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Investigation results were made available.Review of event description: it was reported that patient had pain on the right hip side.Medical examination showed elevated levels of cocr and an implant loosening was observed, why patient then underwent a revision surgery.Review of received data: - letter from the surgeon dated (b)(6) 2021: the patient received a total hip endoprosthesis on the right side consisting of a reinforcement ring with hook combined with cemented metasul insert, metasul head and an cls stem in 1994 in the kantonsspital winterthur.Beginning of 2017 pain occurred in the hip joint.Because previous x-rays could not be found a conclusive assessment of the position of the cup could not be made.As the clinical investigation was inconspicuous and the cobalt and chromium level in blood were normal the further course was observed.This showed a clear loosening and a massive increase of the cobalt and chromium levels (co 21.2 g/l and cr 6.4 g/l, both measured in whole blood).However, the revision could only be performed on (b)(6) 2021 because the patient did not want to have the surgery before.-lab reports: date of receipt (b)(6) 2019, date of sample taking (b)(6) 2019.Results: cobalt 67.4 nmol/l (reference 8.5 ¿ 66.0 nmol/l).Chromium 24.2 nmol/l (reference 15.0 ¿ 75.0 nmol/l).Date of receipt (b)(6) 2020, date of sample taking (b)(6) 2020.Results: cobalt 359 nmol/l (reference < 66 nmol/l).Chromium 124 nmol/l (reference < 75 nmol/l).- surgical report of revision, on (b)(6) 2021: diagnosis: loosening of cup, right hip joint - increased cobalt (359 nmol/l) and chromium (124 nmol/l) levels.- state after hip total prosthesis right 1994 indication.Since one year increasing load-dependent groin pain right.The complaints only occur when lifting the stretched leg otherwise little complaints.With clearly radiological loose cup with increasing vertical position with a metal on metal pairing the determination of the ion level in blood was recommended.It showed highly increased pathological values.With increasing pain the patient now wanted to have the revision surgery.Technical procedure: complete capsulectomy is performed.The joint is dislocated.The head is removed and the acetabulum exposed.The polyethylene is knocked off and the loose screws are removed.The loose reinforcement ring can be removed without problems.5 tissue samples are taken (3 from the joint capsule as well as 2 from the membrane of the acetabular ground).Additionally, two samples from the capsule for histology are taken because of severe metalosis.Jet lavage is conducted.The further report describes the implantation of a versafit cup cc trio 52, a hcl inlay and a 32/m biolox delta head.- histological report, input (b)(6) 2021, output (b)(6) 2021: diagnosis: resected part of the joint capsule (right hip) with papillary synovial hyperplasia with massive macrophage proliferation with phagocytosis of fine granular blackish, non-birefringent micro-particular wear (metal wear, corresponding to the macroscopic metalosis), micro-particular and macro-particular needle-shaped birefringent wear (polyethylene wear) with giant cell foreign body reaction, sparse wear of bone cement and hyalinosis of the capsule wall.- x-rays: (b)(6) 2018, pelvic overview: on both sides total hip endoprosthesis are implanted.On the right side a reinforcement ring with hook anchored with three screws and a cemented metasul cup can be seen.There seems to be a periacetabular radiolucent line in the caudal half of the ring.(b)(6) 2018, pelvic overview and second view right hip: compared to the previous pelvic overview there seem to be no obvious changes.On the second view the periacetabular radiolucent line is visible.(b)(6) 2019, pelvic overview and second view right hip: compared to the previous study date the periacetabular radiolucent line is wider.On the pelvic overview a slightly steeper position of the acetabular construct (ring with cemented cup inside) can be noticed.On the second view it could be that there is a tiny, slightly radiolucent zone in the neck of the stem close to the head on the posterior side.(b)(6) 2020, pelvic overview and second view right hip: compared to the previous pelvic overview the periacetabular radiolucent line is clearly wider resulting in a steeper position of the acetabular construct.Further, there seem to be small radiolucent lines on the cranial side of the shortest and second shortest screw.It could also be that there is a fine, horizontal radiolucent line in the stem proximal to the extraction hole recognizable.On the second view there seem to be no obvious changes.It seems that the tiny, slightly radiolucent zone in the neck of the stem close to the head cannot be seen.However, the position in which the x-ray was taken differs from the previous second view.(b)(6) 2021, pelvic overview and second view right hip: situation after the revision surgery on the right side with change of acetabular construct and head.The tiny, slightly radiolucent zone in the neck of the stem close to the head is clearly recognizable on both views.