The Correlation Between Facet Tropism and Motor Dysfunction of the Upper Limbs in Patients with Cervical Spondylotic Amyotrophy: an Observational Study

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. 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. 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 FTS< 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 FTS< 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). 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.