Hip luxations (Proceedings)

The coxofemoral joint is a ball and socket joint. Normal stability of the hip is provided through a combination joint capsule, ligament of the head of the femur and dorsal acetabular rim. In addition, the joint fluid and acetabular labrum including the ventral acetabular ligament and extraarticular soft tissue structures such as the gluteals, adductors and abductors of the hip joint provide secondary stability. Normally if the femoral head is displaced laterally from the neutral position, negative intraarticular pressure opposes the displacement. This process is also dependent on an appropriate volume and viscosity of the synovial fluid, a competent joint capsule and round ligament.

Normal anatomic landmarks of the pelvis and femur are important in aiding in the diagnosis of luxations. Normally a line drawn between the craniodorsal aspects of the ilial wing, the ischial tuberosity and the greater trochanter of the femur form a triangle when observed from the side or above. A craniodorsal luxation results in flattening or loss of the triangle along with outward rotation of the stifle, craniodorsal displacement of the greater trochanter, increased ischial-trochanteric distance, limb shortening on extension and crepitus/pain.

With ventral or caudoventral luxations the greater trochanter is displaced medially.

The most common luxation in small animals is luxation of the hip. The most common direction of luxation is craniodorsal. This type of luxation typically occurs due to trauma, 'hit by car' causing 60-85% of the injuries but also falls or jumping from moving vehicles. Caudoventral and ventral luxations are less frequent. These typically result from slipping or falling, classically on ice or other slick surfaces. The femoral head may become entrapped in the obturator foramen.

Closed reduction of craniodorsal luxations

Since trauma is the most common cause of hip luxation, the patient should be assessed for concurrent injuries and stabilized. Prior to attempting reduction, pelvic radiographs should be carefully evaluated for contraindications to closed reduction. Contraindications to closed reduction include hip dysplasia or OA, SI luxations, fractures of the femur or pelvis or chronic luxations. Closed reduction should be attempted in uncomplicated luxations within 4-5 days of the luxation with no other orthopedic trauma. Prompt reduction favors prognosis. Delays in reduction result in progressive cartilage damage, muscle contraction and inflammation/fibrosis. Closed reduction should be attempted first before resorting to other means or reduction or other treatment options. If closed reduction is unsuccessful or reluxation occurs other means of reduction or alternate procedures should be performed. The patient should be placed under general anesthesia to allow relaxation of the muscles to facilitate reduction. Even heavily sedated there will be enough muscle tone, not to mention pain, to prevent reduction. The patient is placed in lateral recumbency with the affected leg up. A towel or sling is placed under the leg around the pelvis to resist distraction of the leg. The stifle is rotated externally and traction applied distal and caudal either from the stifle or hock. This maneuver should 'unhook' the femoral head from over the ilium and start to move it into a more normal location. The other hand is used to palpate the greater trochanter and start to guide the trochanter over the rim of the acetabulum. Next, internal rotation of the limb with downward pressure on the greater trochanter should allow reduction. Once reduction is achieved, maintain downward pressure on the trochanter and rotate the hip to dislodge blood clots, debris and granulation tissue. The hip should be placed through a gentle range of motion to assess ease of reluxation. If the hip easily reluxates open reduction or other surgical options should be considered. Radiographs are performed to confirm reduction. Once reduction is confirmed an Ehmer sling is applied for 7-14 days. An appropriately applied Ehmer sling will maintain the limb in flexion with internal rotation of the hip and stifle, external rotation of the hock. This helps drive the femoral head in to the acetabulum while scar tissue develops to maintain the reduction. The Ehmer sling should be monitored both while in the hospital and at home by the owner since problems can occur. Common problems include the sling slipping off the thigh and irritation to the thigh, inguinal region and hock. The worst complication I have seen is necrosis of the foot due to an improperly applied sling. Once the sling is removed the patient should be limited to short, controlled leash walks and rest for 8-12 weeks. Closed reduction is successful on average about 50% of the time. The most common reason for failure of closed reduction is that the hip was never reduced. If closed reduction is unsuccessful or reluxation occurs other means of stabilization are indicated. Use of an ischial-ilial pin or DeVita Pin in association with closed reduction is not recommended. The pin is driven in a caudal to cranial direction starting ventral to the lateral ischium, dorsal to the femoral neck and driven into the ilial wing. The purpose it to temporarily form a lateral extension to the acetabular rim to maintain reduction. Complications from the Devita Pin are unacceptably high, including pin migration (10-27% of cases), sciatic nerve injury (75% of pins contact with sciatic nerve), septic arthritis, pin tract drainage, decubital ulcers and injury to the femoral head.