(b)(6) 2021, pelvic overview and second view right hip: compared to the previous study date there are no obvious changes.Product evaluation: the reinforcement ring shows few nicks and scratches probably due to the revision surgery.Five of the eight screw cones are damaged on the edge.Half of the central screw cone¿s edge is worn.Polished areas including shiny polished spots and lines can be recognized on the hook and flange as well as in the region close to the flange.There are also polished areas on the inside of the ring on the half of the flange partially extending into the screw cones.In three of the screw cones worn and/or indented zones can be noticed most probably due to contact with a screw.One of the holes in the flange exhibits a clear drill mark.Half of the anchoring side of the low profile cup is still covered by bone cement.In the latter the contour of the reinforcement ring is indented and several polished areas can be seen.The whitish appearing area on the cement derived from contact with alcohol used to clean the metasul inlay.In the area that is free of bone cement the polyethylene is slightly yellowish discolored, has a shiny appearance under certain lighting conditions and partially the machining marks are no longer visible.Two indentations from screw head can be observed whereas one shows the screw¿s internal hexagon and around this layer delamination can be noticed.Signs of abrasion can be recognized in the longitudinal recess close to that indentation.On the articulation side of the low profile cup an area of the rim of the polyethylene liner is damaged and partially material is missing.There, the polyethylene has a frayed appearance.Further, next to this area whitish zones in the polyethylene with subsurface cracks are visible.Due to the damage a part of the marking of the lot number is no longer visible.Opposite to this damaged area a smearing on the entire width of the rim of the metasul inlay of about 10 to 15 mm in length and a sickle-shaped worn area on the adjacent polyethylene liner can be seen.Inside the worn area a whitish zone is noticeable.The freed height of the inlay is estimated to be about 1 mm.On the articulation surface of the metasul inlay scratched areas as well as several matt greyish areas are visible.Closer inspection with a low power microscope (leica mz16 a m38) revealed a worn bevel on approximately one third of the inlay¿s circumference.The worn bevel is located in the damaged area of the liner¿s rim.Obvious subsidence / tilting of the metasul inlay in the polyethylene liner cannot be observed.On the articulation surface of the metasul head a complete borderline between the loaded and unloaded area is visible.Along the borderline partially a bluish discoloration most probably deriving from organic deposits can be noticed in the unloaded area.In the loaded area several matt greyish areas are recognizable.Additionally, an elliptically-shaped stripe extends over the pole.Aligned with this is another clearly outlined matt greyish area that exhibits horizontal lines inside and extends into the unloaded area.The articulation surface was inspected under the microscope (nikon epiphot) at 200-times magnification with differential interference contrast (dic).As already visible to the naked eye the borderline between the loaded and unloaded area is well recognizable.In the unloaded area the original surface state with slightly protruding carbides is recognizable.The matt greyish areas consist of micropits of different intensity.The elliptically-shaped stripe extending over the pole appears rough and shows some smearing probably combined with micropits.The clearly outlined matt greyish area shows small pits combined with scratches and smearing.It seems that in the loaded area outside the above described areas the surface is polished and the carbides are visible.However, this type of polishing is different compared to that of the original surface condition in the unloaded area.The head taper appears inconspicuous.Wear measurement: the wear measurement was carried out on a 3d measuring machine type cmm5, sip geneva.The total linear wear value is 47.6 m for the head and 26.8 m for the cup which results in a wear rate of approximately 1.8 m / year for the head and 1.0 m / year for the cup.In alignment with the visual examination the wear map of the cup shows a clear wear zone along the rim of the inlay.Due to its position it has to be assumed that this wear area could not be measured entirely because the measurement only covers the surface from the center of the component up to 80°.Therefore, the above given wear value does not reflect the true amount of wear.For a metasul-pairing with diameter 28 or 32 mm retrieved within the first year an average wear of 27.8 m / year per pairing was found.Retrievals explanted after two and more years in-vivo had an average wear rate of 6.2 m / year per pairing [1].Review of product documentation: - device purpose: all involved devices are intended for treatment.- product compatibility: the product combination was approved by zimmer biomet.