Mechanical Behavior of Tendon & Ligament

PhysiotherapySemester – I

Mechanical Behavior of Tendons and Ligaments

Tendons Strong Viscoelastic

structures Sustain the high

tensile forces Sufficiently flexible to

angulate around bone surfaces

Ligaments Pliant and flexible to

allow natural movements of the bones

Strong & inextensible to offer suitable resistance to applied forces

Stress-Strain CurveStress-Strain Curve

Load-elongation Response 1: Primary or "Toe" region … The tissue elongated easily with a small increase in load2: Secondary or "Linear" region …. The fibers straightened out & fibers’ stiffness increased Greater force is required for elongation Deformation of the tissue began3: End of Secondary Region (P lin.)…. Progressive failure of the collagen fibers Irreversible deformation4: Maximum Load (Pmax) ….. Complete failure occurred rapidly and Lost its ability to

support loads

Load-elongation Curves

Load-elongation Curve of tendon

Load-elongation Curve of lig. flavum

Clinical Consideration

Ligament Failure ……. Progressive failure against

increasing load Stress – Strain Relationship Microfailure & gross failure of

ligament Joint displaced several

millimeter Damage to the surrounding

tissues as well e.g. : ACL Injury in soccer as

a result of an abnormal torque in rotation of the knee

Load-displacement curve of ACL Injury

Load-displacement curve

1. Load imposed on the ACL during the ant. drawer test

2. Load placed on the ligament during physiological activity

3. Load imposed on the ligament from partial injury to complete rupture (Microfailure region)

Note: Why ACL Injury can lead to EARLY osteoarthritis?

Ligament Injuries are classified clinically into three Categories

Grade-I Sprain ….. Mild pain, No joint instability, Micro-tear of few fibers Grade-II Sprain ….. Severe pain, Some joint instability, Partial ligament

rupture (Progressive failure of the collagen fibers) 50% decrease in Ligament strength (increase laxity

with a definite end point) joint stability is tested usually under anesthesia Grade-III Sprain …. Severe pain during trauma but less pain after injury Gross instability (excessive joint laxity with no firm

end point) Complete ruptured but a few may still be intact

Management of Ligament Sprains

Grade I & II Sprain …. First aid Management elecrophysical

agents, joint mobilization & soft tissue massagemuscle strengthening,

proprioceptive training & Functional training Grade III Sprain …. First aid Management surgery ( repair or

reconstruction) / protective bracingmuscle strengthening, proprioceptive training & Functional training

Clinical Consideration of Tendon Injuries

Two additional factors become important in tendons ……

1. The amount of force produced by muscle contraction

2. The cross-sectional area of the tendon Muscle contraction exerts a tensile stress on the

tendon. rapid eccentric contraction of the muscle increases the stress

Tensile strength of a tendon α Cross-sectional area of the tendon

Why muscle ruptures are more common than are ruptures through a tendon?

Load Deformation Curve Of Achilles Tendon Rupture

First region ….. a normal physiological toe-loading response

Linear region …. high load is producing a higher deformation within the tendon structure

Overuse region …. Repetitive higher strains with insufficient time for the healing process

Tendonitis vs. Tendinopathy

Tendonitis …… inflammation of the tendon itself Tendinopathy …. The primary pathology is Collagen degeneration Histological examination reveals separation of

collagen bundles, increased hydrophilic ground substances, increased poor quality blood vessels ( neovascularization), and absent inflammatory cells

Common sites for tendinopathies are rotator cuff, common extensors origion of elbow, extensor carpi redialis brevis, patellar and Achilles tendons

Other sites add. Longus, biceps, tibialis post. And flex. Hallucis longus tendons.

Grading of Tendinopathy

Descriptive Grading of Tendinopathy …. Mild Tendinopathy….

Pain after activity only / no pain during activity Moderate Tendinopathy ….

Pain with sporting activity but not with ADL Severe Tendinopathy ….

Pain during ADL Tendon-specific scoring system….. The VISA Score e.g. patellar tendinopathy

Tendinopathy Characteristic features ….. Pain some time after exercise or, more frequently, the

following morning when the athlete rises Can ‘run through’ the pain or pain disappears in

warming up & return after exercise when cooling down On Examination: Local tenderness, thickening,

swelling, crepitus Management …. Eccentric loading exercises vs. concentric exercise Surgery is indicated on clinical basis ( stripping of

paratenon, release of adhesions, removal of degenerative tissues, repair of a partial tear or excision of a torn flap)

Age- related changes of collagen Collagen cross-links vs. Aging: The greater the no. & quality of cross-links, the more

tensile strength of collagen (Viidik, Danielsen, & Oxlund, 1982) Collagen fibril diameter vs. Aging: Fibril diameter α the tensile strength of ligament and

tendons Fibril diameter in adults (20-60 years) & in elderly (>60

years) decreases remarkably (Strocchi et al., 1996) Water content & concentration of collagen vs. Aging: The water content & collagen conc. decreases significantly

in ligament as age progresses after maturation (Amiel, 1991). So, tensile strength & stiffness of the ligament & tendon decreases

Mobility vs. Mechanical behavior of Ligament & Tendon

Functional adaptation of ligament & tendon in response to the mechanical demands placed on them

The ligaments are more stronger & stiffer when subjected to increasing stress and more weaker & lesser stiffer when subjected to decreasing stress (Noyes et al., 1977a)

Physical training increases the tensile strength of tendons and ligament-bone interface (Woo et al., 1981).

Research study of medial collateral ligament strength: The ligaments of the exercised dogs for 6 weeks were

stronger & stiffer than those of the control dogs & the collagen fiber bundles had larger diameters (Tipton and coworkers, 1970)

Diabetes Mellitus Diabetes mellitus VS. Musculoskeletal disorders Diabetics vs. Nondiabetics …. Higher rates of tendon contracture (29 vs. 9%) Tenosynovitis (59 vs. 7%) Joint stiffness (40 vs. 9%) Capsulitis (16 vs. 1%) Also causes osteoporosis (Carvallo et al., 1991;

Lancaster et al., 1994) The tissue elastic properties did not differ between the

diabetic and the control group. The viscous component of the tissue response, however, was increased in the hyperglycemic group. Insulin therapy seems to lessen such alterations (Duquette, 1996)

Nonsteroidal Anti-inflammatory Drugs

NSAIDs (aspirin, acetaminophen and indomethacin) are frequently used in painful conditions of the musculoskeletal system

also widely used in the treatment of soft tissue injuries such as inflammatory disorders and partial ruptures of tendons and ligaments

Vogel (1977) found that treatment with indomethacin resulted in increased tensile strength in rat tail tendons. An increase in the proportion of insoluble collagen and in the total collagen content also was observed

Ohkawa (1982) found increased tensile strength in the periodontium of rats after indomethacin treatment

Carlstedt and associates (1986a, 1986b) found that indomethacin treatment increased the tensile strength in developing and healing plantaris longus tendons in the rabbit and noted that the mechanism for this increase was probably an increased cross-linkage of collagen molecules