Date Published: November 4, 2011
Publisher: SAGE-Hindawi Access to Research
Author(s): Eric Beaumont, Pierre Beaumont, Daniel Odermat, Isabelle Fontaine, Herbert Jansen, François Prince.
A CT-based navigation system is helpful to evaluate the reamer shaft and the impactor position/orientation during unilateral total hip arthroplasty (THA). The main objective of this study is to determine the accuracy of the Navitrack system by measuring the implant’s true anteversion and inclination, based on pre- and postoperative CT scans (n = 9 patients). The secondary objective is to evaluate the clinical validity of measurements based on postop anteroposterior (AP) radiographs for determining the cup orientation. Postop CT-scan reconstructions and postop planar radiographs showed no significant differences in orientation compared to peroperative angles, suggesting a clinical validity of the system. Postoperative AP radiographs normally used in clinic are acceptable to determine the cup orientation, and small angular errors may originate from the patient position on the table.
The orientation of the acetabular component has been shown to be a significant factor affecting the risk of dislocation, impingement, and wear between components in patients undergoing total hip arthroplasty (THA) [1–3]. The prevalence of implant dislocation following THA ranges between 1% and 5% and represents a significant cause of early failure [4–7]. In addition to dislocation, implant impingement causes excessive wear of the cup liner through the impaction of the neck and creation of debris, a contributor to implant loosening via bone resorption. Therefore, a proper implant positioning is essential in order to reduce the incidence of impingement and the risk of associated complications. Despite the availability of many techniques of stabilizing and positioning the pelvis during the surgical procedure, many surgeons admit that it is difficult to know precisely how the patient’s pelvis is oriented during surgery. This may lead to improper cup placement when using mechanical guides [8–10]. To improve this particular phase of the surgery, a navigation system was designed to help surgeons to evaluate the reamer and the impactor position/orientation during surgery. This system’s precision is crucial because it can have a direct effect on the final cup placement [11, 12]. Several validation studies using plastic bone models and cadavers were undertaken by Orthosoft Inc. to assess the system’s accuracy, which demonstrated a global error in cup orientation (<2° in 95% of cases and <5° for 99% of cases, unpublished data). To evaluate the system's accuracy with patients, data was gathered to estimate the system's validity. In this regard, the precision and validity of the “Navitrack” system at inserting pedicle screws has already been established . The clinical validation was conducted on 9 patients undergoing unilateral THA. The average patient age was 58 years old (range 46–77 years); including 1 woman and 8 men. The affected hip was on the right side in 5 cases and on the left side in 4 cases. The Converge acetabular cup from Zimmer was positioned during surgery using the Navitrack Total Hip Replacement (THR) 1.3 system. This protocol was approved by the Sacré-Coeur hospital research ethics committee, all patients were informed about this protocol before their surgery, and they signed a consent form. When performing a total hip replacement, the use of a navigation device provides an additional tool in order to achieve a better implant positioning. In fact, postoperative CT-scans revealed that the final cup position during the surgery is in agreement with the orientation planned. Therefore, this validation study is relevant and indicates that the use of this navigation system is valid and precise to position the cup. Next, postoperative AP radiographs normally used in clinic are acceptable to determine the cup orientation, considering that knowing the patient's pelvis position on the table will decrease the error when determining the cup orientation from a 2D image, providing a crucial feedback to the surgical outcome. Source: http://doi.org/10.4061/2011/171783