Evaluation of risk factors for luxation after total hip replacement in dogs

OBJECTIVE: To identify risk factors for luxation after canine total hip replacement (THR). STUDY DESIGN: Retrospective study. SAMPLE POPULATION: 256 client-owned dogs that underwent THR. METHODS: Patient data surveyed included signalment, body weight, diagnosis, prior hip surgery, implant size, intraoperative complications, and angle of lateral opening of the acetabular component. RESULTS: Postoperative complications were recorded in 20 cases (7.8%). The most common complication was dorsal luxation which occurred in 12 dogs (4.7%). The interval between joint replacement and luxation ranged from 1 to 116 days (mean, 44 days). In 1 case, luxation was attributable to failure of the repair of an intraoperative fracture of the greater trochanter. Excluding this case, the mean angle of lateral opening in those dogs that sustained luxation was 62 degrees (range, 46 degrees - 75 degrees). The mean angle of lateral opening overall was 48 degrees (range, 18 degrees - 76 degrees). The angle of lateral opening was the only factor that had a statistically significant effect on whether luxation occurred (P = .035). Acetabular revision, performed primarily to reduce the angle of lateral opening, was performed in 8 dogs and successfully prevented subsequent luxation. CONCLUSION: Luxation of the prosthesis is substantially under the control of the surgeon. It is recommended that the acetabular cup be inserted at an angle of lateral opening of 35 degrees to 45 degrees. In those cases of THR luxation in which an inappropriate angle of lateral opening is identified, acetabular revision arthroplasty generally results in a good clinical outcome.     

Pulmonary embolism associated with canine total hip replacement

OBJECTIVE: To determine by pulmonary perfusion scans and ultrasonography if embolemia occurs during total hip replacement (THR) surgery in dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: Forty client-owned dogs that had THR surgery. METHODS: Thoracic radiographs were taken immediately after THR and immediately after completion of (99m)Tc-MAA lung scans. Scintigraphy was performed in 28 dogs, 48 hours after THR. Intraoperative ultrasonography (intercostal or transesophageal) was performed in another 12 dogs that had THR. The right atrium and ventricle and pulmonary outflow tract were observed during and for 5 to 8 minutes after femoral component insertion into medullary canals prepared by reaming, and lavage and aspiration of debris before filling with polymethylmethacrylate in dough stage. A modified Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) classification system was used to evaluate lung scans. RESULTS: No pulmonary radiographic abnormalities were identified. Segmental and subsegmental perfusion defects occurred in 23 (82%) dogs and were classified as severe in 9 (32%) dogs, moderate in 11, and mild in 3. There was no particular lobe predilection. Patchy mulberry-appearing defects, indicative of fat embolism, were most common. Embolemia was observed by ultrasound in 10 dogs. Variable-sized particles occurred in 8 dogs, particles and bubbles in 2 dogs, and no emboli were observed in 2 dogs. Embolemia was observed within 10 seconds after femoral stem insertion and lasted < 1 minute. Pneumoemboli remained in the right atrium for > 8 minutes before dislodgement. CONCLUSIONS: Embolemia of either air, particles, or both occurs in most dogs during THR surgery. CLINICAL RELEVANCE: Most dogs seemingly spontaneously recover from pulmonary embolism that occurs during THR. The risk of clinical complications from this pulmonary embolism should be taken seriously, even though the exact morbidity and mortality rates are unknown.     

Femur fractures associated with canine total hip replacement

OBJECTIVE: To report femur fracture as a complication of canine total hip replacement (THR) and to report the incidence, predisposing factors, treatment options, and outcome. STUDY DESIGN: Prospective clinical study. ANIMALS: Twenty-two client-owned dogs with 24 femoral fractures occurring during or after THR. METHODS: Cemented THR (BioMedtrix, Boonton, NJ) was performed. Medical records and radiographs were used to identify dogs that had femur fracture and to identify risk factors. Follow-up was obtained until dog death or study end. RESULTS: The overall incidence of femur fracture after THR was 2.9%. Femoral fractures occurred intraoperatively, immediately postoperatively, and up to 2196 days after THR. In 17 dogs, fractures resulted from a traumatic event. Osteopathy was present at THR in 5 dogs; all developed femoral fissures during reaming. Three dogs had fractures associated with cortical thinning secondary to aseptic loosening. Fracture treatment included euthanasia (1 dog), strict confinement (3 dogs), full cerclage wires on long oblique fractures (3 dogs), or plate and screw fixation (10 with, and 7 without, cerclage wires). All fractures extended near the distal tip of the femoral stem and all aggressively treated fractures healed. CONCLUSIONS: Predisposing risk factors for femur fracture after THR include osteopathy and iatrogenic fissures created during reaming. Trauma, excessive load concentration, and increased torque can lead to mid-diaphyseal fracture near the end of the femoral stem. Fracture did not disrupt THR implants. Cement fracture exposing the tip of the femoral stem did not affect fracture healing or rehabilitation. Immediate plate and screw fixation resulted in the most favorable outcome; healing occurred in 6-10 weeks. CLINICAL RELEVANCE: Femur fractures that occur after THR should be repaired using plate and screw fixation augmented with cerclage wire when needed. Forces on fissures should be neutralized to prevent propagation and fracture. Owners of high-risk patients (old dogs with osteopathies or previous hip surgery) should be counseled before THR. The prognosis is excellent when fractures are treated correctly.     

