Does soft tissue balancing using intraoperative pressure sensors improve clinical outcomes in total knee arthroplasty? A protocol of a multicentre randomised controlled trial.

INTRODUCTION: Soft tissue imbalance is considered to be a major surgical cause of dissatisfaction following total knee arthroplasty (TKA). Surgeon-determined manual assessment of ligament tension has been shown to be a poor determinant of the true knee balance state. The recent introduction of intraoperative sensors, however, allows surgeons to precisely quantify knee compartment pressures and tibiofemoral kinematics, thereby optimising coronal and sagittal plane soft tissue balance. The primary hypothesis of this study is that achieving knee balance with use of sensors in TKA will improve patient-reported outcomes when compared with manual balancing. METHODS AND ANALYSIS: A multicentred, randomised controlled trial will compare patient-reported outcomes in 222 patients undergoing TKA using sensor-guided balancing versus manual balancing. The sensor will be used in both arms for purposes of data collection; however, surgeons will be blinded to the pressure data in patients randomised to manual balancing. The primary outcome will be the change from baseline to 1 year postoperatively in the mean of the four subscales of the Knee Injury and Osteoarthritis Outcome Score (KOOS4) that are most specific to TKA recovery: pain, symptoms, function and knee-related quality of life. Secondary outcomes will include the surgeon's capacity to determine knee balance, radiographic and functional measures and additional patient-reported outcomes. Normality of data will be assessed, and a Student's t-test and equivalent non-parametric tests will be used to compare differences in means among the two groups. ETHICS AND DISSEMINATION: Ethics approval was obtained from South Eastern Sydney Local Health District, Approval (HREC/18/POWH/320). Results of the trial will be presented at orthopaedic surgical meetings and submitted for publication in a peer-reviewed journal. TRIAL REGISTRATION NUMBER: ACTRN#12618000817246.

Does bone cement influence soft tissue balancing in total knee arthroplasty?

BACKGROUND: Soft tissue tension significantly affects the function of total knee arthroplasties. This study aims to evaluate if there is a difference in soft tissue tension, comparing trails to cemented definitive components in TKA. METHODS: We prospectively compared femorotibial compartment pressures before and after cement fixation of the components in 40 primary TKA. Femorotibial pressures were measured in the medial and lateral compartment with the knee in 10°, 45°, and 90° of flexion (six measurements per TKA), and the difference in pressure between both compartments was calculated in the three positions. RESULTS: The median femorotibial pressures were not significantly different following cement fixation. There was, however, a change in the difference between medial and lateral compartment pressures after cement fixation. The difference between both compartment pressures decreases after cement fixation. This difference is statistically significant only with the knee in 10° of flexion; mean (IQR) pressures change from 8.5 (five to 14) pounds to six (2.25-10) pounds (P = 0.01). CONCLUSION: Compartment pressures in TKA do not significantly change after cement fixation. The number of TKA that qualifies as 'balanced' increases after cement fixation, predominantly because the differences between the medial and lateral compartment pressures decrease.

The Reliability of Sensor-Assisted Soft Tissue Measurements in Primary Total Knee Arthroplasty.

BACKGROUND: In pursuit to improve soft tissue balancing in total knee arthroplasties (TKAs), a wireless device was introduced to assess femorotibial pressures. The aim of this study was to evaluate the reliability of this device. METHODS: After 33 TKAs were balanced by conventional techniques, contact pressures were measured using a wireless sensor 3 times in a row; twice while the examiner was blinded for the result (n = 29); and once while the examiner was able to see the result as visual feedback (n = 32). Femorotibial pressures were measured in the medial and lateral compartments with the knee in 10°, 45°, and 90° of flexion (6 measurements per TKA). Furthermore, both the combined pressure and the difference in pressure between the compartments was calculated throughout the 3 positions (together another 6 measurements per TKA). RESULTS: The intraclass correlation coefficient between the blind measurements was poor in 2 of the 12 (17%), moderate in 4 of 12 (33%), and good in 6 of 12 (50%) measurements. The intraclass correlation coefficient between the blind and observing measurement was poor in 2 of the 12 (17%), moderate in 6 of 12 (50%), and good in 4 of 12 (33%) measurements. Especially measurements in 10° of flexion are associated with poorer reliability. CONCLUSION: The wireless sensor has a moderate to good reliability in 83% of the measurements.