Objective—To objectively evaluate the effect of transecting
the tendon of the biceps brachii muscle
(BBT), tendon of the infraspinatus muscle (IFS), or
medial glenohumeral ligament (MGHL) on shoulder
joint stability in canine cadavers.
Sample Population—81 forelimbs from mature dogs.
Procedure—Cadaver forelimbs were placed in a testing
frame and axially preloaded with 4 kg of weight.
Shoulder joint stability was tested in neutral joint position,
flexion, and extension before and after transection
of the BBT (n = 37), IFS (37), or MGHL (7).
Humeral translation relative to the glenoid was
induced by applying a 3-kg load in each of 3 directions
(cranial, lateral, and medial) and quantitatively measured
by use of an electromagnetic motion tracking
system. Peak translational data were compared in
each joint position before and after transection of the
BBT, IFS, or MGHL.
Results—When tested in neutral position, the cranial,
lateral, and medial translation of the humerus was significantly
increased after BBT transection. In the flexed
position, translation of the humerus in the cranial and
lateral directions was significantly increased after BBT
transection. In the extended position, the medial translation
of the humerus was significantly increased after
BBT transection. Complete medial luxation of all humeral
heads occurred following transection of the MGHL.
Conclusions and Clinical Relevance—The BBT contributes
to passive shoulder joint stability in dogs, particularly
in the neutral and flexed positions. It also provides
medial stability during shoulder joint extension.
Complete luxation of the joint occurs when the MGHL
is transected. (Am J Vet Res 2004;65:1216–1222)