Risk factors for failure of the 36 mm metal-on-metal Pinnacle total hip arthroplasty system: a retrospective single-centre cohort study.

AIMS: To determine ten-year failure rates following 36 mm metal-on-metal (MoM) Pinnacle total hip arthroplasty (THA), and identify predictors of failure. PATIENTS AND METHODS: We retrospectively assessed a single-centre cohort of 569 primary 36 mm MoM Pinnacle THAs (all Corail stems) followed up since 2012 according to Medicines and Healthcare Products Regulation Agency recommendations. All-cause failure rates (all-cause revision, and non-revised cross-sectional imaging failures) were calculated, with predictors for failure identified using multivariable Cox regression. RESULTS: Failure occurred in 97 hips (17.0%). The ten-year cumulative failure rate was 27.1% (95% confidence interval (CI) 21.6 to 33.7). Primary implantation from 2006 onwards (hazard ratio (HR) 4.30; 95% CI 1.82 to 10.1; p = 0.001) and bilateral MoM hip arthroplasty (HR 1.59; 95% CI 1.03 to 2.46; p = 0.037) predicted failure. The effect of implantation year on failure varied over time. From four years onwards following surgery, hips implanted since 2006 had significantly higher failure rates (eight years 28.3%; 95% CI 23.1 to 34.5) compared with hips implanted before 2006 (eight years 6.3%; 95% CI 2.4 to 15.8) (HR 15.2; 95% CI 2.11 to 110.4; p = 0.007). CONCLUSION: We observed that 36 mm MoM Pinnacle THAs have an unacceptably high ten-year failure rate, especially if implanted from 2006 onwards or in bilateral MoM hip patients. Our findings regarding implantation year and failure support recent concerns about the device manufacturing process. We recommend all patients undergoing implantation since 2006 and those with bilateral MoM hips undergo regular investigation, regardless of symptoms. Cite this article: Bone Joint J 2017;99-B:592-600.

Can blood metal ion levels be used to identify patients with bilateral Birmingham Hip Resurfacings who are at risk of adverse reactions to metal debris?

AIMS: We investigated whether blood metal ion levels could effectively identify patients with bilateral Birmingham Hip Resurfacing (BHR) implants who have adverse reactions to metal debris (ARMD). PATIENTS AND METHODS: Metal ion levels in whole blood were measured in 185 patients with bilateral BHRs. Patients were divided into those with ARMD who either had undergone a revision for ARMD or had ARMD on imaging (n = 30), and those without ARMD (n = 155). Receiver operating characteristic analysis was used to determine the optimal thresholds of blood metal ion levels for identifying patients with ARMD. RESULTS: The maximum level of cobalt or chromium ions in the blood was the parameter which produced the highest area under the curve (91.0%). The optimal threshold for distinguishing between patients with and without ARMD was 5.5 µg/l (83.3% sensitivity, 88.4% specificity, 58.1% positive and 96.5% negative predictive values). Similar results were obtained in a subgroup of 111 patients who all underwent cross-sectional imaging. Between 3.2% and 4.3% of patients with ARMD were missed if United Kingdom (7 µg/l) and United States (10 µg/l) authority thresholds were used respectively, compared with 2.7% if our implant specific threshold was used, though these differences did not reach statistical significance (p ≥ 0.248). CONCLUSION: Patients with bilateral BHRs who have blood metal ion levels below our implant specific threshold were at low-risk of having ARMD. Cite this article: Bone Joint J 2016;98-B:1455-62.

A semi-automated method for measuring femoral shape to derive version and its comparison with existing methods.

The measurement of femoral version is important in surgical planning of derotational osteotomies particularly for patients with proximal femoral deformity. It is, however, difficult to measure version accurately and differences of 10° to 15° have been found between repeated measurements. The aim of this work was first to develop a method of measuring femoral version angle where the definition of the neck axis is based on the three-dimensional point cloud making up the neck, second to automate many of the processes involved thus reducing the influence of human error and third to ensure the method could run on freely available software suitable for most computer platforms. A CT scan was performed on 44 cadaveric femurs to generate point clouds of the femoral surfaces. The point clouds were then analysed semi-automatically to determine femoral version angle between a neck axis defined by the bone surface points belonging only to the neck and a femoral condylar axis. The results from the neck fitting method were compared against three other methods typically used in the clinic (Murphy, Reikeras and Lee methods). Version angle measured by the new method gave 19.1° ± 7.3° (mean ± standard deviation) for the set of cadaveric femurs, 3.5° lower than the Murphy method and 6.8° and 11.0° higher than the Reikeras and Lee 2D methods respectively. The results demonstrate a method of measuring femoral version angle incorporating a high level of automation running on free software.

The effect of polyethylene thickness in fixed- and mobile-bearing total knee replacements.

