Femoral head coverage percentage
Femoral head coverage percentage
- Acronym: FHCP
Definition
The femoral head coverage percentage is a measurement used to assess the anatomy of the hip joint in dogs. It quantifies the extent of lateral and dorsal coverage of the femoral head and is used to score coxofemoral dysplasia. It is determined from a ventrodorsal radiograph of the hips or multiplanar reconstructed CT images.
Radiographic evaluation
The dog is placed dorsal recumbency and the pelvic limbs are extended caudally, the femurs are parallel to each other. Positioning is considered satisfactory if :
the pelvis is symmetrical (iliums and obturator foramina are symmetrical)
the femur cortex pass through the middle of the sesamoid bones of the gastrocnemius muscle
the patellas are centered on the trochlea of femur.
A best fit circles outlining the heads of femur are drawn to define their centers and diameters. A line is drawn between the two craniolateral aspects of the acetabular margins. Two perpendicular lines are drawn : the first line touches the medial surface of the femoral head; the second line touches the cranial acetabular margin. The distance between these two lines is divided by the femoral head diameter and multiplied by 100 to yield the femoral head coverage percentage.
CT evaluation
The dog is placed in dorsal recumbency with hip joints extended, adducted, and rotated slightly internally. Measurement is performed on three contiguous images that include an acetabular fossa, a well-defined acetabular sourcil, a round head of femur, and a fovea capitis.
Three vertical lines are drawn perpendicular to the horizontal pelvic axis, defined as a line through the center of both femoral heads: the first line passes along the medial edge of the acetabulum (medial border of the lunate surface), the second along the lateral edge of the acetabulum (lateral border of the lunate surface) and the third along the lateral edge of the femoral head. The femoral head coverage percentage is the ratio of the distance between the first and second (a) and first and third lines (b) multiplied by 100.
Lopez et al (2008) found that the femoral head coverage percentage in adult mixed-breed dogs with laxity of the hip joints was 46.90 ± 8.25 (range 6.78 – 94.10)
Andronescu et al (2015) published the following results for the femoral head coverage percentage in relation to osteoarthritis score:
OA score 0: 50.84 ± 6.35
OA score 1: 47.87 ± 12.92
OA score 2: 42.30 ± 6.33
OA score 3: 30.00 ± 9.67
Andronescu et al. (2015) published the following results for the femoral head coverage percentage in 46 dogs with all osteoarthritis scores combined at each age:
16 weeks of age: 52.80 ± 7.75
32 weeks of age: 47.73 ± 8.86
104 weeks of age: 42.60 ± 11.62
References
Andronescu et al. (2015). Associations between early radiographic and computed tomographic measures and canine hip joint osteoarthritis at maturity. American Journal of Veterinary Research, 76(1), 19–27. doi:10.2460/ajvr.76.1.19
Belkoff SM, Padgett G, Soutas-Little RW. Development of a device to measure canine coxofemoral joint laxity. Vet Comp Orthop Traumatol 1989, 2, 31-36.
Lopez et al. (2008) Relationships among measurements obtained by use of computed tomography and radiography and scores of cartilage microdamage in hip joints with moderate to severe joint laxity of adult dogs. Am J Vet Res. Mar;69(3):362-70. doi: 10.2460/ajvr.69.3.362.
Pinna S, Pizzuti E, Carli F. Effects of intertrochanteric varus osteotomy on Norberg angle and percent coverage of the femoral head in displastic dogs. J Vet Sci. 2013;14(2):185-91. doi: 10.4142/jvs.2013.14.2.185.
Schachner and Lopez (2015) Diagnosis, prevention, and management of canine hip dysplasia: a review. Vet Med (Auckl). May 19;6:181-192. doi: 10.2147/VMRR.S53266.
