A fifty-two-year-old man with diabetes and human immunodeficiency virus (HIV) presented with a six-month history of volar hand pain over the MCP joint of the index finger. The patient had reported sudden onset of pain after a household accident in which a piece of furniture pinned the hand against the wall. Initial radiographs (Figs. 1-A, 1-B, and 1-C) had been interpreted to be normal by the radiologist and the emergency department physician, and the patient had been treated with analgesic medication only. The hand had not been immobilized at that time. However, as the pain worsened, the patient had difficulty with use of the right hand for daily activities. When he was evaluated by us, the fracture was visible on all radiographs, but was most easily visualized on the oblique view. The fracture gap was approximately 1 mm. There was no interval displacement between the initial emergency department radiographs and those at the hand clinic six months later. We initially treated the finger conservatively with splinting, but the patient continued to have extreme pain at the fracture site. The patient was given a choice of local corticosteroid injection and continued observation or surgical treatment. Because of the duration and severity of the symptoms, he selected surgical excision.
With the use of intravenous sedation and local anesthesia, an oblique incision was made over the MCP joint of the index finger. The A1 pulley was released, and the flexor tendons retracted ulnarly. The fractured sesamoid bone was visualized, and the two fragments were sharply excised. A small rent in the volar plate was repaired, and the wound was irrigated and closed. Active finger motion was begun immediately after surgery. Six weeks postoperatively, the wound was well healed, pain was completely resolved, and digital motion was equal to the contralateral hand. Radiographs demonstrated complete excision of the sesamoid bone.
While the adult hand typically has five sesamoid bones, distribution does vary. Sesamoids at the MCP joint of the thumb are a consistent finding, present in 98.2% to 100% of subjects in various studies18,19. Sesamoids are located at the MCP joint of the little finger in 70% of subjects, at the MCP joint of the middle finger in 3% of subjects, and, rarely, at the MCP joint of the ring finger (1% of subjects)20. Approximately 50% of the population has a sesamoid of the index finger, which is firmly embedded in the radial half of the volar plate of the MCP joint and articulates with the metacarpal head. Its average dimensions are 3.5 mm (width) by 4.7 mm (length) by 2.5 mm (thickness)17.
The thumb sesamoid, which is the best characterized, ossifies between years ten and fourteen in girls and years twelve and sixteen in boys. Multiple centers can be involved in ossification, and incomplete union can result in a partite appearance on radiographs. The frequency of partite sesamoids of the MCP joint of the thumb ranges from 0.6% to 6%. A smooth appearance of partite sesamoid fragments helps to differentiate this anatomic variant from a fracture12. Sesamoid fractures are likely underdiagnosed since both incomplete ossification and poor visualization of the bone on standard anteroposterior and lateral radiographs can make a lesion difficult to identify. Oblique radiographs can best demonstrate a fracture8,12. Injury to the sesamoids of the thumb can be associated with partial or complete rupture of the volar plate or the accessory collateral ligaments, and the integrity of these structures must be assessed12. Function of the sesamoid bones has not been definitively determined. It is thought that sesamoid bones may stabilize the joint, modify pressure, diminish friction, extend the articular surface, and possibly alter the vector of tendon pull3,13.
Sesamoid fractures typically present with a history of a hyperextension injury or a direct blow to the palm of the hand. There can be ecchymosis over the palmar surface of the MCP joint as well as tenderness directly over the sesamoid bone. Patel et al.12 have classified sesamoid fractures of the MCP joint of the thumb into two types. In type-I injuries, the volar plate is intact and the patient retains the ability to flex the MCP and interphalangeal joints. A flexed posture of the MCP joint is typical. In type-II injuries, the volar plate is ruptured. The MCP joint is held in hyperextension and the patient cannot flex the joint12. Immobilization alone is typically adequate treatment, with pain resolving in thirty-six of the forty total reported cases of sesamoid fractures affecting any digit. However, if pain persists following a period of immobilization, surgical excision of the fractured sesamoid is curative11,13,16.
Many sesamoid bone fractures, especially type-I injuries in which the patient maintains the ability to fully move the hand, are likely missed. Inadequate radiographs that fail to completely image the sesamoid can contribute to underdiagnosis. Factors that may cause continued symptoms following nonsurgical treatment can include fracture displacement, lack of injury recognition and prompt immobilization, and impaired blood flow to the fracture site. To our knowledge, we have presented the first report of a sesamoid fracture of the index finger requiring operative treatment, highlighting the fact that clinical awareness of this rare fracture is key to proper evaluation and timely treatment.