CASE 6: Revision of a metal-on-metal hip using bone graft and a porous cup
The Story
“Metal on metal hip resurfacing was designed to conserve bone at the first operation and minimise further bone loss due to polyethylene induced osteolysis. However …
At implantation, the femoral component does conserve bone and the acetabular component does not. After implantation, all bearing surfaces wear and for metal on metal hip resurfacing the wear debris is nano-particle sized metal debris (or CoCrMo alloy) together with various de-alloyed and corroded products, including metal ions, from the CoCrMo alloy. This metal wear debris was thought to cause less bone loss (osteolysis) when compared to polyethylene particles that are worn from metal-on-polyethylene bearing hips. However …
Stephanie had received bilateral Birmingham hip resurfacing eight years prior to meeting me. She presented to clinic with hip pain on both sides that was starting to have a huge impact on her activities of daily living. This was getting so bad that it was starting to wake her at night.”
The Investigation
On clinical examination Stephanie was in a lot of discomfort when examining both hip joints. Her mobility was poor with a very slow and antalgic gait.
Blood inflammatory markers helped exclude infection because the CRP was 5mg/L. Her blood cobalt and chromium ion levels were very raised (with a cobalt of 70 parts per billion and a chromium of 50 ppb: normal is approximately 3ppb of each metal for a patient with bilateral MOM hips), suggesting the pain may be due to an adverse reaction to the metal debris.
CT scanning was used to quantify the osteolysis seen on plain radiographs.
The Evidence
Anteroposterior plain radiograph demonstrating bilateral metal on metal Birmingham hip resurfacings. There is osteolysis surrounding both of the implants, which was better quantified on the computer tomography (CT) scan.
Axial CT demonstrating severe osteolysis surrounding the right acetabulum (white arrow) compared to the contralateral side. There is marked loss of trabecular bone with cortical thinning
The Diagnosis
Stephanie was diagnosed with painful bilateral metal-on-metal Birmingham hip replacements secondary to metal ion induced synovitis and osteolysis causing micromovement of the components and subsequent bone pain. There was an imminent risk of periprosthetic fracture around the right hip.
The Plan
A plan was made to revise both of her hip resurfacings in order to treat the pain and prevent further implant loosening and rising metal ion levels. We planned to use bone graft for this procedure to improve the area of contact with the new acetabular cup and the native acetabulum.
The Operation
We revised her right sided hip resurfacing first (as this was causing her more pain and discomfort). We used an allograft bone graft to fill the extensive bone defect. A porous metal cup was used and secure with two iliac screws.
Four months later Stephanie underwent a second revision to replace her left hip resurfacing. On the left hand side there was a good amount of acetabular bone stock so bone allografting was not required.
The Outcome
Anteroposterior plain radiograph of the pelvis demonstrating the bilateral revision with acetabular bone graft on the right hand side.
Stephanie was able to return to all of her normal daily activities within 6-months of the revision surgery to the left hip. By 12-months after the second revision procedure, Stephanie was attending her local aquafit class 3 times week and using a cross-trainer and an exercise bike in the gym.
The Verdict
“Metal-on-metal hips were introduced to solve the problem of polyethylene-induced osteolysis, however in some patients the osteolysis from MOM hips is severe within 10 years of the primary operation. Follow up with an anteroposterior plain radiograph at regular three-yearly intervals after five years after the operation will avoid uncontrolled osteolysis and allow straightforward revision surgery with a good clinical outlook.”
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Investigation of painful MOM hips:
A J Hart, S Sabah, J Henckel, A Lewis, J Cobb, B Sampson, A Mitchell, J A Skinner: The painful metal-on-metal hip resurfacing.. Journal of Bone and Joint Surgery - British Volume 07/2009; 91(6):738-44.
Alister J Hart, Keshthra Satchithananda, Alexander D Liddle, Shiraz A Sabah, Donald McRobbie, Johann Henckel, Justin P Cobb, John A Skinner, Adam W Mitchell: Pseudotumors in association with well-functioning metal-on-metal hip prostheses: a case-control study using three-dimensional computed tomography and magnetic resonance imaging.. The Journal of Bone and Joint Surgery 02/2012; 94(4):317-25.
Shiraz A Sabah, Adam W M Mitchell, Johann Henckel, Ann Sandison, John A Skinner, Alister J Hart: Magnetic Resonance Imaging Findings in Painful Metal-On-Metal Hips A Prospective Study. The Journal of arthroplasty 02/2010; 26(1):71-6, 76.e1-2., DOI:10.1016/j.arth.2009.11.008
The type of debris released from Metal bearing hips:
The chemical form of metallic debris in tissues surrounding metal-on-metal hips with unexplained failure. AJ Hart, PD Quinn, B Sampson, A Sandison, KD Atkinson, JA Skinner, ...Acta biomaterialia 6 (11), 4439-4446
Imaging of MOM hips
Alister J Hart, Keshthra Satchithananda, Alexander D Liddle, Shiraz A Sabah, Donald McRobbie, Johann Henckel, Justin P Cobb, John A Skinner, Adam W Mitchell: Pseudotumors in Association with Well-Functioning Metal-on-Metal Hip Prostheses A Case-Control Study Using Three-Dimensional Computed Tomography and Magnetic Resonance Imaging. The Journal of Bone and Joint Surgery 02/2012; 94(4):317-25., DOI:10.2106/JBJS.J.01508
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Please see the cases above and below this “step on the acetabular reconstruction ladder” to understand when bone graft is used. When the volume of bone graft required is large and the amount of host bone for primary fixation of the cup is small, then bone graft may not work.
