Dissociation of polyethylene liners with the Depuy Pinnacle cup: a report of 26 cases.

BACKGROUND: Although the Pinnacle Acetabular Hip System (DePuy Synthes) has demonstrated excellent survivorship results since it was first introduced in 2003, there have been a growing number of cases indicating that Pinnacle liners may be subject to a higher-than-expected rate of early dissociation failure. Between 2006 and 2020, our Centre received 212 retrieved Pinnacle liners from Western Australian hospitals. Of these, 26 were removed due to liner dissociation. METHODS: To better understand the frequency and cause of this complication we assessed all retrieved Pinnacle acetabular components for type, damage modes and patient demographics. The leverage force required to dissociate Pinnacle liners was also measured and compared with another commonly used acetabular system, the Trident (Stryker Orthopaedics). RESULTS: The estimated minimum incidence of liner dissociation from our data was 0.35%. Characterisation of dissociated Pinnacle cases (n = 26) revealed 73% were female with an average age of 59 compared to all retrieved Pinnacle cases (n = 212) where 58% were female with an average age of 66. Retrieval analysis indicated plastic deformation of the liner into an ovoid shape, signs of impingement on the rim postero-superiorly and shearing of the liner's anti-rotation tabs was common. Mechanical testing indicated that the dissociation strength of Pinnacle cups decreases at approximately 6.6 N/year in situ (p = 0.01). CONCLUSION: The survival rate of Pinnacle acetabular cups is exceptional with only 5% revised at 10 years. However, surgeons should be aware of the clinical symptoms and high-risk demographics when assessing patients with polyethylene Pinnacle liners.

The effect of implant modification: the low contact stress experience.

AIMS: The aim of this study was to conduct the largest low contact stress (LCS) retrieval study to elucidate the failure mechanisms of the Porocoat and Duofix femoral component. The latter design was voluntarily recalled by the manufacturer. MATERIALS AND METHODS: Uncemented LCS explants were divided into three groups: Duofix, Porocoat, and mixed. Demographics, polyethylene wear, tissue ingrowth, and metallurgical analyses were performed. RESULTS: In 104 implants, a decrease in the odds of loosening and an increase in metallosis and tissue staining in the Duofix group relative to Porocoat group was detected (p = 0.028). There was an increased presence of embedded metallic debris in the Duofix group (p < 0.001). Decreased tissue ingrowth was associated with the Duofix surface (p < 0.001). The attached beads had reduced microhardness, indicative of adverse thermal processing, which resulted in bead shedding, particulate debris, and metallosis. CONCLUSION: Hydroxyapatite coating of the LCS femoral component produced unexpected results and led to its recall. The root cause was likely a combination of retained alumina grit and a reduction in bead microhardness (mechanical strength) resulting in increased particle debris, metallosis, and early revision. The Duofix LCS femoral component was not equivalent to the Porocoat version despite its approval through the Food and Drug Administration (FDA) 510(k) equivalance approval process. Regulation of the introduction of modified existing devices needs to be improved and the Duofix LCS should have been considered to be a new device for which equivalence had not been demonstrated at the point of introduction. Cite this article: Bone Joint J 2019;101-B:1248-1255.

Taper Corrosion and Adverse Local Tissue Reactions in Patients with a Modular Knee Prosthesis.

BACKGROUND: Corrosion has been documented in modular knee implants, but it has not been related to negative patient outcomes. We performed an observational retrieval investigation of 13 Stryker Triathlon TS modular knee implants, 3 of which were revised because of osteolysis and adverse local tissue reactions secondary to fretting corrosion at the modular junctions. METHODS: Modular surfaces were examined for the presence and severity of corrosion, and factors that may influence the development of corrosion were investigated. Scanning electron microscopy and energy-dispersive x-ray spectroscopy were performed to evaluate implants with severe corrosion, and tissue samples were sent for histopathological analysis. RESULTS: Mild to severe corrosion was present in association with 62% of modular tibial components and 75% of modular femoral components. Although tibial corrosion was less prevalent than femoral corrosion, it occurred earlier and with greater severity. Scanning electron microscopy and energy-dispersive x-ray spectroscopy demonstrated the appearances of fretting and corrosion of the modular junctions. Histopathological analysis of specimens from the 3 patients with adverse local tissue reactions demonstrated severe reactions to metal debris, including 1 reaction that was consistent with an aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL). CONCLUSIONS: To our knowledge, ALVAL and pseudotumors have not previously been reported secondary to corrosion of modular knee replacements. The threaded taper design and the release of cobalt-chromium ions and/or debris are implicated in the occurrence of the adverse local tissue reactions, osteolysis, and soft-tissue damage that we observed in our investigation. Clinicians should be aware of this possible complication associated with modular knee implants. CLINICAL RELEVANCE: This article should raise clinician awareness of adverse local tissue reactions secondary to corrosion, potentially resulting in earlier recognition of this complication.

