Practical Guide to Plan and Evaluate Bone Cutting & Drilling in CAOS
(2014) 14th Annual Meeting of the International Society for Computer Aided Orthopaedic Surgery (CAOS) — Location: Milan, Italy (18.June.2014)
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- Introduction In orthopaedic surgery, there exist several assistance technologies such as imaging and navigation systems, positioning robots and additive-manufacturing patient-specific instrumentation (PSI). These generic technologies can be used for different applications, i.e. knee arthroplasty, spine instrumentation and bone tumor resection. Practically, these technologies enable surgeons to identify patient anatomy, define preoperative surgical planning and intraoperatively replicate this planning on the patient. Since 2010, there exists a standard protocol from ASTM society to assess technical specifications of navigation systems and positioning robots in CAOS [1]. The standard presents both parameters to be used and tracking tests to be performed to define accuracy and precision (bias and variability) of navigation and robotic systems. The logical continuation of this first ASTM standard is to develop new standard protocols to evaluate quality of bone-preparation tasks, i.e. bone cutting, milling, drilling and assembly of bone fragments, performed with the aid of such CAOS systems. This paper introduces a practical guide for orthopaedic surgeons to plan and evaluate bone-preparation tasks in CAOS. The pratical guide consists in a systematic six-steps approach to plan and evaluate a bone-preparation task, independent from the CAOS systems being used to execute the task. The practical guide also provides guidelines to implement the systematic approach for specific task and surgical application, i.e. femoral and tibial cutting in knee arthroplasty, vertebral drilling in spine instrumentation, and bone cutting and assembly in tumor surgery. Materials and methods Systematic approach to plan and evaluate bone-preparation tasks in CAOS The systematic approach is composed of six steps (Figure): (1) Planning frame is defined as a coordinate system presenting three orthogonal axes (x, y, z) according to patient anatomy; (2) Target specification of the task (cutting, milling, drilling or assembly) is defined in the planning frame as nominal (desired) geometry of the bone being prepared; (3) Accepted tolerances on nominal geometry are defined with relevant quality indicators accounting for desired functional outcomes and the level of accuracy provided by available CAOS systems; (4) Evaluation frame is defined as a new coordinate system with three orthogonal axes being registered to planning frame; (5) Errors on nominal geometry are computed and expressed in the registered planning frame; (6) Computed errors are investigated to determine whether the geometrical tolerances are respected. Validation process The implementation of the systematic approach for a specific task during a CAOS surgery may be validated in two phases. First, in-vitro experimentation on synthetic bone models with realistic simulations of the CAOS surgery will enable to validate the relevancy of the quality indicators used to define the geometric tolerances on bone cutting and drilling. This step will also enable to statistically investigate input factors with potential significant effect on outputs of the planning and evaluation process (i.e. geometric distortion during 3D reconstruction of medical images, manual identification of anatomical landmarks to define planning frame, semi-automatic registration between planning and evaluation frames, automatic identification of cut planes in postoperative images, ...). Second, in-vivo studies with data provided by actual CAOS surgeries will enable to validate the reliability of the planning and evaluation process. This step will also enable to detect potential irrelevancies and inconsistencies in the planning and evaluation of the task (i.e. the postoperative CT images are unsuitable for the evaluation process because of the presence of a metallic implant). Results The systematic approach is currently undergoing the validation process for three specific tasks and surgical applications: bone cutting in knee arthroplasty,
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Cartiaux, O., & Francq, B. G. (2014). Practical Guide to Plan and Evaluate Bone Cutting & Drilling in CAOS. 14th Annual Meeting of the International Society for Computer Aided Orthopaedic Surgery (CAOS), Milan, Italy.