Anterior cervical corpectomy for cervical spondylotic myelopathy ...

Journal of Clinical Neuroscience 13 (2006) 233–238 www.elsevier.com/locate/jocn

Clinical study

Anterior cervical corpectomy for cervical spondylotic myelopathy: Experience and surgical results in a series of 70 consecutive patients S. Chibbaro

b

a,*

, L. Benvenuti a, S. Carnesecchi a, M. Marsella b, F. Pulera` a, D. Serino a, R. Gagliardi a

a Department of Neurosurgery, Livorno City Hospital, Livorno, Italy Department of Neurosurgery, University of Nebraska Medical Centre, Omaha, Nebraska, USA

Received 6 December 2004; accepted 8 April 2005

Abstract Recently the debate over the management of cervical spondylotic myelopathy (CSM) has regained interest; more specifically whether treatment should be operative versus non-operative, raising the question about the real effectiveness of surgery in influencing the natural history of this pathology and about the choice of the most appropriate approach (anterior vs. posterior). The authors report a retrospective review of 70 consecutive patients who underwent elective anterior cervical corpectomy and fusion with iliac crest autograft or titanium mesh and placement of an anterior cervical plate for the treatment of CSM. The patients underwent pre-and postoperative evaluation, including history, and physical and neurological examination. Patients were also evaluated preand postoperatively using a modified version of the Japanese Orthopedics Association Scale (mJOA), which provides a fine semiquantitative graded evaluation of overall function. Upon discharge home, patients were followed for an average of 42 months (range, 12–63 months). Following an anterior cervical decompression of the spinal cord, 94.2% of patients improved their functional status and 5.8% were unchanged; the mean preoperative mJOA score of all patients was 12.2, the postoperative was 15.4 and the amelioration was also documented by neurophysiological studies which showed an increase in amplitude and decrease in latency of somatosensory evoked potentials and motor evoked potential in 47 patients (67%). Older age and longer duration of preoperative symptoms both were not associated with a lower postoperative mJOA score (p < 0.47, p < 0.29, respectively). Single versus multiple level decompression was not predictive of a lower postoperative mJOA score (p < 0.18). Preoperative spinal cord low signal intensity changes on T1-weighted MRI were related to a lower postoperative mJOA score (p < 0.05), whereas spinal cord high-signal intensity changes on T2-weighted MRI were related to a higher postoperative mJOA score (p < 0.01); finally a lower preoperative mJOA score was highly predictive of a lower postoperative mJOA score (p < 0.0005). Anterior cervical corpectomy and fusion for CSM appears to be an effective procedure with a more favorable neurological improvement when compared to posterior decompressive laminectomy, minimally invasive procedures or non-surgical treatment. It is also a safe procedure even in the elderly population, with low morbidity and the potential for permanent spinal cord decompression and excellent bone stability. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Cervical myelopathy; Anterior corpectomy; Bone graft; Titanium mesh

1. Introduction The clinical syndrome of cervical spondylotic myelopathy (CSM) was first described in the early 1950s.1 *

Corresponding author. Present address: Via del Muraglione 2, 34100, Trieste (Italy). Tel.: +39 040 3994093; fax: +39 040 3994285. E-mail address: [email protected] (S. Chibbaro). 0967-5868/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2005.04.011

The surgical management of CSM via an anterior approach, introduced by Smith and Robinson and subsequently by Cloward, although still widely adopted, is not universally accepted as it is still controversial whether this is the best management choice. Indeed, some previous studies describing this technique, have reported postoperative improvement, whereas others have documented no clinical change and, in some studies, even deterioration. These last

