Femoral rotation and relationship between the femoral head and the acetabulum

Abstract

Canine hip dysplasia is a debilitating hereditary orthopaedic disease with a high prevalence in dogs. The aim of this study was to describe the influence of internal or external rotation of the femur on the projected radiographic position of the patella within the trochlear groove, and on the femoral head in relationship to the acetabulum in the standard ventrodorsal hip extended view, i.e., medial or lateral patella displacement, Norberg angle, femoral head subluxation index and femoral head subluxation category. Eleven adult dog cadavers of large and giant breeds were radiographed in standard ventrodorsal hip extended view and with internal and external femoral rotation. The medial and lateral patella displacement, Norberg angle, subluxation index and subluxation category variables were measured on radiographs, and analysed comparing the normal position with positions of different degrees of internal or external rotation of the femur. In the normal ventrodorsal hip extended view, the patella was centred within the distal femoral metaphysis (P > 0.05). A mean ± SD internal femoral rotation of 16.0 ± 5.9° resulted in a medial patella index displacement of 0.23 ± 0.09, and a mean external femoral rotation of 17.9 ± 6.7° resulted in a lateral patella index displacement of 0.24 ± 0.1. The mean Norberg angle was 105.3 ± 4.3°, 107.7 ± 5.5° and 104.2 ± 4.3° (P < 0.05); the subluxation index was 0.15 ± 0.06, 0.12 ± 0.05 and 0.18 ± 0.06 (P < 0.05); the subluxation category was 1.55 ± 0.6, 1.46 ± 0.7 (P > 0.05) and 1.96 ± 0.65 (P < 0.05) in normal, internal and external femoral rotation ventrodorsal hip extended views, respectively. In conclusion, as the Norberg angle, subluxation index and subluxation category are parameters used for classification in the main international hip dysplasia scoring systems, adequate femoral position with the patella centred in the distal metaphysis is of uppermost importance to ensure the technical quality of radiographs.

Effect of the Dog positioning on X-Ray Table on Hip Dysplasia Parameter Evaluation

“…1,10,19 Dysplastic hips show additional changes as osteoarthritic signs and deformation of femoral head and acetabulum. 9,10 Previous studies in cadavers 12,14 and with simulation of a computer program 15 have linked pelvic tilting along its long or short axis, and femoral malpositioning, with changes in the relationship between femoral head and acetabulum and consequently in the technical evaluation performed. In this work, only pelvic and femoral tilting along the long body-axis was evaluated because the lack of radiographic superimposition and absence of symmetry of pelvic and femoral bone structures along the long body dorsal plane make it difficult to measure the grade of pelvic tilting along the short axis.…”

“…2). 14 Canine hip dysplasia parameters were evaluated measuring the NA, the SI and the SC. 12,14 The NA was measured in degrees between a line joining the centres of the femoral heads and the line joining the centre of the femoral head and the craniolateral aspect of the acetabular rim.…”

“…14 Canine hip dysplasia parameters were evaluated measuring the NA, the SI and the SC. 12,14 The NA was measured in degrees between a line joining the centres of the femoral heads and the line joining the centre of the femoral head and the craniolateral aspect of the acetabular rim. 17,18 The SI was measured dividing the distance between the centre of the femoral head and the acetabular centre by the radius of the femoral head.…”

“…[11][12][13] Previous studies on cadavers have shown that longitudinal pelvic and femoral internal or external rotation are directly associated with inadequate NA, femoral head subluxation index (SI) and femoral head subluxation category (SC) measurements. 12,14 Other studies, performed using a bone model 13 and computed tomography simulation, 15 obtained contradictory results in the association of pelvic tilting along the short axis with NA measurements.…”

“…Although some reports on cadavers investigated the effects of dog malposition in canine hip dysplasia scoring, 12,14 no studies that quantify the effect of pelvic tilting and femoral rotation on VDHE radiographic views in live animals are available. The main purpose of this study was to evaluate the relationship between pelvic tilting along the long axis or femoral rotation and the measurements of the NA, the SI and the SC on VDHE view.…”