Introduction
The sagittal band, a critical structure of the extensor hood along with the oblique and transverse bands, restricts proximal displacement of the central slip and allows stable extension at the metacarpophalangeal (MCP) joint [1]. In the groove of the metacarpal head, the sagittal band splits into superficial and deep layers to surround the central slip, and stabilizes its movement [1,2]. Rupture of the two layers of the sagittal band, mainly at the radial slip, may cause consistent pain, swelling, and more importantly subluxation or dislocation of the extensor tendon at flexion of the MCP joint, depending on the degree of injury [3].
Although the exact mechanism is unclear, subluxation or dislocation of the extensor digitorum communis (EDC) tendon at the MCP joint due to sagittal band injury occurs in various conditions. Kleinhenz and Adams [4] found rare congenital anomalies with absence of the radial slip or juncturae tendini, or even with generalized ligamentous laxity making ligaments prone to rupture. Acquired causes, which comprise the vast majority, include traumatic, spontaneous, or rheumatic. In traumatic types, a direct blow or forced flexion of the MCP joint, often resulting from a contusion or a fall, can lead to rupture. For spontaneous types, as classified by Ishizuki [3], normal daily activities, such as finger flicking, finger crossing or crumpling paper are reported to potentially cause rupture [3,4]. In addition, chronic rheumatoid arthritis may lead to attrition and rupture of the sagittal bands, similar to the tears seen in older patients with osteoarthritis, generalized laxity and attritional damage [4,5]. Other than these known causes, it is rare for a non-rheumatoid patient to suffer from chronic sagittal band injury without any decisive event.
In the case we are reporting, a 22-year-old female with no history of trauma developed a bony lesion in the 3rd metacarpal head, which caused chronic irritation to the sagittal band rather than the extensor tendon, leading to a partial injury. Histopathologic examination revealed this bony lesion was an osteoma. To the best of our knowledge, this is the first reported case of sagittal band injury caused by chronic irritation in a patient with a non-rheumatoid joint. Therefore, we report this case to emphasize the clinical significance of considering underlying bony lesions as a potential cause of chronic sagittal band injury.
The research was approved by the Institutional Review Board (IRB No. 2024-N-008), and the patient provided written informed consent for the publication of this case report.
Case
A 22-year-old female patient presented with discomfort of her left middle finger, due to recurrent ulnar subluxation of the extensor tendon at flexion of the 3rd MCP joint. The symptoms started 5 years previously and gradually aggravated. The patient was not able to remember any traumatic or painful events at the time when she first noticed symptoms. Almost 5 mm subluxation of the extensor tendon to the ulnar side with Murray type 2 sagittal band injury [5] was noted on flexing the left middle finger, but the patient did not appeal with pain (Fig. 1) [5]. Plain X-rays did not demonstrate any significant bony abnormalities or signs of arthritic lesions.
Further imaging studies were commenced to examine the problematic joint area. Ultrasonography scans displayed a hypoechoic sagittal band with a partial tear at its radial slip, and a 1.7 mm-sized sessile osteochondroma-like protruding lesion on the dorsoradial aspect of the 3rd metacarpal head was identified. This seemed to irritate the extensor hood above and cause the tear of the sagittal band. These findings were confirmed by computed tomography, where a protruding bony lesion with a sharp surface was observed on the dorsal head of the 3rd metacarpal bone (Fig. 2). Though we suspected the bony lesion to be the cause of sagittal band injury, we first planned for several weeks of conservative treatment with extension splints. After 8 weeks had passed without any relief in the patient’s symptoms, we decided to proceed with surgical repair of the sagittal band and excision of the prominent bony lesion.
