| Summary: | 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 <30 years, 88%); 2793 patients were assigned to the flat foot group and 11,172 individuals to the non–flat foot group matched by age, sex, and index year. The mean follow-up duration was approximately 74 months. In total, 329 (11.78%) patients in the study group and 931 (8.33%) patients in the comparison group developed spinal DJD. The adjusted HR (95% CI) of spinal DJD for study group was 1.423(1.250–1.619) compared with the control. Sensitivity analyses with propensity score match and different scenario about spinal DJD enrollment showed similar results. Subgroup analysis showed that in patients 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.
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