Criteria for Selection of Cases

Medical records of the Mississippi State University Animal Health Center and the University of Missouri Veterinary Medical Teaching Hospital were searched to identify all dogs examined during 2000 through 2005 because of hip joint luxation. Cases were included in the study if open reduction and toggle rod stabilization had been performed and the medical record was complete.

Procedures

Information obtained from the medical records included signalment; history; results of initial diagnostic testing, including clinicopathologic testing and radiography; cause and side of the luxation; concurrent injuries; and whether any attempts at closed reduction had been made. In addition, information was obtained on surgical approach, toggle rod type and size, suture size, duration of anesthesia and surgery, whether other orthopedic problems were treated during the same surgical episode, whether an Ehmer sling was applied after surgery, whether analgesics or antimicrobials were administered after surgery, whether the dog was using the limb 24 hours after surgery and at the time of discharge, the time from surgery to any recheck examinations, and whether any complications developed. For dogs in which the hip joint reluxated, time from surgery to reluxation and mode of failure were recorded. Success of the procedure was defined as no reluxation of the hip joint and no need for additional surgical procedures.

Client questionnaire—To obtain information on long-term outcome and client satisfaction with the procedure, a questionnaire was sent to the owners of all dogs included in the study. Owners were asked to indicate the severity of lameness at the time of discharge (on a scale from 0 to 5, where 0 = no lameness and 5 = non–weight-bearing lame); the degree to which they had complied with recommendations for postoperative confinement and rehabilitation (on a scale from 0 to 5); whether the dog had developed any complications; the severity of lameness at the present time (on a scale from 0 to 5, where 0 = no lameness and 5 = non–weight-bearing lame); current limb function, compared with function prior to injury (on a scale from 0 to 5, where 0 = the same as prior to surgery and 5 = function not regained); primary use of the dog (eg, family pet, sporting dog, show dog, or other athletic use); any medications or therapeutic diets the dog was receiving; and overall satisfaction with the outcome of surgery.

Statistical analysis—Responses to client questionnaires were tabulated, and percentages for each response were calculated. Values were calculated for all dogs and for only those dogs in which an Ehmer sling was not used after surgery and for which limb use 24 hours after surgery was known. The Fisher exact test was used to test for associations between various questionnaire responses and limb use 24 hours after surgery, limb use at the time of discharge, and whether reluxation occurred. Independent-samples t tests were used to compare mean age and mean body weight among groups when dogs were grouped on the basis of limb use 24 hours after surgery, limb use at the time of discharge, and whether reluxation occurred. Independent-samples t tests were also used to compare the mean body weight–to–suture strength ratio when dogs were grouped on the basis of reluxation. All analyses were performed with standard software.^a Values of P < 0.05 were considered significant.

Results

Signalment and history—Sixty-two cases met the criteria for inclusion in the study. Mean ± SD age of the dogs included in the study was 5.3 ± 3.4 years. Nineteen (31%) were sexually intact males, 21 (34%) were castrated males, 9 (14%) were sexually intact females, and 13 (21%) were spayed females. Mean ± SD body weight was 29 ± 14 kg (64 ± 30 lb; range, 8.3 to 78 kg [18 to 172 lb]). There were 14 mixed-breed dogs, 12 Labrador Retrievers, 8 German Shepherd Dogs, and 7 Cocker Spaniels; the remaining dogs represented a variety of breeds. Forty-nine of the 62 (79%) dogs had hip joint luxation as a result of being hit by a car. Other causes of hip joint luxation included falling from a truck, collision with a 4-wheel vehicle, slipping and falling, jumping from a window, catching a paw on a crate, being struck by a falling gate, and severe trauma (1 dog each). In 6 dogs, cause of the luxation was unknown. The duration of luxation prior to examination at the Animal Health Center or Veterinary Medical Teaching Hospital had a bimodal distribution. Twentyfour (39%) dogs were examined between 1 and 2 days after the luxation occurred, 15 (24%) were examined between 3 and 7 days after the luxation occurred, and 23 (37%) were examined > 7 days after the luxation occurred. The right hip joint was affected in 32 (52%) dogs, and the left hip joint was affected in 28 (45%); 2 dogs had bilateral hip joint luxations. Closed reduction had been attempted in 28 (45%) dogs prior to toggle rod stabilization. Four (6%) dogs had previously undergone open reduction and stabilization that had failed. Surgical procedures performed in these dogs included toggle rod stabilization (n = 1), joint imbrication (1), and screw and wire stabilization (1). In the remaining dog, the previous surgical procedure was not described.

