16

Partial Rupture of the Cranial

Cruciate Ligament

Peter Muir

Introduction

Ligament sprains are classified as Grade I
through III, depending on the severity of the
matrix damage. Ligament sprains are defined
biomechanically. Grade I sprains do not affect
joint instability and are associated with sub-
failure damage to the ligament tissue (Proven-
zanoet al. 2002). Grade II sprains are associated
with moderate fiber damage and a stretch to the
point of detectable instability. Grade III sprains
are associated with severe disruption of liga-
ment fibers and obvious joint laxity (Proven-
zanoet al. 2002). Consequently, dogs with a
stable stifle have partial cruciate ligament rup-
ture (CR) and dogs with an unstable stifle
have complete CR. Historically, CR has been
classified as partial or complete, based on an
anatomic definition in some reports. In human
beings, the assessment and grading of partial
anterior cruciate ligament injuries is controver-
sial, as these lesions may involve a variable
amount of the cross-section of the ligament dur-
ing arthroscopic evaluation (Honget al. 2003).

Partial cranial cruciate ligament rupture

In the dog, the cranial cruciate ligament
(CrCL) has cranio-medial and caudo-lateral

components containing bundles of longitu-

dinally orientated collagen fibers (Heffron

& Campbell 1978). The cranio-medial com-

ponent is taut in both flexion and extension,

whereas the caudo-lateral component is only

taut in extension (Arnoczky & Marshall 1977).

Biomechanically,ex vivosectioning of either the

cranio-medial component or the caudo-lateral

component of the CrCL induces the develop-

ment of mild joint instability in partial flexion,

with≤3 mm of cranial drawer motion that is lit-

tle influenced by stifle flexion angle (Heffron &

Campbell 1978). This small amount of cranial

drawer motion would be difficult to detect

on physical examination (Table 16.1) (Hef-

fron & Campbell 1978). Collectively, these

observations suggest that clinicians can infer

that the majority of the CrCL has been dis-

rupted biomechanically when cranial drawer

instability is detected by physical examination

(Heffron & Campbell 1978). In the human

patient, joint translation can also be measured

using an arthrometer (Bach et al. 1990). In

dogs, the development of weight-bearing

standing radiography (Kim et al. 2011) or

recumbent stress radiography (Bleedornet al.

2011) have helped quantify cranial tibial sub-

luxation in affected dogs. Future development

of an arthrometer for the dog stifle that can

Advances in the Canine Cranial Cruciate Ligament, Second Edition. Edited by Peter Muir. © 2018 ACVS Foundation.
This Work is a co-publication between the American College of Veterinary Surgeons Foundation and Wiley-Blackwell.

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