Purpose: Our purpose was to evaluate why some patients achieve excellent range of motion (ROM) following total knee arthroplasty (TKA) and to determine its relation to outcome.

Methods: We evaluated 618 primary unilateral TKA’s for osteoarthritis from a prospective arthroplasty database using a single implant design. 209 TKA’s with ROM greater than 120 degrees at one year follow-up were compared to 409 TKA’s with ROM less than 120 degrees to determine if age, BMI, gender, ASA class, and preop ROM differed between the two groups. Knee society and oxford knee scores were also compared both preoperatively and at one year follow-up using independent samples t-test. A multiple logistical regression analysis was performed to determine predictors of ROM.

Results: Preoperative ROM was higher (115 vs 106, p< 0.0001), BMI was lower (30.7 vs 32.9. p< 0.0001), and there was a higher proportion of males (p< 0.0001) in those patients with exceptional ROM at one year (> 120 degrees). Knee Society Score (93.7 vs 87.8, p< 0.0001) and Oxford Knee Score (20.4 vs 24.4, p< 0.0001) were superior in the exceptional ROM group at one year follow-up. In multiple logistic regression, only preoperative ROM (p< 0.0001) was a significant predictor of postoperative flexion range.

Conclusions: Body habitus may play a role in our ability to achieve exceptional flexion following TKA. Implant design has historically favoured male anatomy which may influence exceptional flexion range. Preoperative ROM still seems to be the biggest predictor of postoperative ROM. Perhaps timely surgical intervention, pre-habilitation and implant design choice can influence our ability to achieve exceptional ROM following TKA.