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Knee: Y. Kalairajah, A. J. Cossey, G. M. Verrall, G. Ludbrook, and A. J. Spriggins Are systemic emboli reduced in computer-assisted knee surgery?: A PROSPECTIVE, RANDOMISED, CLINICAL TRIAL J Bone Joint Surg Br 2006; 88-B: 198-202 [Abstract] [Full text] [PDF]

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Are systemic emboli reduced in computer assisted kne surgery?

Kevin J Daly, Martyn Lovell, Charles N McCollum   (10 April 2006)

Are systemic emboli reduced in computer assisted kne surgery? 10 April 2006
Kevin J Daly, SpR in Surgery Manchester Royal Infirmary, Martyn Lovell, Charles N McCollum Send letter to journal: Re: Are systemic emboli reduced in computer assisted kne surgery? kjdaly{at}tiscali.co.uk Kevin J Daly, et al.	Sir, We read this paper with interest and were pleased to see further research into paradoxical cerebral embolism during orthopaedic surgery. However, we were a little concerned at the reliance on automated software for the detection of emboli. There is no evidence that software is as good as trained observers.1,2 The study which used the same software as Kalairajah et al gave a specificity of 59.9% and a sensitivity of 74.3% compared with a trained observer. This study used a difference of 12 dB to differentiate between artefact and embolic signals rather than a threshold of 12 dB.2 An embolus detection threshold of 12 dB is at the top end of the published range (3 to 12 dB)2,3 and may lead to underestimation of cerebral emboli. In our experience, transcranial Doppler ultrasound (TCD) artefact is common throughout hip and knee arthroplasty due to voluntary patient movement, movement during surgical instrumentation, and diathermy interference. When combined, these factors may adversely affect the sensitivity and specificity of embolus detection. It would be interesting to see whether these results could be replicated by trained observers. For cerebral emboli to be detected during surgery they must first pass from the venous circulation into the arterial circulation through the lung, or through a venous to arterial circulation shunt such as a patent foramen ovale.4 The number of cerebral emboli is associated with the presence and size of a shunt.4 An international consensus provides guidance for the investigation of venous to arterial circulation shunts with TCD.5 However, the clinical relevance for the detection of a single particulate embolus or of a single microbubble following injection of contrast is not clear. It is possible that passage of small numbers of emboli, which may need a diameter less than 22 µM, to avoid being filtered by the lung,6 may have no clinical significance. K. Daly, Specialist Registrar in Transplant Surgery, Manchester Royal Infirmary, M. Lovell, Consultant Orthopaedic Surgeon, C. McCollum, Professor of Surgery, South Manchester University Hospital, Manchester, UK. 1. Dittrich R, Ritter MA, Droste DW. Microembolus detection by transcranial doppler sonography. Eur J Ultrasound 2002;16:21-30. 2. Droste DW, Hagedorn G, Notzold A, et al. Bigated transcranial Doppler for the detection of clinically silent circulating emboli in normal persons and patients with prosthetic cardiac valves. Stroke 1997;28:588-92. 3. Ringelstein EB, Droste DW, Babikian VL, et al. Consensus on microembolus detection by TCD. International Consensus Group on Microembolus Detection. Stroke 1998;29:725-9. 4. Riding G, Daly K, Hutchinson S, et al. Paradoxical cerebral embolisation. An explanation for fat embolism syndrome. J Bone Joint Surg [Br] 2004;86-B:95-8. 5. Jauss M, Zanette E. Detection of right-to-left shunt with ultrasound contrast agent and transcranial Doppler sonography. Cerebrovasc Dis 2000;10:490-6. 6. Butler BD, Hills BA. The lung as a filter for microbubbles. J Appl Physiol 1979;47:537-43.