Introduction. In total knee arthroplasty, the aim is to relieve pain and provide a stable, functional knee. Sagittal stability is crucial in enabling a patient to return to functional activities. Knee implants with a medial pivot (MP) design are thought to more accurately reproduce the mechanics of the native joint, and potentially confer greater antero-posterior stability through the range of flexion than some other implant designs. Aim. This study aims to compare the sagittal stability of four different total knee arthroplasty implant designs. Method. Comparison was made between four different implant designs: medial pivot (MP), two different types of cruciate retaining (CR1 and CR 2) and deep dish (DD). A cohort of 30 Medial Pivot (MP) knees were compared with matched patients from each of the other designs, 10 in each group. Patients were matched for age, body mass index and time to follow up. Clinical examination was carried out by an orthopaedic surgeon blinded to implant type, and sagittal stability was tested using a KT1000 knee arthrometer, applying 67N of force at 30˚ and 90˚. Results. The MP knee was more stable than the CR1 knee at both 30º (mean movement: 1.37mm vs 2.48mm, p=0.037) and 90º (1.68mm vs 2.37mm, p=0.030). The MP knee was more stable than the CR2 knee at 30º (0.98mm vs1.33mm, p=0.013). The MP knee also demonstrated less movement at 90 º (0.98mm vs 1.33mm), but this was not statistically significant (p=0.156). The MP knee was more stable than the DD knee at 30 º (0.48mm vs 1.33mm, p=0.03) and 90 º (0.67mm vs 1.15mm, p=0.048). Overall the medial pivot design was more stable than all non-medial pivot designs at 30 º (0.8mm vs1.66mm, p=0.003) and 90 º (1.1mm vs 1.61mm, p= 0.008). Conclusion. Overall, the medial pivot design demonstrated significantly greater antero-posterior stability than all other design types included in this study. Correlation with patient reported outcome scales will allow insight into whether these statistically significant differences are also clinically significant

Introduction. Although weight-bearing CT of the foot definitely reflects the morphology and deformity of joint, it is hard to obtain the standing CT due to difficulty of availability. Although 3D imaging reconstruction using radiographs has been reported in other joints, there is no study about foot joint. The purpose of this study is to develop a semi-automatic method based on a deformable surface fitting for achieving the weight-bearing 3D model reconstruction from standing radiographs for foot. Methods. Our method is based on a Laplacian surface deformation framework using a template model of foot. As pre- processing step, we obtained template surface meshes having the average shapes of foot bones (talus, calcaneus) from standing CT images (Planmed Verity) in 10 normal volunteers. In the reconstruction step, the surface meshes are deformed following guided user inputs with geometric constraints to recover the target shapes of 30 patients while preserving average bone shape and smoothness. Finally, we compared reconstructed 3D model to original standing CT images. Analysis was performed using Dice coefficients, average shape distance, maximal shape distance. Results. The obtained reconstruction model is close to the actual standing foot geometry (Dice coefficients 0.89, average shape distance 0.88 mm, maximum shape distance 6.33 mm). We present the accuracy and robustness of our method via comparison between the reconstructed 3D models and the original bone surfaces. Conclusions. Weight-bearing 3D foot model reconstruction from standing radiographs is concise and the effective method for analysis of foot joint alignment and deformity

Introduction. Total hip arthroplasty (THA) is a commonly performed surgical procedure for the treatment of hip arthritis. Approximately 50,000 THAs are performed annually in Canada. The costs incurred to the healthcare system are tremendous, amounting to anywhere between 4.3 and 7.3 billion dollars each year. Despite the substantial financial burden of THA to the Canadian healthcare system, few studies have provided accurate cost estimations of this procedure. Purpose. To determine the impact of surgical approach on costs of THA from a hospital perspective, and provide an updated cost estimation of THA within a publically funded healthcare system. Methods. We recruited patients undergoing a THA through an anterior, posterior, or lateral approach for study participation. A single surgeon was designated to perform every case using the surgical approach of their expertise. Each patient received standardized implants: a collared, hydroxyapatite-coated, cementless femoral stem (Corail TM stem, DePuy Orthopaedics Inc., Warsaw, IN), a cementless acetabular cup (Pinnacle Sector II TM acetabular cup, DePuy Orthopaedics Inc., Warsaw, IN), a highly cross-linked polyethylene liner (AltrX TM polyethylene liner, DePuy Orthopaedics Inc., Warsaw, IN), and a cobalt chrome femoral head (Articul/eze TMcobalt chrome, DePuy Orthopaedics Inc., Warsaw, IN). We prospectively recorded costs of operating room time, length of stay in hospital, and medical and surgical interventions using a micro-costing method. Group comparisons were performed using Pearson's Chi-square and one-way Analysis of Variance (ANOVA), with post-hoc testing when necessary. All costs were reported in 2013 Canadian dollars. Results. One-hundred and eighteen patients (40 anterior, 38 posterior, and 40 lateral) completed the study. All three groups were similar with regards to age (p=0.79), sex (p=0.97), and body mass index (p=0.54). Mean operating room time was significantly shorter for the lateral (49.0 minutes, 95%CI 46.5 – 51.5) versus anterior (69.3 minutes, 95%CI 66.0 – 72.6, p<0.001) and posterior approach (61.6 minutes, 95%CI 57.5 – 65.5, p<0.001). Mean length of stay was shorter for the anterior (33.9 hours, 95%CI 29.6 – 38.2) compared to the posterior (65.8 hours, 95%CI 56.8 – 74.8, p<0.001) and lateral approach (64.2 hours, 95%CI 56.7 – 71.7, p<0.001). The operating room costs were significantly higher for the anterior versus posterior (p=0.008) and lateral approach (p<0.001, figure 1). The total inpatient costs were significantly for the anterior versus posterior and lateral approach (p<0.001 for both pair-wise comparisons, figure 2). Total costs were significantly less for the anterior ($7300.22, 95%CI 7064.49 – 7535.95) versus posterior ($8287.46, 95%CI 7906.41 – 8668.51, p<0.001) and lateral approach ($7853.10, 95%CI 7577.29 – 8128.91, p=0.031). Discussion / Conclusion. Total costs for THA were significantly less when performed using an anterior approach. A reduction in hospital length of stay contributed significantly to an overall reduction in costs from a hospital perspective. Future analyses will determine the cost-effectiveness of the anterior approach from both a hospital and societal perspective

