Page 45 - Clinical Manual of Small Animal Endosurgery

Diagnostic Arthroscopy 33

smaller lenses, with smaller fields of view. Consequently, there is a non-
linear progressive decrease in visible area imaged as smaller arthroscopes
are considered, and thus use of the smallest arthroscope requires consid-
erable skill to locate intra-articular structures and instruments.

Working length
The working length describes the length of the shaft of the arthroscope.
The working length of the arthroscope is generally a function of its
diameter, since increased length increases the susceptibility to damage by
bending and hence narrow arthroscopes tend to be short, with a 1.9 mm
arthroscope being approximately 100 mm and a 2.4 mm arthroscope
being approximately 110 mm in length. An arthroscope with a short
working length allows the arthroscopist to ‘finger brace’ the arthroscope
against the joint being examined, giving greater steadiness of hand.
Longer working lengths can be useful for the shoulder joint and for the
stifle joint, where greater depth of soft tissue must be penetrated to access
the joint.

Arthroscope sheath and obturators
The arthroscope requires its own dedicated sheath which is protective
against bending and facilitates administration of fluid into the joint,
around the arthroscope tip, maintaining a clear view within the joint.
The sheath has its own dedicated obturators to protect it during penetra-
tion of soft tissues and through the joint capsule, and to enable passage
of the sheath through the soft tissues without the sheath becoming filled
with soft tissue. The ensheathed obturator is always used to access the
joint, replacing the obturator with the arthroscope once the joint cavity
is entered. This prevents forceful damage to the fragile tip and shaft of
the arthroscope. Both blunt and sharp obturators are available (Fig. 2.2).
Sharp obturators penetrate the joint capsule readily but risk damage to
structures within the joint following entry. Hence a blunt- or semi-blunt-
ended obturator tip is preferable to prevent iatrogenic damage to intra-
articular structures during sheath introduction into the joint. A locking
system fixes the arthroscope or the obturator within the sheath when
in use.

Light source and fibre-optic cable
Suitable light sources for arthroscopy include halogen and xenon, but a
xenon light source is significantly preferable since the light from xenon
is bright and a whiter light, giving better visual clarity and colour rendi-
tion. Lamp wattage varies from 100 to 400 W, with low wattage being
satisfactory for small joints and the higher power being necessary if
other endoscopic procedures are performed (e.g. laparoscopy) using the
equipment. The lifespan of xenon bulbs is limited to approximately