Quantitative Computed Tomography Assessment of Bone Deficits in Ambulatory Children and Adolescents with Spina Bifida: Importance of Puberty

Abstract

Pathologic fractures of the femur and tibia are common in youth with spina bifida (SB). These fractures may be associated with deficient bone accrual due to decreased ambulation and skeletal loading. This prospective cohort study used quantitative computed tomography (QCT) to assess three‐dimensional (3D) bone properties in children and adolescents with SB. Eighty‐three ambulatory youth with SB underwent QCT imaging of the tibia at up to four annual visits between ages 6 to 16 years (294 total visits averaging 3.5 visits/patient). A total of 177 controls without disability and 10 non‐ambulatory youth with SB underwent imaging once. Bone geometric properties (cortical bone area, cross‐sectional area, cortical thickness, cortical density, and moments of inertia) were measured at the mid‐diaphysis (50% of bone length); cross‐sectional area, cancellous density, and density‐weighted area were measured in the proximal (13% of bone length) and distal (90% of bone length) metaphyses. Bone properties were compared between the ambulatory SB and control participants, among SB neurosegmental subgroups (sacral, low lumbar, mid lumbar and above) as a function of pubertal stage (prepubertal, pubertal, postpubertal), and considering SB type (myelomeningocele, lipomyelomeningocele) using linear mixed effects models adjusted for sex, age, height percentile, and body mass index (BMI) percentile. Only cancellous density of both metaphyses and weighted area of the proximal metaphysis differed between ambulatory children with SB and controls before puberty. However, significant deficits in all bone properties manifested during and after puberty as moderate bone growth in the SB group failed to keep pace with the large increases normally observed during puberty. The bone deficits primarily affected patients with myelomeningocele, and similar deficits were observed at all neurosegmental levels except that cancellous density was closer to normal in the sacral group. Descriptive analysis of the 10 non‐ambulatory youth with SB showed greater bone deficits than ambulatory children, particularly for cancellous density in the distal metaphysis. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Independently ambulatory children with spina bifida experience near-typical joint moments and forces during walking

“…Bone strength outcomes for all participants were calculated from quantitative computed tomography scans of each participant’s tibias. Image acquisition and processing procedures are described in a previous study [9]. Of eight bone properties measured, only cancellous bone density at the proximal tibia (p=0.001) was significantly lower (p<0.05) in the group with spina bifida than in the group with typical development (Table 1).…”

“…Data for this study were previously collected at Children's Hospital Los Angeles [9,12]. This dataset contains demographic, step count, physical exam, computed tomography, and gait data of 83 ambulatory children with spina bifida and 179 children with typical development.…”

“…Children with spina bifida have diminished motor abilities [4] and spend less time being active [5] than peers with typical development, in part due to lower-limb muscle weakness. These activity differences are hypothesized to contribute to the population's increased risk of osteoporosis and low-energy fracture in lower-extremity weight-bearing long bones [6][7][8][9]. These increased risks are not constant across the population with spina bifida.…”

“…These increased risks are not constant across the population with spina bifida. With increasing ambulation and function, individuals with spina bifida have better bone health, including increased bone strength properties in the tibia [9,10] and femoral neck [11], increased tibia bone mass and volume [12], more normal tibial development [13], and lower risk for bone fracture [8]. In studying bone outcomes in individuals with spina bifida, it is important to understand why individuals with higher levels of function and ambulation demonstrate better bone health.…”

Increased Asymmetry of Trunk, Pelvis, and Hip Motion during Gait in Ambulatory Children with Spina Bifida

“…The data for our study were retrospectively gathered from children with SB and controls without disability who were seen for previous research studies in our motion analysis laboratory (Table 1) [24,25]. Inclusion criteria for both groups were age 8-13 years and ability to ambulate with or without assistive devices.…”