Open reduction of craniodorsal luxations

Open reduction is indicated if stable closed reduction cannot be achieved, if there is a recurrence of luxation, other orthopedic injuries are present or there are avulsion fractures to the head of the femur or acetabulum. One retrospective study did show success with closed reduction if the avulsion fracture was small. Reduction was maintained 83% of the time with 60% of patients having good function (Basher AWP, Vet Surg, 1986). If there are concurrent orthopedic injuries open reduction may be indicated over closed reduction since an Ehmer sling may not be required. There are many options for open reduction of the hip. Selection is based on quality of joint capsule and surrounding tissues, size of the patient, owner compliance, available resources, finances and surgeon's preference. The surgical approach is either through a craniolateral or dorsal approach to the hip. The approach is made easier by reduction of the hip under anesthesia prior to starting the surgical approach. This allows for more normal anatomical landmarks. The dorsal approach provides the best exposure but requires either an osteotomy of the greater trochanter or tenotomies of the middle and deep gluteals to reflect the muscles. Regardless of the approach, the acetabulum should be cleared of debris including the remnants of the round ligament, which may be swollen. The acetabulum and femoral head should be evaluated for cartilage damage, fractures or other injuries. If there is significant cartilage damage a salvage procedure such as femoral head ostectomy (FHO) or total hip replacement (THR) should be considered. Overall success rate of open reduction is approximately 10-20% with some degree of lameness in 30-35% of dogs depending on the degree of cartilage and soft tissue damage. Medical management of osteoarthritis is appropriate after closed or open reduction of a luxated hip. This should consist of weight management, use of joint supplements (glucosamine/chondroiten), omega 3 fatty acids, use of NSAID's on an as-needed basis and physical rehabilitation.

Primary capsulorrhaphy

This is a consideration if there is a single, simple longitudinal or circumferential tear of the joint capsule however this is rarely the case. A dorsal approach allows the greatest visualization. Sutures may be preplaced to allow more precise placement or placed after reduction. Sutures are placed 3-4mm apart in either a simple interrupted pattern or horizontal mattress pattern. Once tightened, the stability of the hip is assessed. If a trochanteric osteotomy was performed it is repaired with a pin and tension band. Radiographs are performed to confirm continued reduction, assess secondary repairs (pin/tension band) and an Ehmer sling placed for 7-14 days. If stability is not achieved or the quality of capsule is inadequate, another means of internal stabilization is selected or added.

Prosthetic capsule technique

This technique can augment a primary capsulorrhaphy or be used as a primary repair. A craniodorsal or dorsal approach to the hip is made, the acetabulum debrided and the joint components inspected. Two screws with smooth washers are placed in the acetabulum. Care is taken to angle the screws so they do not enter the joint. The screws are positioned in the 10-o'clock and 1-o'clock position for the left hip and the 11-o'clock and 2-o'clock position for the right hip. A third screw with smooth washer is placed in the intertrochanteric fossa. Alternately, a bone tunnel can be drilled through the proximal aspect of the base of the femoral neck. Heavy gauge, nonabsorbable suture is used to make a figure-of-eight pattern between the screw in the intertrochanteric fossa (or through the bone tunnel) and each of the acetabular screws independently. Bone anchors may be used instead of screws with washers. The size of the screw and gauge of the suture is dependent on the size of the patient. Most likely the suture will fail but ultimately scar tissue should stabilize the hip long term. Remnants of the joint capsule should be repaired. Radiographs are performed after surgery to confirm screw placement, assess secondary repairs (pin/tension band) and continued reduction of the hip. An Ehmer sling is applied for 7-14 days.

Iliofemoral suture

This technique can augment a primary capsulorrhaphy or be used as a primary repair. A craniodorsal to the hip is made, the acetabulum debrided and the joint components inspected. A screw with smooth washer is placed in the lateral surface of the caudoventral ilium just in front of the acetabulum. Alternately a bone anchor or bone tunnel can be placed. A bone tunnel is drilled perpendicular through the femur medial to the base of the greater trochanter. A heavy gauge nonabsorbable suture is placed through the bone tunnel in the femur then around the screw, bone anchor or bone tunnel in the ilium. As the suture is tightened it should result in internal rotation of the proximal femur driving the femoral head into the acetabulum. Remnants of the joint capsule should be repaired. Most likely the suture will fail but ultimately scar tissue should stabilize the hip long term. Radiographs are performed after surgery to confirm screw placement and continued reduction of the hip. An Ehmer sling is applied for 7-14 days.

Transarticular pin

A craniodorsal or dorsal approach to the hip is performed, the acetabulum debrided and the joint components inspected. A smooth IM pin is driven from the lateral surface of the femur starting below the greater trochanter, through the femoral neck and exciting at the fovea capitis. The IM pin is retracted so it is flush with the level of the surface of the femoral head. The hip is reduced and the pin driven into the acetabulum. The remnants of the joint capsule are sutured. The pin is left long enough to facilitate removal in 4 weeks. Pin breakage and articular cartilage damage can be seen.

