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An event regarding wear involving a trident liner and ceramic head was reported.An event relating to loosening of a trident shell was also reported.The event was confirmed through a review of the available records and mar by a clinician.Method & results: -product evaluation and results: visual inspection: as per mar the returned device parts were examined with the aid of a stereo microscope at magnifications up to 50x.Damage consistent with the explantation process was observed on the proximal surface of the insert.Wear scars were also observed on the distal rim of the articulating surface of the insert.The wear scars observed on the head and insert, primarily on the distal rim of the two components, are consistent with a wear mechanism between the two components.The wear patterns observed on the articulating surfaces of the explants were not unexpected.Dimensional inspection: not performed as there are no allegations relating to device dimensions.Functional inspection: not performed as the failure mode could not be replicated.Material analysis: as per mar damage consistent with the explantation process was observed on the returned devices.Wear scars were observed on the head and insert, consistent with a wear mechanism between the two components.The wear patterns observed on the articulating surfaces of the explants were not unexpected.Based on the given information, no identifiable materials or manufacturing discrepancies were observed on the surfaces examined.-medical records received and evaluation: a review of the provided medical records and x-rays by a clinical consultant indicated: discussion: revision of trident cup with alumina ceramic bearing due to pain and osteolytic cup loosening some 13-years post implantation in a male patient of (b)(6) with overweight (bmi = 34).The cup shell with bearing insert and femoral head were replaced.The surgeon was concerned about the potential role of ceramic wear debris in the failure.X-rays confirm implantation of a restoration modular stem construct in the left hip with trident cup and ceramic bearing.The stem has adequate size with stable bone ingrowth condition in the femur.There is a dall-miles cerclage wire around the proximal femur.Some heterotopic ossifications are seen around the lower joint space and close to the femoral resection area.The trident cup has correct inclination but absent anteversion as evident by the straight line projection of the cup opening circle.There may have been some hip dysplasia given the protruding superior cup rim into the joint space with correct inclination.The lower cup rim has an anatomically correct position.The cup has extensive osteolysis around a major part of central and superior cup sections (charnley-delee zones i & ii) while the lower cup zone also shows some osteolysis in progress.A materials analysis report concludes about damage consistent with the explantation process was observed on the returned devices.A continuous metal transfer ring was observed at the proximal end of the head taper, consistent with proper seating between the stem trunnion and head taper.Wear scars were observed on the head and insert, consistent with a wear mechanism between the two components.The wear patterns observed on the articulating surfaces of the explants were not unexpected.Based on the given information, no identifiable materials or manufacturing discrepancies were observed on the surfaces examined.No further clinical information is available as per hospital policy.Some comments: - the principal problem of this case is cup malposition leading to an overload condition with cup loosening by osteolysis around a major section of the cup periphery.- total hip components require positioning for optimal rom.Normal cup position is around 45° of inclination (abduction) and some 20° of anteversion, a bit depending upon approach to the hip and surgeon preference.The stem should have an anteversion around 15°, again depending upon surgical approach and stem design.- in this case, the cup has a normal inclination but there is close to zero anteversion where the normal range should be within 15° - 25° of anteversion.Furthermore, there are some heterotopic ossifications in the joint that make the hip joint much stiffer than normal with reduced range of motion.- the absent anteversion makes the arthroplasty vulnerable to impingement between the neck of stem and the acetabular bone or the cup rim during a multitude of hip movements effectively representing device-bone or device-device impingement.- during the stance phase of the gait cycle or with extreme range of motion in the hip, high forces are transmitted across the hip joint and if under such conditions the neck of the stem hits the bone or the cup rim, significant strain may be applied to the articulation with development of an overload condition with shear forces along the implant-bone interface of the cup potentially contributing to loosening.- even without actual impingement, an overload condition is contributed by edge loading or related adverse biomechanical consequences on the implanted cup with bearing.Especially hard-on-hard bearings such as this ceramic bearing are more sensitive for adverse effects by edge loading than polyethylene bearings.- the repetitive shear forces along the implant-bone interface cause excessive micromotion between cup shell and bone adversely influencing component fixation.Overload effects can further be expected in the arthroplasty bearing with increased wear rates or on the proximal stem section.- this is evident from the mar where some wear scars were found, especially along the peripheral edges of the bearing insert.This is clearly consistent with edge loading and confirms the damage mechanism.No clear impingement damage is seen along the metal sleeve rim although this would only exclude metal-metal contact between cup insert and stem neck while not device-bone contact.