Oxidation of Second Generation Sequentially Irradiated and Annealed Highly Cross-Linked X3™ Polyethylene Tibial Bearings.

Since the first use of ultra-high-molecular-weight polyethylene as a bearing material, research and development efforts have sought to improve wear resistance, increase longevity and lessen the potential for debris mediated adverse tissue responses. A series of second generation sequentially cross-linked and annealed tibial bearings were analysed after several bearings sent for routine retrieval analysis showed oxidative degradation including subsurface whitening, cracking and gross material loss. Evaluation incorporated visual and white banding assessment, mechanical testing and spectroscopy analysis. Whilst visual observation and white banding assessment confirmed oxidative changes, a decrease in mechanical properties and increasing ketone oxidation index as a function of time in vivo suggest time dependent oxidative degradation. Clinically relevant degradation of the sequentially cross-linked and annealed tibial bearings was observed.

Polyaxial locking and compression screws improve construct stiffness of acetabular cup fixation: a biomechanical study.

Bone ingrowth into uncemented acetabular components requires intimate cup-bone contact and rigid fixation, which can be difficult to achieve in revision hip arthroplasty. This study compares polyaxial compression locking screws with non-locked and cancellous screw constructs for acetabular cup fixation. An acetabular cup modified with screw holes to provide both compression and angular stability was implanted into a bone substitute. Coronal lever out, axial torsion and push-out tests were performed with an Instron testing machine, measuring load versus displacement. Polyaxial locking compression screws significantly improved construct stiffness compared with non-locked or cancellous screws. This increased construct stiffness will likely reduce interfacial micromotion. Further research is required to determine whether this will improve bone ingrowth in vivo and reduce cup failure.

Rupture of poly implant prothèse silicone breast implants: an implant retrieval study.

BACKGROUND: Poly Implant Prothèse implants were recalled in Australia in April of 2010 following concerns of higher than expected rupture rates and the use of unauthorized industrial grade silicone as a filler material. Although subsequent investigations found that the gel filler material does not pose a threat to human health, the important question of what caused a relatively modern breast implant to have such a poor outcome compared with contemporary silicone breast implants is yet to be addressed. METHODS: From a cohort of 27 patients, 19 ruptured Poly Implant Prothèse breast implants were subjected to a range of mechanical tests and microscopic/macroscopic investigations to evaluate possible changes in properties as a result of implantation. New Poly Implant Prothèse implants were used as controls. RESULTS: All samples, explanted and controls, complied with the requirements for shell integrity as specified in the International Organization for Standardization 14607. Compression testing revealed rupture rates similar to those reported in the literature. Shell thickness was highly variable, with most shells having regions below the minimum thickness of 0.57 mm that was specified by the manufacturer. Potential regions of stress concentration were observed on the smooth inner surfaces and outer textured surfaces. CONCLUSIONS: The high incidence of Poly Implant Prothèse shell rupture is most likely a result of inadequate quality control, with contributory factors being shell thickness variation and manufacturing defects on both inner and outer surfaces of the shell. No evidence of shell degradation with implantation time was determined.

What are the predictors for bead shedding in porous-coated hip and knee arthroplasties?: An implant retrieval study.

Bead shedding has been reported in both hip and knee arthroplasties and can result in increased polyethylene wear and metal ion release. The rates of bead loss were recorded for each device type, and the interfacial bead-substrate shear load to failure and contact areas of the beads were determined. The 3 components with the highest rate of bead loss, namely, S-Rom, Omnifit, and Optifix acetabular shells, recorded the lowest shear loads to failure. Percentage bead-substrate contact area ranged between 7% and 37% and was the most important factor affecting bead shedding. Other factors influencing bead loss in decreasing order of importance were bead fusion, bead size, component type (acetabular or knee), component loosening, and time in situ.

Corrosion of a hip stem with a modular neck taper junction: a retrieval study of 16 cases.