Toggle pin

Toggle pins can be purchased commercially or made with 0.045" k-wire (dogs > 7kg) or 0.062" k-wire for heavier patients. If making toggles the wire should be twisted into a central loop to allow attachment of the suture and 2 'wings' that hook or grab the medial aspect of the acetabulum. A C-aiming device is also useful when creating the bone tunnel through the femoral neck. A craniodorsal, dorsal or even caudolateral approach to the hip can be used based on surgeon's preference. The acetabulum is debrided and the joint components inspected as with all other procedures. A hole is drilled in the acetabulum in the area of the origin of the round ligament. A C-aiming device is used to drill a bone tunnel starting on the lateral aspect of the femur below the greater trochanter and exciting at the fovea capitis. Improper alignment of these 2 holes can result in increased strain in the suture resulting in premature failure. A second bone tunnel in the femur is created perpendicular to the first, approximately 1cm proximal or distal to the first tunnel. One to two strands of heavy gauge, nonabsorbable suture such as number 2 or 5 monofilament nylon or braided polyester suture such as Ticron or Ethibond is used. The suture is looped around the center loop of the toggle leaving 2 long strands if 1 suture is used or 4 long strands if 2 sutures are used. If 2 sutures are used I cut one of the strands a few inches shorter so when it comes time to tie I know which strands belong together. The toggle with sutures is dropped through the hole in the acetabulum. Care is used to ensure the toggle drops all the way through the acetabulum and turns perpendicular to the hole so the 2 'wings' hook on the medial aspect of the acetabulum. Tension is placed on the suture to test placement. Appropriately placed you can lift the dog off the table. A fine gauge wire loop (I make mine out of cerclage wire) is used to pass the strands of suture from the fovea capitis to the lateral surface of the femur. The femur is reduced and tension applied to the suture to remove slack. Next, the sutures are divided and one set is passed cranial to caudal with the wire passer while the other set is passed caudal to cranial and tied securely. The joint should be checked for laxity and remnants of the joint capsule closed. Most likely the suture will fail but ultimately scar tissue should stabilize the hip long term. Radiographs are performed after surgery to confirm placement of the toggle and continued reduction of the hip. An Ehmer sling is not required unless the repair is tenuous.

Salvage procedures

Femoral Head and Neck Ostectomy (FHO) and Total Hip Replacement (THR) are possible treatment options for dyplastic or osteoarthritic patients, failed closed or open reductions, femoral head fractures and chronic luxations. Careful patient selection is recommended. Smaller patients may do fine with FHO where as large to giant breeds will benefit from THR. I strongly recommend physical rehabilitation after FHO to improve limb use, range of motion and patient comfort.

Closed reduction of caudoventral/ventral luxations

The same caveats apply to caudoventral/ventral luxations as craniodorsal luxations: stabilize the patient first, thoroughly evaluate the pelvic radiographs and anesthetize the patient prior to attempting reduction. The patient is placed in lateral recumbency with the affected leg up. A towel or sling is placed under the leg around the pelvis to resist distraction of the leg. Distal traction is applied to the limb above the stifle or hock to 'unhook' the femoral head from the obturator foramen. Slight abduction of the limb may aid in this portion. The opposite hand is placed under/medial to the proximal femur, leveraging against the tuber ischii, to lift the femoral head lateral then cranial into the acetabulum once the head has been freed from the obturator foramen. The hip should be placed through a gentle range of motion to assess ease of reluxation. Stability of the hip after reduction is dependent on the stability of the dorsal support structures. If the hip easily reluxates open reduction or other surgical options should be considered. Radiographs are performed to confirm reduction. Hobbles are placed at the level of the stifles to prevent abduction of the femur. Hobbles placed at the level of the hock do not prevent abduction of the femur sufficiently.

Open reduction of caudoventral/ventral luxations

The same open techniques used for craniodorsal luxations can be applied to ventral/caudoventral luxations. These tend to limit caudal displacement of the femoral head but not ventral displacement. If the joint is still unstable, suturing of the ventral acetabular ligament may be required. Radiographs are performed postoperatively to assess any implants, secondary repairs and confirm continued reduction of the hip. Stifle hobbles are placed prior to recovery and maintained for 2-3 weeks. Exercise is restricted for 8-12 weeks.

Additional reading:

Textbook of Small Animal Surgery, Ed: Douglas Slatter, 3rd edition. Pub. Saunders of Elsevier Science, Philadelphia, 2003

Handbook of Small Animal Orthopedics and Fracture Repair, Ed: D Piermattei, G. Flo, C. DeCamp, 4th edition. Pub. Saunders of Elsevier Science, Philadelphia, 2006

Small Animal Surgery, Ed. T. Fossum, 3rd edition. Pub. Mosby of Elsevier Science, St. Louis, 2007