Predicting range of motion after total knee arthroplasty. Clustering, log-linear regression, and regression tree analysis.
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.
Ritter
Merrill A
MA
The Center for Hip and Knee Surgery, St. Francis Hospital, Mooresville, Indiana 46159, USA.
Harty
Leesa D
LD
Davis
Kenneth E
KE
Meding
John B
JB
Berend
Michael E
ME
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods; D016000:Cluster Analysis; D003663:Decision Trees; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D016014:Linear Models; D008297:Male; D017888:Medial Collateral Ligament, Knee / Q000601:surgery; D008875:Middle Aged; D011237:Predictive Value of Tests; D016059:Range of Motion, Articular; D012044:Regression Analysis; D012189:Retrospective Studies; D012307:Risk Factors; D012727:Sex Characteristics; D013710:Tendons / Q000601:surgery; D013997:Time Factors