Since the early 1990s, there has been a dramatic increase in modular total hip designs ranging from a stem with a proximal taper and modular head, to a distal stem, double taper proximal neck, and modular head. Clinical advantages of the modular neck include intraoperative adjustment of leg length via the neck-head taper and femoral anteversion via the neck-stem taper. Sixteen cases of a double tapered cone, Margron hip prosthesis, were presented for retrieval analysis. Macroscopic inspection, corrosion testing, light microscopy, and scanning electron microscopy were conducted to elucidate mechanisms of failure. In this regard, 6 neck components showed significant fretting, and crevice corrosion of the neck-stem taper with an average implantation time of 39 months compared with the remaining retrievals, which showed no corrosion with and average time in situ of 2.7 months. This retrieval study demonstrates that even with a modern taper design and corrosion-resistant materials, increased modularity can lead to fretting and crevice corrosion, metal ion generation, and particulate debris that may contribute to periprosthetic osteolysis and loosening.

Damage of oxinium femoral heads subsequent to hip arthroplasty dislocation three retrieval case studies.

Oxinium exhibits 4900 times less volumetric wear and 640 times less deep scratches in laboratory wear testing compared with traditional cobalt-chromium alloys. Despite the superior wear resistance because of the thin ceramic surface, the zirconium alloy substrate is relatively soft (Hv = 285) when compared with cobalt-chrome alloy femoral heads (ISO 5832-12; Hv = ~420,) and may deform in contact with acetabular shell materials (ISO5832-3; Hv = 350) in the case of dislocation. Three retrieval cases highlight the damage that may occur during dislocation and/or when performing closed reduction maneuvers. It is recommended that closed reduction be attempted with caution because significant head damage can occur. This may lead to accelerated polyethylene wear. In the case of successful reduction, close patient follow-up is recommended. Open reduction with femoral head inspection and exchange may be preferable if difficulty is encountered in closed reduction maneuvers.

Quantification of polyethylene degradation in mobile bearing knees: a retrieval analysis of the Anterior-Posterior-Glide (APG) and Rotating Platform (RP) Low Contact Stress (LCS) knee.

BACKGROUND: Routine qualitative observations of more than 850 polyethylene fixed and mobile bearings at our institution have noted minimal wear of mobile bearings. The APG mobile bearing is the most recent design variant of the LCS knee, allows multi-directional movement at the tibiofemoral articulation, and is posterior cruciate sparing. Even though it is difficult to perform, quantitative wear measurement is important in determining the likely longevity of new arthroplasty devices, and is especially relevant because of increasing numbers of new mobile bearing designs. PATIENTS AND METHODS: We analyzed 10 retrieved APG and 7 retrieved RP tibial bearings (De Puy) with a mean implantation period of 33 (9-70) months. We used coordinate-measuring techniques to quantitatively determine linear penetration, and optical and scanning electron microscopy to assess wear mechanisms qualitatively. RESULTS: The mean total volume loss (superior and inferior articulations) of the APG and RP designs was 85 mm((3))/year and 77 mm((3))/year, respectively. Burnishing was the predominant wear mechanism, and to a lesser extent scratching, abrasion and pitting. Multidirectional scratching and abrasion were noted on the APG inserts inferiorly, whereas there was circumferential scratching on the RP inserts. INTERPRETATION: Our short-term results for the APG and RP mobile bearing designs are similar and compare more than favorably with reported values for fixed-bearing designs. However, increased backside wear due to multidirectional movement may predispose the APG design to greater wear in the long term.

Selection of primary hip and knee arthroplasties for public hospitals in Western Australia: a clinical evidence approach.

BACKGROUND: The Australian Joint Registry records that there are approximately 84 hip stem designs, 71 acetabular designs and 45 knee systems in common use in Australia, giving the surgeon an extensive and often bewildering choices. METHODS: Since the 1990s, there have been several attempts to rationalize the supply of the products of primary hip and knee arthroplasties to the public hospitals in Western Australia. To continue and improve the rationalization process, the recently awarded 'whole of health' tender was based on a thorough clinical and laboratory evaluation process. The method included commercial analysis by Health Supply Western Australia, clinical evaluation by a committee comprised of senior surgeons and technical assessment by biomedical engineers and scientists. The evaluation process was subdivided into qualitative criteria; being the commercial aspects of the tender (50%) and a fitness for purpose assessment comprising clinically based evidence (40%) and laboratory assessment of product quality (10%). RESULT: The tendering process concluded with the recommendation of 12 hip and 5 knee systems. CONCLUSIONS: A comprehensive method primarily based on clinical evidence was used to assess arthroplasty products tendered to Western Australia public hospitals. Generally, there was good compliance with the commercial aspects of the tender. In contrast, however, clinically based evidence assessment of many arthroplasty devices was difficult because of a distinct lack of quality published work. Inadequate quality control of several devices is also of concern. Evaluation of key performance indicators, including cost savings, acceptance by surgeons, tender compliance and revision rates, will determine the success of the tender.