Application of arthroplasty principles to canine cemented total hip replacement

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Positive intraoperative cultures and canine total hip replacement: risk factors,periprosthetic infection,and surgical success

The results of closing intraoperative cultures from 27 canine total hip replacements (THR) were reviewed. The relationship between these culture results and presurgical and surgical factors, and the short- and long-term success of THR were assessed. Eleven out of 27 cases had a positive culture, but none of these 11 cases were diagnosed with periprosthetic infection at follow-up examination. The duration of the clinical signs of hip disease prior to THR was significantly greater for those cases with a positive culture (P=0.034). The incidence of positive cultures was not related to surgical success.     

Augmentation of the transverse acetabular ligament in canine caudoventral hip luxation.

Open surgical fixation was performed on four hip joints in three dogs who were suffering from caudoventral hip luxations for which closed reduction had previously failed. Stabilization of the joint was achieved with a ventral coxofemoral approach, which augmented the function of the transverse acetabular ligament using a sling implant through a bone tunnel (n = 1), a sling implant around two pelvic screws (n = 1), or an internal fixator plate (n = 2). Transverse acetabular ligament augmentation resulted in successful joint stabilization in all cases, and should be considered for the surgical reduction of caudoventral hip luxations in dogs. The use of an internal fixator plate, while preserving soft-tissue blood supply and resulting in minimal to no long-term arthritic changes, may provide an optimal outcome.     

Femoral component failure in canine cemented total hip replacement: a report of two cases

Femoral stem fracture is reported as an uncommon late complication of cemented total hip replacement in two dogs. In each case surgical salvage was achieved by extirpation of the proximal unstable component of the femoral stem, resulting in acceptable limb function. To the authors' knowledge, intramedullary femoral stem failure has not been previously reported after cemented total hip replacement in the dog. Factors believed to have contributed to implant failure in these dogs are discussed and compared with the same complication in humans.     

Modified De Vita pinning technique for the management of canine hip luxation: preliminary findings

OBJECTIVE: To describe for the first time a modification of the De Vita pinning technique to manage hip luxation in the dog and to assess its use in a preliminary study. DESIGN: A prospective, clinical study using five client-owned dogs with naturally occurring injuries. PROCEDURE: A modified De Vita pinning technique was employed, using a nonthreaded Steinmann pin to reduce the risk of trauma to the sciatic nerve during pin insertion. The pin was anchored by implanted Kirschner-Ehmer clamps in an attempt to lower the risk of postoperative pin migration. RESULTS: Surgical outcome was very favourable with respect to pain on manipulation, restriction of range of movement and lameness in all dogs as assessed by veterinary examination. In four of five dogs, owners also reported normal movement at rest, walk and trot. The fifth dog was lost to follow-up. CONCLUSION: This preliminary study found that a modified De Vita pinning technique was useful in dogs with uni and bilateral hip luxation and hip luxation in the presence of other limb injuries. The modified technique may provide a sound surgical alternative to existing procedures. The described modification allows the use of a nonthreaded pin and also substantially reduces the risk of postoperative pin migration.     

