Abstract. BACKGROUND. Hemi-arthroplasty (HA) as a treatment for fractured neck of femur has slightly increased since 2019 and remarkably after the COVID pandemic. The main drawback of the treatment is ongoing cartilage deterioration that may require revision to THR. OBJECTIVE. This study assessed cartilage surface damage in hip HA by reproducing anatomical motion and loading conditions in a hip simulator. METHODS. Experimental design. HA tests were conducted using porcine acetabula and CoCr femoral heads. Five groups (n=4) were included: a control group comprising natural tissue and four HA groups where the acetabula were paired with metal heads to allow radial clearance (RC) classed as small (RC<0.6mm), large (2mm<RC<4mm), extra-large (4mm<RC), and oversized (RC<−0.6mm). Tests were carried out in an anatomical hip simulator that reproduced a simplified twin peak gait cycle, adapted for porcine hip joints, from the ISO 14242 standard for wear of THR prostheses (peak load of 900N). The test length was 6 hours, with photogrammetry taken at 1-hour intervals. Ringers solution was used as a lubricant. RESULTS. No changes were observed in the control group. However, cartilage surface changes were observed in all hemi-arthroplasty groups. Discolouration on the cartilage surface was noticeable at the posterior-superior part of the acetabulum after 1-hour (extra-large and oversized groups). Damage severity and location were characteristic of each clearance group. Of all the groups, the oversized group showed more significant damage. No labrum separation was seen after the simulation. CONCLUSIONS. These results are relevant to understand the effect of femoral head clearance on cartilage damage risk after HA. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Hip joint biomechanics can be altered by abnormal morphology of the acetabulum and/or femur. This may affect load distribution and contact stresses on the articular surfaces, hence, leading to damage and degradation of the tissue. Experimental hip joint simulators have been used to assess tribology of total hip replacements and recently methods further developed to assess the natural hip joint mechanics. The aim of this study was to evaluate articular surfaces of human cadaveric joints following prolonged experimental simulation under a standard gait cycle. Four cadaveric male right hips (mean age = 62 years) were dissected, the joint disarticulated and capsule removed. The acetabulum and femoral head were mounted in an anatomical hip simulator (Simulation Solutions, UK). A simplified twin peak gait cycle (peak load of 3kN) was applied. Hips were submerged in Ringers solution (0.04% sodium azide) and testing conducted at 1 Hertz for 32 hours (115,200 cycles). Soft tissue degradation was recorded using photogrammetry at intervals throughout testing. All four hips were successfully tested. Prior to simulation, two samples exhibited articular surface degradation and one had a minor scalpel cut and a small area of cartilage delamination. The pre-simulation damage got slightly worse as the simulation continued but no new areas of damage were detected upon inspection. The samples without surface degradation, showed no damage during testing and the labral sealing effect was more obvious in these samples. The fact that no new areas of damage were detected after long simulations, indicates that the loading conditions and positioning of the sample were appropriate, so the simulation can be used as a control to compare mechanical degradation of the natural hip when provoked abnormal conditions or labral tissue repairs are simulated

Abstract. OBJECTIVES. Abnormal joint mechanics have been proposed as adversely affecting natural hip joint tribology, whereby increased stress on the articular cartilage from abnormal loading leads to joint degeneration. The aim of this project was to assess the damage caused by different loading conditions on the articular surfaces of the porcine hip joint in an experimental simulator. METHODS. Porcine hip joints were dissected and mounted in a single station hip simulator (SimSol, UK) and tested under loading scenarios (that corresponded to equivalent of different body mass index's’ (BMI) in humans), as follows:“Normal” (n=4), the loading cycle consisted of a simplified gait cycle based on a scaled version of a simplified twin-peak human gait cycle, the peak load was 900N (representative of a healthy BMI). Representative of an “Overweight” BMI (n=3), as the normal cycle with a peak load of 1,130N Representative of an “Obese” BMI (n=1), as the normal cycle with a peak load of 1,340N Tests were conducted at 1Hz for 14,400 cycles in Ringers solution; photogrammetry was used to characterise the appearance of the cartilage and labrum pre, during and post simulation. the appearance and location of damage was recorded. RESULTS. No significant damage was observed for samples tested under normal conditions. Following “overweight” condition testing, tears and detachment of the labrum were observed during testing in two (of three) samples. In addition to damaged observed in “overweight” tested samples the “obese” showed similar damage and also cartilage bruising and wear tracks on the articular surface of the acetabulum. DISCUSSION. The absence of damage in “normal” loading provides evidence that this is an appropriate methodology and loading regime for porcine hips. Increased damage with increasing loads demonstrates the potential to develop further this experimental simulation to assess adverse loading in natural hip joints. