Radiographic Measurement of Distal Metatarsal Articular Angle Does Not Correlate with In-Vivo Deformity for Juvenile Bunion Deformity

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Correction of juvenile bunion deformities has historically been fraught with high recurrence rates leading to dissatisfaction among patients and surgeons alike. It is now recognized that these historically poor results have likely been due to a failure to correct the elevated distal articular metatarsal angle (DMAA) encountered in the vast majority of juvenile bunions. Though preoperative planning for deformity correction hinges on plain radiographic measurement of the DMAA, accuracy of this measurement in the juvenile population has not been studied. The purpose of this study is to compare plain radiographic measurements of the DMAA to in-vivo DMAA measurement. Methods: This is an IRB-approved retrospective r¬eview of prospectively enrolled patients over a 4-year period at single pediatric institution who underwent a scarf osteotomy for management of a juvenile bunion deformity. Children with neurologic disorders, autoimmune disease, congenital foot or extremity deformities, or history of prior ankle or foot surgery were excluded. Pre-operative DMAA was measured on standardized weight-bearing foot radiographs. In-vivo DMAA goniometric measurement was made at the time of surgery following capsulotomy and direct visualization of the articular surface of the metatarsal head. A Pearson’s correlation coefficient was calculated to assess the relationship between radiographic and in-vivo measurements. Results: 19 feet in 20 patients with an average age at surgery of 15.9 years (range 13.1 -17.9 years) met inclusion criteria. Radiographic DMMA averaged 25.2o (range 7o - 32o) and intra-operative DMAA averaged 18.1o (range 5o - 69o). Pearson correlation coefficient revealed no correlation between radiographic and in-vivo DMAA measurements (r=0.186, p=0.45). Repeat analysis after removing three outliers with very high in-vivo DMAA measurements (greater than 40o) also showed no correlation between radiographic and anatomic DMAA measurements (r=0.051, p=0.85). As the in-vivo DMAA increased, radiographic measurements were more likely to underrepresent the true degree of deformity present (Figure 1). Conclusion: Plain radiographic DMAA measurements do not correlate to actual articular deformity in children with juvenile bunions. Moreover, as the degree of in-vivo DMAA increases, radiographic assessment is increasingly likely to underrepresent the extent of deformity correction required to achieve a normal DMAA intra-operatively. Surgeons should therefore not rely solely on plain radiography for preoperative planning or to assess adequacy of surgical correction of the juvenile bunion deformity. This is of particular importance for those performing minimally invasive bunion surgery as neither the amount of desired correction nor the surgical correction achieved can be reliably determined using plain radiography alone.