Clinical History, Examination and Blood Test Result
Case 7 is a 76-year-old female with pain in her right hip. She had a metal-on-polyethylene Trident Accolade hip replacement in 2007 secondary to end stage osteoarthritis.
In 2013, she started experiencing pain in her right hip region and felt a limp in her groin. The patient was keen to avoid surgery if possible.
In 2017, she presented to clinic using a stick to walk. She had an antalgic gait and her right hip movements were both restricted and painful. She had a fixed flexion deformity of 10 degrees in her right hip and paraesthesia over the region of the femoral nerve distribution.
Her cobalt and chromium levels were 5.9 and 1.3 parts per billion respectively.
Infection was ruled out due to a negative right hip aspiration and normal inflammatory markers.
Her oxford hip score was 10/48.
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Anteroposterior plain radiograph shows calcification of a pseudotumour (arrows) surrounding the metal-on-polyethylene hip replacement to the accolade stem.
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MARS MRI scan shows an intrapelvic calcified pseudotumour which is pressing on the femoral nerve and in close proximity to the femoral and iliac vessels. An extrapelvic pesudotumour is also present with wasting of the right hip abductor muscles.
Right metal-on-plastic hip replacement with pseudotumour causing compression of the femoral nerve due to corrosion between the titanium stem and the cobalt chromium head.
This lady had a revision procedure completed in one stage with two steps.
Initially, using an inguinal, retroperitoneal approach, a vascular surgeon released the femoral/iliac vessels from the pseudotumour and removed the contents of the solid psuedotumour.
This was then washed using Savlon and saline before being closed.
The patient was turned on their side, and using a posterior approach, the metal-on-plastic total hip replacement was accessed.
The metal cobalt chromium head was removed and evidence of corrosion was present within the head taper. The stem, cup and polyethylene liner were retained and a ceramic head used.
The surgical site was then washed and the incision closed. The video below highlights the important steps of the procedure.
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This intraoperative video shows the extent of the damage caused by the metal debris.
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This post-operative anteroposterior radiograph shows the same acetabular cup and femoral stem with the new ceramic femoral head.
The patient is yet to return to clinic after her operation.
The patient consented for the metal cobalt-chromium head to be analysed for research purposes at the London Implant Retrieval Centre.
A roundness measuring machine was used to take over 1,000,000 data points to map the surface of the taper, looking for any peaks and troughs compared to an unworn, uncorroded taper. This allows us to work out the amount of material lost from the taper during its life within the patient.
TAPER ANALYSIS AT THE LIRC
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This video shows Anna Di Laura, a PhD student from the LIRC explaining how we analyse taper corrosion. This analysis is from the femoral head removed in this case. Check out the London Implant Retrieval Centres website - www.lirc.co.uk
Corrosion of the taper junction between a cobalt chromium head and a titanium stem can release metal debris, leading to metal debris disease and the formation of a pseudotumour.
In these cases, the source of the metal debris is not the bearing surface, but the taper junction. The source of the problem is removed by changing the femoral head to a ceramic one. In some cases, when the male taper on the stem of the femoral implant is severely corroded, this needs to be replaced too.
In this case, the femoral stem was in satisfactory condition and extremely well-fixed, so it was retained along with the cup and liner.