pressure was larger than the average flexion gap pressure at both the medial and lateral gaps. CONCLUSIONS: The tension of the soft tissue around the knee joint changes with the joint gap. The tension at the medial side is higher than that on the lateral side, and that of the extension position is higher than that of the flexion position. The use of the pressure sensor insert has a better auxiliary effect on the operation using the gap-balancing technique.