That’s my STYLEoideum- It is not always desirable to be unique, at least anatomically. Os styloideum

2015-12-08 09:33:49

Category: Musculoskeletal Imaging, Region: Upper extremity-Bones-(Meta)Carpals and digits, Plane: Other

Case Report We report the case of a 15-year-old male patient that was admitted to our hospital for persistent localized pain on the dorsal site of the left adominant wrist. Clinical assessment and physical examination revealed punctual localized pain on the dorsal aspect of the left wrist between the base of the 2nd and 3rd metacarpal bones over the third carpometacarpal joint. Inspection showed a slight localized protrusion, asymmetry and concomitant tenderness but no relevant swelling, no other signs for infection. The mobility and strength of the wrist and fingers was symmetrical to the opposite site. There was no history of trauma or prior operation. The sensations of pain occurred mostly when lifting heavy objects. According to his mother he had recently grown noticeably. Basing on clinical symptoms and assessment a slight insertional tendinitis of extensor carpi radialis longus/brevis muscle or a carpe bossu were suspected. To rule out fracture and for the purpose of accurate distinction of the lesion a native multi-slice CT (Siemens Somatom Definition Flash, Siemens Medical Solutions, Germany) of the left wrist was performed. The images revealed no fracture and normal alignment of the carpal bones. An accessory round osseous structure between the dorsal aspect of the capitate and trapezoid bones and the radial aspect of the base of the third metacarpal bone with pseudoarticulation was detected. To determine if the accessory bone was present in the opposite wrist, a further verifying ultrasound examination with the use of a 12 MHz linear transducer (Toshiba Amplio 500, Toshiba Medical Systems Corporation, Japan) was performed. Ultrasonography revealed additional bones on the base of the metacarpal II and III bones on both sides. However, the accessory bone was significantly larger in the left wrist. A corticosteroid infiltration of the third carpometacarpal joint under fluoroscopy resolved pain completely within a few days, verifying the carpe bossu causing the patients clinical symptoms. Discussion An accessory bone called os styloideum is a rare anatomical variant in the construction of a carpometacarpal joint with an incidence of 0.3-1.6% [1]. It is located between the capitate and trapezoid and the bases of second and third metacarpals, and is also called “ninth carpal bone” [1]. Furthermore, in the orthopaedic jargon terms like “carpe bossu” or “carpal boss” stand for the pain in the dorsum of the wrist, thus correlate with the location of the os styloideum [2-4]. Mostly, os styloideum disappears during fetal development while its occurrence is explained as an embryologic developmental variant resulting from non-fusion of the primordial cartilaginous units [5]. Routinely the way from clinical symptoms to the conclusive diagnosis leads through the CT or ultrasound examination to rule out differential diagnoses [6]. A palpable bony prominence on the dorsal site of the wrist in the clinical examination and concomitant unspecified local pain evoke an impressive list of differential diagnoses, with ganglions, tendinopathies and degenerative joint diseases on top of it. Therefore, such as initial finding would be probably not immediately associated with the existence of os styloideum. However in the radiographic imaging it is usually an “aunt minnie”. The current literature keeps silent on the true incidence of symptomatic carpe bossu. Solely the studies on cadavers of Nakamura and Alemohammed point out that the authentic occurrence of additional bones in the hand, appear to be more frequent than previously suspected [7, 8]. Interestingly, the available studies on humans suggest that the incidence of symptomatic carpal boss may rather affect the dominant hand [9]. Moreover, the study of Fusi et al. suggests that the mean age of 116 evaluated patients who were treated surgically for symptomatic carpal boss was 32 years and male and female patients were equally affected [9]. Actually there is no agreement about the “gold standard” therapy, however many authors suggest that the initial treatment should be conservative, either with the anti-inflammatory medication or with corticosteroid injections [10, 11]. Our case is unusual as the patient was only 15 years old, had an accessory os styloideum in both wrists, though symptomatic only on the left adominant side. We assume that his noticeable growth in the recent time might have involved the probably already existing accessory bones and release pain in the dominant hand. We present that the diagnosis could be made by means of CT or ultrasound examination. Furthermore the ultrasonography revealed the existence of an accessory metacarpal bone on a non-symptomatic side. TEACHING POINT Os styloideum may be a bothersome and inconvenient condition but as a rare anatomical variant is usually not immediately suspected and consequently may be missed on clinical assessment. Early detection of this accessory bone can be related with conservative treatment without surgical approach therefore the general awareness of this principally easily detectable lesion should be raised.