Front Matter

432 Canine Sports Medicine and Rehabilitation

There are numerous articles examining the
forces placed upon the articular facets and
intervertebral discs of the canine lumbar spine.
These studies were intended to study the effects
that these forces might have upon the human
spine and many conclusions were found to be
applicable to both species.
Wood and colleagues (1992) found that while
walking, the canine’s L2–L3 vertebrae became
2–3 degrees more kyphotic compared with the
standing position and the average excursion
between opposing facets was 3.4 ± 1.3 mm.
Although it is well recognized that these
motions and their limits protect the spine from
excessive flexion and torsion and help to stabi­
lize the spine, the actual forces involved have
not received much attention. Buttermann and
colleagues (1992) were the first to measure
actual loads on the facet joint in vivo. They
determined the load on the articular joint sur­
face of the L3 cranial articular facet. Using
strain gauges, they measured the forces of the
right L3 articular surface of five mongrel dogs
in various positions and performing various
activities. They verified their findings using
two in vitro studies. A Newton (N) is an interna­
tionally accepted unit of force that by definition
is the force necessary to provide a 1 kg mass
with an acceleration of 1 m/s.
Their results demonstrated the relative forces
placed upon the facets under varying condi­
tions. For the following data, only the right L3
cranial facet was measured in five animals, and
the forces found were:

● While sitting:10–65 N

● While lying, 0–45 N

● When flexing the head to get a treat from

between the thoracic limbs while standing:

0–65 N

● Sitting while having the thoracic limbs held

in the air and then turning (torsion) to the

left: 0–40 N (this activity unloads the forces

on the right facet)

● Sitting while having the thoracic limbs held

in the air and then turning (torsion) to the

right: 65–130 N

● Walking while having the thoracic limbs

held off the ground: 65–140 N

● Climbing stairs: 105–170 N

● Decending stairs: 100–120 N

● Right turning: 45–135 N

● Left turning: 0–80 N

● Sit to stand: 65–110 N.

To put these numbers in some perspective,

the forces measured from a human prosthetic

hip while walking are 800–2200 N. Comparing

the force per unit area of the human coxofemo­

ral joint, the measurement would convert to

1–6 MPa (megapascals). Since the facet joint is

considerably smaller, the forces over the L3

articular surface convert to a maximum of

2 MPa. A megapascal is 10^6 N/M^2. It is worth

noting that although the joint forces on the car­

tilaginous structures in humans and dogs are in

the same range per unit area, the cartilage in the

dog is considerably thinner. Although we do

not usually consider joint function in terms of

Figure 17.10 Lumbar vertebrae 3 and 4 demonstrating the structures that adjoin the two vertebrae.