Preoperative Planning for the Foot and Ankle: A Technique Tip

CATEGORY: Other; Ankle; Midfoot/Forefoot INTRODUCTION/PURPOSE: Computed tomography (CT) advanced imaging techniques are a valuable tool for orthopedic surgeons when evaluating complex foot and ankle pathology. With advances in CT data processing, surgeons can create custom reformation of the imaging data in real time using postprocessing imaging tools. This article presents a technique describing how to manipulate CT data using two of these tools, multiplanar reformation (MPR) and maximal intensity projection (MIP), to better visualize pathology and allow a more definitive diagnosis preoperatively. Despite their availability on most modern picture archiving and communication systems, most surgeons across orthopaedics disciplines fail to utilize these powerful tools. METHODS: Patients with complex midfoot deformities underwent CT scans for diagnosis and preoperative planning. Case 1 underwent percutaneous pinning of multiple metatarsal fractures. Post-operatively she had severe pain localized to the second and third metatarsals. A CT scan obtained in standard axes failed to interpret the multiplanar deformities when viewed initially on PACS. Using MPR/MIP, the axes were rotated to generate a detailed view of the deformities and subsequently template osteotomies. Case two underwent arthrodesis of the second and third tarsometatarsal (TMT) joints for an unstable Lisfranc injury. Post-operatively she presented with severe midfoot pain prohibiting her return to athletics. Radiographs demonstrated normal alignment with hardware obscuring the joints. Standard CT axes were difficult to interpret due to metal artifact and oblique planes of the TMT joints. MPR/MIP reformatting allowed metal artifact reduction through axes adjustment, improving visualization and facilitating diagnosis of nonunion of the second and third TMT fusions. RESULTS: Case One:MIP/MPR allowed manipulation of the CT scan in the axial and coronal planes provided a sagittal reformat of the entire second and third metatarsals. The second metatarsal had a gradual plantarflexion malunion of the diaphysis. The third metatarsal had an acute plantarflexed deformity of the metatarsal neck. Reformatting provided an accurate preoperative template for planned dorsiflexion osteotomies. Case Two: Metal artifact and the oblique orientation of the TMT joints prevented evaluation of previous fusions. MIP/MPR reformatting provided axes which were perpendicular to the TMT joints decreased metal artifact and demonstrated nonunion of the previous fusions. Use of MIP/MPR in this case provided valuable diagnostic information regarding the source of pain and a plan for removal of hardware and revision TMT fusions. CONCLUSION: The MPR/MIP function is available in most PACS systems and allows customizable CT reformats. The technique is easy to learn and can be done quickly in the office or pre-operative setting. The technology has facilitated streamlined pre- operative planning and improvements in injury visualization numerous times, particularly in complex deformities and trauma. Using MIP/MPR reformats, the authors have been able to identify critical fracture lines and relationships between anatomic structures which may otherwise have been missed or less precisely understood. The authors hope that this article will enhance awareness and encourage others to utilize this powerful technology.