Myoarchitectonic spinolaminoplasty: efficacy in reconstituting the cervical musculature and preserving biomechanical function

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Object

Laminoplasty has been used to expand the cervical spinal canal, based on the belief that reconstruction of the laminae preserves musculoskeletal function. The true efficacy of laminoplasty for maintaining spinal alignment, stability, and flexibility, however, remains to be proven. The authors have developed a new method, myoarchitectonic spinolaminoplasty (MSLP), which preserves all of the nuchal muscles and reconstitutes all of the musculoskeletal couplings to the posterior elements of the vertebrae. The details of this technique are described, and the efficacy of the technique in conserving muscle volume, alignment, and motion, as well as in preventing postoperative musculoskeletal discomfort, is assessed.

Methods

The authors' previous midline-splitting laminoplasty procedure, which utilized a hydroxyapatite (HA) implant as a substitute for the spinous process, was improved. Detachment of the muscles is avoided with this new technique by cutting inside the spinous process. The bone–muscle flaps are affixed to the HA spinous process. Radiographs, computed tomography scans, and neurological evaluations obtained at the 1-year follow-up in the groups of consecutive patients assessed immediately prior to and after the modification of the previous technique (the control and the MSLP groups, respectively) were analyzed and compared.

Results

The HA bone constructs became integrated due to osteoconduction. The cross-sectional area of the semispinalis capitis, semispinalis cervicis, and multifidus muscles remained significantly larger in the MSLP group. Slight attenuation in lordosis was observed in the control group, but was prevented in the MSLP group. Range of motion was somewhat restricted in the MSLP group, but the incidence of neck pain and shoulder strain was significantly reduced.

Conclusions

The new MSLP method was effective in preserving the volume and functions of the nuchal musculature and helping to minimize postoperative musculoskeletal complaints.

Abbreviations used in this paper:ANOVA = analysis of variance; CSA = cross-sectional area; CT = computed tomography; HA = hydroxyapatite; MSLP = myoarchitectonic spinolaminoplasty; NCSS = Neurosurgical Cervical Spine Scale; OPLL = ossification of the posterior longitudinal ligament; ROM = range of motion.

Article Information

Address reprint requests to: Phyo Kim, M.D., Ph.D., Department of Neurosurgery, Dokkyo University School of Medicine, 880 Mibu, Tochighi 321–0293, Japan. email: kim@dokkyomed.ac.jp.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Schematic representation of the MSLP procedure. A: Surgical anatomy of the muscles and ligaments (C3–5). Three layers of the dorsal musculature are shown from the surface as follows: the trapezius, splenius capitis, and the deep extensor muscles. The deep muscles consist of semispinalis capitis, semispinalis cervicis, and multifidus muscles. Each of the three layers forms a discrete midline fascial ligament. The fasciae of the splenius capitis are attached to the C-6 and C-7 spinous processes. B: Dividing the three discrete layers of the fasciae comprising the nuchal ligament. The first (fascia of trapezius), second (splenius capitis), and third (semispinalis cervicis) layers are individually cut in the midline. A scalpel and bipolar forceps are used in the sharp dissection process to avoid heat damage to the ligament. C: Splitting the spinous process. While the attachments of the semispinalis cervicis and splenius capitis muscles (at C6–7) are left intact, the spinous processes are split in the midline. D: Separating the spinous process from the lamina. The two separate cortical plates are cut laterally and separated at the junction between the spinous process and the lamina (spinolaminar junction) with the muscles attached. E: A 3-mm diamond bur and thin-profile Kerrison rongeurs are used to bisect the lamina in the midline. F: Cutting the lateral gutters. The drilling maneuver is performed between the bellies of the multifidus muscle. After cutting a groove through the outer cortical and cancellous layers, the inner cortical plate is attenuated. The lateral gutters act as hinges, and the laminal flaps are elevated to swing open. G: Implanting the HA spinous process. The HA implants are fixed to the laminal flaps with monofilament USP 2 nylon sutures, which are passed through the laminal flaps. H: Reconstructing the spinous process and the muscle attachments. The cortical plates with the attached muscles are secured onto the HA spinous process, using USP 2 silk sutures. I: Closing the discrete layers of the nuchal ligament.

