Femoral medullary infarction secondary to canine total hip arthroplasty

Evaluation of the effects of cementless total hip replacement on femoral length in skeletally immature dogs

OBJECTIVE

To describe percentage length changes in the femur after total hip replacement (THR) performed before skeletal maturity.

STUDY DESIGN

Retrospective study.

ANIMALS

Twenty-four dogs younger than 8.5 months which underwent unilateral THR and had radiographic follow up.

METHODS

Preoperative and follow-up radiographs were reviewed. Radiographic measurements included the length of the greater trochanter, femoral diaphysis and distal epiphysis, width of the femur 10 mm distal to the distal aspect of the greater trochanter, width of the femur at 50%, and femoral condylar offset. Percentage changes in length over time were compared among operated and contralateral femurs used as controls. Measurements were collected in triplicate in 10 dogs to evaluate consistency.

RESULTS

All repeated measurements had excellent consistency. The percentage increase in length of the greater trochanter was smaller in operated femurs than controls (mean difference: -11.5%, p = .017), but no differences were observed for the femoral diaphysis and distal epiphysis (-1.0%, p = .595), or the femur overall (-2.3%, p = .232). The percentage increase in femoral cortical width was greater in operated femurs than controls, both 10 mm distal to the greater trochanter (4.6% difference, p = .037) and at 50% length (8.5% difference, p = .030).

CONCLUSION

In growing dogs, cementless THR decreased trochanteric growth by approximately 10% but did not change diaphyseal growth and femoral growth.

CLINICAL SIGNIFICANCE

Cementless THR performed in skeletally immature dogs with severe hip problems did not impact femoral length in a clinically relevant fashion.

Canine Idiopathic Arteriopathy, Appendicular Bone Infarcts, and Neoplastic Transformation of Bone Infarcts in 108 Dogs (Canis lupus familiaris)

Osteosarcoma (OSA) is the most common primary bone tumor in both dogs and humans. The dog is an important research model for OSA, yet dogs have much higher prevalence of bone tumors than do humans, a disparity that has yet to be explained. Neoplastic transformation of cells within or adjacent to bone infarcts into primary bone tumors has been described in humans but only sparsely characterized in the veterinary literature. In this study, 653 cases of canine bone infarcts were received through a referral veterinary osteopathology service over a 14-y period. We identified an idiopathic disorder affecting the nutrient artery, termed canine idiopathic arteriopathy (CIA), which to our knowledge has no direct counterpart in human medicine. This disorder was documented alongside ischemic necrosis of the medullary cavity in 114 bone infarcts in 108 dogs. We hypothesize that CIA precipitated an ischemic environment, resulting in development of a bone infarct down- stream of the abnormal artery. In 52% (59 of 114) of cases, bone infarcts demonstrated evidence of repair (termed reparative bone infarcts [RBI]), while in 48% (55 of 114) of infarcts, a bone tumor was also present, including pleomorphic sarcoma, OSA, fibrosarcoma, and chondrosarcoma. In some cases, a spectrum of tumors was present. We hypothesize that the ischemic infarct environment provoked bone marrow mesenchymal stem cells (MSCs) to attempt repair of the stroma, and in approximately half of cases, MSCs underwent neoplastic transformation (BINT) to produce tumors. The most common sites of bone infarcts were the distal femur, distal radius, proximal humerus, and distal tibia, coinciding with common sites of canine OSA. The authors propose that CIA leading to bone infarcts and infarct-derived tumors, in combination with possible underdiagnosis of canine bone infarcts and misdiagnosis of some RBI as neoplasia, may contribute to the higher reported proportion of bone tumors in dogs compared with humans.

Radiographic features of histologically benign bone infarcts and bone infarcts associated with neoplasia in dogs

OBJECTIVE

To describe the radiographic appearance of benign bone infarcts and bone infarcts associated with neoplasia in dogs and determine the utility of radiography in differentiating benign and malignancy-associated bone infarcts.

SAMPLE

49 dogs with benign (n = 33) or malignancy-associated (16) infarcts involving the appendicular skeleton.

PROCEDURES

A retrospective cohort study was performed by searching a referral osteopathology database for cases involving dogs with a histologic diagnosis of bone infarction. Case radiographs were anonymized and reviewed by 2 board-certified veterinary radiologists blinded to the histologic classification. Radiographic features commonly used to differentiate aggressive from nonaggressive osseous lesions were recorded, and reviewers classified each case as likely benign infarct, likely malignancy-associated infarct, or undistinguishable.

RESULTS

Only 16 (48%) of the benign infarcts and 6 (38%) of the malignancy-associated infarcts were correctly classified by both reviewers. Medullary lysis pattern and periosteal proliferation pattern were significantly associated with histologic classification. Although all 16 (100%) malignancy-associated lesions had aggressive medullary lysis, 23 of the 33 (70%) benign lesions also did. Eight of the 16 (50%) malignancy-associated infarcts had aggressive periosteal proliferation, compared with 7 of the 33 (21%) benign infarcts.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that radiography was not particularly helpful in distinguishing benign from malignancy-associated bone infarcts in dogs.

