Soft Tissue and Biomechanical Challenges Encountered with the Management of Distal Tibia Nonunions

A thoughtful treatment algorithm is required to optimally treat distal tibia nonunion. A healthy respect for the tenuous soft tissue envelope, compromised vascularity, and challenging mechanical environment is advisable. Achieving osseous union and improved functionality requires an individualized plan of care based on the personality of the nonunion and host. Attention must be focused on providing mechanical stability at the site of nonunion and providing biologic supplementation.

An individualized plan of care is of paramount importance when faced with the challenge of managing nonunion of the distal tibia. Successful reconstruction of distal tibia nonunion is predicated on precisely manipulating the local biomechanical milieu to encourage osseous healing. The unique soft tissue constraints and difficult mechanical environment of the lower leg provoke thoughtful consideration of treatment options for any particular host and nonunited fracture.

Nonunion after fracture of the distal tibia is not an uncommon event. Failure of bone healing is greater than 5% after the index operative procedure. Patients diagnosed with distal tibia nonunion frequently are affected profoundly in terms of their physical, mental, and emotional well-being. These patients have significant challenges returning to both their vocational and social lives. Thus, it is of paramount importance to stop the cycle of disability by instituting a well-organized treatment strategy directed at achieving bony union and promoting physical function.

Coincident with the theme of this issue on bone grafting strategies for fracture care, most nonunions of the distal tibia are atrophic, oligotrophic, or variants with bone loss. These often require biologic supplementation to achieve uneventful union. Bone grafting should be considered an integral part of the overall reconstructive strategy.

Tenuous soft tissue environment

Prerequisites for uneventful healing of distal tibia nonunion include optimizing mechanics at the fracture site while respecting the often tenuous surrounding soft tissue envelope. The soft tissue sleeve adjacent to the nonunited fracture has unique characteristics that must be taken into consideration during the planned reconstructive effort. Proper soft tissue management is often predictive of treatment success or failure.

In the uninjured state, the distal leg has a very limited biologic potential because of the paucity of muscular coverage. At least a third of the distal tibia circumference is subcutaneous in location. In the injured state, the quality of soft tissue coverage overlying the distal tibia is even further compromised. Frequently, these fractures are the result of high energy trauma resulting in irreversible damage to the soft tissue sleeve, which is compounded by previous attempts at surgical fracture care.

Compromised vascularity

In addition to the quality of the soft tissue envelope surrounding the nonunited distal tibia, the status of the local vascularity must be considered in the work-up and eventual plan for reconstruction. Etiology for the development of nonunion may be inherent in the poor local blood supply to the distal tibia from the prior trauma, previous surgery, or host disease ( Fig. 1 ). When designing future approaches for nonunion care, the local vasculature needs to be understood and respected to avoid complications such as wound problems, infection, and continued nonunion.

Fig. 1

Delayed union of high-energy open fracture of distal third tibia ( A ) treated with debridement flap, and minimally invasive plate osteosynthesis ( B, C ). Causes for delayed healing were multifactorial including open fracture, vascular insufficiency, poor nutrition (polytrauma patient), tobacco abuse. ( D ) Angiogram demonstrates arterial injury to the anterior and posterior tibial circulation.

Arterial injury is correlated with the development of tibial nonunion. It has been shown that a significant percentage of high-energy distal tibia fractures have occult injury to the arterial tree of the leg. Using computed tomography angiography, an incidence of more than 50% has been reported with the anterior tibial circulation being the most often involved. It is expected that open fractures have an increased risk of occult arterial injury.

Further insult to the local vasculature can occur when open plating is performed at the index operation. Typically, disruption of the intraosseous blood supply occurs with the initial fracture. Thus, the periosteal network is of increased importance for fracture healing. Latex injection studies have demonstrated that open plating techniques can adversely affect the remaining extraosseous blood supply to the metaphysis of the distal tibia.

Biomechanical challenges

After taking into account the management of the tenuous soft tissue envelope and the local vascularity, a well-coordinated strategy needs to be used to improve the local mechanical environment of the bony anatomy. In most cases, revision internal fixation and sometimes deformity correction will be necessary to encourage uneventful bony healing of distal tibia nonunion ( Fig. 2 ). Although a variety of different fixation and reduction techniques can be used, the preoperative plan must be designed to the unique personality of the nonunion and host.

Fig. 2

Preoperative radiograph of oligotrophic distal tibia nonunion with varus deformity ( A, B ). Precise alignment of the anatomic/mechanical axis of the tibia achieved after debridement of the nonunion scar ( C ) and corrective fibular osteotomy ( D ). Peri-articular locking plate used to assist in deformity correction and for rigid fixation of the short osteopenic distal segment. Fibula rigidly fixed and used as biologic lateral column support. Compression of nonunion with interfragmentary compression ( E ). Central bone graft technique used. Patient healed at 4 months ( F–H ).

Aside from the choice of hardware used, there are many factors to consider that are unique to nonunion of the distal tibia. Achieving adequate distal fixation is crucial, but sometimes a significant challenge. In many circumstances, there is a short distal segment. Thus, the corridor for hardware placement is a challenge. Moreover, the bony architecture in the metaphyseal/epiphyseal region is largely cancellous and the distal block is often weakened by disuse osteopenia and previous hardware installation.

