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The Journal of Bone and Joint Surgery (American) 85:1278-1285 (2003)
© 2003 The Journal of Bone and Joint Surgery, Inc.

Scientific Article

Predicting Range of Motion After Total Knee Arthroplasty

Clustering, Log-Linear Regression, and Regression Tree Analysis

Merrill A Ritter, MD, Leesa D Harty, BA, Kenneth E Davis, MS, John B Meding, MD and Michael E Berend, MD

Investigation performed at The Center for Hip and Knee Surgery, St. Francis Hospital, Mooresville, Indiana

Merrill A. Ritter, MD
Leesa D. Harty, BA
Kenneth E. Davis, MS
John B. Meding, MD
Michael E. Berend, MD
The Center for Hip and Knee Surgery, St. Francis Hospital, 1199 Hadley Road, Mooresville, IN 46159

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. One or more of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Biomet stocks). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Background: Range of motion is a crucial measure of the outcome of total knee arthroplasty. The purpose of this study was to determine which factors are predictive of the postoperative range of motion.

Methods: We retrospectively studied 3066 patients (4727 knees) who had a primary total knee arthroplasty with the same type of implant at the same center between 1983 and 1998. Statistical clustering analysis paired with log-linear regression was used to determine groupings along continuous variables. Regression tree analysis was used to characterize the combinations of variables influencing the postoperative range of motion. The variables considered were preoperative and intraoperative flexion and extension, preoperative alignment, age, gender, and soft-tissue releases.

Results: Preoperative flexion was the strongest predictor of the postoperative flexion regardless of preoperative alignment. Other factors that were significantly related to reduced flexion were intraoperative flexion (p < 0.0001), gender (p < 0.0001), preoperative tibiofemoral alignment (p = 0.0005), age (p < 0.0001), and posterior capsular release (p < 0.0001). The removal of posterior osteophytes was related to the greatest increase in postoperative flexion in the group of patients with a varus tibiofemoral alignment preoperatively.

Conclusions: The principal predictive factor of the postoperative range of motion was the preoperative range of motion. Removal of posterior osteophytes and release of the deep medial collateral ligament, the semimembranosus tendon, and the pes anserinus tendon in patients with large preoperative varus alignment and the attainment of a good intraoperative range of motion improved the likelihood that a good postoperative range of motion would be achieved.

Level of Evidence: Prognostic study, Level II-1 (retrospective study). See Instructions to Authors for a complete description of levels of evidence.


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