Material loss at the head-stem taper junction may contribute to the high early failure rates of stemmed large head metal-on-metal (LH-MOM) hip replacements. We sought to quantify both wear and corrosion and by doing so determine the main mechanism of material loss at the taper. This was a retrospective study of 78 patients having undergone revision of a LH-MOM hip replacement. All relevant clinical data was recorded. Corrosion was assessed using light microscopy and scanning electron microscopy, and graded according to a well-published classification system. We then measured the volumetric wear of the bearing and taper surfaces. Evidence of at least mild taper corrosion was seen in 90% cases, with 46% severely corroded. SEM confirmed the presence of corrosion debris, pits and fretting damage. However, volumetric wear of the taper surfaces was significantly lower than that of the bearing surfaces (p = 0.015). Our study supports corrosion as the predominant mechanism of material loss at the taper junction of LH-MOM hip replacements. Although the volume of material loss is low, the ionic products may be more biologically active compared to the particulate debris arising from the bearing surfaces

It has been speculated that high wear at the head-stem taper may contribute to the high failure rates reported for stemmed large head metal-on-metal (LH-MOM) hips. In this study of 53 retrieved LH-MOM hip replacements, we sought to determine the relative contributions of the bearing and taper surfaces to the total wear volume. Prior to revision, we recorded the relevant clinical variables, including whole blood cobalt and chromium levels. Volumetric wear of the bearing surfaces was measured using a coordinate measuring machine and of the taper surfaces using a roundness measuring machine. The mean taper wear volume was lower than the combined bearing surface wear volume (p = 0.015). On average the taper contributed 32.9% of the total wear volume, and in only 28% cases was the taper wear volume greater than the bearing surface wear volume. Despite contributing less to the total material loss than the bearing surfaces, the head-stem taper junction remains an important source of implant-derived wear debris. Furthermore, material loss at the taper is likely to involve corrosion and it is possible that the material released may be more biologically active than that from the bearing surface

Objectives. Mechanical wear and corrosion at the head-stem junction of total hip arthroplasties (THAs) (trunnionosis) have been implicated in their early revision, most commonly in metal-on-metal (MOM) hips. We can isolate the role of the head-stem junction as the predominant source of metal release by investigating non-MOM hips; this can help to identify clinically significant volumes of material loss and corrosion from these surfaces. Methods. In this study we examined a series of 94 retrieved metal-on-polyethylene (MOP) hips for evidence of corrosion and material loss at the taper junction using a well published visual grading method and an established roundness-measuring machine protocol. Hips were retrieved from 74 male and 20 female patients with a median age of 57 years (30 to 76) and a median time to revision of 215 months (2 to 324). The reasons for revision were loosening of both the acetabular component and the stem (n = 29), loosening of the acetabular component (n = 58) and infection (n = 7). No adverse tissue reactions were reported by the revision surgeons. Results. Evidence of corrosion was observed in 55% of hips. The median Goldberg taper corrosion score was 2 (1 to 4) and the annual rate of material loss at the taper was 0.084 mm. 3. /year (0 to 0.239). The median trunnion corrosion score was 1 (1 to 3). Conclusions. We have reported a level of trunnionosis for MOP hips with large-diameter heads that were revised for reasons other than trunnionosis, and therefore may be clinically insignificant. Cite this article: H. S. Hothi, D. Kendoff, C. Lausmann, J. Henckel, T. Gehrke, J. Skinner, A. Hart. Clinically insignificant trunnionosis in large-diameter metal-on-polyethylene total hip arthroplasty. Bone Joint Res 2017;6:52–56. DOI: 10.1302/2046-3758.61.BJR-2016-0150.R2