Retrospective analysis of canine miniature total hip prostheses

OBJECTIVE: To determine the practicality and clinical outcome of miniature total hip replacement (THR) in dogs. STUDY DESIGN: Retrospective study. Sample Population- Seventeen client-owned dogs that had miniature THR. METHODS: Patient data surveyed included signalment, body weight, diagnosis, implant size, surgical technique, and intraoperative and postoperative complications. Radiographic evaluation included angle of lateral opening of the acetabular component, implant positioning, cement mantle quality, and femoral displacement measurement and ratio. Client questionnaire and orthopedic examination were used to obtain long-term follow-up information. RESULTS: Miniature THR was performed to address hip dysplasia and secondary osteoarthritis. In 1 dog, a staged bilateral procedure was performed. Mean body weight was 19 kg (range, 12 to 25 kg). Penetration or fissure of the femoral cortex was the most common intraoperative complication and occurred in 3 dogs. In 3 dogs, there was excessive coxofemoral laxity after reduction of the prosthesis. This instability was addressed specifically in 2 dogs by capsulorrhaphy or capsular prosthesis. Postoperative convalescent complications (craniodorsal luxation, 2 dogs; acetabular cup displacement, 1 dog) were related to surgical errors. Aseptic loosening of the femoral implant was diagnosed in 1 dog at 18 months. Mean follow-up time was 17 months (range, 4 to 42 months). Fifteen of 18 (83%) miniature THRs had good or excellent outcomes. CONCLUSIONS: Miniature THR should be considered a satisfactory alternative to femoral head and neck ostectomy in medium-size dogs affected by hip dysplasia and secondary osteoarthritis. The population of medium-size dogs that might derive more benefit from THR than FHO has yet to be defined. CLINICAL RELEVANCE: Miniature THR is a viable treatment option in medium-size dogs with hip dysplasia.     

The effects of femoral stem and neck length on cement strains in a canine total hip replacement model

OBJECTIVE: To determine the effects of femoral prosthesis stem length and head size on cement strains in a canine hip replacement system. STUDY DESIGN: An in vitro experimental model. SAMPLE POPULATION: (1) Three standard and 3 1-cm shortened femoral implants with +3 femoral heads. (2) Two standard implants with +0, +3, and +6 femoral heads. METHODS: Femoral stems were embedded in polymethylmethacrylate cement. A uniaxial proximodistal-oriented strain gauge was applied to the cement on the medial and lateral aspects of the construct 1.5 cm, 6.0 cm and 7.0 cm distal to the collar. Each construct with a +3 femoral head was mounted in a materials testing system. An axial compressive load (0-200 N) was applied to the femoral head and cement strains were recorded. Additionally, 2 standard length constructs were also tested with +0 and +6 femoral heads. The effects of stem length and neck length on cement strains were assessed with analysis of variance. RESULTS: Strains increased at all locations with increasing loads for all constructs. Shorter implants had higher strains by 152% and 171%, lateral (P =.003) and medial (P =.0025) to the stem tip. No significant strain differences were noted, at any strain gauge location, between different neck lengths (P values ranged from.20 to.67). CONCLUSIONS: Although a shorter implant stem has a potential to improve implant fit, it led to significantly higher cement strains that may increase the risk for aseptic loosening. Changes in femoral neck length did not significantly affect cement strains under the conditions tested. CLINICAL RELEVANCE: Shortening of the femoral stem currently cannot be recommended in canine total hip replacement. The existing use of variable neck lengths likely does not increase the risk of failure of the femoral stem.     

Risk factors for canine tail chasing behaviour in Japan

The aim of this study was to investigate the risk factors for tail chasing behaviour that occurs when a dog spins in tight circles to chase its tail, sometimes biting it. The behaviour is a sign of canine compulsive disorder (CD). A questionnaire about tail chasing behaviour and general information about the animals was used to collect data on seven breeds of pet dogs. The data were gathered at a dog event and at veterinary practices. To determine which variables were associated with tail chasing behaviour, stepwise multiple regression analyses were performed. Regardless of cohort, 'breed' and 'source of acquisition' were significantly associated with tail chasing behaviour. Using a chi-square test, the association between 'source of acquisition' and the behaviour was examined separately in two breeds (Shiba inu and Dachshund) that had the largest number of individuals chasing their tails accompanied by biting and/or growling at them. This factor showed a significant and consistent association across the two breeds. With respect to the risk factors of 'breed' and 'source of acquisition', high percentages of Shiba inu and dogs originating from pet stores were included in the group chasing their tails with biting and/or growling. The results suggest that distinct risk factors exist for tail chasing behaviour and such factors appear to be regulated by both genetics and the environment.     

