Slocum
Enterprises,
Inc.
Quality Veterinary Equipment,
Implants and Diagnostic Aids
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Course 2008
Sept 12-13th TPLO course now accepting registration. |
The Angle of Reduction and the Angle of Subluxation for Evaluation of the Canine Hip By Barclay Slocum, DVM and Theresa Devine Slocum, MS The dog is anesthetized and placed in dorsal recumbency. The femurs are positioned at 90 degrees to the spine of the dog, perpendicular to the table. Without placing any force on the femur, the knee is guided lightly in an abducted position with the femur still at 90 degrees to the spine. There will be a discernible movement of the hip back into the acetabulum from its subluxated position. The angle can be measured by an electronic goniometer from the starting point of zero degrees, and is known as the angle of reduction. The angle of reduction is possible after the hip has moved laterally from its normal position within the confines of the acetabulum. When the femoral head is lateral to the acetabulum it rests in the joint capsule which is stretched by the axial femoral force. As the femur is abducted the point of contact between the dorsal acetabular rim and the femoral head is moved from the dorsomedial aspect of the femoral head to the dorsal aspect of the head. When the point of acetabulum-head contact has moved sufficiently, the line of the axial femoral force is directed medial to the point of contact and the femoral head will spontaneously reduce with a palpable vibration. The ability for the femoral head to produce a vibration is diminished by filling of the acetabulum with osteophytes and thickening of the joint capsule. Clinically, the angle of reduction represents the degree of joint capsule stretching. The angle of subluxation is possible only if the hip can move laterally from its normal position within the confines of the acetabulum. When the femur is adducted and the femoral head is in the acetabulum, the axial femoral forces direct the femoral head into the depth of the acetabulum. This occurs so long as the axial femoral vector forms an acute angle with the slope of the acetabulum at the point of contact between the femoral head and the acetabulum. As the hip is adducted, the angle between the axial femoral force and the slope of the acetabulum at the point of contact between the two goes from acute to obtuse. At that angle the femoral head begins to translate laterally and a palpable vibration is produced as the femoral head moves laterally into the joint capsule. Clinically, the angle of subluxation represents the least slope of the acetabulum which will produce a stable hip and is therefore the ideal angle for a pelvic osteotomy. This angle is measured from vertical with an electronic goniometer.
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