Conventional hip arthroplasty femoral stems bypass the femoral neck for fixation. The femoral neck and proximal femur has a complex anatomy and interosseous structure to facilitate transfer of mechanical load in axial, compression bending and torsion mechanisms. von Mises analysis suggests a short stem, fixed in the femoral neck would maintain proximal femoral biomechanics, achieve physiological load transfer to the femoral neck and preserve bone stock and function. The strong calcar bone provides excellent opportunities for implant fixation and load transfer. The Muscle Sparing Arthroplasty (MSA™) is a short femoral stem designed to achieve implant fixation in the femoral neck. The specific design features including a trapezoidal cross section; proximal conical flare; porous coating and lateral T back enhance proximal fixation and compressive load transfer to the calcar and femoral neck. We report 54 hip arthroplasties in 49 patients with an average follow up of 18 months. All hip arthroplasties showed evidence of new bone formation in the proximal femoral neck and calcar region. This consisted of new bone streaming from the original calcar bone, in a strut fashion up to the conical flare of the implant. In 18 patients additional new bone formation occurred proximal to the neck osteotomy. This pattern of bone formation is consistent with predictions.Method
Results
The response of articular cartilage in joint dislocation is not well documented. We have previously demonstrated that the rate of chondrocyte apoptosis increased with duration of joint dislocation with a significant increase after 1 hour. The purpose of our study was to determine if early joint reduction reduced the rate of chondrocyte apoptosis. Southern Health animal ethics approval was obtained. 36 Sprague-Dawley rats underwent surgical dislocation of the left hip and the hip was reduced after 1, 2 or 4 hours. The rats were then killed at 1 or 8 weeks. Histological assessment of the femoral heads was performed with H+E and TUNEL stain to determine if the apoptotic index (proportion of apoptotic cells present per high magnification field (X 400)) alter after joint reduction in the short to medium term. The mean apoptotic index in the non traumatized right hip was 0.044 ± 0.031 (control). After joint reduction of 1 week the mean apoptotic indices were 0.069 ± 0.023 (1 hr), 0.064 ± 0.031 (2 hr) and 0.138 ± 0.060 (4 hrs). After joint reduction of 8 weeks the mean apoptotic indices were 0.062 ± 0.028 (1 hr), 0.108 ± 0.109 (2 hrs) and 0.135 ± 0.035 (4 hrs). Our results suggests that joint reduction within 1 hour prevents worsening of apoptotic index and that there is a population of delayed apoptosis if the joint is left dislocated for 2 hours. The apoptotic index does not recover after 8 weeks.
Published data has shown that only 45% of acetabular components were in an acceptable position, where positioning was determined clinically by the surgeon intra-operatively. The aim of this study is to assess the accuracy of cup orientation, using computer tomography (CT), when the TAL is used as the intra-operative guide. In this prospective study, the TAL was used as the anatomical reference for positioning the cup. The TAL was graded 1 to 4 based on visibility of the ligament. The version and abduction angles were estimated clinically and recorded by the surgeon after insertion of the cup. Post-operatively the true orientation of the cup was measured using CT. Statistical analyses were carried out to calculate the difference between the intra-operative estimation of cup orientation and the true cup position as measured by CT. Ethical approval was granted and informed consent was obtained for all the patients. Forty-eight hips have been studied to date. The TAL was easily identifiable in the majority of cases. Overall, the cup version was under-estimated by the surgeon when the TAL was utilized as the anatomical landmark. The true mean acetabular component version was 26.5 degrees [range from 11 to 41 degrees]. The true mean abduction angle was 43.6 degrees [range from 35 to 55 degrees]. The mean difference between surgeon estimation and CT measurement for cup version was 4 degrees of underestimation [range from 14 degrees of underestimation to 11 degrees of overestimation]. The mean difference for abduction angle was 0.1 degrees [range from 14 degrees of underestimation to 10 degrees of overestimation]. When using TAL as an intra-operative guide, 64% of acetabular components were within the target range of 15 to 30 degrees of anteversion, as measured by CT, compared to 45% in previously published study (Wines, A &
McNicol, D, J. Arthroplasty, 2006). TAL improves the accuracy of acetabular component version, when utilized as an anatomical landmark during cup insertion in primary total hip arthroplasty. It is reliable and easily identifiable in the majority of cases.
