Can mobile-bearing unicompartmental knee arthroplasty achieve natural gap-balancing： an observational study with novel pressure sensor

BackgroundMobile-bearing unicompartmental knee arthroplasty (MB-UKA) is an effective treatment for anteromedial knee osteoarthritis. Meticulous intraoperative soft tissue balancing remains challenging yet consequential for a successful operation. Currently, surgeons rely mostly on their experience during soft tissue balancing, yielding unreproducible results. This study aimed to further optimize clinical results of MB-UKA through quantitative measurements of intraoperative medial compartment soft tissue tension and determination of target tension values most consistent with the natural state.MethodsThis was an observational study of 24 consecutive patients. All 30 UKAs were performed by a single surgeon. The piezoresistive sensor was custom designed to fit in the medial compartment gap. Contact pressures were measured at 5 angular positions of the knee intraoperatively: 0°, 20°, 45°, 90°, and 110° of flexion. The change in pressure from extension (20° position) and flexion (110° position) was also calculated (E-FPD). Data on age, sex, body mass index, operative side, and bearing size were collected. Outcome measures were measured at baseline and at the 6-month postoperative follow-up; Oxford Knee Score, visual analog scale score, and range of motion were compared to evaluate clinical outcomes. Results There was a significant improvement in patients in all measured outcomes at 6 months from baseline. The E-FPD of 14.9 N (8.9, 24.6) was indicative of appropriate soft tissue balancing throughout the functional range of knee motion. Of 30 knees, 22 were 3-mm bearing and 8 were 4- or 5-mm bearing. The pressure data of the 3-mm bearing group was larger than that of the non-3-mm bearing group for each knee flexion degree, but the difference was not statistically significant.Conclusions Objective data from sensor output may assist surgeons in decreasing loading variability during MB-UKA. The data suggested that MB-UKA could not accurately restore soft tissue tension to the natural state, which was related to the inability of MB-UKA surgical instruments to fine adjust the bone cut and soft tissue release. We suggest designing a new type of 3.5 G-clamp to help better obtain the soft tissue tension close to the natural tension.Study registration:Chinese Clinical Trial Registry (http://www.chictr.org.cn): ChiCTR1900024146.