NON INVASIVE DETERMINATION OF BODY SEGMENT PARAMETERS IN LABRADOR RETRIEVERS Chantal A. Ragetly1, Dominique J. Griffon1, Jason E. Thomas2, Ayman A. Mostafa1, David J. Schaeffer3, Gerald J. Pijanowski3, Elizabeth T. Hsiao-Wecksler2 1 Department of Small Animal Surgery, Small Animal Clinic (firstname.lastname@example.org), 2Department of Mechanical Science and Engineering (email@example.com) 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 statistically.
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