Sonographic Assessment of Hand Injuries: Diagnostic Accuracy and Review of Pathology

Abstract

Background: The high soft-tissue contrast of magnetic resonance imaging (MRI) makes it useful for evaluation of hand injuries, but its limitations include cost, imaging artifacts, and patient claustrophobia. Ultrasound is readily available, fast, noninvasive, and radiation free, but its utility for the evaluation of hand soft-tissue injury and pathology is less well known. Purpose: We sought to examine the accuracy of ultrasound for the evaluation of hand injury at a single institution. Methods: We queried a radiology information system for ultrasound cases between 2014 and 2020 at a tertiary care institution using the keyword “hand” and injury terms. We performed a retrospective chart review of cases found according to the type of injury detected on ultrasound. To evaluate the diagnostic accuracy of ultrasound in hand injury and pathology, we recorded postimaging clinical diagnoses and surgical findings. Results: We found 154 patients who underwent ultrasound for hand injuries and had confirmed surgical diagnosis and/or robust clinical follow-up. Tendon injury was the most commonly diagnosed condition on ultrasound (70/154); others detected were retained foreign body (31), mass (21), ligamentous injury (9), pulley injury (8), nerve injury (11), and traumatic arthropathy (4). Ultrasound correctly characterized hand injury in 150/154 cases (97.4%) based on surgical and/or clinical follow-up. Ultrasound failed to diagnose 3 cases of partial tendon tear and 1 case of digital nerve injury. Conclusion: In this retrospective, single-institution review, ultrasound was found to be highly accurate in the detection of soft tissue hand injury and pathology, demonstrating a high concordance rate with surgical and clinical findings. Further study is warranted.

Introduction

Soft tissue injuries of the hand may affect tendons, ligaments, and nerves and can be quite complex in nature. These injuries may result in significant disability and require prompt and accurate characterization to ensure effective treatment. Magnetic resonance imaging (MRI) has high soft-tissue contrast and is useful for evaluation of hand injuries [6]. However, limitations including cost, imaging artifacts, and patient claustrophobia may be prohibitive. In contrast, ultrasound is a readily available, fast, non-invasive, radiation-free modality that allows for correlation to findings on clinical examination and comparison with the contralateral side [1].

High-frequency ultrasound transducers can produce high-resolution imaging of small, superficial structures [1,14], which is ideal for use in hand injury. Knowledge of the sonographic appearance of pathologies affecting the hand is critical in postinjury assessment and presurgical planning. High resolution linear array transducers with a broad bandwidth should be used for evaluation of hand abnormalities as they can visualize tendons, ligaments, nerves, and joint capsules in exquisite detail [1]. Linear array transducers are preferred over curvilinear transducers as the transmitted beam is perpendicular to the transducer surface, resulting in less beam divergence and better visualization of superficial structures [1,14]. At our institution, we routinely use 15 to 22 MHz linear transducers for scanning the hand.

Scanning should be performed in at least 2 planes (transverse and longitudinal) for a thorough assessment of the regional structures [4]. Cine clips are useful in dynamic evaluation and in 3-dimensional assessment of pathology. On ultrasound, normal tendons appear as multiple closely packed linear reflections [1] (Fig. 1). Placing the ultrasound probe perpendicular to the tendon fibers may avoid anisotropy and thus prevent a misdiagnosis of tear or tendinosis [4]. Peripheral nerves on ultrasound have a honeycomb appearance composed of hypoechoic fascicles surrounded by echogenic perineurium and epineurium [12] (Fig. 2). Peripheral nerves in the hand are best evaluated in short axis, but longitudinal assessment can rule out subtle lacerations or measure the length of an abnormality affecting the nerve. Normal synovial sheaths of the tendon are usually not visible on ultrasound, but they become visible with fluid distension [12]. Color or power doppler imaging shows tissue vascularity and can aid lesion characterization and assessment of active inflammation.

Fig. 1.

Normal sonographic appearance of finger flexor tendons in (a) longitudinal and (b) transverse orientation. Photographs demonstrate ultrasound transducer (rectangle) position and orientation. FDS flexor digitorum superficialis, FDP flexor digitorum profundus, PIP proximal interphalangeal joint, DIP distal interphalangeal joint.

