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Total Hip Replacement
Orthopedic Salvage Procedures
0195-5616/87 $0.00
+
.20
Total Hip Replacement Marvin L. Olmstead, D.V.M., M.S.*
Most salvage procedures that are performed because a joint is no longer able to function properly either alter or eliminate joint motion with the intent of saving overall limb function. Total hip replacement, on the other hand, provides the surgeon with a procedure that will not only preserve normal limb function but will also re-establish normal, pain-free joint mechanics. Prosthetic hip replacements have been successfully used in surgery on human beings since 1951 and are currently performed at an annual rate of 80,000 in the United StatesY In recent years, there have been numerous reports of successful use of the Richard's Canine II Total Hip Prosthesis (Richard's Medical Company, Memphis, Tennessee) to cor~ rect various disabling conditions of the dog's coxofemoral joint. 3• 4• 6• 7• 9• 10• 12 On August 1, 1976, surgeons from The Ohio State University College of Veterinary Medicine and the Berwyn Veterinary Associates Hospital, Berwyn, Illinois, began an ongoing prospective study of clinical total hip replacements in the dog. To date, more than 550 total hip replacements have been performed by veterinarians associated with this study. This work has established the indications and contraindications for total hip replacement, the most effective surgical technique, the complication rate, both short- and long-term, and a long-term functional evaluation of the prosthesis. 4 · 5 • 1}-ll INDICATIONS AND CONTRAINDICATIONS Total hip replacem~nt has been effectively used in treating a number of disabling conditions of the canine coxofemoral joint. The primary indication for performing a total hip replacement is disabling hip dysplasia; however, the procedure has been used to treat dogs with degenerative joint disease caused by conditions other than hip dysplasia, including *Diplomate, American College of Veterinary Surgeons; Associate Professor of Small Animal Orthopedics, Department of Veterinary Clinical Sciences, The Ohio State University College of Veterinary Medicine, Columbus, Ohio Veterinary Clinics of North America: Smllll Animlll Practice-Vol. 17, No. 4, July 1987
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chronic traumatic hip luxations, failed exclSlon arthroplasties, severely comminuted femoral heads, avascular necrosis of the femoral head, nonunions of femoral neck fracture, and malunions of the acetabulum. All of these conditions were the primary cause of the dog's disability. There are certain circumstances in which a total hip replacement is contraindicated even though the dog may have one of the previously mentioned conditions. A dog that has hip dysplasia, no matter how severe, but pain-free normal locomotor function is not a candidate for total hip replacement. An animal in this condition should be reevaluated should its functional status change. A dog that has hip dysplasia and concomitant hindlimb neurologic dysfunction should be evaluated for degenerative myelopathy, intervertebral disc disease, spinal tumors, or other neurologic conditions. If the dog has dysfunction related to its hip dysplasia after the neurologic condition has been treated, it may become a candidate for total hip replacement. A complete orthopedic examination should be performed to rule out conditions in joints other than the hip that might be causing the lameness, such as partial or complete tears of the cranial cruciate ligament. Systemic disease or infective processes anywhere in the body should be controlled before performing a total hip replacement. Total hip replacements should not be attempted on dogs whose available bone will not cover at least 80 per cent of the dorsal rim of the prosthetic acetabular cup or whose femoral intermedullary canal is too narrow to accommodate the shaft of the endoprosthesis. Prosthesis implantation may be precluded by the bone remodeling that occurs following femoral head and neck excision. PRESURGICAL EVALUATION
Patient evaluation begins with history and physical examination. Animals with pain isolated to the hip that causes periodic lameness, exercise intolerance, alterations in normal locomotor function, or diminished ownerintended activity levels may be considered candidates for total hip replacement. The dog should be at least 10 months of age to assure that no further longitudinal femoral growth will occur. There are no upper age limits. Geriatric patients should be in good health and the owners counseled as to the potential remaining life span of their pet. In the aforementioned prospective study, the oldest patient was 14 years of age at the time of implantation, and the average age of implantation was slightly over 4 years. Most dogs weighing 17 kg or less cannot be fitted with the currently available prosthesis. However, the largest available Richard's Canine II Hip Prosthesis will accommodate the largest canine patient (Fig. 1). Along with the general physical examination, each patient should receive a complete orthopedic examination. Range of motion should be evaluated to determine the hip's angle of greatest flexion, angle of greatest extension, and the extent of full inward and outward rotation. The animal should be observed closely for any pain response created by performing this evaluation. Neurologic evaluation should be used to eliminate spinal disorders as a cause of the dysfunction. Ventrodorsal coxofemoral radiographs, including the stifle and lateral pelvic radiographs, should be taken to evaluate the condition of the hips
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Figure l. The most commonly used endoprostheses and corresponding prosthetic acetabular cups are shown. The cups (top left, large; top right, medium) are shown in side view (top left and right) and front view (bottom left and right). From left to right, the endoprostheses are regular large, extended neck large, extended neck medium, and regular medium.
