Prior studies have analyzed growth of musculoskeletal tissues between species or across body segments; however, little research has assessed the differences in similar tissues within a single joint. Here we studied changes in the length and cross-sectional area of four ligaments and tendons, (anterior cruciate ligament, patellar tendon, medial collateral ligament, lateral collateral ligament) in the tibiofemoral joint of female Yorkshire pigs through high-field magnetic resonance imaging throughout growth. Tissue lengths increased by 4- to 5-fold from birth to late adolescence across the tissues while tissue cross-sectional area increased by 10–20-fold. The anterior cruciate ligament and lateral collateral ligament showed allometric growth favoring change in length over change in cross-sectional area while the patellar tendon and medial collateral ligament grow in an isometric manner. Additionally, changes in the length and cross-sectional area of the anterior cruciate ligament did not increase as much as in the other ligaments and tendon of interest. Overall, these findings suggest that musculoskeletal soft tissue morphometry can vary within tissues of similar structure and within a single joint during post-natal growth.

23Prior studies have analyzed growth of musculoskeletal tissues between species or 24 across body segments; however, little research has assessed the differences in similar 25 tissues within a single joint. Here we studied changes in the length and cross-sectional 26 area of four ligaments and tendons, (anterior cruciate ligament, patellar tendon, medial 27 collateral ligament, lateral collateral ligament) in the tibiofemoral joint of female 28Yorkshire pigs through high-field magnetic resonance imaging throughout growth. 29Tissue lengths increased by 4-to 5-fold from birth to late adolescence across the 30 tissues while tissue cross-sectional area increased by 10-20-fold. The anterior cruciate 31 ligament and lateral collateral ligament showed allometric growth favoring change in 32 length over change in cross-sectional area while the patellar tendon and medial 33 collateral ligament grow in an isometric manner. Additionally, changes in the length and 34 cross-sectional area of the anterior cruciate ligament did not increase as much as in the 35 other ligaments and tendon of interest. Overall, these findings suggest that 36 musculoskeletal soft tissue morphometry can vary within tissues of similar structure and 37 within a single joint during post-natal growth. 38 39 Joints within the musculoskeletal system consist of a complex combination of 41 active and passive tissues including ligaments and tendons that have specific 42 morphometric and mechanical properties enabling force generation and movement. 43Many studies have investigated early pre-natal development of ligaments and tendons 44(1-6). In addition, the structure, function, and biochemical makeup of ligaments and 45 tendons undergo major changes throughout both pre-natal and post-natal growth (7-11). 46Specific changes include increasing macroscale size and mechanical stiffness and 47 to the tibial insertion site (17). Interestingly, differences in growth rate coefficients were 63 found between the proximal bones of the hindlimb (femur) and forelimb (humerus) in the 64 porcine model through 3 months of age but not between the distal bones of the same 65 limbs (tibia and radius) (18). The same study found that both the tibia and femur 66 experienced more rapid change in bone area relative to bone length (allometric growth), 67 although the same trend was not found in the humerus (18). A study in human growth 68 insertion of the PT, and some insertion sites extended beyond the field of view of the 131 MRI scans for larger specimens. As such, the location of these insertion sites were 132 measured at the edge of the insertion most proximal to the joint center since this 133 landmark could be consistently identified in all specimens. The insertion was 134 determined as the centroid of points collected around the tissue at this location along 135 the tissue length. Furthermore, to avoid variability caused by the changing CSA near 136 the bony insertions, our CSA analysis was restricted to the midsubstance of the tissues. 137Specifically, the CSA was measured...