LABRADOR RETRIEVERS

    Chantal A. Ragetly1, Dominique J. Griffon1, Jason E. Thomas2, Ayman A. Mostafa1, David J.
                 Schaeffer3, Gerald J. Pijanowski3, Elizabeth T. Hsiao-Wecksler2
    Department of Small Animal Surgery, Small Animal Clinic (, 2Department of
       Mechanical Science and Engineering ( and 3Department of Veterinary
                        Biosciences, University of Illinois, Urbana, IL, USA

INTRODUCTION                                        METHODS AND PROCEDURES

Inverse dynamics gait analyses have greatly         Test subjects were part of a larger study
contributed to the understanding of normal          examining differences in hind limb
and pathological movement in humans;                morphology and gait behavior due to cranial
however, nearly all canine gait analyses            cruciate ligament (CCL) deficiency. Hind
have involved only kinematic or ground              limb morphometric measurements and CT
reaction forces (GRF) gait parameters.              scans were collected on 24 dogs (14 normal
Application of inverse dynamics to dogs has         and 10 with unilateral CCL deficiency).
been limited by the lack of data regarding          Bone, muscle and fat areas were identified
inertial body segment parameters (BSP), i.e.,       according to CT pixel intensity (Figure 1).
mass, location of the center of mass (COM)          BSP were determined based on individual
and mass moment of inertia. Colborne et al.         tissue densities in the thigh, crus and foot
(2005) determined hind limb segment                 (Zatsiorsky, 2002). Stepwise regression
masses and COM locations, but these were            models were used to develop predictive
from a small cadaveric sampling of three            equations to estimate BSP for each leg type.
Labrador Retrievers and four Greyhounds.
   Computerized tomography (CT) allows
for non invasive determination of BSP, but
this approach requires general anesthesia
and is both time-consuming and expensive.
Estimating BSP based on simple
morphometric parameters (such as body
mass and/or segment length, width or girth)         Figure 1: 3-D CT scan pixel values attributed to
provides a basis for wide spread studies            fat (yellow), muscle (red) and bone (dark grey
using inverse dynamics to investigate hind          outline, curved white arrow) in transverse view at
limb biomechanics in dogs. Therefore, the           the hip (A), frontal (B) and para-sagittal (C) views
objectives of the current study were to (1)         at mid femoral level.
determine BSP of hind limb segments using
a non invasive method based CT in a large           RESULTS/DISCUSSION
sampling of living Labrador Retrievers, and
(2) develop regression equations for the            Average BSP values from the test limbs and
estimation of hind limb BSP in Labradors            regression equations to predict these BSP
using simple morphometric measurements.             were documented in normal healthy, CCL-
                                                    deficient, and contralateral hind limbs of
                                                    Labradors. The thigh and crus of CCL-
                                                    deficient limbs were found to be lighter than
their matched contralateral segments (Table      error, standard error of 127):
1). The thigh also weighed less in CCL-          Massthigh = -2723 + 31BM + 51Girththigh +
deficient than normal limbs. The moment of       296Widthstifle
inertia of the thigh was decreased in CCL-
deficient limbs compared to contralateral            We constructed regression equations
values. The COM of the crus was found to         based on parameters that are fast, non
be located more distally in normal limbs         invasive, technically simple and cost
compared to other limbs.                         effective to generate. This novel approach
    Lighter thigh and crus and decreased         will facilitate clinical studies of canine gait
mass moment of inertia are consistent with       mechanics, offering for the first time new
muscle atrophy observed in limbs with CCL        strategies to investigate the pathogenesis of
disease. This is likely secondary to pain and    non-traumatic joint diseases in living
decreased use of the CCL-deficient limb,         animals. Analysis of muscular pattern and
and advanced activity of the compensating        internal force at each joint of interest using
contralateral limb (Rumph et al, 1995). The      an inverse dynamics method will provide
more proximal position of the COM in             valuable insights for orthopaedists or
CCL-deficient and contralateral crus             neurologists.
compared to normal limbs is unlikely to be
solely due to CCL disease since contralateral    SUMMARY
limbs displayed the same distribution. These
contralateral limbs can be considered as         For the first time, the mass, COM and mass
predisposed to CCL deficiency based on the       moment of inertia of hind limb segments in
incidence of bilateral CCL disease in dogs       Labradors were calculated non-invasively
(Doverspike et al, 1993). A relatively greater   from CT imaging. In this study, we also
proportion of bone and/or muscle in the          establish with a series of predictive
proximal portion of the crus may be a factor     equations for estimating BSP based on
predisposing dogs to CCL disease.                simple morphometric parameters. These
    Regression equations based on                equations provide a basis for inverse
morphometric measurements were identified        dynamics studies, which will facilitate
to estimate segment mass, location of the        clinical studies of canine gait biomechanics.
COM relative to the proximal joint, and
mass moment of inertia for all three limb        REFERENCES
types. For example, in a normal healthy          Colborne et al. (2005) Am J Vet Res, 66:
limb, mass (in g) for the thigh could be            1563-1571
predicted for a given dog’s body mass (BM),      Doverspike, et al. (1993) J Am Anim Hosp
thigh circumference (Girththigh), and latero-       Assoc, 29:167-170
medial stifle joint width (Widthstifle) using    Rumph, et al. (1995) Vet Surg, 24:384-389
the following expression (R2 = 0.95, 5.0%        Zatsiorsky (2002) Kinetics of human motion.
                                                    Champaign, IL, Human Kinetics

Table 1: Mean (±SD) of mass, mass moment
of inertia, and COM location relative to the
proximal joint for thigh, crus and foot for
normal, CCL-deficient and contralateral limbs.
A, B: groups with different letters differ

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