Imaging of snapping phenomena

Abstract

Snapping phenomena result from the sudden impingement between anatomical and/or heterotopical structures with subsequent abrupt movement and noise. Snaps are variously perceived by patients, from mild discomfort to significant pain requiring surgical management. Identifying the precise cause of snaps may be challenging when no abnormality is encountered on routinely performed static examinations. In this regard, dynamic imaging techniques have been developed over time, with various degrees of success. This review encompasses the main features of each imaging technique and proposes an overview of the main snapping phenomena in the musculoskeletal system.

Figure 1

28-year-old female with annoying snaps of the right lateral hip when working (as a waitress). (a) The patient lies on the left side in order to expose the area of the right trochanter. Dynamic sonography is performed by firmly applying the probe in the axial plane while the patient is asked to flex and extend the hip, thus reproducing the snaps. (b) Axial sonographic view of the greater trochanter area. While the hip returns from a flexed position, the musculotendinous junction between the gluteus maximus and the iliotibial tract (arrowhead) is shown to glide posteriorly (direction of the arrow) along the greater trochanter (asterisks). (c) Axial sonographic view of the greater trochanter area. When the hip almost reaches full extension, the musculotendinous junction between the gluteus maximus and the iliotibial tract suddenly rubs posteriorly along the greater trochanter in a jerky movement, while the patient recognises the typical snap she suffers from in daily life.

Figure 2

43-year-old male with lateral knee pain and recurrent snaps when flexing the knee. (a) Proton density coronal MRI image with fat saturation of the right knee, showing a vertical tear of the body of the lateral meniscus (arrow). (b) Coronal view of a dynamic sonography performed along the lateral femorotibial joint. In early flexion of the knee, the external wall of the lateral meniscus (arrowheads) remains within the articular space. A vertical tear of the meniscal body is visible (arrow). (c) Coronal view of a dynamic sonography performed along the lateral femorotibial joint. During further flexion of the knee, the external wall of the lateral meniscus (arrowheads) suddenly pops out of the articular space. F, femur; T, tibia.

Figure 3

27-year-old male with intrasheath-type snapping peroneal tendons. (a) Axial view on T₂ weighted image with fat saturation sequence of the right ankle, showing mild tenosynovitis of the peroneal tendons (arrow). (b) Axial view of a dynamic ultrasound examination performed along the lateral retromalleolar groove, showing peroneus brevis tendon against the bone and covered by the peroneus longus tendon. (c) Axial view of a dynamic ultrasound examination performed along the lateral retromalleolar groove. During forceful eversion of the ankle, sudden clockwise rotational movement (arrows on Figure 1b) of both tendons lead the peroneus longus tendon to snap against the malleolar bone. b, peroneus brevis; l, peroneus longus.

Figure 4

36-year-old male with a medial elbow snapping and associated ulnar neuropathy. (a) Axial view of a dynamic ultrasound examination performed along the ulnar tunnel. During early flexion of the elbow, the ulnar nerve (asterisk) moves forward but remains between the posterior aspect of the medial epicondyle and the triceps muscle. (b) Axial view of a dynamic sonography performed along the ulnar tunnel. During flexion of the elbow above 45°, the tendon suddenly dislocates anteriorly above the tip of the medial epicondyle while the triceps muscles glides forward. ME, medial epicondyle; Tr, triceps muscle.

Figure 5

53-year-old female with a snapping extensor carpi ulnaris (ECU). (a) Axial view of a dynamic ultrasound examination performed along the ulnar groove. At rest, the ECU tendon is in position on the radial aspect of the ulnar wall of the groove (asterisk). (b) Axial view of a dynamic sonography performed along the ulnar groove. During supination, the tendon dislocates volarly (arrow) over the ulnar wall of the groove (asterisk), thus producing a typical snap that is recognised by the patient.