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Last decade, a shift towards operative treatment of midshaft clavicle fractures has been observed [T. Huttunen et al., Injury, 2013]. Current fracture fixation plates are however suboptimal, leading to reoperation rates up to 53% [J. G. Wijdicks et al., Arch. Orthop. Trauma Surg, 2012]. Plate irritation, potentially caused by a bad geometric fit and plate prominence, has been found to be the most important factor for reoperation [B. D. Ashman et a.l, Injury, 2014]. Therefore, thin plate implants that do not interfere with muscle attachment sites (MAS) would be beneficial in reducing plate irritation. However, little is known about the clavicle MAS variation. The goal of this study was therefore to assess their variability by morphing the MAS to an average clavicle. 14 Cadaveric clavicles were dissected by a medical doctor (MH), laser scanned (Nikon, LC60dx) and a photogrammetry was created with Agisoft photoscan (Agisoft, Russia). Subsequently a CT-scan of these bones was acquired and segmented in Mimics (Materialise, Belgium). The segmented bone was aligned with the laser scan and MAS were indicated in 3-matic (Materialise, Belgium). Next, a statistical shape model (SSM) of the 14 segmented clavicles was created. The average clavicle from the SSM was then registered to all original clavicle meshes. This registration assures correspondences between source and target mesh. Hence, MAS of individual muscles of all 14 bones were indicated on the average clavicle. Mean area is 602 mm. 2. ± 137 mm. 2. for the deltoid muscle, 1022 mm. 2. ±207 mm. 2. for the trapezius muscle, and 683 mm. 2. ± 132 mm. 2. for the pectoralis major muscle. The sternocleidomastoid muscle has a mean area of 513 mm. 2. ± 190 mm. 2. and the subclavius muscle had the smallest mean area of 451 mm. 2. ± 162 mm. 2. Visualization of all MAS on the average clavicle resulted in 72% coverage of the surface, visualizing only each muscle's largest MAS led to 52% coverage. The large differences in MAS surface areas, as shown by the standard deviation, already indicate their variability. Difference between coverage by all MAS and only the largest, shows that MAS location varies strongly as well. Therefore, design of generic plates that do not interfere with individual MAS is challenging. Hence, patient-specific clavicle fracture fixation plates should be considered to minimally interfere with MAS

A number of advantages of unicondylar arthroplasty (UKA) over total knee arthroplasty in patients presenting osteoarthritis in only a single compartment have been identified in the literature. However, accurate implant positioning and alignment targets, which have been shown to significantly affect outcomes, are routinely missed by conventional techniques. Computer Assisted Orthopaedic Surgery (CAOS) has demonstrated its ability to improve implant accuracy, reducing outliers. Despite this, existing commercial systems have seen extremely limited adoption. Survey indicates the bulk, cost, and complexity of existing systems as inhibitive characteristics. We present a concept system based upon small scale head mounted tracking and augmented reality guidance intended to mitigate these factors. A visible-spectrum stereoscopic system, able to track multiple fiducial markers to 6DoF via photogrammetry and perform semi-active speed constrained resection, was combined with a head mounted display, to provide a video-see-through augmented reality system. The accuracy of this system was investigated by probing 180 points upon a 110×110×50 mm known geometry and performing controlled resection upon a 60×60×15 mm bone phantom guided by an overlaid augmented resection guide that updated in real-time. The system produced an RMS probing accuracy and precision of 0.55±0.04 and 0.10±0.01 mm, respectively. Controlled resection resulted in an absolute resection error of 0.34±0.04 mm with a general trend of over-resection of 0.10±0.07 mm. The system was able to achieve the sub-millimetre accuracy considered necessary to successfully position unicondylar knee implants. Several refinements of the system, such as pose filtering, are expected to increase the functional volume over which this accuracy is obtained. The presented system improves upon several objections to existing commercial CAOS UKA systems, and shows great potential both within surgery itself and its training. Furthermore, it is suggested the system could be readily extended to additional orthopaedic procedures requiring accurate and intuitive guidance