Sciatic nerve injury related to hip replacement surgery: imaging detection by MR neurography despite susceptibility artifacts

Abstract

Sciatic nerve palsy related to hip replacement surgery (HRS) is among the most common causes of sciatic neuropathies. The sciatic nerve may be injured by various different periprocedural mechanisms. The precise localization and extension of the nerve lesion, the determination of nerve continuity, lesion severity, and fascicular lesion distribution are essential for assessing the potential of spontaneous recovery and thereby avoiding delayed or inappropriate therapy. Adequate therapy is in many cases limited to conservative management, but in certain cases early surgical exploration and release of the nerve is indicated. Nerve-conduction-studies and electromyography are essential in the diagnosis of nerve injuries. In postsurgical nerve injuries, additional diagnostic imaging is important as well, in particular to detect or rule out direct mechanical compromise. Especially in the presence of metallic implants, commonly applied diagnostic imaging tests generally fail to adequately visualize nervous tissue. MRI has been deemed problematic due to implant-related artifacts after HRS. In this study, we describe for the first time the spectrum of imaging findings of Magnetic Resonance neurography (MRN) employing pulse sequences relatively insensitive to susceptibility artifacts (susceptibility insensitive MRN, siMRN) in a series of 9 patients with HRS procedure related sciatic nerve palsy. We were able to determine the localization and fascicular distribution of the sciatic nerve lesion in all 9 patients, which clearly showed on imaging predominant involvement of the peroneal more than the tibial division of the sciatic nerve. In 2 patients siMRN revealed direct mechanical compromise of the nerve by surgical material, and in one of these cases indication for surgical release of the sciatic nerve was based on siMRN. Thus, in selected cases of HRS related neuropathies, especially when surgical exploration of the nerve is considered, siMRN, with its potential to largely overcome implant related artifacts, is a useful diagnostic addition to nerve-conduction-studies and electromyography.

Figure 1. ROI-based measurement of T2-signal intensity of muscle, peroneal and tibial division of the sciatic nerve.

siMR neurographic T2-weighted images with fat-saturation (a, b, c). Exemplary ROI-based analysis of signal intensities of the peroneal and tibial portion of the sciatic nerve, the normal appearing musculature, and background noise in patient 5 (a), patient 1 (b) and a healthy control (c). In (a), a distinctive T2-signal increase of the peroneal and tibial nerve in patient 5, and in (b) a T2-signal increase of peroneal division of the sciatic nerve in patient 1 are shown. In the healthy control no pathological nerve signal increase is present (c). In (d) the corresponding SR of the peroneal and tibial portion of the sciatic nerve are shown. In the healthy control, and in the normal appearing tibial portion of the sciatic nerve in patient 1 SR are below 1.7. A SR above 1.7 indicates a lesion of the peroneal portion of the sciatic nerve in patient 1, and in the peroneal and tibial portion of the sciatic nerve in patient 2 (d). Abbreviations: p: peroneal portion of the sciatic nerve or peroneal nerve; SR: nerve-to-muscle T2- signal intensity ratio; t: tibial portion of the sciatic nerve or tibial nerve.

Figure 2. Constriction of the sciatic nerve by surgical material in patient 1 (a, b: siMRN; c, d: intraoperative photographs).

T1-weighted sequences, being less vulnerable to susceptibility artifacts, revealed constriction of the peroneal portion of the subtrochanteric sciatic nerve by a cerclage (a). Below the constriction, the peroneal portion of the sciatic nerve exhibited a pathological T2-signal-increase (b). The constriction of the sciatic nerve by a cerclage (arrow in c, d) was validated intraoperatively. Abbreviations: p: peroneal portion of the sciatic nerve or peroneal nerve; sn: sciatic nerve; t: tibial portion of the sciatic nerve or tibial nerve.

Figure 3. Constriction of the sciatic nerve by surgical material, and denervation of target muscles in patient 2.

siMRN revealed compression of the peroneal portion of the left sciatic nerve by a small susceptibility prone foreign body (arrow in a). Besides denervation of the peroneally innervated muscles at the lower leg (c), denervation of the long head of the biceps femoris muscle (b) and slight denervation of the posterior tibialis muscle and the gastrocnemius muscle (c) indicated accompanying affection of the tibial nerve as well. Abbreviations: atm: anterior tibialis muscle; bfm: biceps femoris muscle; edlm: extensor digitorum longus muscle; gm: gastrocnemius muscle; p: peroneal portion of the sciatic nerve or peroneal nerve; plm: peroneus longus muscle; ptm: posterior tibialis muscle; sn: sciatic nerve; t: tibial portion of the sciatic nerve or tibial nerve.

Figure 4. Localization and fascicular distribution of T2-nerve lesion, and denervation pattern of target muscles.

siMRN in patient 5 (a, b, c: transversally orientated T2-weighted TSE with fat-suppression) and patient 7 (d: coronally orientated T2 STIR; e, f: transversally orientated T2-weighted TSE with fat-suppression). Depending on the extent of implant-related artifacts, evaluation of the sciatic nerve may be impaired or even impossible for a certain region (d). Regular depiction of the nerve roots and lumbar pexus in patient 7 (d), but the subtrochanteric sciatic nerve exhibits a peroneally accentuated T2-lesion (e), and the peroneally innervated muscles of the proximal lower leg show signs of denervation (f). In patient 5 the proximal sciatic nerve showed a T2-lesion in proximity of the ischial tuberosity (a), affecting all fascicles of the nerve at level of the hip (a) and thigh (b). Furthermore the denervation of the biceps femoris and semimembranosus muscle of the thigh (b), and the anterior tibialis, extensor digitorum, peroneus longus, popliteus and gastrocnemius muscle of the lower leg (c) indicate affection of the tibial and peroneal division of the sciatic nerve. Abbreviations: atm: anterior tibialis muscle; bfm: biceps femoris muscle; edlm: extensor digitorum longus muscle; gm: gastrocnemius muscle; p: peroneal portion of the sciatic nerve or peroneal nerve; plm: peroneus longus muscle; pom: popliteus muscle; sem: semimembranosus muscle; sn: sciatic nerve; t: tibial portion of the sciatic nerve or tibial nerve.