Preoperative diagnostic imaging—Pelvic radiographs were obtained prior to surgery in 56 of the 62 (90%) cases, and in 33 of the 56 (59%), abnormalities in addition to hip joint luxation were identified. The most common concurrent abnormalities were fractures (16/56 [29%]), osteoarthritis of the hip joint or hip dysplasia (13 [23%]), and sacroiliac joint luxation (9 [16%]). Of the 16 dogs with concurrent fractures, 5 had fractures of the contralateral pelvic limb, 2 had fractures of the ipsilateral pelvic limb, and 4 had fractures of the ipsilateral acetabulum (avulsion fracture of the acetabulum, 1; avulsion fracture of the femoral head, 3); the remaining 5 had fractures unrelated to the hindlimbs. Of the 9 dogs with sacroiliac joint luxation, 4 had luxation of the contralateral sacroiliac joint, 3 had luxation of the ipsilateral sacroiliac joint, and 2 had bilateral sacroiliac joint luxation.

Thoracic radiographs were obtained in 42 of the 62 (68%) dogs, and abnormalities were seen in 15 of the 42 (36%). Abnormalities that were identified included an increased interstitial pattern (n = 8), pulmonary contusions (4), pneumothorax (2), and diaphragmatic hernia (1).

Surgical procedure—A craniolateral approach to the hip joint was used in 58 of the 62 (94%) dogs, a caudolateral approach was used in 2 (3%), and a craniodorsal approach was used in 1 (2%); surgical approach was not identified in the remaining dog. In 5 (8%) dogs, surgery lasted < 1 hour; in 21 (34%), surgery lasted between 1 and 1.5 hours; in 14 (23%), surgery lasted between 1.5 and 2 hours; in 6 (10%), surgery lasted between 2 and 2.5 hours; in 6 (10%), surgery lasted between 2.5 and 3 hours; and in 10 (16%), surgery lasted > 3 hours. Total anesthesia time was < 2 hours in 9 (15%) dogs, 2 to 2.5 hours in 10 (16%) dogs, 2.5 to 3 hours in 15 (24%), and > 3 hours in 28 (45%).

In 31 of the 62 (50%) dogs, procedures in addition to toggle rod stabilization were performed during the same anesthetic episode. This included fracture fixation (17/31 [55%]), repair of sacroiliac joint luxation (6 [19%]), and various soft tissue repairs (4 [13%]). In 10 of the 62 (16%) dogs, other hip joint stabilization techniques were used in addition to toggle rod stabilization. This included transposition of the greater trochanter, placement of bone anchors, capsulorrhaphy, and triple pelvic osteotomy.

Toggle rod stabilization procedure—Toggle rod type was recorded in 58 of the 62 (94%) dogs. Commercially available toggle rods^b were used in 45 of the 58 (78%), and toggle rods made of Steinmann pins or Kirschner wires were used in the remaining 13 (22%). In all but 1 dog, a single toggle rod was used in each hip joint. In the remaining dog, a second toggle rod was placed after the first was deemed too loose.

