【INTRODUCTION】Lumbar spinal stenosis (LSS) and knee osteoarthritis (KOA), both of which are age-related degenerative diseases, are independently correlated with increased pain and dysfunction of the lower extremities. However, there have been few studies to investigate whether LSS patients with KOA exhibit poor clinical recovery following lumbar spinal surgery. The aim of this study is to elucidate the surgical outcomes of lumbar spinal surgery for LSS patients with KOA using multiple health-related quality of life (HRQOL) parameters.

【METHODS】A total of 865 consecutive patients who underwent posterior lumbar spinal surgery for LSS were retrospectively reviewed. Patients with failed back syndrome, past history of orthopaedic surgery at other sites, major postoperative complications and medical history of hip osteoarthritis were excluded. Following the initial identification of KOA based on medical history, cases with radiographic KOA of Kellgren-Lawrence grade ≥ 2 were included in this study. Baseline characteristics, radiographic parameters, visual analog scale (VAS) and multiple HRQOL parameters were analyzed preoperatively and at 1-year follow-up. HRQOLs included Zurich Claudication Questionnaire (ZCQ), Oswestry Disability Index (ODI), Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36), and Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ). Statistical analyzes were performed using Student t-test, Mann-Whitney U-test, Pearson’s chi-square test, and Wilcoxon signed-rank test.

【RESULTS】A total of 32 LSS patients with KOA were identified; 128 age- and sex-matched LSS patients without KOA were selected as controls. There were no differences in the baseline characteristics between the two groups. In the preoperative radiographic parameters, pelvic tilt was significantly higher in the KOA group than in the control group (27.3° ± 8.6° vs. 24.1° ± 9.2°, P = 0.046). Although there were no significant differences in postoperative ZCQ and ODI scores between the two groups, all HRQOL parameters markedly improved at the 1-year follow-up compared with preoperative scores in both groups (P < 0.01). Postoperative VAS scores for pain in buttocks and lower limbs were significantly higher in the KOA group than in the control group (3.8 ± 3.3 vs. 2.4 ± 2.8, P = 0.007). In SF-36, the postoperative mean score for physical functioning (59.7 ± 25.7 vs. 69.9 ± 23.9, P = 0.035), role physical (61.1 ± 28.0 vs. 72.7 ± 24.1, P = 0.034) and vitality (49.0 ± 20.5 vs. 56.9 ± 16.3, P = 0.048) was significantly lower in the KOA group than in the control group. The effective rate of social life domain in the JOABPEQ was lower in the KOA group than in the control group (22.6% vs. 62.2%, P < 0.001).

【DISCUSSION】The surgical outcomes of LSS patients with KOA are favorable, although poorer than those of LSS patients without KOA, particularly in terms of social life and activities. These results indicate that LSS patients with KOA experience difficulty in routine work or ordinary activities due to knee pain or restricted knee ROM even after lumbar spinal surgery. Hence, preoperative KOA status warrants consideration when planning lumbar spinal surgery and estimating surgical outcomes of LSS.