Study design: This is a retrospective radiographic study of a consecutive case series of dropped head syndrome (DHS) at a single tertiary referral center.
Objective: The aim was to clarify the spinal sagittal alignment of DHS.
Summary of background data: DHS is characterized by chin-on-chest deformity and devastatingly impedes activities of daily living in affected individuals. Among various forms of DHS, isolated neck extensor myopathy (INEM) is considered to cause the chin-on-chest symptom in the absence of specific abnormality. There is a paucity of literature about spinal sagittal alignment, of this condition however.
Methods: Thirty-seven patients diagnosed with INEM DHS were enrolled. Radiographic measurements were made, including the following parameters: C2 slope (C2S), C2-C7 A, C2-C7 sagittal vertical axis (SVA), T1 slope (T1S), C7-S1 SVA, T1-T4 thoracic kyphosis (TK), T4-T12 TK, lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI). Sixty-one patients with cervical spondylosis were enrolled as a control group.
Results: C2-C7 SVA was greater in INEM DHS (52.0 ± 2.9 vs. 18.6 ± 1.9 mm). C2S and T1S were larger to the control (C2S: 52.6° ± 2.0° vs. 13.0° ± 1.4°, T1S: 37.3° ± 2.2° vs. 22.7° ± 1.4°). C2-C7 A was smaller in INEM DHS (-7.8° ± 2.6° vs. 15.2° ± 2.7°). Among sagittal parameters, C2S, T1S, and T1-T4 TK positively correlated with C2-C7 SVA (r = 0.63, r = 0.54, and r = 0.58). For these correlations with C2-C7 SVA, both logistic and linear regression models predicted threshold of 40° for C2S, 40° for T1S, and 15° for T1-T4 TK responsible for C2-C7 SVA > 40 mm, respectively.
Conclusion: Increased offset of the gravity axis of the head represented by C2-C7 SVA was observed in INEM DHS. Magnified offset of the gravity axis of the head was affected by enlarged C2S, T1S, and T1-T4 TK for the strong correlation with C2-C7 SVA, respectively. Cervical kyphosis was considered as some of the anthropometric characteristics due to regressive changes in affected individuals; a correlation between C2-C7 A and C2-C7 SVA was exhibited.
Level of evidence: 4.