High-pressure injection injury of the hand: Clinical usefulness of ultrasound as an early diagnostic tool

High-pressure injection injuries of the hand are uncommon accidents with potentially catastrophic complications. We present a case of a 49-years-old male with a high-pressure injection of motor oil in his left hand. Ultrasound accurately demonstrated soft tissue infiltration and late complications, playing a fundamental role in the treatment choice. A 49-year-old male presented to the emergency department reporting a high-pressure injection injury of cold motor oil in the volar aspect of his left hand. The patient complained of mild pain at the level of the injected area without decreased sensation in the hand or neurological symptoms. At the clinical examination the thenar eminence appeared diffusely swollen and edematous with a pinpoint-sized entry wound. The hand range of motion was intact, and there were no signs of neuro-vascular complications. A plain left-hand X-ray showed a pronounced soft-tissue swelling between the first and second metacarpal bones (Figure 1). Antibiotic therapy was prescribed, and the patient was discharged and referred to ultrasound (US) evaluation 4 days later. US examination demonstrated increased echogenicity and thickness of the subcutaneous tissue over the thenar eminence, without any distinct fluid collection (Figure 2). Therefore, the patient was treated conservatively. Given the persistence of the hand swelling and local pain, an MRI of the left hand was performed 40 days after the injury and confirmed infiltration of the subcutaneous fat around the injection site without drainable collections. At the MRI follow-up, 5 months after the injury, more diffuse infiltration of the subcutaneous tissue of the radial side of the hand was noted (Figure 2). Moreover, diffuse thickening of the subcutaneous tissue of the thumb abutted the flexor pollicis longus tendon along the proximal phalanx, keeping with the progressive impaired flexion of the thumb complained by the patient (Figure 3). At the concomitant dynamic US examination, relevant hypomobility of the flexor pollicis longus tendon due to the impingement exerted by the overlying infiltrated subcutaneous fat was present (Figure 3 and Video 1). Both US and MRI demonstrated the integrity of the neurovascular bundles of the thumb (Figure 3). Since no fluid collections have formed, the patient continued his rehabilitative treatment without indications to surgery. The outcome of high-pressure injection injuries is variable, depending on several factors, the most important of which are the injected material, its pressure, and its location.1 Plain radiographs are routinely required in the acute setting to rule out the presence of foreign bodies, and to assess the distribution of the injected material if radio-opaque.2 On the contrary, CT or MRI is employed rarely, usually to assess complications in the subacute phase.3 In this context, US has no clearly defined role in the diagnostic work-up, partly due to the absence of data in the literature. As demonstrated by our case, US could be an effective tool in the early assessment of high-pressure injection injury of the hand helping to define promptly the neurovascular status, the amount of the injected material, and its distribution, thus influencing the treatment planning. Indeed, US can demonstrate fluid infiltration within the stromal matrix of the subcutaneous fat, resulting in increased echogenicity and thickness of the subcutaneous tissue, even in the absence of true fluid collection.4 Furthermore, dynamic US well depicts complications such as adhesions between tendons and adjacent infiltrated soft tissues. MRI may be of benefit to study osseous injury and to further characterize soft-tissue complications. Overall, the combined use of MRI and US can help to detect early and late complications, playing a central role in the treatment choice. The authors declare no conflicts of interest. Open Access Funding provided by Universita degli Studi di Genova within the CRUI-CARE Agreement. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Video S1. Longitudinal 14–2 MHz dynamic US examination over the proximal phalanx of the thumb demonstrates impingement of the flexor pollicis longus tendon under the infiltrated subcutaneous tissue. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.