Foot
The easy images of the foot to diagnose are the dislocations as in image 1 and the fractures of the long bones as in image 2. Occasionally however the patient may present with an occult fracture of the metatarsal known as a march fracture, named because soldiers are prone to them from too much marching. These are undisplaced fractures which are either very difficult or impossible to see. Image 3 shows the appearance when the patient returns for follow up. The fracture can be seen here but the important thing to notice is the callus formation around the fracture.

Images 4 to 11 cover the appearances of the base of the fifth metatarsal. This is quite a popular site for fractures in adults but not so much for children. It is the children however that get the mistaken diagnosis of a fracture. There is a general rule that says if the separation is transverse, image 4, it is a fracture and if the separation is longitudinal, image 5, it is an apophysis. However as with all rules they can be broken, see image 6, here the apophysis is multicentric (more than one ossification centre) and has a  transverse component as well as the usual longitudinal one, and in adulthood some fractures are longitudinal but it is a very good guide. Just remember as always, check for cortication of the fragment. Image 7 shows the early stage of ossification which is often mistaken for an avulsion fracture. Image 8 is another variation which appears to have been avulsed distally. Image 9 is an unusual appearance caused by irregular mineralisation of the apophysis. Images 10, 11 and 12 show that the fractures are not always so obvious, check for the disruption in the trabeculae. There is also a normal growth variant of an un-united apophysis, see the normal variants below.

Images 13 and 14 (14 courtesy of Michael Cotter, Bromley Hospital, Kent) show Lisfrank disruptions of the tarso-metatarsal joints. This is where there is a dislocation of the tarso-metatarsal joints often associated with a fracture at the base of the second metatarsal. The second metatarsal is longer than the others and sits, as it were, in a hole formed by the cuneiforms, and acts as a locating peg holding the tarso-metatarsal joints in place. This is demonstrated in image 15 which is a normal foot, if the image is clicked on it will outline the joint line showing the depression in which the second metatarsal is located. When the base of the second metatarsal is fractured the other joints become unstable and can dislocate quite easily. The example in image 13 is quite a bad one in that it can be seen that the first metatarsal along with the medial cuneiform has been forced proximally as well as the other metatarsals being dislocated proximally and slightly laterally, the base of the second metatarsal can be seen still articulating with the middle cuneiform while the shaft has displaced proximally all the way to the navicular. Dr. Lisfrank was a Napoleonic surgeon who would amputate the anterior foot across the tarso-metatarsal junction when an injured soldier had had his foot run over by a gun carriage, as there was little other treatment available.

Image 16 shows a fracture of the anterior horn of the calcaneum. This fracture is usually only seen on the oblique view or the lateral ankle. Take care as there is a normal growth variant, the os calcaneus secundrius, see below and image 30, which looks very similar, is it corticated?

Images 17 and 18 show some unusual avulsion fractures of the tarsals. Image 17 is an avulsion from the antero-lateral border of the calcaneum while image 18 is an avulsion from the postero-lateral border of the cuboid, both due to inversion injuries. Do not mistake these appearances for accessory ossicles as shown in images 36 to 38.

Fractures of the tarsal bones are often difficult to see. In image 19 it should be possible to see a lucency across the cuboid in the oblique view of the foot. Image 20 shows the DP projection where the widened fracture line is seen more clearly. Click on the image to have the fracture highlighted. Click on the new image to have the fragments highlighted. The viewer can scroll back up to see the original images.

Image 21 shows a normal calcaneum. This is here to demonstrate Bohler's angle which will help in the diagnosis of a calcaneal fracture if one is not obvious. If a line is drawn from the highest point of the posterior aspect to the highest mid point, then a second line is drawn from the highest anterior point to the highest midpoint, the bisecting angle should be in the region of 30-40 degrees. Image 22 will demonstrate this. In image 23 there is a fairly obvious fracture but it demonstrates well the decrease in Bohler's angle as seen in image 24. However the rule can always be broken as in image 25. A fairly obvious fracture with little reduction in Bohler's angle. As always these techniques are only guides. Image 26 shows an impacted fracture of the calcaneum which could easily be missed by an untrained eye. The fracture shows as a "sclerotic" line along with some disruption of the trabeculae, arrowed. The axial view, image 27 shows the step in the cortex proving the presence of a fracture.

Fractures of the smaller tarsal bones can be a little more difficult to see as the bones overly each other to some degree. Image 28 shows what is almost certainly a fracture of the superior aspect of the navicular, which was only visible on this lateral view. Care should be taken to check for cortication as this could be a large os supra-naviculare. The same rules of reporting apply in that all the bones should be checked individually looking at all the borders, articulations and trabecula patterns.

Images 29 and 30 show the unusual appearances of fractures of the medial cuneiform.

NORMAL VARIANTS.

