Cervical spondylotic myelopathy (CSM), a degenerative spine disease, is the most common cause of spinal cord dysfunction in patients older than 55 years. A wide range of symptoms may be seen including impaired gait, numb hands, and weakness. Surgical intervention has proven to be an effective treatment option for patients with mild-to-severe CSM. It is important to determine which clinical variables can predict surgical outcomes to manage patient expectations.

“Although many previous studies have analyzed important predictors of outcomes, evidence in the form of high-quality, prospective studies using validated outcome measures is lacking,” said Lindsay Tetreault, HBSc, coauthor of a study presented at the 2012 annual meeting of the Cervical Spine Research Society last December.

Ms. Tetreault, lead author Michael Fehlings, MD, PhD, FRCSC, and other investigators of the CSM-North American study formulated a clinical prediction rule to determine surgical outcomes in CSM patients using data from a prospective, multicenter study. According to the results, valuable predictors include patient age, duration of symptoms, baseline severity score, psychological comorbidities, impaired gait, and smoking status.

Collecting data
The researchers analyzed data from 272 patients (160 males, 112 females; mean age: 56.5 years) enrolled in the CSM-North America trial from 12 different North American sites (December 2005 to September 2007). Patients were asked to participate in this study, provided they satisfied the following criteria:

• Older than 18 years
• Presenting with symptomatic CSM, with at least one clinical sign of myelopathy
• No previous surgery

“All patients received surgical decompression and fusion, with the approach determined by the attending surgeon,” said Ms. Tetreault.

Researchers collected extensive data at baseline, as well as at 6 months, 12 months, and 24 months after surgery. They evaluated patients’ functional status using the modified Japanese Orthopaedic Association (mJOA) scale. Each patient also had a baseline and follow-up magnetic resonance imaging scan.

In addition, the investigators collected patient demographic data, symptomatology, and medical history. The study’s follow-up rate was 80 percent.

Predictors and results
After performing logistic regression, the investigators defined a successful surgical outcome as having an mJOA score greater than or equal to 16, while a failed outcome was defined as an mJOA score less than 16.

The important predictors for the final model were chosen based on statistical findings, literature support, and author consensus. The final logistic regression model consisted of the following six predictors:

• Age (P = 0.0057)
• Duration of symptoms (P = 0.023)
• Smoking status (P = 0.052)
• Impairment of gait (P = 0.036)
• Psychological comorbidities (P = 0.0034)
• Baseline severity score (P = 0.0018)

“We found that the odds of a successful outcome were 2.66 times better when a patient did not have an impaired gait, compared to when a patient did have that symptom,” said Ms. Tetreault. “In addition, odds of a successful outcome were 1.02 times greater for every square millimeter increase in transverse area, and 1.22 times greater for every 1 point increase in baseline mJOA.”

The following factors decreased the odds of a successful surgical outcome:

• Psychological comorbidities (67 percent decrease)
• Longer duration of patient symptoms (22 percent decrease)
• Every 1-year increase in age (3 percent decrease)
• Smoking (50 percent decrease)
• Ms. Tetreault noted the model had “excellent discriminative ability.”

Drawing conclusions
“This study confirms that severe, long-standing compression in the spinal cord leads to irreversible damage, as suggested by the significance of baseline severity scores and duration of symptoms,” said Ms. Tetreault.

She also noted that “despite controversy in the literature, age was found to be an important predictor of outcome. Additionally, smoking leads to an unfavorable outcome.”

Finally, she asserted that “we can conclude that certain comorbidities such as psychological disorders and symptoms such as impaired gait do carry predictive value.”

This study was sponsored by AO Spine North America.

Dr. Fehlings and Ms. Tetreault’s coauthors on “A Clinical Prediction Rule to Determine Outcomes in Patients with Cervical Spondylotic Myelopathy Undergoing Surgical Treatment: Data from the Prospective, Multicentre AOSpine North America CSM Study” are Branko Kopjar, MD; Sangwook Tim Yoon, MD; Paul M. Arnold, MD, FACS; Eric Massicotte, MD; and Alexander R. Vaccaro, MD, PhD.

Disclosures: Dr. Fehlings—DePuy, A Johnson & Johnson Company; Covidien; Synthes; Bioaxone; Depuy Spine. Ms. Tetreault—no conflicts. Drs. Kopjar and Massicotte—no information available. Dr. Yoon—Meditech; Biomet; Stryker; Phygen; Meditech Advisors; Medyssey; SpineNet; The Spine Journal; Journal of Orthopaedic Research; Journal of Bone and Joint Surgery–American; Spine; International Society for the Study of the Lumbar Spine; North American Spine Society (NASS); Korean American Spine Society. Dr. Arnold—Stryker; K2; Integra; Medtronic Sofamor Danek; Synthes; Smith & Nephew; Medtronic; Orthofix, Inc.; Cerapedics; LANX; ATRM Johnson & Johnson; BHR Pharma; Alphatec Spine; Journal of Neurosurgery; Journal of Spinal Disorders & Techniques; The Spine Journal; Spine; AO Spine North America; American Association of Neurological Surgeons/Congress of Neurological Surgeons Joint Section on Neurotrauma & Critical Care; NASS Ethics. Dr. Vaccaro—Aesculap/B.Braun; DePuy, A Johnson & Johnson Company; Globus Medical; Medtronic Sofamor Danek; Stout Medical; Applied Spinal Intellectual Properties; Progressive Spinal Technologies; Advanced Spinal Intellectual Properties; Computational Biodynamics; Paradigm Spine; K2M; Replication Medica; Spinology; Spine Medica; Orthovita; Vertiflex; Small Bone Technologies; NeuCore; Crosscurrent; Syndicom; In Vivo; Flagship Surgical; Location Based Intelligence; Gamma Spine; Spinicity; AO North America; Cerapeutics; Nuvasive; Elsevier; Thieme; Jaypee; Spine; J. Neurosurgery Spine; Pan Arab J. Neurosurgery; European Spine Journal; Cervical Spine Research Society; NASS.

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org

Bottom Line

• As noted by the investigators, this is the first prospective, multicenter study of its size to analyze important predictors of surgical outcomes in patients with cervical spondylotic myelopathy (CSM).
• Based on statistical findings and other clinical significance, investigators created a model consisting of six predictors: age, duration of symptoms, smoking status, impairment of gait, psychological comorbidities, and baseline severity score.
• Investigators concluded that severe and long-standing compression in the spinal cord leads to irreversible damage, and that age, smoking status, and certain comorbidities are also important outcome predictors.