It was reported that 14 years after the implantation, a revision surgery was performed on the left hip due to signs of metalosis.Pre-revision cobalt and chromium ion levels were 214nmol/l each.The removed devices, a hi cup, metal insert, metal ball head and an sl stem, used in treatment, were returned for investigation.The liner was disassembled from the cup and the ball head was removed from the stem after the reception of the patient's consent.Furthermore, it was reported that the right hip was revised as well, captured under (b)(4).The liner shows some minor scratches on the contact area with the ball head.The ball head shows a similar pattern.The shell shows some minor signs of use.The stem has some major scratches on the surface, which most likely originate from the explantation procedure.The cone of the stem shows discoloration on the surface.A technical evaluation was conducted.The linear wear of the ball head and the liner were assessed using a roundness machine for the head and a surface profiler for the cup.The linear wear on the ball head was measured to be 54.2 ¿m, the linear wear on the liner was 53.0 ¿m (combined 107.2 ¿m, 7.6 ¿m/year).The volumetric wear could only be assessed for the ball head and resulted in 20.6 mm3.The presence of a marked wear patch on the acetabular liner shows that edge loading has occurred.Taper analysis for the linear wear of the ball head measured the maximum depth of material loss measured at 56.1 ¿m.Compared to former cases, the findings regarding the wear on the bearing surface is higher than expected.A production documentation of all four implants, including the material certificates, did not show any deviation.The certificates demonstrate that the raw material is a wrought cobaltchromium-molybdenum alloy as specified in the product files.There are no indications that the parts failed to match specification at the time of manufacturing.A complaint history was conducted and it was shown that the reported failure mode is covered by the risk management file in severity and occurrence.The combination of the devices was approved by smith and nephew.The ball head and the liner are no longer available on the market.Abrasion of implant surfaces and development of osteolysis as a reaction to foreign bodies is a possible side effect from hip arthroplasty according to the ifu versions, lit no.12.23, ed.09/05 and lit no.12.07, ed.01/03.Based on the received information a medical assessment was conducted.It is stated that the inclination of the cup is pretty flat with about 24 degrees.According to the surgical technique (lit.No.01773-en, v6, 07/20), the acetabular component is to be impacted with 10-20 degrees anteversion and 40-50 degrees inclination.The provided medical information confirms the reported blood cobalt ion level of 214 nmol/l and chromium ion level of 214nmol/l.The reported loosening of the acetabular component can be seen as a result of metallosis but loosening and the migration of the cup from the reported fall could also accelerate wear, lead to metal debris, and result in metalosis.However, the confirmed edge loading cannot be ruled out as a contributing factor.Therefore, the relationship between the reported event and the devices can be confirmed.The devices in questions, ball head stem and liner, are no longer available on the market.A wear patch was observed on the metal-on-metal joint.The investigation performed demonstrate that the material of all implants is within specification and that the material characteristics did not cause the observed metal wear.The alignment of cup and ball head may have contributed to the formation of a wear patch on the metal-on-metal joint.The root cause is therefore attributed to a known inherent risk.The need for further actions is not indicated.Smith and nephew will monitor these devices for further similar issues.The returned devices will be retained.
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