O1080: Radiographically Defining Skewfoot Deformity in Pediatric Patients: A Reliability Study

Background: Skewfoot deformity is clinically defined as a combination of forefoot adduction with hindfoot valgus giving the bones of the foot a “Z” pattern that is variably associated with Achilles tendon shortening. Important to developing a strategy for the management of this unique foot condition is appropriately defining the deformity radiographically; however, previous studies of radiographic measures have had poor intra-observer reliability. The purpose of this investigation is to develop and assess the reliability of three novel radiographic measurements on weight-bearing anteroposterior (AP) and lateral X-ray views of the foot. These new measurements include, 1) the Naviculo-1st Metatarsal Angle, 2) the Calcaneal-1st Metatarsal Angle on the AP view, and 3) The Dorsal Subluxation Angle of the Talo-Navicular Joint on the lateral view (Figure 1). We hypothesize that these measurements will show excellent intra- and inter-rater reliability.

Methods: A keyword search was conducted to identify skewfoot patients ages 3-17.99, treated at our tertiary care center between 1990 and 2020. “Normal” feet were identified from a patient group with healed metatarsal fractures. Radiographs were deidentified and raters were blind to patient diagnosis. All raters were board-certified, board-eligible orthopaedic surgeons, or nonoperative orthopaedic providers. The reliability of each measurement was evaluated by estimating the intraclass correlation coefficient (ICC) and 95% confidence interval (CI). Intrarater reliability was assessed using an ICC (3, 1) model and interrater reliability was assessed using an ICC (2, 2) model. Interpretations for reliability estimates were based on the criteria of Fleiss and Ciccheti and Sparrow: < 0.40, poor; 0.40-0.59, fair; 0.60-0.74, good; and >0.74, excellent.

Results: Five independent raters reviewed radiographs of 30 patients (16 normal; 14 skew foot). The average age of the cohort was 11.7 years (SD, 3.6), and 43% female. Across all five raters’ measurements (N=150), the mean Naviculo-1st Metatarsal Angle was 19 degrees (SD, 16.0 and range, -14 to 54), the mean Calcaneal-1st Metatarsal Angle was 23 degrees (SD, 13.9 and range, -11 to 56), and the mean The Dorsal Subluxation Angle of the Talo-Navicular Joint was 8 degrees (SD, 11.9 and range, -26 to 40). One rater read the radiographs of an additional 10 patients at two separate time points for intrarater reliability assessment. Intrarater reliability was excellent for all three radiographic measurements with all ICC>0.90. Similarly, interrater reliability across five raters was excellent with all ICC>0.90 (Table 1).

Conclusion: All three novel radiographic measurements had excellent reliability. This demonstrates that these newly defined measurements may be useful for distinguishing a skewfoot from a normal foot, pes planus, and metatarsus adductus. Future study is necessary to establish the clinical utility of these measures for prognosis and in guiding treatment.