Tuberculosis (TB) infection of bones and joints accounts for
6.7% of TB cases in England, and is associated with significant
morbidity and disability. Public Health England reports that patients
with TB experience delays in diagnosis and treatment. Our aims were
to determine the demographics, presentation and investigation of
patients with a TB infection of bones and joints, to help doctors
assessing potential cases and to identify avoidable delays. This was a retrospective observational study of all adults with
positive TB cultures on specimens taken at a tertiary orthopaedic
centre between June 2012 and May 2014. A laboratory information
system search identified the patients. The demographics, clinical presentation,
radiology, histopathology and key clinical dates were obtained from
medical records.Aims
Patients and Methods
Metal-on-metal (MOM) total hip arthroplasty using large diameter femoral heads offer clinical advantages however the failure rates of these hips is unacceptably high. Retrieved hips have a wide range of wear rates of their bearing and taper surfaces and there is no agreement regarding the cause of failure. Detailed visual inspection is the first step in the forensic examination of failed hip components and may help explain the mechanisms of failure. The aim of this study was to determine if there was a correlation between the results of detailed inspections and the volumetric wear of the bearing and taper surfaces of retrieved hips. Detailed, non-destructive macroscopic and stereomicroscopic examinations of 89 retrieved MOM hip components were performed by a single experienced examiner using quantitative assessment to document the severity of 10 established damage features: Light scratches, Moderate scratches, Heavy scratches, Embedded particles, Discolouration, Haziness, Pitting, Visible wear zone, Corrosion, Fretting Each surface was considered in terms of zones comprising of quadrants (cup, head, and taper) and subquadrants (cup and head), Figure 1. Each zone was scored on a scale of 0 to 3 by determining the percentage of the surface area of the zone that exhibited the feature in question: a score of 0=0%, 1<25%, 25%<2<75%, 3>75%. The sum of the scores of each zone was used for the assessment of each damage feature. The volume of wear at the surfaces of each hip was measured with a Zeiss Prismo coordinate measuring machine (cup and head) and a Talyrond 365 roundness measurement instrument (taper), using previously reported methods1, 2. Simple linear regression models were used to asses the univariable associations between the inspection scores and wear volumes. Multiple linear regression models were subsequently used to asses the simultaneous contribution of the inspection scores, found significant in univariable analyses, on the wear outcome variables. All statistical analysis was performed using Stata/IC version 12.1 (StataCorp, USA) and throughout a p value < 0.05 was considered statistically significant.Introduction
Method
There has been widespread concern regarding the adverse tissue reactions after metal-on-metal (MoM) total hip replacements (THR). Concerns have also been expressed with mechanical wear from micromotion and fretting corrosion at the head/stem taper junction in total hip replacements. In order to understand the interface mechanism a study was undertaken in order to investigate the effect of surface finish and contact area associated with modular tapers in total hip replacements with a single combination of materials of modular tapers. An inverted hip replacement setup was used (ASTM F1875-98). 28 mm Cobalt Chrome (CoCr) femoral heads were coupled with either full length (standard) or reduced length (mini) 12/14 Titanium (Ti) stem tapers. These Ti stem tapers had either a rough or smooth surface finish whilst all the head tapers had a smooth surface finish. Wear and corrosion of taper surfaces were compared after samples were sinusoidally loaded between 0.1 kN and 3.1 kN for 10 million cycles at 4 Hz. In test 1 rough mini stem tapers were compared with rough standard stem tapers whilst in test 2 rough mini stem tapers were compared with smooth mini stem tapers. Surface parameters and profiles were measured before and after testing. Electrochemical static and dynamic corrosion tests were performed between rough mini stem tapers and smooth mini stem tapers under loaded and non-loaded conditions.Introduction:
Methods:
It has been suggested that corrosion and fretting at the taper junctions of stemmed metal-on-metal hip replacements may contribute to their high failure rates. A peer-reviewed semi-quantitative scoring system [Goldberg et al., 2002] has been used to visually assess the severity of corrosion and fretting of the taper junction but has not been validated using multiple examiners. The aim of this study was to assess the inter-observer variability of this method. Macroscopic and stereomicroscopic examinations of the femoral head and stem tapers of 100 retrieved large diameter metal on metal (MOM) hip components were performed by two independent observers using the methods defined by Goldberg et al. [2002] to quantify corrosion and fretting. Scores ranging from 1 (none) to 4 (severe) were assigned to the medial, lateral, posterior and anterior quadrants of the neck taper and the distal and proximal regions of the head taper. An overall score was then assigned to each surface as a whole. Cohen's weighted Kappa statistic (κ) was used to measure the inter-observer agreement. A quadratic weighting scheme, that allocated weights to the importance of disagreements that are proportional to the square of the number of categories apart, was used to take account of scaled disagreement. Kappa values were assessed using previously established criteria where κ ≤ 0 = poor, 0.01 to 0.20 = slight, 0.21 to 0.40 = fair, 0.41 to 0.60 = moderate, 0.61 to 0.80 = substantial, 0.81 to 1 = almost perfect. A sample size of 100 was used in order to detect a coefficient of 0.60 to within 0.25 with 95% confidence with two experienced observers. Statistical analysis was performed using Stata/IC version 12.1 (StataCorp, College Station, TC, USA) and a p value < 0.05 was considered statistically significant.Introduction