Suture material used for toggle rod stabilization consisted of leader line (26/51 [51%]), fishing line (23/51 [45%]), and polyester suture material^c (2/51 [4%]). For 40 of the 49 (82%) dogs in which leader line or fishing line was used, test weight of the monofilament nylon was 60 or 80 lb. For these 49 dogs, mean ± SD test weight of the leader line or fishing line was 1.07 ± 0.35 lb/lb of body weight. Various techniques were used to secure the suture material, with a polypropylene button being used most often (36/62 [58%]). Other techniques used to secure the suture material were a femoral tunnel (22 [35%]) and an additional toggle rod (2 [3%]). In 2 dogs, the method used to secure the suture material was not specified.

Postoperative diagnostic imaging—Postoperative radiographs were obtained in all dogs, and adequate reduction was seen in 61 of the 62 (98%). One dog still had luxation of the hip joint following the initial surgery. Surgery was repeated the following day, and the toggle rod was replaced.

Postoperative management—All 62 dogs received opioid drugs for analgesia while hospitalized, with 59 (95%) dogs receiving an opioid drug in combination with at least 1 other form of analgesia (eg, epidural administration of an opioid and bupivicaine, oral administration of a nonsteroidal anti-inflammatory drug, application of a fentanyl patch, or constant-rate infusion of ketamine). For all dogs, an analgesic was prescribed at the time of discharge, with nonsteroidal anti-inflammatory drugs prescribed in 59 of the 62 (95%) dogs. Fifty-six (90%) dogs received cefazolin during surgery, and 43 (69%) dogs received antimicrobials after surgery. However, only 7 (16%) dogs received antimicrobials for ³ 10 days.

An Ehmer sling was applied after surgery in 6 of 61 (10%) dogs (for 1 dog, information on whether an Ehmer sling was applied after surgery was not available); 3 of these 6 dogs had radiographic evidence of hip dysplasia. The duration of luxation prior to surgery was > 7 days in 4 of the 6 (67%) dogs in which an Ehmer sling was applied after surgery. In 4 dogs, the sling was still in place at the time of discharge. For 34 of the 62 (55%) dogs, duration of hospitalization ranged from 3 to 5 days, with 44 (71%) dogs being discharged within 1 week after surgery.

Complications—Postoperative complications developed in 16 of the 62 (26%) dogs, with complications developing within 1 week after surgery in 10 of the 16. Three (5%) dogs developed a seroma after surgery, and 1 each developed a fever, infection, sciatic damage, and wound dehiscence. Three dogs had > 1 complication. The most common complication was reluxation, which occurred in 7 dogs (8 hip joints). Of the 7 dogs with reluxation, only 1 had radiographic evidence of hip dysplasia. In this dog, the hip joint reluxated 7 days after the initial surgery, and femoral head and neck osteotomy was subsequently performed. The hip joint did not reluxate in the remaining 9 dogs with dysplasia of the hip joint that underwent toggle rod stabilization.

In the remaining 6 dogs (7 hip joints) with reluxation, the cause of reluxation was attributed to breakage or loosening of the suture (n = 2) or failure of the toggle rod (2) or could not be determined (3). In both dogs with failure of the toggle rod, the toggle rods had been homemade, and they had bent in 1 and broken in the other. There was no significant (P = 0.48) association between the body weight–to–suture strength ratio and reluxation. In 1 dog in which reluxation was attributed to breakage or loosening of the suture, the suture material had been wrapped around the femur and adjacent muscles where it exited from the greater trochanter and subsequently loosened. In the other dog, 40-lb test fishing line had been used and the suture material subsequently broke. This was 1 of the 2 dogs with bilateral hip joint luxation, and the contralateral hip joint reluxated because of breakage of the toggle rod. Of the 6 dogs without radiographic evidence of hip dysplasia that had reluxation, 3 underwent femoral head and neck osteotomy and 1 underwent total hip replacement. Final outcomes for the remaining 2 dogs were not known.

