Chapter 108 Disorders of the Coxofemoral Joint
The coxofemoral joint is the most proximal of the free-moving joints of the pelvic limb. Surgery is frequently performed on or near this joint to treat conditions such as coxofemoral luxations and hip dysplasia. Avascular necrosis of the femoral head, which occurs infrequently, also can be treated surgically.
ANATOMY
• In a normal animal, the joint capsule attaches to the rim of the acetabulum and around the circumference of the femoral neck just distal to the junction of the head and neck. When the limb is taken through range-of-motion exercises, the joint capsule helps maintain joint congruency.
• The ligament of the head of the femur runs between the acetabular fossa and the fovea capitis of the femoral head.
• The blood supply to the femoral head is extensive.
• Small arterial loops arise from the iliolumbar artery cranially; the lateral circumflex femoral artery dorsally, cranially, and ventrally; and the medial circumflex femoral artery dorsally, caudally, and ventrally. They all penetrate the femoral head at the joint capsule attachment.
• Several surgically important muscles have their insertions or origins close to the coxofemoral joint, either on the proximal femur or the pelvis (see Chapter 107).
• The middle and deep gluteal muscles originate on the wing of the ilium and insert on the dorsal and cranial border of the greater trochanter.
• The superficial gluteal muscle originates on the sacrum and the first coccygeal vertebra and inserts on the third trochanter.
• The vastus lateralis and intermedius muscles originate on the cranial aspect of the femur, whereas the rectus femoris originates on the pelvis cranial to the acetabulum.
• The tensor fascia lata muscle originates along the caudolateral edge of the femur, covering the vastus lateralis muscle, and along the cranial edge of the biceps femoris muscle via three or more tissue slips.
• Two angles of surgical significance have been described in the proximal femur:
• Angle of inclination: When the femur is viewed from a cranial position, the angle of inclination is the angle formed between a line that bisects the long axis of the femur and a line that bisects the femoral neck. In the normal dog, this angle is 135 to 145 degrees.
• Angle of anteversion: When the femur is viewed from a straight lateral position, part of the femoral head is displaced forward of the femoral shaft due to the anteversion angle of the femoral neck. One method of measuring this angle involves taking radiographs of the femur with the dog on its back with the long axis of the femur positioned 90° to the radiographic plate and the stifle joint flexed 90°. The radiographic beam must pass directly down the center of the femur, parallel to its long axis. One line is drawn parallel to the caudal edge of the femoral condyles, and a second line is drawn that bisects the femoral head and neck. The angle created by the intersection of these two lines is the anteversion angle, which in normal dogs is 20 to 27 degrees.
COXOFEMORAL LUXATIONS
Most coxofemoral luxations are craniodorsal displacements of the femoral head; almost all others are caudoventrally displaced. Usually these are associated with motor vehicle accidents; thus, fully evaluate other organ systems for trauma (see Chapters 3 and 166), as well as coxofemoral joint evaluation.
Diagnosis
• Animals with a luxated hip usually will not bear weight on the affected limb. If a craniodorsal luxation is present, the limb may be externally rotated and adducted.
• Range-of-motion evaluation of the hip may reveal grating and/or pain in the area of the coxofemoral joint.
• Evaluate the relationship between the caudal edge of the greater trochanter and the cranial edge of the ischiatic tuberosity to determine the position of the proximal femur.
• If a craniodorsal luxation is present, there will be a wide space that does not close (as in the normal animal) when the limb is externally rotated.
• When both hindlimbs are pulled directly caudally, they will be of equal length in a normal animal. If they are uneven in length, this is a strong indication that the coxofemoral joint is dislocated.
• The primary method of diagnosis is radiography of the coxofemoral joint to rule out fractures of the proximal femur, which can mimic a luxation on physical examination.
Treatment: Closed Reduction
If there is no avulsion fracture, perform closed reduction of the joint under general anesthesia.
• The longer the femoral head is luxated craniodorsally, the more damage that is done to the dorsal joint capsule. An intact joint capsule is helpful in maintaining reduction.
• If the reduced hip snaps solidly into position, place the hip in a flexion sling for a craniodorsal luxation; place the legs in hobbles for a caudoventral luxation (Fig. 108-2). Apply these restriction bandages for 10 to 14 days in the adult and 7 to 10 days in the immature animal. Limit exercise during this period, and for an additional 2 to 4 weeks.
• Examine the reduced hip physically on a daily basis or instruct the owner to do this, until the restriction bandage is removed.
• If there is any question about the hip’s position, reevaluate with lateral pelvic radiographs. If the hip is reluxated, perform an open reduction.
Treatment: Open Reduction
Surgical Procedures
Techniques
1. The standard approaches used for surgical repair of luxations are the cranial lateral approach to the hip and the trochanteric osteotomy approach (see Chapter 107). Occasionally a caudal approach (caudal to the greater trochanter of the femur) to the coxofemoral joint may be used.
2. Initially, assess the overall damage and the status of supporting tissues, remove abnormal tissue and debris from the acetabular cup, and reduce the femoral head into the acetabulum.
3. Once reduced, use one or more stabilization techniques to secure the femoral head into the acetabulum.
4. If the joint capsule is minimally damaged and adequate capsular tissue is present on either side of the tear, suture the capsule (this may be the only support necessary).
a. Use an absorbable monofilament suture of significant size (2-0, 0, or 1, depending on the animal’s size), placed in a cruciate pattern.
b. If adequate capsule is attached to the acetabular rim but not enough solid capsule is attached to the femoral neck, drill an anchor hole with lateral to cranial orientation in the proximal femur. Pass one-half of the suture strands through the hole and tie them tightly to the other half of the strands (Fig. 108-3).
5. The capsule may be so severely damaged that it cannot hold a conventionally placed suture. (This may occur if there is a long delay between the time of injury and repair.)
a. In these cases suture support can be provided by making anchor points for the sutures. Drill a hole (as described in Step 4b above) for an anchor site in the femur. Place one to three bone screws (usually a 3.5-mm cortical screw) in the dorsal rim over the acetabulum as anchor points on the pelvis. Place the suture support between these to form a dorsal reinforcement (Fig. 108-4).
b. Alternatively, place a temporary intramedullary pin in the proximal femur, parallel with the neck axis, and through the acetabular fossa. Be sure that the pin does not extend too far into the pelvic canal (Fig. 108-5). Keep the limb immobile with a flexion sling until the pin is removed, 7 to 10 days after surgery.
c. Another alternative is to place a toggle pin through a hole in the acetabular fossa with suture attached to it. This creates an artificial ligament between the head of the femur and the acetabulum. Pass the suture through a hole drilled, from lateral to medial, in the proximal femur. The hole enters the femur just dorsal to the third trochanter and exits at the insertion point of the ligament of the head of the femur on the femoral head. Pull all the suture strands through this hole, and then pass half the suture strands through a second hole in the femur drilled in a cranial to caudal direction. Tie the two sets of suture strands together.
6. Rotate the femoral head inwardly, and tighten the gluteal muscle pull on the femur by moving the greater trochanter to a position caudal and distal to its original location. This technique can be used with a trochanteric osteotomy approach.
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