An unusual ankle injury

This report discusses the near-missed diagnosis of a rare case of a Maisonneuve fracture occurring in conjunction with an ankle dislocation.

Case report

A 47-year-old woman was brought into the Emergency Department having twisted her left ankle while walking on flat ground earlier that day. There was no evidence of direct impact injury to either the left ankle or leg. Prior to this event, the patient had no medical problems, was not on any regular medication, and had no previous history of ligamentous laxity or ankle sprains.

On examination, the left ankle was grossly swollen and the whole foot was displaced medially. This provided somewhat of a distraction and comprehensive examination of the remainder of the leg was not performed. The ankle injury was closed and there was no neurovascular deficit. Beighton's score was zero.¹ A preliminary diagnosis of a medial ankle dislocation was made and immediate closed reduction was performed in the Emergency Department. Closed reduction took precedence over radiological investigation of the injury since any delays in the restoration of normal anatomy could potentially compromise the integrity of the overlying skin and also increase the risk of neurovascular damage. Accordingly, it is institutional policy that ankle dislocations are reduced immediately without the need for X-rays.

Having reduced the dislocation confirmatory X-rays were then taken. While the patient was being positioned on the X-ray table it was noted by the radiographer that she had some tenderness around the upper leg. Radiographs were therefore taken of this anatomical region too. These illustrated a fracture of the proximal fibula in conjunction with a widened syndesmosis (Figures 1 and 2). Interestingly there was no malleolar fracture seen. The injury was therefore considered to be in keeping with a Maisonneuve fracture and thus operative intervention was planned.

Figure 1.

Antero-posterior post reduction radiograph of the left ankle illustrating a proximal fibula fracture and a widened syndesmosis

Figure 2.

Lateral post reduction radiograph of the left ankle illustrating a proximal fibula fracture

The patient was taken to theatre the following day for further examination of the injury with a view to stabilize the syndesmosis. Under general anaesthesia and tourniquet control the ankle was screened under image intensification. This illustrated a grossly unstable syndesmosis and therefore two trans-syndesmosis screws were inserted (Figures 3 and 4). A below-knee non-weight-bearing cast was then applied and following an uneventful postoperative recovery the patient was discharged two days later. The patient was kept strictly non-weight-bearing for eight weeks following which the syndesmosis screws were removed under general anaesthesia. Following this, progressive weight-bearing was commenced in conjunction with physiotherapy. At the latest clinic review the patient had returned to normal activities with few restrictions and has been discharged with no further follow-up.

Figure 3.

Antero-posterior postoperative radiograph showing two trans-syndesmosis screws in the left ankle

Figure 4.

Lateral postoperative radiograph showing two trans-syndesmosis screws in the left ankle

Discussion

The Maisonneuve fracture was initially described following cadaveric studies and is typically characterized by four progressive patho-anatomical stages.² Stage I is rupture of the deltoid ligament or fracture of the medial malleolus. Stage II consists of disruption of the interosseous membrane. Stage III is characterized by a fracture of the proximal fibula and stage IV entails either rupture of the posterior syndesmosis or fracture of the posterior tibia at the level of the ankle joint. The injury is associated with 1–11% of all ankle fractures and is recognized as being one of the most unstable.^3,4

The mechanism of injury implicated in the majority of cases is that of high-energy trauma.⁴ This is unsurprising since the force causing the proximal fibula fracture must first traverse the medial ankle structures, syndesmosis and then the interosseous membrane. That being said, the current case occurred as a result of trivial low-energy trauma in a patient who was otherwise not predisposed to fracture. To the best of the authors' knowledge very few similar cases have been reported in the literature and therefore no plausible suggestions describing how such a complex injury pattern may occur have been proposed.

Upon its initial description it was stated that that the fibula fracture was ‘always proximal’ and that ankle dislocations do not occur because ‘… the fibula continues to splint the foot laterally preventing a complete dislocation’.³ In the current case though a medial ankle dislocation was clearly evident on clinical examination, and once reduced, was found not to be associated with a malleolar fracture. Dislocation of the ankle joint without concomitant malleolar fracture (pure dislocation) is an extremely rare injury in itself.^5,6 This can be attributed to the relative weakness of the bones in relation to the strength of the surrounding ligaments.⁷ These structures constitute a supporting strut that is inherently stable and therefore high-energy trauma is most frequently implemented in such cases.⁶ Several predisposing factors have also been described including medial malleolus dysplasia, ligamentous laxity, previous ankle sprains or peroneal muscle weakness.^6,8 What makes the current case unusual is that not only did it occur as a result of trivial low-energy trauma; the patient did not also possess any of the aforementioned risk factors.

In the acute setting distraction injuries often mask the symptoms of other more minor injuries and thus can potentially lead to a delayed diagnosis. In the current case for instance, had it not been for the awareness of the radiographer the proximal fibula fracture may not have been seen thereby giving a false impression of the mechanism of injury and underestimating the true instability of the ankle joint itself. In light of this, one should be vigilant of a Maisonneuve fracture even in cases of ankle dislocation since missed or delayed diagnosis may lead to persistent instability and even acute compartment syndrome.⁹ Clinically, the ‘squeeze test’ may be utilized to diagnose the injury. This entails compression of the fibula against the tibia at the level of the mid-calf resulting in pain at the syndesmosis. This in conjunction with proximal fibula tenderness has been suggested to be indicative of a Maisonneuve fracture.⁴

Conclusion

We have reported the first case of a Maisonneuve fracture associated with pure dislocation of the ankle. This is an unusual association since the literature states that the two should be mutually exclusive. Furthermore, for such an injury pattern to be caused by trivial low-energy trauma and be associated with a distraction injury (ankle dislocation), the authors' advocate diligence in all similar cases and reinforce the principle of examining both ends of a long bone when a potential fracture is present at one end.

DECLARATIONS

Competing interests

None declared

Funding

None

Ethical approval

Written informed consent to publication has been obtained from the patient

Guarantor

TT

Contributorship

TT conceived the case, reviewed the case-notes, reviewed the literature and wrote the manuscript; AB reviewed the case-notes and assisted with formulating the manuscript; ST reviewed the literature and assisted with formulating the manuscript; ME led the care of the patient

Acknowledgements

None

Reviewer

Ayaz Lakdawala