High whole-body bone mineral density in ossification of the posterior longitudinal ligament

BACKGROUND CONTEXT Recent studies suggest that ossification of the posterior longitudinal ligament (OPLL) is exacerbated by systemic metabolic disturbances, including obesity. However, although an increase in bone mineral density (BMD) measured at the lumbar spine has been reported in patients with OPLL, no studies have investigated the systemic BMD of patients with OPLL in detail. PURPOSE We investigated whether patients with OPLL develop increased whole-body BMD. STUDY DESIGN Single institution cross-sectional study. PATIENT SAMPLE Data were collected from Japanese patients with symptomatic OPLL (OPLL [+]; n = 99). Control data (OPLL [-]; n = 226) without spinal ligament ossification were collected from patients who underwent spinal decompression, spinal fusion, or hip replacement surgery. OUTCOME MEASURES Demographic data, including age, body mass index (BMI), comorbidities, history of treatment for osteoporosis, and history of vertebral and non-vertebral fractures, was obtained from all participants. In addition, whole-body BMD, including the lumbar spine, thoracic spine, femoral neck, skull, ribs, entire upper extremity, entire lower extremity, and pelvis, were measured in all participants using whole-body dual-energy X-ray absorptiometry (DXA). METHODS Patient data were collected from 2018 to 2022. All participants were categorized based on sex, age (middle-aged [<70 years] and older adults [≥70 years]), and OPLL type (localized OPLL [OPLL only in the cervical spine], diffuse OPLL [OPLL in regions including the thoracic spine]), and OPLL [-]) and each parameter was compared. The factors associated with whole-body BMD were evaluated via multivariable linear regression analysis. RESULTS Compared with the OPLL (-) group, the OPLL (+) group of older women had significantly higher BMD in all body parts (P <0.01), and the OPLL (+) group of older men had significantly higher BMD in all body parts except the ribs, forearm, and skull (P <0.01). The factors associated with increased BMD of both the femoral neck (load-bearing bone) and skull (non-load-bearing bone) were age, BMI, and co-existing diffuse OPLL in women and BMI and co-existing localized OPLL in men. CONCLUSIONS Patients with OPLL have increased whole-body BMD regardless of sex, indicating that it is not simply due to load-bearing from obesity. These findings suggested that OPLL is associated with a systemic pathology.