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
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.
To compare the functional outcome of Distal Tibial Metaphyseal fracture treated with Circular frame compared vs. Locking Plate Distal Tibial Metaphyseal fractures were retrospectively identified over an 18 month period. Each fracture was assessed individually using radiographs. All paediatric, compound, tibial plateau and intra-articular fractures were excluded from the study. Other methods of fixation including intramedullary nailing were also excluded. The remaining fractures were assigned to either the circular frame fixation or the locking plate intervention group. Outcomes were assessed using radiographs for union dates and microbiology results for evidence of infection. Patients were followed up by postal questionnaires, which included a modified American Orthopaedic Foot and Ankle Score (AOFAS), the Olerud and Molander Score (O&M) and a custom questionnaire. The custom questionnaire asked about co-morbidities, smoking status and work days lost following surgery. After exclusions, 30 patients (Frame=15, Plate=15), were sent out questionnaires via post. We received completed questionnaires from 21 patients (Frame=11, Plate=10) giving us a response rate of 70%. Results show no difference in infection rates, skin necrosis, non-union or re-operation rates. There was also no significant difference in patient AOFAS and O&M scores at follow up.Statement of Purpose
Methods and Results
This study demonstrates the utility of a modified postero-medial surgical approach to the knee in treating a series of patients with complex tibial plateau injuries with associated postero-medial shear fractures. Postero-medial shear fractures are under-appreciated and their clinical relevance have recently been characterised. Less invasive surgery and indirect reduction techniques are inadequate for treating these postero-medial coronal plane fractures. The approach includes an inverted ‘L’ shaped incision and reflection of the medial head of gastrocnemius, while protecting the neurovascular structures. This is a more extensile exposure than described by Trickey (1968). Our case series includes 8 females and 8 males. The average age is 53.1 years. The mechanism of injury included 7 RTAs, 5 fall from height, 1 industrial accident and 3 valgus injuries. All patients' schatzker grade 4, or above, fractures with a posteromedial split depression. Two were open, two had vascular compromise and one had neurological injury.Hypothesis
Methods
