Electronic Letters to:

Hip: H. Pandit, S. Glyn-Jones, P. McLardy-Smith, R. Gundle, D. Whitwell, C. L. M. Gibbons, S. Ostlere, N. Athanasou, H. S. Gill, and D. W. Murray Pseudotumours associated with metal-on-metal hip resurfacings J Bone Joint Surg Br 2008; 90-B: 847-851 [Abstract] [Full text] [PDF]

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Pseudotumours in hip resurfacings

Koen A De Smet, Patricia A. Campbell   (25 July 2008)

MoM bearings - beware of small, malpositioned cups

Simon S. Jameson, David J. Langton, Tom J. Joyce, Tony V. F. Nargol   (11 July 2008)

Pseudotumours in hip resurfacings 25 July 2008
Koen A De Smet, Hip Surgeon ANCA Clinic, Gent, Belgium, Patricia A. Campbell Send letter to journal: Re: Pseudotumours in hip resurfacings dr.desmet{at}heup.be Koen A De Smet, et al.	Sir, We read this paper with interest and would like to make some comments. The authors described a variety of soft tissue problems in 17 female patients in whom the common finding was a soft tissue mass in association with hip resurfacings performed by a number or surgeons of varying levels of experience with the procedure. The problems included pain since surgery, recurrent dislocation and cystic lumps. The authors conducted a clinical overview, assessed the radiological features and measured the cup angles of each patient. Unfortunately, the authors did not measure the amount of wear that had occurred on the implants, or the serum ion levels in the patients, and they did not conduct histological analysis of the involved tissues in each case. Because of this, they could not definitively explain the cause of the pseuodotumour in these 17 patients. Rather, they concluded that the pseudotumours arose either from a toxic reaction to an excess of particulate metal debris, an idiosyncratic response to a moderate release of cobalt-chrome particles or were a hypersensitivity reaction to a normal amount of debris. We have had the opportunity to study 64 cases of revisions of hip resurfacings that included patients with metallosis caused by high wear, as well as patients with metal sensitivity-related soft tissue problems.1 Like the cases described by Pandit et al, these hip resurfacing operations had been performed by a number of surgeons with varying degrees of experience, and included several different designs of resurfacing implants. Soft tissue features that have been described variously in the literature as cysts, fluid hernias, masses and, in the Pandit article, pseudotumours, were predominantly found in hips with malpositioned components, such as steep cups (>50 degrees), implants with excessive anteversion, and/or with impingement and edge-loading. Serum metal ion measurements taken prior to revision, wear measurements of the explanted implants, and histology of the periprosthetic tissues verified that there had been unusually high wear in these malpositioned implants. Only two patients were found to have soft tissue masses in the absence of high wear and, in both cases, the histology was consistent with metal sensitivity. It is becoming clear that there are distinctive histological features that can help differentiate a tissue reaction caused by a high amount of wear from an allergic reaction to a normal amount of wear, and histology should be performed on each case revised for unexplained pain or pseudotumour. It should be noted that this is not a problem unique to hip resurfacing; total hip arthroplasties with large diameter metal-on-metal bearings can also produce high wear and subsequent tissue reaction, similar to the way that pseudoabscesses and intrapelvic masses formed around some hips with polyethylene–on-metal bearings undergoing high wear.2,3 Based on our experience, which includes the analysis of nearly 500 metal ion measurements performed on patients at the ANCA clinic (KDS4) and the evaluation of 250 retrieved hip resurfacing specimens at the Implant Retrieval Lab, Orthopaedic Hospital / UCLA (PC5), we feel that there is an important role for the monitoring of metal ion levels in patients with hip resurfacing arthroplasties. We have not encountered a pseudotumour in a hip with normal wear unless the patient had a metal sensitivity reaction. We share the concern expressed by the authors that soft tissue problems could be an increasing cause for revision. However, since in our experience the vast majority of these were caused by high wear, we are hopeful that, with increased awareness of the problems that component malpositioning can cause, the incidence of wear related pseudotumours can be reduced. K.A. De Smet, MD, ANCA Medical Center, Gent, Belgium. P. Campbell PhD, Orthopaedic Hospital/UCLA Los Angeles, California, USA. 1. De Haan R, Campbell P, Su E, De Smet K. Revision of metal-on-metal resurfacing arthroplasty of the hip. The influence of malpositioning of the components. J Bone and Joint Surg [Br] 2008;in press. 