Abstract
Introduction
Patient-specific cutting guides entered into clinical practice few years ago, first introduced in total knee replacement and recently also for other joint replacements. Advantages claimed are improving accuracy and repeatability in implant placement. New patient-specific guides to perform an accurate femoral neck resection and provide a precise alignment reference for acetabular reaming in total hip arthroplasty (THA) were recently developed by Medacta International: MyHip Technology. To date femoral guides can be designed for both anterior and posterior approaches, whereas acetabular guides are available only for posterior approach.
Evaluation of the repeatability and reproducibility of MyHip guides placement on cadavers is performed using a navigation system. Accuracy of femoral MyHip guides is evaluated also through one author's clinical experience (RP).
Materials and Methods
During each cadaveric session one body (2 hips) was available. A pre-operative CT scan has been obtained and used in order to create the 3D bone model of the pelvis and proximal femurs. Afterwards, a surgical planning for THA has been performed for each case, and, once it was approved by the surgeons, the designed patient-specific blocks were made.
Intraobserver and interobserver agreement in positioning the guides was assessed getting measures of femoral head resection height (mm), femoral head plane inclination/anteversion (°) and acetabular reaming axis orientation (°). 9 surgeons, through 2 cadaveric sessions, positioned each guide, removed it and re-positioned it 5 times alternatively. The system is judged as accurate if all measures differ less than 3mm and 5°for lengths and angles respectively from the average among all the acquisitions.
Clinical experience includes 68 THA which were performed between March 2014 and April 2015. Anterior femoral MyHip guides were used for the femoral head resection, while the acetabular side was prepared using the standard metal instrumentation for minimally invasive anterior approach. Intra-operative complications, as well post-operative leg length difference and implant positioning are assessed.
Results
During cadaveric sessions, all measures taken meet the acceptance criteria with the exception of two measures, which are −5,98° and −5,57°, in femoral head plane anteversion and inclination respectively with femoral anterior guides. Looking at intraobserver variation, MyHip Femoral anterior guide positioning average deviation was between −0.91 mm and 1.44 mm (resection height), −1.25° and 1.41° (anteversion), and −0.85° and 0.82° (inclination); MyHip Femoral posterior guide positioning average deviation was between −0.47 mm and 0.67 mm (resection height), −1.33° and 1.50° (anteversion), −0.66° and 1.50° (inclination); MyHip Acetabular posterior guide had an average z-axis deviation from the mean value between −0.91° and 0.91°.
All surgeries were successfully performed. The surgeon feels a good fitting and stability of the guide during each surgery. A preliminary analysis suggests optimal outcomes in terms of accurate prosthetic component positioning and reduction of occurrence of leg length inequality.
Conclusion
Cadaveric sessions show intraobserver and intraobserver agreement, demonstrating reproducibility and repeatability in placement of MyHip patient specific cutting guides. Clinical experience confirms the advantages claimed by this technique, suggesting a possible reduction of complications usually linked to implant malpositioning, such as wear, impingement, risk of luxation.