The foot is a mine field of normal growth variants and accessory ossicles set to confuse the reporter. They just have to be learnt.

Image 31 shows the os calcaneus secundrius  which is a small accessory ossicle at the anterior horn of the calcaneum. This can easily be mistaken for a fracture as seen in image 16, but the difference here is that it is corticated.

Images 32 and 33 show the appearance of the os tibiale externum which is an accessory ossicle related to the navicular. As can be seen, they can be of varying size and separation from the navicular. The appearance on the lateral view as seen in image 34 is even more confusing as it looks like a fracture of the talus.

Image 35 shows the unusual appearance of irregular mineralisation of the apophysis of the base of fifth metatarsal.

 Image 36 shows the appearance of an un-united apophysis of the base of fifth metatarsal.

Image 37 is not for the fracture of the fifth metatarsal but the appearance of the os peroneum adjacent to the cuboid. These are usually singular but may be multiple as in image 38, and can be quite large as in image 39.

Image 40 shows the os supra-naviculare. Image 41 shows a smaller version which in this case is partially incorporated into the navicular. Image 42 shows a large articulated os supra-naviculare.

Images 43 and 44 show the os supra-talar. These often look very much like avulsion fractures, but the rule as always is to check the cortex. See image 45, this is an avulsion fracture from the superior aspect of the talus, see how it is not corticated.

Image 46 shows a talar beak with separation. Again, checking the cortex will show this to be a normal variant, not a fracture.

Image 47, although looking very much like a fracture, is os talus accessorius. Image 48 shows it in the A.P. view lying laterally with the line of separation arrowed. In the oblique foot view in image 49, it appears more corticated than the original lateral view.

Image 50 shows the very unusual appearance of a pair of accessory ossicles adjacent to the medial cuneiform.

Images 51 to 54 show normal variations of the calcaneal apophysis. It can have multiple ossification centres as in image 51 or a single one as in image 52. Image 53 shows a variation with a high secondary centre resembling an avulsion fracture. Image 54 (courtesy of Michael Cotter, Bromley Hospital, Kent) shows the appearance of a very dense apophysis.

Image 55 shows an interesting combination. This patient came to hospital after stubbing their little toe. There is an obvious fracture at the base of the proximal phalanx but note also the normal growth variant at the base of the distal phalanx. Due to the nature of the injury, this could easily be mistaken for a fracture, but note the different appearance of the un-corticated fracture and the corticated normal variant.

Image 56 shows the appearance of an accessory ossicle at the base of the distal phalanx of the hallux. Note also the unusual sesamoid projected to the left of the ossicle. The ossicle lies within the joint whereas the sesamoid lies within a tendon on the plantar aspect of the toe.

Images 57 and 58 show what appears to be a fracture of the medial aspect of the head of the first metatarsal. Careful scrutiny shows the fragment to be well corticated. This is in fact a normal growth variant which is probably due to fat necrosis.

Image 59 shows a small fragment of bone adjacent to the base of the proximal phalanx of the hallux. As this appears well corticated it will not be due to recent trauma and it is possible that it is due to an old injury. However, the M.T.P. joint is reduced due to degenerative changes and this fragment may also be due to those changes and could be the early stages of a hallux valgus.

Image 60 shows a small os intermetatarseum between the bases of the first and second metatarsals. These can be as long as the adjacent metatarsals.

 Image 61 shows a soft tissue anomaly. Appearances suggest an oblique fracture of the proximal phalanx of the fourth toe but in fact this appearance is caused by air trapped in the skin fold under the toe. See how the lucency curves and extends outside the margin of the bone to the right of the image. Another example of this can be seen on the paediatric arm page. Image 62 is a similar appearance but note there are no soft tissue shadows close to the phalanx on this occasion and there is a step in the cortex medially, this is a fracture!

Images 63 and 64 show a fused proximal and middle phalanx of the second toe.

Image 65 shows the appearance of the remnants of a bifid terminal phalanx. These can also occur in the fingers and can close at the end giving the appearance of a hole.

Image 66 has quite an array of normal growth variants, all arrowed. It shows "odontoid peg" like epiphyses at the base of the proximal phalanx of the third toe and the base of the terminal phalanx of the second toe, pseudo fractures at the heads of the middle phalanges of the second and third toes, and developmental linear lucencies in the terminal phalanx of the third toe.

Image 67 shows an exostosis which has occurred after a mal-union of the fracture seen in image 68.

Image 69 shows a simple bone cyst in the calcaneum, exclude other pathology such as a lipoma by referring to a radiologist.

Image 70 shows what appears to be a fracture of the navicular. It is actually quite well corticated and is an unfused cleft navicular, a normal growth variant. A similar example is seen on the "Paediatric Leg" page. Image 71 is the same foot at an earlier stage of development and it is seen quite clearly that this navicular has a very irregular ossification.