Novel Radiographic Indexes for Elbow Stability Assessment: Part A-Cadaveric Validation

Abstract

Introduction: Elbow bony stability relies primarily on the high anatomic congruency between the humeral trochlea and the ulnar greater sigmoid notch. No practical tools are available to distinguish different morphotypes of the proximal ulna and herewith predict elbow stability. The aim of this study was to assess inter-observer reproducibility, evaluate diagnostic performance and determine responsiveness to change after simulated coronoid process fracture for three novel elbow radiographic indexes.

Methods: Ten fresh-frozen cadaver specimens of upper limbs from human donors were available for this study. Three primary indexes were defined, as well as two derived angles: Trochlear Depth Index (TDI); Posterior Coverage Index (PCI); Anterior Coverage Index (ACI); radiographic coverage angle (RCA); olecranon-diaphisary angle (ODA). Each index was first measured on standardized lateral radiographs and subsequently by direct measurement after open dissection. Finally, a type II coronoid fracture (Regan and Morrey classification) was created on each specimen and both radiographic and open measurements were repeated. All measurements were conducted by two orthopaedic surgeons and two dedicated musculoskeletal radiologists.

Results: All three indexes showed good or moderate inter-observer reliability and moderate accuracy and precision when compared to the gold standard (open measurement). A significant change between the radiographic TDI and ACI before and after simulated coronoid fracture was observed [TDI: decrease from 0.45 ± 0.03 to 0.39 ± 0.08 (p = 0.035); ACI: decrease from 1.90 ± 0.17 to 1.58 ± 0.21 (p = 0.001)]. As expected, no significant changes were documented for the PCI. Based on these data, a predictive model was generated, able to identify coronoid fractures with a sensitivity of 80% and a specificity of 100%.

Conclusion: New, simple and easily reproducible radiological indexes to describe the congruency of the greater sigmoid notch have been proposed. TDI and ACI change significantly after a simulated coronoid fracture, indicating a good responsiveness of these parameters to a pathological condition. Furthermore, combining TDI and ACI in a regression model equation allowed to identify simulated fractures with high sensitivity and specificity. The newly proposed indexes are, therefore, promising tools to improve diagnostic accuracy of coronoid fractures and show potential to enhance perioperative diagnostic also in cases of elbow instability and stiffness.

Level of evidence: Basic science study.

Clinical relevance: The newly proposed indexes are promising tools to improve diagnostic accuracy of coronoid fractures as well as to enhance perioperative diagnostic for elbow instability and stiffness.

Keywords: Cadaveric study; Elbow joint; Olecranon; Radiographic study; Ulna.

Fig. 1

Digital elbow radiographs in lateral projection of the same elbow, depicted in its native state (a) and after simulated coronoid fracture (b). The Trochlear Depth Index (TDI) is the ratio between the distance from the olecranon to the coronoid tip (AC) and the distance between this line and the deepest point of the trochlea (TDI = BD/AC). Box plots (c) illustrating the comparison between the radiographic and open TDI in native elbows and after coronoid osteotomy (*p value < 0.05). Data represent minimum, maximum (box) and mean (line). RX Radiographic

Fig. 2

Digital elbow radiographs in lateral projection of the same elbow, depicted in its native state (a) and after simulated coronoid fracture (b). The Anterior Coverage Index (ACI) is the ratio between HC and H (ACI = HC/H); the Posterior Coverage Index (PCI) is the ratio between HA and H (PCI = HA/H). Box plots (c) illustrating the comparison between radiographic and open ACI in native and fractured elbows (**p value < 0.01). Data represent minimum, maximum (box) and mean (line). RX radiographic

Fig. 3

Open measurements; (a) olecranon–coronoid tip distance; (b) olecranon height

Fig. 4

Box-and-whiskers plots illustrating the comparison between the accuracy observed for the subgroups of orthopaedic surgeons and musculoskeletal radiologists for the three indices (*p value < 0.05). The solid line indicates the perfect accuracy (difference = 0 with respect to the real value)