Patient-specific instrumentations for complex knee surface preparation

Abstract

Osteoarthritis of the knee is one of the most prevalent diseases. The primary treatment for young patients is regenerative cartilage repair. The best treatment for the middle aged group is cartilage substitution material. Although in the worst case scenario, knee replacement becomes an option, giving proper treatment in advance, most patients can postpone or even avoid the irreversible replacement procedure. Since the surface varies in size and shape among patients, the conventional standard sized instruments are not appropriate for these novel treatments. The existing preparation technique used by surgeons is freehand debridement, which relies on highly skilful and experienced surgeons to yield good results. Although there are some patient-specific instrumentations on the market, the majority of them are designed to assist the conventional knee replacement implants, and are not applicable on curved surfaces. The aim of this study was to develop effective, simple and standardized patient-specific instrumentations for large joint surface preparation. The study started from verifying the accuracy of experimental equipment and proposed patient-specific techniques and instruments. Then, an experiment on plastic bone samples was performed. The outcomes showed that the errors of repairing surface, depth, and position were less than ±0.5 mm, ±0.5 mm and ±1.0 mm respectively. This is regarded as sufficiently accurate to prepare the knee surface. Then, some improvements were made on the surgical jigs and procedures for the later cadaveric experiment. Eight cadaveric samples were tested. The outcomes showed that the 5% and 95% percentiles of errors in repairing surface, position errors and depth errors were -0.22 mm to 0.56 mm, -1.40 mm to 1.04 mm, and -0.58 mm to 0.20 mm respectively. Furthermore, patient-specific instrumentations were designed for arthroscopic procedures, which is the only patient-specific guide that can be used arthroscopically for orthopaedic surgeries. A tibial preparation guide was also designed, but further tests are needed for this device.