Advances in the Canine Cranial Cruciate Ligament, 2nd edition

70 Etiopathogenesis of Cruciate Ligament Rupture

7.5

5.0

2.5

0.0

30 30

Knee joint flexion (°)

90 90

Greyhound Labrador Retriever

* **

*

**

CC Laxity (mm)(Mean+/– SEM)

p = 0.04 p^ = 0.04

Figure 8.5 Cranio-caudal (CC) laxity testing in
Greyhounds (n=11) and Labrador Retrievers (n=11) at
100 N with the joint in 30◦and 90◦of flexion. Source:
Comerfordet al. 2005. Reproduced with permission from
John Wiley & Sons, Inc.

75

50

25

0

Greyhound Labrador Retriever

Expression of

pro-MMP–2 (% std)

(Mean+/– SEM)

p = 0.02

Figure 8.6 Levels of pro-MMP-2 (% inactive zymogen)
in Labrador Retriever and Greyhound cranial cruciate
ligaments. Source: Comerfordet al. 2005. Reproduced
with permission from John Wiley & Sons, Inc.

Greyhounds (Figure 8.7). This implies the
presence of partially degraded collagen triple
helices in Labrador CrCLs. Increased collagen
degradation, as indicated by the high levels of
MMP-2, is consistent with the thermal proper-
ties of the collagenous matrix of the Labrador
CrCL, as well as the increased stifle joint laxity
within this breed. Interestingly, gender or body-
weight did not correlate significantly with any
of the mechanical, biochemical, or thermal anal-
yses in this study.

Conclusions

Differences in cruciate ligament metabolism
(ACL and CrCL) indicated by greater MMP-2
expression and collagen denaturation are

100

75

50

25

0

Greyhounds Labrador Retrievers

Enthalpy (J/g collagen)

(Mean+/– SEM)

p = 0.05

Figure 8.7 The enthalpy of denaturation (J/g collagen)

of the differential scanning calorimetry thermograms from

Labrador Retriever and Greyhound cranial cruciate

ligaments. Source: Comerfordet al. 2005. Reproduced

with permission from John Wiley & Sons, Inc.

consistent with identified mechanical proper-

ties in guinea pigs and dogs. The ligaments

examined in these studies had no apparent

pathology and, therefore, the changes identi-

fied may be intrinsic to ligament metabolism.

This may be related to genetics (influencing

factors such as stifle joint morphology), and

may account for the differing breed predisposi-

tion to CR within these two species. Therefore,

subtle changes in cruciate ligament metabolism

and its influence on joint mechanics may play a

role in canine CrCL, and possibly human, ACL

rupture.

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