1st Study to Test Surgeon Force Effect on Knee Balance

Collaborative work between Hospital for Special Surgery in New York and the Faculty of Engineering at Cairo University in Egypt has looked into the art of soft tissue balancing with the recent publication, “Arthroplasty Surgeons Differ in Their Intraoperative Soft Tissue Assessments: A Study in Human Cadavers to Quantify Surgical Decision-making in TKA,” which appears in the August 2022 edition of Clinical Orthopaedics and Related Research.

“This study covers a gap in the literature regarding the extent to which the variation in performing intraoperative knee balance assessment among surgeons impacts intraoperative decision-making,” said co-author Shady Elmasry, Ph.D. to OTW. “It’s important to highlight this heterogeneity among surgeons now since there are many tools that are being developed to assist surgeons in achieving knee balance that ignore these variations in how different surgeons approach/define a balanced knee after total knee arthroplasty (TKA).”

The researchers used seven human cadavers (lower extremities from pelvis to toe) with posterior cruciate ligament substituting (posterior stabilized) TKA implants on the right knees to test and collect data. Five fellowship-trained knee surgeons (with 24, 15, 15, 7, and 6 years of clinical experience) and one chief orthopedic resident assessed soft tissue balance in each knee for extension (0° of flexion), midflexion (30° of flexion), and flexion (90° of flexion) and then selected a polyethylene insert.

The team used pliable force sensors on the leg to measure the loads applied by each surgeon. The team measured knee kinematics with 3D motion capture and also used dynamic analysis software to estimate the medial and lateral gaps.

Dr. Elmasry summarized the outcome of this study OTW, “My most important results were:

1. During the intraoperative assessment of knee balance in TKA, five surgeons and one chief resident applied different moments in midflexion and flexion angles and targeted different gaps in extension, midflexion, and flexion angles;
2. in the manual intraoperative knee balance assessment, changes in the surgeon’s applied moments of 9 and 11 Nm (22 to 27 N on the surgeons’ hands) in flexion and extension, respectively, yielded at least a 1-mm change in choice of insert thickness.”

A “Must Have”—Force Measurement

“The main recommendation of this study,” said Dr. Elmasry to OTW, “was that developers of tools to standardize soft tissue assessment in TKA should consider controlling the force applied by the surgeon to better control for variations in intraoperative decision-making. Also, the study quantified for the first time the variations among surgeons in performing knee balance exams and how they may be related to the final decision-making, which may contribute to better-achieving knee balance following TKA.”