Electronic Letters to:

Hip: J. Daniel, H. Ziaee, C. Pradhan, and D. J. W. McMinn Six-year results of a prospective study of metal ion levels in young patients with metal-on-metal hip resurfacings J Bone Joint Surg Br 2009; 91-B: 176-179 [Abstract] [Full text] [PDF]

eLetters: Submit a response to this article

Electronic letters published:

Size matters

David Langton, Simon Jameson, Thomas Joyce, Anthoni Nargol   (20 February 2009)

Size matters 20 February 2009
David Langton, Research registrar NHS, Simon Jameson, Thomas Joyce, Anthoni Nargol Send letter to journal: Re: Size matters djlangton22{at}doctors.org.uk David Langton, et al.	Sir, We read with great interest the paper by Daniel et al. We appreciate the ongoing efforts by the authors in maintaining this prospective study and we are encouraged by the reassuring findings concerning the reduction in blood metal ion levels at mid-term follow-up. We would, however, like to raise some important points regarding the references to our published work1 on blood metal ion concentrations. The authors state that our paper included only “small numbers of patients in each size.” In fact there were 16 patients with femoral diameters of 51mm, and 21 with femoral diameters larger than this size. These numbers compare well with the total number of 24 patients reported in the study by Daniel et al. They also suggest that size is not an important variable in their large volume of unpublished data, but are unable to support this claim on the basis of the latest work. The published work appears to support the contrary. As Daniel correctly points out, one variable which was not controlled in our study was the time from implantation to blood sampling. However, analysis was only performed at a minimum of 12 months post surgery. According to the current study, the decrease in cobalt levels over time is not statistically significant from 12 months to six years. Regarding joint orientations, while our cup inclination angles were not as tightly controlled as those of the Birmingham group, we feel that our data set is a more accurate representation of resurfacing practice outside the inventors’ series. We also feel that the authors have missed the salient point of our article: in terms of metal ion generation, the impact of sub optimal cup position is reduced as component size increases - in the short term at least! D. Langton, Research Registrar, NHS, S. Jameson, T. Joyce, A. Nargol, Joint Replacement Unit, University Hospital of North Tees, Stockton, England. 1. Langton DJ, Jameson SS, Joyce TJ, Webb J, Nargol AV. The effect of component size and orientation on the concentrations of metal ions after resurfacing arthroplasty of the hip. J Bone Joint Surg [Br] 2008;90-B:1143-51.