We present a series of 35 patients (19 men and 16 women) with a mean age of 64 years (36.7 to 75.9), who underwent total hip replacement using the ESKA dual-modular short stem with metal on-polyethylene bearing surfaces. This implant has a modular neck section in addition to the modular head. Of these patients, three presented with increasing post-operative pain due to pseudotumour formation that resulted from corrosion at the modular neck-stem junction. These patients underwent further surgery and aseptic lymphocytic vaculitis associated lesions were demonstrated on histological analysis.
Retrieval analysis of two modular necks showed corrosion at the neck-stem taper. Blood cobalt and chromium levels were measured at a mean of nine months (3 to 28) following surgery. These were compared with the levels in seven control patients (three men and four women) with a mean age of 53.4 years (32.1 to 64.1), who had an identical prosthesis and articulation but with a prosthesis that had no modularity at neck-stem junction. The mean blood levels of cobalt in the study group were raised at 50.75 nmol/l (5 to 145) compared with 5.6 nmol/l (2 to 13) in control patients.
Corrosion at neck-stem tapers has been identified as an important source of metal ion release and pseudotumour formation requiring revision surgery. Finite element modelling of the dual modular stem demonstrated high stresses at the modular stem-neck junction. Dual modular cobalt-chrome hip prostheses should be used with caution due to these concerns.
The authors wish to thank the Department of Bioengineering, Royal Perth Hospital, for Implant retrieval analysis, Mr J. Ma, Engineer, Bioengineering Department, Royal Perth Hospital, for performing the finite element analysis and Dr J. Parry, Consultant Pathologist, Department of Pathology, Royal Perth Hospital, for histological examination of the specimens.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
Supplementary material. Two tables detailing the cobalt and chromium metal ion levels for the 35 patients treated with the modular neck-stem prosthesis and the seven patients treated with the non-modular neck-stem prosthesis are available with the electronic version of this article on our website www.bbj.boneandjoint.org.uk
- Received January 13, 2012.
- Accepted March 8, 2012.
- ©2012 British Editorial Society of Bone and Joint Surgery