Can Smartphones Quantify Ambulatory Recovery After Lumbar Spine Surgery? A Pilot Study of Deformity and Degenerative Pathology Using 35,000 Days of Objective Mobility Data

Study Design. Pilot retrospective cohort Objective. Using smartphones, we compared degenerative lumbar spine surgery and thoracic/lumbar deformity surgery regarding: 1) long-term changes in daily mobility parameters, and 2) timelines for postoperative recovery. Summary of Background Data. Although degenerative lumbar disease and adult spinal deformity (ASD) impair ambulation differently, postoperative mobility is typically evaluated using the same subjective questionnaires. Methods. We enrolled patients undergoing degenerative lumbar surgery (decompression or ≤4-level fusion) or thoracic/lumbar deformity surgery (≥5-level fusion with sagittal and/or coronal malalignment) to share iPhone mobility data. Mobility parameters were daily steps, walking distance (miles), and flights climbed. Primary outcomes were change in daily mobility from preoperatively to last follow-up, adjusting for age, sex, and baseline mobility, as well as timelines for postoperative ambulatory recovery , using segmented regression analysis. Results. 49 patients (39 degenerative, 10 deformity) contributed 35,249 patient-days of data. Mean age was 52.3±16.9 years; 44.9% were female. Both cohorts experienced an immediate postoperative decline in all mobility parameters, followed by recovery beginning at approximately 2-months in degenerative patients and 4-months in deformity patients. At last follow-up, walking distance improved most after degenerative surgery, while flights climbed improved most after deformity surgery. Among degenerative patients, ambulatory improvement significantly correlated with lower disability and leg pain, while among deformity patients, larger postoperative reductions in in L1-pelvic angle and T4-pelvic angle were both associated with greater improvement in flights climbed (r< -0.60 for both). Conclusion. In this pilot study of patients with uncomplicated postoperative courses, both degenerative and thoracic/lumbar deformity surgery resulted in sustained long-term mobility improvement, though recovery timelines differed. Objective ambulatory improvement correlated with subjective improvement in disability and leg pain, while greater sagittal correction correlated with improved vertical mobility, highlighting smartphone mobility as a potential objective correlate of both subjective and radiographic improvement. Level of Evidence. IV