International Journal of Research in Orthopaedics

Palaniappan G et al. Int J Res Orthop. 2021 Jan;7(1):162-164

http://www.ijoro.org

Case Report

DOI: https://dx.doi.org/10.18203/issn.2455-4510.IntJResOrthop20205582

A fracture of OS trigonum: a rare case report

Gnanaprakash Palaniappan*, Chetan John Rasquinha, Major K. Kamlanathan

Department of Orthopaedics, PSG Institute of Medical Sciences and Research, Coimbatore, Tamil Nadu, India

Received: 28 September 2020

Revised: 04 November 2020

Accepted: 04 November 2020

*Correspondence:

Dr. Gnanaprakash Palaniappan,

E-mail: pagprakash@gmail.com

Copyright: © the author(s), publisher and licensee Medip Academy. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Fractures of os trigonum is an extremely rare event. It is one of the accessory ossicles of the foot found in about 7 % of the population. Very few cases have been reported in the literature about a fracture of the ostrigonum. We present a case of fracture of ostrigonum with associated fracture of the fibula and a large lacerated wound in the leg, in a young man sustained due to road traffic accident. The initial radiological examination with Xray ankle showed a doubtful fracture of posterior process of talus but was not clear. The diagnosis was clinched by CT scan of the ankle with 2mm cuts, which showed clearly a fracture of the os trigonum. It was treated by flap cover for the wound and plaster immobilisation for the fracture. So, any doubtful fracture near the posterior process of talus should be fully assessed radiologically with a CT scan to guide in the treatment.

Keywords: OS trigonum, Talus, Posterior process, Fracture

INTRODUCTION

OS trigonum is one of the accessory ossicles of the foot due to failure of fusion of a secondary center with the main bone of talus.6 Fracture of this bone is extremely rare event. To the best of our knowledge very few cases-less than ten, have been reported in the literature.1-3

CASE REPORT

A 30-year-old man presented to our emergency department with history of road traffic accident-he was a two-wheeler driver hit by a speeding car and he was thrown out and landed on his right leg. His vitals were stable. He had a deep lacerated wound on the anteromedial aspect of his right leg (Figure 1) with swelling around his ankle.

All movements of ankle, particularly plantar flexion was extremely painful. X-rays revealed comminuted fracture of shaft of fibula at mid third distal third junction with a fracture fragment at the posterior aspect of talus. (Figure 2-4).

Figure 1: Clinical pictures.
Figure 1: Clinical pictures.

To clarify the nature of the fragment a CT scan was taken and axial, and sagittal cuts revealed a fracture of the ostrigonum-which is extremely rare (Figure 5-10). He was treated by wound debridement and flap cover and short leg plaster of Paris slab.

Figure 2: X-ray leg showing fracture fibula.
Figure 2: X-ray leg showing fracture fibula.
Figure 3: X-ray R ankle-no obvious fracture.
Figure 3: X-ray R ankle-no obvious fracture.
Figure 4: X-ray R ankle-showing fracture of ostrigonum.
Figure 4: X-ray R ankle-showing fracture of ostrigonum.
Figure 5: X-CT scan-sagittal image.
Figure 5: X-CT scan-sagittal image.
Figure 6: X-CT scan-sagittal image showing fracture of ostrigonum.
Figure 6: X-CT scan-sagittal image showing fracture of ostrigonum.
Figure 7: CT scan showing fracture ostrigonum.
Figure 7: CT scan showing fracture ostrigonum.
Figure 8: CT scan-sagittal image showing fracture ostrigonum.
Figure 8: CT scan-sagittal image showing fracture ostrigonum.
Figure 9: CT axial image showing fracture ostrigonum.
Figure 9: CT axial image showing fracture ostrigonum.
Figure 10: CT axial image showing fracture ostrigonum.
Figure 10: CT axial image showing fracture ostrigonum.

DISCUSSION

Os trigonum is one of the ossicles of the foot and found in about 7 percent of the population and in some cases can be bipartite or fragmented.6 It appears between 8 to 11 years as secondary center of ossification and fuses with the posterolateral tubercle of talus talus within one-year appearance. If it fails to fuse it is known an os trigonum. In such cases it is connected to the lateral process of talus by a fibrous band. 6Some people may develop os trigonum syndrome where there is pain in posterior ankle triggered by injury or by repeated pointing of toes downwards like ballet dancers any forceful plantar flexion of toes.5,6 But a fracture of ostrigonum is extremely rare and very few cases have been reported In the literature.1-3 To our knowledge less than ten cases have been reported worldwide. The mechanism of injury is forced plantarflexion where the ostrigonum is crushed between the posterior malleolus of tibia and the tubercle of calcaneum.4 In our patient clinical signs include a large lacerated wound in the anteromedial aspect of leg and swelling around the ankle with tenderness over the posterior part. Plantar flexion was exteremely painful. X-ray showed a doubtful fracture of the posterolateral process of talus. But CT scan revealed a fracture of the os trigonum.

Such fractures are easily missed in routine X-ray of the ankle and may be source of persistent pain. It may be mistook for fracture of the posterolateral process of talus or simply as ostrigonum syndrome. CT scan with axial and sagittal cuts, with 2 mm cuts, will clinch the diagnosis and help in differentiating beween an os trigonum fracture and fracture of posterolateral process of the talus or a an ostrigonum syndrome. Such fractures usually heal by conservative treatment but a high degree of suspicion is required to detect them. Otherwise it may cause persistent pain in the ankle without proper treatment.

CONCLUSION

Injuries of the hindfoot should be carefully assessed clinically and radiologically. If there is any suspicion or a doubtful fracture near the posterior process of talus, or if there is an unfused ostrigonum with pain and tenderness in the hindfoot, A CT scan with at least 2 mm cuts should be taken to avoid missing a fracture in the ostrigonum. Such fractures do well with conservative management with immobilsation with splints like plaster of Paris. But if missed and not properly immobilsed, they may cause persistent pain in the hindfoot and morbidity.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

REFERENCES

  1. 1. Kose O, Okan AN, Durakbasa MO, Emrem K, Islam NC. Fracture of the os trigonum: a case report. J Orthopaed Surg. 2006;14(3):354-6.
  2. 2. Ince S. A rare accessory bone fracture of ostrigonum. Eurorad Musculoskeletal system Case 15397.
  3. 3. Yan YY. Fracture of os trigonum –A report of two cases and review of literature. Fo Ank Surg. 2016;22(4):21-4.
  4. 4. Jones DM, Saltzman CL, El-Khoury G. The diagnosis of the os trigonum syndrome with a fluoroscopically controlled injection of local anesthetic. Iowa Orthopaed J. 1999;19:122.
  5. 5. Xiaoyoung FU. Implications of Classification of Os Trigonum: A Study Based on Computed Tomography Three-Dimensional Imaging. Med Sci Monit. 2019;25:1423-8.
  6. 6. MP AG, Aparisi F, Bartoloni A, Fons F, Battista G, Guglielmi G, et al. Anatomical variation in the ankle and foot: from incidental finding to inductor of pathology. Part I: ankle and hindfoot. Insigh Imag. 2019;10(1):74.