title: Frequent femoral neck osteolysis with Birmingham mid-head resection resurfacing arthroplasty in young patients.
abstract: BACKGROUND
  Mid-head resection total hip resurfacing arthroplasty was promoted as an alternative to traditional total hip resurfacing for patients with poor femoral head bone quality or abnormal femoral head morphology, because those patients are at high risk of failure with traditional total hip resurfacing. It is a large-headed metal-on-metal device that uses a short, bone-conserving stem. Good performance of the implant has been reported at short-term followup, but no information on the implant performance in the mid- or long-term is available.
  
  
  OBJECTIVE
  In this study, we report (1) on the mid-term implant survivorship and hip scores in a single nondesigner surgeon series. Because of the occurrence of femoral neck osteolysis and pseudotumor in a subgroup of patients, we also investigated the following: (2) Were there any preoperative parameters that are associated with osteolysis? (3) Could we differentiate the osteolysis group from the others on the basis of implant component sizes, positions, and radiologic parameters? (4) Could we differentiate the osteolysis group from the others on the basis of metal ion levels?
  
  
  METHODS
  Between 2006 and 2011, one surgeon performed a total of 49 Birmingham Mid-head Resection total hip resurfacing arthroplasties in 47 patients. The general indications for this procedure were young patients who were considered suitable for hip resurfacing arthroplasty but had avascular necrosis, large cysts, or severe deformity of the femoral head. Clinical followup including Oxford Hip Score (OHS) and UCLA hip scores were available preoperatively and at a mean of 6 years (range, 3-8 years) on all patients (100%), radiographic followup on 45 of 47 (96%), MRIs on 18 (38%), and metal ion levels on 37 (79%). Mean age at surgery was 50 years. Spearman's correlation was used to test the association between femoral neck osteolysis and preoperative parameters, implant component sizes and positions, and blood metal ion levels.
  
  
  RESULTS
  We found 100% survival. Patients' median OHS was 46 of 48 (range, 35-48) and UCLA 8 of 10 (range, 4-10). However, 16% of the hips (seven of 45) demonstrated osteolysis in the femoral neck. Of the preoperative parameters, the osteolysis was associated with low weight (r = -0.337, p = 0.031) and to a lesser degree with female sex (r = 0.275, p = 0.067). Radiologically, the osteolysis was strongly associated with the presence of a pseudotumor on MRI (r = 0.663, p = 0.004). We could not differentiate the osteolysis group from the rest of the cohort on the basis of the implant sizes or radiographic implant component positions. The cohort's median whole blood cobalt was 1.77 ppb (range, 0.18-10.27 ppb) and chromium 1.88 ppb (range 0.36-10.09 ppb). There was no difference in the metal ion levels between the osteolysis group and the rest of the cohort.
  
  
  CONCLUSIONS
  The high rate of silently developing femoral neck osteolysis associated with this implant is concerning and is expected to cause a high rate of failure at longer followup. We have instituted a program of annual clinical and radiologic followup for this group of patients. We have stopped implanting this device and recommend against its use.
  
  
  METHODS
  Level IV, therapeutic study.
authors.affiliation: The London Hip Unit, 30 Devonshire Street, London, W1G 6PU, UK. asaad.asaad.10@ucl.ac.uk.|Institute of Orthopaedic and Musculoskeletal Science, University College London, The Royal National Orthopaedic Hospital, London, UK. asaad.asaad.10@ucl.ac.uk.
authors.forename: Asaad
authors.initials: A
authors.lastname: Asaad
authors.affiliation: Institute of Orthopaedic and Musculoskeletal Science, University College London, The Royal National Orthopaedic Hospital, London, UK.
authors.forename: Alister
authors.initials: A
authors.lastname: Hart
authors.affiliation: The Royal National Orthopaedic Hospital, London, UK.
authors.forename: Michael M Y
authors.initials: MM
authors.lastname: Khoo
authors.affiliation: Institute of Orthopaedic and Musculoskeletal Science, University College London, The Royal National Orthopaedic Hospital, London, UK.
authors.forename: Kevin
authors.initials: K
authors.lastname: Ilo
authors.affiliation: The London Hip Unit, 30 Devonshire Street, London, W1G 6PU, UK.
authors.forename: Gavin
authors.initials: G
authors.lastname: Schaller
authors.affiliation: The London Hip Unit, 30 Devonshire Street, London, W1G 6PU, UK.
authors.forename: Jonathan D J
authors.initials: JD
authors.lastname: Black
authors.affiliation: The London Hip Unit, 30 Devonshire Street, London, W1G 6PU, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Muirhead-Allwood
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008670:Metals; D008875:Middle Aged; D010014:Osteolysis / Q000175:diagnosis / Q000209:etiology*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D020127:Recovery of Function; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D008670:Metals