Selective denervation of the levator scapulae muscle: an amendment to the Bertrand procedure for the treatment of spasmodic torticollis

Transcription

1 J Neurosurg 108: , 2008 Selective denervation of the levator scapulae muscle: an amendment to the Bertrand procedure for the treatment of spasmodic torticollis Laboratory investigation WILLIAM S. ANDERSON, PH.D., M.D., HERMAN CHRISTOPHER LAWSON, M.D., ALLAN J. BELZBERG, M.D., F.R.C.S.(C), AND FREDERICK A. LENZ, M.D., PH.D., F.R.C.S.(C) Department of Neurosurgery, The Johns Hopkins Hospital, Baltimore, Maryland Object. The purpose of this cadaveric study was to explore a modification to the Bertrand procedure for the treatment of spasmodic torticollis, namely the denervation of the levator scapulae (LS) muscle for laterocollis. Methods. The authors performed a series of 9 cadaveric dissections. Five were done to identify the anterior innervation of the LS, and the remaining 4 were to identify the tendinous insertions of the LS onto the lateral masses of the cervical spine via a posterior approach. The nerve supply to the LS from the anterior divisions of the C-3 and C-4 nerve roots and the contribution from the dorsal scapular nerve were identified over the anterior surface of the muscle. Results. The C-3 and C-4 nerve root branches were situated within 2 cm of each other and inferior to the punctum nervosum. The dorsal scapular contribution was clearly identified in 2 cadavers. Selective denervation of this muscle is possible through the same posterior triangle incision used for denervating the sternocleidomastoid muscle of its accessory nerve branches. This approach will be helpful in patients with laterocollis contralateral to the direction of chin turning. The authors compare this approach to the posterior approach for sectioning the insertions of the LS muscle onto the C1 4 posterior tubercles. The latter approach is appropriate for ipsilateral laterocollis. Conclusions. The posterior triangle approach for denervating the LS muscle is a safe and easy addition to the Bertrand procedure and can be helpful in selected cases of torticollis with a laterocollis component. (DOI: /JNS/2008/108/4/0757) KEY WORDS Bertrand procedure cervical dystonia levator scapulae spasmodic torticollis D YSTONIA is a movement disorder that causes slow, twisting movements and sustained postures. 29 Spasmodic cervical dystonia is the most common type of focal dystonia and involves rotation or tilting of the head in a lateral or anteroposterior direction; this may be tonic or tremulous. Prevalence rates reported in the literature have amounted to cases per million people, 27,39,44 with possibly greater prevalence in particular geographic areas. 40 The current medical therapy for this disease is based on injections of botulinum toxin, both types A and B. 10,11,28 In some patients, cervical dystonia is refractory to this treatment, and in some of those in whom injections of the type B toxin was initially successful, a decreasing benefit has been shown over time. 22,28 For patients with medically refractory cervical dystonia, surgery becomes an important Abbreviations used in this paper: DBS = deep brain stimulation; DSN = dorsal scapular nerve; LS = levator scapulae; MS = middle scalene; PN = punctum nervosum; SCM = sternocleidomastoid muscle; TWSTRS = Toronto Western Spasmodic Torticollis Rating Scale. option. The most common surgical treatments for this condition are selective denervation procedures performed on the affected muscles. 3,6,9,12 14,17,18,21,25,33,46 Deep brain stimulation for dystonia is now a widely accepted procedure, and the authors of some small case series have reported device implantations specifically for cervical dystonia. 8,19,37,38 The denervation procedure used at the beginning of the last century was often not selective and frequently involved bilateral sectioning of the anterior roots of C-1, C-2, C-3, and sometimes C-4, in an effort to eliminate tone in the posterior cervical muscles. 5,24,34,41 Congenital torticollis in children is typically not of dystonic origin but is caused by a shortened, fibrotic SCM. Treatments for this condition have typically involved muscle sectioning or Z-plasty procedures, with physical therapy and bracing as adjuncts. 26,30,42 Due to the problems with swallowing and upper airway control produced by bilateral C-1 and C-2 rhizotomy, Bertrand developed a more precise selective denervation procedure. This was initially performed in conjunction with thalamotomy for dystonia but was later found to be an effective therapy on its own. 2,4,6,7 We refer to this selective approach as the Bertrand procedure. In most cases 757