Fig. 2.

Normal sonographic appearance of the digital nerves in transverse orientation. Nerves show echogenic (bright) epineurium and hypoehoic (dark) internal fascicles. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the distal metacarpals. MC metacarpal bone.

This study aimed to review the range of pathology diagnosed at a single tertiary institution and assess the diagnostic accuracy of ultrasound for hand injury by assessing surgical findings and/or final clinical diagnosis. A pictorial review of representative cases is presented.

Methods

After Institution Review Board approval, we queried a radiology information system for ultrasound cases between 2014 and 2020 at a single, tertiary care institution, using the keywords “hand” and injury terms including “laceration,” “trauma,” “rupture,” and “foreign body.” A retrospective chart review was performed on the cases. The types of injury detected on ultrasound were recorded and categorized. To evaluate the diagnostic accuracy of ultrasound, surgical findings and final clinical diagnoses postimaging were recorded. Ultrasound diagnoses and surgical findings and/or final clinical diagnoses were compared for concordance.

Results

A total of 154 patients who underwent ultrasound for hand injuries had confirmed surgical diagnosis and/or robust clinical follow-up. Of the 154 patients, 91 (59%) patients were women and 63 (41%) were men. The average age was 44.8 years.

Types of injury detected on ultrasound were recorded and categorized (Fig. 3). Tendon injuries were the most common injury in our sample of patients (70/154; 45.4%). The extensor tendons were injured more frequently than the flexor tendons (52.5% vs 47.5%). Other injuries diagnosed on ultrasound include retained foreign body (31), mass (21), ligamentous injury (9), pulley injury (8), nerve injury (8), and traumatic arthropathy (4). Ultrasound characterized 3 hand cases as normal, confirmed after review of clinical follow-up. Pulley injuries were detected at the A2 (4) and A4 (4) pulleys. In our study, ligamentous injuries were detected at the metacarpophalangeal (MCP) joint, mainly at the thumb: 7 ulnar collateral ligament (UCL) (5 thumb) and 2 radial collateral ligament (RCL). A total of 11 cases of nerve injury were diagnosed, affecting the digital nerves. The most common foreign bodies identified on ultrasound were glass (15/31) and wooden splinters/thorns (9/31). The most commonly diagnosed masses included ganglion/retinacular cyst (7), vascular abnormality (5), adventitial bursitis (2), and suture granuloma (2). The vascular abnormalities were posttraumatic venous thrombosis, pseudoaneurysm, and hematoma.

Fig. 3.

Chart showing frequency of hand injury diagnoses on ultrasound.

Ultrasound correctly characterized hand injury in 150/154 cases, with a concordance rate of 97.4% based on surgical and/or clinical follow-up. Ultrasound failed to diagnose partial tendon tear in 3 cases (2 flexor, 1 extensor), and 1 digital nerve injury (radial nerve). The radial digital nerve laceration not identified on ultrasound was described as a partial thickness laceration intraoperatively.

Discussion

This retrospective review found that ultrasound was accurate in detecting soft-tissue hand injury and pathology, demonstrating a high concordance rate with surgical and clinical findings. Sonography does have its limitations in evaluating hand injury. As shown in the results of our retrospective review, partial thickness nerve and tendon injuries were more likely to be missed on ultrasound than full thickness injuries. While fractures can be detected using ultrasound, detailed characterizations such as intraarticular extension are better performed using X-ray and computed tomography. Outside of ganglion cysts, definitive characterization of masses can be difficult using sonography and MRI is often better suited to evaluate masses. The following conditions were detected.

Tendinopathy

Tendon injuries were the most common injury in our sample of patients (45.4%). Both partial and complete tears were diagnosed on ultrasound. Partial tear was diagnosed when there was incomplete radial-ulnar OR palmar-volar tendon fiber involvement [4]. These tears are more difficult to diagnose on ultrasound and may appear as linear hypoechoic clefts or defects which are often perpendicular to the long axis of the tendon fibers (Fig. 4). All 3 discordant tendon diagnoses in our cohort were partial tears. In a complete rupture, all of the tendon fibers are disrupted, although the degree of separation between the 2 torn ends is variable, depending on the position of the hand and how much tension the torn tendon is under [4] (Fig. 5). There may be associated hyperemia, hematoma, or tendon sheath effusion. In some cases, tendon injury is accompanied by an avulsion fracture (Fig. 5). Because many tendon tears must be surgically repaired, knowledge of the exact location of the tear, amount of retraction and site of retracted fibers is critical for surgical planning and can be accurately assessed on ultrasound.