Duration of luxation before open surgical reduction was > 7 days in 5 of 7 dogs that had a reluxation and 18 of 53 (34%) dogs without a reluxation; these proportions were not significantly (P = 0.058) different. Time from surgery to reluxation was < 2 weeks in 4 of 7 dogs (5/8 hip joints). The prevalence of orthopedic polytrauma in dogs with reluxation (5/7) was not significantly (P = 0.16) different from the prevalence in dogs without reluxation (26/55).

Three of the 7 dogs that had a reluxation had an Ehmer sling applied after surgery. A total of 6 dogs had an Ehmer sling placed immediately after surgery, and 4 dogs were discharged with an Ehmer sling in place (3 of the 6 dogs in which a sling was applied immediately after surgery and 1 additional dog).

Outcome—Information on limb usage while hospitalized was available for only 51 of the 56 dogs in which an Ehmer sling was not applied after surgery. Thirty-three of the 51 (65%) were toe touching or bearing weight 24 hours after surgery, and 45 (88%) were toe touching or bearing weight at the time of discharge. All dogs that were bearing weight on the affected limb 24 hours after surgery were also bearing weight on the limb at the time of discharge.

In 34 dogs, a follow-up examination was performed at one of the participating institutions. In most of these dogs, the follow-up examination was performed between 4 and 6 weeks after surgery. Six of the 34 (18%) would not bear weight on the affected limb or required additional surgery because of pain or reluxation. In 4 of the 6, femoral head and neck excision was performed (2 of these were dogs with reluxation of the hip joint), and in 1, total hip arthroplasty was performed because of repeated reluxation of the hip joint. Information on long-term outcome was not available for the remaining dog.

Mean body weight of dogs that were bearing weight on the affected limb at the time of discharge (31.3 kg [68.6 lb]) was significantly (P = 0.02) different from mean body weight of dogs that were not bearing weight on the affected limb at the time of discharge (16.9 kg [37.1 lb]). Sexually intact male dogs were significantly (P = 0.04) more likely to be bearing weight on the affected limb 24 hours after surgery (17/21) than were castrated male dogs (5/11), spayed female dogs (5/11), or sexually intact female dogs (6/8).

Dogs in which surgery time was < 2 hours (n = 26) were significantly (P = 0.002) more likely to be bearing weight on the affected limb 24 hours after surgery than were dogs in which surgery time was ³ 2 hours (6). Dogs that were not bearing weight on the affected limb 24 hours after surgery were significantly (P = 0.05) more likely to have had multiple procedures performed during surgery (14/20 [70%]) than were dogs that were bearing weight on the affected limb 24 hours after surgery (13/32 [41%]). In addition, dogs that were not bearing weight on the affected limb 24 hours after surgery were significantly (P = 0.009) more likely to have had an anesthetic time > 3 hours (14/20 [70%]) than were dogs that were bearing weight on the affected limb 24 hours after surgery (9/32 [28%]).

Dogs with successful toggle rod surgeries were not significantly (P = 0.059) less likely to have been discharged with an Ehmer sling. Five of the 7 dogs (6/8 hip joints) with reluxation were initially examined at the referral hospital > 7 days after the injury, but this was not significantly (P = 0.095) different from the proportion of dogs without reluxation that were examined > 7 days after injury.

Dogs in which surgery time was < 2 hours (n = 38) were significantly (P = 0.01) less likely to have a reluxation than were dogs in which surgery time was 2 to 3 hours (11) or > 3 hours (6). Four of 5 dogs with reluxation of the joint were bearing weight on the affected limb at the time of discharge, but this proportion was not significantly different from the proportion of dogs without reluxation that were bearing weight on the affected limb at the time of discharge (41/47 [87%]).

