Session IX - Foot & Ankle

Analysis of Failure of Hybrid External Fixation Techniques for the Treatment of Distal Tibial Pilon Fractures

J. Tracy Watson, MD; David E. Karges, DO; Kathryn E. Cramer, MD; Berton R. Moed, MD, Wayne State University, Detroit, MI

Purpose: The use of "hybrid" external fixation techniques for the treatment of distal tibial pilon fractures has involved primarily the use of 2 fixator types (a large-pin monolateral anklebridging fixture, EBI®, Orthofix®, or a small-wire ring fixator). These devices are used in conjunction with a closed ligamentotaxis reduction or limited open reduction and internal fixation (ORIF). We have seen an increase in referral of patients for the treatment of "failed hybrids." The purpose of this study was to evaluate the prior treatment of patients with complications resulting from the use of hybrid techniques to see if any common patterns of device failure or technical surgical errors could be determined.

Methods: From 1993 to 1999, 43 patients with a history of prior pilon fracture were referred to our institution for the treatment of complications resulting from failed hybrid techniques. Following resolution of their complication, retrospective analysis was conducted of their prior treatment course. Original films, initial fixation, and interim follow-up films were obtained. These studies along with the patients' clinical course were evaluated for device failure, technical application errors, or patient factors, such as fracture type, open fractures, or pin-tract infection which may have contributed to their failure.

Thirty-nine patients with previous clinical notes and radiographs were available for review. Patient variables, fixation construct, and follow-up care were analyzed using ANOVA to determine any correlations or consistent patterns of hybrid failure.

Twenty-nine patients (74%) presented with either an A-type (OTA classification) (10 patients) or B-type (19 patients) fracture patterns. Of these, 22 (75%) were open fractures. Retrospectively, the grade of fracture was not easily determined; however, 2 required free-flap coverage and 5 required split-thickness skin grafting. Ten patients (26%) presented as a complex C-type injury, 50 percent of which were open. Three of these patients required flap or skin graft procedures.

Twenty patients were initially treated with a small-wire circular "hybrid" fixator, with simultaneous fibular plating occurring in 10 patients (50%). Eighty percent (16 patients) of those patients had initial open or percutaneous fixation at the articular surface. Nineteen patients had application of a monolateral ankle-bridging fixator in conjunction with fibular plating. Sixteen patients (84%) had additional open or percutaneous articular fixation.

At our institution, 87 percent (34 patients) were treated for malunion (nine patients) or nonunion with deformity (25 patients) of the diametaphyseal junction. Eight percent (3 patients) underwent revision surgery for malunion, nonunion of the periarticular metaphyseal region for gross malreduction (greater than 5-mm step-off of the articular surfaces). Two patients (5%) were treated for both periarticular and diametaphyseal pathology.

Results: Twenty-five patients (64%) developed malunion/nonunion at the diametaphyseal junction as the result of unrecognized tibial comminution or bone loss in this area. All these patients had intact or plated fibulas, which prevented compression at the fracture site following frame dynamization using both types of fixators. The tibial component gradually underwent varus deformation, collapse and healed as a malunion or progressed to nonunion with deformity. The fibular plates either pulled out, fractured, or the fibula underwent varus stress fracture. Bone grafting to this area had not been performed in any of these patients.

Fifteen percent (6 patients) were treated with small-wire frames with inadequate metaphyseal wire fixation (2 wires only), which allowed for translation and angulation of the distal metaphyseal component. These patients demonstrated comminution at the diametaphyseal junction, which did not receive bone grafting.

Seven percent (3 patients) demonstrated adequate articular wire fixation, but lacked proximal shaft stability with only 2 Schanz pins attaching a solitary bar to the distal metaphyseal ring. Diametaphyseal comminution was not addressed, nor did these unstable frame constructs control the cantilever bending moments, and nonunion with deformity resulted.

Seven percent (3 patients) presented with metaphyseal fracture fragments, malreduced (>5 mm of articular step-off). Ligamentotaxis reduction alone was inadequate, and no open procedure had been performed to improve the reduction. Fibular plating was not performed, nor was the normal relationship of the distal fibula to the mortise maintained.

Five percent (2 patients) with inadequate articular reduction were fixed in situ with insufficient metaphyseal wire configuration and diaphyseal instability, which resulted in these patients presenting with articular and diametaphyseal nonunion or malunion.

Discussion and Conclusion: Monolateral ankle bridging frames are rigid and provide excellent stability of the fracture configuration. No inherent mechanical failure could be attributed to these frame types. Fifty-five percent of the circular fixators demonstrated frame instability as a direct cause of their complications. Untreated comminution and bone loss, as well as a previous open fracture at the diametaphyseal junction, combined with fibular plating was predictive of failure (P = 0.01). The inability to dynamize both frame types with an intact fibula was the primary cause of hybrid complications, even in spite of adequate frame stability.

While the relationship of the distal fibula to the ankle mortise is a priority to achieve and maintain, routine plating of the fibular shaft in the face of tibial comminution may prevent these two frame types from achieving their dynamization potential and may lead to malunion/nonunion. This problem may be alleviated if bone loss is recognized and early bone grafting is performed. For ring-type fixators, an adequate number of metaphyseal wires should be used for articular stability (3 or more). Frames with diaphyseal instability and cantilever loading should be avoided.

Ligamentotaxis articular reduction should be thoroughly evaluated, and, if step-off remains, an open procedure to improve the reduction should be carried out.