SLR - November 2016 - Catlea M. Gorman
Radiographic Anatomy of the Pediatric Lisfranc Joint
Reference: Knijnenberg LM, Dingemans SA, Terra MP, Struijs PA, Schep NW, Schepers T. Radiographic Anatomy of the Pediatric Lisfranc Joint. J Pediatr Orthop. 2016 Sep 3.
Scientific Literature Review
Reviewed By: Catlea M. Gorman, DPM
Residency Program: Regions Hospital/HealthPartners Institute for Education and Research, St. Paul, MN
Podiatric Relevance: Lisfranc injuries can be divided into high-impact and low-impact injuries. High-impact injuries are generally associated with high-energy trauma resulting in fracture-dislocations, while low-impact injuries are commonly associated with only ligamentous injuries. The majority of literature concerning Lisfranc injuries focuses on the adult population, where Lisfranc injuries are reported to be initially misdiagnosed 20 to 50 percent of the time. The mechanism of injury is similar among both the adult and pediatric populations. However, these injuries are often misdiagnosed in the pediatric population due to incomplete ossification, making the normal radiographic relationships used to assess for Lisfranc injury not applicable. On an adult anteroposterior (AP) radiograph, the average distance between the first and second metatarsal base is reported to be 1.3 mm. If the distance is 2 mm or greater, a diastasis is noted and a Lisfranc joint injury is suspected. The adult distance between the medial cuneiform and second metatarsal should be < 2mm. If the distance is greater, there is concern for injury to the Lisfranc ligament. The goal of this retrospective study was to establish normal radiographic values for the anatomy of the pediatric Lisfranc joint to further assist in the diagnosis of traumatic Lisfranc injuries.
Methods: Data was collected from the emergency department and outpatient clinic of a level-1 trauma center from August 2014 to February 2015. Only nonweightbearing radiographs were included in the study. Inclusion criteria consisted of patients under the age of 18 who were skeletally immature. These patients were included if they had a nonweightbearing foot AP radiograph taken that was read by a radiologist as negative for fracture, dislocation and anatomic abnormality. Exclusion criteria consisted of history of previous fracture or underlying anatomic abnormality like brachymetatarsia or clubfoot. In addition, the patient was excluded if there was suspicion for Lisfranc injury. For example, localized pain over the first and second metatarsal bases, persistent pain and/or the inability to bear weight at the one-week clinic follow-up appointment.
The caliper tool under magnification on the Picture Archiving and Communication System (PACS) was used by an emergency medicine resident, an orthopaedic trauma surgeon and a radiologist to measure the shortest distance between the base of the first and second metatarsal (MT1-MT2) and the shortest distance between the medial cuneiform and the base of the second metatarsal (MC-MT2). Measurements were noted to be precise to 0.1 mm. The intraobserver and interobserver variability were calculated using the intraclass correlation (ICC). Greater ICC values are indicative of greater intraobserver and interobserver agreement. An ICC of 0.6 to 0.74 indicates good agreement and an ICC of > 0.75 indicates excellent agreement.
Results: A total of 243 out of the 352 patients screened met the inclusion criteria. Patients were found in each age group from zero to 17 years of age. Of note, the MC-MT2 distance was not measured for newborns since the MC is not yet ossified. The MT1-MT2 distance was noted to be below 3 mm in all the patients despite the age. The MC-MT2 distance ranged between 7.5 to 3.1 mm and varied by age with the values reaching adult measurements (< 2mm) after the age of six. Both measurements approached adult values at the age of six. Two of the ICC values for the interobserver variability were in the 0.6 to 0.74 range, indicating good agreement. The rest of the ICC values for interobserver and intraobserver variability were > 0.75, indicating excellent agreement among the observers’ radiographic measurements.
Conclusions: This study provided normal pediatric values for the distance between MT1-MT2 and MC-MT2 on a nonweightbearing radiograph. The authors found that pediatric measurements approach adult measurements at the age of six, concluding that a Lisfranc injury could be present if the measurements are greater than the distances found in the study, especially in children under six years of age. Given how rare and how often misdiagnosed these injuries are, this study provides a baseline for radiographic measurements that could be useful in initial diagnosis of traumatic Lisfranc injuries. The main limitation of the study was that the radiographs were all nonweightbearing. The authors mentioned that in their emergency department and outpatient clinic, nonweightbearing radiographs are the standard for foot trauma, making these findings only applicable when assessing nonweightbearing radiographs. A future study involving weightbearing radiographs would be helpful since weightbearing radiographs are preferred when evaluating for Lisfranc injury.