Client questionnaire—Client questionnaires were returned by owners of 27 of the 62 (44%) dogs; time from surgery to completion of the questionnaire ranged from 6 months to 5 years. Mean score for severity of lameness at the time of discharge (0 = no lameness and 5 = non–weight-bearing lame) was 4.2 (mode, 5), and mean score for degree to which owners complied with recommendations for postoperative confinement and rehabilitation (0 = agree and 5 = disagree) was 0.25 (mode, 0). Postoperative complications were reported by 13 of the 27 (48%) respondents, with pain being the most commonly reported complication (9/27 [33%]), followed by reluxation (4 [15%]), dehiscence (2 [7%]), seroma (2 [7%]), infection (1 [4%]), and protrusion of a wire used for trochanteric transposition from the incision (1 [4%]). When asked to rate current limb function (0 = no lameness and 5 = non–weight-bearing lame), 23 of the 27 (85%) indicated a score of 0 or 1 and 1 indicated a score of 5; the remaining 3 did not respond to this question. Mean score for current limb function, compared with limb function prior to injury (0 = same and 5 = did not regain function), was 1.1 (mode, 1). Twenty-five of the 27 (93%) dogs were reportedly family pets, 1 was a sporting dog, and 1 was a show dog. Owners of 6 (22%) dogs reported that they were giving their dogs medications for treatment of osteoarthritis.

When asked whether they agreed or disagreed with the statement that they were satisfied with the outcome of the surgical procedure (0 = agree and 5 = disagree), 22 of the 27 (81%) owners provided a score of 2 or less and 4 owners provided a score of 5 (1 owner did not respond to this question). All 4 owners that provided a score of 5 had dogs that had had reluxation of the hip joint.

Discussion

Results of the present study suggest that toggle rod stabilization is an effective treatment for hip joint luxation in dogs, in that owners of 23 of 27 (85%) dogs reported a score of 0 or 1 on a scale from 0 to 5 (0 = no lameness and 5 = non–weight-bearing lame) when asked about limb function in their dogs a minimum of 6 months after surgery. However, complications were common, and reluxation occurred in 7 of 62 (11%) dogs. Postoperative limb function was reported by the owners to be comparable to limb function prior to injury, with mean score for current limb function, compared with limb function prior to injury (0 = same and 5 = did not regain function), being 1.1. Fixation failure was not significantly associated with repair of chronic luxations or with treatment of dogs with multiple injuries, and postoperative application of an Ehmer sling did not prevent reluxation.

The most frequent cause of hip joint luxation in the present study was trauma, particularly being hit by a car, as was the case in previous studies.^4,11,13,22 Thirtythree of 56 (59%) dogs had additional injuries visible on pelvic radiographs obtained prior to surgery, and 15 of 42 (36%) dogs had thoracic radiographic abnormalities. These findings point out the need for complete radiographic evaluation of dogs that had major trauma, even though hip joint luxation can be diagnosed on the basis of physical examination findings alone.

In the present study, we found a bimodal distribution in time between injury and examination at the Animal Health Center or Veterinary Medical Teaching Hospital. This may have been attributable, at least in part, to the distance owners had to travel to reach these referral centers. Both referral centers were located in smaller urban areas, and it seems that most owners would have had to travel a substantial distance to reach them. However, travel distance was not investigated further because time between injury and examination at a referral center was not associated with any of the outcomes we examined. The bimodal distribution in time between injury and examination at a referral center could also have been attributable to delays in referral because treatment was initially attempted at a local veterinary clinic.

The success rate in the present study was comparable to success rates previously reported.^{1,2,9,10,13-22} The most common complication in the present study was reluxation, which occurred in 7 (11%) dogs, with reluxation occurring within the first 2 weeks after surgery in 4 of the 7 (5/8 hip joints). This reluxation rate was lower than rates reported in 2 previous studies.^13,22 That reluxation commonly occurred soon after surgery was not surprising, as the stability of the repair depends entirely on the toggle pin device during this period. In dogs with polytrauma, injuries to other limbs may necessitate early excessive weight bearing, leading to reluxation, and 4 of 7 dogs in the present study with reluxation had had polytrauma. A potential advantage of toggle rod stabilization, compared with other stabilization techniques, is that it allows an early return of joint function, thus preserving joint range of motion and cartilage heath. However, our findings indicate that caution is needed in the initial week after surgery to avoid reluxation.

