Page 68 - Clinical Manual of Small Animal Endosurgery

56 Clinical Manual of Small Animal Endosurgery

Investigative arthroscopy of the shoulder

A lateral arthroscopic approach enables a good-quality examination of
all of the structures of the shoulder joint with the exception of the lateral
aspect of the joint, the lateral joint capsule and the lateral collateral liga-
ment. This is because the lateral arthroscopic approach reveals the lateral
structures only at the periphery of the arthroscopic field and skill and
considerable care are required for inspection of these structures because
of the tendency to withdraw the arthroscope from the joint cavity while
performing this manoeuvre.
The egress portal is established in the cranial compartment of the
shoulder joint using an 18-gauge, 40 mm hypodermic needle. The needle
is inserted caudomedially at 70° from the middle of the midpoint of the
proximal ridge of the greater tubercle (see Fig. 3.12). Aspiration of joint
fluid confirms intra-articular placement and once a sample of synovial
fluid is obtained the joint is distended first with irrigation fluid containing
7.5% ropivacaine (1 mg/kg), then with a distending volume of irrigation
fluid. When the needle is correctly placed, fluid is instilled easily and
reverse pressure is detected on the syringe plunger when approximately
10 ml of fluid is instilled. Articular distension is maintained by thumb
pressure on the syringe plunger by a scrubbed assistant. A few minutes
are required for the onset of action of the local anaesthetic agent. The
arthroscope portal is established by inserting a second needle directly
vertical, just distal to the acromial process of the scapula. Fluid egress
confirms intra-articular placement and the needle is advanced to the hub,
confirming the correct line of penetration that travels between the articu-
lar surfaces of the humerus and of the glenoid cavity. Traction on the limb
assists to widen the articular separation, facilitating this procedure. A
3 mm-long, deep incision is made into the skin and superficial soft tissues
adjacent to and following the direction of the needle. The arthroscope
cannula with the blunt obturator is inserted into the joint following the
direction of the locator needle. Firm pressure is required to puncture the
joint capsule and the index finger is placed against the shoulder to brace
the scope against overinsertion into the joint while the cannula is pushed
firmly through the joint capsule. The obturator is removed and fluid
egress from the cannula confirms its intra-articular location. Free move-
ment of the cannula in a craniocaudal direction but resistance to proxi-
modistal tilting additionally confirm its location in the articular space.
When the arthroscope is inserted into the joint, the initial view gener-
ally shows the medial structures of the joint capsule. Gentle retraction
of the arthroscope reveals the convex articular surface of the humeral
head and the concave surface of the glenoid cavity of the scapula, ena-
bling orientation. Continued distraction of the joint by the surgical
assistant enables a systematic inspection of the structures of the shoulder
joint.
In the distant foreground the cranial component of the Y-shaped
medial glenohumeral ligament is visible (Fig. 2.23) adjacent to the sub-