Case StudyMSK Imaging

Post-Traumatic “Floating Fat” in the Extensor Tendon Sheaths of Wrist

Published Date: June 1, 2025
By Parag Vijaysingh Patil, MD, DNB

Case Summary

An adult presented with pain and swelling of the right wrist after a fall.

Imaging Findings

Sagittal reformatted CT of right wrist ( Figure 1 ) demonstrated a comminuted intra-articular fracture of the distal end of the radius (Frykman type VIII). Fat density was noted in the wrist joint space. Axial CT images ( Figure 2 ) demonstrated fat-fluid levels in the extensor pollicis longus (EPL), extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB) tendon sheaths. Coronal reformatted CT images ( Figure 3 ) also showed fat densities in EPL, ECRL, and ECRB tendon sheaths.

Figure 1.

Sagittal and coronal reformatted CT images of the right wrist with bone reconstruction. Comminuted intra-articular fracture of the distal end of the radius is noted (A), while fat densities are noted in the wrist joint space (B, arrows).

Figure 2.

Axial CT images of the right wrist with bone reconstruction (A) and soft-tissue reconstruction (B). Fat-fluid levels are noted in the synovial sheaths of extensor pollicis longus (EPL), extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB) tendons.

Figure 3.

Coronal reformatted CT images of the right wrist with bone reconstruction (A) and soft-tissue reconstruction (B). Fat densities are noted in the synovial sheaths of extensor pollicis longus (P), extensor carpi radialis longus (L), and extensor carpi radialis brevis (Br) tendons.

Diagnosis

Post-traumatic floating fat in the extensor tendon sheaths of the wrist. Differential diagnosis includes a true synovial lipoma and lipoma arborescens.

Discussion

Post-traumatic fat-density effusion in the extensor tendon sheath on CT was first reported by Le Corroller et al in 2010.1 Ali et al observed a similar finding in multiple patients and thought it was an underreported finding.2 They also suggested that floating fat is a secondary sign of an intra-articular fracture or an occult fracture. In 2017, von Schneider-Egestorf et al retrospectively analyzed MDCT scans of individuals with distal radial intra-articular fractures and found that most of the individuals demonstrated fat-fluid levels in the extensor tendon sheaths.3 They also found that fracture severity was not related to frequency and severity of tendon sheath involvement.

Bone marrow fat leakage in joints with torn tendon sheaths has been postulated as a cause of fat-density effusion in the joint and tendon sheaths.3 Tendons of the second extensor compartment (ECRL, ECRB) of the wrist are most often involved, followed by the tendons of the third compartment (EPL). Involvement of both compartments is also common, owing to the existence of a normal foramen between the EPL and ECRB tendon sheaths.4

Involvement of the tendon sheaths can be assessed using the Likert scale of semi-quantitative grading from 0 to 2.3

Conclusion

Although floating fat in the extensor tendon sheaths is not uncommon, the condition is an important finding that can indicate the intra-articular extension of a distal radial fracture or an occult fracture and should be recognized.

References

1. Le Corroller T , Parratte S , Zink J-V , Argenson J-N , Champsaur P . Floating fat in the wrist joint and in the tendon sheaths. Skeletal Radiol. 2010; 39 ( 9 ): 931 - 933. 10.1007/s00256-010-0929-x
2. Ali S , Huebner S , Groshek F , Schaffer A . The floating fat sign of trauma. Can Assoc Radiol J. 2014; 65 ( 2 ): 106 - 112. 10.1016/j.carj.2013.02.008
3. von Schneider-Egestorf A , Meyer B , Wacker F , Rosenthal H , von Falck C . Systematic evaluation of concomitant extensor tendon sheath injury in patients with distal intra-articular radial fractures in MDCT using the floating fat sign. Eur Radiol. 2017; 27 ( 10 ): 4345 - 4350. 10.1007/s00330-017-4787-y
4. Cvitanic OA , Henzie GM , Adham M . Communicating foramen between the tendon sheaths of the extensor carpi radialis brevis and extensor pollicis longus muscles: imaging of cadavers and patients. AJR Am J Roentgenol. 2007; 189 ( 5 ): 1190 - 1197. 10.2214/AJR.07.2281

Citation

Patil PV. Post-Traumatic “Floating Fat” in the Extensor Tendon Sheaths of Wrist. Appl Radiol. 2025;(3):1 - 2.
doi:10.37549/AR-D-25-0080

June 1, 2025