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    Intraoperative photographs of the MSLP procedure. A: Sharp dissection of a discrete layer of the nuchal ligament. B: Division of the second layer of the nuchal ligament, the midline raphe of the fascia of the splenius capitis muscle, which converges with the C-6 spinous process. C: After cutting and lateral retraction of the spinous process plates with attached muscles (semispinalis cervicis and semispinalis capitis), the lamina with the multifidus muscle attached to the caudal edge is exposed and bisected in the midline. Lateral gutters are drilled between the bellies of the multifidus. D: Completion of the drilling procedure. The laminae are split in the midline and the lateral gutters are drilled. Note that the multifidus muscles are left intact. E: Elevation of the laminal flaps with the lateral gutter acting as the hinge. The dural tube is decompressed. F: Fixation of the HA spinous process to the elevated laminal flaps using a monofilament USP 2 nylon suture. G: The spinous cortical bone plates, with the muscles attached, are drilled to allow the suture to pass through. H: Affixing the spinous process bone plates to the HA spinous implant. I: Tight closure of each discrete layer of the nuchal ligament.

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    Photograph (upper left) and schematic illustrations show the precise dimensions of the artificial spinous process HA implant. The quadrangular pyramid-shaped implant is composed of HA with 40% porosity and has three tunnels to allow passage of sutures.

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    Dorsal extensor muscles, visualized on an axial CT image at the C5–6 level. The splenius capitis (1), semispinalis capitis (2), semispinalis cervicis (3), and multifidus muscles (4) can be carefully identified. The CSA of each muscle was measured using Image J software, with calibration to the scale provided in this CT image.

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    Radiographs demonstrating the measurement of cervical alignment and ROM. The angle between C-2 and C-7 on lateral flexion/extension radiographs was measured, and the ROM was defined as the sum of the angles on flexion (a) and extension (b) (ROM = a + b). Postoperative alterations in the C2–7 angle in the neutral position (c) were calculated by subtracting the angle in the neutral position from the postoperative change in angle. A positive value indicated a decrease of lordosis after surgery, and a negative value indicated an increase in lordosis.

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    Axial CT scans obtained 1 year after surgery demonstrating the construct of the cervical spine after MSLP. Note the ossifications in the gutters (small arrows) and the integration of the laminal flaps (large arrows) and the spinous bone plates (arrowheads) with osteoconduction surrounding the HA implants.

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    Bar graphs comparing the alterations in cervical ROM (A) and lordotic angles (B) between the non-MSLP and MSLP groups after surgery. A: The values are calculated as percentage ratio of postoperative and preoperative ROM. B: Postoperative alterations in the C2–7 angle measured in the neutral position (δ angleneut) are shown. *p < 0.05.

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    Representative CT scans (upper) and bar graph (lower) demonstrating the measurement of the muscle CSA. Upper: Preoperative (a and c) and 1-year postoperative (b and d) images of the C5–6 level in two patients after MSLP (b) or non-MSLP (d). In a patient who underwent a conventional exposure (c and d), the ratio of the postoperative/pre-operative measurement ratios of the muscle CSA were 0.90 for splenius capitis (1), 0.76 for semispinalis capitis (2), 0.43 for semispinalis cervicis (3), and 0.58 for multifidus muscles (4). In a patient who underwent MSLP (a and b), the postoperative/preoperative ratios were 1.21 (1), 1.03 (2), 1.07 (3) and 0.87 (4) for the same muscle groups, respectively. Note the postoperative widening of the gap between the bilateral bellies of the trapezius in the non-MSLP patient. Lower: Bar graph comparing alterations in the muscle CSA ratios after surgery between the non-MSLP and MSLP groups. N.S = not significant; Semi Cap = semispinalis capitis; Semi Cerv = semispinalis cervicis; Spl Cap = splenius capitis. *p < 0.05; ** p < 0.005; and *** p < 0.00005.

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    Bar graph comparing the questionnaire scores related to postoperative neck pain and shoulder strain between the non-MSLP and MSLP groups. Scores were obtained at the 1-year follow-up visit. * p < 0.05; ** p < 0.01.

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