and the bone available in the acetabulum and femur. These radiographs may also reveal other causes of lameness such as panosteitis, lower lumbar discospondylitis, or tumors. Clinical pathologic laboratory evaluations should consist of those blood and urine tests that are standard for any class I surgical patient undergoing a major elective procedure. Factors such as age, history, and physical and radiographic findings will dictate the extent of the laboratory evaluation. Any dog being considered for total hip replacement should have the hair on the affected limb clipped 24 hours prior to surgery so that the skin can be examined for evidence of bacterial dermatitis. Should this condition exist, it must be resolved before the patient can undergo surgery. SURGICAL TECHNIQUE Prophylactic antibiotic therapy is initiated (sodium cephalothin 25 mg per kg four times a day) at the time of anesthetic induction . Following sterile preparation of the limb and surgical field , sterile plastic and paper drapes are used to isolate the area completely. A craniolateral approach is made to the hip joint (Fig. 2). The skin incision, which is started dorsal and caudal to the trochanter, is arched forward and distally along the femoral shaft to a point at the proximal one third of the femur. By starting the skin incision caudal to the trochanter, the skin is better protected from trauma during the femoral reaming process. The tensor facia lata muscle is
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Figure 2. The craniolateral approach to the hip exposes the femoral head and neck area.
reflected cranially, and the middle gluteal muscle is reflected dorsally. An incision is made in the tendon of the deep gluteal muscle perpendicular to the muscle fibers. When one half to two thirds of the tendon has been cut, the incision is extended parallel with the muscle fibers almost to their insertion on the ilium. This portion of the muscle is reflected cranially. An incision is made in the joint capsule parallel with the long axis of the femoral neck and at the level of and extending through the origins of the vastus lateralis and intermedius muscles. The joint capsule is incised as it inserts ventrally along the femoral head. The femoral head is luxated by externally rotating the leg 90°. The front edge of the femur is exposed with a periosteal elevator. After the endoprosthesis stem has been aligned parallel with the long axis of the femur, an osteotomy is performed at the femoral head-neck junction along a plane that parallels the angle created where the base of the prosthesis collar meets the stem (Fig. 3). The osteotomy should also be cut so that the prosthesis will be implanted at close to 0° of antiversion. The osteotomized femoral head is preserved in a sterile manner on the surgical table until after the procedure is over. Occasionally, it has been necessary to use a cancellous bone graft from the femoral head to fill defects in the acetabular bed or to build up the dorsal rim of the acetabulum. The femoral shaft is reamed to an appropriate size that will accommodate the stem of the endoprosthesis. Reamers are available that match the different sizes of endoprosthesis. Care must be taken to see that adequate bone is removed from the lateral and medial aspects of the hole in the femoral shaft. These are two places where the endoprosthesis can prematurely engage bone, preventing full seating of the device. The proximal femur is retracted caudally and the acetabular bed is
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Figure 3. An osteotomy is performed at the junction of the femoral head and neck. The endoprosthesis can be used as a guide for this cut if it is aligned as shown.
reamed with an appropriate sized reame~* until medial cortical bone is exposed. Three to five large anchor holes are drilled around the dorsal circumference of the acetabular bed. The most critical of these holes is the one drilled into the wing of the ilium because the greatest depth can be achieved in this area. The depth of the other holes is limited by the cortical wall of the pelvis. All cancellous bone should be removed from the bed of the acetabulum. Space permitting, secondary 2.7- or 3.2-mm holes are drilled around the rim of the acetabulum (Fig. 4). Two separate 20-gm packs of polymethylmethacrylate, t into which 1 gm of sterile sodium cephalothin powder has been added, are used to cement the components of the prosthesis into place. The separate batches of cement are injected into the acetabular bed and the femoral shaft with the use of separate 35-cc syringes with catheter tips. When the cement reaches the liquid phase as it is mixed, it is poured into the 35-cc syringe (Fig. 5). The polymethylmethacrylate is first injected into the individual holes in the acetabular bed, and then the bed is filled until it is level with the lateral bone margins. The prosthetic acetabular cup is seated in slight retroversion with the acetabular positioner and is held until the cement hardens (Fig. 6). By positioning the cup in slight retroversion, the caudal edge of the cup will not act as a fulcrum point for the neck of the *Robert Mathys Co., Bettloch, Switzerland. tSurgical Simplex P. Howmedica, Rutherford, New Jersey.
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Figure 4. The acetabular bed is prepared with reamers, curettes, and drill bits of various sizes. Polymethylmethacrylate will be injected to fill the holes and acetabular bed.
Figure 5. As soon as the polymethylmethacrylate reaches the liquid phase during mixing, it is poured into a 35-cc syringe with a catheter tip. A finger is held over the opening in the catheter tip to keep the cement in the syringe until it is injected .
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Figure 6. The acetabular cup is positioned in slight retroversion along a line that parallels the iliac crest and the top of the ischium.
endoprosthesis when the leg is externally rotated, thus helping to prevent dislocations. The catheter tip of a 35-cc syringe is fully inserted into the femoral intermedullary canal, and polymethylmethacrylate is injected. Approximately 10 to 15 cc of cement will fill the average-sized femoral canal. While the syringe is removed, the injection is continued, filling the proximal femur. Excess bone cement is removed, and the endoprosthesis is inserted into the femoral canal. The head of the prosthesis is reduced into the acetabular cup (Fig. 7). Deep bacterial cultures are taken, and the joint capsule is closed with a cruciate pattern. The surgical site is closed in layers, reattaching muscles, fascia, and skin at or near their original position. POSTSURGICAL CARE
Oral cephalexin therapy is continued until intraoperative culture results are available. Antibiotics are discontinued if the results are negative. Appropriate antibiotic therapy should be instituted for 4 to 6 weeks if the results are positive. At this time, it is not known if prolonged antibiotic therapy will be efficacious, as there have been few occasions to test this protocol. Hospital compartmental confinement with leash exercise periods is maintained until culture results are known. After the dog is returned to
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Figure 7. This model shows the position of the head of the e ndoprosthesis once it has been reduced into the acetabular cup.
the home environment, a 4-week period of very limited activity is essential. Restriction to one level of the house, avoidance of slippery surfaces, and leash restraint when outside are manditory. During the second postoperative month, exercise levels are gradually increased by lengthening leash walks. During the 2-month period of limited activity, soft tissues around the surgical site are given adequate time to heal. This step is extremely important in maintaining the prosthesis in a reduced position (Fig. 8). Physical and radiographic evaluations are performed 3 months postopera-
Figure 8. This dog had normal hip function until its death 6'12 years after total hip replacement. The joint capsule has been cut away at necropsy. Part of the capsule that is undisturbed can be seen conforming to the neck and head of the prosthesis. This helps prevent dislocations.
