A new acute scaphoid fracture assessment method: a reliability study of the ‘long axis’ measurement

Scaphoid fractures represent around 2–3% of all fractures and around 10% of all fractures in the hand, while the younger population is more typically affected although fractures do occur in the elderly [1]. Fractures of the mid-portion of the scaphoid, the so-called ‘waist’, are the most common [1]. The existing evidence suggests that the risk non-union is considerably higher for more proximal fractures [2]. Despite large numbers of publications on outcomes of scaphoid fracture management there are large inconsistencies in the published data. Combining these data groups is notoriously difficult for a number of reasons including variable demographics, inconsistent definitions of fracture type, and inconsistent methodology for defining outcome. There is particular interest in the behaviour of proximal pole fractures but no consensus on how this subgroup should be defined. This method could be used to give more reliable and reproducible descriptions of fracture type.

A number of classification systems have been described, with the most widely used being the Herbert, Russe and Mayo methods. However the reliability of these tools has been shown to be rather limited [3]. Despite the frequently-discussed distinction between proximal pole and waist fractures, there is no published reliable method of distinguishing between the two. The Mayo classification system divides the scaphoid into proximal, middle and distal third fractures, as well as distal tubercle and distal intra-articular fractures. Russe divided fractures into those with horizontal oblique, transverse or vertical oblique fracture lines [4]. The Herbert system divides acute fractures into either stable (Type A) and unstable (Type B), with various subdivisions with these types [5]. No study has described a method for determining precisely the location or the size of the proximal pole. For example the SWIFFT study protocol defines a proximal pole fracture as involving the ‘proximal fifth’ but does not describe how one can reliably determine when a fracture involves the proximal fifth [6]. This makes it difficult to compare studies and particularly difficult to perform meta-analysis on data from published cohorts. While the anatomical and radiological definition of proximal pole, waist and distal pole fractures is likely to remain contentious, looking at a more continuous measure of fracture site may give more clarity.

The primary aim of this study was to assess the reliability of acute scaphoid fracture assessment metrics including the new ‘long axis’ measurement. The secondary aims were to compare the reliability of this new method with three established classification systems, and to compare the reliability of each of these methods when using plain radiographs and CT. The null hypothesis was that there would be no difference in reliability between the older methods and the new ‘long axis’ measurement.

Using local surgical databases we retrospectively identified sixty patients with acute scaphoid fractures across two centres that had been investigated with both plain radiographs and a CT scan within 4 weeks of injury. We excluded non acute scaphoid fractures as well as those associated with acute carpal dislocation. All injuries were sustained from the beginning of 2013 to the end of 2016.

The patient demographics were recorded. Two senior surgical trainees and an experienced hand surgeon analysed the plain radiographs and CT scans in each centre. The observers were briefed on recent literature which describes the long axis passing from the proximal point through the centre of the waist to the most distal point, with the most distal point being very close to the centre of the tubercle just radial to its apex [7, 8].

The Classification according to Russe, Herbert and Mayo systems were recorded. In addition the observers recorded the long axis length of the scaphoid, the distance at which the fracture line crossed the long axis, distance at which the proximal fracture line crossed a line perpendicular to long axis on ulnar border, distance at which fracture line crossed a line perpendicular to long axis on radial border, presence of a sagittal plane deformity, presence of a coronal plane deformity, presence of significant fragmentation and the scapholunate angle. The presence of coronal/sagittal deformity or significant comminution was a subjective observer-based decision, i.e. the observer made a subjective decision as to whether any coronal or sagittal deformity and whether comminution was present in binary terms, no quantifiable metric was used.

The classification and characteristics were recorded separately at different times for both plain radiographs and CT scans. The long axis length of scaphoid was measured from the most proximal ulnar corner of the scaphoid to the centre of the scaphoid tubercle distally (distal point (dp)) (Figs. 1 and 2).

The radiographs were analysed pragmatically with the specific (long axis/radial/ulnar) measurements taken from what was deemed the best long axis view by each observer. The CT scans were analysed using InSight PACS (Insignia medical systems, UK) and the scaphoid orientated to obtain the best long axis view in the opinion of the observer for the specific measurements in this plane. The fracture position was measured using the mid-sagittal coronal image. One observer at each centre repeated the X-ray and CT based assessments six months later to test intra-observer reliability.

A simple ‘long axis’ measurement of the relative distance of the fracture site along the long axis of the scaphoid demonstrates a substantial level of inter observer reliability which is significantly better than other scaphoid classification systems. We found The Mayo to be the most reliable of among popular scaphoid classification systems with a moderate level of inter observer reliability. The new ‘long axis’ metric can be reliably measured on both X-ray and CT, while its other significant advantage over other classification systems is that it provides a way of quantifying fracture position with significant potential benefits for use in clinical research.

Our results are consistent with previous work in this area showing limited reliability of traditional methods [3, 12, 13]. Desai et al. demonstrated that the Russe and Herbert systems had fair levels of agreement, similar to the level of reliability shown in this study [12], while assessments of fracture level, comminution and displacement showed moderate inter- and intra-observer reproducibility [12]. Bhat et al. demonstrated that measures such as the intra-scaphoid angles (sagittal and coronal), the height-to-length ratio and the dorsal scaphoid cortical angle have poor reproducibility [13]. To our knowledge no system for quantifying how relatively proximal or distal an acute fracture has either been created or assessed for reliability, although a method with demonstrable reliability has previously been described relating to scaphoid non-unions [14]. We found that assessing the position of the fracture in relation to the long axis was reliable when measuring from plain radiographs and CT scans. While the use of CT scans is important when measuring union [6] they are not uniformly used in treatment planning initially and it is useful to have a valid measure of fracture position based on plain radiographs alone. This method can be used to allow analysis of a more continuous measure of fracture site and outcome, or alternatively as a tool to allocate fractures into categories such as ‘proximal 20%’ or ‘proximal third’. When publishing raw data for meta-analysis this method might allow research teams to remove and reassign category boundaries. It is also likely that with greater standardisation of methodology the data will become more reliable [10]. It is important to note that this study is one of reliability and not validity. It is not possible to state whether the new ‘long axis’ measurement is ‘better’ than any other method, this study has simply shown that it is more reliable. Certainly, future research is necessary to demonstrate that the ‘long axis’ measurement is of real clinical meaning, for example in predicting the likelihood of scaphoid fracture union.

This study describes a novel pragmatic ‘long axis’ method for the quantification of acute scaphoid fractures which demonstrates substantial inter and intra observer reliability. The ‘long axis’ method offers benefits over traditional classification in terms of reliability, allocation of fractures to anatomical subgroups, and contributing to future debate on the definition and implications of proximal pole injuries.