Hindlimb unloading alters ligament healing

Abstract

We investigated the hypothesis that hindlimb unloading inhibits healing in fibrous connective tissue such as ligament. Male rats were assigned to 3- and 7-wk treatment groups with three subgroups each: sham control, ambulatory healing, and hindlimb-suspended healing. Ambulatory and suspended animals underwent surgical rupture of their medial collateral ligaments, whereas sham surgeries were performed on control animals. After 3 or 7 wk, mechanical and/or morphological properties were measured in ligament, muscle, and bone. During mechanical testing, most suspended ligaments failed in the scar region, indicating the greatest impairment was to ligament and not to bone-ligament insertion. Ligament testing revealed significant reductions in maximum force, ultimate stress, elastic modulus, and low-load properties in suspended animals. In addition, femoral mineral density, femoral strength, gastrocnemius mass, and tibialis anterior mass were significantly reduced. Microscopy revealed abnormal scar formation and cell distribution in suspended ligaments with extracellular matrix discontinuities and voids between misaligned, but well-formed, collagen fiber bundles. Hence, stress levels from ambulation appear unnecessary for formation of fiber bundles yet required for collagen to form structurally competent continuous fibers. Results support our hypothesis that hindlimb unloading impairs healing of fibrous connective tissue. In addition, this study provides compelling morphological evidence explaining the altered structure-function relationship in load-deprived healing connective tissue.

Instrument-Assisted Cross-Fiber Massage Accelerates Knee Ligament Healing

“…21 The alignment and organization of newly formed collagen fibers in the direction of tensile loads during healing influences ligament mechanical properties. 19,20 The qualitatively improved collagen fiber organization observed within the scar region of IACFM-treated ligaments in the current study is a possible explanation for why IACFM-treated ligaments had enhanced tensile mechanical properties. This will be the focus of future quantitative studies into IACFM effects on ligament morphology.…”

“…First, the study was performed in an animal model, wherein the knee MCL was injured via surgical transection. This is a highly reproducible and established model for the preclinical testing of interventions for ligament injuries 16,20,29,31 ; however, the ability of the model to predict the clinical scenario wherein ligaments are injured via excessive tensile load has not been established. Second, the size of rodent tissues in relation to those of humans raises scaling issues in terms of intervention application and response.…”

“…MCL thickness and width were measured optically at the knee joint line, and MCL area estimated using an elliptical geometry. 20 Each FMT complex was placed in a customized testing jig, with the knee joint positioned in 70° flexion, for MCL testing. This position appears to load all ligament fibers simultaneously.…”

“…This position appears to load all ligament fibers simultaneously. 20 The femoral and tibial portions were embedded in Wood's low-melting-point metal (bismuth alloy LMA-117; Small Parts, Inc, Miami Lakes, FL) for fixation. The jig was coupled to an electromagnetic material testing device (TestBench 200 N ELF LM-1; EnduraTEC Systems Group, Bose Corp, Minnetonka, MN), equipped with a 50-N load cell ( 2A).…”

Tibio‐femoral loading during human gait and stair climbing

“…The loading within musculoskeletal structures influences biological processes including fracture healing [ 17,351, bone remodelling [29,36], and ligament repair [45]. Loading is also believed to play a role in the onset of osteoarthritis [7,26].…”