Open Navicular Dislocation With Midfoot Dissociation in a 45-Year-Old Man

Discussion

The naviculocuneiform joints are important for the dissipation of loading stresses on the midfoot but provide little motion. The plantar and dorsal ligaments are thick structures that stabilize these joints, predisposing the navicular to fracture rather than isolated dislocation. The stability of the foot is dependent on both the medial and lateral longitudinal columns, and it is thought impossible to injure one column without disrupting the other.⁶ Several patterns of associated lateral column disruptions have been documented, including 3 cases similar to our patient’s, involving navicular dislocation with associated calcaneocuboid joint injuries.^5,6,10

Authors have proposed several mechanisms accounting for navicular dislocations. In the setting of acute trauma, the navicular displaces dorsally as the result of forefoot plantar flexion and axial loading.⁴ A severe abduction/pronation injury leading to a midtarsal dislocation followed by a spontaneous reduction can force the navicular to dislocate medially.⁶ This disruption of the naviculocuneiform joint and concurrent “nutcracker” injury to the lateral column can produce an associated disruption of the calcaneocuboid joint.⁶ Depending on the direction of the deforming force, the forefoot can dislocate superolaterally if the force is plantar or inferolaterally if the force is dorsal. The remaining soft-tissue attachments help determine the position of the navicular. A third postulated mechanism involves a complex wringing injury to the forefoot.¹⁰Most specialists agree that navicular dislocations are best treated with open reduction.^4,6 The goal of surgical intervention is to establish a stable plantigrade foot and to minimize pain. The current literature supports using either wires or screws to maintain reduction of midfoot injuries. Wires can be used for both talonavicular and naviculocuneiform fixation. Screws can be placed across the naviculocuneiform joints, as there is little normal physiologic motion through these joints.⁴ The talonavicular joint and the cuboid-metatarsal joints provide most of the motion in the midfoot and should not be readily fused.⁵ Stabilization of both columns is considered necessary to avoid complications such as subluxation and midfoot deformity.Given the postreduction stability of the lateral column in the present case, bicolumnar stabilization was not considered necessary. It is possible that subsequent collapse of the midfoot may have been attenuated in the presence of lateral fixation, but this would not necessarily have prevented complications of AVN.

Midfoot fractures that are recognized and treated early have generally favorable outcomes,^5-11 though chronic pain and subsequent deformity are not uncommon. Perhaps the most frequently reported complication of navicular dislocation is AVN, which is thought to occur in approximately 25% of cases.¹² AVN is a well-recognized complication of hindfoot and midfoot trauma. In the tarsal navicular, blood supply to the central-third watershed region is marginal. Small branches of the posterior tibial and dorsalis pedis arteries that supply the medial and lateral areas are readily injured. Not surprisingly, the risk for AVN is high when the dislocated bone is severely displaced.⁶ In some circumstances, the shared blood supply of the posterior tibialis may be the only remaining osseous supply. The tendon and its soft-tissue attachments should therefore be carefully monitored during dissection and reduction.⁶ In most cases, AVN of the foot manifests clinically within the first 10 months after injury, as was the case with our patient.¹³ AVN can result in the Charcot-like collapse of the medial column, leading to progressive midfoot plantar deformities.⁴ Variations of midfoot fusion are often required.^4,6AVN may be difficult to differentiate from posttraumatic arthritis. These conditions can have similar clinical presentations and appearances on plain radiographs. In such situations, magnetic resonance imaging or bone scintigraphy may determine the diagnosis. Damage to the articular surface at time of injury and residual articular displacement, instability, and joint subluxation after injury are considered risk factors for the development of posttraumatic arthritis in the foot and ankle.¹⁴ Reports suggest that the severity of the damage to the articular surface is directly proportional to the degree of arthritis.¹⁴ Such damage may not be initially visible, especially in axial impaction injuries, but latent deterioration of the articular surface can occur.¹⁵ For patients with significant dislocations of the naviculocuneiform joints, some authors advocate primary and early fusion¹⁵ instead of the more conservative approach used here. Primary fusions are argued to have minimal deleterious effects on function, secondary to the absence of normal physiologic motion through the affected joints.¹⁵ However, there is relatively little published evidence on long-term outcomes in primary versus secondary naviculocuneiform fusions.

Successful treatment of midfoot fractures and dislocations requires intimate knowledge of foot and ankle anatomy and mechanics. Surgeons must be able to anticipate, identify, and counsel patients about acute and delayed complications in these already challenging injuries.

Am J Orthop. 2017;46(3):E186-E189. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.