2 W. S. Anderson et al. of rotatory cervical dystonia, there is hyperactivity of the SCM on the side opposite to the direction of chin turning and of the posterior cervical paraspinal muscles ipsilaterally. 5 The Bertrand procedure for rotatory cervical dystonia consists of 2 parts: denervation of the contralateral SCM by sectioning branches from the accessory nerve to the SCM via a posterior triangle approach; and ipsilateral posterior division ramisectomy from C1 5 to eliminate innervation of the ipsilateral paraspinal muscles. 5,46 Patients with cervical dystonia also frequently present with elements of retro-, antero-, and laterocollis. 5,16 In these patients preoperative studies also consist of electromyography recordings to determine which other muscle groups are involved. 5 In the case of laterocollis (which represents 35% of patients presenting with cervical dystonia), the LS frequently has increased activity. 21 Bertrand and Benabou 5 describe a posterior approach to the LS when the laterocollis is ipsilateral to the direction of chin turning. These authors section nerve branches to the LS (discerned through intraoperative stimulation) and then resect the tendinous insertions onto the lateral masses of the C1 4 vertebrae. Bouvier and Molina-Negro 9 have also described denervation of the LS from an anterior approach, in the context of contralateral laterocollis with respect to the chin turning direction, but as far as we are aware, no formal anatomical descriptions of this approach have been published. There is an extensive cadaveric description of the innervation of the LS written with the purpose of preserving the nerve supply in neck dissection procedures for the treatment of head and neck tumors. 32 We outline a cadaveric study of the innervation of the LS, undertaken with the goal of denervating the muscle from an anterior approach namely, using the same incision used for denervation of the SCM. We compare the ease of approach and depth of anatomical structures in the anterior approach with that of the posterior approach to denervation and sectioning of the LS. Materials and Methods Dissections were performed in 9 cadavers: an anterior approach in 5 cadavers and a posterior approach in 4. Anterior Approach The classic initial incision for approaching the accessory nerve runs from the ear to the junction of the vertical and horizontal portions of the trapezius muscle. The nerve crosses a point one third of the way down the posterior border of the SCM, measured from the mastoid origin to the clavicular insertion. 3 We extended this incision medially and laterally, as well as superiorly and inferiorly to increase the exposure for this study. The platysma overlying the posterior border of the SCM was then incised. The first cutaneous nerves were identified, including the greater auricular nerve and the lesser occipital nerve as they swing from under the SCM superiorly behind the ear (Fig. 1). The point at which the greater auricular nerve enters the posterior triangle from under the SCM is referred to as the PN, 32 and several other cervical cutaneous nerves also emerge at this point. The fibrofatty and lymphatic tissue in the floor of the posterior triangle were then opened to reveal the spinal accessory nerve on the anterior surface of the LS in its course to the trapezius. This nerve was traced proximally as it crossed under the SCM to reveal the branches innervating the SCM. There are frequently several anastamotic branches between the spinal accessory nerve and the cervical plexus. 20 The posterior margin of the SCM was dissected out to free it from the underlying tissue, and then elevated anteriorly off of the neck. When this muscle is folded back, the innervation to the LS from the C-3 and C-4 nerve roots is revealed as the nerves pass under the SCM enroute to the anteromedial surface of the LS. These branches to the LS are typically found 1 2 cm from the PN, as determined by Frank et al. 32 The authors found that most specimens have 2 main identifiable branches into the LS, at distances of 1.0 and 1.5 cm on average, measured along the SCM inferomedial to the PN. Occasionally, the third and fourth branches are also found at average distances of 1.5 and 2.1 cm from the PN. Next, the phrenic nerve was identified as it crossed over the anterior surface of the MS muscle. This nerve was traced proximally to the C-5 root. The DSN was identified at the point where it branches from C-5 at approximately the same position as the phrenic nerve. The DSN branching point was found on the posterolateral aspect of the root and followed laterally as it penetrated the MS muscle and entered the inferomedial aspect of the LS. This then identified the C3 5 innervation to the LS. Posterior Approach For the posterior approach to the tendinous origins of the LS, a hockey stick incision was used, with the long arm extending down the midline from the inion to approximately C-6. The transverse limb extends from the midline laterally