Inter-Rater and Intra-Rater Reliability of the Lawrence and Botte Classification System of Fifth Metatarsal Base Fractures

Abstract

Category: Trauma; Midfoot/Forefoot Introduction/Purpose: Fractures of the proximal fifth metatarsal are common injuries with a unique history. Treatment of these fractures is controversial, in part due to confusion regarding the nomenclature of the fracture subtypes. The most commonly utilized classification system is the Lawrence and Botte classification, which separates fractures into zones 1, 2, and 3 based on their relationship to the tuberosity and the 4th-5th intermetatarsal articulation. The purpose of this study was to evaluate the inter-rater and intra-rater reliability of the Lawrence and Botte classification of fifth metatarsal base fractures. Methods: Thirty sets of x-rays representing an equal number of zone 1, zone 2 and zone 3 fractures of varying chronicity were sent to eleven fellowship trained orthopedic foot and ankle surgeons. Surgeons were asked to classify each fracture according to the Lawrence and Botte classification system (round 1). No review of the classification system or visual aids were provided. Two weeks later, the same set of x-rays were reordered and renumbered in a random fashion. The surgeons then re-classified each fracture in a blinded fashion under the same conditions (round 2). Inter-rater and intra-rater reliability was summarized using the kappa statistic. To determine the source of variability between the zones, additional analyses were performed to determine the kappa statistic for a) combined zone 1 and 2 fractures versus zone 3 fractures and b) combined zone 2 and 3 fractures versus zone 1 fractures. Results: The Lawrence and Botte classification demonstrated substantial overall inter-rater agreement for both rounds 1 and 2 (kappa = 0.66 and 0.65, respectively). Zone 1 fractures demonstrated the highest inter-rater reliability (kappa = 0.83 and 0.83). There was moderate agreement for zone 2 fractures (kappa = 0.51 and 0.50). There was substantial agreement for zone 3 fractures (kappa = 0.64 and 0.65). Dichotomous evaluation of the zone 1 vs. combined zones 2-3 boundary yielded excellent agreement (kappa = 0.83, 0.83). The combined zones 1-2 vs. zone 3 boundary yielded a much lower agreement (kappa = 0.66, 0.65). Intra-rater reliability varied by individual, with kappa values ranging from 0.60 to 0.90, corresponding to modest to almost perfect agreement. Conclusion: The Lawrence and Botte classification system has overall substantial inter-rater and intra-rater reliability, but assessment of the interface between zone 2 and zone 3 fractures is much less reliable than that between zone 1 and zone 2. Previous studies of isolated zone 1 fractures most likely contain a homogenous fracture cohort, while studies of zone 2 or zone 3 fractures are likely to include a mixture of fracture types. Future studies may utilize supplemental imaging or modify the classification to best determine treatment of these more distal fractures.