- Properties
- resting length
- elastic deformability
- plastic deformability
lig. tension vs. length (dist b/w Orig and ins)
concepts: strength, laxity (rotational=translational), elasticity, biochemical composition, anatomic variation, use/disuse, age, disease, injury, surgery
Ligamentous stabilization
- checkrein vs. countervailing force function.
N.B. – obligate translation of the humeral head due to tight ligamentous structures at the exteremes of motion (think posterior capsular tightness in throwers)
Adhesion-Cohesion ==> like 2 microscope slides
N.B. joint fluid has high tensile strength and low shear strength (tough to pull apart, allows easy sliding)
reduced by any factor that reduces cohesion of joint fluid (inflamm jt. disease), reduces wettability of joint surfaces (DJD), decreases Gh contact area (fracture of articular surface).
Adhesion-Cohesion does not occur in metal on poly joint because of inssuficient congruence and non-adherence of water.
Glenohumeral “suction cup”
- noncompliant centrally, flexible peripherally.
- completely eliminated by labral defect.
Limited joint volume
- relative vacuum
- because a normal joint is sealed, attempted distraction of the joint lowers the intra-articular pressure further, progressively adding resistance to displacement.
Stability at rest = adhesion/choesion, glenoid suction cup, limited joint volume
Superior stability — compression into glenoid fossa
- n.b. supraspinatus
- in absence of supra, balanced force couple from infra and subscap can replace function.
- CA lig applies downward force through rotator cuff.
Wrist ligaments: their significance in carpal instability
Turkish Journal of Trauma & Emergency Surgery Ulus Travma Derg 2005
http://uk.msnusers.com/PalmarMidcarpalInstabilityPMCIRSD/Documents/More%20Documents%2FWrist%20Ligaments%20Their%20Significance%20In%20Carpal%20Instability%20Turkish%20Journal%20Of%20Trauma%20And%20Emergency%20Surgery.%202005..pdf
BACKGROUND
Understanding the exact contribution of the supporting
ligaments to the functional integrity of the wrist is crucial
for the diagnosis and treatment of carpal instabilities. The
present study evaluates the functional significance of the
wrist ligaments with respect to carpal instabilities..
Materials and Methods: Sixteen fresh cadaver wrists were
dissected. Extrinsic and intrinsic ligaments of the wrists
(ligamentum radioscaphocapitatum, ligamentum radiolunotriquetrum
and ligamentum triquetrohamatocapitatum)
were sectioned sequentially. After sectioning of each ligament,
the wrist was examined for clinical signs of instability
such as misalignement of carpal bones, limited range of motion
and dorsal translation. When instability was suspected,
radiographs were taken and if instability was confirmed,
then the ligament was repaired.
RESULTS
Although none of the dorsal ligaments sectioning resulted
in instability, sectioning of ligamentum scaphotrapeziotrapezoideum,
ligamentum radioscaphocapitatum, ligamentum
radiolunotriquetrum and ligamentum triquetrohamatocapitatum
displayed scaphotrapeziotrapezoidal, dorsal intercalated segment, lunotriquetral and capitohamate instability respectively.
In two wrists with arthrosis, sectioning of all ligaments
didn’t lead to any instability
CONCLUSION
Instability of the wrist can be classified on anatomical basis after the name of these four ligaments involved i.e. l.
scaphotrapeziotrapezoideum, l. radioscaphocapitatum, l. radiolunotriquetrum
and l. triquetrohamatocapitatum respectively.
This approach clarifies the etiology and treatment of
carpal instabilities.