5

Biomechanics of the Normal

and Cranial Cruciate

Ligament-Deficient Stifle

Antonio Pozziand Stanley E. Kim

Normal stifle

The stifle is a complex, diarthrodial, synovial
joint that allows motion in three planes (Fig-
ure 5.1). The round femoral condyles articu-
late with the flat tibial condyles with a range of
motion about the medial-lateral axis of approx-
imately 120◦. Normal stifle angles range from
160 ◦in full extension, to 40◦in full flexion (Jaeg-
geret al. 2002; Allenet al. 2009). Based on fluoro-
scopic kinematics during trot, walk, stair ascent
and sit, the stifle flexes to 35◦and extends to
145 ◦during these activities (Kimet al. 2015).
The flexion–extension motion occurs through a
combination of rolling and gliding of the femur
on the tibia. With rolling alone, the femoral
condyle would roll off the tibial plateau before
maximum flexion was achieved, whereas with
gliding alone the femoral shaft would impinge
on the tibia. Rollback is asymmetric: femorotib-
ial contact translates more caudally on the lat-
eral than on the medial plateau, resulting in
internal tibial rotation during stifle flexion with
a range of motion that can vary from 6◦to 15◦
during sitting and trot (Vasseur & Arnoczky
1981). This change in rotational constraint over
a range of motion, which also occurs in the
human knee, has been termed the ‘screw-home’
mechanism.

Due to the slight tibial translation in the sagit-

tal plane that is coupled with flexion and exten-

sion, it is clear that the stifle does not function as

a pure hinge joint. Medial-lateral and proximal-

distal translation is tightly constrained by the

collateral ligaments, but still allows for rota-

tion about the medial-lateral and longitudi-

nal axes. Although the rotational motion about

the medial-lateral axis far exceeds the motion

about the other two axes, approximately 20◦

of varus–valgus and internal–external rotation

occurs over an entire walking–gait cycle in nor-

mal dogs (Korvicket al. 1994). Understanding

stifle kinematics in three dimensions rather than

simply attempting to address cranio-caudal sta-

bility is important for the treatment of cra-

nial cruciate ligament (CrCL) deficiency. Both

a lack of neutralization (e.g., tibial osteotomies)

or absolute constraint (e.g., extracapsular stabi-

lization) of internal–external rotation may lead

to abnormal mechanical stresses on the artic-

ular surfaces and progression of osteoarthritis

(Chailleuxet al. 2007; Kimet al. 2008).

The patellofemoral joint is an important

contributor to complex stifle biomechanics

(Mooreet al. 2016). Patellofemoral kinematics is

closely coupled with femorotibial kinematics,

as patellar flexion angle increases and the

patella translates distally as the femorotibial

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.

39