Reproducibility of an Intraoperative Pressure Sensor in Total Knee Replacement

Appropriate soft tissue tension in total knee replacement (TKR) is an important factor for a successful outcome. The purpose of our study was to assess both the reproducibility of a modern intraoperative pressure sensor (IOP) and if a surgeon could unconsciously influence measurement. A consecutive series of 80 TKRs were assessed with an IOP between January 2018 and December 2020. In the first scenario, two blinded sequential measurements in 48 patients were taken; in a second scenario, an initial blinded measurement and a subsequent unblinded measurement in 32 patients were taken while looking at the sensor monitor screen. Reproducibility was assessed by intraclass correlation coefficients (ICCs). In the first scenario, the ICC ranged from 0.83 to 0.90, and in the second scenario it ranged from 0.80 to 0.90. All ICCs were 0.80 or higher, indicating reproducibility using a IOP and that a surgeon may not unconsciously influence the measurement. The use of a modern IOP to measure soft tissue tension in TKRs is a reproducible technique. A surgeon observing the measurements while performing IOP may not significantly influence the result. An IOP gives additional information that the surgeon can use to optimize outcomes in TKR.

COMPARISON OF COMMERCIAL PATELLOFEMORAL ARTHROPLASTY SYSTEMS ON THE BASIS OF PATELLA KINEMATICS, PERI-PATELLAR SOFT TISSUE TENSION AND PROSTHESIS DESIGN

Patellofemoral arthroplasties are desirable when treating isolated patellofemoral osteoarthritis, due to preservation of the tibiofemoral joint. Since few studies report on new commercial patellofemoral prosthesis biomechanics, a musculoskeletal model enabling analysis of subject-specific knee biomechanics was used to compare four patellofemoral replacement systems (A, B, C, and D) to one another. The prostheses were implanted according to manufacturer guidelines, after which the knee flexed and extended under active muscle loading. An increased patellotrochlear index enabled early patella-trochlear groove engagement. The resurfaced patellae were stable in mediolateral shift and anteroposterior displacement, but only Prosthesis A and D provided a smooth transition between the distal prosthesis border and femoral cartilage. A reduction in the anteroposterior condylar distance displaced the patella posteriorly, resulting in reduced peri-patellar soft tissue tension but an increased patella tendon–quadriceps tendon ratio. The tibial tubercle–trochlear groove distance became pathologic in all replacements. The patella will be stable irrespective of the prosthesis used, but Prosthesis A and D seem to provide a better fit to the trochlear groove anatomy. The increased tibial tubercle–trochlear groove distance emphasizes the importance of extensor alignment in combination with the placement of the prosthesis: an increased Q-angle might lead to excessive lateral wear on the patella button. The extensor mechanism load will increase post-surgery based on the rise in the patella tendon–quadriceps tendon ratio which points to a reduced moment arm. This work provides insight into the dynamic biomechanical function and the design of current commercial patellofemoral replacement systems.