Femoral head osteonecrosis: Volumetric MRI assessment and outcome

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Abstract

Effective treatment of femoral head osteonecrosis (FHON) requires early diagnosis and accurate assessment of the disease severity. The ability to predict in the early stages the risk of collapse is important for selecting a joint salvage procedure. The aim of the present study was to evaluate the outcome in patients treated with vascularized fibular grafts in relation to preoperative MR imaging volumetry. We studied 58 patients (87 hips) with FHON. A semi-automated octant-based lesion measurement method, previously described, was performed on the T1-w MR images. The mean time of postoperative follow-up was 7.8 years. Sixty-three hips were successful and 24 failed and converted to total hip arthroplasty within a period of 2–4 years after the initial operation. The rate of failures for hips of male patients was higher than in female patients. The mean lesion size was 28% of the sphere equivalent of the femoral head, 24 ± 12% for the successful hips and 37 ± 9% for the failed (p < 0.001). The most affected octants were antero-supero-medial (58 ± 26%) and postero-supero-medial (54 ± 31%). All but postero-infero-medial and postero-infero-lateral octants, showed statistically significant differences in the lesion size between patients with successful and failed hips. In conclusion, the volumetric analysis of preoperative MRI provides useful information with regard to a successful outcome in patients treated with vascularized fibular grafts.

Introduction

Femoral head osteonecrosis (FHON) is a potentially disabling disease of the hip with multi-factorial etiology, most commonly affecting young adults. Early diagnosis and accurate assessment are crucial factors for the salvage of the hip joint. Prediction of the course of the disease is difficult, but it is very important for the decision about the appropriate management and especially the applicability of a hip preserving treatment method. Several classification systems have been proposed for the assessment of FHON [1] but their value for establishing prognosis has been proven controversial [2], [3].

Several studies have shown that the course of the disease is associated to the size and the topographical distribution of the necrotic lesion [4], [5], [6], [7]. MR imaging is the most suitable means for the early diagnosis and for the accurate description of the lesion [1], [3], [4]. In the majority of the methodologies proposed for evaluating the extent of the lesion, either a single or a limited number of slices are used. The few reports which evaluated the actual volume and location of the affected area were based on manual tracing of the necrotic lesion, which is time-consuming and of questionable repeatability [8]. A semi-automated method for the volume assessment of the lesion has been described, based on MR imaging [9]. For hips with high risk of failure, the volumetric assessment offers additional valuable information in predicting the outcome and may assist in making the decision for their management [4], [5].

The purpose of the present study was to correlate the outcome with a volumetric analysis, using long-term follow-up data from patients with FHON treated with free vascularized fibular grafting (FVFG). Based on the results, a simple classification schema is described in Appendix A which is easy to apply and able to depict the high-risk osteonecrotic hip.

Section snippets

Materials and methods

From a large database of patients with FHON referred to a tertiary care facility, a subgroup has been treated with FVFG. The patients’ records include complete clinical and laboratory data, information about the presence of one or more risk factors, operative records and postoperative regular follow-up and imaging data (radiographs, MR imaging, CT scans and bone scans). The present study includes 58 patients with 87 hips treated with FVFG. There were 33 male and 25 female patients (age range

Results

The volumetric analysis was possible in all but four hips, where an additional manual tracing was performed. The mean lesion size of the 87 hips was 28 ± 12% of the sphere equivalent of the femoral head. The necrotic lesion was generally located towards the superior, medial and anterior areas of the femoral head. The most affected octants were ASM (58 ± 26%) and PSM (54 ± 31%), or the superior-medial quarter of the femoral head. The next most affected octants were ASL (42 ± 23%) and PSL (32 ± 24%),

Discussion

Treatment with FVFG in patients with FHON allows decompression and provides structural support as well as vascular supply that had been for long limited or absent in the necrotic area [12]. One study on 101 hips treated with vascularized grafts showed a successful 5-year outcome in 61% [13]. Berend et al. analyzed 224 collapsed osteonecrotic hips treated with vascularized fibular grafts and found a survival rate of 64.5% at a mean of 4.3 years [14]. Our rate of failure, although lower, is

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