The performance of total hip replacement (THR) devices can be affected by the quality of the tissues surrounding the joint or the mismatch of the component centres during hip replacement surgery. Experimental studies have shown that these factors can cause the separation of the two components during walking cycle (dynamic separation) and the contact of the femoral head with the rim of the acetabular liner (edge loading), which can lead to increased wear and shortened implant lifespan1. There is a need for flexible pre-clinical testing tools which allow THR devices to be assessed under these adverse conditions. In this work, a novel dynamic finite element model was developed that is able to generate dynamic separation as it occurs during the gait cycle. In addition, the ability to interrogate contact mechanics and material strain under separation conditions provides a unique means of assessing the severity of edge loading. This study demonstrates these model capabilities for a range of simulated surgical translational mismatch values, for ceramic-on-polyethylene implants. The components of the THR were aligned and constrained as illustrated in Figure 1. CAD models of commercially available implant geometries were used (DePuy Synthes, Leeds, UK) modified for model simplicity by removing anti-rotation features. The polyethylene cup liner was given elastic-plastic behaviour. An axial load following the Paul cycle pattern (5 repetitive cycles) with maximum of 3KN and swing phase load of 0.3KN, was applied through the cup holder. The effect of translational mismatch was implemented by using a spring element connected to the cup unit on the lateral side. The spring was compressed by a fixed amount to replicate a degree of medial-lateral mismatch of the components. The instantaneous resultant force vector dictated the dynamic sliding behaviour of the cup against the head. In this study, translational medial-lateral mismatch values of 1, 2, 3 and 4mm were used and the medial-lateral dynamic separation, contact pressure maps and plastic strain were recorded.Introduction
Methodology
Emerging research has indicated that ‘significant others’ (spouses/relatives) may have important influences on continued work participation for individuals with chronic non-specific musculoskeletal pain (CMP). In order to expand on this novel area of research, data from studies conducted in The Netherlands and the UK were assimilated. In both studies, worker and significant other perceptions of pain self-efficacy, perceived partner responses to pain, pain catastrophizing, and contribution to work participation were explored in relation to the worker's CMP. In the Netherlands, questionnaire data were collected from workers with CMP and their significant others (n=103), and in the UK, in-depth semi-structured interviews were conducted (n=10). Appropriate quantitative and qualitative analysis techniques were applied.Background
Method
Individual illness perceptions have been shown to be important influences on both clinical and work outcomes for those with back pain, yet the influence of ‘significant others’ (spouse/partner/close family member) illness perceptions is rarely explored, particularly in relation to work participation. Semi-structured interviews based on the Illness Perceptions Questionnaire were conducted with two purposive samples of chronic back pain patients (working and work disabled), along with their significant others (n=28). Data were analysed using template analysis.Background
Method
Individual illness perceptions have been shown to be important influences on clinical outcomes for low back, yet significant others' illness perceptions are rarely explored, particularly in relation to work disability. Semi-structured interviews based on the Illness Perceptions Questionnaire were conducted with a purposive sample of UK disability benefit claimants, along with their significant others (n=5 dyads). Data were analysed using template analysis.Background
Method
Shoulder instability is a common cause of morbidity amongst Professional Rugby Union players. This study explores whether the risk of shoulder dislocation is associated with innate shoulder laxity. A randomised controlled study was completed in which all the Premiership Rugby Clubs in England were visited in 2006. 169 professional rugby players (mean age 25.1 years) with no history of instability in either shoulder were assessed and 46 injured players with one shoulder with a history of Bankart lesion or dislocation (mean age 27.5 years) also took part in this study. Shoulder laxity was measured by dynamic ultrasound. Anterior, posterior and inferior translations were measured in both shoulders for healthy players and the uninjured shoulder only for injured players.Objective
Methods
Shoulder instability is a common cause of morbidity amongst Professional Rugby Union players. This study explores whether the risk of shoulder dislocation is associated with innate shoulder laxity. A prospective, randomised controlled study was completed in which all the Premiership Rugby Clubs in England were visited. 169 professional rugby players with no history of instability in either shoulder and 46 players with one shoulder with clinical instability symptoms were assessed. Shoulder laxity was measured by clinical evaluation, questionnaires and ultrasound. Anterior, posterior and inferior translation was measured in both shoulders for healthy players and the uninjured shoulder only for injured players. The results showed there was no significant difference between the left (anterior: mean 2.92 +/− 1.15 mm; posterior: mean 5.10 +/− 1.75 mm; inferior: mean 3.08 +/− 1.00 mm) and right (anterior: mean 3.07 +/− 1.14 mm; posterior: mean 4.87 +/− 1.61 mm; inferior: mean 2.91 +/− 0.99 mm) shoulders in healthy players (P >
0.05). The comparison between healthy shoulders (anterior: mean 3.00 +/− 1.15 mm; posterior: mean 4.99 +/− 1.68 mm; inferior: mean 3.00 +/− 1.00 mm) from healthy players and the uninjured shoulder (anterior: mean 4.16 +/− 1.70 mm; posterior: mean 6.16 +/− 3.04 mm; inferior: mean 3.42 +/− 1.18 mm) from injured players identified that players with unstable shoulders have a significantly higher shoulder translation in their normal shoulder than healthy players (P <
0.05). This is the first study looking at laxity and the risk of shoulder dislocations in sportsmen involved in a high contact sport. These results support the hypothesis that rugby players with “lax” shoulders are more likely to sustain a dislocation or subluxation injury to one of these lax shoulders in their sport.