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tively and annually thereafter. Should the other hip need a total hip replacement, a minimum of 2 months should elapse before the second procedure is performed. Our prospective study has found that bilateral replacement is only necessary in 20 per cent of the cases. After 60 days of restrictions, the animal can return to normal activity leve ls. Dogs intended for working purposes should be placed on a gradually increasing exercise program. RESULTS Comprehensive evaluation of the total hip replacements performed in our prospective study has been done for two different time periods: August 1, 1976 through July 31, 1981, and August 1, 1981 through July 31, 1984. During those time periods, 221 and 174 total hip replacements were evaluated, respectively. The dogs were examined physically, historically, and radiographically to establish data related to hip function and incidence of complications. Function was graded as either satisfactory or unsatisfactory during both evaluation periods. Animals with satisfactory function had full clinical range of motion with no pain, increased muscle mass, and no limping (Fig. 9).
Figure 9. This dog had full pain-free hip function until its death SV2 years after bilateral total hip replacement. Full hip extension and normal muscle mljSS are demonstrated in this photograph.
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The dog with periodic transient stiffness was considered satisfactory. Unsatisfactory animals had overt lameness that caused the animal to be either partially or totally non-weight-bearing. Functional determinations were only made if a reevaluation at least 4 weeks after the last hip surgery was obtained. Satisfactory function was observed in 91.2 per cent of the 216 dogs with adequate follow-up in the first study period and 95.2 per cent of 146 dogs in the second study period. Total hip replacements have been performed in both pet and working dogs with no difference in success. Several working dogs have competed with a total hip replacement in place without problems. One dog even won an international field trial. Smaller case studies by other investigators have demonstrated similar high percentages of satisfactory results. 3 · 6 • 7 • 12 COMPLICATIONS
The complication rate for the first study group was 20.3 per cent of the total hip replacements having one or another form of a complication and 6.3 per cent in the second group. This clearly demonstrates the learning-curve effect during the first 5 years of this ongoing study. Approximately 60 per cent of the complications in each study period were satisfactorily resolved. During the first 5 years, the following 75 complications in 46 total hip replacements were encountered: (1) 38 dislocations; (2) 17 infections; (3) eight loose acetabular components; (4) seven fractures; and (5) five sciatic neuropraxia. In the second study group, the following 13 complications in l l total hip replacements were encountered: (1) five dislocations; (2) five loose acetabular components; (3) two infections; and (4) one loose femoral component. Although dislocations were the most commonly encountered complication, the risk of this occurrence can be minimized through proper placement of the acetabular cup and strict activity restriction for a 2-month period following surgery. If a dislocation occurs, the most effective treatment is open reduction following the same rigid aseptic guidelines used during total hip replacement. Should it be determined that the acetabular cup is malpositioned, then it will be necessary to reposition the cup to increase the probability of achieving a satisfactory result. The most disasterous complication is infection. This complication is treated by removal of both the cement and the prosthesis. Following removal of an infected prosthesis, approximately 70 per cent of the dogs improved their function,,- but they never achieved the same results as a dog with a normally functioning total hip replacement. The infection rates for primary total hip replacement in the two study groups was 2. 9 per cent and 0.55 per cent, respectively. If a secondary procedure was performed on a hip, then there was a much greater risk of infection. Because of this, any surgical procedures performed on dogs with total hip replacements must be done under the strictest aseptic conditions, particularly if the limb that has the total hip replacement is being operated on. A noninfected loose acetabular cup usually causes a partial weightbearing lameness. Either a bone-cement interface or a cement-prosthesis
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interface failure will occur. The bone-cement interface failure is accompanied by resorption of bone around the cement. It should be noted that oftentimes a 1-mm lucent line will be observed radiographically around the acetabular cup. Only if this line is found to be widening with subsequent radiographic evaluations is the prosthesis considered to be loosening. Failure at the cement-prosthesis interface usually occurs when there is inadequate acetabular bone cover over the dorsal aspect of the prosthetic cup. This bone cover acts as a buttress, preventing the forces of normal weight-bearing activity from being great enough to cause failure at the cement-prosthesis interface. Loose acetabular cups can usually be replaced through an anterior-lateral approach; however, sometimes it is necessary to perform a trochanteric osteotomy in order to gain greater exposure. Proper preparation of the acetabular bed and anchor holes is critical in preventing loosening of the acetabular cup. The currently used technique of injecting the cement while it is still in a low-viscosity state may reduce the number of loosenings encountered. Of the fractures that have been encountered, slightly over half were related to the total hip replacement procedure. The rest of the fractures were associated with traumatic events. In all cases, fractures ultimately healed using either