Nonunion of fracture is a delayed complication of fracture. Literally it means absence of union. But by definition a bone can be labeled as in non union only when the union has not occurred in the bone even after passage of sufficient time [in which the bone normally would have united]. Fractures of shaft of long bone should not be considered nonunion until at least 6 months post injury but in contrast, a central fracture of the femoral neck can sometimes be defined as a non-union after only 3 months.
After fracture has occurred, body initiates a complex overlapping sequence of events, including inflammation , repair and remodeling.
This sequence can restore normal bone structure, biologic function, and mechanical strength in patients of any age.
Despite the potential for successful hearing through regeneration of normal bone, certain types of bone injury and, in some instances, the treatment of bone or soft tissue injury, lead to complications such as delayed union, nonunion, malunion, or bone necrosis that prevent the rapid restoration of normal structure and function.
These complications of fractures and their treatment are inevitable in some patients, but it is possible to avoid or minimize complications and becomes important to diagnose and treat them.
Definitions of Slow Union, Delayed Union and Nonunion
Time a fracture should take to unite cannot be determined arbitrarily. This is so because various factors play a role in fracture healing, including the severity of injury, the fracture pattern, the type of bone, and the age and nutritional status of the patient.
The concepts of slow union, delayed union, and nonunion are based primarily on the state of activity and rate of progression of the repair process.
This term basically implies that fracture union is present but slow. This is a fracture that maintains the appearance of the early stages of healing for more than a few weeks. The fracture line remains clearly visible, but there is no unusual separation of the fragments, and no cavitation of the surfaces, decalcification, or sclerosis.
A slow union does not result necessarily in a delayed union or nonunion. Such fractures often unite if immobilization is maintained long enough.
The term delayed union refers to fracture in which repair is not complete within the interval expected for that specific fracture.
Clinical and radiographic evidence of healing is present. The fracture line is evident on radiographs and usually appears woolly and ill-defined. A delayed union if given proper mileu has potential to join.
A nonunion exists when repair is not complete within the period expected for a specific fracture, and cellular repair activity at the fracture site ceases. Clinically, a nonunion is diagnosed when a repair process has stopped completely and union will not occur without therapeutic intervention.
This cessation of activity is the most important feature that differentiates between nonunion and slow/delayed union.
In an established nonunion, sclerosis develops around the bone ends and the medullary canals are sealed off. The bone ends are joined by dense fibrous tissue.
For a fracture of the shaft of a long bone in an adult, at least 6 months must elapse after injury before this diagnosis can be made.
Thus it must be re-ephasized that terms slow union, delayed union, and nonunion all imply a time frame. This time frame depends on the factors that influence the rate of fracture healing, including the location of the fracture and the amount of soft tissue injury.
Once nonunion has occurred, the fracture would not unite without intervention.
Radiological and clinical features of a given injury help to reach at the diagnosis.
However, time elapsed since injury was used in classical definitions and was important for defining surgical indications.
In the past, surgery was done only in cases where all possibility of healing without intervention was nil.
But with changing times, a more aggressive approach to obtaining fracture union often is taken, and the time frames are less important.
For example surgery may be contemplated after 4 months of conservative treatment, although technically this does not meet the criteria for a nonunion.
The focus is to decrease the morbidity and enable early return to function. Similarly fractures that carry high risk for nonunion may be grafted primarily. This is mainly done in open fractures and comminuted fractures.
Pathophysiology of Fracture Nonunion
There are multiple factors responsible for development of nounion and all the factors responsible for the event may not be known.
Inadequate fracture stabilization and poor blood supply are most common factors leading to nonunion. Infection is other factor.
Some bones like scaphoid, distal tibia, base of the 5th metatarsal are at higher risk for nonunion due to precarious blood supply in these areas. Fracture patterns like segmental fractures segmental fractures and those with butterfly fragments are at increased risk of nonunion as blood supply is compromised to the broken fragment.
Causes of Nonunion of Fracture
There is a long list of causes of non-union of fracture. These are patient related like age, injury related like open fractures and treatment related. Few of them are modifiable and others are not.
Patient Related Factors
- Older age
- Poor nutrition
- Steroid therapy
- Radiation therapy
- Anticoagulant therapy
- High alcohol intake
Injury Related Factors
- Open injuries
- Soft tissue interposition
- Bone loss resulting in gap
- Compromised blood supply following injury to nutrient artery
- Stripping injury to muscle and periosteum
- Severe comminution
Treatment Related Factors
- Inadeuqate immobilisation
- Distraction of fragments from traction or internal fixation
- Malposition of fragments
- Implant failure
Types of NonUnion of Fracture
Callus is formed, but the bone fractures have not joined. This can be due to inadequate fixation of the fracture or inadequate mobilisation. Fracture is capable of a healing response to injury.There is increased uptake on radionuclide scans.
The callus is absent and occur after major displacement of fractures, distraction of fragments, or internal fixation without correct apposition of fragments. Blood supply is usually good. They demonstrates uptake on radionuclide scans but the healing response is inadequate.
No callus is formed. This is often doeto impaired bony healing due to decreases blood supply. They show radionuclide uptake failure.
There is a loss of a fragment of the diaphysis of a bone. The ends of the fragments are viable but as time passes the ends of the fragments become atrophic. Occurs after open fractures, sequestration in osteomyelitis, and resection of tumors.
The term pseudarthrosis implies a nonunion with false joint formation in which the medullary canal is sealed off, with new cartilaginous surfaces covering the bone ends and the nonunion surrounded by a fibrous capsule having a synovial lining.