Under brachial plexus anesthesia, the dorsum of the 3rd MCP joint was dissected to expose the extensor hood, and the ruptured radial slip of the sagittal band was observed. Underneath the rupture site, a bony lesion was present and removed using an osteotome. The excised bony lesion was 0.4×0.3 mm in size. As we suspected preoperatively, the bony lesion seemed to be the reason for the chronic rupture. This is because it had a sharp bulging contour specifically facing the ruptured site of the radial sagittal band. Due to chronic degenerative changes, there was insufficient tissue at the radial slip for primary repair. Therefore, after centralizing the central slip, we used the McCoy method to stabilize the EDC tendon. Partial resection of the EDC tendon slip from the proximal side was performed and we sutured it with the lateral band and lumbricalis muscle [2] in a continuous epitendinous fashion with PDS 5-0 and 6-0(Ethicon Inc.) (Fig. 3).
The excised bony lesion was sent for histopathological examination, which confirmed an osteoma (Fig. 4). A volar protective extension splint was first applied postoperatively. On the 4th day, the splint was changed to a sagittal band bridge splint, and early active and passive motion was encouraged. Physical therapy commenced on the 4th week postoperatively. At the 12th week follow-up, the 3rd MCP joint returned to full active extension and 90° active flexion, with no sign of extensor tendon subluxation (Fig. 5).
Discussion
The sagittal band is a crucial component of the extensor hood, playing an essential role in stabilizing the EDC during MCP joint flexion. It is composed of compact fibers oriented perpendicular to the EDC, with attachments to the volar plate and deep transverse metacarpal ligament. The band divides into superficial and deep layers that collectively encapsulate the EDC [1,3]. Notably, the radial slip of the sagittal band is thinner than its ulnar counterpart, with the middle finger having the longest and thinnest radial sagittal band [1-4,6]. Kichouh et al. [1] also noted that the prominence of the 3rd metacarpal head places the sagittal band in a more superficial and distal position, increasing its susceptibility to subluxation. Consequently, rupture predominantly occurs on the radial side, particularly in the middle finger, due to these anatomical vulnerabilities. These observations align with our case, where the rupture was confined to the radial sagittal band of the middle finger.
Sagittal band injuries can occur under various conditions, including congenital anomalies, generalized ligamentous laxity, and even low-energy activities. Trauma or degenerative diseases like osteoarthritis and rheumatoid arthritis may also lead to rupture through chronic synovitis and weakening of the radial sagittal bands.
Sagittal band injuries are classified as chronic if symptoms persist for more than 6 weeks after onset, or if the injury fails to heal following 6 to 8 weeks of conservative treatment [5-8]. Rayan and Murray [5] defined the non-operative treatment period for acute injuries as 3 weeks of immobilization splinting followed by 3 weeks of dynamic splinting. Injuries that do not resolve within this timeframe are categorized as chronic, for which they recommend an additional 6 to 8 weeks of buddy splinting. Peelman et al. [8] proposed a slightly different approach, setting the non-operative treatment period for acute injuries at 3 weeks. They classify injuries that do not heal within 3 to 6 weeks as subacute and those persisting beyond 6 weeks as chronic [8].
In older patients, there are several reports of products of arthritis such as osteophytes that cause rupture of ligaments. As the degenerative changes in the joints progress, bony lesions tend to grow most rapidly within the first 3 years [9]. Although uncommon, these bony lesions may at times irritate ligaments and tendons to cause injury, resulting in rupture. Cases such as flexor tendon injury from Kienbock’s disease, extensor indicis proprius or index EDC tendon injuries by scaphoid lesions, and rotator cuff tears by olecranon bony lesions have been reported [10,11]. However, in previous reports, most injuries occurred in older patients with osteophytes and degenerative arthritis in the contingent joint; chronic injury of the sagittal band was known to be rare for patients with non-arthritic healthy joints.
Our case is the first reported chronic injury of the sagittal band in a patient with non-arthritic, healthy joints that failed to heal over a period of more than 8 weeks, as confirmed by surgical exploration. This case highlights the importance of considering an underlying metacarpal head osteoma when patients with otherwise healthy joints present with a chronic, non-traumatic rupture of the sagittal band.
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