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Hip: G. Heinert, J. Hendricks, and M. D. Loeffler Digital templating in hip replacement with and without radiological markers J Bone Joint Surg Br 2009; 91-B: 459-462 [Abstract] [Full text] [PDF]

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Digital templating in hip replacement with and without radiological markers

Ashwin Kulkarni, Paul Partington, Scott Muller   (7 May 2009)

Digital templating in hip replacement with and without radiological markers 7 May 2009
Ashwin Kulkarni, Specialist Registrar Northern Deanery, Wansbeck Hospital, Ashington, Northumberland, UK, Paul Partington, Scott Muller Send letter to journal: Re: Digital templating in hip replacement with and without radiological markers ashwin_kulkarni{at}hotmail.com Ashwin Kulkarni, et al.	Sir, We read this paper with great interest. The authors have calculated magnification of the hip in digital radiographs using trigonometric method, measuring the focus (X-ray tube) to object (hip) distance and the focus to film/cassette distance using a built-in tape measure in X-ray tube/collimator. It is easy to measure the distance between the x-ray tube and the cassette but it remains unclear what method the authors have used to measure the distance of the hip joint accurately in relation to the film/cassette. This distance varies from patient to patient as we have shown in our paper2, where we have used computed tomography to measure this distance. The authors have misquoted our paper2 and suggested that the use of a marker on the cassette only calibrates the cassette but in fact the size of the marker is predetermined to allow calibration of the hip, not the cassette. This is explained on the trigonometric principle in our paper. The authors, Heinert et al, have used the same principle but have not mentioned how they measure the distance between the x-ray tube and hip joint, and/or THE hip joint to cassette accurately. Additionally, we have suggested using a large and a small disc for a very large and a very small patient. Furthermore, our discs are specific to each table as the thickness of the table can be different. We feel that this paper is based on the accurate measurement of hip to cassette distance, which is not explained and which is of fundamental importance to the accuracy of the technique. We feel this is a major oversight in the paper and we would be interested to hear the authors' comments. A. Kulkarni, P. Partington, S. Muller, Wansbeck Hospital, Ashington, Northumberland, UK. 1. Kulkarni A, Partington P, Kelly D, Muller S. Disc calibration for digital templating in hip replacement. J Bone Joint Surg [Br] 2008;90-B:1623-6.