Original article
Intraoperative flexion against gravity as an indication of ultimate range of motion in individual cases after total knee arthroplasty

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Abstract

To assess a method of predicting the final postoperative flexion in individual cases after total knee arthroplasty, 364 primary posterior cruciate-retaining total knee arthroplasties were reviewed retrospectively. The knees were subdivided into three preoperative flexion groups—I: poor motion (0° to 85°), II: intermediate motion (90° to 110°), and III: good motion (115° to 140°). There were 302 cases of osteoarthritis and 62 rheumatoid knees (12 juvenile rheumatoid). Correlation was made between preoperative; intraoperative, and postoperative (minimum 2-year follow-up) passive knee flexion for individuals. Intraoperative flexion against gravity was measured after capsular closure by passively flexing the patient's hip 90° and allowing the weight of the lower leg to flex the knee joint. The overall mean value of postoperative flexion for all three groups was similar to preoperative and intraoperatire flexion in both osteoarthritis and rheumatoid arthritis. In the poor motion group (I) postoperative flexion (103°) was increased over preoperative flexion (84°) but similar to intraoperative flexion (104°). In the intermediate group (II), postoperative flexion (110°) was similar to both the preoperative flexion (108°) and intraoperative flexion (110°). In the good group (III), postoperative flexion (119°) tended to be less than preoperative flexion (123°) and more than intraoperative flexion (116°), but the differences were not statistically significant. When comparing preoperative and intraoperative flexion to postoperative flexion for individual cases, 55% of knees had postoperative flexion ±10° of their preoperative value, while 97% of knees had postoperative flexion ±10° of their intraoperative value. This study indicates that the final postoperative mean flexion for a group of patients with poor preoperative flexion (<85°) and for individual cases (regardless of their preoperative mobility) can best be predicted by intraoperative flexion against gravity rather than by a preoperative value.

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