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Journal of Bone and Joint Surgery - British Volume, Vol 90-B, Issue 12,
1623-1626.
doi: 10.1302/0301-620X.90B12.20238 Copyright © 2008 by British Editorial Society of Bone and Joint Surgery Disc calibration for digital templating in hip replacementA. Kulkarni, MBBS, D(Orth), DNB(Orth), FRCSEd(Trauma & Orth), SpR Orthopaedics1; P. Partington, MBBS, FRCS(Trauma&Orth), Consultant Orthopaedic Surgeon1; D. Kelly, Medical Student2; and S. Muller, MBBS, MD, FRCS(Trauma&Orth), Consultant Orthopaedic Surgeon1
1 Wansbeck General Hospital, Woodhorn Lane, Ashington NE63 9JJ, UK. Correspondence should be sent to Mr A. Kulkarni; e-mail: ashwin_kulkarni{at}hotmail.com
Digital radiography is becoming widespread. Accurate pre-operative templating of digital images of the hip traditionally involves positioning a calibration object at its centre. This can be difficult and cause embarrassment. We have devised a method whereby a planar disc placed on the radiographic cassette accounts for the expected magnification. Initial examination of 50 pelvic CT scans showed a mean hip centre distance of 117 mm (79 to 142) above the gluteal skin. Further calculations predicted that a disc of 37.17 mm diameter, placed on the cassette, would appear identical to a 30 mm sphere placed at the level of the centre of the hip as requested by our templating software. We assessed accuracy and reproducibility by ‘reverse calibration’ of 20 radiographs taken three months after hip replacement using simultaneous sphere and disc methods, and a further 20 with a precision disc of accurate size. Even when variations in patient size were ignored, the disc proved more accurate and reliable than the sphere. The technique is reliable, robust, cost effective and acceptable to patients and radiographers. It can easily be used in any radiography department after a few simple calculations and manufacture of appropriately-sized discs. This article has been cited by other articles:
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