Fig. 4.

A 51-year-old woman with laceration to the palm. Longitudinal ultrasound imaging shows a partial thickness laceration cleft (arrowheads) through the superficial fibers of the flexor digitorum superficialis (FDS) tendon, consistent with a partial tear. The cleft does not involve the entire tendon. The underlying flexor digitorum profundus (FDP) tendon is intact. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the palm.

Fig. 5.

A 61-year old woman with laceration at the wrist. Longitudinal ultrasound imaging shows a full thickness laceration of the extensor pollicis longus (EPL) tendon with the distal tendon stump at the base of the first metacarpal (arrowheads). Hypoechoic material in the tendon sheath (asterisks) is consistent with posttraumatic tenosynovitis. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the base of the thumb.

Pulley injuries

Pulley injuries are usually sustained from hyperflexion at the proximal interphalangeal joint [12]. These are common in rock climbers and usually affect the middle and ring fingers. The A2 pulley is the most common and typically the first pulley to rupture [12], and additional pulley injury may be concomitant. A normal pulley appears as a thin hypoechoic band of tissue superficial to the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendons in the fingers [12]. With pulley injuries, the thin hypoechoic bands are disrupted or thickened. With pulley rupture, there is resultant separation of the flexor tendons from bone (bowstringing) that is visible sonographically (Fig. 6). When acute, pulley injuries can be associated with soft tissue edema or tenosynovitis (Fig. 6). In more chronic stages of injury, edema may resolve but tendon bowstringing may still be apparent if the pulley rupture was not appropriately treated.

Fig. 6.

A 35-year-old man with middle finger rock climbing injury. Longitudinal ultrasound image of the middle finger (a) shows separation of the flexor tendons from the proximal phalanx, consistent with an A2 pulley rupture. Associated posttraumatic tendon sheath effusion (*) is at the middle finger. Comparative longitudinal ultrasound image of the normal right ring finger (b) demonstrates no separation of the flexor tendon from the proximal phalanx in the region of the A2 pulley. Photographs demonstrate ultrasound transducer (rectangle) position and orientation at the middle and ring fingers.

Ligament injuries

Traumatic ligament injuries have a similar appearance to tendon injuries. Ultrasound has been shown to be accurate in assessing the collateral ligaments, largely at the thumb MCP joint [12]. Thumb UCL injuries occur from traumatic hyperabduction at the thumb MCP joint. The UCL injuries can be sprains, partial thickness tears, or full thickness tears. Normal UCL has hyperechoic linear fibers that lie deep to the thin echogenic adductor aponeurosis [5]. Sprain will present as thickening of the UCL without frank fiber discontinuity. Tears are seen as discrete hypoechoic defects within a thickened UCL (Fig. 7). A Stener lesion results when the adductor aponeurosis becomes wedged between the torn UCL and proximal phalanx of the thumb, preventing proper reduction of the torn UCL [7]. In some cases, the UCL injury is associated with a small avulsion fracture (Fig. 8), also detectable by sonography.

Fig. 7.

A 61-year-old woman with thumb pain after a fall. Ultrasound of the ulnar aspect of the thumb metacarpophalangeal joint demonstrates a defect (*) in the ulnar collateral ligament (UCL) consistent with a tear. The intact overlying adductor aponeurosis (arrows) is demonstrated. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the thumb.

Fig. 8.

A 19-year-old man with thumb pain after a fall. Ultrasound of the ulnar aspect of the thumb metacarpophalangeal joint demonstrates the ulnar collateral ligament (UCL) attached to an avulsion fracture fragment off the base of the proximal phalanx (*). The intact overlying adductor aponeurosis (arrows) is clearly demonstrated. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the thumb.

