Variations in Rupture Site and Surface Strains at Failure in the Maturing Rabbit Medial Collateral Ligament

Abstract

The relationship between the pattern of surface strain and the site of failure in maturing rabbit ligaments was studied in vitro. Bone-medial collateral ligament (MCL)-bone complexes of 24 female New Zealand White rabbits at 3, 6, 9 and 12 months of age (n = 6 rabbits, 12 MCLs per group) were tested in tension to failure. A video dimension analysis (VDA) system was used to map the surface strain at failure across the width and along the length of the medial side of each MCL during testing. Results showed that the highest strains were consistently located at the femoral insertion decreasing towards the midsubstance, with the highest strain occurring in the anterior portion of the MCL immediately adjacent to the femoral insertion. Strains of the complex at failure increased with rabbit maturation. The strain distribution however, did not change dramatically, even though the locations of MCL failure changed from exclusively tibial avulsion in the three month old rabbits to predominantly midsubstance failures in the 12 month old rabbits. In the six month old rabbits, there was a particular dissociation with all MCLs failing near the tibial insertion while femoral strains were apparently the highest. These results suggest two possibilities beyond that of some unknown artifacts of optical strain measurement. First, since failure sites rarely correlated with areas of maximum surface strain in this study, it seems possible that higher strains could exist deeper in the tissue, particularly at the bone-ligament interface of the tibial insertion in immature animals and somewhere within the midsubstance of the MCL in the adult. Secondly, it is possible that the ligament material may be heterogeneous.

Comparative Analysis of the Structural Properties of the Collateral Ligaments of the Human Knee

“…The femoral attachment has been shown to contain relatively few osseous interdigitations, which govern the strength of the attachment, 8 and coincides with the site of peak strain during loading in vitro. 16 While the preponderance of avulsion failures may also reflect the relatively slow loading rate employed in the current investigation (500 mm/min or approximately 20%/s), 21 it is worthy to note that the ultimate tensile strength and stiffness values of the LCL and MCL are comparable to those reported in the literature for isolated tests (TABLE 1), despite considerable differences in the age of specimen donors and the loading rates employed. Thus, these findings tend to support those of previous studies, in which the properties of knee ligaments have been shown to be only weakly influenced by age 2 and were relatively insensitive to loading rates ranging from 1%/s to 100%/s.…”

Understanding Entheses: Bridging the Gap Between Clinical and Anthropological Perspectives

“…Doschak and Zernicke (2005) suggest these four regions correspond to the transitional zones of increased stiffness outlined on stress/strain curves for tendon. Additionally, tendon failure studies consistently demonstrate the biomechanical efficiency of fibrocartilaginous entheses, with avulsion fractures often occurring within adjacent subchondral bone (Lieber et al, 1992;Lam et al, 1995;Gao et al, 1996;Chu et al, 2003;Thomopoulos et al, 2003). There also may be an association between subchondral avulsion fractures and accumulated microdamage adjacent to entheses .…”

The effect of out-of-plane deformation on ligament surface strain measurements

“…Previous studies have shown that the shoulder and knee ligaments are often ruptured near the insertion sites [10][11][12][13]; typically, the common regions where the higher strain occurs in the ligaments compared to mid-substance [5,6,8,11,14]. Therefore, neglecting the out-of-plane deformation may mask the actual strain value and earlier failure may occur than expected based on 2d strain.…”

“…This variation may be due to differences in collagen fiber distribution, alignment, and crosslinking [15][16][17][18]. The variation in strain may also be a result of the compositional contributions of water, collagen, and glycosaminoglycan (GAG) [5,19]. Further research to measure the local mechanical response and micro-structural analysis would be useful to explain the inhomogeneity and microstructurefunction relationships.…”

“…Several methods have been used to measure the ligament and capsule strain distribution such as photoelastic coating, high speed films, dye lines, marker bead etc [4][5][6][7][8]. In most cases, the strain measurement is based on in-plane deformation; neglecting the out-of-plane deformation and reports of strain is limited to the axis of loading [9].…”