Altering ligament water content affects ligament pre‐stress and creep behavior

Abstract

The water content of a ligament can be altered by injury and surgical intervention in vivo, and inadvertently or purposely during in vitro tests. We investigated how altering the water content of the rabbit medial collateral ligament (MCL) affected its resulting creep behaviour (defined as an increase in strain from sequential cyclic and static creep tests). The water content of normal MCLs (n = 4) was compared to that of MCLs soaked for 1 h in a sucrose solution ( n = 4) or phosphate buffered saline (PBS; n = 8). Sucrose exposure decreased hydration and PBS exposure increased hydration. In addition, soaking in PBS caused a shift in "ligament zero" (the position where there was 0.1 N of tension on the ligament). Following the same single solution treatment, additional MCLs were creep tested at 4.1 MPa using a load based on the ligament cross-sectional area measured before solution treatment: sucrose (n = 4), PBS new "ligament zero" (n = S), and PBS old "ligament zero" ( n = 6). Normal MCLs were also tested at 4.1 MPa (n = 7) in a humidity chamber that maintained normal ligament water content. Additional MCLs were treated with both solutions in series (n = 12) to examine the reversibility of the mechanical changes caused by single solution treatment. This was the first investigation to show that ligament creep behaviour was clearly affected by the initial state of hydration: creep decreased with decreased hydration and creep increased with increased hydration. Another unique finding was that ligaments with increased hydration had decreased ligament functional length and increased ligament pre-stress. The creep behavioiir of these ligaments was decreased if they were loaded from the pre-stressed state compared to the unloaded state. These results suggest that maintenance of physiological water content is important for in vitro mechanical testing of ligaments and controlling the low-load stress state of ligaments in situ.

Time-dependent mechanical behavior of human amnion: Macroscopic and microscopic characterization

“…In addition to fiber recruitment and uncrimping, global fiber alignment towards the direction of loading needs to be considered as an important mechanism that contributes to the time-dependent response. Creep [54] and relaxation [41] behavior are also affected by tissue hydration, due to the fact that fibers move in a viscous hydrated matrix. The present data indicate a pronounced volume decrease during loading and holding phases, related to water outflow from the collagenous network.…”

Medial collateral ligament autografts have increased creep response for at least two years and early immobilization makes this worse

“…First, increased tissue water content may have an effect. We have shown previously that a 5% increase in water content from normal (using phosphate buffered saline) can create a pre-stress in the rabbit MCL [36]. If this shift was not taken into account, the apparent measured creep behaviour was comparable to the non-immobilized grafts.…”

“…Noyes 7742. [36] found that a small percentage ( 13'%) of patients had a loose graft as early as 4 weeks post-surgery. Lerat et al [35] documented that such laxity increased over the first 6 months and levelled off thereafter.…”

Asynchronous Muscle and Tendon Adaptation After Surgical Tensioning Procedures

“…The initial elongation of the tendon was thought to be promoted by stress relaxation of tendon material and/or suture loosening, which may occur on the hour time scale under the considerable tension produced by the stretch, although water content (which is directly related to relaxation parameters in tendons 26,27 ) did not increase one day after the transfer. The other cause, described below, may exist for the late tendon elongation.…”