Subjects:
A total of 47 patients with incomplete cervical SCI and 34 healthy subjects were analyzed retrospectively in this study. In the present study, seventeen patients with cervical SCI underwent early surgical treatment (≤ 72 hours), and the other 30 patients underwent delayed surgical treatment (> 72 hours) (Table 1). All subjects in cervical SCI patient group were recruited in SongJiang Hospital from December 2015 to June 2017. The study protocol was approved by Human Ethics Committees (Shanghai Songjiang District Central Hospital, KYLL2015-263). All subjects gave informed consent.
The subjects in normal control group were chosen based on the inclusion and exclusion criteria published previously [5]. The inclusion criteria for cervical SCI patients includes (1) a clear history of trauma; (2) different degrees of sensory and motor impairments in both upper limbs and/or the lower limbs with a variable effect on bladder function; (3) magnetic resonance imaging (MRI) and/or Computed tomography (CT) demonstrating SCI at the cervical segment without the injuries in the level of thoracic and lumbar spine injuries. The exclusion criteria for cervical SCI patients includes previous spinal surgery, polyneuropathies, radiculopathies, plexopathies, focal neuropathies, muscle disorders, diabetes, diseases of the central nervous system, syringomyelia, spinal cord tumour/inflammation/infection, spinal deformities and severe degenerative diseases of thoracic and lumbar segments.
Table 1:Characteristics of patients with cervical SCI in both surgical treatment groups
|
|
Early surgical treatment group
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Delayed surgical treatment group
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Number of subjects
|
17
|
30
|
Age range (years)
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45.0 ± 12.2
|
47.4 ± 13.1
|
Height range (cm)
|
164.7 ± 8.9
|
165.9 ± 9.2
|
Gender (Male vs. Female)
|
12 vs. 5
|
24 vs. 6
|
Time from injury to surgery (days)
|
1.9 ± 0.7
|
17.2 ± 7.9
|
Severity of SCI
|
ASIA B
|
2/17 (11.8%)
|
2/30 (6.7%)
|
ASIA C
|
10/17 (58.8%)
|
13/30 (43.3%)
|
ASIA D
|
5/17 (29.4%)
|
15/30 (50%)
|
Imaging abnormalities (n/total patient (%))
|
Cervical fracture
|
5/17 (29.4%)
|
8/30 (26.7%)
|
Intramedullary high-signal lesion
|
7/17 (41.2%)
|
18/30 (60.0%)
|
Mechanism of injury (n/total patient (%))
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Falls
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6/17 (35.3%)
|
9/30 (30.0%)
|
Vehicle accidents
|
11/17 (64.7%)
|
21/30 (70.0%)
|
Surgical approach (n/total patient (%))
|
Anterior
|
5/17 (29.4%)
|
7/30 (23.3%)
|
Posterior
|
13/17 (76.5%)
|
20/30 (66.7%)
|
Combined
|
1/17 (5.9%)
|
3/30 (10.0%)
|
SCI: Spinal cord injury; ASIA: ASIA (American Spinal Injury Association) impairment scale
|
Testing methods:
Motor unit number index
The MUNIX detection was applied in both 47 patients with incomplete cervical SCI approximately 1 year after operation and 34 healthy subjects. The MUNIX method described by Nandedkar et al. was used in this study [8]. The maximal compound muscle action potential (CMAP) was recorded bilaterally from the tibialis anterior (TA), extensor digitorum brevis (EDB) and abductor hallucis (AH) in a belly-tendon montage (filters: 3 Hz-10 kHz) to supramaximal stimulation. Subsequently, surface interference pattern (SIP) for ten different force levels of isometric contraction was recorded in a 300-ms window (filters: 10 Hz-1000 Hz). According to these measurements, both MUNIX values and motor unit size index (MUSIX) values for these three muscles were measured.
For the evaluation of the reproducibility, left-side MUNIX measurements of 15 healthy subjects and 21 patients with cervical SCI were tested twice by the same examiner. The intervals between these 2 tests were longer than 60 min, and the electrodes were completely removed after the initial test.
All electrophysiological examinations were carried out by Keypoint EMG machine (Medtronic Dantec, Skovlunde, Denmark) with a skin temperature > 32°C. MUNIX values cannot be measured when the following conditions occur: SIP area < 20 mV.ms, ideal case motor unit count (ICMUC) > 100, SIP area/CMAP area < 1, or CMAP amplitude < 0.5 mV.
Clinical function examination:
All 47 patients with cervical SCI accepted American spinal injury association (ASIA) classification to identify the severity of SCI at the time of admission. All of these patients further underwent muscle strength examination in all tested muscles graded by the Medical Research Council (MRC) scales and American spinal injury association (ASIA) motor scores approximately 1 year after operation.
Statistical methods:
The measurements were analyzed by SPSS 18.0 (IBM, Armonk, NY), and Medsci simple size tools (Shanghai, China) were used to calculate sample size. The measurements among healthy subjects and different cervical SCI patient groups were tested using one-way ANOVA (least significant difference correction). The preoperative and postoperative ASIA motor scores were compared by the paired t-test.
Pearson or Spearman correlation coefficient analysis (CCA) was used to evaluate the relationship between MUNIX values and MRC scales in each patient group. The test-retest reproducibility of MUNIX in healthy subjects and patients with cervical SCI was analyzed using interclass correlation coefficient (ICC) methods.
A P-value less than 0.05 was considered significant.