Cervical Intervertebral Disc Heights and Paraspinal Muscle Morphology Changes Following Long-term Spaceflight and 30-Day Recovery

Abstract

Exposure to microgravity during long-duration spaceflights lengthens the spine is associated with a 5-fold greater incidence of herniated nucleus pulposus (HNP), particularly in the cervical region, compared with age-matched ground controls. Concurrent muscle atrophy or deconditioning may also contribute to increased HNP risk. PURPOSE: To evaluate cervical IVD height change and associated paraspinal muscle change following a 6-month International Space Station (ISS) mission and a 30-day post-flight recovery period. METHODS: Cervical spine MRI images were conducted pre-flight, immediate post-flight and 30-to-45 days post-flight recovery of 3 astronauts. IVD heights were measured at the anterior, middle and posterior sections from the upper C2-C3 to lower C7-T1 disc levels. Functional cross-sectional area measurements of the axial cervical paraspinal muscles at the C5-C6 level were performed. The fractional portion of lean muscle area was measured from a standardized region of interest within the posterior cervical extensors. Student-T tests were used to determine significant changes at p<0.05. RESULTS: Cervical IVD heights increased 0.35±0.42mm during the 6-month exposure to microgravity and recovered an average of 0.08±0.37mm over 30 days. The posterior aspect of the IVD heights was significantly decreased during recovery (0.30±0.36mm) while the anterior and middle segments remained swollen (Table 1). An average 9.9±17.8% decrease in cervical lean muscle tissue was measured post flight with a 30-day recovery of 2.2±3.8%. CONCLUSIONS: In the 30 days following ISS missions, there was significant reduction of the posterior cervical IVD heights associated with decreased lean muscle mass of posterior extensors. Supported by NASA grants NNX10AM18G and NNX13AM89G.