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Case Report: Hip Septic Arthritis in a German Shepherd Dog

History

fig 1 - extended ventrodorsal view of the right hip showing subluxation of the joint with degenerative changes to the proximal femoral metaphysis. There is remodelling of the femoral head and new bone formation at the insertion of the joint capsule consistent with osteoarthrosis secondary to hip dysplasia.

A nine–year-old, female, neutered German Shepherd Dog presented for assessment of right pelvic limb lameness.

The owner reported progressive lameness since the patient had fallen 10 days previously.  The referring veterinarian’s radiographs revealed marked degenerative changes to the right hip (see figs. 1 & 2).

fig 2 - flexed ventrodorsal view of right hip showing degenerative changes to the joint. There is also evidence of irregular endosteal bone deposition, but the trabecular pattern appears intact.

Examination

fig. 3 - Dorsoventral radiograph of chest - there are several, small, mineralised masses towards the periphery of both lung fields consistent with osteoma.

The patient appeared bright despite 5/5 lameness on the right pelvic limb.  General physical examination was unremarkable.  Orthopaedic examination revealed marked discomfort on manipulation of the right hip.

fig. 4 - STIR (fat-suppression) sequence MR-scans in dorsal plane of the right hip showing inflammatory changes within the femoral head and acetebulum.

Haematology and biochemistry revealed no abnormalities.  Urine analysis, including bacteriology, was unremarkable.  Blood culture yielded a heavy, pure growth of Staphylococcus aureus sensitive to all antimicrobials tested.  Thoracic radiology revealed several, small, rounded, mineralised opacities throughout both lung fields, consistent with osteomas (see fig. 3).  However, disseminated metastases could not be entirely excluded.  MR-scans of the right hip (see fig. 4) revealed increased signal on STIR weightings within the right femoral head and acetebulum, consistent with an inflammatory response.

The differential list for the above findings includes septic/ sterile arthritis, ‘acute-on chronic’ osteoarthrosis precipitated by trauma and synovial cell sarcoma/ other neoplasia.

Treatment

The patient received IVFT with trial cefuroxime 1g q12h pending bacteriology results.  NSAID/ opiate analgesia was provided concurrently.  24 hours later, the lameness had resolved.

The patient was discharged with a three week course of cephalexin 500mg q12h P.O., meloxicam 0.1mg/kg q24h P.O. and a trans-dermal fentanyl patch 100ug/hr.

Antimicrobials were continued for a further three weeks once sensitivity testing was known, and there has been no evidence of lameness in the two months since antimicrobials were stopped.

Discussion

Septic arthritis is usually seen in juveniles secondary to haematogenous spread, or in older animals by direct inoculation of the joint secondary to traumatic wounds, including nosocomial infection as a post-surgical complication.

Isolated, primary, joint infections in mature animals are rare, but should be included as a differential diagnosis for unusually sore joints especially where there is chronic inflammation – as seen in this case, where there was significant osteoarthritis secondary to dysplasia.

MR-scans were useful in rapidly confirming the intra-articular/ intra-osseous inflammatory pattern typical of infection without the loss of structural integrity seen in most neoplastic conditions.

Blood culture results should be interpreted with caution as contamination and in vitro proliferation remain a possibility.

Bacteriology of joint-fluid aspirates and/ or synovial membrane samples would have provided a more reliable result, but these were not obtained given the rapid response to the above treatment.

Joint infections should be managed aggressively as irreversible and devastating changes to the joint will occur should treatment be delayed; if marked improvement is not seen to intravenous antimicrobials within 24-48 hours, consideration should be given to serial joint lavage and debridement.   Appropriate samples can be taken for histopathology and bacteriology at this juncture so as to confirm the diagnosis and check sensitivity to selected drugs.