Triple Pelvic Osteotomy
WHAT IS TRIPLE PELVIC OSTEOTOMY?
Triple osteotomy of the pelvis is a surgery designed to improve the short- and long-term quality of life for large dogs afflicted with canine hip dysplasia. Osteotomy means to cut the bone; triple pelvic osteotomy (TPO) means that the pelvis is cut in three places. This allows the surgeon to change the position and orientation of the acetabulum (hip socket), which is found at the junction of the three pelvic bones (the ilium, the ischium, and the pubis), and attempt to restore a congruent fit with the femoral head.
WHAT ARE THE REQUIREMENTS FOR TPO?
This is a corrective procedure which seeks to “undo” the main feature of hip dysplasia; i.e., the incongruency and instability between the femoral head (ball) and acetabulum (socket). Its success is dependent on a number of factors. First, the femoral head which is subluxated (dislocated) from the acetabulum must be “reducible”, which means it can manually be seated back into the socket. The position and angle of the leg at which this can be achieved is important, since this determines how much the acetabulum is rotated at the operating table; if too much rotation is needed, an abnormal gait will be induced post-operatively, and the operation will be less successful. Second, the upper shelf (dorsal acetabular rim) of the socket must not be worn too far away, or else the hip may continue to dislocate after surgery. Third, there should be no degenerative changes (osteoarthritis) already present, since long-term success is dependent upon putting good cartilage of the femur against good cartilage of the acetabulum. Fourth, the ideal candidate should still be able to remold the bones to adapt to the biomechanical redirection of forces around the hip joint. These factors are evaluated by carefully questioning the owner about the dog’s history and present function, orthopedic examinations awake and with the dog sedated/anesthetized, and by evaluation of radiographs (x-rays). In some cases more advanced tools are used to assess the joints. These include computed tomography (CT scans), magnetic resonance imaging (MRI) and arthroscopy.
IS THERE AN AGE LIMIT FOR TPO?
Most bones in the dog cease growth by approximately one-year of age. After this time the “plasticity” of bone, or its ability to remodel according to new stresses, is severely reduced. Thus, it is advantageous to do this operation as early as possible, and take advantage of the younger dog’s greater potential for remodeling. In addition, hip dysplasia is a progressive disorder, and the degree of laxity, breakdown of cartilage and bone and development of arthritis all worsen with time. Because these are factors which mitigate against the long-term success of the operation, it is imperative to perform TPO before such severe changes occur. Since many of these problems may be seen even before a year of age, most dogs will be candidates for the procedure only during the first year of life. The one year age limit is only an approximation, however, and an individual decision needs to be made not only for each patient, but for each hip in a given patient. Sometimes dogs as young as 7 or 8 months of age will already have such severe secondary changes from their hip dysplasia that they cannot be benefitted by TPO. Occasionally some older dogs will not, in spite of ongoing hip dysplasia and mechanical lameness, have many of these disqualifying factors, and so may still be considered for the operation.
SHOULD ALL YOUNG DOGS WITH HIP DYSPLASIA HAVE A TPO?
The decision to pursue corrective surgery is based not only the criteria listed above, but finally on the present and anticipated function of the dog. If an animal has mild hip dysplasia found on radiographs, but has no clinical indication of lameness, pain, etc., it may be better to follow that patient with examinations and x-rays over time, rather than selecting surgery immediately. For this animal, the TREND will be more important. If the dog starts to develop signs, and/or the x-ray appearance of the hips is clearly deteriorating, then surgery should probably be performed. If a puppy has asymptomatic hip dysplasia, but is intended for athletic function in the future (e.g. police work, hunting, field trials, keeping up with an owner who is an avid runner, etc.), it may also be prudent to consider TPO before problems arise. One of the problems is that not all dogs with hip dysplasia, even after arthritis has developed or gotten severe on the x-rays, show outward clinical signs of disability. Some dogs who have a triple pelvic osteotomy may never have been destined to have a clinical problem in the first place. Thus, there is a great deal of judgment needed in selecting appropriate candidates for TPO.
WHAT DOES THE OPERATION INVOLVE?
Dogs are placed under general anesthesia, and, if not done previously, x-rays are taken and the hips examined and measured. Before the dog is taken to surgery, it receives intravenous antibiotics through a catheter placed in one of its forelimbs. This catheter is also used to administer fluids throughout surgery. Most dogs will as well have an epidural injection of analgesics and anesthetics. The entire rear limb is widely clipped so that a sterile surgical field can be maintained. Only one hip is operated on at a time. There are usually three surgical incisions made. One is in the groin, in order to allow cutting and removal of a portion of the pubic bone, which attaches to the bottom of the acetabulum. A second incision is made over the rump area for osteotomy of the ischial bone, which attaches to the back of the acetabulum. The third and longest incision is over the side of the pelvis in order to expose and cut the ilium (the main bone of the pelvis), which attaches to the front of the acetabulum. Once the three osteotomies have been performed, the acetabulum can be rotated appropriately to restore congruency with the femoral head.
The bones are fixed in their new positions using stainless steel orthopedic implants. The osteotomy of the ilium is stabilized using a bone plate which has been appropriately twisted and bent to conform to the position of the bones; it is secured in place with bone screws which pass through holes in the plate, into the underlying bone. A bone graft is taken from the piece of pubis removed earlier, and packed around the ileal osteotomy to promote faster healing. The osteotomy of the ischium is stabilized using a stainless steel wire. No fixation is used for the pubis. The wounds are irrigated (rinsed) with a saline solution, and then closed with multiple layers of sutures. The skin incisions are closed either with stitches or special surgical staples (the latter are surprisingly comfortable!).
Postoperative x-rays are taken to evaluate the positioning of the bones and orthopedic implants, and the patient is then awakened from anesthesia. No bandages are applied to the wounds, since dogs are notorious for getting these off very quickly.
