9

Morphological Risk Factors for

Cruciate Ligament Rupture

Eithne Comerford

Introduction

Biologists use the term ‘morphology’ to
describe the size, shape, and structure of an
organism or one of its parts. The morphology
and function of the cruciate ligaments has
been discussed in Chapter 1. This chapter will
describe the morphology of the bones involved
in stifle joint articulation in dogs, and highlight
comparative aspects of knee joint morphology
in non-contact anterior cruciate ligament (ACL)
injury in human beings.
Stifle joint morphology may play a causative
role in canine cruciate ligament degeneration
and rupture (CR). Conformational variation of
canine pelvic limbs such as a straight stifle
joint, narrow intercondylar notch, steep tib-
ial plateau slope and increased distal femoral
torsion, may contribute to cruciate ligament
microinjury, which in turn has been hypothe-
sized to cause progressive ligament rupture and
arthritis (Aikenet al. 1995; Comerfordet al. 2006;
Duerret al. 2007; Mostafaet al. 2014).

Distal femur

The distal femoral intercondylar notch (ICN)
contains both the cranial cruciate ligament

(CrCL) and the caudal cruciate ligament, as

they twist around each other from their femoral

attachment to their tibial attachment sites.

The distal femoral ICN is narrowed in dogs

and human beings with CR/ACL rupture and

arthritis because of increased osteophyte forma-

tion (Aikenet al. 1995; Wadaet al. 1996; Lewis

et al. 2008; Chenet al. 2016). Stenotic or nar-

rowed ICNs have been implicated as a risk fac-

tor in a recent meta-analysis of human ACL

injuries (Zenget al. 2013).

A stenotic ICN causes impingement by the

medial aspect of the lateral femoral condyle

or the intercondylar roof on the CrCL/ACL

(Aikenet al. 1995). If a normal-sized ACL passes

through a narrowed ICN, the reduced space

could impede the normal function of the ACL,

causing impingement and therefore damage

to the ACL (Munetaet al. 1997). One study

suggested that ACL impingement may occur

at the anterior and posterior roof of the notch

during tibia external rotation and abduction,

resulting in ligament microinjury (Dienstet al.

2007). This study also found a significant cor-

relation between ACL cross-sectional area to

notch surface area, with a smaller notch being

associated with a smaller mid-substance cross-

sectional area of the ACL. Some patients with

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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