Role of biomechanics in the understanding of normal, injured, and healing ligaments and tendons

Abstract

Ligaments and tendons are soft connective tissues which serve essential roles for biomechanical function of the musculoskeletal system by stabilizing and guiding the motion of diarthrodial joints. Nevertheless, these tissues are frequently injured due to repetition and overuse as well as quick cutting motions that involve acceleration and deceleration. These injuries often upset this balance between mobility and stability of the joint which causes damage to other soft tissues manifested as pain and other morbidity, such as osteoarthritis.The healing of ligament and tendon injuries varies from tissue to tissue. Tendinopathies are ubiquitous and can take up to 12 months for the pain to subside before one could return to normal activity. A ruptured medial collateral ligament (MCL) can generally heal spontaneously; however, its remodeling process takes years and its biomechanical properties remain inferior when compared to the normal MCL. It is also known that a midsubstance anterior cruciate ligament (ACL) tear has limited healing capability, and reconstruction by soft tissue grafts has been regularly performed to regain knee function. However, long term follow-up studies have revealed that 20-25% of patients experience unsatisfactory results. Thus, a better understanding of the function of ligaments and tendons, together with knowledge on their healing potential, may help investigators to develop novel strategies to accelerate and improve the healing process of ligaments and tendons.With thousands of new papers published in the last ten years that involve biomechanics of ligaments and tendons, there is an increasing appreciation of this subject area. Such attention has positively impacted clinical practice. On the other hand, biomechanical data are complex in nature, and there is a danger of misinterpreting them. Thus, in these review, we will provide the readers with a brief overview of ligaments and tendons and refer them to appropriate methodologies used to obtain their biomechanical properties. Specifically, we hope the reader will pay attention to how the properties of these tissues can be altered due to various experimental and biologic factors. Following this background material, we will present how biomechanics can be applied to gain an understanding of the mechanisms as well as clinical management of various ligament and tendon ailments. To conclude, new technology, including imaging and robotics as well as functional tissue engineering, that could form novel treatment strategies to enhance healing of ligament and tendon are presented.

Current Approaches and Future Trends to Promote Tendon Repair

“…A tendon, a group of fibrous bundles, is surrounded by a thin connective tissue sheath (epitenon), which is even surrounded by other loose connective tissue layer (paratenon). 20,22,29 Collagen fibrils present an elongated shape when they are stretched and a crimped, waveform appearance when they are no stretched, as observed in Figs. 1c and 1d.…”

“…16,29,43 The maximum force, maximum strain, stiffness and Young's modulus depend on the thickness and collagen content of the studied tendon type, patient gender and age. 20,29,43 Mechanical experiments using several tendons reported Young's modulus values in the range of 1-2 GPa; ultimate stress values in the range of 50-100 MPa; ultimate strain values of 4-10% and toughness values in the range of 1000-4500 J/kg. 29,43 …”

Results of Conservative Treatment of First Time Acute Lateral Patella Dislocation

“…It is known that healing capacity of injuries due to ruptures of ligament structures from the bone adhesion is higher than the injuries occurring in any other point on the ligament (12). In a recent study investigating healing potentials according to the anatomic localization of MPFL rupture after the first patellar dislocation, it was reported that good results after conservative treatment were obtained only for MPFL ruptures in the place of adhesion to the patella.…”

Structural Basis of Joint Instability as Cause for Chronic Musculoskeletal Pain and Its Successful Treatment with Regenerative Injection Therapy (Prolotherapy)

“…As a full recovery to its pre-injury abilities does not occur, the joint is subjected to instability. This inevitably leads to biomechanical changes across joint surfaces, increasing the risk for degenerative changes and the development of osteoarthritis [24,28,32,33]. In few cases, through a three-stage overlapping healing process (hemorrhage with inflammation, cellular and matrix proliferation and finally, remodeling and maturation), the body may be able to repair the injury enough for a full clinical recovery of the initial structural/functional abilities (i.e., strength and ability to stabilize the joint), but this healing process can take months to resolve itself and underlying instability may still be present.…”