A recent collaboration of HSS spine surgeons and musculoskeletal radiologists sought to determine how diagnostic images could be used to help diagnose the severity of a common painful spinal condition known as cervical spondylotic myelopathy – or CSM.
The collaborators also wanted to know if pre-surgical imaging could help suggest which patients with CSM might most benefit from surgical treatment.
Problems that occur along the spine are medically known as myelopathies. As people age, one of the most common myelopathies happens in the cervical spine. Bones and discs that cushion and separate the vertebrae in the neck can degenerate, compressing the spinal cord, and causing weakness, numbness, inability to walk, bowel or bladder incontinence and other severe neurologic sequelae.
Surgery is a recognized treatment option to prevent progressive neurologic impairment. Surgeons may treat CSM with cervical decompression with or without spinal fusion. Decompression can be performed from either an anterior or posterior approach.
Despite the relatively high prevalence of CSM there has been a paucity of high-level clinical data on how MRI or x-ray studies can predict the severity of a patient’s CSM, or indicate potential outcomes from treatment.
In this large study of patients treated surgically for CSM, comparison of pre- and post-surgical radiographic images did reveal some consistent patterns of change among the patients, including improvement in the spinal alignment of those who improved after surgery. Data also suggested that imaging could be used to successfully indicate the severity of CSM. However, that severity would not suggest any likely outcome of surgery.
Previous observations had indicated that patients had a lower likelihood of beneficial recovery from surgery for CSM if intramedullary cord signal changes were found on specific MRIs. Data from this study supported that observation to be true.
Because of the large volume of patients at HSS, the research team could review the electronic medical records and radiographs of 254 patients who were surgically treated for CSM by three spine surgeons at the hospital. The patients included 70 females and 184 males. Mean age of the patients was 59.6. Their mean Body Mass Index was 28.4.
All the patients were treated by spinal fusion and decompression, with 212 patients receiving anterior cervical decompression and 42 treated from the posterior approach.
To assess the severity of the patients’ CSM both before and after surgery, two standard test scores were used – the Nurick and modified Japanese Orthopaedic Association (mJOA) scores. Since these tests are recognized as markers of disease severity, improvement in the scores would indicate degree of recovery following surgery.
Specific measurements from MRIs and x-rays were compared before and after surgery. Using standing lateral x-rays, the global cervical alignment of each patient’s spine was assessed and measured.
MRI reports from musculoskeletal radiologists were reviewed for comments on changes in the measurement of intramedullary cord signals on T2 weighted MRI studies. To further document pre- to post-surgical changes in the spinal cord and canal, fellowship-trained spine surgeons determined several measurements in specific areas both before and after surgery. Narrower diameters of the spinal cord and canal can indicate compressed areas that may be contributing to neurological dysfunction. If the diameters widen after surgery, this indicated adequate decompression and improvement of severity of CSM.
The areas measured were the diameters of the midsagittal antero-posterior spinal canal and cord, as well as the diameters of both the axial antero-posterior cord (APcord) and the medial-lateral cord (MLcord) cords. Using those two measurements, the compression ratio (CR) of the spinal cord was calculated as APcord/MLcord. CR is also an indication of CSM severity, reduced CR in the spinal cord would indicate reduced severity.
Comparing the Nurick and mJOA scores before and after surgery, showed that disease severity improved significantly after surgical treatment. Standing lateral x-rays taken both before and after surgery were available for 142 patients. Comparing the two sets of images, also showed that overall cervical alignment improved after surgery.
When comparing the measurements of the spinal cord and canal in the pre- and post-operative MRI studies available for review, improvements in CSM disease severity were found, suggesting these measurements taken by MRIs could be reliably used to indicate CSM severity.
After surgery, the diameters of the measured areas were not as narrow, indicating potential relief of compression. Specifically, the midsagittal antero-posterior diameter of the spinal canal, at the level of most compression found before surgery, improved from average 5.42 (±1.93) millimeters to 7.86 (±1.88) millimeters.
The CR also showed significant improvement before and after surgery. However, while before surgery, the CR was shown to correlate significantly with the mJOA scores, after surgery, improved mJOA scores did not correlate with changed CR measurements. These findings suggest CR can be used as an indicator of disease severity rather than the potential for surgical recovery.
Of that group of 99 patients, those who did not have intramedullary cord signal changes on their T2- weighted MRIs were more likely to benefit from surgery. No matter whether or not signal changes were seen on their T1-weighted MRIs, those patients with no intramedullary cord signal changes recovered more frequently to Nurick grade 0 after surgery than patients who did have intramedullary cord signal changes on their pre-surgical T2-weighted MRIs.
With a large set of data documenting significant improvement in disease severity when comparing pre- and post-surgical x-rays and MRIs, the HSS study does demonstrate the effectiveness of cervical decompression and fusion surgery for the treatment of CSM patients.
However, while diagnostic imaging does show reduction in CSM severity after treatment, so far there is no correlation between degree of severity before surgery and which patients most improve after surgery.
What the study does support with larger data is the previously observed reports that intramedullary cord signal changes can predict a lower likelihood of recovery following surgical treatment. This study serves as a foundation upon which to build further investigations, including additional data from prospective trials, that can help improve understanding of radiographic predictors of disease severity and surgical outcomes in patients with CSM.
Study presented by HSS at the 2013 Annual Meeting of the American Academy of Orthopedic Surgeons