Is There a Threshold for Stiffness Complaints Following TKA on the WOMAC Stiffness Subscale?

Background: Stiffness complaints after total knee arthroplasty (TKA) are frequent, yet poorly understood and can be challenging for surgeons to address. The WOMAC stiffness subscale is a widely used measure of stiffness and can serve as a simple screening tool for complaints. Questions/Purposes: We aimed to identify a threshold for stiffness complaints on the WOMAC stiffness subscale and investigate its overlap with range of motion (ROM) in TKA patients. Methods: TKA patients were enrolled preoperatively and followed for 6 months. At follow-up, patients reported their ROM, completed the WOMAC stiffness subscale (range 1–8 with 8 continuous stiffness) and indicated whether they experienced more stiffness than expected. To identify a threshold for complaints, we compared patients’ WOMAC stiffness scores to when they experienced more stiffness than expected, visually, and statistically. We also mapped ROM limitations at 6 months to WOMAC stiffness scores. Finally, we determined if baseline characteristics were associated with stiffness complaints. Results: Two hundred and forty-six TKA patients were enrolled preoperatively with 82% follow-up rate at 6 months. Our results showed that patients with a WOMAC stiffness score = 3+ were significantly more likely to experience more stiffness than expected. Patients reporting full ROM (54%) reported a wide range of WOMAC stiffness subscale scores (1–6). Baseline WOMAC pain and function scores were the only factors associated with stiffness complaints. Conclusions: ROM is a poor surrogate of patient-reported stiffness, and the patients’ perception of “stiffness” is clearly more complex than just ROM. We identified a WOMAC threshold that could potentially easily serve this purpose.