Delayed Presentation of a Locked Metacarpophalangeal Joint Secondary to Incarcerated Sesamoid with Associated Proximal Ulnar Collateral Tear in a 15-Year-Old Boy

Abstract

A 15-year-old right-handed boy presented 7 weeks after a hyperextension injury while playing basketball with a suspected metacarpophalangeal (MCP) joint dislocation to his right thumb and subsequent reduction by his mother at the time of injury. Initial radiographs were negative for acute fracture or dislocation. However, pain and stiffness persisted in the MCP joint, and subsequent magnetic resonance imaging demonstrated an incarcerated radial sesamoid and a proximal ulnar collateral ligament (UCL) injury with migration of the ulnar sesamoid under the proximal UCL, a finding not previously documented in the literature. He underwent surgical excision of the sesamoid bone and repair of the UCL injury with successful improvement in symptoms and return to all activities, including basketball, by his 4-month postoperative visit. This case demonstrates that it is imperative to scrutinize radiographs and consider advanced imaging when evaluating a locked MCP joint following a hyperextension injury.

Locked or “incarcerated” thumb metacarpophalangeal (MCP) joints because of radial sesamoid entrapment are rare. Reported mechanisms most often involve forced hyperextension and, less commonly, forced flexion of the MCP joint.¹ During both motions, the sesamoid can become interposed within the MCP joint and block further motion. Many cases occur in young, active patients, and frequently occur during sports-related trauma. They commonly present acutely with painful loss of MCP motion and mechanical block.¹

Accurate diagnosis can be challenging. Plain radiographs are the first-line imaging modality but may fail to demonstrate sesamoid position or associated soft tissue injury.² Advanced imaging, such as computed tomography (CT) or ultrasound, can help to delineate sesamoid displacement, whereas ultrasound and magnetic resonance imaging (MRI) can provide additional information regarding the integrity of the surrounding soft tissue structures, including the volar plate and the ulnar collateral ligament (UCL). It is crucial to identify the presence of a Stener lesion, defined as a tear of the distal UCL from the base of the thumb, leading to an interposition of the aponeurosis of the adductor pollicis muscle between the MCP joint and the torn UCL. The UCL is the primary stabilizer of the thumb MCP joint, and displaced tears, particularly in the setting of a Stener lesion, do not reliably heal without surgical repair.³

Management strategies for sesamoid incarceration range from attempted closed reduction to open surgical intervention.⁴ Early presentations without a mechanical block may be amenable to closed reduction; however, residual instability or associated volar plate injury can necessitate subsequent surgical treatment.⁴ Delayed presentation or persistent mechanical obstruction typically requires open reduction or sesamoid excision.⁴ We present the unusual case of an adolescent boy who presented in subacute fashion following a thumb hyperextension injury and was diagnosed with an incarcerated sesamoid and proximal UCL rupture.

Written and informed consent was obtained by the patient and his parents to share this case information and digital photos for educational purposes.

Case Presentation

A 15-year-old right-handed boy with no notable past medical history presented with his mother to the emergency department following a hyperextension injury of his right thumb while playing basketball. His mother noted a deformity of MCP joint following this incident. She applied axial traction, resulting in a “click” consistent with a reduction of a MCP joint dislocation. The patient had pain, swelling, and ecchymosis about the MCP joint. Radiographs at this time demonstrated no acute fracture or dislocation. He was discharged without immobilization or referral to a hand surgeon.

Because of continued pain and stiffness in the thumb, the patient was seen by a hand-fellowship trained surgeon 4 weeks following the initial injury. His examination at that visit demonstrated a notable loss of motion of the MCP joint from full extension to just 10° of flexion. The distal flexor and extensor tendons were intact. X-rays demonstrated no acute fracture or dislocation but did reveal a cortical irregularity of the first metacarpal with surrounding calcifications as seen in the Figure 1. Given his persistent symptoms and abnormal radiographs, an MRI was performed, which demonstrated a tear of the proximal attachment of the ulnar collateral ligament (UCL) (Fig. 2). Additionally, it was noted that the ulnar sesamoid bone had migrated under the UCL, and the radial sesamoid had become incarcerated between the proximal phalanx and the metacarpal (Fig. 3). Given the chronicity of these symptoms, a closed reduction of the entrapped sesamoid bone was not attempted, and the patient was indicated for open reduction versus excision of the sesamoid bone and repair of the UCL tear.

Figure 1.

Preoperative posteroanterior and oblique views of the right thumb demonstrating an ulnarly deviated ulnar sesamoid bone and a radial sesamoid within the MCP joint.

Figure 2.

Axial and coronal T1 MRI views demonstrating proximal UCL injury with migration of the ulnar sesamoid under the torn fragment.