to a point ~ 4 cm medial to the posterior aspect of the mastoid process. The trapezius, splenius capitis, and semispinalis capitis were all divided superiorly and reflected laterally to expose the paraspinous muscles and the suboccipital triangle from above. The C2 5 dorsal rami, ensconced in their respective neurovascular bundles, were identified and divided (Fig. 2). At this point, the muscles of the suboccipital triangle, including the rectus capitis posterior, major and minor, and the obliquus capitis inferior were divided to further expose the posterior aspect of the C-1 ring and to demonstrate the suboccipital nerve exiting superiorly over the ring (Fig. 3). After dividing the C2 5 dorsal rami, slips of the LS could be observed extending superiorly to their origins on the posterior tubercle of the transverse processes of the C1 4 vertebrae. The very thin splenius cervicis muscle overlies the LS from this approach (C1 3 posterior tubercles) and was easily taken down before addressing the LS tendinous origins. Another very thin muscle, the longissimus cervicis, is found below the LS and also inserts at the posterior tubercles of C2 4. The insertion of the LS at the vertebral border of the scapula was verified. The tendinous origins were divided, and the LS was reflected inferiorly to reveal the MS muscle below. Anterior Approach Results In the 5 cadavers used for the anterior approach to the LS (A E), the procedure for opening the posterior cervical triangle as outlined in the Materials and Methods section was followed, including identification of the cutaneous nerves (greater auricular, lesser occipital, and the PN). The SCM was dissected out and the lateral surface was elevated to reveal the fibrofatty tissue layer underneath. This tissue was subsequently dissected, revealing the spinal accessory nerve as it passed along the anterior surface of the LS to innervate the SCM. Once the medial border of the LS had been cleared, the C-3 and C-4 contributions to the LS innervation were identified coming from under the SCM and entering the muscle along its anteromedial surface (Fig. 4). In each cadaver, only 2 branches were clearly identified, and these were located within 2 cm of the PN, in agreement with the findings of Frank and colleagues. 32 Frequently, as an aid in identifying the innervation to the SCM, the muscle is sectioned in the middle, 21 and this can greatly aid identification of the innervation on the surface of the LS by providing a wider field of view. More inferiorly under the 758

3 Selective denervation of the levator scapulae muscle FIG. 1. Photographs of cadaveric dissections demonstrating the superficial posterior triangle nerves and nerve supply to the LS. The SCM has been dissected and retracted supermedially. Left: Superficial nerves in Cadaver A. Right: Innervation of the LS in Cadaver C. n. = nerve. elevated SCM it was also possible to identify the MS and the overlying phrenic nerve. In 2 cadavers (A and C) it was possible to trace the phrenic nerve proximally to its C-5 contribution, and then to find the DSN as it penetrated the MS en route to the LS (Fig. 1). This penetration of the MS is a defining characteristic of the DSN and aids in its identification.47 The entrance of the DSN into the LS was ~ 2 cm below the PN in cadavers A and C. FIG. 2. Artist s illustration of the posterior approach to selective denervation of the paraspinal muscles in the context of the Bertrand procedure. The dorsal rami from C1 5 are generally divided. The tendinous slips from the LS attaching to the posterior tubercles of the lateral masses of C1 4 are also shown. Arrowheads indicate the sectioned dorsal rami, numbered 1 5. a. = artery; i = insertion; m. = muscle; mm. = muscles; o = origin; sup. = superior; v. = vein. 759

4 W. S. Anderson et al. Fig. 3. Representative photograph of a cadaveric dissection showing the LS tendons, numbered C-1 through C-4. Intraoperative Results We recently mapped out the LS innervation procedure intraoperatively during the Bertrand procedure in 2 patients. Case 1 This 56-year-old woman presented with chin rotated to the right. Preoperative electromyography studies demonstrated increased activity in the SCM and LS on the left side. After denervation of the left SCM was performed and the branches to the LS were identified, it was clear from their intraoperative stimulation that only the LS was contracting. These branches were found medial and inferior to the accessory nerve as they crossed from under the SCM. After these branches were clearly identified, they were avulsed from the muscle. Of note, anastamotic branches between the cervical plexus and the spinal accessory nerve were also identified at the time of surgery. Postoperatively, the patient has done well, with great improvement in her disability. This patient