Peripheral nerve injuries

Trauma to the nerves of the hand generally occurs with penetrating injuries. Peripheral nerves on ultrasound appear as hypoechoic fascicles surrounded by echogenic epineurium (Fig. 2) [12,10]. In laceration injuries, the epineurium and fascicles are disrupted due to partial or complete transection (Fig. 9). Neuromas may form at the ends of a chronically transected nerve, appearing as hypoechoic mass-like nodules [10,11] These neuromas make chronic, high-grade nerve transection injuries more conspicuous. Partial nerve transection injury, particularly in the acute setting, may be more difficult to detect in small digital nerves, as they are less likely to form neuromas. Surrounding soft tissue edema may also obscure low-grade nerve lesions after acute injury. In our cohort, the digital nerve lesion missed on ultrasound was a partial laceration injury presenting 1 day after injury. In some instances, disordered nerve healing may produce a neuroma-in-continuity, which appears as nodular, hypoechoic thickening along a continuous nerve [11].

Fig. 9.

A 35-year-old woman with laceration to base of fourth finger, numbness at the radial fourth finger and tingling at the ulnar third finger. Transverse ultrasound image at the fingers revealing laceration scar tract (arrow) through the radial digital nerve to the fourth finger at the distal palm/webspace. Ulnar digital nerve to the third finger is thickened but not involved by the laceration (arrowhead). The radial digital nerve to the third finger is normal (oval), for comparison. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the distal metacarpals.

Foreign body detection

Detection of radiolucent (radiographically occult) foreign bodies after penetrating injuries is one of the common indications for ultrasound in the extremities. Foreign bodies are hyperechoic on ultrasound with varying degrees of acoustic shadowing [8,9]. Sonography is superbly suited to identify foreign bodies in the extremities, as high-resolution imaging allows sensitive detection of foreign bodies in the subcutaneous tissue. Ultrasound can also identify related injury to or impingement on regional structures (Fig. 10), in preparation for safe removal. Preoperatively, the location of the body can by annotated on the skin surface before incision using ultrasound guidance, aiding efficient surgical exploration. Ultrasound-guided extraction of the foreign bodies can also be performed [3], and ultrasound can confirm complete fragment removal, as a residual fragment may lead to abscess or granuloma formation.

Fig. 10.

A 67-year-old man with splinter puncture wound in the fifth finger and intermittent paresthesia. Transverse ultrasound image at the distal fifth metacarpal shows a linear echogenic foreign body (calipers), with the end directly adjacent to the radial digital nerve. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the palm.

Masses

Ganglion cysts are common soft tissue mass lesions in the hand and wrist, which are usually posttraumatic or from chronic use [2]. On ultrasound, simple cysts appear as well demarcated, hypoechoic/anechoic masses with posterior acoustic enhancement and without internal vascularity. Small cysts may be seen along the flexor tendons, on or adjacent to a pulley (Fig. 11).

Fig. 11.

A 57-year-old man with a painful lump at the thumb after gripping injury. Longitudinal (a) and transverse (b) ultrasound images show an anechoic mass (*) along the flexor pollicis longus (FPL) tendon. This anechoic mass is consistent with a ganglion cyst. Photographs demonstrate ultrasound transducer (rectangle) position and orientation at the thumb.

Venous thrombus formation and pseudoaneurysm in the hand is rare but can be seen in patients after traumatic injury or intravenous line placement [13]. Doppler ultrasound is the modality of choice for evaluation of venous thrombosis and can characterize arterial injury (Fig. 12). Foreign body reactions may produce granuloma formation or abscess, appearing mass-like. Although sonography can aid characterization of masses in the hand, MR imaging, with or without contrast administration, can be recommended when further characterization is needed.

Fig. 12.

A 77-year-old man with a painful nodule at the thumb after a gripping injury. Longitudinal ultrasound image at the ulnar aspect of the thumb shows a fusiform hypoechoic mass along an artery with patchy internal pulsatile blood flow, consistent with a partially thrombosed pseudoaneurysm. Photograph demonstrates ultrasound transducer (rectangle) position and orientation at the thumb.

In conclusion, this retrospective review of experience at a single institution suggests that ultrasound is effective in the detection of soft tissue hand injury, with the ability to diagnose injury to tendons, ligaments, and nerves, and to detect retained foreign bodies and masses.