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| IMAGE QUIZ ARCHIVE | ||||||
| Image Quiz | ||
| Pain in the Hand in a Baseball Player1 (continued) | ||
| Answer: Occult fracture of the trapezoid bone | ||
| Technetium bone scans showed increased uptake in the area of the trapezoid bone (Fig. 1). Sagittal T1-weighted magnetic resonance images (repetition time, 500 msec; echo time, 14 msec) showed a decreased bone-marrow signal area with a high-signal-intensity line between the trapezoid and a dorsal trapezoid fragment. T2-weighted images (repetition time, 2200 msec; echo time, 100 msec) also demonstrated a high-signal-intensity fracture line between the bone fragment and the trapezoid (Fig. 2). | ||
 Fig. 1 |
 Fig. 2 |
For larger view, click on image |
| Fig. 1 Technetium bone scan revealing increased uptake in the area of the trapezoid bone (arrowhead). Fig. 2 T2-weighted sagittal magnetic resonance image of the hand (repetition time, 2200 msec; echo time, 100 msec), revealing a low-signal-intensity bone fragment lying between the dorsal aspect of the trapezoid bone (arrowhead) and the extensor carpi radialis longus tendon (arrow). |
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| The fragment was removed through a dorsal surgical approach. The diameter of the fragment was 4 mm. Histologically, it had a core of viable bone including bone trabeculae with osteoblast-lining and osteoclast, surrounded with thick fibrous tissue. | ||
| Discussion | ||
| The trapezoid is rigidly fixed to the trapezium, capitate, and scaphoid by strong ligaments, which protect it from fracture or dislocation. The mechanism of trapezoid injury is thought to be axial disruption. However, we are aware of no previous reports of occult fracture of the trapezoid bone, such as was described in this paper. | ||
| The injury in our patient may have been a stress fracture or a nonunion of an initial dorsal intra-articular fracture. The histological examination of the excised fragment showed viable bone surrounded with fibrous tissue. These findings were consistent with a nonunion. | ||
| In our patient, the mechanical process of injury may have been repetitive impact stress on the dorsal edge of the trapezoid bone when the patient hit balls with a baseball bat. In this condition, the metacarpal is both extended and pulled by the extensor carpi radialis longus tendon attached to the radial portion of the metacarpal base. The dorsal radial edge of the base of the metacarpal bone impacts the dorsal edge of the trapezoid. Magnetic resonance images revealed that the fragment was at the same level as the extensor carpi radialis longus tendon, further substantiating our theory of mechanical stress. As a result of the repetitive force, the bone fragment did not unite. | ||
| When the diagnosis is in doubt and radiographs are not diagnostic, technetium bone scintigraphy may reveal a focal increase in radioisotope uptake to suggest the presence of a structural defect. However, this sensitive technique has poor specificity and resolution, and other imaging modalities such as computed tomography and magnetic resonance imaging are often used to help in the specific diagnosis, as was done in the case of our patient. Magnetic resonance imaging is very sensitive in depicting the cortex and marrow changes that occur in occult fractures. | ||
| Reference | ||
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