gms | German Medical Science

Questionnaire: Hip resurfacing (HR) represents a bone-conserving total joint replacement option for young and active patients. Major short-term risks include periprosthetic femoral neck fracture and aseptic loosening of the femoral component. In this context, varus malpositioning and femoral neck notching are critical. The aim of the study was to evaluate the effects of image-free computer-assisted surgery (CAS) on the accuracy of cap positioning and on the short-term clinical outcome in hip resurfacing using a randomized prospective design.

Methods: A total of N=73 consecutive patients undergoing HR (Durom^TM Hip Resurfacing, Zimmer, Warsaw, USA) were randomly allocated to CAS (n=36; Navitrack^®, ORTHOsoft Inc., Montreal, Canada) and conventional (n=37, standard Durom^TM K-wire positioning jig) group, respectively. Surgery was performed using the posterolateral approach by two surgeons experienced for both HR and CAS. Preoperatively and at 6 months postoperatively algofunctional scores (WOMAC, Harris Hip Score, EQ-5D, UCLA activity score) were registered and standardized pelvic anteroposterior x-rays were in a blinded manner using mediCAD^® software (HECTEC GmbH, Niederviehbach, Germany). Cap malpositioning as the primary endpoint of the study was defined as >5° deviation from the planned stem shaft angle (SSA) in the frontal plane. SPSS 17.0.0 package was used for statistical analysis. The study was approved by the local institutional review board (EK108052008).

Results and Conclusions: Sex (overall m/f ratio 57/16), age (overall mean 49.6 years), body mass index (27.9 kg/m²), operative time (99.4 min.), CCD angle (131.8 °), and cap size (48.7 mm) did not differ significantly between CAS and conventional group. Absolute mean differences between postoperative and planned SSA in the frontal plane were similar (4.6±4.6° vs. 3.2±2.8° in conventional vs. CAS group, p=0.103). However, using CAS significantly fewer caps were malpositioned (12/37 vs. 4/36, Fisher p=0.046). All algofunctional scores had significantly improved 6 months postoperatively (p< 0.0001) and no intergroup differences were observed. Two conversions to stemmed prostheses (both CAS group) were performed due to periprosthetic femoral neck fracture and symptomatic implant-bone impingement, respectively. Radiological signs of femoral neck notching without clinical relevance were observed in 2 of the conventionally implanted caps. Mild heterotopic ossifications (Brooker 1) were observed in 7 patients (conventional/CAS = 4/3) 6 months postoperatively.

Using a randomized prospective study design we observed that the rate of malpositioned femoral hip resurfacing components was significantly reduced by use of CAS. However, the clinical significance of this finding is uncertain. In addition two major complications necessitated revision in the CAS group. Besides these adverse events no intergroup differences were observed for the short-term clinical outcome. Future studies need to address the clinical long-term relevance of CAS in HR.