Figure 3.

Coronal and sagittal T1 MRI views demonstrating entrapment of the radial sesamoid bone.

Seven weeks following the initial injury, the patient underwent surgical fixation. Intraoperatively, it was noted that the radial sesamoid was interposed between the proximal phalanx and metacarpal radial condyle. Following the excision of the sesamoid, there was considerable improvement in the range of motion of the MCP joint with flexion to 45°. The UCL injury was explored and found to have abundant fibrous scar tissue that was debrided. The proximal stump was then repaired using a knotless suture anchor technique. Radiographs demonstrated appropriate positioning of the ulnar sesamoid following UCL repair. He was immobilized in a thumb spica splint, followed by a cast for 4 weeks, followed by a removable thumb spica brace. He participated in hand therapy to improve the range of motion and strength in the thumb.

The patient has performed well after surgery. Postoperative radiographs revealed preserved joint alignment and interval healing of the proximal UCL repair (Fig. 4). At his 4-month postoperative follow-up appointment, he demonstrated complete restoration of his range of motion measured from 0 to 40 with 55° degrees of radial abduction and full opposition to the fifth metacarpophalangeal joint. His grip strength measured to be 105 pounds on the surgical right extremity compared to 85 on the left extremity. Importantly, he reported he has returned to all preoperative activities, including basketball.

Figure 4.

Postoperative posteroanterior and oblique views of the right thumb demonstrating appropriate positioning of the ulnar sesamoid and removal of the radial sesamoid with callous formation over area of osseous fixation of the UCL.

Discussion

Locked MCP joints secondary to incarcerated sesamoids are an uncommon injury. Case reports exist in the literature detailing a locked metacarpophalangeal joint secondary to an entrapped sesamoid bone; however, none of these previously published cases involve an adolescent patient with a delayed presentation leading to operative fixation. Ahn et al² discuss a case of a 15-year-old boy with a more acute presentation of this injury successfully treated with closed reduction as confirmed with ultrasound imaging. Carroll et al⁴ detailed the case of a 24-year-old woman with a subacute presentation of this injury that also necessitated operative management. Our case builds upon these two cases by drawing attention to the possibility of a delayed presentation of this injury in the adolescent population that is more likely to require operative management. This case also highlights the importance of scrutinizing imaging studies to identify these unusual injury patterns given that the initial injury images were interpreted to be without any abnormality, yet the repeat radiographs in clinic demonstrated displacement of the sesamoids without any interval additional injury to the thumb.

The mechanism for these injuries is not fully understood, but concomitant injuries to the soft tissues of the joint and fractures of the involved bones have been well documented. Desai et al⁵ performed a cadaveric dissection and posited that for the sesamoid bone to become entrapped in the joint there is inherent injury to the proximal volar plate. Xiong et al⁶ proposed that the sharp proximal pole of the radial sesamoid may contribute to joint locking as it can damage the volar plate. Others have suggested that the morphology of the metacarpal head may also contribute to the risk of becoming locked after a trauma.² This necessitates advanced imaging evaluation of the surrounding tissues, often using ultrasound, CT, or MRI for adequate surgical planning.

In this case, the MRI demonstrated a finding not previously documented in the current literature by identifying the migration of the ulnar sesamoid bone under the proximal fragment of the UCL tear. As previously noted, a Stener lesion is a well documented finding in which the adductor pollicis aponeurosis prevents adequate UCL healing following a tear at the distal attachment; however, in this case, the ulnar sesamoid acted as an osseous block to UCL healing of the proximal insertion. Tears of the proximal attachment of the UCL are also rare, accounting for just 5% to 6% of all UCL injuries.^7,8 Prior case reports have described ulnar sesamoid fractures associated with UCL injuries, and another proposed an idea of a pseudo-Stener lesion caused by an overgrowth of granulation tissue preventing healing of a proximal UCL tear; however, to the authors’ knowledge, no other report has documented a finding similar to that seen in this case.^9,10

This case highlights several key considerations for clinicians evaluating thumb MCP injuries in adolescents and young athletes. It is imperative to consider an entrapped sesamoid when evaluating a patient with a locked MCP joint, especially following a suspected closed reduction of a dislocation. It is equally important to fully evaluate the soft tissues surrounding the joint for associated injury, either via ultrasound, CT, or, as in this case, with an MRI to evaluate for injuries to the proximal volar plate, collateral ligaments, and the sesamoid bone itself. Interestingly, this case revealed a previously undocumented finding with the ulnar sesamoid acting as an “osseous pseudo-Stener” lesion by migrating under the torn proximal aspect of the UCL.

Conflicts of Interest

No benefits in any form have been received or will be received related directly to this article.