Bone densities and bone geometry in children and adolescents with arthrogryposis

Objective: To describe bone densitometry results using lumbar spine dual-energy X-ray absorptiometry and forearm peripheral quantitative computed tomography (pQCT) in children with arthrogryposis multiplex congenita (AMC).

Study design: Prospective study.

Results: Lumbar spine areal bone mineral density (BMD) was measured in 58 participants (mean age 6.8 years, range 1 month to 19.7 years; 26 males). The diagnostic subgroup was Amyoplasia in 27 participants, distal arthrogryposis (unclassified, n = 13; type 2A, n = 1; type 2B, n = 2; type 8, n = 2) in 18 patients, an unclassified form of arthrogryposis in 6 patients, and a syndromic form of arthrogryposis in 7 patients. The mean lumbar spine areal BMD was -0.4 (SD: 1.5) which was significantly below 0 (p < 0.05, one-sample t-test). The mean lumbar spine bone mineral apparent density z-score (+0.4 [SD: 1.4]), a measure that is largely independent of bone size, was not significantly different from 0 (P > 0.05). A subset of 22 patients aged 6 years or older (mean age 10.9 years, 11 males) had forearm pQCT analysis. Mean z-scores for trabecular and cortical volumetric BMD at the radius were similar to healthy controls. Radius periosteal bone circumference and bone mineral content were appropriate for height. These densitometric results did not differ between patients with Amyoplasia or individuals with other diagnoses.

Conclusions: Low areal BMD in children and adolescents with AMC reflects their smaller bone size rather than a specific bone mass deficit. These data do not suggest that children and adolescents with AMC in general require regular monitoring by bone densitometry unless there are specific clinical concerns.