The process of fracture healing requires a precise balance of biology and stabilization during the healing process. There are four pillars for adequate bone healing: mechanics, osteogenic cells, scaffolds, and growth factors. In some circumstances, this process does not go as expected, and healing does not occur without additional intervention. Definitions vary among different studies, but overall, a diagnosis can be made when there is no evidence of progression of the healing process for 3 months or no healing after 9 months of the injury. This condition will not only have a detrimental effect on the patient’s quality of life, comparable to advanced hip arthrosis and worse than congestive heart failure; but it also has a high impact on the total care costs, double the cost of fractures that heal adequately. Despite the different options available, treatment of tibial nonunions still is challenging for the surgeon.,,,
The "diamond concept” was introduced by Giannoudis et al., aiming to describe what is needed to achieve adequate fracture healing. This concept highlights the importance of three biological factors: osteogenic cells, osteoconductive scaffolds, and growth factors and a fourth factor known as mechanical stabilization. If one or more of these factors are altered, adequate fracture healing will be threatened.
Approximately 6 million fractures are reported per year in the United States. Of these, between 1.9% to 15% result in nonunion. This rate will vary depending on the fractured bone and the characteristics of the fracture (i.e., open vs. closed). In tibial fractures, the rate of non-union is close to 1.1% if treated nonoperatively and nearly 5% if treated operatively. The likelihood of nonunion drastically increases in cases of open fractures.
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:
Fracture and Injury-Related Factors
Biology and Patient-Related Factors (Local and Systemic)
The evaluation of patients with a suspected or established nonunion should begin with a thorough review of the medical history so risk factors can be identified. Collect information about the type of fracture, fixation method, and previous treatments. When interviewing patients, they might manifest persistence of pain at the fracture site and/or functional limitations. One indication that a nonunion is not present is the patient will not have pain with ambulation or when using the extremity. The physical exam should be done in a standard fashion, with evaluation of the neurovascular status and range of motion. Special attention should be drawn to any signs of infection (skin or soft tissue changes) and mobility at the fracture site, which might indicate the absence of adequate callus formation.
Patients with a suspected nonunion should be initially evaluated with plain radiographs, including AP, lateral, oblique, and weight-bearing films. It is important to look for signs (e.g., gaps or callus formation) or absence of healing, bone quality, signs of infection, associated deformities or length discrepancies, as well as the characteristics of the two fragments (i.e., contact, stability, and bone loss). Once this has been done, the nonunion can be adequately categorized as atrophic, hypertrophic, or oligotrophic. If possible, a comparison with original and postoperative follow-up films should be done to create a timeline and better understanding of the nonunion process. In cases where the fracture site cannot be adequately visualized as a consequence of the hardware or the bone quality, a CT scan is advised. This study will allow better identification of the fracture site and assessment of any rotational deformity. Finally, bone scans can be used to assess bone metabolism. Radiologic studies should be complemented with laboratory workup to evaluate any associated metabolic disease or infection that could explain the nonunion. This workup should include endocrine (i.e., Vitamin D, calcium levels) and inflammatory markers.
Depending on its cause, nonunion classifications are as follows:
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:
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.
Ultrasound (low-intensity pulsed ultrasound [LIPUS]): Low sine waves will promote bone healing by increasing the osteoblastic response.
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:
Nail dynamization and nail exchange: Nail Dynamization and exchange have two similar indications; comminuted fractures and absence of cortical contact after IM Nail.
Partial fibulectomy: 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 fibulectomy 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 grafting: Traditionally, 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).
Amputation: Considered when adequate functional outcomes cannot be achieved.
Delayed unions are fractures with a slow progression to healing and require some type of intervention.
Prognosis of tibial fractures can be evaluated using the RUST (Radiographic Union Score for Tibial fractures) score, in which all the bone cortices are evaluated, looking for the presence/absence of fracture line and bone callus. The Nonunion Risk Determination (NURD) score considered are the RUST scores, open/closed fracture, compartment syndrome, fracture classification (IIIB tibia), concomitant chronic disease, smoking status, infection, female sex, and American Society of Anesthesiologists (ASA) score. This model allows the clinician to identify those patients at risk of nonunion within 3 months of injury.
This condition has myriad presentations, and each patient and their expectations are different, so the surgeon must act accordingly. Consult plastic surgery in those cases in which the soft tissue is compromised or a flap is expected and infectious diseases in cases of an infected nonunion. Consult with physical and occupational therapy should be considered, aiming to achieve independence and early range of motion.
Keep in mind the "diamond concept." Minimizing the risk of nonunion is based on patient factors and surgeon-related factors (mechanical). The following can help a practitioner avoid additional risk factors to the patient: