Soft tissue balance in total knee arthroplasty: does stress relaxation occur perioperatively?

The restoration of correct soft tissue tension is key to achieving a successful total knee arthroplasty. However, it remains unclear whether the status achieved immediately after the operation will persist over time. Some surgeons believe soft tissue stress relaxation occurs and therefore the knee loosens somewhat after the procedure. It was the aim of this study to investigate this hypothesis. We analyzed 25 in vivo total knee implantations using contemporary computer navigation technology to assess and quantify perioperative soft tissue relaxation. Mediolateral joint laxity and maximal passive extension were analyzed immediately intraoperatively and 30 minutes later under the same conditions. Stress relaxation occurred in all cases, leading to increased mediolateral laxity by an average of 1 mm on the medial and lateral sides. Maximal passive extension increased by an average of 3 degrees. This data confirms the hypothesis the knee becomes looser in the early phase after total knee arthroplasty.