Bone infection in dogs – osteomyelitis symptoms and treatment

Overview

Infection can involve different bone layers

Osteomyelitis can affect the marrow cavity, bone cortex and surrounding periosteum. Common locations in dogs include limb bones and the jaw. Disease can start suddenly or gradually become chronic. A postoperative infection may produce signs only long after the procedure.

Bone infection differs from inflammation confined to the skin or wound surface because the lesion lies in bone tissue. It may require both medication and surgery. Prognosis depends on severity and how chronic the infection is.

In a group of 52 dogs with bacterial osteomyelitis, the tibia accounted for 31% of bacterial findings examined. The femur accounted for 28%. The radius and ulna accounted for 25%. The humerus accounted for 16%.

Causes

Microbes can reach bone by different routes

An open fracture can contaminate bone with microbes from the skin or environment. A deep puncture or bite can also carry infection into tissues. Infection elsewhere in the body may instead spread to bone through the blood. Surgery-related infection is another possible route.

A Brazilian study examined long-bone infection starting from an external source in 52 dogs: a traffic injury was responsible in 78% of cases. Bites accounted for 17%. Infection extending from paw dermatitis explained 5%. These are causes in that particular patient group, rather than general disease risks for dogs.

Bacteria and biofilm

Staphylococci are common causes, but other bacteria also occur. Some staphylococci belong to a healthy dog's normal skin microbiota. Bacteria entering damaged bone is different from their presence on intact skin.

An implant surface can develop a biofilm, a protective structure produced by bacteria. It helps bacteria attach to foreign material. Such bacterial growth can persist despite the body's defences and medication.

Staphylococci have been estimated to account for around 50% of bone infections in dogs and cats. The biofilm's protective layer consists of bacterial polysaccharides, or sugar chains. It supports bacterial growth on foreign material.

Killing bacteria in a biofilm may require a higher drug concentration than killing free bacteria.

Risk factors

Open fractures, deep puncture wounds and bites predispose bone to contamination. Complications involving orthopaedic plates, screws and rings placed around bone can increase bone infection risk. Poor blood supply and already damaged or dead bone tissue make infection easier to establish. Reduced immune defences increase risk, particularly for infections spreading from elsewhere in the body.

A tooth root abscess can sometimes involve jawbone infection as well. The possibility of fungal infection depends on the dog's environment and travel history. In the south-western United States, Coccidioides is a possible cause. Aspergillus moulds occur worldwide.

Bone infection can also develop after treatment of a closed fracture: all 5 affected dogs in an implant patient study group originally had closed fractures.

In a group of 5 dogs with implant-associated bone infection, mean age was 6.6 years with a standard deviation of 4.7 years. Mean weight was 35.2 kg with a standard deviation of 12.6 kg. These describe affected patients, rather than risks calculated from breed or weight.

A tooth root abscess can develop after a tooth fracture or periodontal disease.

Typical symptoms

Signs may be localised or affect the whole body. You may notice:

• Lameness or reduced use of a limb.
• Pain over the infected bone.
• Visible swelling and an infected-looking wound.
• Pus draining from a wound opening onto the skin.
• Fever, tiredness or unusual weakness.
• Reduced appetite.

Jawbone infection can cause pain when eating and bad breath. Not every dog has obvious general illness: among 5 affected dogs in the implant study group, 2 had fever, tiredness or loss of appetite.

All patients in the 5-dog bone infection group had local swelling, pain and lameness.

Complications and consequences

Bone destruction and persistent infection

Bone infection can cause bone breakdown, or osteolysis. In chronic disease, bone blood flow may decline and bone tissue die. Lack of blood supply makes it harder for immune cells and antimicrobials to reach the infection. Implant-associated infection can also lead to fixation failure.

Draining tracts and recurrence

Bone infection can form a fistula, a draining passage from tissue to the skin. Local bacterial growth may remain around an implant and reactivate when conditions change. Difficult-to-control chronic infection can sometimes lead to limb amputation. Full recovery is nevertheless possible with appropriate treatment.

Diagnosis at the vet

History and bone imaging

Your vet asks about onset, previous injuries, operations and travel. Examination assesses both the painful area and the whole dog's condition. Blood tests may include a blood count and biochemistry assessing organ function. A urine sample may also be needed. White blood cell numbers can rise during an active inflammatory response.

X-rays are checked for bone destruction, an abnormal periosteal reaction and separated bone fragments. Implant loosening may be visible. Imaging can assess the extent of bone changes. A difficult case may need ultrasound or a surgically collected bone biopsy.

Images may show reduced bone density, or osteopenia. The bone's spongy trabecular pattern may also disappear. New bone can form on the surface at the same time.

