Effect of microgravity during long-duration spaceflight on transverse relaxation times of the femorotibial cartilage (MRI T2) – the ESA Cartilage Health study

BACKGROUND
Immobilization alters the morphological and biomechanical characteristics of synovial joint components,
including cartilage. Findings from spaceflight analogue model research, such as bed rest studies, indicate that
unloading exposure is associated with changes in cartilage metabolism (Liphardt et al., 2009, 2018). This study
aims to investigate the effect of microgravity during long-duration spaceflight on knee cartilage quality by
magnetic resonance imaging (MRI) transverse relaxation time (T2) in medial and lateral femorotibial cartilage of
crew members of the International Space Station (ISS).
METHODS
For the ESA (European Space Agency)-funded ESA CARTILAGE HEALTH study, 12 USOS (United States
Operational Segment) crew members, with a mission length of 4 – 6 months on the ISS, were recruited for this
study after giving written informed consent. A 2DMESE (multiple echo spin echo) T2 mapping sequence (TR =
1500 ms, TE = 10, 20, 30, 40, 50, 60, 70 ms, flip angle = 180°, field of view = 159 mm, matrix = 269 × 384 pixels,
slice thickness = 3 mm, in-plane resolution = 0.31 mm²) of the knee joint was obtained pre-flight (launch (L)-60)
and at three time points after landing (return (R)+7 days, +30 days and +365 days) after a 45 minutes supine rest
using a 3 tesla MRI scanner (Siemens Healthineers, Erlangen, Germany or Philipps Archieva, Hamburg,
Germany). Mean T2 time (miliseconds, ms) was computed for the deep and superficial cartilage layers for all
medial and lateral femorotibial cartilage compartments. Linear Mixed-Effects Models were used to detect
significant changes in the MRI T2 of knee articular cartilage in response to 4 -6 months on the ISS, considering
time points as predictors.
RESULTS
Baseline (pre-flight), T2 relaxation times are summarized in Table 1. T2 relaxation times of the medial tibia
superficial layer (p=0.024) was affected by time points. Mean T2 was increased after landing for the medial tibia
superficial layer (3.1% at R+7 (β=0.76, 95% CI: 0.11 – 1.42) p=0.024; 3% at R+30 (β=0.73, 95% CI: 0.05 – 1.41)
p=0.035) compared to preflight values. No effect for T2 mean was detected for superficial layer of the lateral tibia,
medial and lateral femur and for the deep layer of all compartments.
Table 1: Baseline T2 relaxation times at pre-flight in
milliseconds (ms) reported as means and standard
deviation (SD) for 12 crew members.
Compartment
T2 relaxation
time (ms)
mean(SD)
deep layer T2 21.3(3.5)
superficial T2 33.7(5.7)
deep layer T2 21.9(2.8)
superficial layer T2 32.8(3.6)
deep layer T2 16.2(1.9)
superficial layer T2 22.8(3.0)
deep layer T2 18.1(2.4)
superficial layer T2 29.4(3.4)
CONCLUSION
Immobilization by microgravity during 4 – 6 months spaceflight results in regional increases in T2 relaxation times
of knee articular cartilage. Greater T2 relaxation times for the medial tibia superficial layer may reflect an increase
of relative water content that can be indicative of tissue matrix perturbation. These results support our previous
findings of a shift of cartilage metabolism towards cartilage degradation in response to immobilization measured
by urine and serum biomarkers. Further research is needed to better understand the role of mission duration for
the magnitude of tissue matrix perturbations and to identify countermeasures against these changes.
REFERENCES
Liphardt et al. 2009, Dec;17(12):1598-603; Liphardt et al. 2018, J Orthop Res. May;36(5):1465-1471.
Acknowledgements
This work was funded by the Federal Ministry for Economic Affairs and Climate Action, Germany & German
Aerospace Centre (DLR e.V.) – German Space Agency (Project #: DLR 50WB0913, DLR 50WB1217, DLR
50WB1719, DLR 50WB1520, DLR 50WB2021, DLR 50WB2022) and the European Space Agency and partially
supported by the German Research Foundation (DFG) under Grant CRC 1483 EmpkinS - Project-ID 442419336.