2. Howie DW, Cain CM, Cornish BL. Pseudo-abscess of the psoas bursa in failed double-cup arthroplasty of the hip. J Bone Joint Surg [Br] 1991;73-B:29-32. 3. Lachiewicz PF. Case report: a thigh mass resulting from polyethylene wear of a revision total hip arthroplasty. Clin Orth 2007;455:274-6. 4. De Smet K, De Haan R, Calistri A, et al. Correlation of Wear and Serum Metal Ion Levels in Patients with Metal-on-Metal Hip Replacement: A Proposal for a Diagnostic Tool. J Bone and Joint Surg [Am] 2008;in press. 5. Campbell P, Beaulé PE, Ebramzadeh E, et al. The John Charnley Award: a study of implant failure in metal-on-metal surface arthroplasties. Clin Orth 2006;453:35-46.
MoM bearings - beware of small, malpositioned cups 11 July 2008
Simon S. Jameson, Specialty Registrar, Trauma & Orthopaedics Northern Metal-bearing Analysis Group, David J. Langton, Tom J. Joyce, Tony V. F. Nargol Send letter to journal: Re: MoM bearings - beware of small, malpositioned cups simonjameson{at}doctors.org.uk Simon S. Jameson, et al.	Sir, We read with interest the article by Pandit et al, describing a series of female hips with an unusual complication, resulting in revision. A periarticular mass and thick, aseptic fluid tracking around the joint is reported. Histological specimens showed necrosis, inflammatory changes and vasculitis. Possible explanations include a hypersensitivity reaction to metal ions or a toxic effect of wear debris. The authors predict an overall incidence of 1% in metal-on-metal (MoM) hip resurfacing. These complications are not specific to design (three different implants are described). The authors analysed cup abduction angle, and found a weak correlation with time to onset of symptoms, but noted that there were also ‘well-positioned’ cups in the series. As they acknowledge, contact between the head and the cup rim at high abduction angles may occur leading to local deformation and wear.1 This may increase surface roughness, resulting in a change of the lubrication regime from fluid-film to boundary, thereby creating a large metal debris load.2 However, the authors fail to discuss component size, which may influence wear,3 and anteversion angle, both of which significantly correlate with metal ion levels.4 Smaller, malpositioned components may also function in boundary lubrication, thus female patients could be more susceptible to this mechanism of failure. Our experience of ten metal-debris-related complications in a series of over 500 large head MoM bearings is similar to the findings of this latest study. All were found in female patients with small (≤51.5 mm articulating diameter), malpositioned (≥45° inclination OR ≥25° anteversion) cups at three years. However, in accurately sited cups our results are comparable with the medium-term BHR data.5,6 Thorough investigation is required to establish correctable variables associated with wear-debris-related failure. Surgeons should consider this in problem patients with small, malpositioned MoM components. S.S. Jameson, Specialty Registrar, Trauma & Orthopaedics, D.J. Langton, T.J. Joyce, T.V.F. Nargol, Northern Metal-bearing Analysis Group. 1. Campbell P, Beaulé PE, Ebramzadeh E, et al. The John Charnley Award: a study of implant failure in metal-on-metal surface arthroplasties. Clin Orthop 2006;453:35-46. 2. Joyce TJ, Langton DJ, Jameson SS, Nargol AVF. Analysis of ex vivo resurfacing hip prostheses and comparison with clinical data [abstract]. J Bone Joint Surg [Br] 2009;91-B(Suppl):in press. 3. Smith SL, Dowson D, Goldsmith AA. The effect of femoral head diameter upon lubrication and wear of metal-on-metal total hip replacements. Proc Inst Mech Eng (H) 2001;215:161-70. 4. Langton DJ, Jameson SS, Joyce TJ, Webb J, Nargol AVF. Metal ion concentrations following hip resurfacing: the importance of component size and acetabular orientation. J Bone Joint Surg [Br] 2008;90-B:in press. 5. Treacy RB, McBryde CW, Pynsent PB. Birmingham hip resurfacing arthroplasty. A minimum follow-up of five years. J Bone Joint Surg [Br] 2005;87-B:167-70. 6. Hing CB, Back DL, Bailey M, et al. The results of primary Birmingham hip resurfacings at a mean of five years. An independent prospective review of the first 230 hips. J Bone Joint Surg [Br] 2007;89-B:1431-8.