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S. Chibbaro et al. / Journal of Clinical Neuroscience 13 (2006) 233–238

studies have raised concerns about the effectiveness of an anterior approach in influencing the natural history of this disease.2,3 It is our opinion, however, that some of these studies are not representative for the following reasons: small size of the population studied; clinical heterogeneity; variability of symptoms ranging from pure neck pain to severe radiculopathy with or without myelopathy; unclear preoperative neurological status and imprecise surgical indications.4 We feel that many variables negatively influenced the populations studied, therefore no accurate patient stratification can be made.5–7 Recently, debate over the management of CSM has regained interest; specifically, over operative versus nonoperative treatment and about the choice of the most appropriate approach (anterior vs. posterior).8–14 A thorough review of the current literature points to a number of factors affecting the postoperative outcome; these include: 1. age 2. duration of symptoms at presentation 3. preoperative neurological status 4. T1-weighted and T2-weighted MRI signal intensity changes within the cord indicating cord damage.15,16 As any combination of these factors may be predictive of the postoperative outcome, documenting them preoperatively is crucial for surgical decision-making. Our aim is to clarify the efficacy and safety of anterior cervical decompression in improving the functional status of patients with CSM and in influencing the natural history of the disease. To this purpose we reviewed the results obtained at the neurosurgery department of Livorno City Hospital (Italy) from October 1997 to June 2002. Outcome, fusion rates, procedure-related complications, instrumentation failure and prognostic factors are assessed, along with pathophysiology and management of CSM. Relevant literature is also reviewed. 2. Methods and materials We included in our study 70 patients (47 males, 23 females) out of a total of 77 electively treated. Seven patients were excluded because 12-month follow-up was not available. The age range was 29–76 years (average age, 57 years). These patients were treated consecutively in our institution, in a period of 56 months by the same senior surgeon. To be included, the patient matched at least one of the following criteria: a. Clinical evidence of cervical myelopathy as determined by spasticity, hyperreflexia, ankle clonus, positive Babinski and/or positive Hoffman sign. b. Sensory deficits determined by clinical exam and confirmed by neurophysiological studies. c. Motor deficits including extremity weakness, muscle atrophy, paraparesis or frank quadriparesis.

d. Sphincter disturbances not explained otherwise. e. A minimum of two levels, MRI documented, of cervical disc degenerative disease. Exclusion criteria included: a. Pure cervical radicular pain. b. Decreased reflexes. c. A soft disk prolapse documented with MRI within 6 months. d. A pure radicular motor deficit. e. Follow-up shorter than 12 months. Patients’ neurological and general functions were assessed preoperatively using a modified version of the Japanese Orthopedics Association Scale (mJOA) (Table 1). According to mJOA, we stratified our patients in 4 groups depending on the severity of their neurological deficits: Group I (score 0–4) with very severe disability; no patients were in this group. Group II (score 5–9) included 15 patients (21.4%) whose disability was severe. Group III (score 10–13) included 41 patients (58.6%) with moderate disability. Group IV (score 14–17) included 14 patients (20%) with mild disability. All patients had pre- and postoperative plain cervical Xrays as well as postoperative flexion-extension views which

Table 1 Modified Japanese Orthopaedic Association Scalea I. Motor dysfunction of the upper extremity 0: Unable to feed oneself 1: Unable to use knife and fork; able to eat with a spoon 2: Able to use knife and fork with much difficulty 3: Able to use knife and fork with slight difficulty 4: None II. Motor dysfunction of the lower extremity 0: Unable to walk 1: Can walk on flat floor with walking aid 2: Can walk up and/or down stairs with handrail 3: Lack of stability and smooth gait 4: None III. Sensory deficit 0: Upper extremity, severe sensory loss or pain 1: Upper extremity, mild sensory loss 2: Upper extremity, none 0–2: Lower extremity 0–2: Trunk IV. Sphincter dysfunction 0: Unable to void 1: Marked difficulty in micturition (retention) 2: Difficulty in micturition (frequency, hesitation) 3: None a

A normal patient scores 17 points.


