Variations in pelvic anatomy are a major risk factor for misplaced percutaneous sacroiliac screws used to treat unstable posterior pelvic ring injuries. A better understanding of pelvic morphology improves preoperative planning and therefore minimises the risk of malpositioned screws, neurological or vascular injuries, failed fixation or malreduction. Hence a classification system which identifies the clinically important anatomical variations of the sacrum would improve communication among pelvic surgeons and inform treatment strategy. 300 Pelvic CT scans from skeletally mature trauma patients that did not have pre-existing posterior pelvic pathology were identified. Axial and coronal transosseous corridor widths at both S1 and S2 were recorded. Additionally, the S1 lateral mass angle were also calculated. Pelvises were classified based upon the sacroiliac joint (SIJ) height using the midpoint of the anterior cortex of L5 as a reference point. Four distinct types could be identified:. Type-A – SIJ height is above the midpoint of the anterior cortex of the L5 vertebra. Type-B – SIJ height is between the midpoint and the lowest point of the anterior cortex of the L5 vertebra. Type-C – SIJ height is below the lowest point of the anterior cortex of the L5 vertebra. Type-D – a subgroup for those with a lumbosacral transitional vertebra, in particular a sacralised L5. Differences in transosseous corridor widths and lateral mass angles between classification types were assessed using two-way ANOVAs. Type-B was the most common pelvic type followed by Type-A, Type-C, and Type-D. Significant differences in the axial and coronal corridors was observed for all pelvic types at each level. Lateral mass angles increased from Types-A to C, but were smaller in Type-D. This classification system offers a guide to surgeons navigating variable pelvic anatomy and understanding how it is associated with the differences in transosseous sacral corridors. It can assist surgeons’ preoperative planning of screw position, choice of fixation or the need for technological assistance

Introduction. A recent study to identify clinically meaningful benchmarks for gait improvement after total hip replacement (THA) has shown that the minimum clinically important improvement (MCII) in gait speed after THA is 0.32 m/sec. Currently, it remains to be investigated what preoperative factors link to suboptimal recovery of gait function after THA. This study aimed to identify preoperative lower-limb muscle predictors for gait speed improvement after THA for hip osteoarthritis. Method. This study enrolled 58 patients who underwent unilateral primary THA. Gait speed improvement was evaluated as the subtraction of preoperative speed from postoperative speed at 6 months after THA. Preoperative muscle composition of the glutei medius and minimus (Gmed+min) and the gluteus maximus (Gmax) was evaluated on a single axial computed tomography slice at the bottom end of the sacroiliac joint. Cross-sectional area ratio of individual composition to the total muscle was calculated. Result. The females (n=45) showed smaller total cross-sectional areas of the gluteal muscles than the males (n=13). Gmax in the females showed lower lean muscle mass area (LMM) and higher ratios of the intramuscular fat area and the intramuscular adipose tissue area to the total muscle area (TM) than that in the males. Regression analysis revealed that LMM/TM of Gmed+min may correlate negatively with postoperative improvement in gait speed. Receiver operating characteristic curve analysis for prediction of MCII in gait speed at ≥ 0.32 m/sec resulted in the highest area under the curve for Gmax TM with negative correlation. The explanatory variables of hip abductor muscle composition predicted gait speed improvement after THA more precisely in the females compared with the total group of both sexes. Conclusion. Preoperative Gmax TM could predict gait speed MCII after THA. Preoperative muscle composition should be evaluated separately based on sexes for achievement of clinically important improvement in gait speed after THA

Introduction. The THR is the second most successful and cost-effective surgical procedure of all time. Data shows that hip cup failure is a significant problem. The aim of this study is to improve methods of cemented cup fixation through validation experiments and FEA. Methods. Five Sawbones composite pelves with cemented UHMWPE cups were tested. Each pelvis was instrumented with triaxial strain gauges at four locations of predicted high strain. Each sample (n = 5) was bolted at the sacroiliac joint in a uniaxial testing machine. A load of 500 N was applied in the direction of the peak force during normal walking, for five repetitions. The directional surface strains were used to evaluate the equivalent strain. Specimen specific finite element models were developed based on CT scan data using ScanIP. Each mesh consisted of an average of 2.5 million linear tetrahedral elements and was solved in ANSYS. Results. The experimentally measured strains were compared against the finite element predictions. The mean linear gradients and SD of the mean at each gauge location were: 1.00 (16%), 0.78 (17%), 0.90 (13%) and 1.05 (4%). Discussion. The agreement between the predicted and experimental equivalent strains was good, but varied across the population. This was caused by the variation in mechanical properties between specimens, and the sensitivity of the gauges to location (steep surface strain gradients). This is most evident with the second strain gauge (0.78, 17%), which is at a suboptimal location. This specific methodology of conducting finite element analyses of the pelvis based on CT image data has been validated. The same methodology has been used to develop a patient specific FEA model, including a bone remodelling algorithm and muscle forces, based on the CT images from the Virtual Human Project. This model is currently being used to optimize the cemented fixation and will be verified experimentally using composite pelves. This research is aimed at informing clinical practice and enhancing long-term cemented fixation. Reducing the need for revision surgery will greatly improve patient quality of life, whilst also reducing the burden on the healthcare delivery system

Finite element analysis was used to examine the initial stability after hip resurfacing and the effect of the procedure on the contact mechanics at the articulating surfaces. Models were created with the components positioned anatomically and loaded physiologically through major muscle forces. Total micromovement of less than 10 μm was predicted for the press-fit acetabular components models, much below the 50 μm limit required to encourage osseointegration. Relatively high compressive acetabular and contact stresses were observed in these models. The press-fit procedure showed a moderate influence on the contact mechanics at the bearing surfaces, but produced marked deformation of the acetabular components. No edge contact was predicted for the acetabular components studied.

It is concluded that the frictional compressive stresses generated by the 1 mm to 2 mm interference-fit acetabular components, together with the minimal micromovement, would provide adequate stability for the implant, at least in the immediate post-operative situation.