An active constraint robot improves outcome in total knee arthroplasty

摘要

Objectives: We wish to report the reliability of the Acrobot approach in total knee arthroplasty, as demonstrated in a prospective randomized double blind trial. Background: Computer assistance devices have developed to help the surgeon improve the operative results. Navigation systems have been shown to reduce some of the errors in arthroplasty [1], but some outliers persist. Active robots are very much more accurate [2], but have not yet convinced surgeons of their user-friendliness [3]. The Acrobot~R, an active constraint "hands-on" robotic system, gives navigation cues to the surgeon, and also assists him in the surgery, using active software constraints if he tries to depart from the preoperative plan. It is currently in the midst of a prospective randomized controlled trial for total knee replacement, against conventional instrumentation. Methods: The Acrobot~R system for precision total knee arthroplasty comprises the following components: A CT-based planning system which allows: (a) virtual surgery on three dimensional models of the patient's skeleton, (b) identification of preliminary registration points on the bones, and (c) the addition of the constraints or boundaries for the surgeon within the operative field. The limb positioning system which: (a) allows precise positioning of the bones before bone preparation begins, (b) holds the bones immobilized relative to the bed without transfixion pins, and (c) enables easy access to the tissues for the surgeon. The Acrobot's hardware components: (a) a gross positioning device with separate brakes and encoders, locked off for safety during the procedure, (b) a fully back-drivable low force robot, and (c) a force control handle on the robot close to the high-speed milling tool. The Acrobot's software which: (a) imports the preoperative plan, (b) allows recording of the preliminary registration points and an iterative closest point matching of a subsequent set of about 15 further points (no fiducial marker screws are required for registration), (c) provides navigation feedback on screen about boundaries, in all three dimensions, throughout the procedure, and (d) physically assists in the accurate milling of hard bone and prevents the surgeon from milling away precious structures such as the posterior cruciate ligament, according to the preoperative constraint boundaries set by the surgeon. Patients who were due for arthroplasty were approached, and randomized, with the only principal exclusions being the very obese, and premenopausal women (because of the irradiation). Each patient's postoperative CT scan was compared with the preoperative plan. With artifact reduction algorithms, accuracy of this method is sensitive to error at the level of 1mm and 1 degree. The distance of the joint line from the hip and ankle joint, and its angulation and rotation were compared to the preoperative plan.