Simon C. Roe, BVSc, PhD, DACVS
Traumatic hip luxation causes tearing of the round ligament and varying degrees of disruption of the joint capsule. Radiographs are important in the evaluation of the luxation, as fractures from the femoral head or the acetabular rim may be associated with the luxation, and their presence alters the treatment plan. Well positioned, high quality films are necessary, as some of the avulsion fragments may be small.
If no fractures are present, closed reduction may be attempted. The limb is externally rotated while traction is applied and, once the femoral head is in the region of the acetabulum, the limb is internally rotated and abducted, while firm pressure is applied to the trochanter. If there is a large amount of capsular tissue covering the acetabulum, it may be difficult to get the femoral head to seat. If the hip has been luxated for more than 4 to 5 days, muscle contraction and initial healing attempts of the capsular tissue may prevent reduction. If the hip is reduced, it should be manipulated vigorously while firm pressure is applied to the trochanter. This will squeeze out the hematoma, and reduce the size of the swollen round ligament remnants. Once the hip has been well seated, its stability should be assessed. External rotation is carefully performed. If this does not produce luxation, the hip is slowly adducted while simulating weight bearing. If it appears stable with these manipulations, there is a reasonable chance that it will stay reduced. If it is somewhat unstable on external rotation, and the limb has a long, thin conformation, and Ehmer sling that maintains some degree of internal rotation can be applied. If luxation occurs easily with any of the manipulations, it is unlikely that the hip will stay reduced, and open reduction is indicated. Open reduction is also the best choice if a bone fragment is present on the radiographic study.
The hip is exposed through a craniolateral approach that preserves the deep gluteal tendon and muscle as much as possible. These structures are often significantly damaged following craniodorsal luxation. The femoral neck and head are visualized first. The femur is flexed and externally rotated and the articular surface is assessed for injury. Round ligament is removed. The femur is then retracted caudodorsally to expose the acetabulum, if possible. If the joint capsule is mostly intact, the exposure may be limited. Ideally, no further damage is done to the capsule. Hematoma and remnants of the round ligament are removed. The articular surface and dorsal acetabular rim are assessed for damage both visually and by feel. The state of the joint capsule is assessed. Simple tears in line with the femoral neck or circumferential tears in the mid-portion of the capsule can be sutured after reduction and the hip will likely be very stable.
If the capsule has stripped from the dorsal rim or from the femoral neck, and is still firmly attached at the opposite aspect, stability can often be achieved by reattaching the capsule to where it has been stripped. Small bone screws or specifically designed suture anchors can be used as anchors for sutures in the dorsal rim. If the capsule is stripped from the dorsal acetabular rim, implants in the dorsal and craniodorsal locations are usually sufficient. If the capsule is stripped from the femoral neck, one or two anchors may be used in the neck. Sutures from the dorsal rim to the base of the greater trochanter have been used when there is complete capsule stripping. These sutures do have the potential to do significant damage to the dorsal portion of the femoral head if the rub on the articular surface.
If the capsule is completely stripped or shredded, reduction can be maintained by anchoring a synthetic round ligament to the medial wall of the acetabulum using a toggle pin or rod. Toggle pins are paper clip like implants formed by bending a K-wire. The toggle rod is a 10 mm long 3.2 mm diameter rod with a central hole and two grooves along the sides. One or two strands of 60 or 80 lb-t nylon leader line is usually used to replace of the round ligament. The nylon line is threaded through the hole in the rod. A 3.2 mm hole is drilled through the femoral neck. Drill guides have been developed to improve the accuracy of placement. If the hip is very unstable, this can be done from the articular surface, outward. In the various texts, this hole is aligned with the axis of the femoral neck. However, I prefer to orient it in a more horizontal plane relative to the ground. I start the hole in the middle of the greater trochanter. It will usually pass across the intertrochanteric notch before entering the femoral head. The reason for this orientation is to reduce the angle in the suture between the femoral head and the acetabulum. The 3.2 mm drill bit is placed in the hole through the neck, the hip reduced, the leg held in a normal standing position, and the drill bit advanced into the medial wall of the acetabulum. The hip is dislocated and the hole in the medial wall identified. The toggle rod is pushed through the medial wall and the suture pulled to cause it to turn and lock against the inner surface of the acetabulum. The sutures are pulled up the hole in the femoral neck using a pulling rod, the hip reduced and limb held in a standing position, and the sutures tensioned and secured with a crimp over a button on the surface of the trochanter. Post-operative restriction of activity is very important to protect the suture while the capsule heals.
A second approach to maintaining reduction if capsule repair is weak or impossible is an ilio-femoral suture. The aim of this suture is to prevent external rotation of the hip, and to limit lateral translation, thus maintaining reduction. It is anchored to the ilium in the region of the origin of the rectus femoris muscle. While the original description suggests that passing the suture through the fibrous origin of the muscle is sufficient, I prefer a bone tunnel or suture anchor. The important aspect of this suture is to ensure that the suture is anchored on the ventral aspect of the pelvis, and that it is close to the acetabulum. If it is too dorsal, or too cranial, the suture will not be able to limit the hip. The other end of the suture is passed through bone tunnels drilled transversely through the greater trochanter. I use hard-type nylon leader line, with the size determined by the size of the patient, and secure it with either a knot or a crimp.