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Investigation results were made available.Event description: it was reported that the prosthesis was revised after approximately 24 years in vivo to neuralgic gluteal pain since the (b)(6) of 2018, suspected pelvic discontinuity and malposition of the reinforcement ring.Review of received data: due diligence: no further due diligence required as all required information to support the conclusion is available or was already requested.Letter from the surgeon dated 23 march 2020: the implantation was performed in (b)(6).Since the revision performed on (b)(6) 1995, there was an abductor insufficiency, with a corresponding limp.In the (b)(6) of 2018, neuralgic pain occurred, which would correspond to either the inferior gluteal nerve or the sciatic nerve.The cause of the pain was a malposition of the ring.Revision on (b)(6) 2019 revealed a pelvic discontinuity, which could only be suspected preoperatively.Lab report: whole blood samples taken on (b)(6) 2019.Results: chromium 46.2 nmol/l (reference < 75 nmol/l).Cobalt 154.3 nmol/l (reference < 66 nmol/l).Consultation report of (b)(6) 1996, dr.(b)(6): anamnese: the patient has no pain, but complains of persistent weakness in her left leg.She still uses canes to walk outside the house.Inside the house she walks without canes, but then has to support herself on objects.The maximum walking time with 2 canes is 2 hours.X-ray: pelvis overview from (b)(6) 1996: regular conditions, no indication of loosening.Assessment dr.(b)(6): the problem with the patient is the still insufficiently developed muscle strength.This is certainly also due to the patient's habit to use walking canes.Revision report of (b)(6) 2019 performed by dr.(b)(6): diagnosis: neuralgic gluteal pain on the left, most likely compression syndrome from the inferior gluteal nerve or ischiadic nerve due to malposition of a hip implant.Pelvic discontinuity with bone substance defect of the anterior and posterior acetabular wall as well as malposition of the ring after revision of a hip prosthesis (transgluteal with metal-metal pairing) on the left side on (b)(6) 1995.Indication: the patient complains in particular of neuralgic pain radiating gluteally and into the thigh during movement, and especially when sitting down.The acetabular ring has not changed for years, but was placed with the distal flange into the foramen ischiadicum, with contact to the sciatic nerve.Technical procedure: the sciatic nerve is easily identified in the tissue and can be traced proximally.Several larger osteolysis areas are seen in the trochanteric region, but further distally the stem appears to be well integrated.The prosthesis is dislocated and the stem is removed.The stem shows islands of bone ongrowth but could be removed so easily that there was actually loosening.The acetabular ring is exposed.The cranial flange lies posteriorly to the spina iliaca anterior inferior, and is partially covered with bone that must be chiseled away.The insert is chiseled out.The five cranial screws are removed.One of them proves to be broken.The acetabular ring is removed easily.The ossifications around the distal flange that protruded into the foramen ischiadicum turn out to be the posterior wall of the acetabulum.There is a transverse pseudarthrosis present.The anterior wall has a large defect, which also affects the anterior column.There, a bursa iliopectinea has formed, or a cyclops of the psoas tendon, with also hardened wear particles.This is partially debrided and although it has wear particle deposits, there is no metallosis.Further the revision report shows the step to prepare the hip joint and implant a new prosthesis.X-rays: pelvis overview and second view of the left hip, (b)(6) 2019: there are hip prostheses implanted in both hips.Concerning the left hip prosthesis, the inclination angle of the insert was measured to be approximately 38°.The distal flange of the reinforcement ring covers the linea iliopectinea while the cranial flange is fixed with several screws to os illium.The posterior edge of the acetabulum cannot be demarcated and pronounced bone formation can be seen along the linea iliopectinea at the location of the distal flange.In the second view, there is no contact between the distal flange of the reinforcement ring and os ischium.A large bony fragment can be seen between the lower edge of the ring and the femur.Osteolytic bone changes can be recognized in the femur in gruen zones 1, 7, 8, 13 and 14.Product evaluation: visual examination: in the as-received condition the metasul head was still mounted on the cls stem.For further investigation an attempt to disassemble the parts was made.Before, the head to stem position was marked.As the head was firmly attached to the stem the attempt to remove it was stopped to avoid coarser damage to the components.On both the inner and anchoring side of the burch-schneider reinforcement ring remains of cement attachments are visible.The cement is brown discolored.On the inner side of the ring the cement has the imprints of the design features of the anchoring side of the insert.Signs of contact with the screws can be seen on the screw holes located in the cranial flange region.Revision damage in the form of scratches and nicks can be seen mainly on the inner side but also slightly on the anchoring side of the ring.The polyethylene liner of the insert shows some damage on the articulation and anchoring side.The polyethylene is slightly yellowish discolored.On the anchoring side there are some areas where the yellow discoloration is darker.There are no backside changes on the polyethylene.On the anchoring side there are some cement