Molecular biology and biomechanics of normal and healing ligaments - a review

Objective: In this review article, we discuss current data and concepts concerning the molecular biology and biomechanics of both normal and healing ligaments in a rabbit model. Method: Data is presented from light microscopy, transmission electron microscopy, molecular biology (RT-PCR), and biomechanical measurements (laxity, stress at failure, modulus, and static creep) of normal, pregnant and healing rabbit medial collateral ligaments. Results: 'Flaws' in scar matrix, smaller-than-normal diameter collagen fibrils, and failure of collagen cross-link maturation may be particularly important deficiencies which appear to be related to ligament scar weakness and perhaps to scar creep. The mechanical behaviours of both normal and healing ligaments are altered by relative states of joint motion and normal ligaments are affected by systemic hormones (particularly during pregnancy). Discussion: Molecular analysis of ligaments and ligament scars, combined with ongoing morphological and biomechanical studies of ligament structure and function, will ultimately reveal which factors can be manipulated clinically to optimize the restoration of normal ligament properties after ligament injuries. Further studies on the mechanisms of ligament healing, genetic markers of repair, and gender-specific differences in ligament repair responses are required.