were taken at each follow up, in order to assess the degree of fusion and the stability of the construct and were independently reviewed using the following criteria: documentation of bony trabeculation and absence of bony lucency across the graft and/or change in strut height over time for static investigation; absence of kyphotic angulation and less than 4 mm of interbody translation on dynamic investigation. All patients received preoperative cervical MRI scan. In addition, 30 selected cases (42.9%) underwent a CT scan with bony windows of the specific level planned to be decompressed (to better define the anatomy and extent of cord compression which could not be determined with certainty by MRI). All patients had pre- and postoperative somatosensory evoked potentials (SSEP) and motor evoked potentials (MEP), 25 (35.7%) underwent preoperative EMG. After discharge, patients returned for follow-up conducted by the same two physicians who were part of the surgical team, after 6 weeks, 3 months, 6 months and then every year thereafter when applicable. To evaluate preoperative variables and their relationship with outcome in our study group a multivariate analysis using the final postoperative mJOA scores and the change between pre- and postoperative scores was conducted. 2.1. Operative management All patients underwent a standard microsurgical anterior approach regardless of whether one or more levels were to be decompressed. The standard surgical procedure included a corpectomy, removal of osteophytes and degenerated disk and opening of the posterior longitudinal ligament, harvest from the iliac crest of an adequate size graft and its placement in the anterior trench as well as positioning of an anterior plate (AtlantisÒ Medtronic, Minneapolis, MN); more recently the choice of graft has switched from autograft to titanium mesh (in the last five patients) (PyrameshÒ Medtronic). This is to avoid the potential complications related to graft collection (including infection, haematoma and the rare lateral femoro-cutaneous nerve meralgia). Twenty-eight patients (40%) were monitored intra-operatively with SSEPs, when available, by a neurophysiologist. In four selected cases the surgical procedure was performed with the aid of image guided virtual fluoroscopy (Stealth StationÒ, Medtronic) as the interbody spaces were difficult to detect in the preoperative images due to spontaneous vertebral body fusion. 3. Results The mean preoperative duration of symptoms was 13.4 months, (range 4–120 months). In all cases symptoms and neurological status worsened progressively, of course with variable patterns and times of evolution. However, no patient experienced significant spontaneous improvement in the course of their disease. The most common preoperative symptoms were (Table 2): deficit of motor function in the

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upper extremities in 34 patients (48.6%), particularly, clumsiness of the hands in 31; (44.3%) gait disturbances in 29 (41.4%); upper extremity sensory symptom in 42 (60%); lower extremity sensory symptoms in 18 (25.7%); sexual dysfunction in three (4.3%); and bowel/bladder dysfunction in seven (10%). The most common preoperative signs and deficits were: hyperreflexia in 46 patients (65.7%), spastic gait in 29 (41.4%) and wasting of the intrinsic muscles of the hand in 26 (37.1%). A total of 93 levels were decompressed in 70 patients (C3–C4: 9; C4–C5: 18; C5–C6: 40; C6–C7: 25; C7–T1: 1). Fifty-four patients received a single level decompression, 11 a double level decompression, five a triple level decompression. After anterior cervical decompression, function was evaluated and compared to the preoperative status using the mJOA scale. The mean follow-up time was 42 months, ranging between 12–63 months. It is worth noting that the mean preoperative mJOA score of all patients was 12.2, the postoperative was 15.4. Eleven patients in preoperative Group II, with an mJOA score of 8–9, improved to 10, moving into the next group; eight patients in preoperative Group III, having an mJOA score of 10, improved to 13, remaining in the same group. On the other hand, the remaining 32, having an mJOA of 12–13, improved to 15–17, moving into the higher group. Fourteen patients in preoperative Group IV, having an mJOA score of 14– 15, all improved to 17, although they remained in the same group (Table 3). Summarising, 65/69 (94.2%) patients improved their functional status regardless of whether they moved into a higher mJOA group. Their functional improvement was also demonstrated by postoperative neurophysiological studies which showed an increase of amplitude and decrease of latency of SSEP and MEP in 47 patients (67%).17 By using serial cervical X-rays in the postoperative period, a radiological fusion rate of 100% has also been documented; a solid fusion was seen in most patients after 12 weeks, in four it was documented after 16 weeks. No instrumentation failure was detected. In our study three patients developed complications; two were related to the surgical procedure. One patient developed an incisional haematoma and underwent emergency evacuation at the Table 2 Preoperative symptoms and signs Symptom