internal fixation techniques or slings for nondisplaced fractures where the prosthesis cement column acted as a support. Sciatic neuropraxia, encountered only in the first group of dogs, may have resulted from cement extruding through a penetrating anchor hole in the ischium. As the cement cures, there is an exothermic reaction that produces heat great enough to denature protein. The neuropraxia could also be caused by stretching or bruising of the nerve during the surgical procedure. By being cognizant of the potential causes of this complication, it can be eliminated. It has been found to be a temporary condition that requires only that the animals be protected from self-abuse until nerve function has returned. The only complication observed in the second group of dogs, but not the first, was loosening of a femoral component. The component was replaced and the dog developed satisfactory function. For the most part, complications have occurred within 1 V2 years of implantation of the total hip replacement. Complications occurring after this time period are extremely infrequent. Of the 395 total hip replacements done in the two previously mentioned time periods, 12 have been followed for 7 years or more, 38- for 5 to 7 years, 102 for 3 to 5 years, 144 for 1 to 3 years, and 66 for 4 weeks to 1 year. Thirty-three have been followed for less than 4 weeks. The longest follow-up period is 9 years 10 months, and that dog continues to have satisfactory function. It would appear from this follow-up data that latent complications such as prosthesis loosening or failure will rarely be encountered. Our experience to date suggests that the prosthesis will last the dog's lifetime (Fig. lOA, B, and C). It is debatable whether total hip replacement or excision arthroplasty should be performed on dogs over 18 kg. In this author's experience, larger dogs with excision arthroplasties do not function as well as dogs with a satisfactory total hip replacement. Others have reported that dogs over 18 kg do not have as good a result with excision arthroplasties as those under
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Figure 10. A , This preoperative radiograph of a 1V2-year-old Labrador shows rightsided hip dysplasia. An excision arthroplasty was performed on the left hip for treatment of a comminuted fracture of the femoral head when the dog was 4-months-old. The dog was presented for bilateral hindlimb weakness. B , Immediate postoperative radiographs of a right-sided total hip replacement. The amount of bone present in both the left femur and acetabulum is inadequate to support a prosthesis. Lateral radiographs (not shown) showed the left proximal femur to be displaced 4 em above the acetabular rim. This caused hyperextension of this limb. C, Only minimal bone changes are noted adjacent to the prosthesis 8 years and 1 month after total hip replacement. The dog continues to function satisfactorily on that limb.
18 kg. 1• 2 · 8 In a large study of 267 arthroplasties, 30 per cent of the owners indicated that some lameness was still present after the procedure. 1 These animals would have been considered unsatisfactory in this study if the same result had been reported in a dog with a total hip replacement. Slightly less than 5 per cent of total hip replacement dogs in the second study period of our prospective study had lameness. The same large study also reported that after excision arthroplasty muscle atrophy was a "frequent finding even after 8 years ," and large dogs had "difficulty in jumping and in climbing stairs." 1 These observations would have classified a total hip replacement as unsatisfactory. Apparently, some dogs have taken up to 19 months to start walking again after excision arthroplasty. 1 It has been reported that it takes an average of 2 to 3 months before the animal can achieve acceptable weight-bearing while walking. 1' 8 Almost all successful total hip replacement patients have returned to full weight-bearing by 4 weeks. Dogs with marked preoperative deterioration may require a slightly longer convalescence. It is logical that the best way to restore normal function is to duplicate as closely as possible normal joint conformation. Total hip replace ment does this for the dog with disabling disease of the hip.
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REFERENCES 1. Duff R, Campbell JR: Long-term results of excision arthroplasty of the canine hip. Vet Rec 101:181-184, 1977 2. Gendreau C: Excision of the femoral head and neck: The long-term results of35 operations. J Am Anim Hosp Assoc 13:605-608, 1977 3. Hoefle WD: A surgical procedure for prosthetic total hip replacement in the dog. J Am Anim Hosp Assoc 10:269-276, 1974 4. Hohn RB, Olmstead ML, Turner TM, et al: Der huftgelenkersatz beim hund. Tierarztl Prax 14:377-388, 1986 5. Konde LJ, Olmstead ML, Hohn RB: Radiographic evaluation of total hip replacement in the dog. Vet Radio! 20:98-106, 1982 6. Leighton RL: The Richards II canine total hip prosthesis. J Am Anim Hosp Assoc 15:73-77, 1979 7. Lewis RG, Jones JP: A clinical study of canine total hip arthroplasty. Vet Surg 9:20-23, 1980 8. Lippincott CL: Improvement of excision arthroplasty of the femoral head and neck utilizing a biceps femoris muscle sling. JAm Anim Hosp Assoc 17:668-672, 1981 9. Olmstead ML, Hohn RB: Ergebisse mit der hufttotalprostheses bei 103 klinischen fallen an der Ohio State University. Klin Prax 25:407-415, 1980 10. Olmstead ML, Hohn RB, Turner TM: A five year study of 221 total hip replacements in the dog. JAm Vet Med Assoc 183:191-194, 1983 11. Olmstead ML, Hohn RB, Turner TM: Technique for canine total hip replacement. Vet Surg 10:44-50, 1981 12. Parker RB, Bloomberg MS, Biletto W, et al: Canine total hip arthroplasty: A clinical review of 20 cases. JAm Anim Hosp Assoc 20:97-104, 1984 13. Walker PS: Biomechanics of joints. In Resnick D, Newayama G (eds): Diagnosis of Bone and Joint Disorders. Philadelphia, WB Saunders Co, 1981, pp 197-220 Department of Veterinary Clinical Sciences College of Veterinary Medicine The Ohio State University 1935 Coffey Road Columbus, Ohio 43210
