A computational orthopaedic biomechanics study of osteoporotic hip fractures

Abstract

Low dual energy X-ray absorptiometry (DXA) measured bone mineral density (BMD) is used as an indicator of reduced bone strength and increased risk of fracture. BMD is widely used to identify patients for fracture prevention treatment. However, many fracture patients are not osteoporotic and would not have been identified by BMD screening. Also, BMD screening vastly overpredicts the number of patients who will progress to fracture. In summary, there is a need to improve explanation and prediction of femoral fracture.

The overall aim of this thesis was to develop a finite element (FE) methodology that can explain (better than BMD) femoral fractures. An additional aim was to develop a novel experimental methodology, computed tomography (CT)-based digital volume correlation (CT-DVC). This method measures internal strain and fracture and served as validation for the FE methodology.

The study included three groups of femur specimens; Group 1: 15 cadavers served as non-fracture controls, Group 2: 14 patients who had suffered a femoral fracture and Group 3: 13 patients scheduled for arthroplasty due to osteoarthritis served as a second non-fracture control group.

The correlation of FE-predicted fracture load with in-vitro testing of cadaveric femurs was superior to that of BMD predictions (R2 = 0.77 and R2 = 0.59). Also, the match between CT-based FE models and the experimental observations was reasonably good (73% match) whereas BMD is unable to explain the fracture type. FE-predicted fracture types matched 13 of 14 patient-specific clinical fractures. Including bone quality and load (fall) direction, FE explained many of the clinical fractures that BMD was unable to explain and critical fall directions were identified. FE predicted lower strength of the fracture group which was associated with smaller sizes of anatomical parameters. Also the CT- DVC method demonstrated consistent results and was deemed to have great potential for a wide range of orthopaedic applications.