Radial sesamoid fracture of the second MCP joint - a case report.

A fracture of the sesamoid bone of the hand is rarely seen. In most cases, it is strictly associated with the trauma. The patient complains of a long-lasting, due to unclear diagnosis, painful swelling of the joint with an inability to flex the affected finger. Limited blood supply makes the untreated fracture prone to avascular necrosis. Thus, it is extremely important to make a proper diagnosis early. Bilateral comparing the affected areas with ultrasonography seems to be the method of choice. The treatment is conservative or surgical when needed. We present a case of a radial sesamoid fracture of the second metacarpophalangeal joint without a history of trauma.

Introduction

Sesamoid bone (os sesamoideum, sezamon – leguminous plant of sesame) is in most cases a small, rounded mass embedded in a certain tendon and usually related to the joint capsule(. Being put under a considerable strain, especially in trauma, it fractures.

Usually, a painful swelling with an inability to flex the nearby finger is reported. In the hand, a fracture can occur in one of the two sesamoid bones in hyperextension trauma to the metacarpophalangeal joint of the thumb(. Rarely, according to the prevalence, it can be reported in a different localization.

Bearing in mind that sesamoid bones have a limited blood supply, it is extremely important to make a diagnosis instantly to prevent avascular necrosis from developing.

Case report

A 33-year-old female patient with a clinical suspicion of systemic connective tissue disease was referred for an ultrasound of the hand with painful swelling of the second metacarpophalangeal (MCP) joint of the left hand, lasting several months. Until now, she had no symptoms, did not undergo any serious diseases, including injuries, was not treated for any chronic illnesses, did not carry out activities (professional work) causing mechanical stress to the painful joint.

Firstly, an X-ray of the hand was taken and no pathology was found (fig 1).

Fig. 1

An X-ray reveals no pathology including the sesamoid bone of the second left MTP joint

Secondly, ultrasonography of the hand was performed with Toshiba Aplio 500 using a linear PLT probe with a frequency of 18 MHz.

The examination of the second MCP joint showed no evidence of synovitis (no presence of exudate, thickening nor hypervascularisation of the synovial membrane). Fibers of extensor and flexor tendons, flexor tendons sheath, and retinacula of the second finger showed no pathologies. From the palmar side at the level of the second MCP joint, a fracture of the radial sesamoid bone, 5 mm in length, was visible (fig. 2). Connected to the injury site, spot calcifications spread over the length of 9 mm, probably related to the organized hematoma and built into the capsular ligamentous complex, were seen.

Fig. 2

Standard B-mode ultrasonography. Left: fracture of the radial sesamoid bone of the 2nd MCP joint of left hand; right: normal radial sesamoid bone in the contralateral hand

In the ultrasound examination of the painful joint, in addition to the standard B-mode imaging, modern MicroPure option was applied, available on Toshiba ultrasound scanners, allowing detection of microcalcifications in soft tissues (fig 3A, B). MicroPure imaging is an option mainly used for the detection of microcalcifications in breast cancer.

Fig. 3

Standard B-mode sonography and with MicroPure option: A. a fracture of the radial sesamoid bone of the 2nd MCP joint of the left hand: left in standard B-mode ultrasonography; right in MicroPure option. B. spot calcifications spread over the length of 9 mm, built into the capsular ligamentous complex: left in standard B-mode ultrasonography; right with the use of MicroPure option

No other pathologies of the hand were found.

Discussion

Sesamoid bones are found in both extremities, bilaterally. In the upper extremity the common location is the palmar surface of the hand. There are two sesamoids at the metacarpophalangeal joint of the thumb (MCP 1). The medial located in the flexor pollicis brevis tendon is larger than the one fou nd on the ulnar side of the thumb in the adductor pollicis tendon(. They are found frequently in the corresponding joint of the little finger(. Figure 4 presents the prevalence of sesamoids in the joints of the hand(. Their existence in the proximal interphalangeal (PIP) joints is proven(. In the wrist a constant sesamoid is the pisiform within the tendon of the flexor carpi ulnaris(. In the lower extremity, on the plantar aspect of the foot, there are two sesamoid bones always present at the metatarsophalangeal joint of the great toe. In some cases the fabella is present – a small sesamoid bone embedded in the tendon of the lateral head of the gastrocnemius muscle behind the lateral condyle of the femur. The greatest one in the human body is the patella within the quadriceps tendon.

Fig. 4

The prevalence of sesamoids in the joints of the hand(. Red dot: constant; blue dot: frequent; yellow dot: rare

Their most probable functions are: diminishing friction, altering the direction of the force of the muscle to improve its efficiency and above all protecting the stability of the position of the flexor tendon system over the joint.

As sesamoids are located in areas of extra pressure (palm of the hand, sole of the foot) and have a limited blood supply, they are vulnerable to different pathologies. A fracture of the radial sesamoid bone of the metacarpophalangeal joint of the thumb due to hyperextension trauma in a gymnastic trainer(, locking of the ring finger at proximal interphalangeal joint due to a trapped sesamoid bone inside a dislocated joint following an injury during basketball practice(, sesamoid's periostitis in Reiter's syndrome were reported(. In acromegaly, an enlarged medial sesamoid bone of the thumb MCP joint may be a reliable indicator of the disease(. A common foot ailment in dancers and women wearing high-heeled shoes is sesamoiditis in the vicinity of metatarsophalangeal joint of the great toe.

Thanks to the development of the ultrasonography, many minor pathologies not found on the plain radiographs can be diagnosed, such as sesamoid fracture. The method is cost-effective, available and above all safe to the patient. Its use in differential diagnosis is dependent on the operator's experience, an in-depth anatomical knowledge of musculoskeletal system and on the class of the equipment(.

The sooner the proper diagnosis is made the better as sesamoids with their diminished blood supply are prone to avascular necrosis. Moreover, a misdiagnosis of the injury of the ligamentous apparatus of the thumb can lead to long-term hyperextension instability on pinching or post-traumatic, post-inflammatory scars in these ligaments(.

During the processes of diagnosis and treatment the Patel's classification should be taken into consideration, which originally applies to the most common sesamoids of the MCP joint of the thumb, but according to the authors can be used in other digits as well. Fractures of the MCP joint of the thumb categorize into two types:

type I with volar plate, stability of the joint and flexor tendon intact thus stable, and

instable type II with ruptured volar plate with hyperextension causing an inability to flex the metacarpophalangeal joint(.

The treatment of type I fracture is conservative with immobilized joint in 20–30° flexion for 2–4 weeks or taping. In type II, as for its instability, ruptured volar plate should be rearranged with consecutive immobilization in 20–30° flexion for 4–6 weeks(.

If sesamoiditis with chronic pain appears despite the treatment, a sesamoidectomy achieves good results in 80% of patients, yet complicated with decreased range of motion (ca. 17% in the case of the thumb trauma)(.

The dynamic ultrasound examination of the joint in our case showed no pathology of the volar plate. An orthopedic consultation was recommended.

Conclusion

Sesamoid bones of the hand and the foot rarely fracture. In case of long-lasting, painful swelling, especially in the area of the metacarpophalangeal joint of the thumb and the metatarsophalangeal joint of the great toe, sesamoid bones’ pathology along with chip fracture and pathologies of rheumatic etiology should be taken into differential diagnosis. Knowing the prevalence of sesamoids and bilateral comparison of their morphology in diagnostic imaging methods attribute to making a proper diagnosis thus preventing from complications by applying an appropriate treatment.