0195-5616/87 $0.00
+
.20
Total Hip Replacement Marvin L. Olmstead, D.V.M., M.S.*
Most salvage procedures that are performed because a joint is no longer able to function properly either alter or eliminate joint motion with the intent of saving overall limb function. Total hip replacement, on the other hand, provides the surgeon with a procedure that will not only preserve normal limb function but will also re-establish normal, pain-free joint mechanics. Prosthetic hip replacements have been successfully used in surgery on human beings since 1951 and are currently performed at an annual rate of 80,000 in the United StatesY In recent years, there have been numerous reports of successful use of the Richard's Canine II Total Hip Prosthesis (Richard's Medical Company, Memphis, Tennessee) to cor~ rect various disabling conditions of the dog's coxofemoral joint. 3• 4• 6• 7• 9• 10• 12 On August 1, 1976, surgeons from The Ohio State University College of Veterinary Medicine and the Berwyn Veterinary Associates Hospital, Berwyn, Illinois, began an ongoing prospective study of clinical total hip replacements in the dog. To date, more than 550 total hip replacements have been performed by veterinarians associated with this study. This work has established the indications and contraindications for total hip replacement, the most effective surgical technique, the complication rate, both short- and long-term, and a long-term functional evaluation of the prosthesis. 4 · 5 • 1}-ll INDICATIONS AND CONTRAINDICATIONS Total hip replacem~nt has been effectively used in treating a number of disabling conditions of the canine coxofemoral joint. The primary indication for performing a total hip replacement is disabling hip dysplasia; however, the procedure has been used to treat dogs with degenerative joint disease caused by conditions other than hip dysplasia, including *Diplomate, American College of Veterinary Surgeons; Associate Professor of Small Animal Orthopedics, Department of Veterinary Clinical Sciences, The Ohio State University College of Veterinary Medicine, Columbus, Ohio Veterinary Clinics of North America: Smllll Animlll Practice-Vol. 17, No. 4, July 1987
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chronic traumatic hip luxations, failed exclSlon arthroplasties, severely comminuted femoral heads, avascular necrosis of the femoral head, nonunions of femoral neck fracture, and malunions of the acetabulum. All of these conditions were the primary cause of the dog's disability. There are certain circumstances in which a total hip replacement is contraindicated even though the dog may have one of the previously mentioned conditions. A dog that has hip dysplasia, no matter how severe, but pain-free normal locomotor function is not a candidate for total hip replacement. An animal in this condition should be reevaluated should its functional status change. A dog that has hip dysplasia and concomitant hindlimb neurologic dysfunction should be evaluated for degenerative myelopathy, intervertebral disc disease, spinal tumors, or other neurologic conditions. If the dog has dysfunction related to its hip dysplasia after the neurologic condition has been treated, it may become a candidate for total hip replacement. A complete orthopedic examination should be performed to rule out conditions in joints other than the hip that might be causing the lameness, such as partial or complete tears of the cranial cruciate ligament. Systemic disease or infective processes anywhere in the body should be controlled before performing a total hip replacement. Total hip replacements should not be attempted on dogs whose available bone will not cover at least 80 per cent of the dorsal rim of the prosthetic acetabular cup or whose femoral intermedullary canal is too narrow to accommodate the shaft of the endoprosthesis. Prosthesis implantation may be precluded by the bone remodeling that occurs following femoral head and neck excision. PRESURGICAL EVALUATION
Patient evaluation begins with history and physical examination. Animals with pain isolated to the hip that causes periodic lameness, exercise intolerance, alterations in normal locomotor function, or diminished ownerintended activity levels may be considered candidates for total hip replacement. The dog should be at least 10 months of age to assure that no further longitudinal femoral growth will occur. There are no upper age limits. Geriatric patients should be in good health and the owners counseled as to the potential remaining life span of their pet. In the aforementioned prospective study, the oldest patient was 14 years of age at the time of implantation, and the average age of implantation was slightly over 4 years. Most dogs weighing 17 kg or less cannot be fitted with the currently available prosthesis. However, the largest available Richard's Canine II Hip Prosthesis will accommodate the largest canine patient (Fig. 1). Along with the general physical examination, each patient should receive a complete orthopedic examination. Range of motion should be evaluated to determine the hip's angle of greatest flexion, angle of greatest extension, and the extent of full inward and outward rotation. The animal should be observed closely for any pain response created by performing this evaluation. Neurologic evaluation should be used to eliminate spinal disorders as a cause of the dysfunction. Ventrodorsal coxofemoral radiographs, including the stifle and lateral pelvic radiographs, should be taken to evaluate the condition of the hips
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Figure l. The most commonly used endoprostheses and corresponding prosthetic acetabular cups are shown. The cups (top left, large; top right, medium) are shown in side view (top left and right) and front view (bottom left and right). From left to right, the endoprostheses are regular large, extended neck large, extended neck medium, and regular medium.
