Flat foot and spinal degeneration: Evidence from nationwide population-based cohort studyKey points

Background/Purpose: Flat foot can alter the lower limb alignment and cause knee and back pain. To explore the association between flat foot and spinal degeneration. Methods: By using a claims dataset containing 1 million random samples, individuals with flat foot were identified between January 1, 2000, and December 31, 2013. The study assembled a flat foot group and a matched non–flat foot group. Definition of flat foot was according to International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes. The diagnosis date was defined as the index date for follow-up initiation. The follow-up period was defined as the duration from the index date (or nested index date for controls) to the occurrence of spinal degenerative joint disease (DJD), or December 31, 2013. The primary outcome was record of spinal DJD retrieved from the same database. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), with the control group as a reference. Results: We identified 13,965 patients (most aged 45 years with history of flat foot, the adjusted hazard ratios were 1.434, 3.065, 3.110, and 2.061 in association with spondylosis, intervertebral disc disorder, cervical stenosis, thoracic-lumbar-sacral stenosis, respectively. Conclusion: Flat foot was found to be an independent risk factor for subsequent spinal DJD