The Effects Of Pregnancy And Maternal Exercise On Knee Ligaments In The Rat

There is little information in the literature about the effects of pregnancy and maternal exercise on peripheral skeletal ligaments. To study these effects on the femur-medial collateral ligament-tibia complex of the knee, tensile biomechanical testing was conducted on age matched adult rats: sedentary (N = 8), endurance trained (N = 12), pregnant sedentary (N = 8), and pregnant endurance trained (N = 9). The exercise protocol consisted of treadmill running for one hour/day, five days/week for six to eight weeks at a work rate equivalent of 60% to 70% maximal oxygen uptake in nonpregnant rats. The pregnant endurance trained group was exercised for three to five weeks prior to pregnancy and from Days 2 to 18 of pregnancy (term = 21 days). Animals were sacrificed on Day 20 of pregnancy and equivalent times for nonpregnant groups. Specimens were dissected to femur-medial collateral ligament-tibia complexes and mounted in clamps in a 37{dollar}\sp\circ{dollar}C phosphate buffered saline bath, pH 7.4. Tensile testing at 10 mm/min (1.7%/s) was conducted. All specimens failed at the tibial insertion of the ligament. Two-way analysis of variance demonstrated no significant differences in the structural properties of load, deformation and stiffness of the ligament complexes. Molecular organization of collagen of the lateral collateral ligament was evaluated by the measurement of phase retardation, a technique of polarized light microscopy. No significant differences in ligament phase retardation were not among groups. This suggested that no significant change in the molecular organization of collagen of a peripheral skeletal ligament occurred with pregnancy and maternal exercise, and supported the results of the biomechanical tests. When maximum load was normalized for body mass at time of sacrifice, values for pregnant animals were significantly lower than values for nonpregnant animals. It does not appear that ligament insertional strength responds to the increase in body mass that occurs during pregnancy. While extrapolation to humans must be made with caution, the results suggest that it would be wise for women during the last trimester of pregnancy to avoid any weightbearing activities where the risk of ligament injury is increased.