and the bone available in the acetabulum and femur. These radiographs may also reveal other causes of lameness such as panosteitis, lower lumbar discospondylitis, or tumors. Clinical pathologic laboratory evaluations should consist of those blood and urine tests that are standard for any class I surgical patient undergoing a major elective procedure. Factors such as age, history, and physical and radiographic findings will dictate the extent of the laboratory evaluation. Any dog being considered for total hip replacement should have the hair on the affected limb clipped 24 hours prior to surgery so that the skin can be examined for evidence of bacterial dermatitis. Should this condition exist, it must be resolved before the patient can undergo surgery. SURGICAL TECHNIQUE Prophylactic antibiotic therapy is initiated (sodium cephalothin 25 mg per kg four times a day) at the time of anesthetic induction . Following sterile preparation of the limb and surgical field , sterile plastic and paper drapes are used to isolate the area completely. A craniolateral approach is made to the hip joint (Fig. 2). The skin incision, which is started dorsal and caudal to the trochanter, is arched forward and distally along the femoral shaft to a point at the proximal one third of the femur. By starting the skin incision caudal to the trochanter, the skin is better protected from trauma during the femoral reaming process. The tensor facia lata muscle is
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Figure 2. The craniolateral approach to the hip exposes the femoral head and neck area.
reflected cranially, and the middle gluteal muscle is reflected dorsally. An incision is made in the tendon of the deep gluteal muscle perpendicular to the muscle fibers. When one half to two thirds of the tendon has been cut, the incision is extended parallel with the muscle fibers almost to their insertion on the ilium. This portion of the muscle is reflected cranially. An incision is made in the joint capsule parallel with the long axis of the femoral neck and at the level of and extending through the origins of the vastus lateralis and intermedius muscles. The joint capsule is incised as it inserts ventrally along the femoral head. The femoral head is luxated by externally rotating the leg 90°. The front edge of the femur is exposed with a periosteal elevator. After the endoprosthesis stem has been aligned parallel with the long axis of the femur, an osteotomy is performed at the femoral head-neck junction along a plane that parallels the angle created where the base of the prosthesis collar meets the stem (Fig. 3). The osteotomy should also be cut so that the prosthesis will be implanted at close to 0° of antiversion. The osteotomized femoral head is preserved in a sterile manner on the surgical table until after the procedure is over. Occasionally, it has been necessary to use a cancellous bone graft from the femoral head to fill defects in the acetabular bed or to build up the dorsal rim of the acetabulum. The femoral shaft is reamed to an appropriate size that will accommodate the stem of the endoprosthesis. Reamers are available that match the different sizes of endoprosthesis. Care must be taken to see that adequate bone is removed from the lateral and medial aspects of the hole in the femoral shaft. These are two places where the endoprosthesis can prematurely engage bone, preventing full seating of the device. The proximal femur is retracted caudally and the acetabular bed is
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Figure 3. An osteotomy is performed at the junction of the femoral head and neck. The endoprosthesis can be used as a guide for this cut if it is aligned as shown.
reamed with an appropriate sized reame~* until medial cortical bone is exposed. Three to five large anchor holes are drilled around the dorsal circumference of the acetabular bed. The most critical of these holes is the one drilled into the wing of the ilium because the greatest depth can be achieved in this area. The depth of the other holes is limited by the cortical wall of the pelvis. All cancellous bone should be removed from the bed of the acetabulum. Space permitting, secondary 2.7- or 3.2-mm holes are drilled around the rim of the acetabulum (Fig. 4). Two separate 20-gm packs of polymethylmethacrylate, t into which 1 gm of sterile sodium cephalothin powder has been added, are used to cement the components of the prosthesis into place. The separate batches of cement are injected into the acetabular bed and the femoral shaft with the use of separate 35-cc syringes with catheter tips. When the cement reaches the liquid phase as it is mixed, it is poured into the 35-cc syringe (Fig. 5). The polymethylmethacrylate is first injected into the individual holes in the acetabular bed, and then the bed is filled until it is level with the lateral bone margins. The prosthetic acetabular cup is seated in slight retroversion with the acetabular positioner and is held until the cement hardens (Fig. 6). By positioning the cup in slight retroversion, the caudal edge of the cup will not act as a fulcrum point for the neck of the *Robert Mathys Co., Bettloch, Switzerland. tSurgical Simplex P. Howmedica, Rutherford, New Jersey.
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Figure 4. The acetabular bed is prepared with reamers, curettes, and drill bits of various sizes. Polymethylmethacrylate will be injected to fill the holes and acetabular bed.
Figure 5. As soon as the polymethylmethacrylate reaches the liquid phase during mixing, it is poured into a 35-cc syringe with a catheter tip. A finger is held over the opening in the catheter tip to keep the cement in the syringe until it is injected .
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Figure 6. The acetabular cup is positioned in slight retroversion along a line that parallels the iliac crest and the top of the ischium.
endoprosthesis when the leg is externally rotated, thus helping to prevent dislocations. The catheter tip of a 35-cc syringe is fully inserted into the femoral intermedullary canal, and polymethylmethacrylate is injected. Approximately 10 to 15 cc of cement will fill the average-sized femoral canal. While the syringe is removed, the injection is continued, filling the proximal femur. Excess bone cement is removed, and the endoprosthesis is inserted into the femoral canal. The head of the prosthesis is reduced into the acetabular cup (Fig. 7). Deep bacterial cultures are taken, and the joint capsule is closed with a cruciate pattern. The surgical site is closed in layers, reattaching muscles, fascia, and skin at or near their original position. POSTSURGICAL CARE
Oral cephalexin therapy is continued until intraoperative culture results are available. Antibiotics are discontinued if the results are negative. Appropriate antibiotic therapy should be instituted for 4 to 6 weeks if the results are positive. At this time, it is not known if prolonged antibiotic therapy will be efficacious, as there have been few occasions to test this protocol. Hospital compartmental confinement with leash exercise periods is maintained until culture results are known. After the dog is returned to
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Figure 7. This model shows the position of the head of the e ndoprosthesis once it has been reduced into the acetabular cup.
the home environment, a 4-week period of very limited activity is essential. Restriction to one level of the house, avoidance of slippery surfaces, and leash restraint when outside are manditory. During the second postoperative month, exercise levels are gradually increased by lengthening leash walks. During the 2-month period of limited activity, soft tissues around the surgical site are given adequate time to heal. This step is extremely important in maintaining the prosthesis in a reduced position (Fig. 8). Physical and radiographic evaluations are performed 3 months postopera-
Figure 8. This dog had normal hip function until its death 6'12 years after total hip replacement. The joint capsule has been cut away at necropsy. Part of the capsule that is undisturbed can be seen conforming to the neck and head of the prosthesis. This helps prevent dislocations.
