DETECTING AND GRADING LAMENESS IN DOGS, especially that of the pelvic limb, can be challenging.
At least two studies (Waxman, 2008; Quinn, 2007) have demonstrated poor agreement between clinicians, and between subjective scores and force platform results.
Still, gait analysis is a skill that can be learned and constantly improved, but resources on the subject are scarce.
In a small survey of six orthopaedic-minded colleagues (including three specialists) on the kinematic markers that they look for when assessing lameness, there was unanimous consensus that a “head nod” is the most useful marker for thoracic limb lameness.
At stand, approximately 60% of a dog’s bodyweight is distributed via the two thoracic limbs. The cranio-caudal centre of gravity (COG) of a dog is believed to lie just behind the elbow. This is because the head and the neck “overhang” the forelimbs by some distance, whereas there is very little mass overhanging the pelvic limbs caudally (only the tail). This overhang of mass offers the dog an opportunity to shift the COG in a caudal direction by elevating the head and effectively shortening the lever-arm of the head and neck mass.
If we are considering lameness as an adaptation to reduce force transfer through a painful region, then this shift of mass may be an effective and reliable way to reduce force through the forelimbs. Remember Newton’s second law of motion: “Force = Mass x Acceleration”.
In the same survey as above, there was no consensus on a single marker for pelvic limb lameness, and the total list was much longer.
There is much less capacity for dogs to shift their COG further forward to reduce mass through hind limbs. This does occur, and dogs with severe, bilateral hind-limb lameness may ambulate with very low head carriage, or even completely on their forelimbs.
Some dogs also demonstrate a confusing hind-limb lameness head nod. However, there is a more reliable and repeatable marker for asymmetric hind limb lameness: the pelvic lift.
If the head nod aims to reduce the “mass” in Newton’s equation, the pelvic lift may be an adaptation to reduce the “acceleration”. Not the forward acceleration of the dog as a whole, but the downward acceleration of bodyweight as the painful limb enters stance phase. The dog effectively “throws” its pelvis upwards, minimally supporting it with the painful limb, and “catches” it again when the non-painful limb enters stance phase.
In Figure 2, compare the height of the pelvis in image 2 (lame, left hind-limb in stance phase) with that in image 4 (sound, right hind-limb stance phase). By carefully watching a dog at trot, the observer can appreciate the pelvic lift, and identify the lame hind limb as the one starting stance phase when the pelvis is at its highest point.
Unlike the forelimb lameness head nod, which is usually evident at walk and trot, the pelvic lift is best assessed in the trotting dog. At a walk, other gait adaptations to pelvic limb lameness are easier to observe.
One is a difference in stance time: the dog will generally try to spend less time with the painful limb in weight bearing: this is best appreciated by trying to appreciate a difference in paw speed during the swing phase of each limb. When a limb is in swing phase, the opposite limb is, by definition, in stance phase. The sound limb will generally move through swing phase more quickly in order to minimise the duration of the stance phase of the lame limb.
Another useful kinematic marker for pelvic limb lameness at walking gait is the “hip sway”. Some resources describe the hip sway as being characteristic of hip dysplasia, but in fact it may be present in other conditions. For example, many dogs with failure of the cranial cruciate ligament (CCL) walk with a more flexed stifle.
This stifle flexion effectively “shortens” the working length of the limb. To compensate for this shortening, the dog may walk with a more extended tarsus, but may also regain lost stride length by lateral bending of the spine to “swing” the pelvis towards the lame side: this is another useful marker to look for in asymmetric hind limb lameness. In cases of bilateral CCL failure, this pelvic swinging may occur bilaterally, resulting in a “swaying gait”.
Dogs and cats have an impressive capacity to adapt their gaits in response to pain, mechanical limitations and neurologic deficits. Detecting and describing lameness properly within the temporal and spatial constraints of a typical consultation can be challenging. But, with some basic knowledge (and a slow-motion app for your smartphone), accurate assessment is easily achievable.
- The author has posted a video tutorial on canine lameness assessment on YouTube, and will be presenting an interactive session rich in video resources at VetsNorth 2016 on 22nd June.
