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.
