Explant analysis of the Biomet Magnum/ReCap metal-on-metal hip joint

Investigation of the short-term in vivo performance of metal-on-carbon fibre reinforced poly ether ether ketone Motec wrists: an explant analysis

Total wrist arthroplasty (TWA) aims to restore pain-free motion to diseased joints. One such TWA, the Motec, has demonstrated good results with acceptable complication rates. It has recently been suggested that the metal-on-carbon fibre reinforced poly ether ether ketone (Mo-CFR-PEEK) version of the Motec TWA be implanted instead of the metal-on-metal version. An explant analysis was undertaken on seven Motec Mo-CFR-PEEK TWAs, revised for a variety of reasons, after a mean time of 2 years in vivo. Compared to a new Motec implant, five of the explanted metal heads and three of the CFR-PEEK cups became smoother in vivo, suggesting self-polishing and negative skewness, indicating some material loss in vivo. Two explanted cups showed indentation marks on their rims and one of these was from component impingement with embedded metallic debris. In the short-term, the articulating surfaces of Motec Mo-CFR-PEEK TWAs did not show major damage.Level of evidence: IV.

Novel Use of an Accelerometer to Assess Load Asymmetry Over Time After Hip Resurfacing Arthroplasty

INTRODUCTION

There is limited knowledge regarding usage of wearable technology to guide return to sport after hip resurfacing arthroplasty (HRA). This study evaluated the use of accelerometers to identify when symmetry is restored between operative and non-operative limbs.

METHODS

A total of 26 primary HRA patients performed five validated physical tests before, 3 and 6 months after HRA: broad jump, double leg vertical jump (DLVJ), hop test, lateral single leg jump (LSLJ), and vertical single leg jump (VSLJ). Impact load and average intensity data (g-force units) were collected using accelerometers. Strength data (pounds (lbs.)) for internal and external rotation was collected with a dynamometer. Univariate and correlation analyses analyzed interlimb asymmetries.

RESULTS

At pre-operation, there were significant impact load asymmetries for DLVJ (P=.008), hop test (P=.021), and LSLJ (P=.003), and intensity asymmetry for DLVJ (P=.010) and LSLJ (P=.003). At 3 months, there was impact load asymmetry for DLVJ (P=.005) and LSLJ (P=.005), and intensity asymmetry for broad jump (P=.020), hop test (P=.042), and LSLJ (P=.005). There were significant strength asymmetries at pre- and 3 months post-operation for internal (P=.013) and external rotation (P=.037). All significant asymmetries indicated the non-operative leg had greater output. No significant asymmetries were found for any exercises at 6 months post-operation. An increase in Harris Hip Score was significantly associated with a decrease in impact asymmetry (r_s = -0.269, P=.006).

DISCUSSION AND CONCLUSION

Impact loads and strength reach interlimb symmetry at 6 months post-HRA. Wearable accelerometers provide useful metrics to distinguish limb asymmetries for recovery monitoring.

Correlation of MARS MRI findings with cup position, metal ion levels and function in metal-on-metal total hip arthroplasty

INTRODUCTION

Metal-on-metal (MoM) total hip arthroplasties (THAs) have been linked with increased incidence of pseudotumours and revision rate. magnetic resonance imaging (MRI) is useful in diagnosing adverse reaction to metal debris (ARMD) disease but it is not known if MRI findings correlate with cup position.

PATIENTS AND METHODS

From a cohort of 79 MoM THA, 34 MRI studies were available. MRI was classified according to Anderson classification. Mean follow-up was 7.1 years. Evaluation included cup position including margin of safety, measurement of metal ion levels and evaluation of function.

RESULTS

44% of patients had definite ARMD. We did not find any correlation between MRI stage and Co, Cr, margin of safety (MOS) or functional scores. However, patients with a margin of safety angle < 21° had more severe findings in MRI.

CONCLUSIONS

Patients with MoM THA experience high degree of ARMD. In our study, the disease did not correlate with metal ion levels but correlated with cup position, evaluated with the MOS angle.

Effect of wear, acetabular cup inclination angle, load and serum degradation on the friction of a large diameter metal-on-metal hip prosthesis

BACKGROUND

The large-scale clinical problem caused by unacceptable tribological behaviour of certain large diameter metal-on-metal prosthetic hips has directed attention to adverse condition testing. High metal-on-metal wear is connected with adverse reaction to metal debris. Friction is important because high friction may be associated with high wear, risk the fixation of the cup, and cause detrimental heating of periprosthetic tissues.

METHODS

A friction measurement system was added to a multidirectional, established hip joint wear simulator, and its functionality was evaluated. In preliminary tests, a 50 mm diameter metal-on-metal prosthesis was tested in an optimal acetabular cup inclination angle (48°) and in a steep angle (70°) using a normal peak load (2 kN) and an increased peak load (3 kN). The test length was 100 h. Long-term adverse condition tests of 3 million cycles were run for three 52 mm metal-on-metal prostheses. The lubricant was diluted calf serum at 37 °C.

FINDINGS

In the 100 h tests, metal-on-metal frictional torque was not highly sensitive to the angle, load and serum degradation, and it was close to that of a conventional 28 mm prosthesis with a polyethylene cup, mostly below 5 Nm. However, a manyfold higher frictional torque (10 to 20 Nm) was observed in long-term metal-on-metal tests with substantial wear.

INTERPRETATION

To obtain a realistic prediction of the frictional behaviour of a hip design, long-term, multidirectional wear tests are necessary. The friction should preferably be measured during the wear test. In addition to normal conditions, adverse condition testing is strongly recommended.

Is the rate of revision of 36 mm metal-on-metal total hip arthroplasties with Pinnacle acetabular components related to the year of the initial operation? an interrupted time-series analysis using data from the National Joint Registry for England and Wales

AIMS

The aim of this study was to determine whether the rates of revision for metal-on-metal (MoM) total hip arthroplasties (THAs) with Pinnacle components varied according to the year of the initial operation, and compare these with the rates of revision for other designs of MoM THA.

PATIENTS AND METHODS

Data from the National Joint Registry for England and Wales included 36 mm MoM THAs with Pinnacle acetabular components which were undertaken between 2003 and 2012 with follow-up for at least five years (n = 10 776) and a control group of other MoM THAs (n = 13 817). The effect of the year of the primary operation on all-cause rates of revision was assessed using Cox regression and interrupted time-series analysis.

RESULTS

For MoM THAs involving Pinnacle components, those undertaken between 2007 and 2012 had higher rates of revision compared with those undertaken between 2004 and 2006 (hazard ratio (HR) 2.01; 95% confidence interval (CI) 1.57 to 2.57; p < 0.001). For THAs undertaken during and after 2007, the number of revisions per 1000 implant-years at risk significantly increased by 5.20 (95% CI 0.52 to 9.89; p = 0.033) compared with those undertaken before this time. In the control group, THAs undertaken between 2007 and 2012 also had higher rates of revision (HR 1.77; 95% CI 1.49 to 2.10; p < 0.001), with revisions per 1000 implant-years for those undertaken during and after 2007 significantly increasing by 6.13 (95% CI 1.42 to 10.83; p = 0.016).

CONCLUSION

The five-year revision rates were significantly increased for all primary MoM THAs undertaken from 2007 onwards. Contrary to recent reports, this finding was not specific to those involving Pinnacle acetabular components and may be explained by increased surveillance and recent lowering of the threshold for revision. Cite this article: Bone Joint J 2018;100-B:33-41.