Current classification systems

In 1972, Dr Nurick described his grading scale for spinal cord disorder associated with cervical spondylosis [5]. The Nurick classification is graded from 0 to 5 and is based on the patient’s ability to ambulate and to work. This classification system has been referred to countless times in the literature and is a reliable, easily reproducible method of assessing myelopathy severity. One minor critique of this classification is the assessment of the patient’s ability to engage in full employment. “Fully employable” may include a broad spectrum of neurological function, depending on the work.

In 1976, Japanese Orthopedic Association (JOA) presented a scoring system to assess myelopathy. This system quantifies motor function in the arms and legs, sensation, and bladder function. This scoring system has also been used extensively in the literature [6]; however, its weakness is that it is specific towards the Asian population. Fine motor function is graded upon a patient’s ability to use chopsticks and the use of the JOA score in a non-Asian community will likely provide skewed results.

The Ranawat neurological classification was originally presented describing rheumatoid patients [7]. This also has been widely used in studying rheumatoid patients, but difficulty can be encountered when differentiating a Grade II and Grade IIIA patient. In this classification scheme a Grade II rheumatoid has subjective weakness with hyper-reflexia and dysesthesia. A Grade III rheumatoid has objective weakness and long tract signs, but is still able to walk. Rheumatoid arthritis has numerous other musculoskeletal targets and it can be difficult to ascertain if weakness is from peripheral arthritis or spinal arthritis.

Summary

Each classification system has its own strengths and weaknesses. In regard to directing treatment, this is generally not problematic as the large majority of symptomatic myelopaths are advised to undergo surgical intervention. The primary goal of surgery in myelopaths is to halt progression of neurological deterioration and neurological recovery, while ideal, is never guaranteed. Our ability to predict which patients recover neurologically and to what extent is inexact, at best. Studies have demonstrated that less severe myelopaths are more likely to gain neurological recovery than severe myelopaths [1]. While clinical presentation is important in assessing severity, a classification that includes additional factors such as duration of symptoms and radiographic signal changes in the cord maybe useful in predicting patient outcomes.

Current classification systems

The most commonly used dimension to assess cervical stenosis is the midsagittal canal diameter. Prior to the advent of advanced imaging, this measurement was assessed on standard lateral cervical spine x-rays. Edwards and La Rocca evaluated the cervical spine of sixty-three patients and correlated measurements to clinical symptoms [2]. Based on their study, they predicted that patients with a: 1) sagittal canal diameter of greater than 17 mm were asymptomatic, 2) a canal diameter of 13 mm to 17 mm were not prone to myelopathy, but prone to cervical spondylosis, 3) a canal diameter of 10mm to 13 mm were premyelopathic, and 4) a canal diameter of less than 10 mm were myelopathic. Other studies have supported these numbers. Boden et al, in a landmark study evaluating the cervical spine in rheumatoid patients, concluded that a patient with a space available for the cord, or a canal diameter of 14 mm or less was at risk for neurological compromise, and surgical stabilization was recommended [1].

The measurements from the aforementioned studies were based on x-rays. The dimensions seen on a x-ray are dependent upon how a x-ray is performed. Changes in the distance from the patient to the film, the patient to the beam, or the beam to the film can cause magnification of varying degrees, thus making direct measurement inconsistent. For these reasons, Pavlov et al devised a ratio to assess cervical stenosis [4]. Normal was defined as a ratio of the sagittal canal diameter to the sagittal vertebral body diameter (as measured on a lateral cervical spine x-ray) greater than 1.0. A ratio of less than 0.8 was indicative of stenosis. While commonly referenced, numerous studies have questioned the accuracy of the ratio [8–11].

Advanced imaging allows for a more accurate assessment of cervical canal diameter. A direct assessment of bony dimensions can be assessed with CT, and the extent of stenosis can be further evaluated with a concurrent myelogram. MRI allows for direct visualization of cord morphology, displacement, the absence or presence cerebrospinal fluid, and myelomalacia. These findings, in correlation with clinical presentation, provide important information to the clinician.

To date, there has been one attempt to classify cervical stenosis based on MRI findings. Muhle et al evaluated eighty one patients with cervical spondylosis using kinematic MRI [12]. Cervical spines were evaluated in the neutral, flexed, and extended position. A Grade 0 stenosis showed no sign of subarachnoid space narrowing. Grade 1 stenosis was defined as “partial obliteration of the anterior or posterior subarachnoid space”. Grade 2 was defined as “complete obliteration” of the subarachnoid space, and Grade 3 was defined as anterior or posterior cord impingement. This study found that significant cord impingement was observed in extension 27% of the time and 5% of the time in flexion.

Summary

While cervical stenosis is almost always present with compressive myelopathy, cervical stenosis has been commonly observed in the absence of symptoms [13, 14]. The presence of “subarachnoid obliteration” or even mild myelomalacia may not necessarily translate into clinical symptoms. The significance of asymptomatic stenosis has been debated and discussed. Some surgeons prefer to preemptively decompress and stabilize, while others prefer to observe periodically. To date, there have been no prospective natural history studies in the patient population with asymptomatic stenosis.

Devising a useful classification scheme for cervical stenosis is challenging. The presence of asymptomatic stenosis does not necessarily allow for correlation of measurements of MRI findings to symptoms. In addition, reference measurement studies were performed on x-rays, which were subject to various degrees of magnification. Furthermore, the use of measurements may not be the most accurate way to assess stenosis. Studies have shown that there is substantial variation in canal and cord diameters between gender and race. A 12 mm canal may clinically present differently in a large male athlete than in a diminutive female.

The decision for surgical intervention for symptomatic cervical spine stenosis is based on both clinical presentation and correlating radiographic appearance. At this time a comprehensive classification system assessing the clinical and radiographic severity of symptomatic cervical spine stenosis does not exist. While such a classification system is not likely to alter decision making regarding the need for surgical intervention, it may provide further insight regarding patient outcomes and its relationship to preoperative severity (both clinical and radiographical).

SCALE DESCRIPTION

Myelopathy severity is assessed by 10 items relating to the following functions:

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  Rising from chair and bed (6 points)

  
  
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  Eating (6 points)

  
  
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  Walking (6 points)

  
  
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  Hygiene (6 points)

  
  
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  Grip (6 points)

Each item scored on a scale with a minimum score of 0 and a maximum score of 3.

Interpretation:

All items summed and converted to a percentage.

Maximum score: 100 points

Minimum score: 0 points

The higher the score, the greater the severity.

METHODOLOGY

Predictive validity

No reliability studies were identified

Reliability

References

Casey AT, Bland JM, Crockard HA (1996) Development of a functional scoring system for rheumatoid arthritis patients with cervical myelopathy. Ann Rheum Dis; 55:901–906.