Pseudarthrosis means false joint.
These nonunions are excessively mobile and often are associated with near ankylosis of a neighboring joint.
Diagnosis of Non Union of Fracture
Diagnosis is made on clinical examination and xrays. On clinical examination, the fracture fragments would show relative mobility and there would be absence of tenderness on the fracture site. Absence of tenderness differentiates non union from delayed union and denotes absence of any biological activity.
Xrays would show
- Absence of bone crossing the fracture site (bridging trabeculae)
- Sclerotic fracture edges
- Persistent fracture lines
- No changes toward union on serial xray
Presence or absence of callus is not a very reliable finding especially in cases of rigid fixation.
Treatment of Non Union of Fracture
Non union is a failure of healing process. The treatment principle is to augment the healing process by freshening the ends of bone and one grafting and provide adequate immobilisation.
Some superficial fractures may respond to bone stimulation which may be tried as part of nonoperative treatment. Few selected nonunions may be tried with fracture brace immobilization
contraindications to non-operative treatments are synovial pseudoarthroses, nonunions that move and greater than 1 cm between fracture ends.
Typical treatment of non union of fracture is surgical. Following are the essential steps
- Exposure of fracture site
- Freshening of sclerotic edges to get a bleeding surface.
- Opening of intramedullary cavities of fragments to facilitate flow of blood circulation
- Rigid fixation
- Bone grafting to augment bone healing
- External splintage if required.
These nonunions often have biologically viable bone ends and may be treated with internal fixation to provide mechanical stability. Bone grafting may not be required.
Oligotrophic/ Atrophic nonunions
Because the biological activity is reduced, these nonunions may require biological stimulation along with internal fixation. The biological stimulation is by bone graft taken from autologous iliac crest is gold standard.
First step is to control infection and the treatment requires staged approach. There is need to need to remove all infected/devitalized soft tissue. Infection is controlled by using local/systemic antibiotics. There may be associated gap which is treated by bone graft/bone transport. Soft tissue coverage procedures may be needed.
Pseudarthrosis may be found in association with infection and principles to control infection remain same. The treatment requires removal of atrophic, non-viable bone ends, internal fixation with mechanical stability. Soft tissue coverage procedures may be needed.
Malunion of Fractures
Malunion refers to fracture union in abnormal position. The abnormal position may be shortened, lengthened, angled, or rotated. Malunion may result in, though not always, insufficient or abnormal function and cosmetically unacceptable limb.
Malnuion may cause alteration of normal dynamics of joint motion. For example, limited pronation-supination after forearm fractures or the development of pelvic obliquity, scoliosis, and back pain secondary to leg-length inequality.
Malunion may be result of inaccurate initial reduction or loss of position because of inadequate immobilization. In physeal fractures of children physeal damage or growth disturbances may result in deformitieis.
The clinical problems presented by malunion of long bones differ
- According to their location
- Diaphyseal and metaphyseal
- Articular surface
- Skeletal maturity of the patient
Diaphyseal and Metaphyseal Malunion
The abnormal position of a healed fracture alters the biomechanics of a specific joint by shifting the weight-bearing axis. The abnormal joint mechanics lead to joint instability and cause local stress overload on the articular cartilage. Both instability and increased or abnormal loads can increase the probability of post-traumatic arthrosis specially in weight bearing joints.
However, the degree of gross deformity is not always related directly to the degree of loss of function or to the long-term development of osteoarthrosis and for the same deformity, function affected varies among the individuals.
The functional impairment also depends on the bone and its compensation offered by body. For example, a malunion of a proximal humeral fracture often results in minimal functional limitation and cosmetic irregularity.
The deformities near joints, especially those that are not in the plane of motion of the joint, may impair function seriously.
Rotational deformities are not apparent on radiographs, may be disabling.
In lower limbs, shortening of a limb by more than 2.5 cm may present enough of a functional and cosmetic problem to warrant shortening of the opposite limb or, in some circumstances, lengthening of the affected segment.
The object of surgery for malunion is to restore function. If the functional disability is minimal, surgical correction of maluion may not be justified. A period of intense physical therapy or weight bear¬ing may be necessary before surgical intervention for malunion to restore atrophic muscle strength.
Articular Surface Malunion
Like metaphyseal/diaphyseal malunions, the amount of functional impairment cannot be quantified for a given grade of malunion though the causal relationship between articular surface step off resulting from malunion of an intraarticular fracture and the development of arthrosis is clearer.
Other factors that may affect the final outcome are variations among joints, associated injuries, joint stability and expected loads.
All said and done, intra-articular malunions are less acceptable than diaphyseal/metaphyseal and rigid criterias have been developed for different joints to serve as guidlelines of intra-articular fractures.
The treatment of articular malunion is directed best at prevention, because the role of surgery in correction is limited. Associated joint arthrosis often makes joint-ablating procedures such as arthrodesis or arthroplasty the only option. Joint realigning osteotomies sometimes may help.
Diaphyseal and metaphyseal fractures in children can result in growth stimulation and overgrowth.
Physeal and Epiphyseal Fractures
The possible consequences of injury to a physis and epiphysis are progressive angular deformity, progressive limb-length discrepancy, and joint incongruity with resultant posttraumatic arthrosis. Causes include avascular necrosis of the epiphysis, crushing or infection of the physis, bony bridge formation at the periphery, joining of the epiphysis and metaphysis, nonunion, and hyperemia producing local overgrowth.
Anatomical reduction is therefore of utmost importance in epiphyseal fractures.
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