BIOMECHANICS

2. LIGAMENT BIOMECHANICS
Composition and Structure of Ligaments
ligaments have fibroblasts that are found within
the ligament substance aligned with the collagen
fibrils.
 Like tenocytes, ligamentous fibroblasts also
form an extensive network with other cells via
cytoplasmic extensions that are linked by gap
junctions.
The extracellular matrix is also composed mainly
of type I collagen

3. CONT………
The fibers are not parallel and are
multidirectional .
 Most are in line with the axis of the ligament.
Although ligaments generally sustain tensile loads
in one predominant direction, they may also
bear smaller tensile loads in other directions,
Which suggests that the fibers are interlaced
even if they are not completely parallel .
Thus, the specific orientation of the fiber bundles
varies to some extent among the ligaments and
depends on the function of the ligament.
(Amiel et al.,
1984).

4. Ligaments are surrounded by a loose areolar
connective tissue.In ligaments, this tissue is called
the epiligament.
Ligaments are intimately connected to fascia.
It has been suggested that this interconnection
serves three important biomechanical functions:
Dissipation of loads to reduce wear and tear,
 Facilitate linkage to form mechanical chains,
(Benjamin et al., 2008).

5. Biomechanical Properties of
Ligaments
ligaments are viscoelastic structures with unique
mechanical properties.
The ligaments are pliant and flexible,
Allowing natural movement of the bones to which they
attach, but are strong and inextensible so as to offer
suitable resistance to applied forces.
Sustain chiefly tensile loads during normal and
excessive loading.
When injury happens, the degree of damage is related
to the rate of loading as well as the amount of load.

6.  Ligaments are often evaluated by using mounted
specimens such as a bone-ligament-bone specimen.
However,
 recent advances have allowed for some instrumentation to
be used in the measurement of in situ forces in humans.
 These include the use of buckle transducers,
instrumentation at insertion sites,
magnetic resonance
imaging, kinematic linkage measurements,
and implantable transducers
(Woo et al., 2000).

7. In a loade longation curve the stiffness of the
structure (N/nm) is the slope of the curve
between two limits of elongation.
 It represents how much load and or
elongation the structure can sustain before it
fails.

8. Toe Region
 Load-elongation curves have several regions that
characterize the behavior of the tissue .
 The first region of the load-elongation curve is called
the “toe” region.
 The elongation reflected in this region is believed to
be the result of a change in the wavy pattern or crimp
of the relaxed collagen fibers.
 In this region, the tissue stretches easily without
much force, the collagen fibers become straight and
lose their wavy appearance, and sliding occurs
between fibrils and fascicles as the loading progresses
(Woo et al., 1994).

10. Elastic or linear
Region
 As loading continues, the stiffness of the tissue
increases and there is a resultant change in the tissue
elongation.
 This region is called the elastic or linear
region of the curve.
 It is observed as a sudden increase in the slope of the
curve.
 When the linear region is surpassed, major failure of
fiber bundles occurs in an unpredictable manner. The
curve can end abruptly or curve downward as a result of
irreversible changes (failure)
(Woo et al., 1994).

11. With the attainment of maximum load that
reflects the ultimate tensile strength of the
specimen, complete failure occurs rapidly,
And the load-supporting ability of the
ligament is substantially reduced (complete
failure).
The tissue is elongated then until it ruptures,
and the resulting force, or load (P), is plotted.

12. Yield Point
• Where the curve levels off toward the
elongation axis,
• The load value is designated as Pline. The
point at which this value is reached is the yield
point for the tissue.
• The Energy uptake to Pline is represented by
the area under the curve up to the end of the
linear region.

14. Factors That Affect the Biomechanical
Properties of Ligaments
Numerous factors affect the biomechanical
properties of tendons and ligaments.
The most common are aging,
Pregnancy,
Mobilization and immobilization,
Comorbidities
(diabetes mellitus, connective tissue disorders,
renal disease),
 Pharmacologic agents (steroids, nonsteroidal
Anti-inflammatory drugs or NSAIDs).