s TWSTRS 23 severity subsection score changed from 17 preoperatively to 14 postoperatively. Her score in the disability subsection changed from 11 to 8, and her score in the pain subsection changed from 0 to 1. Case 2 This 44-year-old woman underwent recent denervation surgery for cervical dystonia with chin turn to the left. Only 1 branch to the LS could be easily identified via stimulation. A line drawing of the intraoperative findings in both patients is presented in Fig. 4, and a summary of the anterior approach findings is provided in Table 1. Posterior Approach In all 4 cadavers (F I) examined in the posterior approach to the LS, the trapezius and splenius capitis muscles were divided at the midline, as outlined in the Materials and Methods section, and reflected laterally. The semispinalis capitis was dissected out at its medial border, and after freeing the superior attachment, it was reflected inferolaterally to expose the exiting dorsal rami below. The suboccipital triangle was exposed by taking down all of the small suboccipital muscles to reveal the exiting suboccipital nerve. At this point, the C1 5 dorsal rami were sectioned. After dissecting through the thin splenius cervicis muscle (present from C1 3 in all examined cadavers), the LS could be identified at its tendinous origins along the posterior tubercle of the transverse processes of C1 4, and anterior to this muscle, the MS muscle was identified. Further verification of the LS from the posterior approach was provided by tracing the muscle inferiorly to its insertion at the spine of the scapula. In 1 cadaver (G), the C3 4 innervations to the LS were identified from the posterior approach as they entered the muscle ~ 3 cm distal to the neural foramen. Discussion Anteriorly, when addressing the accessory nerve innervation of the SCM in the context of the Bertrand procedure, it is very easy to dissect under the SCM and medially to uncover the C3 5 innervation of the LS. This would be particularly useful in the context of laterocollis ipsilateral to the active SCM and would not imply a modification of the incision we currently use in the posterior triangle of the neck. We believe the innervation we describe to the LS in 5 cadavers and 2 patients verifies and adds to the data from the previous larger cadaveric study of Frank and colleagues. 32 Our presentation of cadaveric results should serve as an introduction to the variations in innervation patterns seen in the posterior triangle and help to define the relevant anatomy in the posterior and anterior approaches of the Bertrand procedure. As an aid to identification of this innervation, intraoperative stimulation is also valuable, especially when it is clear that the stimulated branch causes contraction solely in the LS. 9 The posterior approach to this muscle is most relevant in patients with laterocollis contralateral to the active SCM. The posterior approach to the tendons of the LS is aided by the fact that the covering semispinalis capitis originates from the C7 T7 transverse processes as well as the articular processes of C4 6. This represents the lower margin of the region (lateral aspects of C1 4) that must be exposed so that the LS tendons can be sectioned. 20 The underlying semispinalis cervicis inserts at the C1 5 spinous processes after originating from below (T1 6 transverse processes) and generally resides medial to the dissection. Bouvier and Molina-Negro 9 describe not only sectioning the tendinous insertions of the LS from the posterior approach, but also via stimulation, demonstrating the C-3 and C-4 innervations to the LS after the tendons have been cut. We were able to demonstrate this innervation in 1 of 4 cadavers from the posterior approach, but the nerves themselves entered the muscle body of the LS 3 cm below the tendinous insertions. We feel that this distance is too great to attempt the denervation from the posterior approach with the risk of endangering other neurovascular structures blindly anteriorly. Immediately anterior to the LS from the posterior approach, one encounters the scalene muscles, with the posterior scalene originating at the posterior tubercles of C4 6, 760