Outcome and complications after dual mobility total hip replacement

Objectives: To report the clinical and radiographic outcome of a canine total hip prosthesis with a dual mobility acetabular component, with a minimum of six months follow-up.

Methods: The outcome of dogs that underwent primary cemented unilateral dual mobility hip prosthesis surgery by one of the authors for hip dysplasia or trauma, and which had a minimum of six months clinical and radiologic follow-up, was evaluated.

Results: Fifty dogs were included in the study. Follow-up ranged from six to 38 months (mean 14.4 months). Perioperative complications were acetabular collapse (n = 1) and greater trochanter fracture (n = 1), both of which were successfully managed perioperatively. Postoperative complications were aseptic loosening of the acetabular component (n = 2; both surgically revised), implant sepsis (n = 3; all explanted), acetabular fracture (n = 1; conservatively managed), greater trochanter fracture (n = 1; conservatively managed) and sciatic neurapraxia (n = 1). No cases of postoperative luxation or femoral implant aseptic loosening were encountered. Outcome was poor for three cases (3 implant sepsis), fair for three cases (including 1 acetabular component loosening and 1 acetabular fracture), and good or excellent for 44 cases (88%).

Clinical significance: There were not any cases of postoperative coxofemoral luxation observed in this series of 50 dogs with dual mobility hip prosthesis. Studies with more patients and longer follow-up are needed to confirm the satisfactory results observed to date with this implant.

Dislocation of a dual mobility total hip replacement following fracture of the polyethylene liner

An eight-year-old male English Setter was referred for management of a dislocation of a cemented dual mobility canine total hip prosthesis that occurred four months after the initial surgery. Revision surgery showed that the dislocation was associated with fracture of the ultra-high molecular weight polyethylene liner. The dislocation was successfully reduced after replacing the liner. A dual mobility acetabular component is composed of a mobile polyethylene liner inside a metallic cemented cup. Chronic wear of the components of a canine dual mobility total hip replacement has not been described previously. The use of this type of implant is fairly recent and limited long term follow-up of the implanted cases may be the explanation. Acute rupture of a polyethylene liner has never been described in humans, the only case of rupture of a polyethylene liner occurred 10 years after implantation. The case presented here of rupture of the polyethylene liner of a dual mobility total hip replacement is a hitherto unreported failure mode in this model of acetabular cup in the dog.

Suspected intramedullary bone infarct subsequent to tibial plateau levelling osteotomy in a dog

BACKGROUND

Bone infarction is a syndrome associated with disruption to the medullary blood supply of a long bone and may present as either a cause of lameness or, more commonly, an incidental finding. Bone infarction is a known complication of total hip replacement in the dog and may be associated with several other systemic diseases.

CASE REPORT

A 3-year-old female desexed Labrador Retriever presented for acute lameness 4 weeks following tibial plateau levelling osteotomy (TPLO). Subsequent radiographs revealed an increase in medullary bone opacity, radiographically consistent with a medullary bone infarction. The lesion was followed with serial radiographs and appeared to spontaneously resolve.

CONCLUSION

This is the first reported case of bone infarction following TPLO in the dog. Bone infarction should be considered as an unlikely but potential complication of TPLO.

Femoral medullary infarction prevalence with the Zurich Cementless Canine Total Hip arthroplasty

OBJECTIVE

To document the prevalence of femoral medullary infarction associated with the Zurich Cementless Total Hip Replacement (ZCTHR) system in dogs.

STUDY DESIGN

Case series.

ANIMALS

Dogs (n=35) with 41 ZCTHR implants.

METHODS

Medical records (February 1999-December 2002) were reviewed for dogs that had ZCTHR and at least 1 year follow-up with radiographic evaluation. Thirty-five dogs (41 ZCTHR) met the inclusion criteria. Femoral morphologic data, implant to bone relationships, and medullary infarcts were recorded. Data were analyzed for associations between infarct occurrence and morphologic details and dog characteristics.

RESULTS

Eight of 41 femurs had radiographic evidence of infarcts (19.5%). Dogs with infarcts were significantly younger (mean [+/-SD] age, 18.5+/-5.2 months) compared with those without infarction (mean age, 44.4+/-5.6 months; P=.027). None of the other variables were significantly different between dogs with and without infarcts. Three femurs with infarcts ultimately developed stem loosening.

CONCLUSION

A higher prevalence of femoral medullary infarcts was identified with ZCTHR compared with incidence reported for other total hip systems. Younger dogs were more likely to develop infarction.

CLINICAL RELEVANCE

Femoral infarction appears to be associated with stem loosening. Adjustments in surgical technique or delaying surgery beyond 18 months of age may reduce incidence of infarction but needs further evaluation.

