The correlation between facet tropism and motor dysfunction of the upper limbs in patients with cervical spondylotic amyotrophy: an observational study.

Purpose: To identify the frequency of facet tropism (FT) in patients with cervical spondylotic amyotrophy (CSA) and to analyze the correlation between FT and motor dysfunction in CSA.

Methods: The side-to-side differences in facet orientation (FO) (≥ 7°) were measured from C3-4 to C7-T1 levels via 3D computed tomography to diagnose FT in 84 CSA patients (proximal- vs. distal-type: 36 vs. 48) and 363 patients with cervical spondylosis (CS). Both the motor unit number index (MUNIX) and Medical Research Council scores were assessed in CSA patients.

Results: Compared with CS patients, both CSA patient groups presented a greater frequency of FT at any cervical level in all different planes (axial, sagittal and coronal) (P < 0.05). Furthermore, more proximal-type CSA patients with FT presented axial FT_{S< less-S} (smaller FO on the symptomatic side) at C4-5 level, and more distal-type CSA patients with FT exhibited both axial and sagittal FT_{S< less-S} at C6-7 and C7-T1 levels. In addition, both compound muscle action potential (CMAP) and MUNIX values in proximal-type CSA patients with C4-5 axial FT were lower than those in patients without FT (P < 0.05), and both CMAP and MUNIX values were negatively associated with the side-to-side differences in axial FO at C4-5 and/or C5-6 levels in these patients (P < 0.05).

Conclusion: The frequency of FT in CSA patients is greater than that in CS patients. Importantly, axial/sagittal FT may be positively associated with motor dysfunction of upper limbs in CSA patients. Thus, a cautious approach should be taken when treating CSA due to possible comorbid FT.