Introduction: Lumbar spinal stenosis (LSS) is symptomatic in 10-14% of the adult population and is the leading cause of pain and disability, and the most frequent indication for spinal surgery in older adults. While laminectomy surgery with or without fusion is effective in many patients; approximately one-third of the patients are not satisfied with the postoperative outcomes in long-term, mainly in terms of residual leg pain and poor function. We have recently evaluated walking biomechanics of patients prior to surgical treatment and found that LSS symptoms (neurogenic claudication) cause increased pelvic tilt and lumbar loading. However, biomechanical assessment of spine posture and gait changes with surgical treatment are lacking in this population. The purpose of this study was to investigate the effects of laminectomy (decompression surgery) with or without fusion on spinal posture and loading in standing and walking in patients with LSS.

Methods: Six participants (4F, 2M) with symptomatic LSS, aged 50 to 82, underwent a 3D optoelectronic motion analysis of standing and walking in 2 states (with and without LSS symptoms present) 2-10 days before surgery and 4-6 months after surgery. To provoke LSS symptoms, participants performed a standard walking capacity test. Passive reflective marker clusters were attached to participants at spinal levels, head, pelvis, and extremities. A whole body patient-specific musculoskeletal model was created for each participant and then inverse kinematics and static optimization analysis were performed to evaluate body positions and estimate maximum spine compressive loading, respectively. Fusion surgery was simulated by applying rigid constraints at the fused intervertebral segments, allowing no motion but full force and moment transmission. Primary outcome variables were average pelvic tilt, lumbar flexion, and lumbar compressive loads. Mixed effects regression models were used for statistical analysis.

Results: Following surgery, average pain score significantly decreased from 5.5 to 0.25, and walking capacity time and distance increased from 7.6 min to 15 min, and 798 m to 1020 m, respectively. 5 out of 6 patients underwent lumbar spine fusion along with laminectomy. After surgery, subjects had less pelvic tilt (vs a posterior pelvic tilt pre-surgery) and less spine flexion during walking, and lower spine loading during standing (p < 0.05). Prior to surgery, symptoms tended to cause more forward pelvic tilt and greater spine loading (both p <0.1), but these effects were not seen after surgery. However, following surgery patients showed increased spine flexion during symptomatic walking (p < 0.05).

Discussion: This is the first biomechanical study of the effects of surgical treatment on spine posture and loading in patients with LSS. Results showed that surgery significantly change spine and pelvis posture during walking, but had limited effect on spinal loading. Treatment seems to mitigate previously noted effects of claudication symptoms on pelvic tilt and spinal loading, but a new effect on spinal flexion was observed in post-surgical testing. Understanding walking biomechanics and its contribution to the post-treatment changes in patient outcomes is essential for informed decision-making on surgical treatments and developing novel rehabilitation techniques to improve patients’ walking and physical activity.