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tively and annually thereafter. Should the other hip need a total hip replacement, a minimum of 2 months should elapse before the second procedure is performed. Our prospective study has found that bilateral replacement is only necessary in 20 per cent of the cases. After 60 days of restrictions, the animal can return to normal activity leve ls. Dogs intended for working purposes should be placed on a gradually increasing exercise program. RESULTS Comprehensive evaluation of the total hip replacements performed in our prospective study has been done for two different time periods: August 1, 1976 through July 31, 1981, and August 1, 1981 through July 31, 1984. During those time periods, 221 and 174 total hip replacements were evaluated, respectively. The dogs were examined physically, historically, and radiographically to establish data related to hip function and incidence of complications. Function was graded as either satisfactory or unsatisfactory during both evaluation periods. Animals with satisfactory function had full clinical range of motion with no pain, increased muscle mass, and no limping (Fig. 9).
Figure 9. This dog had full pain-free hip function until its death SV2 years after bilateral total hip replacement. Full hip extension and normal muscle mljSS are demonstrated in this photograph.
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The dog with periodic transient stiffness was considered satisfactory. Unsatisfactory animals had overt lameness that caused the animal to be either partially or totally non-weight-bearing. Functional determinations were only made if a reevaluation at least 4 weeks after the last hip surgery was obtained. Satisfactory function was observed in 91.2 per cent of the 216 dogs with adequate follow-up in the first study period and 95.2 per cent of 146 dogs in the second study period. Total hip replacements have been performed in both pet and working dogs with no difference in success. Several working dogs have competed with a total hip replacement in place without problems. One dog even won an international field trial. Smaller case studies by other investigators have demonstrated similar high percentages of satisfactory results. 3 · 6 • 7 • 12 COMPLICATIONS
The complication rate for the first study group was 20.3 per cent of the total hip replacements having one or another form of a complication and 6.3 per cent in the second group. This clearly demonstrates the learning-curve effect during the first 5 years of this ongoing study. Approximately 60 per cent of the complications in each study period were satisfactorily resolved. During the first 5 years, the following 75 complications in 46 total hip replacements were encountered: (1) 38 dislocations; (2) 17 infections; (3) eight loose acetabular components; (4) seven fractures; and (5) five sciatic neuropraxia. In the second study group, the following 13 complications in l l total hip replacements were encountered: (1) five dislocations; (2) five loose acetabular components; (3) two infections; and (4) one loose femoral component. Although dislocations were the most commonly encountered complication, the risk of this occurrence can be minimized through proper placement of the acetabular cup and strict activity restriction for a 2-month period following surgery. If a dislocation occurs, the most effective treatment is open reduction following the same rigid aseptic guidelines used during total hip replacement. Should it be determined that the acetabular cup is malpositioned, then it will be necessary to reposition the cup to increase the probability of achieving a satisfactory result. The most disasterous complication is infection. This complication is treated by removal of both the cement and the prosthesis. Following removal of an infected prosthesis, approximately 70 per cent of the dogs improved their function,,- but they never achieved the same results as a dog with a normally functioning total hip replacement. The infection rates for primary total hip replacement in the two study groups was 2. 9 per cent and 0.55 per cent, respectively. If a secondary procedure was performed on a hip, then there was a much greater risk of infection. Because of this, any surgical procedures performed on dogs with total hip replacements must be done under the strictest aseptic conditions, particularly if the limb that has the total hip replacement is being operated on. A noninfected loose acetabular cup usually causes a partial weightbearing lameness. Either a bone-cement interface or a cement-prosthesis
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interface failure will occur. The bone-cement interface failure is accompanied by resorption of bone around the cement. It should be noted that oftentimes a 1-mm lucent line will be observed radiographically around the acetabular cup. Only if this line is found to be widening with subsequent radiographic evaluations is the prosthesis considered to be loosening. Failure at the cement-prosthesis interface usually occurs when there is inadequate acetabular bone cover over the dorsal aspect of the prosthetic cup. This bone cover acts as a buttress, preventing the forces of normal weight-bearing activity from being great enough to cause failure at the cement-prosthesis interface. Loose acetabular cups can usually be replaced through an anterior-lateral approach; however, sometimes it is necessary to perform a trochanteric osteotomy in order to gain greater exposure. Proper preparation of the acetabular bed and anchor holes is critical in preventing loosening of the acetabular cup. The currently used technique of injecting the cement while it is still in a low-viscosity state may reduce the number of loosenings encountered. Of the fractures that have been encountered, slightly over half were related to the total hip replacement procedure. The rest of the fractures were associated with traumatic events. In all cases, fractures ultimately healed using either internal fixation techniques or slings for