In addition to achieving sufficient fixation, correction of deformity is integral to the overall success of reconstruction as defined by bony union and improved functionality. Deformity is commonplace after initial treatment for these fractures with reported rates of 16% after intramedullary nailing and 13% after plate osteosynthesis. Thus, the individualized plan of care must be designed to address restoration of the mechanical/anatomic axis of the tibia when warranted.

Biologic requirements

All distal tibial nonunion variants except hypertrophic or infected cases require biologic supplementation. Therefore, a critical step for achieving osseous healing in atrophic/oligotrophic nonunions or cases with significant bone loss is the delivery of biomaterials to the fracture site. These materials optimally are osteoconductive, osteoinductive, and osteogenic. Osteoconductive biomaterials will serve as a scaffold for new bone growth across the nonunited fracture, whereas osteoinductive and osteogenic agents will stimulate the formation of new bone.

Principles of nonunion care

The unique characteristics of distal tibial nonunion have been discussed. The treatment algorithm prescribed must be custom tailored to the specific patient and nonunion variant. General principles of nonunion care, however, are applicable to these patients/nonunions.

Although these reconstructive surgeries are not entirely elective cases, a sufficient amount of time should be devoted to counseling the patient and preoperative planning. A contract needs to be made between surgeon and patient outlining the expectations for continued limb salvage. The patient’s general wellness both physically and psychologically needs to be maximized. Negative behaviors such as tobacco or alcohol use should be curtailed. Consideration for endocrine work-up should be considered to determine potential systemic etiology contributing to nonunion.

At a minimum, infection should be worked up as a potential cause of nonunion with laboratories. A CT scan is valuable to determine the pattern and type of nonunion (atrophic, oligotrophic, hypertrophic, nonunion with deformity or bone loss). Vascular studies such as CT angiogram could be ordered if treatable vascular lesion is suspected and to determine areas for safe surgical exposure.

The surgery should be purely a technical exercise based on a well-organized preoperative plan. For atrophic and oligotrophic nonunions or variants with bone loss, the fibrous scar at the nonunion needs to be thoroughly debrided to healthy-appearing bone. If possible, the bone ends are manicured to allow for maximal compression and deformity correction. In an effort to increase surface healing for union, the medullary canal should be reestablished and the bone ends “feathered.” Bone graft is packed into and around the nonunion site. Strategic hardware is placed to obtain and maintain an optimal mechanical environment to encourage bone healing.

Plate osteosynthesis

An integral part of nonunion surgery for the distal tibia is addressing mechanical instability. The workhorse is revision internal fixation with plate osteosynthesis; however, a balance must be achieved. Injudicious use of excessive or bulky hardware in a compromised soft tissue envelope leads to a multitude of severe complications. Wound-related complication and deep infection infamously plague this type of reconstruction. Further, excessive bone stripping during open procedure often can foster continued nonunion.

Fixed angle plates are ideally suited for definitive reconstruction of distal tibia nonunion. Classically, the blade plate has been used with clinical success as defined by union and improved functionality. Reduction and compression of the nonunion is facilitated with the use of this implant. Fixation of the short osteopenic distal segment is optimized. However, technical expertise with these devices is warranted for treatment success.

Another option for increasing fixation of the compromised distal segment is with precountoured locking implants. Low profile plates are available for use anterolaterally, medially, and posteriorly. Implant design allows for the placement of multiple fixed angle screws into the distal segment to invite increased control over the nonunited fracture. Further, deformity correction is often facilitated by using the plate as a template for restoring the geometry of the distal tibia. Compression at the site of nonunion can be achieved with eccentric screw placement in the shaft through the dynamic compression slots. Additionally, an articulating tension device can be applied to most of these plates.

Strategic fibula management

Creative use of the fibula can increase the chances of successful union of the distal tibia nonunion. The fibula can be manipulated in a variety of ways depending on the management strategy of the associated tibial nonunion. When developing a definitive strategy for the distal tibia nonunion it is important to realize that the fibula can be used mechanically, biologically, or to assist with deformity correction.

The fibula should be considered a potential lateral column stabilizer for the nonunited tibia. The fibula can act as a biologic plate to further enhance the mechanical environment for tibial healing. As the fibula will span the nonunion site, syndesmotic type screws can be placed above and/or below the primary tibial fracture line to enhance stability.

The fibula and adjacent syndesmotic membrane can serve as a perfect host for bone graft incorporation creating a single bone leg distally. The graft is typically placed under the muscular envelope overlying the syndesmosis. This vascularized environment is ideally suited for graft incorporation.

Manipulation of the fibula is of utmost importance for either gaining compression of the tibial nonunion or for correcting deformity. To compress (shorten) the tibia nonunion, resection of a portion of the fibula or oblique slide osteotomy is often required. Correction of deformity in the coronal or sagittal plane is exceedingly difficult without simultaneously correcting fibula deformity. As the fibula will often heal, strategic osteotomy needs to be considered.

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Feb 23, 2017 | Posted by in ORTHOPEDIC | Comments Off on Soft Tissue and Biomechanical Challenges Encountered with the Management of Distal Tibia Nonunions

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