Diane E. Powell

Regional Differences in Mechanical and Material Properties of Femoral Head Cancellous Bone in Health and Osteoarthritis

AbstractOsteoarthritis (OA) is a debilitating condition common among the aging population. In this study we have determined mechanical and material properties of cancellous bone cores from two differently loaded regions of femoral heads obtained from healthy subjects and those with end-stage osteoarthritis. Densitometric properties were determined prior to compression testing for Youngs modulus (EC) and yield strength (sy), after which bones were powdered for analysis of collagen and mineral content. In both OA and normal cancellous bone, volumetric bone mineral density (BMDv), apparent density (rA), EC, and sy were systematically greater in the superior than in the inferior region (P<0.05). In the OA inferior region, median BMDv (0.434 g-cm-3) and rA (0.426 g-cm-3) were significantly greater than in normals (0.329 and 0.287 g-cm-3, respectively, both P<0.05) reflecting an increased amount of tissue. The mineral:collagen ratio was decreased in OA, but this was only significant in the superior region (P<0.008). Relationships between EC and both BMDv and rA were weaker in OA bone cores (r2 = 0.66 and r2 = 0.59) than in normals (r2 = 0.86 and r2 = 0.77, respectively). Likewise, sy and both BMDv and rA were weaker in OA (r2 = 0.74 and r2 = 0.70) than in normals (r2 = 0.83 and r2 = 0.77, respectively). For the same value of density measure, EC and sy tended to be lower in OA bone when compared with normal bone. In conclusion, femoral head cancellous bone mass in end-stage osteoarthritis is increased but undermineralized, and is neither stiffer nor stronger than normal cancellous bone.

Increased circulating Dickkopf-1 in Paget's disease of bone

UNLABELLED Dickkopf-1 (Dkk-1) is a secreted inhibitor of Wnt signaling which in adults regulates bone turnover. Dkk-1 over-production is implicated in osteolytic disease where it inhibits bone formation and stimulates bone breakdown. Recently it was reported that osteoblastic cells from Pagets disease of bone (PDB) over-expressed Dkk-1. OBJECTIVE To see if increased Dkk-1 was detected in serum from patients with PDB. RESULTS Dkk-1 and total serum alkaline phosphatase activity (tsAP) were significantly elevated in sera from PDB patients. Patients with polyostotic PDB had significantly higher levels of tsAP but not Dkk-1, than monostotic patients. TsAP but not Dkk-1, was significantly lower in sera from bisphosphonate treated versus untreated PDB patients. Dkk-1 and tsAP were not significantly correlated. CONCLUSIONS Dkk-1 may be a useful biomarker of PDB and we speculate that Dkk-1 may play a central role in the etiology of PDB.

Plasma osteocalcin in healthy Nigerian children and in children with calcium-deficiency rickets

Osteocalcin is an osteoblast-specific protein believed to be associated with events occurring during bone mineralization, which has been widely used clinically as an indicator of osteoblast function. Plasma osteocalcin concentrations (pOC) were studied in 94 (59 male, 35 female) healthy and 44 (21 male, 23 female) rachitic Nigerian children, all one to five years of age. The study was aimed at establishing a reference range for healthy Nigerian children determining any changes in plasma osteocalcin levels occurring in children with calcium-deficiency rickets. In the controls, pOC levels ranged from 3–89 ng/ml, with a mean value of 23±19 ng/ml. The values were higher in girls (29±21 ng/ml) than in boys (21±18 ng/ml), though not significantly. The controls had values consistent with other published pediatric ranges from Europe and North America. In the younger rachitic children (under 3 years) the mean pOC was lower than in the controls (P=0.04) despite the much elevated plasma levels of 1,25(OH)2D. In the controls, pOC correlated with 1,25(OH)2D (r=0.59, P=0.003), alkaline phosphatase (r=0.22, P=0.03), and inorganic phosphate (r=0.27, P=0.01). These correlations were lost in the rickets group. The findings in the controls confirm the known association between plasma 1,25(OH)2D and circulating osteocalcin levels, whereas the findings in the rickets group suggest that the stimulatory effects of 1,25(OH)2D on osteocalcin may depend on other permissive factors, such as normal circulating levels of calcium and phosphate.