nondisplaced fractures where the prosthesis cement column acted as a support. Sciatic neuropraxia, encountered only in the first group of dogs, may have resulted from cement extruding through a penetrating anchor hole in the ischium. As the cement cures, there is an exothermic reaction that produces heat great enough to denature protein. The neuropraxia could also be caused by stretching or bruising of the nerve during the surgical procedure. By being cognizant of the potential causes of this complication, it can be eliminated. It has been found to be a temporary condition that requires only that the animals be protected from self-abuse until nerve function has returned. The only complication observed in the second group of dogs, but not the first, was loosening of a femoral component. The component was replaced and the dog developed satisfactory function. For the most part, complications have occurred within 1 V2 years of implantation of the total hip replacement. Complications occurring after this time period are extremely infrequent. Of the 395 total hip replacements done in the two previously mentioned time periods, 12 have been followed for 7 years or more, 38- for 5 to 7 years, 102 for 3 to 5 years, 144 for 1 to 3 years, and 66 for 4 weeks to 1 year. Thirty-three have been followed for less than 4 weeks. The longest follow-up period is 9 years 10 months, and that dog continues to have satisfactory function. It would appear from this follow-up data that latent complications such as prosthesis loosening or failure will rarely be encountered. Our experience to date suggests that the prosthesis will last the dog's lifetime (Fig. lOA, B, and C). It is debatable whether total hip replacement or excision arthroplasty should be performed on dogs over 18 kg. In this author's experience, larger dogs with excision arthroplasties do not function as well as dogs with a satisfactory total hip replacement. Others have reported that dogs over 18 kg do not have as good a result with excision arthroplasties as those under
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Figure 10. A , This preoperative radiograph of a 1V2-year-old Labrador shows rightsided hip dysplasia. An excision arthroplasty was performed on the left hip for treatment of a comminuted fracture of the femoral head when the dog was 4-months-old. The dog was presented for bilateral hindlimb weakness. B , Immediate postoperative radiographs of a right-sided total hip replacement. The amount of bone present in both the left femur and acetabulum is inadequate to support a prosthesis. Lateral radiographs (not shown) showed the left proximal femur to be displaced 4 em above the acetabular rim. This caused hyperextension of this limb. C, Only minimal bone changes are noted adjacent to the prosthesis 8 years and 1 month after total hip replacement. The dog continues to function satisfactorily on that limb.
18 kg. 1• 2 · 8 In a large study of 267 arthroplasties, 30 per cent of the owners indicated that some lameness was still present after the procedure. 1 These animals would have been considered unsatisfactory in this study if the same result had been reported in a dog with a total hip replacement. Slightly less than 5 per cent of total hip replacement dogs in the second study period of our prospective study had lameness. The same large study also reported that after excision arthroplasty muscle atrophy was a "frequent finding even after 8 years ," and large dogs had "difficulty in jumping and in climbing stairs." 1 These observations would have classified a total hip replacement as unsatisfactory. Apparently, some dogs have taken up to 19 months to start walking again after excision arthroplasty. 1 It has been reported that it takes an average of 2 to 3 months before the animal can achieve acceptable weight-bearing while walking. 1' 8 Almost all successful total hip replacement patients have returned to full weight-bearing by 4 weeks. Dogs with marked preoperative deterioration may require a slightly longer convalescence. It is logical that the best way to restore normal function is to duplicate as closely as possible normal joint conformation. Total hip replace ment does this for the dog with disabling disease of the hip.
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REFERENCES 1. Duff R, Campbell JR: Long-term results of excision arthroplasty of the canine hip. Vet Rec 101:181-184, 1977 2. Gendreau C: Excision of the femoral head and neck: The long-term results of35 operations. J Am Anim Hosp Assoc 13:605-608, 1977 3. Hoefle WD: A surgical procedure for prosthetic total hip replacement in the dog. J Am Anim Hosp Assoc 10:269-276, 1974 4. Hohn RB, Olmstead ML, Turner TM, et al: Der huftgelenkersatz beim hund. Tierarztl Prax 14:377-388, 1986 5. Konde LJ, Olmstead ML, Hohn RB: Radiographic evaluation of total hip replacement in the dog. Vet Radio! 20:98-106, 1982 6. Leighton RL: The Richards II canine total hip prosthesis. J Am Anim Hosp Assoc 15:73-77, 1979 7. Lewis RG, Jones JP: A clinical study of canine total hip arthroplasty. Vet Surg 9:20-23, 1980 8. Lippincott CL: Improvement of excision arthroplasty of the femoral head and neck utilizing a biceps femoris muscle sling. JAm Anim Hosp Assoc 17:668-672, 1981 9. Olmstead ML, Hohn RB: Ergebisse mit der hufttotalprostheses bei 103 klinischen fallen an der Ohio State University. Klin Prax 25:407-415, 1980 10. Olmstead ML, Hohn RB, Turner TM: A five year study of 221 total hip replacements in the dog. JAm Vet Med Assoc 183:191-194, 1983 11. Olmstead ML, Hohn RB, Turner TM: Technique for canine total hip replacement. Vet Surg 10:44-50, 1981 12. Parker RB, Bloomberg MS, Biletto W, et al: Canine total hip arthroplasty: A clinical review of 20 cases. JAm Anim Hosp Assoc 20:97-104, 1984 13. Walker PS: Biomechanics of joints. In Resnick D, Newayama G (eds): Diagnosis of Bone and Joint Disorders. Philadelphia, WB Saunders Co, 1981, pp 197-220 Department of Veterinary Clinical Sciences College of Veterinary Medicine The Ohio State University 1935 Coffey Road Columbus, Ohio 43210