attachments visible.There is no obvious change of the position (subsidence / tilting) of the metasul inlay in the liner.The bevel of the spherical calotte is worn on approximately one quarter of its circumference.Numerous fine scratches can be seen on the articulation surface of the metasul inlay.Closer inspection of the articulation surface with a low power microscope revealed some areas with denser scratches forming a curved line.The cls stem shows bone attachments on its anchoring surface except for the anterior and lateral side of the proximal region.Damage most probably due to the removal of the stem in the form of scratches and instrument marks are visible mainly in the neck region and proximal part of the anchoring surface.On the articulation surface of the metasul head an almost complete borderline between the loaded and the unloaded area as well as a matt area close to the pole are visible under certain lighting conditions.The articulation surface was inspected under the microscope at 200-times magnification with differential interference contrast (dic).The borderline between loaded and the unloaded area is well identifiable.The matt area close to the pole is probably an organic deposit.In the loaded area numerous fine scratches are recognizable while in the unloaded area the original surface state with slightly protruding carbides can be found.In the loaded area several various indentations and parallel scratches could also be detected.Wear measurement: the wear measurement was carried out on a 3d measuring machine type cmm5, sip geneva.The total linear wear value is 29.1 m for the head which results in an annual wear rate of 1.2 m.For the insert, the wear map shows a wear zone close to the bevel.The total, linear wear value is 36 m, which results in an annual wear rate of 1.5 m.Due to the measuring method it is not possible to measure the entire articulation surface of the insert.The measurement only covers the surface from the center of the component up to 80°.Thus, due to the position of the wear zone it could not be measured entirely.Therefore, the wear value indicated above does not reflect the complete 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.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 could not be performed.Conclusion: the hip prosthesis had to be revised after more than 23 years in vivo due to neuralgic gluteal pain since the (b)(6) of 2018, suspected pelvic discontinuity and malposition of the reinforcement ring.The indication section of the revision report states that the burch-schneider reinforcement ring has not changed for years, but was placed with the distal flange into the foramen ischiadicum, with contact to the sciatic nerve.During revision the sciatic nerve could be easily identified in the tissue and could be traced proximally but there is nothing mentioned about contact with the distal flange.Intraoperatively a direct connection between the patient¿s pain and the positioning of the ring could not be confirmed.The ring could be removed easily during revision and it was observed that around the distal flange there was a transverse pseudarthrosis of the posterior wall of the acetabulum.Also, a large defect of the anterior wall and the anterior column was seen.The osteolytic changes in the area of the trochanter major that can be seen on the pre-revision x-rays could be confirmed intraoperatively.However, most of the anchoring surface of the stem shows bone attachments and signs of loosening could not be recognized.The consultation report from march 1996 mentions that the patient had insufficient developed muscles strength and that the x-ray taken at that time showed regular conditions and no indication of loosening.On the x-rays taken just before revision it can be observed that the distal flange of the reinforcement ring covers the linea iliopectinea.According to the surgical technique the distal flange should be fixed in or on the ischium.However, as there is no clinical information available from 1996 until 2019 (i.E.X-ray follow-up, medical reports, etc.) the position of the implants as well as the condition of the acetabular and femoral bone immediately after implantation and any potential changes during time in vivo stay unknown.The appearance of the articulation surface of the metasul inlay points to a rim loading situation.The wear rate measured for the metasul pairing is low compared to.However, due to the position of the wear zone of the inlay the wear area could not be measured completely.The lab results from (b)(6) 2019 reported a level of 46.2 nmol/l chromium and 154.3 nmol/l cobalt in the patient¿s blood.For chromium, the measured value is below the reference range indicated in the lab report while cobalt is outside this range.A subluxation situation leading to rim loading would be a possible source for these reported levels.As the head could not be removed from the stem, the condition of the taper surfaces and their potential influence to the cobalt and chromium levels could not be assessed.Rim loading is influenced by the position of the implants (mostly cup inclination and anteversion).The x-rays taken before revision show a relatively low inclination of the insert and the anteversion cannot be evaluated based on the planar x-rays.With limited information available from implantation until revision (e.G.Range of motion of the patient, inclination and anteversion angles of the cup and any potential changes over time in vivo) it stays unknown at what point in time the rim loading situation occurred.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.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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