Focal osteoporosis defects play a key role in hip fracture

Abstract

BackgroundHip fractures are mainly caused by accidental falls and trips, which magnify forces in well-defined areas of the proximal femur. Unfortunately, the same areas are at risk of rapid bone loss with ageing, since they are relatively stress-shielded during walking and sitting. Focal osteoporosis in those areas may contribute to fracture, and targeted 3D measurements might enhance hip fracture prediction. In the FEMCO case-control clinical study, Cortical Bone Mapping (CBM) was applied to clinical computed tomography (CT) scans to define 3D cortical and trabecular bone defects in patients with acute hip fracture compared to controls. Direct measurements of trabecular bone volume were then made in biopsies of target regions removed at operation.MethodsThe sample consisted of CT scans from 313 female and 40 male volunteers (158 with proximal femoral fracture, 145 age-matched controls and 50 fallers without hip fracture). Detailed Cortical Bone Maps (c.5580 measurement points on the unfractured hip) were created before registering each hip to an average femur shape to facilitate statistical parametric mapping (SPM). Areas where cortical and trabecular bone differed from controls were visualised in 3D for location, magnitude and statistical significance. Measures from the novel regions created by the SPM process were then tested for their ability to classify fracture versus control by comparison with traditional CT measures of areal Bone Mineral Density (aBMD). In women we used the surgical classification of fracture location (‘femoral neck’ or ‘trochanteric’) to discover whether focal osteoporosis was specific to fracture type. To explore whether the focal areas were osteoporotic by histological criteria, we used micro CT to measure trabecular bone parameters in targeted biopsies taken from the femoral heads of 14 cases.ResultsHip fracture patients had distinct patterns of focal osteoporosis that determined fracture type, and CBM measures classified fracture type better than aBMD parameters. CBM measures however improved only minimally on aBMD for predicting any hip fracture and depended on the inclusion of trabecular bone measures alongside cortical regions. Focal osteoporosis was confirmed on biopsy as reduced sub-cortical trabecular bone volume.ConclusionUsing 3D imaging methods and targeted bone biopsy, we discovered focal osteoporosis affecting trabecular and cortical bone of the proximal femur, among men and women with hip fracture.

Spatial Differences in the Distribution of Bone Between Femoral Neck and Trochanteric Fractures

“…Furthermore, the SPM endocortical density results of Poole and colleagues from a recent acute hip fracture study involving UK and Czech subjects are actually quite in agreement with those presented here for Chinese women. In that study, the authors confirmed that focal osteoporosis was specific to fracture type by using SPM of cortical and endocortical density parameters associated with targeted biopsies for micro‐CT measures . Unfortunately, the femoral head was not included in our surface‐based SPM analyses, thus limiting our visual comparisons to the rest of the proximal femur.…”

“…These statistical atlases provide an opportunity to visualize a physical parameter of interest, such as vBMD or Ct.Th, in relation to a variable of interest . For example, Li and colleagues and Carballido‐Gamio and colleagues applied VBM to identify regions in the proximal femur where vBMD was significantly associated with acute and incident hip fractures, respectively, whereas Poole and colleagues applied surface‐based SPM to identify regions where Ct.Th and cortical and endocortical trabecular density parameters were significantly associated with acute hip fractures . These four studies demonstrated biological relevance by showing significant bone differences between fracture cases and controls in regions commonly involved with hip fracture …”

“…In this study, we applied statistical multiparametric mapping to investigate spatial differences in proximal femoral density and cortical bone properties between two major types of hip fracture—femoral neck and trochanteric fracture—and healthy controls. In contrast to previous studies, we identified acute hip fracture–related features with both VBM of vBMD and SPM of cortical bone properties, thus providing a more comprehensive QCT assessment of the proximal femur. Investigated features included vBMD, Ct.Th, Ct.vBMD, and EndoTb.vBMD.…”

“…However, the potential differences in vBMD and bone structure between femoral neck and trochanteric fractures are currently unclear. To our knowledge, three studies have used statistical atlases to identify differences between the two types of fracture, one using VBM and two applying SPM of cortical bone properties . There have not been any studies integrating these different mapping approaches into the same subjects in relation to fracture type.…”

Heterogeneous Spatial and Strength Adaptation of the Proximal Femur to Physical Activity: A Within-Subject Controlled Cross-Sectional Study

“…In contrast, there was a lack of any appreciable tissue adaptation in the superior femoral neck region. This region is clinically relevant as: (1) it is exposed to greatest stress/strain during impact from a fall onto the greater trochanter; (2) femoral neck fractures appear to initiate in the region during a sideways fall; (3) the region experiences greater bone loss during aging compared with the more preserved inferior femoral neck; and (4) deficits in the region are associated with incident femoral neck fracture …”