Nonunion – Causes, Symptoms, Treatment

Nonunion
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Nonunion is a permanent failure of healing following a broken bone unless intervention (such as surgery) is performed. A fracture with nonunion generally forms a structural resemblance to a fibrous joint and is therefore often called a “false joint” or pseudoarthrosis (the Greek stem “pseudo-” means false and “arthrosis” means joint). The diagnosis is generally made when there is no healing between two sets of medical imaging such as an X-ray or CT scan. This is generally after 6–8 months.

Types of Nonunion

Types of Nonunion

Judet and Judet, Muller, Weber and Cech, and others classified nonunions into two types according to the viability of the ends of the fragments: Hypervascular nonunions and avascular nonunions.

Hypervascular nonunions are subdivided as:

  • “Elephant foot” nonunions: These are hypertrophic, rich in callus, and are a result of inadequate immobilization, insecure fixation, or premature weight-bearing.
  • “Horse hoof” nonunions: Mildly hypertrophic, poor in callus and is due to unstable fixation.
  • Oligotrophic nonunions: They are not hypertrophic but vascular, no callus seen, and is due to severely displaced fracture or fixation without accurate apposition of fragments.

Avascular nonunions are subdivided as

  • Torsion wedge nonunions have an intermediate fragment with decreased or absent blood supply. This fragment has healed to one main fragment but not to the other.
  • Comminuted nonunions have one or more intermediate fragments that are necrotic.
  • Defect nonunions have a gap in the diaphysis of bone due to a loss of a fragment.
  • Atrophic nonunions usually are the final result when the intermediate fragments are missing and scar tissue that lacks osteogenic potential is left in their place.

Depending on its cause, nonunion classifications are as follows:

  • Septic (infected) or aseptic 
  • Pseudarthrosis
  • Hypertrophic – characterized by inadequate immobilization, but adequate blood supply persists
  • Atrophic – characterized by inadequate immobilization and inadequate blood supply in the early stages of fracture healing
  • Oligotrophic – characterized by inadequate reduction with the persistence of fracture diastasis; no callus can form
  • Hypertrophic non-union – Callus is formed, but the bone fractures have not joined. This can be due to inadequate fixation of the fracture and treated with rigid immobilization.
  • Atrophic non-unionNo callus is formed. This is often due to impaired bony healing, for example, due to vascular causes (e.g. impaired blood supply to the bone fragments) or metabolic causes (e.g. diabetes or smoking). Failure of the initial union, for example, when bone fragments are separated by soft tissue may also lead to atrophic non-union. Atrophic non-union can be treated by improving fixation, removing the end layer of bone to provide raw ends for healing, and the use of bone grafts.

As mentioned, an adequate interplay between host biology and reduction technique are key to achieve fracture healing. The development of a nonunion is multifactorial. Factors that contribute to the development of a nonunion include the following, listed here with known risk factors

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Causes of Nonunion

The reasons for non-union are

  • avascular necrosis (the blood supply was interrupted by the fracture)
  • the two ends are not opposed (that is, they are not next to each other)
  • infection (particularly osteomyelitis)
  • the fracture is not fixed (that is, the two ends are still mobile)
  • soft-tissue imposition (there is muscle or ligament covering the broken ends and preventing them from touching each other)

Fracture and Injury-Related Factors

  • High-energy fractures with significant comminution
  • Type of fracture (closed/open)
  • Location and pattern (highly comminuted or butterfly fragments)
  • Extent of soft tissue injury
  • Bone loss and fracture gaps (greater than 3 mm)
  • Lack of cortical continuity
  • Infection

Biology and Patient-Related Factors (Local and Systemic)

  • Nutritional status
  • Diabetes
  • Smoking
  • Inadequate blood supply
  • Vitamin D deficiency
  • Renal insufficiency
  • Medications (steroids, NSAIDs, opiates, etc.)

Surgical-Related Factors

  • Inadequate stabilization

Related to the person

  • Age: Common in old age
  • Nutritional status: poor
  • Habits : Nicotine and alcohol consumption
  • Metabolic disturbance: Hyperparathyroidism
  • can be found in those with NF1
  • Genetic predisposition

Causes related to fracture

  • Related to the fracture site
  • Soft tissue interposition
  • Bone loss at the fracture
  • Infection
  • Loss of blood supply
  • Damage of surrounding muscles

Related to treatment

  • Inadequate reduction
  • Insufficient immobilization
  • Improperly applied fixation devices.

Symptoms of Nonunion

  • A history of a broken bone is usually apparent. The patient complains of persistent pain at the fracture site and may also notice abnormal movement or clicking at the level of the fracture. An x-ray plate of the fractured bone shows a persistent radiolucent line at the fracture. Callus formation may be evident but callus does not bridge across the fracture. If there is doubt about the interpretation of the x-ray, stress x-rays, tomograms or CT scan may be used for confirmation.
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Treatment of Nonunion

Treatment of nonunions should aim to achieve healing of the fracture while preserving functionality. The following are available options for the treatment of non-unions:

Nonoperative Treatment

  • Removal of all scar tissue  – from between the fracture fragment immobilization of the fracture with internal or external fixation. Metal plates, pins, screws, and rods, that are screwed or driven into a bone, are used to stabilize the broken bone fragments.
  • Conservative treatment/weight-bearing  In some circumstances and special patient characteristics (e.g., elderly patients not eligible for operative treatments), nonunions can be treated with weight-bearing and watchful waiting. Weight-bearing can be coupled with operative methods such as dynamization or bone excision.
  • Electrical stimulator/electromagnetic fields  Growth factors are stimulated in response to the electric and electromagnetic fields.
  • Ultrasound (low-intensity pulsed ultrasound [LIPUS])  Low sine waves will promote bone healing by increasing the osteoblastic response.

Operative Treatments

When an operative treatment has been considered, intraoperative culture should always be performed to diagnose a subclinical infection. Radiologic findings and patient characteristics should guide the clinician in the decision of what operative treatment should be done. The following are treatment options:

  • Bone grafting – Donor bone or autologous bone (harvested from the same person undergoing the surgery) is used as a stimulus to bone healing. The presence of the bone is thought to cause stem cells in the circulation and marrow to form cartilage, which then turns to bone, instead of a fibrous scar that forms to heal all other tissues of the body. Bone is the only tissue that can heal without a fibrous scar. The autologous bone graft is the “gold standard” treatment of the nonunion the bone is obtained from the iliac crest.
  • Nail dynamization and nail exchange Nail Dynamization and exchange have two similar indications; comminuted fractures and absence of cortical contact after IM Nail.
  • Nail dynamization – A relatively low-cost treatment done when axial stability has been achieved and maintained. The dynamization is achieved by removing interlocking bolts distant to the fracture site facilitating compression and loading across the fracture site.
  • Nail exchange – Removal of the prior intramedullary nail, reaming, and use of a nail with a larger diameter. With this, the reaming process will biologically activate the fracture site, and better axial and mechanical stability can be achieved.[rx]
  • Partial fistulectomy  This procedure can be done on its own or combined with other procedures. Two important requisites have to be fulfilled, a stable nonunion and the fistulectomy has to be done in another site different.
  • External fixation Considered in complex nonunions (e.g., when internal fixation is not possible or not recommended due to infection, substantial deformity, and/or bone loss).
  • Bone graftingTraditionally, iliac crest bone graft has been used when poor vascular supply is present. This treatment option aims to provide an adequate environment for bone formation (biological factors of the diamond concept).
  • Cell therapy – The use of mesenchymal cells within the fracture gap creates a healing environment.  
  • Amputation  Considered when adequate functional outcomes cannot be achieved.
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References

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