Sampling identifies the organism

A deep needle sample and cytology can help identify the cause. Culture establishes which bacterium or fungus grows in the sample. Bacterial susceptibility testing guides antibiotic choice. Blood or urine culture may complement the search for an infection source.

Bone infection samples from the 52 dogs studied yielded positive cultures in 88%. Mixed growth occurred in 42% of cases. More than one microbial species can therefore be involved.

Distinguishing implant bacterial growth from bone infection

In a study of removed bone plates, osteomyelitis was diagnosed in 5 of 51 dogs, or 9.8%. In the same group involving dogs and cats, implant bacterial growth was found in 33 animals, or 50.8%. Bacteria were therefore also present on implants from clinically healthy animals. A positive implant culture is assessed alongside other findings.

Staphylococcus pseudintermedius was found in all 5 dogs with bone infection. An MRSP strain, the meticillin-resistant form, was found in 1 dog. This illustrates why susceptibility testing is needed when selecting medication.

Needle sampling yielded pus in 4 of the 5 dogs with bone infection. One dog was not sampled.

Treatment

Targeting the identified infection

Antibiotics for bacterial osteomyelitis are selected using culture and susceptibility testing. A dog with sudden general illness may need treatment before the final culture result. In chronic disease without general signs, sample-based selection helps prevent resistant bacteria developing. Fungal infection requires an antifungal medicine suitable for the organism involved. Medication and its monitoring are directed by your vet.

Hospital care may be needed to provide initial support. Wounds are treated and a fractured limb supported at the same time. A severe fracture is fixed and repaired under general anaesthesia.

Surgical debridement of the infection site

Surgery can remove dead, damaged and infected tissue. The focus is flushed and the infected area cleaned. Debridement reduces microbial numbers and helps medication work. Some patients need open wound management or closed drainage. A drain is a tube or another route allowing discharge to leave.

Loose or failed implants may need removal. Adequate fracture support must nevertheless be arranged as part of treatment. A cancellous bone graft collected from the dog's own bone may be used at a later stage where needed. Amputation may sometimes be necessary for difficult-to-control chronic infection.

Home care and monitoring response

Exercise may need restriction, and your dog may require prolonged crate rest. Follow discharge instructions for wound care. Licking and scratching are prevented because they can infect the surgical area. Medication continues according to your vet's prescribed plan.

Follow-up may include repeat blood tests and images to assess healing. Close monitoring of response is also needed in chronic infection. Recovery depends on the cause, duration and severity of infection and the extent of concurrent injuries. Return to normal exercise therefore follows reassessment findings and individual instructions.

Prevention

A deep wound or bite is examined promptly so that damage can be treated before infection progresses. A paw wound easily dirtied outdoors is protected during walks. A collar prevents wound licking where needed. A dirty or wet dressing is changed.

Report new health changes to the treating service after orthopaedic surgery. A tooth root abscess or sudden facial swelling is treated without delay. Not every bone infection starts with a visible skin injury because infection can also spread through the blood.

Important for dog owners

What should you monitor at home?

Record lameness, pain changes, appetite and general condition. Also monitor wound discharge and swelling. Contact your vet if discharge becomes thick and foul-smelling or the area becomes red and painful. Rapid deterioration requires urgent assessment.

At the consultation, describe previous operations, medication used and travel. Arrange follow-up visits and attend investigations because they assess bone healing. Do not stop prescribed antimicrobial medication on the basis of outward improvement alone. Ask for clear instructions on permitted exercise and wound care in the discharge plan.

Frequently asked questions

Can a dog have bone infection without fever?

Yes. In a small implant patient group, only 2 of the 5 dogs with bone infection had fever, tiredness or loss of appetite. All had local swelling, pain and lameness. This was a limited study group, but the finding shows that local signs can predominate without obvious general illness.

Does a positive implant culture always mean bone infection?

No. Bacteria were also found on removed bone plates from clinically healthy animals. Bone infection diagnosis considers signs, X-ray changes and samples together. The result may nevertheless matter for treatment because bacterial growth can persist on an implant surface.

Are metal plates or screws always removed for bone infection?

Loose or failed implants may need removal to treat the infection site. Adequate fracture support must be maintained at the same time. Your vet assesses fixation and the overall treatment plan using investigations. An implant's presence alone therefore does not dictate the same procedure for every patient.

Can medication stop once lameness improves?

Complete prescribed antibiotic or antifungal treatment according to your vet's instructions. Follow-up may require repeat laboratory and imaging investigations to assess healing. Response to bone infection treatment is closely monitored. Improvement in an outward sign therefore does not replace monitoring included in the treatment plan.

Can a tooth abscess cause jawbone infection?

Bone infection can sometimes develop alongside a tooth root abscess. Jawbone infection may cause pain when eating and bad breath. Sudden facial swelling or an obvious abscess warrants prompt veterinary contact. Treatment is planned according to mouth and bone findings.