1. Cervical Intervertebral Disc Heights and Paraspinal Muscle Morphology
following Long-term Spaceflight and 30-Day Recovery
Robert M. Healey1, Jacquelyn A. Holt1, Brandon R. Macias1, Alexander J. Snyder1, Jeffrey C. Lotz2, Alan R. Hargens, FACSM1, Douglas G. Chang1
1University of California, San Diego, San Diego, CA. 2University of California, San Francisco, San Francisco, CA.
INTRODUCTION: Exposure to microgravity during long-duration (6 months) spaceflights lengthens the spine1,2 and is associated with a 4-fold greater incidence of herniated nucleus pulposus (HNP), particularly in the cervical region, compared with age-matched ground controls. 3 Concurrent muscle atrophy or deconditioning may also contribute to increased HNP risk.
PURPOSE: To evaluate cervical intervertebral disc (IVD) heights and paraspinal muscle morphology following a 6-month International Space Station (ISS) mission and a 30-day post-flight recovery period.
MATERIALS AND METHODS: Supine cervical spine MRI scans were produced pre-flight, immediate post-flight and at least 30 days post-flight recovery for 3 astronauts visiting the ISS. 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 total region of interest containing the posterior cervical extensors (multifidus, semispinalis cervicis, semispinalis capitis, splenius capitis, and upper trapezius)4 (Figure 1). Student-T tests were used to determine significant changes at p<0.05. C2 C3 C4 C5 C6 C7 T1 C
Pre-Flight
Immediate Post-Flight
30-Day Post-Flight A B
Ant
Mid
Post
Figure 3. Cervical lean muscle cross-sectional area at C5-C6 level (as a percentage of total ROI) pre-, immediate post- and 30-day post-flight. (n=3)
Figure 2. MR images from three time points (pre-flight, post-flight, and 30-days post-flight) showing A) Sagittal cervical IVD levels C2 to T1, B) Axial cervical extensors at C5-C6 level and C) IVD height measurement locations (Anterior, Middle and Posterior).
DISCUSSION: These preliminary results demonstrate an increase in cervical IVD heights with associated atrophy of paraspinal muscles which may contribute to the reported neck pain and increased incidence of herniated nucleus pulposus in astronauts in long-duration missions.
SIGNIFICANCE: This research is important in understanding spinal deconditioning during both spaceflight and inactivity on Earth.
REFERENCES:
1. Brown J. Crew height measurements. In: The Apollo-Soyuz Test Project: Medical Report. In: Washington DC: NASA; 1977:
2. Thornton W, TP M. Height Changes in Microgravity. In: Results of the Life Sciences DSOs Conducted Aboard the Space Shuttle 1981–1986. (Bungo M, Bagian T, Bowman M, Levitan B, eds.). Houston, TX: NASA-Johnson Space Center; 1987.
3. Johnston SL, Campbell MR, Scheuring R, Feiveson AH. Risk of herniated nucleus pulposus among U.S. astronauts. Aviat Sp Environ Med 81(6): , 2010.
4. Snyder A, Macias B, Healey R, Chang D, Holt J, Lotz J, Hargens A. Lumbar Paraspinal Muscle Atrophy during Long Duration Spaceflight. Exp Bio Boston, MA; 2015.
Table 1. Changes in IVD heights during spaceflight (pre-flight to immediate post-flight) and recovery (immediate post-flight to post-flight + 30 days) (n=3, *p<0.05)
RESULTS: These preliminary results present cervical IVD heights with an increase, on average, of 0.5±0.4mm during the 6-month exposure to microgravity and a recovery on average of 0.1±0.4mm decrease over the following 30 to 45 days relative to post-flight return (Figure 2). The posterior aspect of the IVD heights was significantly decreased during recovery (0.3±0.4mm) compared with anterior and middle segments which remained swollen (Table 1). An average 9.9±17.8% decrease in cervical lean muscle cross-sectional area was measured post-flight. A 2.2±3.8% recovery from immediate post-flight was observed after 30 days post-flight (Figure 3).
ACKNOWLEDGEMENT: Project supported by NASA Grants NNX10AM18G and NNX13AM89G.
Figure 1. Location of posterior cervical extensors identified for lean muscle area measurement at C5-C6 level.