The co-existence of osteoporosis (OP) and osteoarthritis (OA) remains obscure. No systematic studies have been carried out to exclude the possibility that especially female osteoarthritic patients selected for cementless total hip arthroplasty (THA) suffer from primary or secondary OP.
A subgroup of fifty-three female patients (average age, 64.7 years) with advanced primary hip OA scheduled for cementless THA were recruited for DXA and laboratory screening. Before surgery, bone mineral density (BMD) of the lumbar spine, the proximal femurs and the distal forearm were measured. The serum concentrations of calcium, 25-hydroxyvitamin D, parathyroid hormone and biochemical markers of bone resorption and formation were determined to exclude secondary OP.
The prevalence of OP (T score <-2.5) and osteopenia (-1.0 >T score >-2.5) were 28% and 45%, respectively. Statistically, OP was related to patient's age, low BMI, postmenopausal status and not having estrogen replacement therapy. Five patients (9%) had laboratory findings of secondary OP. Two of them were found to have a parathyroid adenoma. The prevalence of vitamin D insufficiency [S-25(OH)D levels <or=50 nmol/l] was 36% (n=19). As a sign of high bone turnover, the patients with reduced BMD values showed significantly increased serum levels of osteocalcin (p=0.049), intact procollagen type I N propeptide (p=0.040) and N-terminal crosslinking telopeptide of type I collagen (p=0.046). The BMC of the femoral necks of the osteoarthritic hips were significantly higher (p<0.001) and the BMC of the trochanter regions significantly lower (p=0.005) compared to the contralateral hips.
Against a general belief, OA does not seem to protect a patient from generalized primary OP. The majority (74%) of the female hip OA patients were osteopenic or osteoporotic with signs of increased bone turnover. The observed prevalence of reduced BMD corresponds with the published data of age-matched population. An unexpectedly high number of patients required preoperative consultation with an endocrinologist. The altered distribution of BMD observed in the proximal femurs may explain the lower prevalence of fractures reported in the femoral necks of osteoarthritic hips.