An in vitro simulation method for the tribological assessment of complete natural hip joints.

The use of hip joint simulators to evaluate the tribological performance of total hip replacements is widely reported in the literature, however, in vitro simulation studies investigating the tribology of the natural hip joint are limited with heterogeneous methodologies reported. An in vitro simulation system for the complete natural hip joint, enabling the acetabulum and femoral head to be positioned with different orientations whilst maintaining the correct joint centre of rotation, was successfully developed for this study. The efficacy of the simulation system was assessed by testing complete, matched natural porcine hip joints and porcine hip hemiarthroplasty joints in a pendulum friction simulator. The results showed evidence of biphasic lubrication, with a non-linear increase in friction being observed in both groups. Lower overall mean friction factor values in the complete natural joint group that increased at a lower rate over time, suggest that the exudation of fluid and transition to solid phase lubrication occurred more slowly in the complete natural hip joint compared to the hip hemiarthroplasty joint. It is envisaged that this methodology will be used to investigate morphological risk factors for developing hip osteoarthritis, as well as the effectiveness of early interventional treatments for degenerative hip disease.

Three-dimensional assessment of impingement risk in geometrically parameterised hips compared with clinical measures.

Abnormal bony morphology is a factor implicated in hip joint soft tissue damage and an increased lifetime risk of osteoarthritis. Standard 2-dimensional radiographic measurements for diagnosis of hip deformities, such as cam deformities on the femoral neck, do not capture the full joint geometry and are not indicative of symptomatic damage. In this study, a 3-dimensional geometric parameterisation system was developed to capture key variations in the femur and acetabulum of subjects with clinically diagnosed cam deformity. The parameterisation was performed for computed tomography scans of 20 patients (10 female and 10 male). Novel quantitative measures of cam deformity were taken and used to assess differences in morphological deformities between males and females. The parametric surfaces matched the more detailed, segmented hip bone geometry with low fitting error. The quantitative severity measures captured both the size and the position of cams and distinguished between cam and control femurs. The precision of the measures was sufficient to identify differences between subjects that could not be seen with the sole use of 2-dimensional imaging. In particular, cams were found to be more superiorly located in males than in females. As well as providing a means to distinguish between subjects more clearly, the new geometric hip parameterisation facilitates the flexible and rapid generation of a range of realistic hip geometries including cams. When combined with material property models, these stratified cam shapes can be used for further assessment of the effect of the geometric variation under impingement conditions.

High prevalence of sleep disordered breathing in patients with diabetic macular edema.

BACKGROUND: Diabetic retinopathy is more common and severe in patients with sleep disordered breathing (SDB). This study aimed to establish whether this is also true for patients with diabetic clinically significant macular edema (CSME). It is hypothesized that SDB, through intermittent hypoxia and blood pressure oscillations, might provoke worsening of CSME. METHODS: Patients with CSME had a home sleep study (ApneaLink; ResMed) to identify SDB. These results were compared with relevant control populations. Macular thickness was measured using optical coherence tomography, and retinal photographs were graded to assess the severity of retinopathy. RESULTS: Eighty of 195 patients (40 men) consented, with average age of 64.7 (11.7) years, neck circumference of 40.4 (5.4) cm, body mass index of 30.2 (6.2) kg/m2, glycosylated hemoglobin (HbA1c) 7.8% (1.4%) [62 (8.0) mmol/mol], and Epworth sleepiness scale of 7.4 (4.8). Overall, 54% had an oxygen desaturation index ≥ 10, and 31% had an apnea-hypopnea index ≥ 15. This SDB prevalence is probably higher than would be expected from the available matched control data. Those with SDB were not sleepier, but they were older and more obese. No significant relationship was identified between the degree of macular thickness and the severity of SDB. CONCLUSION: Individuals with CSME have a high prevalence of SDB. Sleep disordered breathing may contribute to the pathophysiology of CSME, but the mechanism remains unclear. Given the high prevalence, retinal specialists should perhaps consider a diagnosis of SDB in patients with CSME.

Visual improvement following continuous positive airway pressure therapy in diabetic subjects with clinically significant macular oedema and obstructive sleep apnoea: proof of principle study.

BACKGROUND: Diabetic retinopathy and diabetic macular oedema are more prevalent in patients with coexistent obstructive sleep apnoea (OSA). OBJECTIVES: We assessed if treatment of OSA with continuous positive airway pressure (CPAP) might improve visual acuity (VA). METHODS: A total of 35 patients with clinically significant macular oedema (CSMO) and OSA [oxygen desaturation index (ODI) ≥10 or apnoea-hypopnoea index (AHI) ≥15] were identified and agreed to be studied. VA (expressed as the logarithm of the minimum angle of resolution, logMAR), macular thickness, fundal photographs, glycosylated haemoglobin (HbA1c) and rhodopsin mRNA were measured twice at baseline and at 3 and 6 months post-CPAP. Fluorescein angiography and the Epworth Sleepiness Scale (ESS) were obtained once at baseline and at 6 months. RESULTS: Three patients withdrew before the first trial visit. Thus, a total of 32 patients (17 males) entered the study, and 4 subsequently withdrew; thus 28 completed 6 months of follow-up. Baseline characteristics of the subjects were as follows [mean (SD or inter-quartile range)]: age 66.2 (7.1) years, body mass index 31.7 (6.3), HbA1c 7.4% (1.44) [57.1 (15.7) mmol/mol], AHI 16.5 (11-25), ODI 16.0 (12-25), ESS 6.5 (4.0-12.0) and duration of diabetes 9.5 years (5.0-16.5). Participants were divided into 13 high and 15 low CPAP compliers (≥ and <2.5 h/night over the 6 months, respectively). At 6 months, the adjusted treatment effect on VA of high compliance versus low compliance was 0.11 (95% confidence interval 0.21 to -0.002; p = 0.047), equivalent to a one-line improvement on the logMAR chart. There was no significant improvement in macular oedema or fundal photographs. CONCLUSIONS: This hypothesis-generating, uncontrolled study suggests that ≥2.5 h/night CPAP usage over 6 months in individuals with CSMO and OSA may be associated with improvement in VA. This provides justification for a randomised controlled trial of CPAP therapy in such patients.