6

Histology of Cruciate

Ligament Rupture

Kei Hayashi

Pathology of cranial cruciate

ligament rupture

The exact etiopathogenesis of canine cruciate
ligament rupture (CR) is not defined. Although
acute cranial cruciate ligament injury does
occur with trauma, a number of previous stud-
ies have suggested that the majority of CR cases
are the result of chronic degenerative changes
within the ligament (Vasseuret al. 1985; Hayashi
et al. 2003a).
The development of progressive CR appears
to involve a gradual degeneration of both cruci-
ate ligaments, inflammatory disease in the stifle
joint, partial CR, and eventually complete rup-
ture. After rupture, secondary changes such as
progressive arthritis and meniscal injury often
develop. Initially, slight weakening or stretch-
ing of the cranial cruciate ligament (CrCL)
may not cause lameness, but can produce mild
instability within the joint, and therefore initi-
ate arthritic joint degeneration. However, it is
unclear whether this represents the initial phase
of the condition, or whether the development
of stifle synovitis is an initial event. Dogs with
incipient or partial CR have a stable joint, but
are presented with lameness, effusion of the sti-
fle joint, and synovitis. Complete CR produces
obvious instability of the stifle joint, resulting in

more severe joint pain, lameness, and progres-

sive degenerative changes within the joint. Clin-

ical observations have demonstrated that these

changes consist of periarticular osteophyte for-

mation, capsular thickening, and meniscal dam-

age. As these changes progress, the joints may

become more stable, although a recent experi-

mental study suggested that periarticular fibro-

sis does little to improve dynamic instability

during locomotion (Tashmanet al. 2004). Dogs

with advanced or end-stage pathologic changes

within the stifle may have little palpable pas-

sive instability because of extensive periartic-

ular fibrosis. After a partial or complete CR,

some degree of tissue repair response arises in

the epiligamentous region of the CrCL(Hayashi

et al. 2003a). In the human anterior cruciate lig-

ament (ACL), distinct histologic phases of tis-

sue repair, including an inflammatory phase,

a epiligamentous repair phase, a proliferative

phase and a remodeling phase, develop after

rupture (Murrayet al. 2000). Whether simi-

lar phases exist in dogs is not known. Expan-

sion of the volume of the epiligamentous tis-

sue does occur in the dog during a repair phase

that lasts many weeks. However, a bridging

scar does not form in the rupture site. Eventu-

ally, synovial tissue covers the ruptured ends of

the CrCL.

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.

47