Deciding to Image the Foot and Ankle
- The Ottawa Ankle and Foot Rule states that an ankle series is only required if there is pain in the malleolar zone AND either bony tenderness in the distal 6cm of the posterior edge or tip of either the lateral OR medial malleolus OR the patient is unable to weightbear 4 steps both immediately and in the emergency department.
- It also states that a foot series is only required when there is pain in the midfoot AND there is tenderness of either the base of the 5th metatarsal OR navicular OR the patient is unable the weightbear for 4 steps both immediately and in the emergency department.
- For injuries that are not acute, clinical judgement would need to be utilised.
- Stress fractures may not show on x-ray and CT scan, bone scan or MRI may be required
- If you request an ankle x-ray, you will usually be presented with an AP, and oblique (mortise view) and a lateral.
- The foot series is a different subset and must be requested separately.
- In the emergency department, ultrasound is of little clinical use as it generally does not change acute management.
- For suspected ligament tears / ruptures, ultrasound can assist in diagnosis, although acute management generally does not change and thorough clinical assessment provides more detailed information regarding options for conservative management. Nonetheless, ultrasound is generally not indicated for acute injuries.
- Tendon tears / ruptures / avulsions on the other hand, do change management. The most often seen tendon that is ruptured about the ankle is the achilles tendon. Most often these can be diagnosed clinically, however ultrasound can assist in ambiguous cases. Other commonly ruptured tendons include tibialis posterior and the peroneals.
Ankle – Different Views
Ankle – AP and Oblique
- On the AP, the distal fibula overlaps the superolateral corner of the talus.
- In the mortise view, the ankle is rotated 15 degrees to allow viewing of the mortise. <5mm space is normal
Ankle – Fracture with Talar Shift
Ankle – Weber A Fracture
- Fracture of the distal fibula, below the syndesmosis
- Fracture of the distal fibula at the level of the syndesmosis
- Fracture of the distal fibula above the syndesmosis
- A Salter Harris Type III fracture involving avulsion of anterolateral tibial epiphysis which usually occurs in older adolescents
- If you request a foot x-ray, you will usually be presented with an AP and a lateral.
- Calcaneal views are indicated if there is potential injury to the calcaneus.
- For NON-ACUTE foot injuries, or injuries of the foot other than the midfoot, clinical judgement needs to be applied.
- Stress fractures may not show up on plain films and may require bone scan or CT / MRI to adequately image.
AP and Oblique
Calculating Bohler’s Angle
Foot – Abnormal X-rays
Foot – Fifth Metatarsal Base Fracture
The avulsion fracture does NOT extend into the 4th/5th intermetatarsal joint.
Foot – Jones Fracture
A Lis Franc injury involves the union with the medial cuneiform and the 2nd metatarsal base. If missed, this can be a particularly debilitating injury. In this film, there is a “fleck” sign – a small avulsed fragment from the base of the 2nd metatarsal.
Foot – Navicular Avulsion
The plantar calcaneonavicular (“spring”) ligament attaches to the proximal navicular and is one of the major structures providing support for the medial longitudinal arch.
Foot – Os TrigonumThe os trigonum is an accessory ossicle resulting from incomplete fusion of the posterior process of the talus. This is a normal anatomical variant.