Abstract. Background. Optimal acetabular component position in Total Hip Arthroplasty is vital for avoiding complications such as dislocation, impingement, abductor muscle strength and range of motion. Transverse acetabular ligament (TAL) and posterior labrum have been shown to be a reliable landmark to guide optimum acetabular cup position. There have been reports of iliopsoas impingement caused by both cemented and uncemented acetabular components. Acetabular component mal-positioning and oversizing of acetabular component are associated with iliopsoas impingement. The Psoas fossa (PF) is not a well-regarded landmark to help with Acetabular Component positioning. Our aim was to assess the relationship of the TAL and PF in relation to Acetabular Component positioning. Methods. A total of 12 cadavers were implanted with the an uncemented acetabular component, their position was initially aligned to TAL. Following optimal seating of the acetabular component the distance of the rim of the shell from the PF was noted. The Acetabular component was then repositioned inside the PF to prevent exposure of the rim of the Acetabular component. This study was performed at Smith & Nephew wet lab in Watford. Results. Out of the twelve acetabular components that were implanted parallel to the TAL, all had the acetabular rim very close or outside to the psoas notch with a potential to cause iliopsoas impingement. Alteration of the acetabular component position was necessary in all cadavers to inside the PF to prevent iliopsoas impingement. It was evident that the edge of PF was not aligned with TAL. Conclusion. Optimal acetabular component position is vital to the longevity and outcome following THA. TAL provides a landmark to guide acetabular component position. We feel the PF is a better landmark to allow appropriate positioning of the acetabular component inside bone without exposure of the component rim and thus preventing iliopsoas impingement at the psoas notch. 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

Evidence supporting the use of virtual reality (VR) training in orthopaedic procedures is rapidly growing. However, the impact of the timing of delivery of this training is yet to be tested. We aimed to investigate whether spaced VR training is more effective than massed VR training. 24 medical students with no hip arthroplasty experience were randomised to learning the direct anterior approach total hip arthroplasty using the same VR simulation, training either once-weekly or once-daily for four sessions. Participants underwent a baseline physical world assessment on a saw bone pelvis. The VR program recorded procedural errors, time, assistive prompts required and hand path length across four sessions. The VR and physical world assessments were repeated at one-week, one-month, and 3 months after the last training session. Baseline characteristics between the groups were comparable (p > 0.05). The daily group demonstrated faster skills acquisition, reducing the median ± IQR number of procedural errors from 68 ± 67.05 (session one) to 7 ± 9.75 (session four), compared to the weekly group's improvement from 63 ± 27 (session one) to 13 ± 15.75 (session four), p < 0.001. The weekly group error count plateaued remaining at 14 ± 6.75 at one-week, 16.50 ± 16.25 at one-month and 26.45 ± 22 at 3-months, p < 0.05. However, the daily group showed poorer retention with error counts rising to 16 ± 12.25 at one-week, 17.50 ± 23 at one-month and 41.45 ± 26 at 3-months, p<0.01. A similar effect was noted for the number of assistive prompts required, procedural time and hand path length. In the real-world assessment, both groups significantly improved their acetabular component positioning accuracy, and these improvements were equally maintained (p<0.01). Daily VR training facilitates faster skills acquisition; however weekly practice has superior skills retention

Abstract. Objectives. Non-technical skills including teamwork play a pivotal role in surgical outcomes. Virtual reality is effective at improving technical skills, however there is a paucity of evidence on team-based virtual reality (VR) training. This study aimed to assess if multiplayer virtual reality training was superior to solo training for acquisition of both technical and non-technical skills in learning the complex anterior approach total hip arthroplasty operation. Methods. 10 novice surgeons and 10 novice scrub nurses, were randomised to solo or team virtual reality training to perform anterior approach total hip arthroplasty. Solo participants trained with virtual avatar counterparts, whilst teams trained in pairs (surgeon and scrub nurse). Both groups underwent 5 VR training sessions over 6 weeks. Then, they underwent a real-life assessment in which they performed AA-THA on a high-fidelity model with real equipment in a simulated operating theatre. Teams performed together and solo participants were randomly paired up with a solo player of the opposite role. Videos of the assessment were marked by two blinded expert assessors. Outcomes were procedure time, procedural errors from an expert pre-defined protocol and acetabular component positioning. Non-technical skills were assessed using the NOTECHs II and NOTSS scores. Results. Teams were 28.11% faster than solos in the real world assessment (31.22 minutes ±2.02 vs 43.43 ±2.71, p=0.01), with 34.91% less errors (−15.25 errors ±3.09 vs −23.43 ±1.84, p=0.04). Teams had significantly higher NOTSS and NOTECHS II scores when compared to solos (p<0.001). 8/10 surgeons placed the acetabular component within the target safe zone. Conclusions. Multiplayer training appears to lead to faster surgery with fewer technical errors and the development of superior non-technical skills. VR learnt skills appear to translate to the physical world. This supports the application of multidisciplinary learning to create a more integrated approach to surgical team training