No. of patients (%)

Gait disturbances Deficit of upper extremity motor function Clumsiness of the hands Upper extremity sensory complaints Lower extremity sensory symptoms Sexual dysfunction Bowel/bladder dysfunction

29 (41.4%) 34 (48.6%) 31 (44.3%) 42 (60%) 18 (25.7%) 3 (4.3%) 7 (10%)

Sign Spastic gait Hyperreflexia Hand wasting

29 (41.4%) 46 (65.7%) 26 (37.1%)

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Table 3 Pre- and postoperative function evaluation using the modified Japanese Orthopedics Association Scale (mJOA) Group

Preoperative mJOA/Number in group

Improveda

Unchangeda

Worsened

Postoperative mJOA

I (0–4) score II (5–9) score III (10–13) score IV (14–17) score

0 15 (21.4%) 41 (58.6%) 14 (20%)

0 11/15 32/41 0

0 4/15 8/41 14/14

0 0 0 0

– 4 (5.8%) 19 (27.5%) 46 (66.7%)

a A patient is considered improved only if postoperatively they moved into a higher group. Patients defined as unchanged actually improved their score, but remained in the same group. (See results section for more details.)

bedside. Another patient developed a wound infection, successfully treated with intravenous antibiotics. A third patient died 3 days after surgery following an episode of acute pancreatitis (despite the fact he was medically cleared), thus leaving 69 patients available for long-term follow-up. The analysis of our series demonstrated that although the majority of patients improved, some of them scored better than others. We therefore evaluated some preoperative variables to determine a relationship with outcome. For this purpose we performed a multivariate analysis of the data considering the final postoperative mJOA scores and also the change between preoperative and postoperative scores. In this model, analysing the final postoperative mJOA score, older age and longer duration of preoperative symptoms both were not associated with a lower postoperative mJOA score (p < 0.47, p < 0.29). The number of levels (single versus multiple) decompressed did not have any significant impact on the postoperative functional recovery and was not predictive of a lower mJOA score (p < 0.18). MRI changes detected preoperatively within the cord had, on the contrary, a significant prognostic impact; indeed most patients with low-signal intensity change on their noncontrast MRI T1-weighted sequences had a lower postoperative mJOA score (p < 0.05), whereas patients with high-signal intensity on their non-contrast MRI T2weighted sequences had a higher mJOA score (p < 0.01); additionally a lower preoperative mJOA score was highly predictive of a lower postoperative mJOA score (p < 0.0005). 4. Discussion It is our opinion that, generally speaking, a successful treatment is based on a clear understanding of the pathophysiology and natural history of the disease being treated.3,18,19 In this way, appropriate management can be planned, known complications can be anticipated20,21 and, if a clinical study is entertained, then reliable data can be obtained. Decompressive surgery for CSM has been the treatment of choice for many patients. Neurological improvement has been documented following either anterior or posterior approach. The poorer long-term results following cervical laminectomy reported in the literature may be due to changes in the biomechanics of the cervical spine2,22 as this procedure may be ex-