- device-bone impingement does not leave any signs of metal damage but was quite likely present as well as related to the adverse effects of heterotopic ossifications.A large heterotopic bone sleeve was present extending from the lower proximal femoral and extending far into the hip joint space towards the acetabulum where it given its size and location must certainly have contributed to mechanical derangement of the arthroplasty.- given the pattern of wear scars around two opposing sections of the cup bearing periphery, this would quite likely be the effect of small subluxations taking place during certain movements of the hip where the absence of metal damage would suggest this was caused by bony impingement.- heterotopic ossifications should be considered a patient-related factor because some patients are more sensitive to heterotopic bone formation although the underlying mechanisms are still incompletely understood.Genetic predisposition is a prominent feature where several gene patterns have been identified to be involved in ho.- however, also surgical technique related factors such as surgical approach and tissue handling play a role and as such determine ho partially also as a procedure-related problem.Revisions have higher ho rates than primary arthroplasties.Although not explicitly reported, the presence of a restoration modular stem together with a dall- miles cable would suggest that the implantation in 2004 was a revision surgery.- ho usually develops during the first year of implantation and often becomes evident within the first few months post implantation.Ho as such is independent from type or kind of hip arthroplasty device although there is still discussion in literature on differences between cemented and uncemented devices.Differences are however marginal anyway.Also gender differences appear relevant, males are usually a bit more often affected than female patients.- remains the potential relationship between wear particles and osteolysis.Particulate debris of any source is capable to generate osteolysis although ceramic wear debris is less aggressive than polyethylene wear debris due to lower inflammatory characteristics.Given the observed wear rates in the mar as ¿not unexpected¿ we might conclude that ceramic wear was not excessive with regard to the implantation time of some 13-years and should not have significantly contributed to the osteolysis observed.- osteolysis requires some kind of minimum threshold for the amount of wear debris to become effective which does not appear very likely under the conditions reported.Therefore device-bone impingement according to the mechanisms discussed was more likely the causal factor with micromotion impairing bone ingrowth fixation and progressively causing cup loosening.- an unstable cup may cause a secondary fluid pressure effect under repetitive load to contribute to the osteolysis.The ¿balloon¿ pattern of osteolysis around the cup shell is suggestive for this type of pressure osteolysis.- from the further patient-related perspective, there is the patient overweight condition with a bmi of 34 where 25 represents the upper limit of normal.Excessive weight is however not normally a root cause for device failure although it may increase the effects of overload conditions from other causes such as discussed.- multiple adverse mechanisms contributing to overload are thus present in the arthroplasty of which cup malposition in lack of anteversion should be considered the principal and this is a procedure-related factor because the surgeon is responsible for optimal component positioning.The heterotopic ossifications and overweight condition as patient-related factors may magnify the overload condition.- no evidence is available to suggest that device-related matters might have contributed to the problem as also supported by the mar findings where no materials or manufacturing defects were observed on the surfaces explanted while the discussed factors provide a plausible explanation for the failure scenario.This pi case is not device related.Procedure-related factors: - cup malposition in absent anteversion.- heterotopic bone formation has procedure-related aspects.Patient-related factors - heterotopic bone formation has also patient-related aspects.- overweight condition (bmi = 34) a secondary factor device-related factors: - none as also supported by mar findings.Diagnosis: - cup malposition in absent anteversion with additional contributing factors of heterotopic ossification and patient overweight have in concert contributed to an overload condition in the arthroplasty contributing to cup loosening with wear scar formation on the ceramic bearing surfaces and secondary osteolysis requiring revision surgery.-product history review: all devices were manufactured and accepted into final stock with no relevant reported discrepancies.-complaint history review: there have been no other similar events for the reported lot.Conclusions: the investigation concluded that wear of the trident liner was caused by malposition of the trident shell.The review of the available records and mar by a clinician concluded the wear was a result of cup malposition in absent anteversion with additional contributing factors of heterotopic ossification and patient overweight have in concert contributed to an overload condition in the arthroplasty contributing to cup loosening with wear scar formation on the ceramic bearing surfaces and secondary osteolysis requiring revision surgery.The results of the investigation indicate that the surgical protocol was not followed for the positioning of the shell.
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