[Bone remodeling assessment after total hip replacement]

It is known that total hip arthroplasties (THA) lead to adaptative remodeling changes resulting in periprosthetic bone loss. DEXA is recognized as the most precise and accurate method for quantifying bone mineral density (BMD) in humans. The present study compares over two years after THA, DEXA data to those of urinary deoxypyridinoline (uDPYR), a pyridinium crosslink of bone collagen fibrils proven to be a reliable bone resorption marker. 41 patients (21 postmenopausal female, 20 male) underwent cemented THA. Urinary excretion of DPYR was determined using ACS : 180 SE (Bayer Diagnostics) and normalized for creatinine excretion while periprosthetic BMD (g/cm2) was measured (QDR 4500, Hologic), at post-operative day, 3 months, 1 year and 2 years after surgery. The 7 periprosthetic subregions (R1-R7) of the Gr en method are the regions of interest for evaluating bone remodeling process. uDPYR showed a significant decrease between postoperation and 1 year: 10.6 0.80 vs 4.8 0.6 nmol/mmol, p < 0.0001 (Wilcoxon Test for paired samples and statistical significance accepted at p < 0.05) and non significant variation between 1 and 2 years. Between post-operation and 3 months global and regional BMDs decrease significantly (p < 0.04) followed by an increase in distal BMD (R3, R4, R5). During the second year BMD increases also for other regions. At 2 years BMD in distal regions is recovered except in the proximal R7 when comparing post-operation and 2 years, pattern consistent with literature. Thus, a discrepancy is observed between uDPYR and DMO results that does not allow us to use a bone resorption urinary marker to monitore local bone periprosthetic remodeling.