A Biomechanical Evaluation to Optimize the Conﬁguration of a Hinged External Fixator for the Primary Treatment of Severely Displaced Intraarticular Calcaneus Fractures with Soft Tissue Damage Lutz Besch, MD, 1 Ina Schmidt, MD, 2 Michael Mueller, MD, 1 Mark Daniels-Wredenhagen, MD, MA, 2 Ralf-Eric Hilgert, MD, 1 Deike Varoga, MD, 2 and Andreas Seekamp, MD, PhD 3 The purpose of this investigation was to develop an optimized hinged external ﬁxator for the primary treatment of dislocated, intra-articular calcaneus fractures with associated soft tissue damage. To this end, a calcaneus model was made out of a polyurethane block, and a steel cylinder served as the ankle joint and was connected to a synthetic model of the tibia via a metal clamp. A saw cut served as the fracture in the model. A Steinmann nail and Schanz screw were placed in deﬁned positions in the model and connected medially and laterally with longitudinal support rods. The ﬁxator allowed a total of 20° of plantar- and dorsiﬂexion, with rotation in the virtual axis of the upper ankle joint. Changes in the model fracture were measured during cyclical strain, and at different screw positions in the model tibia and calcaneus. Miniature force sensors located on the longitudinal support rods, and a plantar tension spring, were used to measure pressure and tension. Reproducible values were determined and, with the optimal conﬁguration, shifting within the osteotomy was minimal. In the experimental conﬁguration, optimal tibial screw placement was 70 mm proximal to the rotation axis of the upper ankle joint, and optimal placement of the Steinmann nail was in the posterior surface of the calcaneus. These ﬁndings indicated that the hinged ﬁxator allows 20° of ankle movement without alteration of the rotation axis, and suggest that this type of external ﬁxator can be used in all types of calcaneal fracture regardless of the soft tissue damage. ACFAS Level of Clinical Evidence: 5c. ( The Journal of Foot & Ankle Surgery 47(1):26 –33, 2008) Key Words: biomechanical experiment, calcaneus, external ﬁxation, hinged external ﬁxator, model fracture, open fracture C omplex intra-articular open calcaneal fractures with se- vere soft tissue damage and can be difﬁcult injuries to manage (1, 2). Superﬁcial and deep infections occur at a rate of 10% to 15% when open osteosynthesis methods are used to treat these fractures (3–7). Critical judgment of the op- erative intervention is an essential part of reﬁning the treat- ment of these injuries. Despite standardized procedures that entail immediate administration of intravenous antibiotics, radical debridement of heavily contaminated and necrotic tissues, and prompt plastic soft tissue coverage, there is still a high risk of developing superﬁcial and/or deep infection with resultant osteitis, osteomyelitis, and the need for am- putation (8). Distraction, reduction, and stabilization of complex calcaneus fractures can be achieved with the ap- plication of a rigid external ﬁxator (9). Application of a rigid external ﬁxator prohibits ankle motion, although numerous studies support the advantages of immediate motion therapy following a calcaneus fracture (10 –21). Since 1993, mem- bers of the Department of Traumatology, University Med- ical Center Schleswig-Holstein, Kiel, Germany, have, there- fore, used hinged external ﬁxators for the deﬁnitive Address correspondence to: Lutz Besch, MD, Department of Trauma- tology, University Medical Center Schleswig-Holstein, Kiel, Arnold-Heller-Strae 7, 24105 Kiel, Germany. E-mail: lutz.besch@ uksh-kiel.de; lutz.besch@web.de 1 Consultant Surgeons, Department of Traumatology, University Medi- cal Center Schleswig-Holstein, Kiel, Germany. 2 Resident, Department of Traumatology, University Medical Center Schleswig-Holstein, Kiel, Germany. 3 Director, Department of Traumatology, University Medical Center Schleswig-Holstein, Kiel, Germany. Copyright © 2008 by the American College of Foot and Ankle Surgeons 1067-2516/08/4701-0006$34.00/0 doi:10.1053/j.jfas.2007.10.014 26 THE JOURNAL OF FOOT & ANKLE SURGERY