Summary. Carriers for local delivery of stem cells into degenerative intervertebral discs need to be tested under physiological loading since stem cell viability, density and differentiation, as well as carrier stability are strongly affected by loading. Introduction. The success of the local delivery of mesenchymal stem cells (MSCs) to degenerative discs relies on three main factors: (i) an appropriate delivery method, (ii) a suitable carrier, (iii) resistance to loading forces. Bioreactors allow the application of loading to whole intervertebral discs and represent a useful tool to screen the potential of new regenerative therapies. We have previously shown that hydrogel delivery through the endplate (EP) leaves the annulus fibrosus (AF) intact (as opposed to an approach through the AF). Furthermore, we have found that the physiological loading needs to be adapted for nucleotomised discs. In this study we compare the behaviour of two MSCs carriers under loading in a whole IVD bioreactor. Materials & Methods. MSCs were isolated from human bone marrow after approval by the local ethical commission and written consent of the patient (age: 20–60 years). Whole IVDs were harvested from calf tails obtained from the local abattoir. Partial nucleotomies were achieved by mechanically removing the nucleus pulposus (NP) through the endplate. Firstly, hMSCs suspended in hyaluronan thermoreversible hydrogel. 2. (6×10. 6. cells/ml) were supplied to the nucleotomised IVDs and the removed EP was re-inserted. Discs were either loaded for one week at 0.06 ± 0.02 MPa, 0.1 Hz, 4 hours/day (n=4) or kept unloaded in culture medium (control). Secondly, hMSCs suspended in fibrin (100 mg/ml fibrinogen and 500 IU/ml thrombin) were applied to IVDs as above described. Discs were kept unloaded in culture medium for one week and then loaded for two weeks at 0.06 ± 0.02 MPa, 0.1Hz, 3 hours/day (n=4) or kept unloaded (control). Analyses included histology, gene expression and cell viability. Results. On the gene level, it was found that loading is required to induce aggrecan (a major component of the NP tissue) up-regulation in MSCs for both carriers. Aggrecan was up-reguled in MSCs already after one week of loading in the thermoreversible hyaluronan, but only after two weeks MSCs in fibrin. Additionally, the highest expression of keratin-19 (NP marker) was found in the loaded thermoreversible hyaluronan group. However, there was a high cell and material loss under loading in this group. Fibrin was more stable in the chosen experimental conditions, as shown in the safranin O-Fast green staining of the IVD. Indeed, the NP cavity was still filled with fibrin gel after 2 weeks of loading. No significant cell loss or decrease in cell viability was found in the fibrin gel after 2 weeks of loading. Discussion/Conclusion. The hyaluronan thermoreversible hydrogel is superior in promoting the differentiation of MSCs toward the disc phenotype, as attested by the aggrecan up-regulation. However, the fibrin gel has a better stability and is more effective at maintaining a high density of MSCs, even under loading. In conclusion, stem cell carriers need to be evaluated in a relevant setting, e.g. in an IVD under load. The study was partially supported by a NASS Research grant

Summary. Four highly cross-linked UHWMPEs except vitamin E-stabilised explants. Introduction. The development of both first and second generation highly cross-linked material focused on stabilizing radiation-induced free radicals as the sole precursor to oxidative degradation; however, secondary in vivo oxidation mechanisms have been identified in both conventional and highly cross-linked UHMWPE, induced by absorbed lipids and cyclic mechanical load. Retrieval studies are reporting in vivo oxidation highly cross-linked retrievals with up to ten year in vivo durations. Preclinical aging tests did not predict these in vivo material changes. With only a decade of these materials in clinical use, retrieval studies are limited to mid-term follow-up. In vitro studies face a challenge in effectively replicating the precise in vivo conditions that lead to this loss of oxidation resistance. In this study, we bypass replicating these in vivo variables by examining surgically-retrieved components, thereby testing material that has been affectively “pre-conditioned” by their in vivo service. After a preliminary post-operative analysis, we subjected retrievals to accelerated aging tests in order to predict the extent to which their oxidative stability had been uniquely compromised in vivo. Patients & Methods. Twenty-four highly cross-linked retrievals of four manufacturing methods (n=6 each of Longevity™, Prolong™, X3™ and E1™) and in vivo durations (1–4 years) were analyzed post-operatively and after accelerated aging (70°C, 5atm O. 2. for 2 weeks; ASTM F2003). Never-implanted components (n=1) of each material type were also aged. Infrared microscopy was used to evaluate lipid absorption, oxidation (per ASTM F2102-01ε1) and hydroperoxide levels after 16 hrs of nitric oxide staining for oxidation potential, and gravimetric swelling analysis assessed cross-link density (ASTM F2214). Results. All retrievals contained absorbed lipids penetrating below both loaded (penetration depth=1.3 ± 0.5 mm) and unloaded (0.6 ± 0.2 mm) surfaces. Each material type subset contained retrievals with and without detectable oxidation after in vivo service (Max OI=0.01–0.94). After aging, all post-irradiation thermally-treated, highly cross-linked retrievals, regardless of initial lipid levels or oxidation, showed oxidative degradation, demonstrated by subsurface oxidative peaks (MOI=0.30–2.63), increased hydroperoxides (3–5X), and decreased cross-link density (−34–90%). In contrast, vitamin E-stabilised retrievals showed below MOI<0.2 with no significant loss of cross-link density. Never-implanted controls for each material type showed no oxidative changes after accelerated aging. Discussion/Conclusion. Accelerating aging after in vivo service has shown oxidative instability characterised by high oxidation and material property loss in the three highly cross-linked materials without an incorporated antioxidant. This oxidative degradation took place regardless of post-operative oxidation levels, indicating that even without detectable oxidation the material had undergone changes during in vivo service, as compared to the lack of oxidative response in never-implanted controls. These findings also suggest that the presence of an antioxidant may be able to slow down and/or stabilise in vivo mechanisms compromising long-term oxidative stability and increase the longevity of highly cross-linked UHMWPE materials