Abstract. Objectives. Evidence supporting the use of immersive virtual reality (iVR) training in orthopaedic procedures is rapidly growing. However, the impact of the timing of delivery of this training is yet to be tested. This study investigated whether spaced iVR training is more effective than massed iVR training for novices learning hip arthroplasty. Methods. 24 medical students with no hip arthroplasty experience were randomised to learning total hip arthroplasty using the same iVR simulation training either once-weekly or once-daily for four sessions. Participants underwent a baseline physical world assessment to orientate an acetabular component on a saw bone pelvis, and a baseline knowledge test. In iVR, we recorded procedural errors, time, numbers of prompts required and path lengths of the hands and head across 4 sessions. To assess skill retention, the iVR and baseline physical world assessments were repeated at one-week and one-month. Results. Baseline characteristics between the groups were comparable (p > 0.05). The daily group demonstrated faster skills acquisition, reducing the mean number of procedural errors from 76.8±37.5 (S1) to 11.1±10.1 (S4), compared to the weekly group improvement from 71.1±19.1 (S1) to 17.2±10.6 (S4), p < 0.001. The weekly group error count plateaued remaining at 16±6.7 at 1-week and 17.5±8.5 at one-month, the daily group however, showed poor retention with error counts rising to 17.8±10.5 at 1 week and becoming higher than the weekly group at one-month to (23.2±13.0 vs 17.5±10.5). A similar effect was noted for procedural time and the number of assistive prompts. In the real-world assessment, both groups significantly improved the accuracy of their acetabular component positioning, these improvements were equally maintained. Conclusions. Daily iVR training facilitates faster skills acquisition, however weekly practice has superior skills retention. Skills learnt using both regimes demonstrate sustained transfer to the real-world

Background. Positioning of the acetabular component in total hip arthroplasty has profound effects on the biomechanics, stability and wear of the prosthesis. Normal anatomical position in females is 57 degrees (50 – 67 degrees) inclination with 19 degrees (9 – 32 degrees) of anteversion, whilst in males 56 degrees of inclination (48 – 66 degrees) with 19 degrees (9 – 32 degrees) is normal. In total hip arthroplasty, inclination recommendation ranges from 30 – 50 degrees. The aim of this study was to radiographically measure acetabular component position in total hip arthroplasty and compare to normal values. Method. The Widmer method was used by two independent observers to radiographically measure inclination in 522 patients using standard AP radiographs. Primary measures and variables were statistically analysed as was inter and intra observer reliability. All patients included within the study received total hip arthroplasty for age related degenerative changes to the hip. Operations were undertaken by 17 separate consultants or senior registrars under their care. Results. Overall mean inclination was measured at 45.27 degrees with a range of 26 – 68 degrees. Statistically significant differences were observed between cemented 45.9o and non-cemented hips 43.9 degrees (p= 0.018), Simple 45.5 degrees vs complex 42.1 degrees (p=0.003) and Male 44.3 degrees vs Female 46.2 degrees (p=0.0198). No statistical difference was seen between consultant and registrar (p=0.211) and right vs left (p=0.768). Inter observer reliability was seen to be 0.91 whilst intra observer reliability 0.96. Conclusion. Although a large range of outcomes were observed, 95% of radiographs reviewed fell within a range of 33.6 – 56.9 degrees Variables such as surgical positioning, patient anatomy/body habitus, surgical technique, instrumentation likely influenced abnormal results. Abnormal positioning may have effects such as eccentric wear and dislocation, however, and such findings are yet to be observed in the study group

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.

The cortical strains on the femoral neck and proximal femur were measured before and after implantation of a resurfacing femoral component in 13 femurs from human cadavers. These were loaded into a hip simulator for single-leg stance and stair-climbing. After resurfacing, the mean tensile strain increased by 15% (95% confidence interval (CI) 6 to 24, p = 0.003) on the lateral femoral neck and the mean compressive strain increased by 11% (95% CI 5 to 17, p = 0.002) on the medial femoral neck during stimulation of single-leg stance. On the proximal femur the deformation pattern remained similar to that of the unoperated femurs.

The small increase of strains in the neck area alone would probably not be sufficient to cause fracture of the neck However, with patient-related and surgical factors these strain changes may contribute to the risk of early periprosthetic fracture.

Nanometre-sized particles of ultra-high molecular weight polyethylene have been identified in the lubricants retrieved from hip simulators. Tissue samples were taken from seven failed Charnley total hip replacements, digested using strong alkali and analysed using high-resolution field emission gun-scanning electron microscopy to determine whether nanometre-sized particles of polyethylene debris were generated in vivo. A randomised method of analysis was used to quantify and characterise all the polyethylene particles isolated.

We isolated nanometre-sized particles from the retrieved tissue samples. The smallest identified was 30 nm and the majority were in the 0.1 μm to 0.99 μm size range. Particles in the 1.0 μm to 9.99 μm size range represented the highest proportion of the wear volume of the tissue samples, with 35% to 98% of the total wear volume comprised of particles of this size. The number of nanometre-sized particles isolated from the tissues accounted for only a small proportion of the total wear volume. Further work is required to assess the biological response to nanometre-sized polyethylene particles.