In this paper fixed- and mobile-bearing implants were simulated using a multibody dynamic model and a finite element model to investigate the contact pressure distribution in the ultra high molecular weight polyethylene tibial bearing component. The thickness of polyethylene varied from 6.8 to 12.3 mm and the polyethylene was modelled as a non-linear material. It was found that the contact pressure on the polyethylene decreased in the fixed-bearing implant when the thickness of polyethylene increased from 6.8 to 8 and 9.6 mm, but there was little further decrease in pressure with the increase of polyethylene thickness from 9.6 to 11.0 and 12.3 mm. In the mobile-bearing implant, no increase in contact pressure on the superior surface was found with the increase in the thickness of the polyethylene; however, the contact pressures on the inferior contact surface of the thicker designs were higher than those in the 6.8 mm design. The numerical results obtained in this paper are in good agreement with published experimental test results. Moreover, the paper presents a detailed pressure distribution on the tibial bearing component during a full gait cycle.

Measuring the rib hump in scoliosis with ISIS2.

The three-dimensional shape of the back of 60 patients attending a spinal deformity clinic was measured using ISIS2, a non-commercial surface topography system using digital photography and structured light. Wire-frame and contour plots were displayed, presenting quantitative information and providing a useful pictorial representation of the whole back. A numerical parameter representing the height of the rib hump was also recorded. Repeat measurements, with the patient walking around the room between photographs were carried out. The mean difference between the pairs of measurements was -0.08 mm (sd 4.18 mm) and the 95% tolerance limits were -9.82 mm to 9.66 mm. Changes of greater than +/-10 mm are therefore necessary as indicative of clinical change.

Thoracic kyphosis angle measurements with ISIS2.

Thoracic kyphosis angle measurements using surface topography with ISIS2 were carried out to estimate the inherent variability in the parameter caused by natural change in the patient's stance, breathing and muscle tension. A mean kyphosis angle of 33.8 degrees (sd 13.4 degrees , range 6 degrees -66 degrees ) was measured from repeat tests on 61 patients. The mean difference between the pairs of measurements was -0.02 degrees (sd 3.18 degrees ) and the 95% tolerance limits were -7.41 degrees to 7.38 degrees . This variability is lower than the clinically significant change in kyphosis angle reported in the literature. Thus kyphosis angle in ISIS2 is suitable for monitoring progress in kyphotic deformities.

New method of Scoliosis Deformity Assessment: ISIS2 System.

Scoliosis deformity has been assessed using radiographic angle measurements. Surface topography systems are an alternative and complementary methodology. Working systems include the original ISIS1 system, Quantec and COMOT techniques. Over the last five years the new ISIS2 (Integrated Shape Imaging System) has been developed from basic principles to improve the speed, accuracy, reliability and ease of use of ISIS1. The aim of this study was to confirm that ISIS2 3D back shape measurements are valid for assessment and follow up of patients with scoliosis. Three-dimensional back measurements were performed in Oxford. ISIS2 includes a camera/projector stand, patient stand with a reference plane, and Mac computer. Pixel size is approximately 0.5 mm with fringe frequency of approximately 0.16 fringes/mm ( approximately 6.5 mm/fringe). Clinical reports in pdf format are of coloured images with numerical values. Reports include a height map, contour plot, transverse section plots, coronal plot, sagittal sections and bilateral asymmetry maps. A total of 520 ISIS2 scans on 242 patients were performed from February 2006 to December 2007. There were 58 male patients (median age 16 years, SD 3.71, min 7, max 25) and 184 female patients (median age 14.5 years, SD 3.23, min 5, max 45). Average number of scans per patient was 2.01 with the range of 1-10 scans. Right sided thoracic curves were the most frequent pattern. The median values and 95% CI are reported of back length; pelvic rotation; flexion/extension; imbalance; lateral asymmetry; skin angle; kyphosis angle; lordosis angle; volumetric asymmetry. ISIS2 scoliosis measurements are non-invasive, low-cost, three-dimensional topographic back measurements which can be confidently used in scoliosis assessment and monitoring of curve progression.

Adult-onset motor neuron disease in three cats.

Motor neuron diseases of domestic animals have rarely been described. Three cats with adult-onset, chronic, progressive generalized muscle weakness characterized initially by trembling on exertion and later by extreme difficulty in walking, cervical ventroflexion, dysphagia, and marked muscle atrophy were elevated. Spinal reflexes were evident early but were nondetectable as the disease progressed. Electromyography revealed fibrillation potentials, with nerve conduction velocities within the reference range. Histologic examination of muscle specimens revealed denervation. Marked neuron loss and gliosis were detected in the ventral horns of the spinal cord, with atrophy of ventral nerve rootlets. Less dramatic neuron loss was seen in brain stem motor nuclei. Electron microscopic examination of the ventral horns disclosed hypertrophied astrocytes, with densely arrayed intermediate filaments, swollen axons with large filamentous accumulations, and many macrophages with lipofuscin-like inclusions. Clinical and pathologic findings were consistent with a progressive neurodegenerative disease affecting spinal and some bulbar motor nuclei.

Astrocytoma in a dog causing convulsions.

An adult, male, 7 Kg. dog was presented because of a convulsion. This progressed and interictal signs became apparent. A slight left spastic hemiparesis was present with a normal gait and posture. A partial left visual deficit with intact pupillary reflexes became evident. All signs were referable to a right cerebral lesion. Necropsy revealed an astrocytoma in the right cerebrum compressing the internal capsule and optic tract.