Robert Wescott, Johann Henckel, Anna Di Laura and Alister Hart discuss the factors associated with the clinical outcome and longevity of knee and hip implants
Introduction
The clinical outcome and longevity of knee and hip implants is associated with surgeon, implant and patient factors. In both total hip arthroplasty (THA) and total knee arthroplasty (TKA), the implant position contributes to the survival and clinical functionality of the implant [1,2].
The position of the femoral and the acetabular components in a THA affect patient satisfaction [3], as this position determines the final leg length and the range of motion within the hip joint [4,5]. Mal-positioned THA components have demonstrated increased rates of wear, impingement and dislocation [6,7]. Poor placement of the tibial component in TKAs has been associated with loosening [8], therefore, one way to improve the lifespan of prosthesis is to implant them into the “correct” position.
Over the last decade, computer-assisted navigation and robotic systems have been introduced to aid in the intraoperative positioning of implants. Robotic systems are either active or semi-active and require a pre-operative CT scan to create a map of the patient’s anatomy. Active systems direct the surgeon’s instrument placement while semi-active surgical robots create pre-defined boundaries for bony preparation [9]. Although these systems have demonstrated an increased accuracy in component positioning for THA, they have a high initial cost and they increase the total operative time [10-12].
Navigation systems are always passive. They work by visually guiding the surgeon in to aid their operative technique. CT-based navigation systems have demonstrated good long-term clinical results for THAs, however they have issues due to the increased exposure to radiation. Other navigation systems use fluoroscopic imaging, however they have had a low acceptance due to concerns over their accuracy [13].
Figure 1: This image depicts the process of producing a 3D computer generated model from CT imaging to allow for the planning of the surgical procedure and the production of PSI jigs. A) Thin CT slice th