1 Diagnosis topenlarge
These fractures are often the result of high-energy injuries, and are often associated with other injuries, both in the foot and the rest of the body.
In the multiply-injured patient, foot fractures are often overlooked and are picked up on the secondary survey. In the unconscious patient one must rely on a careful physical examination. Swelling, crepitus and a deformity are suggested signs of underlying injury and should be followed up with appropriate x-rays.
In many cases there is swelling and tenderness. In comminuted fractures, deformity may be present.
Conventional x-rays will often show the fracture.
CT with sagittal and coronal reformation is useful in obtaining a three-dimensional understanding of the injury. The CT protocol should call for thin cuts with large overlap. The fragments are small and easily missed on thicker cuts.
2 Principles topenlarge
Talonavicular joint function
The talonavicular (TN) joint allows for hindfoot motion in all planes. Loss of TN motion results in loss of complex hindfoot circumduction. It is therefore extremely important to retain TN function as it has a protective function for the adjacent joints. Loss of TN motion leads to adjacent joint degeneration (DJD). Retaining even a small amount of motion is thought to be protective for the adjacent joint function. The TN joint, because of its extensive range of motion, is also known as the “coxa pedis”.
Click here to view animations of TN-joint motion in AP and lateral views.
As described above, the shape of the TN joint is important. In comminuted fractures of the navicular, there is great danger of losing the normal geometry. Every attempt should be made to reconstruct the shape of the navicular while maintaining soft-tissue attachments and blood supply.
The navicular has an oval shape on cross-section. Small branches of the posterior tibial and dorsalis pedis arteries comprise the blood supply of the navicular. The medial and lateral areas are more or less well supplied while the central section has the most marginal blood supply.
Maintain medial column length
Medial column length is crucial in maintaining the shape of the medial arch of the foot.
If the navicular injury has resulted in comminution with loss of length, in reconstruction we must regain length, as well as normal geometry. Bridging the hardware distally and using bone graft will assure proper length of the medial column, overall shape and alignment of the foot.
The form and function of the foot is dependent on the normal relationship between the medial and lateral columns. If the relative lengths of the medial and lateral columns are not maintained, foot deformity such as cavus or planus results.
Relative shortening of the medial column leads to cavus whereas relative shortening of the lateral column leads to flat foot.
3 Reduction topenlarge
Preparation of the fracture site
Due to the high-energy injury of these fractures, the soft tissues, including capsule and periosteum are disrupted. Care should be taken to minimize soft-tissue stripping during the approach. This will help maintain blood supply to the fragments.
Intraoperative use of a small distractor is needed to restore the medial column and navicular length.
Pin placement into the talus is critical. It is placed into the mid-axial line at the base of the neck. Care must be taken not to penetrate adjacent joints.
Distraction allows access to the fracture site and the joint surfaces.
Care must be taken to maintain column alignment.
Restoration of the articular surface
Free fragments with articular surface should be salvaged and secured with K-wires.
Use a curved elevator to restore the joint surface. The opposing articular surface of the head of the talus or the cuneiforms serve as a template.
Elevators come in many shapes and sizes, and having a variety of these is helpful with foot surgery.
Bone graft and preliminary fixation
Once the articular surface has been reconstructed, the distraction can be adjusted. It is helpful to have comparative x-rays from the uninjured side. This allows one to judge the proper length and morphology.
Any remaining defects, if necessary, are filled with either a bone graft or a substitute.
While reconstructing the joint surface, check frequently to make sure no malreduction ensues.
While the opposing surface serves well as a template, if one secures the assembled fragments to it with K-wires, the verification of joint congruency becomes very difficult.
4 Bone-specific plate fixation topenlarge
Bone-specific plate fixation
The fractured navicular is secured at the end once reduced with a special navicular plate.
This plate is contoured and any extra holes are removed. When inserting the screws (in the proximal row, adjacent to the talonavicular joint), care must be taken to prevent the screws from entering the dome-shaped joint. If one is using the new generation of navicular plates, which provide the variable-angle screw insertion, the screws should be aimed distally, away from the talonavicular joint. This can also be accomplished by contouring non variable-angle locking plates, or using non-locking plates.
In the case of severely comminuted fractures where stable / rigid internal fixation is not possible, the medial column distractor is replaced by means of a bridging plate. Instead of a bridging plate, one can also leave the distractor or an external fixator in its place. This is then left, until the bone heals.
In plating, we can avoid extensive dissection by sliding subcutaneously the contoured plate along the medial aspect of the navicular. A small medial incision is made to facilitate placement of the more proximal screws.
5 Bridge plating topenlarge
In cases where the comminution does not allow single-bone osteosynthesis, bridge plating is indicated.
Bridge plating can be carried out by bridging the navicular and the cuneiforms. This gives the construct added stability. If possible, one should try to use lag screws independently of the plate.
Severe comminution of the navicular is a major problem. If the comminution of the navicular-cuneiform joint is too severe to allow reconstruction, carry out a primary navicular-cuneiform fusion.
Severe comminution of the talonavicular joint is a greater problem. One should avoid at all cost a TN fusion, because this robs the hindfoot of all mobility. In these cases, reconstruct the talar surface of the navicular and bridge the joint either with an external fixator or a plate. Such a plate must be removed subsequently to permit restoration of some joint motion. Plating can be done through the dorsal, or through the medial incision, however, soft-tissue stripping should be avoided.
If bone-specific plates are not available, then bridging or more widely available mini-plates can be used (along with K-wires) to restore medial column length and salvage as much TN joint range of motion/function as possible.
The plate should be removed when there is radiographic evidence of navicular healing. Unfortunately, there can be degenerative changes. Bony osteophytes can be debrided at the time of plate removal.