For Cervical Myelopathy from Spondylosis, Which Surgical Approach is Better — Anterior or Posterior?

Abstract & Commentary

By Michael S. Virk, MD, PhD, and Roger Härtl, MD. Dr. Virk is Resident in Neurosurgery, Weill Cornell Medical College. Dr. Härtl is Leonard and Fleur Harlan Clinical Scholar in Neurological Surgery, Associate Professor, Neurological Surgery, Weill Cornell Medical College. Dr. Virk reports reports no financial relationships relevant to this field of study. Dr. Härtl reports that he is a consultant for Synthes and Brainlab.

Synopsis: In this non-randomized comparative trial, dorsal (posterior) decompressive spinal surgery resulted in longer lengths of stay and higher costs compared to ventral (anterior) surgery.

Source: Ghogawala Z, et al. Comparative effectiveness of ventral vs dorsal surgery for cervical spondylotic myelopathy. Neurosurgery 2011;68:622-631.

Cervical spondylosis is the most common non-trau- matic cause of myelopathy in the cervical spine, and cervical spondylotic myelopathy (CSM) is the most frequent cause of spinal cord dysfunction.1-3 In 2000, there were 112,400 procedures performed to address degenerative cervical spine disease, a two-fold increase since 1990.4 The number of patients admitted with CSM doubled between 1993-2002 and 42% of these people underwent spinal fusion, which represents a seven-fold increase over this period.5 Hospital charges for these procedures exceeded $2 billion in 2000, representing an inflation-adjusted increase of 48%.4 The incidence of degenerative cervical spine disease increases with age, and as our population ages, so too will surgical treatment and hospital charges. As government and private insurers seek outcomes data and comparative effectiveness studies to use value as the primary measure driving reimbursement, it is of increasing importance to understand which procedures best treat CSM while minimizing complications and cost. Ghogawala et al reported the results of a non-randomized, prospective clinical pilot study comparing ventral and dorsal surgery for treating CSM.6 Data from such trials is the foundation of evidenced-based practice and guides clinical decision-making. However, study design is challenging and the constraints inherent to these kinds of studies must be understood.

In this pilot investigation, 50 patients were enrolled at seven sites over 2 years (2007-09) with clinical assessments obtained pre-operatively and at 3-month, 6-month, and 1-year intervals post-operatively. A panel of 14 surgeons reviewed each patient's imaging and individually confirmed or rejected eligibility for either ventral (anterior cervical discectomy and fusion) or dorsal (laminectomy with posterior instrumentation and fusion) approach. If a majority of panel surgeons agreed, the case was considered eligible for enrollment. The treating surgeon then met with the patient and together they made the final decision regarding surgical approach. There were two significant differences between the groups. First, patients undergoing dorsal surgery had more severe myelopathy as measured by the Japanese Orthopedic Association (mJOA) score (11.6 vs 13.4; P = 0.03). Second, dorsal surgery was performed on more vertebral levels than ventral surgery (3.1 vs 2.6; P < 0.001). These differences prohibit direct comparison between the two groups and indicate that the decision to use one surgical approach vs the other was not random. Although both groups showed improvement in the mJOA scores, there was no difference in the amount of improvement when adjusting for baseline. The 30-day complication rate was not significantly different for dorsal or ventral approaches (13.6% vs 17.9%). However, the length of stay was significantly longer for the dorsal approach compared to ventral approach (4.0 vs 2.6; P < 0.01), and general health-related quality of life at 1 year improved significantly in the ventral group compared to the dorsal group on 1 of 2 measures (SF 36 Physical Component Summary vs EuroQol-5D). Finally, the mean unadjusted costs were lower for the ventral vs dorsal approach ($19,245 vs $29,465, P = 0.005). Given the difference in baseline myelopathy as assessed by the mJOA and the number of levels addressed between the two groups, drawing conclusions from these results is not possible.

Commentary

The goals of treating CSM include spinal cord decompression, spine stabilization, restoring alignment or sagittal balance, and minimizing the potential for further degeneration. Despite being grouped into a single diagnosis, each CSM patient presents with unique pathology. For example, disc-osteophyte complexes and ossification of the posterior longitudinal ligament contribute to anterior compression while hypertrophy or buckling of the ligamentum flavum narrows the spinal canal posteriorly. Subluxation and straightening or kyphosis of the cervical spine further contributes to narrowing of the canal. Finally, congenital cervical stenosis diminishes the capacity of any patient to accommodate such degenerative changes and is another independent factor contributing to CSM.

Different surgical approaches vary considerably in their ability to address different etiologies and must be selected appropriately. Primary surgical management of CSM includes anterior cervical discectomy and fusion (ACDF), corpectomy and fusion, laminoplasty, laminectomy alone, and laminectomy with posterior instrumentation and fusion. Additionally, in some cases, a combination of procedures — anterior and posterior — may be required to most effectively treat CSM. For example, corpectomy as well as laminectomy with posterior fusion are most appropriate in cases involving anterior and posterior disease with kyphotic deformity. Restoration of lordosis is important to create sagittal balance by shifting the weight-bearing axis posteriorly and serves to open the spinal canal as well as to slow the dynamic process of degenerative progression. While cord decompression is required to halt ischemic changes thought to underlie myelopathy, biomechanical considerations must be addressed for long-term pain control and prevention of future degenerative change. In addition to CSM etiology, factors such as patient age, medical comorbidities, and number of involved segments all must be incorporated into the decision-making algorithm when selecting the appropriate procedure.

References

1. Baron EM, et al. Cervical spondylotic myelopathy: A brief review of its pathophysiology, clinical course, and diagnosis. Neurosurgery 2007;60:S35-S41.

2. Cusick JE. Pathophysiology and treatment of cervical spondylotic myelopathy. Clin Neurosurg 1991;37:661-681.

3. Fehlings MG, Skaf G. A review of the pathophysiology of cervical spondylotic myelopathy with insights for potential novel mechanisms drawn from traumatic spinal cord injury. Spine 1998;20;2730-2737.

4. Patil PG, et al. National trends in surgical procedures for degenerative cervical spine disease: 1990-2000. Neurosurgery 2005;57:753-758.

5. Lad SP, et al. National trends in spinal fusion for cervical spondylotic myelopathy. Surg Neurol 2009;71:66-69.

6. Ghogawala Z, et al. Comparative effectiveness of ventral vs dorsal surgery for cervical spondylotic myelopathy. Neurosurg 2011;68:622-632.