Patient satisfaction after total knee arthroplasty is better in patients with pre-operative complete joint space collapse

AIM OF THE STUDY: To determine if pre-operative radiologic minimal joint space width (mJSW) is related to the outcome of total knee arthroplasty (TKA) (primary hypothesis). Likewise, the aim was to test if pre-operative mJSW is related to prosthesis survival (secondary hypothesis). METHODS: A retrospective comparative analysis was performed. Group 1 was comprised of patients with pre-operative mJSW 0–1 mm. Group 2 were patients with pre-operative mJSW ≥ 2 mm. The clinical outcome was determined with the Western Ontario and MacMaster Universities Osteoarthritis Index (WOMAC) score pre-operatively and one year after TKA. Only patients with pre-operative weight-bearing radiographs and complete WOMAC score data were accepted. RESULTS: Available for analysis were 377 patients, of whom 188 were allocated to Group 1 (118 female, 70 male, age 70 ± 11 years) and 189 to Group 2 (118 female, 71 male, age 70 ± 13 years). Pre-operative WOMAC total and WOMAC subscores showed no significant differences between groups. Post-operatively, the WOMAC total was significantly better in Group 1 than in Group 2, 10 ± 22 and 19 ± 31, respectively (p < 0.001, Power 97.5%). Similarly, the WOMAC subscores for pain, stiffness, and function were also significantly better in Group 1 than in Group 2. Five-year prosthesis survival was 94.2 and 91.6% in Groups 1 and 2, respectively (p = 0.07, Power 71%). DISCUSSION: Patients with pre-operative complete joint space collapse (0 to 1 mm mJSW) achieve a significantly better WOMAC result from TKA than do those with a mJSW equal to or greater than 2 mm. From our findings, it is recommended that “complete joint space collapse” especially be used as an indication for TKA surgery. CONCLUSION: Our study was underpowered to sufficiently show an effect of pre-operative mJSW on prosthesis survival. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00264-018-4185-3) contains supplementary material, which is available to authorized users.