Contributors: Neil Burton, John Innes
Species: Canine | Classification: Miscellaneous
- Assessing lame dogs is not easy. For many years the veterinarian has relied on a visual assessment of the dog at various gaits (usually walking or trotting), combined with a history from the owner and a clinical examination. However, a recent study has shown that there are significant errors with visual scoring of canine lameness compared to objective measurement of lameness (Waxman et al, 2008).
- Whilst subjective assessment of gait will always be a day-to-day activity for small animal clinicians, an understanding of objective methods is useful because, increasingly, this is how medical and surgical treatments are assessed by researchers and veterinary medical regulatory authorities.
Objective assessment of lameness and mobility
- Objective assessment of gait, the science of kinesiology, has progressed significantly in the last 10-20 years assisted by advances in computer assisted technologies.
- Kinematics is the description of movement without reference to the influences of mass and force, whereas kinetics is the study of the forces involved in movement.
- Kinetic studies of canine limb function have most commonly utilized force platform technology and kinematic studies have typically used video or infrared motion analysis systems. This article will review the current status and uses of these methods as they apply to canine studies.
What is a force platform and what does it do?
- A force platform resolves the forces of movement in to three orthogonal planes vertical (Fz), craniocaudal (Fx) and mediolateral (Fy) and it measures these forces in Newtons at high frequency (eg 1000 Hz).
- Force platforms are typically based on either piezoelectric or strain gauge technology and are sited inconspicuously in the middle of a walkway which is usually approximately 10m in length . Dogs are lead by a handler along the walkway and the limb in question must strike the platform centrally at a controlled velocity (measured force is related to velocity). It is recommended that a minimum of five measurements for each limb are collected to allow for inter-trial variation.
- For each valid measurement, the force-time curve is plotted and various parameters are derived. The most commonly used parameters are the peak vertical force (PVF) and the area under the Fz-time curve, the vertical impulse (VI) and it is documented that limb pain and lameness reduce both PVF and VI. Conversely, effective analgesics and surgical treatments can increase these parameters in the index limb in lame dogs. Thus a force platform provides a sensitive method with which to assess lame dogs and to evaluate the efficacy of medical (Innes et al, 2003; Vasseur et al, 1995) and surgical (Conzemius et al, 2005) interventions.
- However, whilst there are many advantages to the use of force platforms, there are limitations. Firstly, small dogs and cats may not be suitable because their stride length is too short and they have more than one limb on the force platform at any one time; this can also be a problem with very lame dogs. The vertical impulse (area under the vertical force-time curve) is a useful parameter but may be difficult to measure in very lame dogs. This is because they can have complex force-time curves with overlap between the thoracic and pelvic limbs, making calculation of impulse very difficult.
- Pressure platforms and mats such as the Tekscan® and RS Footscan® have started to become popular for use in small dogs and cats. These systems appears to be useful for estimation of PVF and vertical impulse (Besancon et al, 2004; Lascelles et al, 2006) as well as pressure distribution across the paw, but they cannot resolve the force of movement.
Motion analysis systems
- Motion capture systems may be two- or three-dimensional, with the latter being preferred. Three-dimensional systems use infrared cameras that emit an infrared beam and this is reflected back from small retroreflective markers placed on the subjects limbs. Because the beam is emitted and reflected back to the camera, it is possible to calculate the distance of the marker from the camera and thus generate three-dimensional data on the co-ordinates of the marker in space. Cameras operate at 100-500 Hz and are thus able to capture all canine gaits, although most studies have thus far concentrated on the walk and trot.
- Previous work has documented the angular motion and angular velocities of normal dogs (Owen et al, 2004; Clements et al, 2005; Hottinger et al, 1996; Allen et al, 1994) and to a limited extent for dogs with common orthopedic conditions (Bennett et al, 1996; DeCamp et al, 1996) although there has been limited use of kinematics to evaluate candidate therapies (Bolliger et al, 2002; Lee et al, 2007). Powerful software is available to collect and analyse these data .
Combining kinetics and kinematics
- By combining kinetics and kinematic data, along with morphometric data, researchers have recently developed biomechanical models (eg using inverse dynamic modelling) to estimate forces, moments and powers acting through individual joints of canine subjects (Colborne et al,2005; Nielsen et al, 2003). Although such models have been around for some considerable time for human locomotion studies, it is clear that breed-specific models are required for dogs (Colborne et al,2005). However, such approaches will allow us to investigate function and dysfunction of the canine musculoskeletal system in a powerful way and also facilitate evaluation of medical and surgical treatments.