- dhr review: review of the device history records identified no deviations or anomalies during manufacturing.Conclusion: in 1994 the patient received a total hip endoprosthesis on the right side consisting of a reinforcement ring with hook combined with cemented low profile cup with metasul inlay, metasul head and cls stem.Beginning of 2017 pain occurred in the hip joint.Because previous x-rays could not be found a conclusive assessment of the position of the cup could not be made.As the clinical investigation was inconspicuous and the cobalt and chromium level in blood were normal the further course was observed.On the first x-ray at hand dated (b)(6) 2018 a periacetabular radiolucent line in the caudal half of the reinforcement ring seems to be recognizable.In the further course this line gets wider resulting in a little by little steeper position of the acetabular construct (reinforcement ring with cemented low profile cup).It could be that on the second view x-ray dated (b)(6) 2019 a tiny, slightly radiolucent zone in the neck of the stem close to the head on the posterior side is recognizable.On the pelvic overview dated (b)(6) 2020 it could be that there is a fine, horizontal radiolucent line in the stem proximal to the extraction hole visible.However, it seems that the radiolucent zone cannot be observed on the second view x-ray of the same date.On the x-rays taken after the revision this zone/line is visible on both views most probably due to the fact that it is no longer covered by the metasul inlay of the low profile cup.The visual examination revealed polished areas including shiny polished spots and lines on the anchoring side as well as on the inside of the reinforcement ring with hook.Additionally, on the cement that is still attached to the anchoring side of the low profile cup polished areas are visible.The different polished areas can be interpreted as signs of loosening.In the surgical report of revision, it is described that the cup is knocked off and the loose screws and the loose reinforcement ring is removed.Considering this and the x-ray evaluation it seems that there was at least some micromotion between the ring and the cemented cup and a gross loosening on the interface bone/ring.On the anchoring side of the low profile cup, that is free of bone cement, the polyethylene has a shiny appearance under certain lighting conditions and partially the machining marks are no longer visible.This could point to slight micromotion between the cement and the cup.The layer delamination around the screw hole indentation as well as the whitish zones with subsurface cracks and the whitish zone in the sickle-shaped worn area on the rim of the polyethylene liner can be attributed to oxidation of the material in combination with the mechanical forces that acted in those locations.On the articulation side of the low profile cup a smearing on the entire width of the rim of the metasul inlay and a sickle-shaped worn area on the adjacent polyethylene liner is present.Opposite to this area the bevel of the spherical calotte of the inlay is worn.These phenomena indicate impingement in combination with a rim loading situation.This probably led to the metalosis mentioned in the surgical report of revision as well as to the increase of the cobalt and chromium levels measured in patient¿s blood in (b)(6) 2020.The rim loading is also confirmed by the wear measurement.However, the wear rate for the metasul pairing is compared to [1] low.The greyish matt areas seen on the articulation surfaces of the metasul pairing are probably concomitants of the rim loading situation.About 23 years after implantation the patient experienced pain.In the following years a clear loosening of the acetabular construct and a change to a more vertical position was observed.This resulted in a rim loading situation and an impingement between the stem¿s neck and the rim of the low profile cup.The reason for the loosening of the acetabular construct remains unknown.It could be hypothesized that the tiny, slightly radiolucent zone on the posterior side of the stem¿s neck, that could be seen firstly on the second view x-ray dated (b)(6) 2019, is a worn zone deriving from the impingement.After the revision surgery this worn zone seems to be clearly visible on the x-rays.However, there was nothing described about the appearance of the stem in the surgical report of revision.The histological examination of the tissue samples taken during revision surgery revealed among other things metal, polyethylene as well as sparse bone cement wear.The occurrence of these types of wear can be confirmed by the examination of the retrieved components at hand.Based on the investigation the reported event can be confirmed.The quality records show that all specified characteristics have met the specifications valid at the time of production.Therefore, the investigation did not identify a nonconformance or a complaint out of box (coob).Based on the given information and the results of the investigation, we were not able to identify a specific root cause for this issue.- references [1] rieker cb, schoen r, koettig p, shen m, krevolin j, 2006, in-vitro versus in-vivo analysis of metal-on-metal articulations, abstract 7892 of the 5th world congress of biomechanics, jul 29-aug 4, munich, germany, journal of biomechanics 2006; vol.39 suppl.1, p.120.The need for corrective measures is not indicated and zimmer switzerland manufacturing gmbh considers this case as closed.Zimmer biomet's reference number of this file is (b)(4).
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