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Hip Shape May Predict Likelihood of Surgery 10 Years Later
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Scores from statistical shape models based on dual-energy X-ray absorptiometry images of the hip were associated with total hip replacement 10 years later, as well as other indicators for osteoarthritis progression, according to a recently published study.
“[In] this population-based study, two-dimensional hip shape measured on entry to the study is shown to be associated with [radiographic osteoarthritis] ROA and muscle strength at baseline,” Harbeer G. Ahedi, in the Menzies Institute for Medical Research at the University of Tasmania in Australia, and colleagues wrote. “More interestingly, shape is also strongly predictive of [total hip replacement] THR, as well as indicators of OA, such as hip pain, [bone marrow lesions] BMLs, effusion-synovitis and hip structural changes occurring up to 10 years later.”
Using an 85-point statistical shape model, Ahedi and colleagues assessed dual-energy X-ray absorptiometry (DXA) left hip images of 831 subjects from the Tasmanian Older Adult Cohort. They used the WOMAC to assess hip pain; a dynamometer to examine muscle strength; an MRI to assess hip structural changes; and plain radiographs to examine ROA.
Researchers found 68% of shape variation was described by six shape modes. At baseline, investigators found modes 1, 2, 4 and 6 were associated with hip ROA. Modes 1, 3, 4 and 6 were associated with hip cartilage volume. All modes except for mode 2 were associated with muscle strength. Higher mode 1 and lower mode 3 and 6 scores were associated with hip pain at follow-up. Investigators found higher mode 1 and 2 scores were linked with hip effusion-synovitis. Higher mode 2 and lower mode 4 scores were associated 10-year THR. Researchers noted higher mode 4 scores was associated with BMLs, effusion-synovitis and increased cartilage signal.
“These data suggest that different morphological features identified by shape modes have relevance for multiple facets of hip osteoarthritis, both radiographic and clinical,” the researchers wrote. “It adds further evidence for the use of [statistical shape models] SSM as an imaging biomarker for the incidence and progression of OA. Where standardized radiographs or DXA images are available, we believe that in due course it may be possible to include a measure of shape into clinical practice for the early detection and staging of OA.” – by Will Offit
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Roy Davis Altman, MD
The authors continue to derive valuable clinical and imaging information from a prospective cohort of adult Tasmanians with osteoarthritis followed for as much as 10 years. In addition to demographics, baseline information included hip pain and function using the WOMAC; muscle strength using a dynamometer; pelvic X-rays for radiographic features of the hips; and MRI to determine hip synovitis, effusion cartilage volume, and bone marrow lesions. In this more than 800-patient subset analysis, bone densitometry obtained at baseline — with a method of custom-written SHAPE software — was used to measure 85 points around the hip to develop statistical 2-dimentional shape modelling of the hip.
The technique defined six femoral head shapes that explained 68% of the hip variations. There were tendencies of progression, joint replacement, femoral neck shortening, pistol grip changes, femoral acetabular impingement and other clinical and radiographic features. This study seems to further define structural features of the shape of the femoral head that are prognostic. Further research appears needed to make the computer-defined modules that will more clearly define femoral head shapes (modes) that provide specific clinical and prognostic changes.
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