Non-displaced distal radius fracture with fat-fluid levels in the adjacent extensor tendon sheaths on MRI
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- McConnell, M., Cohen, H. & Scuderi, M. Skeletal Radiol (2013) 42: 1761. doi:10.1007/s00256-013-1685-5
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We report a rare case of fat-fluid levels in the extensor tendon sheaths of the wrist on MRI. An 18-year-old female sustained a direct injury to her left hand while playing soccer. Plain radiographs showed soft tissue swelling with no definite fracture plane appreciated on the initial review of the images. The pain and swelling were severe and an MRI was obtained to evaluate for fracture and soft tissue injury. The MRI demonstrated a cortical defect near Lister’s tubercle and multiple fat-fluid levels within the extensor tendon sheaths. This is the first reported case of fat-fluid levels within the extensor tendon sheaths on MRI, with only one previous case report of this entity on CT.
KeywordsWristExtensor tendonsFat-fluid levels
Fat-fluid levels are commonly associated with intra-articular fractures and are the result of the traumatic release of fat from the bone marrow mixed with hemorrhage associated with the fracture. The presence of fat-fluid levels within a joint is known as lipohemarthrosis. This entity has been described in the knee, hip, shoulder, and elbow . A lipohemarthrosis could occur in any joint. We found one previous case report describing a distal radius fracture with associated lipohemarthrosis in the radiocarpal joint and fat-fluid levels within the extensor tendon sheaths on CT . We report a case of a distal radius fracture with isolated fat-fluid levels within the extensor tendon sheaths of the wrist on MRI without associated lipohemarthrosis in the joint space. To our knowledge, there has been no previous report of this in the literature.
The injury was treated with a cast to allow the swelling to decrease and to rest the injured wrist. The patient was encouraged to facilitate range of motion in all fingers, passively at first and progressing to more active function. She was seen on follow-up approximately 10 days later for cast removal and clinical inspection. The pain and swelling had significantly decreased and no follow-up imaging was obtained at that time. The patient later followed-up with the physical therapist at her school for 4 weeks prior to returning to soccer practice. She continued to tape the wrist during soccer practice and games for the rest of the season.
Intra-articular fractures may result in extrusion of fat from the bone marrow at the fracture site into the joint space. The fat is then mixed with hemorrhage associated with the traumatic injury. Since fat is less dense than blood, the two densities separate with the blood layering more inferiorly and the fat layering superiorly. Fat-fluid levels within the joint are known as lipohemarthrosis.
Fat-fluid levels within tendon sheaths are not common. There is one previous case report detailing a fat-fluid level in the extensor tendon sheaths of the wrist on CT . This is the first reported case of such an entity on MRI.
In our case, there was a nondisplaced fracture in the region of Lister’s tubercle immediately adjacent to the extensor pollicis longus tendon sheath. There appeared to be a region extending from the fracture site to the tendon sheath that was continuous with and isointense to the distal radius bone marrow signal (Fig. 2, arrows). These findings are suspicious for a traumatically induced communication between the fracture involving Lister’s tubercle and the adjacent extensor pollicis longus tendon sheath. This communication would explain the presence of the fat-fluid level within the tendon sheath.
The presence of fat-fluid levels in the extensor carpi radialis longus and brevis and extensor digitorum tendon sheaths may result from communication between these tendon sheaths and the extensor pollicis longus tendon sheath. There has not been extensive research regarding communication between the extensor tendon sheaths. Previous studies have shown normal communication between the extensor carpi radialis brevis and extensor pollics longus tendon sheaths [3, 4]. Communication between the first and second dorsal extensor compartments has also been seen with tenography in cadaver specimens . Alternatively, the fat-fluid levels could have resulted from multiple tendon sheath injuries. The presence of soft tissue edema adjacent to the tendon sheaths could support this explanation for the multiple tendon sheath fat-fluid levels, although no fat-fluid levels were seen within these soft tissues. The absence of soft tissue fat-fluid levels, however, does not exclude this explanation because there may have been fat within the soft tissue edema adjacent to the tendon sheaths that had not separated from the fluid or the fat content may have been too small to appreciate on the MRI.
This case demonstrates some unique features. This is only the second reported case of fat-fluid levels within tendon sheaths and the first to our knowledge reported on MRI. There was no associated lipohemarthrosis in the joint space, unlike in the previous reported case. The fracture site in the region of Lister’s tubercle was directly adjacent to the extensor pollicis longus tendon sheath and there appeared to be a region extending from the fracture site to the tendon sheath that was continuous with and isointense to the bone marrow signal. This raises the possibility of a traumatically induced communication between the fracture site and the extensor pollicis longus tendon sheath to explain the presence of the peritendinous fat-fluid level. The presence of fat-fluid levels in the extensor digitorum and extensor carpi radialis longus and brevis tendon sheaths may be due to communication between these extensor tendon sheaths and the extensor pollicis longus tendon sheath, although multiple tendon sheath injuries could also explain the findings. Further investigation into the exact nature of communication between the extensor tendon sheaths would be helpful because communication has not been demonstrated between the tendon sheaths of the extensor pollicis longus and extensor digitorum or the extensor carpi radialis brevis and longus and extensor digitorum. To our knowledge, no studies have investigated communication between these tendon sheaths.
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