318 Canine Sports Medicine and Rehabilitation
Carpal injuries
Cause
The most common cause of carpal injury
appears to be acute hyperextension (Figure
12.25) that results from excessive loading of the
limb due to traumatic events from falls, includ
ing jumping down from heights or with a twist
ing motion at the limb (Kapatkin et al., 2012).
Fractures along with luxations/subluxations
often will occur concurrently with ligamentous
injuries. The fractures tend to be intra‐articular
in nature and as such fit the criteria for ana
tomic reconstruction and internal rigid fixation.
Acute injuries tend to result in a significant to
non‐weight‐bearing lameness.
Chronic repetitive sprains and strains to the
supportive structures of the joint occur over
time. These stressors do not usually cause an
acute significant lameness but rather an incon
sistent to low‐grade consistent lameness. The
mechanical properties of the carpal ligaments
have been evaluated. The accessoro‐metacar
pal ligaments have the highest elastic modu
lus, which likely contributes to preventing
hyperextension. The intra‐articular palmar
radiocarpal and palmar ulnocarpal ligaments
have the second highest elastic modulus and
are responsible for restricting cranial and cau
dal instability. The lowest elastic modulus is
found in the medial and lateral collateral liga
ments, which support valgus and varus devi
ation. Failure was documented in all of these
ligaments and revealed that 58% fail at the
mid‐ligament, 23% are a result of avulsion,
and close to 19% fail at the bone–ligament
interface (Shetye et al., 2009).Injuries
Carpal injuries can be broadly classified
into sprains, strains, luxations, fractures, or a
combination of these injuries. Many varia
tions of carpal injury can occur including: (1)
hyperextension (Figure 12.26A) with disrup
tion of the palmar ligaments with or without
disruption of the joint capsule; (2) hyperflex
ion (Figure 12.26B) with rotation of the dorsal
ligaments and collateral ligaments with or
without disruption of the joint capsule; and
(3) medial or lateral collateral ligament inju
ries or degeneration of the carpal ligaments
as a result of disease processes (immune‐
mediated disease, metabolic disease, etc.).
Flexor carpi ulnaris (FCU) injuries can range
from strains to core lesions or complete dis
ruption and avulsion.
A sprain is an injury to a ligament that can
occur in the mid‐portion of the ligament or at
its attachment to the bone. Historically, sprains
can be classified into three grades of severity.
Grade 1 sprains are mild and are described as
an overstretching of the ligament without dis
ruption or loss of function of the ligament.
Grade 2 sprains are moderate in severity and
are described as a partial tear of the ligament.
The general continuity of the ligament is intact
although the strength of the ligament is signifi
cantly reduced. Grade 3 sprains are severe and
result from complete disruption or tearing of
the ligament, resulting in instability of the joint.
Since ligaments have a poor blood supply and
require the formation and organization of col
lagen for their repair, ligament healing times
can be quite lengthy (Dirks & Warden, 2011).
Studies show that ligaments regain between
50% and 70% of their original strength after 1
year (Bishop & Bray, 1993; Frank, 1996; Frank et
al., 1999). If a gap forms or is present at the junc
tion of the ligament ends during healing, per
manent ligament elongation and subsequent
instability may result even if an intact ligament
reforms (Hildebrand & Frank, 1998).
Carpal hyperextension injuries occur due to
Figure 12.25 Dog with carpal hyperextension. damage to the flexor retinaculum and palmar