WHAT DO I HAVE TO DO FOR POSTOPERATIVE CARE? HOW WILL MY DOG WALK AFTER SURGERY?
Most dogs are able to go home within one to two days after TPO. In most cases, the dog will be at least partially weight bearing on the limb the day after surgery. Because the muscles are still working to pull the bones back where they were originally, it is critical to limit activity for at least six (6) weeks after surgery. Dogs should be kept on a short leash outside, and walks limited to short distances, especially in the first three to four weeks. Although going up and down one or two steps is acceptable, dogs should not be allowed to climb or descend flights of stairs, nor should they jump on or off furniture. Allowing too much activity early on, or if the animal slips and falls, could result in loosening of the bone plate, and subsequent loss of correction. It is sometimes helpful to support the rear end of the animal with a towel or specially designed sling under the belly, especially when on slippery surfaces, or if the animal is having difficulty using its leg.
Antibiotics are usually given for several after surgery as a precautionary measure. Typically, analgesic medications will be prescribed for a short period as well.
WHEN IS THE SECOND SIDE OPERATED ON?
Assuming that both hips are suitable candidates for TPO, the operations are usually staged two to four weeks apart. Because time can be so critical in the selection of TPO as a correction for hip dysplasia, we do not want to wait too long before tackling the second side, even if the dog is not yet fully recovered on the first side. On occasion, a delay of longer than four weeks is made before operating on the second side. This may be due to complications from the first surgery, or other illness that makes anesthesia and surgery less safe.
WHAT IS THE LONG-TERM FOLLOW-UP PROCEDURE?
Additional x-rays are obtained (and an orthopedic recheck examination made under sedation or anesthesia) approximately six weeks after surgery on the second hip, which is usually nine to ten weeks after the first surgery. Because pelvic osteotomy is done with caution not to over-correct the incongruency, the immediate postoperative examination and x-rays usually reveal continued incongruency and instability in the hip. However, as the muscles tighten in response to the new bone positions, we expect to see and feel progressive improvement in the seating of the hip. This is what we are evaluating during the subsequent rechecks. If all appears to be going well, additional x-rays are usually scheduled at six months postoperatively, and then annually thereafter. The long-term evaluations are important, not only for determining the success of the operation for the individual dog, but also for evaluating the overall effectiveness of the procedure. This latter information can then be used to suggest necessary refinements of patient selection or of the operation itself, as well as to provide more meaningful prognostic information to subsequent owners for whom TPO is a suggested option.
WHAT ARE THE POTENTIAL COMPLICATIONS OF TPO?
All surgeries carry some inherent risk, and the risks for patients undergoing TPO are no greater than for any other orthopedic procedure. Because these are usually young, healthy dogs, and because strictly sterile conditions are maintained, such problems as deep infections are rare. Problems particular to pelvic osteotomy include loosening of implants and loss of proper orientation, nerve or vessel injuries, superficial infections of the incisions, short-term straining to urinate, and long-term failure of the procedure to accomplish its intended purpose, namely prevention of degenerative joint disease, and allowing normal use of the operated limb. Implant loosening is usually prevented by good owner compliance with instructions for exercise limitation postoperatively. Superficial wound complications are managed with appropriate topical therapy, and the use of restraint devices to prevent licking and chewing the incisions. Because TPO entails cutting of major pelvic bones, stretching, overheating, or tearing injuries can be sustained to important nearby nerves, such as the sciatic nerve. Every effort is made to protect these structures during surgery, but owning usually to anatomical variation among dogs, some dogs will wake up from surgery with signs of nerve weakness. Fortunately, it is an uncommon complication, and, even when observed, is usually transient. If a dog does develop a neurapraxia (reversible injury to the sheath surrounding the nerve, with mild loss of function), signs usually include “knuckling” of the toes, and some laxity in the ankle (hock) joint. Pain is rarely encountered. Treatment consists of protecting the toes from mechanical trauma, assisting the animal to walk using a sling, if necessary, and delaying surgery on the second side where applicable. In most cases the signs disappear in two to six weeks. Rarely, a more severe and long-lasting nerve deficit is seen, and may require additional surgery to strengthen the ankle and toe muscles. Because the urethra (tube connecting the urinary bladder to the external genitalia) lies directly on the floor of the pelvis, it can be injured or inflammed by TPO. This is a rare complication that could result in some straining. It is usually self-limiting, but may require some temporary treatment.
WHAT CAN BE DONE IF I ELECT NOT TO PURSUE TPO FOR MY DOG, AND IT DEVELOPS PAINFUL ARTHRITIS LATER ON?
Because judgment is required in deciding which dogs are suitable candidates for TPO, we may guess wrong in some cases. On the one hand, some dogs may be operated on who ultimately may never have developed any arthritis or pain; such dogs will do well, but the role of TPO in their good result may be questionable. This is probably uncommon, since most dogs being operated on were brought to the veterinarian’s attention because they were having lameness problems. On the other hand, we may evaluate a dog’s clinical function and hips to be acceptable, when in fact the dog could benefit from the corrective effects of TPO. This is why re-evaluation is so important, and monitoring the trend in un-operated dogs may cause a change in plans at a subsequent date. Nonetheless, some dogs who would best be treated by TPO will not have the operation, either because of faulty veterinary judgment, or because of financial or other constraints faced by the owner. In such cases, there are still salvage operations available (assuming medical management is inadequate for controlling clinical signs), and these can be discussed with your veterinarian or board-certified veterinary orthopaedist. An advantage of the salvage operations is that they are not limited to young dogs, and can be done at any point in an adult dog’s life. Thus, even if finances limit choices now, it may be possible to save funds for later use.