Teaching Case

A 26-year-old female patient presented at the Emergency Department of our institution with complaints of severe pain on the dorsal face of the wrist due to a fall while performing Crossfit. On observation, there was significant oedema and haematoma. A wrist radiograph and, two weeks later, a wrist MR were performed for further clarification.

The wrist radiograph revealed correct alignment of bone structures, with no evidence of fracture lines (Fig. 1). Considering the persistent oedema and haematoma on the dorsal aspect of the wrist, an MR was performed and revealed a horizontal, non-displaced fracture line of the distal radius with significant bone marrow oedema, especially on its dorsal surface near Lister’s tubercle (Fig. 2a, b). Additionally, there was soft tissue swelling and distension of the synovial sheath of the tendon of the Extensor Pollicis Longus (EPL) with T1-hyperintense content, compatible with blood (Fig. 3), without evidence of tendon rupture. Distally, at the crossing with the extensor carpi radialis longus and brevis (ECRL; ECRB), there was exuberant distension of the sheath of the second compartment that was filled with similar content (Fig. 4). The extensor retinaculum was intact (Fig. 4).

The second extensor compartment is composed of ECRB and ECRL, and lies between the first compartment and Lister’s tubercle. The second and third compartment tendon sheaths communicate through a foramen and, for that reason, tenosynovitis can affect both, as it occurred on our case. The third compartment, composed solely of the EPL, should be recognised as being particularly prone to lesions due to its superficial location [2]. EPL tendon rupture is a well-known complication in fractures without misalignment of the distal radius [1]. In these fractures, the extensor retinaculum is usually intact [3], which is in line with the case we present. The mechanism of injury occurs when fluid and blood accumulate and cause irritation in the third extensor compartment [4]. This accumulation results in an increase in pressure and friction over the bone, leading to a possible delayed rupture of the tendon of the EPL that usually occurs between 3 weeks to 3 months after the traumatic event [1, 4]. This does not usually occur on displaced radial fractures since the retinaculum is ruptured and, for this reason, intracompartment pressure does not rise significantly. The MR was performed 13 days after the initial injury. This fact explains, at least in part, why the tendon is intact. The timely recognition of this type of lesions is of a higher degree of importance since this tendon, in the region of Lister's tubercle, has very poor vascularisation, known as a critical zone [5]. In the context of high intracompartmental pressure, this critical zone is even at a higher risk, leading to an increased potential for rupture or necrosis [1]. Treatment in this case should be focused on decompression of the sheaths, thus avoiding a possible delayed tendon rupture.

As far as the authors know, this is one of the few cases that clearly depicts the presence of acute haemorrhage in the wrist extensor tendon sheaths on MR. This may be because there are not many cases that go through an MR in such an acute setting. 

The key to a correct diagnosis and thoughtful clinical guidance, in this case, should focus on three aspects:

1. Knowledge of the injury mechanism and non-displaced radial fracture possible complications

2. Anatomical specificities of the second or third extensor compartment

3. Observing the distension of the synovial sheaths with hyperintense content on T1-weighted images, corresponding to haemorrhage, very rarely documented on MR.

Written informed patient consent for publication has been obtained.