Objective. Sarcomas are a rare group of tumours, which pose numerous problems regarding correct diagnosis and appropriate management. This study aimed to examine whether symptom duration and tumour size at diagnosis have changed over time, using size and symptom duration as methods of comparison. Methods. All patients diagnosed with sarcoma were identified retrospectively from a prospective database from 1963 to 2005. Demographic data concerning age at diagnosis, sex and diagnosis were recorded. Data were also collected on duration of symptoms and size of tumour at diagnosis. Symptom duration is defined as the length of time the patient was experiencing symptoms for until the date of diagnosis. Changes in size and symptom duration over time were compared by grouping date of diagnosis into time periods and comparing them against each other using non-parametric statistical analysis. Results. 4560 met our inclusion and exclusion criteria, with 2492 Bone Sarcomas (BS) and 2068 Soft Tissue Sarcomas (STS). Overall analysis of both BS and STS showed that size at diagnosis has decreased and symptom duration has increased. Analysis of STS showed that size has decreased over time, particularly following the introduction of referral guidelines in 1999 (median size pre 99 = 10cm, post = 8cm, Mann-Whitney-U test p=0.000 to 3 sig. fig.), but symptom duration has remained unaltered over time. Duration of symptoms reported for BS has significantly increased over time; however, size at diagnosis has remained unchanged over time. Conclusions. It appears from this study that STS are being diagnosed more quickly and that this is most likely due to the introduction of specific STS guidelines in 1999. This result is particularly heartening, and should encourage further promotion of such guidelines. Awareness of BS still appears to be low as size at diagnosis remains unchanged over time

Representative pre-clinical analysis is essential to ensure that novel prosthesis concepts offer an improvement over the state-of-the-art. Proposed designs must, fundamentally, be assessed against cyclic loads representing common daily activities [Bergmann 2001] to ensure that they will withstand conceivable in-vivo loading conditions. Fatigue assessment involves:. –. cyclic mechanical testing, representing worst-case peak loads encountered in-vivo, typically for 10 million cycles, or. –. prediction of peak fatigue stresses using Finite Element (FE) methods, and comparison with the material's endurance limit. Cyclic stresses from gait loading are super-imposed upon residual assembly stresses. In thick walled devices, the residual component is small in comparison to the cyclic component, but in thin section, bone preserving devices, residual assembly stresses may be a multiple of the cyclic stresses, so a different approach to fatigue assessment is required. Modular devices provide intraoperative flexibility with minimal inventories. Components are assembled in surgery with taper interfaces, but resulting residual stresses are variable due to differing assembly forces and potential misalignment or interface contamination. Incorrect assembly can lead to incomplete seating and dissociation [Langdown 2007], or fracture due to excessive press-fit stress or point loading [Hamilton 2010]. Pre-assembly in clean conditions, with reproducible force and alignment, gives close control of assembly stresses. Clinical results indicate that this is only a concern with thick sectioned devices in a small percentage of cases [Hamilton 2010], but it may be critical for thin walled devices. A pre-clinical analysis method is proposed for this new scenario, with a case study example: a thin modular cup featuring a ceramic bearing insert and a Ti-6Al-4V shell (Fig. 1). The design was assessed using FE predictions, and manufacturing variability from tolerances, surface finish effects and residual stresses was assessed, in addition to loading variability, to ensure physical testing is performed at worst case:. –. assembly loads were applied, predicting assembly residual stress, verified by strain gauging, and a range of service loads were superimposed. The predicted worst-case stress conditions were analysed against three ‘constant life’ limits [Gerber, 1874, Goodman 1899, Soderberg 1930], a common aerospace approach, giving predicted safety factors. Finally, equivalent fatigue tests were conducted on ten prototype implants. Taking a worst-case size (thinnest-walled 48 mm inner/58 mm outer), under assembly loading the peak tensile stress in the titanium shell was 274 MPa (Fig. 2). With 5kN superimposed jogging loading, at an extreme 75° inclination, 29 MPa additional tensile stress was predicted. This gave mean fatigue stress of 288.5 MPa and stress amplitude of 14.5 MPa (R=0.9). Against the most conservative infinite life limit (Soderberg), the predicted safety factor was 2.40 for machined material, and 2.03 for forged material, or if a stress-concentrating surface scratch occurs during manufacturing or implantation (Fig. 3). All cups survived 10,000,000 fatigue cycles. This study employed computational modelling and physical testing to verify the strength of a joint prosthesis concept, under worst case static and fatigue loading conditions. The analysis technique represents an improvement in the state of the art where testing standards refer to conventional prostheses; similar methods could be applied to a wide range of novel prosthesis designs