Direct anterior approach (DAA) arthroplasty has generated great interest because of its minimally invasive and muscle sparing nature. Obese patients are reported to be associated with greater incidence of complications in primary joint replacement. The purpose of this study was to compare patient outcomes and complication rates between obese and non-obese patients undergoing primary total hip arthroplasty (THA) through a Bikini direct anterior incision. This retrospective, single surgeon study compared the outcome of 258 obese patients and 200 non-obese patients undergoing DAA THA using a Bikini incision, over a 7-year period. The average follow-up was 4.2 years (range 2.6-7.6 years). There were no statistically significant differences in the complication rate between the two groups. The obese group recorded 2 major (venous thromboembolism and peri-prosthetic fracture) and 2 minor complications (superficial wound infection), compared with the non-obese group, which recorded 2 major (deep-wound infection and peri-prosthetic fracture) and 1 minor complication (superficial wound infection). Patient-reported outcomes (WOMAC and Harris Hip Scores) showed significant post-operative improvements (p < 0.001) and did not differ between the two groups. Bikini DDA THA does not increase the complication rate in obese patients and offers similar clinical improvements compared to non-obese patients. (200 words)
Joint kinematics following total knee replacement (TKR) is important as it affects joint loading, joint functionality, implant wear and ultimately patient comfort and satisfaction. It is believed that restoring the natural motion of the joint (such as the screw-home mechanism) with a medial pivot knee implant will improve clinical outcomes. Daily activities such as stair climbing and stair descent are among the most difficult tasks for these patients. This study analysed dynamic knee joint motion after implantation of a medial pivot knee implant using fluoroscopy during stair ascent and descent activity. Ethics approval was granted by Macquarie University to undertake fluoroscopic testing. Four patients who had undergone a TKR were asked to participate in the study. All patients were operated by a single surgeon (JS) and were implanted with a medial pivot knee prosthesis (Sphere, Medacta International). Participants were tested at the 12 month post-operative time- point. Participants were asked to step up or down a short stair-case at a comfortable self-selected speed. Fluroscopic images were taken using a flat panel Artis Zeego (Siemens Healthcare GmbH, Erlangen) angiography system during the dynamic activity. Images were processed using Joint Track Auto (Banks, University of Florida), whereby the specific femoral and tibial component CAD files were superimposed onto the fluoroscopic images, ensuring an optimised match to the outlined components. Joint kinematics were calculated using custom written code in Matlab 2017a.Introduction
Methods
Squeaking ceramics bearing surfaces have been recently recognised as a problem in total hip arthroplasty. The position of the acetabular cup has been alluded to as a potential cause of the squeaking, along with particular combinations of primary stems and acetabular cups. This study has used the finite element method to investigate the propensity of a new large diameter preassembled ceramic acetabular cup to squeaking due to malpositioning. A verified three-dimensional FE model of a cadaveric human pelvis was developed which had been CT scanned, and the geometry reconstructed; this was to be used to determine the behaviour of large diameter acetabular cup system with a thin delta ceramic liner in the acetabulum. The model was generated using ABAQUS CAE pre-processing software. The bone model incorporated both the geometry and the materials properties of the bone throughout based on the CT scan. Finite element analysis and bone material assignment was performed using ABAQUS software and a FORTRAN user subroutine. The loading applied simulated edge loading for rising from a chair, heel-strike, toe off and stumbling. All results of the analysis were used to determine if the liner separated from the shell and if the liner was toggling out of the shell. The results were also examined to see if there was a propensity for the liner to demobilise and vibrate causing a squeaking sound under the prescribed loading regime. This study indicates that there is a reduction in contact area between the ceramic liner and titanium shell if a patient happens to trip or stumble. However, since the contact between the liner and the shell is not completely lost the propensity for it to squeak is highly unlikely.
The Birmingham Hip Mid Head Resection (BMHR) was designed to accommodate patients with lower quality bone in the proximal half of the femoral head. It is a relatively new conservative hip implant with promising early results. Finite element modelling may provide an insight into mid-term results. A cadaveric femur was CT scanned and 3D geometry of the intact femur constructed. The correctly sized BMHR implants (with and without visual stop) were positioned and these verified by a surgeon; hence constructing the post-operative models. Walking loads were applied and contact surfaces defined. Stress analyses were performed using the finite element method and contact examined. Also, a strain-adaptive bone remodelling analysis was run using 45% gait hip loading data. Virtual DEXA images were computed and were analysed in seven regions of the bone surrounding the implants. The BMHR was found to be mechanically stable with all surfaces indicating micromotion less than the critical 150 microns. Stress distribution was similar to the intact femur, with the exception of the head-neck region where some stress/strain shielding occurs. This is mirrored in the bone remodelling results, which show some bone resorption in this region. The visual stop, which is designed to ensure that the stem is not overdriven during implantation, did not affect the stress/strain results; only on a very local scale. There is minimal data available in the literature regarding conservative hip implants and no data regarding the BMHR. This study is the first to look at the mechanical response of the bone to this implant.
The advantages of unicompartmental knee arthroplasty (UKA) include its bone preserving nature, lower relative cost and superior functional results. Some temporary pain has been reported clinically following this procedure. Could this be related to bone remodeling? A validated bone remodeling algorithm may have the answers… A 3D geometry of an intact human cadaveric tibia was generated using CT images. An all poly unicompartmental implant geometry was positioned in an inlay and onlay configuration on the tibia and the post-operative models created. An adaptive bone remodeling algorithm was used with finite element modeling to predict the bone remodeling behavior surrounding the implant in both scenarios. Virtual DEXA images were generated from the model and bone mineral density (BMD) was measured in regions of interest in the AP and ML planes. BMD results were compared to clinical results. The bone remodelling algorithm predicted BMD growth in the proximal anterior regions of the tibia, with an inward tendency for both inlay and onlay models. Looking in the AP plane, a maximum of up to 7% BMD growth was predicted and in the ML plane this was as high as 16%. Minimal BMD loss was observed, which suggests minimal disturbance to the natural bone growth following UKA. Positron emission tomography (PET) scans showed active hot spots in the antero- medial regions of the tibia. These results were consistent with the finite element modeling results. Bone remodeling behavior was found to be sensitive to sizing and positioning of the implant. The adaptive bone remodeling algorithm predicted minimal BMD loss and some BMD growth in the anterior region of the tibia following UKA. This is consistent with patient complaint and PET scans.