Method
Recent retrieval studies and registry reports have demonstrated an alarming incidence of early failure of metal-on-metal THR. This appears to be due to fretting and corrosion at the taper junction (trunnion) between the neck and large diameter heads in metal-on-metal hip implants. It has been proposed that designs with lower bearing clearances and greater cup flexibility deform during implantation leading to increased frictional torque and micromotion at the head-neck taper junction. Small movements at the trunnion may suggest elastic deformation, but large movements may suggest slippage at the friction interface. This study was conducted using retrieved metal-on-metal components to test the hypotheses that: 1. Cup deformation through localized compression leads to increased bearing torque, and 2. Increased torques generated in large head metal-on-metal bearings cause motion of the head-neck taper junction. Nine metal-on-metal hip implants were received from a national joint retrieval service and tested in a mechanical testing machine. The components were of three different designs (ASR, BHR, and Durom) and ranged in diameter from 42–54 mm. A custom jig was constructed to generate controlled radial compression at opposite points on the rim of an acetabular component. The jig was positioned inverted to the normal anatomical position and was angled to simulate the anatomical orientation of the cup (35° inclination, 10° anteversion). With the exception of an initial compression load of 100N, the cups were compressed at 200N intervals to a maximum of 2000N. Three trials at each cup compression load were performed. The torque developed about the trunnion axis was measured as the head articulated through a motion arc of 60° and the friction factor was calculated. Head–neck micromotion was continuously monitored using a non-displacement inductive transducer. Changes in micromotion from the 100N compression load were calculated.Introduction
Materials and Methods
Metal-on-metal (MOM) total hip arthroplasty and hip resurfacing using large diameter femoral heads offer clinical advantages, however the failure rates of these hips are unacceptably high. Retrieved MOM hips have a wide range of wear rates of their bearing surfaces and there is ongoing research to identify the causes of failure. Detailed visual inspection is the first step in the forensic examination of failed hip components, but there is no universally accepted description or process. Visible features may help explain the mechanism of failure of MOM hips. During our analysis of 2000 MOM hip components, we have developed protocols to undertake detailed, non-destructive macroscopic and stereomicroscopic examinations of each component, using quantitative assessment to document the presence of types of damage. We have established a systematic terminology to describe the types of damage that are observed, allowing for consistency and clarity in the vocabulary used. These include (but are not limited to):
Scratching – when there is an increase in the number and/or magnitude of scratches present on the surface, typically increasing measured roughness parameters. The severity of scratching is determined by rubbing a 0.18 mm thickness acetate gage or fingernail over the surface:
Light –visible but not detectable with gage. Moderate – visible and detectable with gage. Heavy – depth clearly visible and will catch a fingernail or gage. Pitting – indentations in the surface for which the dimensions are similar in all directions. Embedded Particles – hard particles that have become embedded in the bearing surface. Discolouration – observed as a change in the appearance of the surface, often as colour diffraction patterns. Polishing, gouges, etching (from corrosion), surface films, surface deposits and tribochemical reaction layers. To assess the distribution of these types of damage on the components, each surface is considered in terms of zones defined by quadrants (cup, head, stem and taper) and sub-quadrants (cup and head only), Figure 1. Each zone is scored on a scale of 0 to 3 by determining the percentage of the surface area of the quadrant that exhibits the feature in question:
a score of 0 indicates 0%
indicates greater than 0% but less than 25% indicates between 25% and 75% inclusive indicates greater than 75%. The use of zones to differentiate between the polar and equatorial regions of the cup and head surfaces can offer important information relating to the articulation of the bearing surfaces. For example in a cohort of 90 inspections, a score of 3 for light scratching was recorded in all areas of the bearing surface in 40% of cups, whilst approximately 5% had evidence of pitting, occurring near the rim. Current research at our retrieval centre involves correlating the results of detailed inspections with a range of variables, including implant design, size and surgical position.
We present the medium to long term clinical results of 112 Uncemented custom Computer Assisted Design Computer Assisted Manufactured (CAD-CAM) total hip arthroplasties performed between 1992 and 1998 in 111 patients. Fifty three males and 58 females were included. Mean age was 46.2 years (range 24.6yrs - 62.2 yrs). Average duration of follow up was 156 months (120 – 204 months). The mean Harris Hip Score (HHS) improved from 42.4 to 90.3, mean Oxford Hip Score (OHS) improved from 43.1 to 18.2 and the mean WOMAC hip score improved from 57.0 to 11.9. There was 1 revision due to failure of the acetabular components but there were no failures of the femoral components. There were no revisions for aseptic loosening. The worst case survival in this cohort of custom femoral components at an average 13 year follow up (range 10-17 years) was 98.2% (95% Confidence interval 95% to 99%). Survival of the femoral component alone was 100%. These results are comparable with the best medium to long term results for femoral components used in primary total hip arthroplasty (THA) with any means of fixation.
