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Delayed and non-union fractures in small animals...

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01 March 2014, at 12:00am

Dr Helen Floyd managing director of Curar, discusses the use of low intensity pulsed ultrasound to promote healing of fractures, tendons and ligaments

FOR any given fracture the normal time to healing will vary according to the breed, age, general health, the bone involved, severity of the fracture (especially comminuted fractures), soft tissue damage and type of fixation.

Delayed union can be diagnosed when no or minimal union of the bone is observed in what would be considered a “normal” healing time. “Normal” relates to that of a similar fracture, in the same bone of a patient of similar breed, age and general health, which has been repaired in the same way, and heals without complication.

The causes of delayed union are typically one or more of: inadequate immobilisation, distraction, excessive compression, impaired blood supply, infection, excessive implant quantities or excessive fracture gap.

Fracture gap may be the prime cause of delayed union because it often leads to other causes such as excessive motion at the site. This may cause soft tissue disruption, affecting vascular supply and ultimately callus formation.

With internal fixation, external fixation and external coaptation, adequate stability is the key to the progress of healing.

Cast immobilisation allows relatively large amounts of movement between fracture ends during the progression through haematoma, fibrin clot, cartilage and finally bone. Each stage will tolerate varying degrees of movement within the limits of each tissue.

This tolerance varies over time and is susceptible to slight changes in treatment such as modification of casts or splints. This means re-examination and regular radiographic assessment is required as it may be necessary to modify support depending on whether the delay in healing is temporary or evolves into non-union.

Following internal fixation, bone ends are fixed relative to each other and the gap between them is maintained. This may delay healing as lack of stimulation may prevent effective ingrowth of granulation tissue.

Non-union fracture

The difference between delayed and non-union is difficult to interpret. The standard definition of non-union fracture is the cessation of all reparative processes of healing without bony union. 

Diagnosis of non-union is both subjective and dependent on a range of factors. There may be extremity non- use which may lead to muscle atrophy, stiffness, reduced range of motion in joints and malalignment of the bone.

If fixation is too stiff the patient may bear weight comfortably, effectively “walking on implants”. This can be seen particularly in the radius and ulna of small dogs, where osteoporosis and resorption of bone can occur when there is extended immobilisation with no weight bearing, or internal fixation is too rigid. These changes can be difficult to reverse without further intervention, and can result in implant fatigue and failure before healing.

Radiographically, a radiolucent line will remain at the fracture site. The medullary cavity may be sealed with sclerosis at the edge of the bone and resorption of bone or osteoporosis may be present. The fracture fragments may have rounded ends or a hypertrophic “elephant’s foot” callus may be present.

Once non-union is diagnosed but before treatment, examination is required to identify the presence of associated pathology such as nerve damage or soft tissue injury, as well as limitations in joint function. Even if bone union itself can be achieved through further intervention, it may be that adequate function cannot be restored due to ongoing problems.

Treatment options

Both surgical and non-surgical techniques may be required. In many cases increasing or decreasing the level of fixation will be required. In some, reduction of external coaptation may be sufficient to promote healing if some stability is present.

If revision surgery is required, open reduction with compression plating to increase stability is common. This may be necessary in cases that have initially been managed conservatively, or to revise previous internal fixation. 

Depending on alignment of the original reduction, this may be achieved with minimal disturbance. It may be necessary to debride fibrous tissue, or resect fragment ends. This may result in limb shortening. This is particularly true if the original reduction is inadequate. Cancellous bone grafts may be applied in isolation or in conjunction with revised fixation, depending on the scenario.

Other methods used to address non-union and delayed healing include shockwave, electrical stimulation and low intensity pulsed ultrasound (LIPUS). The use of extracorporeal shockwave therapy is well-established and has been used to treat non-union of long bone fracture.

Bioelectrical stimulation has been used since the 1950s and invasive, semi-invasive and non-invasive devices exist with specific applications to particular bones.

Non-invasive LIPUS is a relatively new therapy in the veterinary world but well-established in the treatment of humans where it has a large clinical evidence base including guidance from NICE supporting use in treating fresh fractures as well as delayed and non- unions.

One of its advantages in delayed or non-union fractures is that it can be used alongside invasive techniques as its effect on healing is not compromised by the presence of wires or other fixations.

Recent reviews from a wide range of human and animal studies concluded that LIPUS accelerated the healing of fresh fractures on average by 38% and had a success rate in delayed and non-unions of 86%.

Case study

One-year-old Labrador Retriever treated after referral to Mark Morton, Davies Veterinary Specialists, Hertfordshire. Condition: fracture to proximal calcaneus 10 weeks prior to referral which had been conservatively managed with a cast. Radiographs revealed a non-union with further proximal displacement of the tuber calcanei.

Treatment: fibrous tissue was debrided and the proximal fragment stabilised with k- wires and tension band wire. A combination of allogeneic cancellous chips and demineralised bone matrix was applied to promote healing. After six weeks, follow- up radiographs showed no evidence of healing and resorption of the proximal fragment, leaving a large gap and loosening of the k-wire. 

Due to poor bone quality in the proximal fragment, revision surgery to improve fixation and apply further graft was undesirable. LIPUS (using the Sonivet device) was employed to aid healing. A splinted dressing was also applied whilst daily 20-minute treatments were performed at home for three weeks. A small window was left in the dressing so treatment could be applied.

Outcome: three weeks after treatment, radiographs revealed bone density and quantity had increased significantly enabling the supportive dressing to be removed and exercise levels gradually increased. Normal function was achieved. Radiographs performed following an unrelated tibial fracture four months later showed almost complete healing of the calcaneus.

  • The author wishes to thank Mark Morton Davies of Veterinary Specialists (www.vetspecialists.co.uk) for his contribution to this article. More information on the Sonivet device is on www.curar.co.uk.