Introduction

Diffusion tensor imaging (DTI) is an advanced magnetic resonance (MR) imaging technique, which can visualize neural tracts and provides information about the microstructure of nerve fibers noninvasively1.The sciatic and femoral nerves are the two major nerves around the hip joint. The mechanisms of hip pain are not fully understood, but degenerative changes of the nerves might contribute to hip pain in patients with diseases such as osteoarthritis of the hip (OA) or osteonecrosis of the femoral head (ONFH)2.DTI can be useful to investigate the mechanism of hip pain by evaluating sciatic and femoral nerves nerve in OA and ONFH. The purpose of this study was (1) to visualize the tractography and investigate the fractional anisotropy(FA) values of the sciatic and femoral nerves in patients with unilateral OA and ONFH, (2) to compare the values in each group.

Methods

A total of 68 subjects were enrolled in this study, with a control of 24 healthy volunteersand 44 patients (22 OA and 22 ONFH). The study protocol was approved by the Institutional Review Board, and all subjects gave written informed consent. MR imaging was performed on a 3 Tesla MR scanner (Discovery MR750; GE Healthcare, Milwaukee, Wisconsin) with a Sense XL Torso coil. DTI was performed using a special sensitivity array encoding protocol, with the factor = 2, chemical shift selective suppression, and an echo-planar imaging sequence with a free breathing scan technique. The following imaging parameters were set: b value = 800 s/mm2, motion probing gradient (MPG), 11 directions, time to repetition (TR)/echo time (TE) = 9000/72.6 ms, flip angle = 90°, axial slice orientation, slice thickness = 3.0 mm with no inter-slice gap, field of view = 320 × 320 mm, 96 × 192 matrix, 75 slices, number of acquisitions = 4.For anatomical reference, a MERGE (Multiple Echo Recombined Gradient Echo) sequence was obtained. Image analysis was performed on a workstation (Readyview, GE Healthcare, Milwaukee, Wisconsin). The tractography-based FA values were evaluated as follows.The regions of interest (ROIs) of the FA values for the sciatic nerve were defined at the level of the center of the femoral head in the axial image and the S1 root, and for the femoral nerve were defined at 3-4 cm proximal from the center of the femoral head. We measured the FA values on both sides for the normal group and on the affected side for OA and ONFH groups. The FA values of the sciatic and femoral nerves and the S1 root were compared between the normal, OA and ONFH groups. The correlations between the FA values and the VAS and pain duration of the affected side were calculated using the Spearman’s rank correlation coefficient test.

Results

The sciatic and femoral nerves were visualized in both hip joints for all patients (Figure). There were no defects or narrowing of the nerves visually. There was no statistically significant difference in FA values between the normal, OA and ONFH groups (Table). A weak negative correlation was observed between the FA value of the sciatic nerve in the OA group and the pain duration (r = -0.414, p = 0.045). No correlation was identified between the FA values at the other locations (femoral nerve and S1 root) in the OA and ONFH group and the pain duration. No correlation was found between the FA values at any location (sciatic nerve, femoral nerve, and S1 root) and the VAS pain score in both groups.

Discussion

The sciatic nerves mainly innervate the sensory of the posterior aspect of the lower extremity and the femoral nerves innervate the anterior aspect. From the distribution of the hip pain, we thought that nerves associated with pain may be different in diseases or nerves may be degenerated. But, our results indicated that the two major nerves around the hip joint were not degenerated by entrapment or demyelination.

Conclusion

This study indicates thatthe FA values for the sciatic and femoral nerves in patients with OA and ONFH showed no significant differences with normal hips indicating no degeneration or demyelination occurred in either nerve. DTI may be able to differentiate hip diseases from lumbar nerve radiculopathy.

Acknowledgements

This study was supported by JSPS KAKENHI Grant Number 17K10954.

References

1. Eguchi Y, Ohtori S, Yamashita M, et al. Diffusion-weighted magnetic resonance imaging of symptomatic nerve root of patients with lumbar disk herniation. Neuroradiology. 2011;53(9):633–41.2. Nakamura J, Oinuma K, Ohtori S, et al. Distribution of hip pain in osteoarthritis patients secondary to developmental dysplasia of the hip. Mod Rheumatol. 2013;23(1):119–24.