Getting it Right with Navigation   |    
Learning How to Resurface Cam-Type Femoral Heads with Acceptable Accuracy and Precision: The Role of Computed Tomography-Based Navigation
Justin P. Cobb, MCh, FRCS1; Vijayaraj Kannan, MD1; Wael Dandachli, MD1; Farhad Iranpour, MD1; Klaus U. Brust, MD1; Alister J. Hart, MA, FRCS(Orth)1
1 Department of Orthopaedics, Imperial College London, 5 Devonshire Place, London W1G 6HL, United Kingdom. E-mail address for J.P. Cobb: j.cobb@imperial.ac.uk
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the Furlong Research Charitable Foundation. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (Acrobot) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Aug 01;90(Supplement 3):57-64. doi: 10.2106/JBJS.H.00606
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Background: Resurfacing arthroplasty for cam-type deformities, which are a common cause of early osteoarthritis, is a technically demanding operation. Like any other arthroplasty, it requires both accuracy and precision. On the basis of the results of series reported by expert surgeons, we considered it desirable that this operation should be performed within ±10° of the desired angular orientation and ±6 mm of entry-point translation in 95% of hips. Technological aids are now available to help surgeons achieve that level of accuracy. Three models of cam-type hips of increasing severity were used to assess the efficacy of three systems of instrumentation at delivering the required level of accuracy and precision.

Methods: Thirty-two students of surgical technology were instructed in hip resurfacing and shown detailed plans of the desired operative outcome for the three hips with cam-type deformity. They then used conventional instruments, imageless navigation, and computed tomography-based navigation to perform the operation as accurately as possible.

Results: Conventional instrumentation produced an unacceptably wide range of entry-point errors. Imageless navigation was able to deliver adequate accuracy and precision in varus-valgus angulation and superoinferior translation, but was less satisfactory in version and anteroposterior translation. Computed tomography-based navigation enabled novice surgeons to navigate hips that had difficult cam-type deformity with acceptable precision in all four degrees of freedom measured.

Conclusions: Only computed tomography-based navigation appears to be appropriate for delivering both the accuracy and the precision needed by surgeons on the steep part of their learning curve. Neither conventional neck-based instrumentation nor imageless navigation provided enough help for novice surgeons learning to perform this technically challenging operation.

Clinical Relevance: Training with this computed tomography-based navigation system may shorten the learning curve for inexperienced surgeons, leading to a reduction in the prevalence of poor results and revision surgery.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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