Risk Factors for Ventral Luxation in Canine Total Hip Replacement

OBJECTIVE

To identify risk factors associated with ventral luxation (VL) of canine total hip replacement (THR), and outcome.

STUDY DESIGN

Retrospective study.

ANIMALS

Dogs (n=602) that had THR (563 cemented, 35 cementless, 4 hybrid).

METHODS

Dogs (1999-2004) with VL after THR were compared with dogs with uncomplicated THR. Data included signalment, body weight, diagnosis, implant size, acetabular cup orientation, and femoral displacement ratio (FDR).

RESULTS

VL was diagnosed in 11 (1.8%) dogs after primary THR. Including 2 other dogs that had VL after the study period, 10 (77%) of 13 dogs had VL within 7 days of surgery. Risk factors for VL included Saint Bernard-type dogs (P=.0001), short neck extension (P=.0005), and high angle of lateral opening in other breeds (P=.018). There were trends toward higher risk of VL with lower FDR in Saint Bernard types (P=.060), and with cementless implants (P=.061). Twelve dogs had revision arthroplasty that was successful in all cementless and 2 cemented VL cases. Five dogs had recurrent VL and a poor outcome.

CONCLUSION

VL is generally an early complication of THR, with no single common risk factor identified.

CLINICAL RELEVANCE

Saint Bernard types and short neck extensions are associated with increased risk of VL. Poor cup orientation is a determining factor for VL in some dogs, but a protective orientation of the acetabular cup was not found. Revision is successful in most dogs, but recurrent VL merits a guarded prognosis.

Total joint replacement in the dog

Total joint replacement has evolved over the past 50 years from a concept that was first attempted in people suffering from osteoarthritis to a commonly applied practice in veterinary medicine. Although many questions have been answered, several controversies still exist, with many implant and technical options being explored. Currently, total hip and elbow replacement are commercially available options viable for use in dogs. These options are detailed in this article. Joint replacement for other canine joints (ie, knee, hock, shoulder) that develop osteoarthritis likely will be developed in the near future.

The Effect of Stem Length on Femoral Component Positioning in Canine Total Hip Arthroplasty

OBJECTIVE

To determine the effects of femoral prosthesis stem length on positioning of the femoral component within the canine femur.

STUDY DESIGN

An in vitro experimental study.

SAMPLE POPULATION

Eleven adult, mixed breed, canine cadaver femurs.

METHODS

Polymethylmethacrylate centralized Biomedtrix size 5, 6, and 7 standard and 1cm shortened implants were placed in specimens, manipulated to achieve maximal displacements of the implant tip in each plane, and radiographed. Measurements of the implant angle, tip offset, and minimal tip to endosteal surface distance were obtained with image processing software. The effects of implant length and size on implant positioning were evaluated with the use of Student's t, chi(2) exact, and 2-way ANOVA testing.

RESULTS

Statistically significant increases were noted in tip to caudal cortex distance in the sagittal plane, and available angle variability and tip offset variability in the transverse plane for shortened size 6 and 7 stems relative to the standard stems. No significant differences were noted in size 5 stems. Statistically significant increases in tip to caudal cortex distance and transverse plane available angle variability for standard 6 compared to standard 7 stems were noted.

CONCLUSIONS

Shortened stems result in statistical improvement of several variables of femoral component positioning. However, the improvement appears to be clinically negligible.

CLINICAL RELEVANCE

Alteration of current stem lengths is not recommended. The use of undersized standard implants may improve femoral component positioning in total hip arthroplasty.

Intrapelvic granuloma formation six years after total hip arthroplasty in a dog

A 9-year-old Golden Retriever that had undergone left total hip arthroplasty 6 years previously was evaluated because of constipation and tenesmus. Abdominal radiography and ultrasonography revealed a large intrapelvic mass that was contiguous with a mass of polymethyl methacrylate that had been extruded through a defect in the medial wall of the acetabulum at the time of total hip arthroplasty. Clinical signs resolved following resection of the mass and associated polymethyl methacrylate from the pelvic canal. Results of histologic examination of the mass were consistent with a diagnosis of foreign body granuloma, most likely secondary to particulate debris. There was no clinical or radiographic evidence of aseptic loosening of the acetabular or femoral components, and the mass may have represented a response to wear debris.

Update on the biology and management of canine osteosarcoma

Osteosarcoma (OSA) is the most common primary bone tumor diagnosed in dogs. Our understanding of the risk factors and genetic changes in canine OSA patients is growing, but specific, innovative therapeutic strategies are slow in coming. Appendicular skeletal osteosarcoma, the most frequent form of this disease, is typically seen in large to giant breeds, with males being overrepresented in most reports. Axial skeletal OSA is less common than appendicular OSA, but the biologic behavior of the disease is equally aggressive in all skeletal sites except for the mandible. Though the current standard of care for dogs with osteosarcoma remains surgical resection of the affected site, followed by chemotherapy with either a platinum- (cisplatin or carboplatin) or doxorubicin-based protocol, novel therapies are being actively investigated.

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.