5 Selective denervation of the levator scapulae muscle FIG. 4. Diagrams of the anatomical findings in 5 cadavers and 2 patients. Five cadavers (A E) were used to explore the posterior triangle approach to denervation of the LS. Contributions to the innervation of the muscle from the C-3 and C-4 roots were identified in all 5 cadavers, but the DSN contribution as it penetrated the MS was only confirmed in Cadavers B and D. In Cadaver A there was a large anastamotic branch between the spinal accessory nerve and the cervical plexus, and in Cadaver C there were multiple peripheral and motor branches from the C-4 root branching very closely to the offshoot entering the LS. The last 2 drawings demonstrate the intraoperative findings in Cases 1 and 2. In the patient in Case 1, the innervation to the LS from the C-3 and C-4 is demonstrated, as well as anastamotic connections from the cervical plexus to the spinal accessory nerve, and a long sensory branch from the C-4 root crossing the field from medial to lateral. In Case 2, only 1 branch to the LS was uncovered via stimulation, ~ 1.5 cm below the crossing of the accessory nerve under the SCM. Anastamotic connections to the accessory nerve were also demonstrated. The distances between the entering C-3 and C-4 LS branches and the PN as measured along the SCM were all within 1 2 cm. the MS originating at the posterior tubercles of C2 7, and the anterior scalene originating at the anterior tubercles of C3 6. These muscles are innervated by the anterior rami of the C6 8 (posterior scalene), C3 8 (MS), and C5 6 spinal roots (anterior scalene). 20,36 The MS extends the most superiorly of these 3 and is the first muscle encountered anterior to the LS. Fortunately, it also represents the last substantial muscular layer of protection between the surgeon and 761

6 W. S. Anderson et al. TABLE 1 Summary of findings in the anterior approach to the posterior triangle Cadaver No. of C-3/C-4 LS Dorsal Scapular Spinal Accessory Nerve or Case Branches Identified* Innervation Identified Anastamoses Present Cadaver A 2 no yes B 2 yes (2 cm no below PN) C 2 no no D 2 yes (2 cm no below PN) E 2 no no Case 1 2 no yes 2 1 no yes *All branches identified were 2 cm inferior to the PN. the underlying neurovascular structures. The brachial plexus is classically described as passing between the anterior scalene and MS as it descends inferiorly; however, this is true in ~ 60% of specimens, 36 with the most significant variations involving various combinations of the C-5 and/or C-6 nerve roots penetrating the anterior scalene. 36,43 In general, the vertebral artery runs medial to the muscular attachments of the posterior and anterior tubercles, but ectatic specimens and vessel loop formation in the gaps between the transverse foramina are well described 16,45 and add a further element of caution to dissections in this region. Deep brain stimulation of the globus pallidus internus is another option for patients with cervical dystonia or generalized dystonia with severe torticollis. Peripheral denervation has the advantage of not being an intracranial procedure, and as such it does not carry the major risks associated with the latter, such as intracranial hemorrhage, which arises in 1 3% of patients. 1,35 The anterior approach to denervation of the SCM and LS is essentially a superficial anterior neck dissection, in which hemostasis is readily achieved. As it stands, DBS might be an effective treatment for patients in whom denervation fails. Similarly, a denervation procedure might be considered for patients in whom DBS was ineffective, and in some groups of patients maximal treatment effect might be derived by using both therapies. Preliminary results of DBS for the treatment of torticollis have demonstrated a 59% improvement in TWSTRS scores at 2 years of follow-up in 12 patients. 9 Another study showed improvement in TWSTRS severity scores by 54.8% after an average follow-up of 32 months in 10 patients. 37 One efficacy study of denervation procedures performed without using the TWSTRS score 15 as a rating tool demonstrated a 70% moderate-to-excellent improvement in head position and pain after 3.4 years of follow-up in 130 patients. 21 In their study in a group of 16 patients, Ford and associates 31 demonstrated an improvement in TWSTRS scores by ~ 30%, comparable with the improvement seen in the patients treated with DBS but without the risk of intracranial complications. In general, patients with torticollis should receive close follow-up by a neurologist specializing in movement disorders, as well as a neurosurgeon to rule out musculoskeletal causes for torticollis or other movement disorders before any surgical procedure is entertained. Conclusions The posterior triangle approach to the innervation of the LS is a useful and safe addition to the Bertrand procedure in patients with cervical dystonia and laterocollis contralateral to the chin turning direction. The innervation to this muscle typically consists of 2 nerve branches found within 2 cm under the lateral edge of the SCM inferior to the PN. When the laterocollis is ipsilateral to the chin turning direction, the tendinous slips of the LS can be divided before their insertion at the posterior tubercles of C1 4 as previously described. 2,3,5 7,9 References 1. Beric A, Kelly PJ, Rezai A, Sterio D, Mogilner A, Zonenshayn M, et al: Complications of deep brain stimulation surgery. 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