tended across several levels and this may create joint instability.23 On the other hand, the use of an anterior approach, in general, cannot be extended beyond three levels.11,24–30 Considering minimally invasive techniques, it is not possible to achieve a generous decompression of the spinal canal through a small foraminotomy hole despite preserving spinal stability. This technique also has a long and difficult learning curve and has to be mastered with cadaveric dissection, limiting its application currently to a few centres.31 From a clinical standpoint, despite the fact that many reports show that symptoms of CSM tend to stabilise over time,1,3 we found the opposite to be true; in fact, in our series, over time the majority of our patients experienced some degree of deterioration, particularly gait worsening. In any case we have never observed spontaneous improvement. Given this important observation, we believe that spontaneous stabilisation of neurological status should be considered the exception rather than the rule. Since the goal of our study was to demonstrate the effectiveness of an anterior cervical approach for the management of patients with cervical myelopathy, we included only patients who presented with symptoms exclusively related to spinal cord compression. It is noteworthy to mention that there are reports of electromyographyc studies32 in patients with CSM showing alterations of the muscle groups under C7 and T1 motor root control. These alterations were caused by anterior horn cell loss (as documented by post mortem). Some authors postulate that this loss may be due to spondylotic obstruction of cord venous drainage.33 As cord venous flow runs in a rostral direction34 the anterior horn cells most likely to be affected are those at the C4–C5 and C5–C6 level, which are the most common sites of compression. With regard to the lower extremities, patients in our series experienced weakness in proximal muscles. Although gait disturbance was one of the most common presenting signs, the majority of patients complained about their spasticity rather than the weakness. In our series, postoperative residual spasticity was also a cause of gait dysfunction, more than muscle weakness; indeed motor function globally improved in most patients. Ebersold et al. in 19954 reported a series of 51 patients who had undergone cervical laminectomy for CSM: 19 patients (37.3%) improved, 19 (37.3%) worsened and 13 were unchanged. Nurick in 19723 reported slightly better results: 56% of patients who had undergone cervical laminectomy


improved, 19% worsened and 25% were unchanged. Isu et al. in 199735, describing a new graft technique for anterior cervical decompression, reported excellent results; all except one of 40 patients improved. Emery et al. in 199836 reported a series of 108 patients, pointing out that pseudarthrosis and/or other complications occur mostly in patients undergoing multivel discectomy and/or with a history of one or more previous operative procedures. Groff et al. in 200337 reported excellent results from a series of partial corpectomy, with a 95.8% fusion rate and a higher non-union rate in smokers, although it was a heterogeneous group of patients including degenerative, trauma and tumor disease. Koc et al. in 200438 reported a series of 26 patients undergoing oblique corpectomy with good to excellent results in 76.9% for myelopathy and 84% for radiculopathy, relating the degree of postoperative myelopathy recovery to age and severity of preoperative deficit. Finally, Jho et al. in 200231, using an anterior microforaminotomy, reported good to excellent surgical results in 80–90% of patients, although these last two were small series. In our study 94.2% of patients improved their functional status, 5.8% were unchanged and none worsened, demonstrating that successful treatment is based on rigorous patient selection and clear surgical indication, which allows for planning best management. Finally, in our study we also considered prognostic factors. We found that older age and longer preoperative symptom duration were not associated with a lower postoperative mJOA score; and the number of levels decompressed (single vs. multiple) was not predictive of a lower postoperative mJOA score. Interestingly cord T1-weighted low-signal intensity changes detected on the preoperative MRI were related to a lower postoperative mJOA score. On the other hand cord high-signal intensity changes on T2-weighted MRI were related to a higher mJOA score with a significant and stable functional improvement. We also found that a lower preoperative mJOA score was highly predictive of a lower postoperative mJOA score. 5. Conclusion Our study documents that anterior cervical corpectomy and fusion for CSM appears to be a more effective procedure with a more favorable neurological outcome when compared to posterior decompressive laminectomy, minimally invasive procedures and/or non-surgical treatment. It is also a safe procedure in the elderly,25,28,29,39 carrying low morbidity with the potential of permanent spinal cord decompression and excellent stability. In our study population we found no statistical evidence that prognostic factors such as age and duration of preoperative symptoms affect the outcome as reported in the literature. However, this study has shown that severity of preoperative dysfunction and MRI signal change within the spinal cord can be considered as unfavorable predictive factors.

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