In 2 dogs in the present study, reluxation was attributed to failure of homemade toggles, and one of these dogs had reluxation of the second hip joint because of failure of the suture material. Although size of the suture material in this dog seemed appropriate given the dog's body weight, it is possible that failure of the toggle and subsequent reluxation of the contralateral hip joint resulted in excessive stress on the suture material. In another dog, reluxation occurred because of tearing of the muscles distal to the greater trochanter to which the suture was anchored.

In 10 (16%) dogs in the present study, various hip joint stabilization techniques were used in addition to toggle rod stabilization. Despite this, reluxation occurred in 1 of these 10 dogs. Although it is not known whether reluxation would have occurred in the other 9 dogs had these additional stabilization measure not been used, it appears augmentation of toggle rod fixation by use of capsulorrhaphy, trochanteric transposition, or triple pelvic osteotomy may be beneficial in some cases. Results of the present study suggest that use of an Ehmer sling to augment toggle rod stabilization may not be as effective as additional surgical techniques.

In 7 of the 62 (11%) dogs in the present study, an Ehmer sling was applied after surgery (in 6 dogs, the sling was applied immediately after surgery, and in 1, the sling was applied before discharge), and 4 (6%) dogs were discharged with an Ehmer sling in place. Nevertheless, reluxation occurred in 2 of these 7 dogs. The reluxation rates for dogs in which an Ehmer sling had been applied immediately after surgery (1/6) and in dogs in which an Ehmer sling was in place at the time of discharge (2/4) were higher than the overall reluxation rate for the study (11%); however, significant differences in reluxation rates in dogs with and without an Ehmer sling were not found. Nevertheless, use of an Ehmer sling did not eliminate the risk of reluxation.

In the present study, dogs for which surgery time was ³ 2 hours were more likely to have a reluxation than were dogs for which surgery time was < 2 hours. This was likely due to the fact that dogs with longer procedure times had had other injuries and, in some cases, underwent multiple surgical procedures. These additional injuries may have led to increased weight bearing on the stabilized hip joint in the immediate postoperative period, when reluxation was more likely to occur. However, polytrauma and total anesthesia time were not significantly associated with risk of reluxation. Alternatively, it may be that prolonged surgical time was indicative of difficulty reducing the hip joint or placing the toggle rod or suture. Dogs for which surgery time was ³ 2 hours were less likely to be bearing weight on the affected limb 24 hours after surgery than were dogs for which surgery time was < 2 hours. Although all dogs received analgesics after surgery, there may have been additional pain or discomfort in dogs that underwent longer procedures that resulted in a delayed return to weight bearing. Overall, weight-bearing status immediately after surgery and at the time of discharge was not associated with reluxation rate.

When asked whether they agreed or disagreed with the statement that they were satisfied with the outcome of the surgical procedure (0 = agree and 5 = disagree), 22 of the 27 (81%) owners provided a score of 2 or less, suggesting overall satisfaction with the procedure. In addition, when asked to rate current limb function (0 = no lameness and 5 = non–weightbearing lame), 23 of the 27 (85%) indicated a score of 0 or 1, suggesting that most dogs had no or only negligible lameness a minimum of 6 months after surgery. One of the dogs was reported to be a show dog whose owner indicated that the dog did not have any lameness, and another was a sporting dog that reportedly was able to return to hunting. Only 6 dogs were reported to be receiving medications for treatment of osteoarthritis. However, because follow-up radiography was not performed, the prevalence of hip joint osteoarthritis following toggle pin stabilization could not be determined.

There are several limitations to the present study. In particular, follow-up examinations were most often performed by the referring veterinarians, and some complications may not have been reported. Also, longterm outcome was based on owner assessments, which can be limited and subjective. Statistical analysis of factors associated with reluxation was limited by the low number of dogs in which this complication occurred.