Acetabular component orientation as an indicator of implant luxation in cemented total hip arthroplasty

OBJECTIVE: To determine the sensitivity and specificity with which acetabular component angles of inclination and version could be used, alone or in combination, to predict luxation of cemented total hip arthroplasties (THA). STUDY DESIGN: Comparison of retrospectively selected cases and controls SAMPLE POPULATION: All THA performed at the University of Florida between 1991 and 1998 with the BioMedtrix system and for which at least 2 months of radiographic follow-up were available. All THA performed at the University of Georgia with the BioMedtrix system which subsequently luxated. METHODS: Acetabular component inclination angle (IA) and acetabular version angle (VA) were determined for each THA. Data were grouped according to outcome - luxation or no luxation - with the luxated cases from the 2 institutions pooled. Receiver operator characteristic (ROC) analysis was used to evaluate decision rules for using IA and VA as tests for detecting postoperative luxation. Sensitivity and specificity for luxation and 95% confidence bounds were computed with selected values of IA and VA as cut-points. RESULTS: The nonluxation group consisted of 68 THA with a median follow-up time of 5 months (range, 2-60 months). The luxation group consisted of 12 THA with a mean time to luxation of 36 days. The nonluxation group had a mean +/- standard deviation (SD) IA and VA of 40.3 degrees +/- 8.9 degrees and 71.1 +/- 13.6 degrees, respectively, whereas the luxation group had a mean +/- SD IA and VA of 34.7 degrees +/- 12.6 degrees and 72.9 degrees +/- 16.6 degrees, respectively. An IA cut-point of 37.8 degrees achieved 58.3% sensitivity and 57.4% specificity. A VA cut-point of 73 degrees achieved 75.0% sensitivity and 51.5% specificity. IA and VA considered simultaneously achieved a 50.0% sensitivity and 88.2% specificity. CONCLUSIONS AND CLINICAL RELEVANCE: ROC analysis indicated that both IA and VA considered individually or simultaneously were poor indicators of luxation. Although extreme values of IA may predict luxation with high specificity, the potential for luxation cannot be excluded based on apparently appropriate values of IA and VA. The results of this study also indicate that a successful outcome is possible with a wide range of acetabular component positions.     

Use of the cumulative summation technique to quantitatively assess a surgical learning curve: canine total hip replacement

Objective: To quantitatively assess a surgical “learning curve” using the cumulative summation (CUSUM) score technique. Study Design: Application of a CUSUM technique to a consecutive series of surgical cases. Animals: Consecutive primary cemented total hip replacement (THR; n=116) in 106 dogs. Methods: Records of all dogs that had primary canine THR were reviewed. Data retrieved included date of surgery, postoperative complications, and duration of follow‐up. The 12‐week outcome was analyzed graphically and with a CUSUM technique. Results: One hundred and one (87%) procedures were “successful” and 15 (13%) developed major complications within 12 weeks (failures). The CUSUM chart clearly demonstrated an initial “learning curve” of ～44 THR. Conclusion: The CUSUM technique can be used to demonstrate the learning curve for canine THR surgery.     

Femoral medullary infarction secondary to canine total hip arthroplasty

OBJECTIVE: To evaluate the prevalence of femoral intramedullary infarction after total hip arthroplasty (THA) and to determine whether any specific femoral morphology predisposes to bone infarction. STUDY DESIGN: Retrospective clinical study. SAMPLE POPULATION: All dogs from our hospital population undergoing THA between 1984 and 1997 with radiographic follow-up available at 1 year or more postoperatively. METHODS: A case control study was conducted within the THA group to determine risk factors predisposing to femoral infarction after THA. Medical records and radiographs were reviewed. Data were collected on clinical parameters, femoral morphology, prosthesis, and bone changes. Radiographic diagnosis was confirmed using histopathology in 11 femora. Radiographs of 50 age-matched control dogs weighing more than 20 kg with coxofemoral degenerative joint disease were randomly chosen to determine the prevalence of bone infarction in nonoperated dogs. RESULTS: Ninety-one dogs with 110 THA were included in the study. Fifteen of the 110 femora with THA had radiographic evidence of infarction (14%). Infarction was not present in any femora in the control group. There was no significant difference in the prevalence of infarction between dogs that received cemented or uncemented prostheses. Clinical signs were not reported in any patient that developed femoral infarction. Young age (P = .03) and a distance between the greater trochanter and nutrient foramen greater than 79 mm (P = .008) predisposed dogs to femoral infarction. Over time, three infarcts decreased in size radiographically, five remained unchanged, and three expanded. An osteosarcoma developed at the site of a bone infarct in one dog. CONCLUSION: Femoral intramedullary infarction occurred in 15 of 110 THA. Young age at the time of THA and a greater distance between the greater trochanter and the nutrient foramen predisposed to infarction. CLINICAL RELEVANCE: Intramedullary infarction occurs after canine THA. These bone infarcts do not appear to cause clinical signs; however, they may present a diagnostic challenge. Malignant transformation could potentially result from medullary infarction.