Diagnostics of Scaphoid Fractures With HRpQCT

Overview

The scaphoid bone is the most common fractured carpal bone. Scaphoid fractures represent 2-6% of all fractures and occur mainly in young, active patients aged 15 to 40. The scaphoid bone has an essential role in functionality of the wrist, acting as a pivot. Correct treatment of a scaphoid fracture depends on accurate and timely diagnosis, and inadequate treatment can result in avascular necrosis (up to 40%), nonunion (5-21%) and early osteoarthritis (up to 32%) that may seriously impair wrist function. In addition, impaired consolidation of scaphoid fractures results in longer immobilization leading to significant functional and psychosocial impairment thus having considerable socio-economic consequences and negative impact on the quality of life. Current diagnostic pathways can take up to two weeks to diagnose (or exclude) a scaphoid fracture, leading to overtreatment in patients with a suspected scaphoid fracture since only 15 to 30% of suspected scaphoid fractures in the Netherlands annually is found to be an actual fracture. Thus, there is significant room for improvement in the diagnostic pathway of scaphoid fractures.

Scaphoid fractures The scaphoid bone is the most frequently occurring fracture of the carpal bones. Scaphoid fractures represent 2-6% of all fractures and 90% of all carpal fractures in the Netherlands. Scaphoid fractures typically occur in young, active patients aged 15 to 40 years old. The exact incidence is unknown, but approximately 21,000 scaphoid fractures are suspected in the Netherlands each year. However, only 15 to 30% represent real fractures. Because a significant amount of fractures (up to 65% immediately after injury) remain radiographically occult with conventional radiographic imaging, there is a trend of overtreatment of suspected scaphoid fractures, which means a lot of wrists are immobilized unnecessary. A scaphoid fracture has potentially far reaching consequences for the patient, considering the unique nature of this bone in the human body, as it articulates with five surrounding bones in the wrist. Because of this, it has an essential role in functionality of the wrist, acting as a pivot. The treatment of scaphoid fractures is found to be a challenge. Failure can result in avascular necrosis (up to 40%), nonunion (up to 21%) of the fracture and subsequently early osteoarthritis (up to 32%). Displaced fractures of the scaphoid bone can lead to an even higher rate of complications. The results of surgical treatment are variable13 and surgery is often initiated in a late phase of the treatment. Both complicated fracture healing and surgical treatment in a late phase of the treatment have severe socio-economical consequences. Diagnosis and follow up of scaphoid fractures The accurate diagnosis of a scaphoid fracture is the first step of successful treatment of this injury. Delay in treatment has been shown to negatively affect outcome, with adequate treatment of a scaphoid fracture increasing union rates from 55% to 90-100%. However, this knowledge supports the overtreatment-tendency in patients suspected of having a scaphoid fracture at the emergency department. It is estimated that only 15-30% of these patients actually have a scaphoid fracture, 1,3-5 resulting in a substantial number of patients wearing a cast for a limited period of time when they do not need it. As studies have shown, the clinical evaluation directly after trauma is not capable of reliably proving or excluding a scaphoid fracture. Current clinical practice in the Netherlands consists of conventional X-ray, followed by CT one week later when the initial radiographs are negative, but repeated clinical examination does not exclude scaphoid injury. Other imaging modalities such as MRI or bone scintigraphy are also being used. CT scan gives more useful information about the anatomy of a possible fracture and is more easily available in the Dutch situation than MRI and bone scintigraphy. Aside from the diagnostic delay it is difficult to objectify fracture healing with x-ray, CT scan, MRI or bone scintigraphy. Therefore, there is room for improvement of the arsenal to accurately and timely diagnose and classify scaphoid fractures and to evaluate scaphoid fracture healing. High resolution peripheral quantitative computed tomography The current clinical imaging techniques used in the diagnosis of scaphoid fractures as described above lack the resolving power needed for detailed cortical measurements and visualization of the trabecular morphology, for which a spatial resolution lower than 200 µm is needed. The development of high resolution CT scanners with a spatial resolution of 150 to 95 µm enables these measurements, specifically for the extremities. These so-called high-resolution peripheral quantitative CT (HR-pQCT) scanners are smaller and less expensive than current clinical whole body CT scanners. A specific HR-pQCT scanner to visualize and assess trabecular structure of peripheral bones in a clinical (trial) setting is the XtremeCT platform (Scanco Medical AG, Switserland). The most recent iteration of this scanner, the XtremeCT-2, has a voxel size of 61 µm and a spatial resolution of 95 µm, which enables the direct assessment of bone micro-architectural parameters. In addition, after digitalization of the trabecular structure a so called virtual bone biopsy is available, which enables the estimation of bone strength parameters by micro-finite element analysis (µFEA). Validation and reproducibility studies of both the HR-pQCT scanner as well as µFEA have been performed, and in the last decade widespread experience has been gathered concerning the use of these techniques in (clinical) research.