Orthopaedic X-Ray Interpretation
February 15th, 2021
Overview
X-rays are commonly used in clinical practice to diagnose fractures. Characteristics of the fracture such as the type, deformity and soft tissue / joint involvement are used to guide management.
First Steps
Ensure that you are looking at the correct patient - check the name and date of birth.
Look at the film details - the date and time the film was taken, what site has been imaged, and what side was imaged.
Look at what projections have been taken. Aim to get at least two views for any fracture film - e.g. AP, lateral or oblique.
Assess the exposure of the film - whether the image appears overpenetrated or underpenetrated.
Assessment of Bone
To assess for a fracture, follow the edges of the bone around carefully looking for an obvious discontinuity of the cortex.
Location of Fracture
- If a fracture is seen, note the location of the fracture: whether it is proximal or distal, and whether it involves the growth plate in children.
Type of Fracture
- Assess for whether the fracture is complete or incomplete, and what type of fracture is present - this will suggest a potential mechanism, and guide management.
A complete fracture is a break all the way through the bone, producing two or more fragments.
- Transverse fracture - a fracture straight across the bone
- Oblique fracture - a fracture at an angle to the bone
- Spiral fracture - a corkscrew-shaped fracture around the boneOccurs due to twisting of a long bone
- Comminuted fracture - the bone has been shattered into multiple pieces
- Avulsion fracture - avulsion of a fragment of bone away from the main body of the bone
An incomplete fracture (fissure, torus or greenstick fracture) is a break that does not pass through the entirety of a bone. This may be associated with bending of a long bone. Incomplete fractures tend to occur in children, whose bones are more flexible than adults. If the force applied on the bone is greater than the mechanical strength of the bone then it will remain bent.
- Bowing fracture - bending of a bone without a visible breakOccurs due to an angulated longitudinal force
- Fissure - an incomplete cortical break without bending
- Torus (buckle) fracture - bending of a bone with a compression fracture and outward bulging of the cortexOccurs due to axial loading
- Greenstick (buckle) fracture - bending of a bone on one side with a crack on the opposite sideOccurs due to an angulated longitudinal force or direct perpendicular trauma
Fracture Deformity
- Look For displacement, shortening, angulation or rotation of a fracture fragment. This is reported as the deformity of the distal fragment in relation to the proximal fragment.
- Displacement - dorsal (posterior), volar (anterior) or lateral displacement of the distal fragment with respect to the proximal fragment.
- Shortening - overlapping of fracture ends
- Angulation - the angle created between the distal fragment and the proximal fragment due to the fracture.
- Rotation - of the bone along its long axis
Soft Tissue Involvement
- Look for obvious protrusion of bone through the soft tissues, or air within the soft tissues.
A compound / openfracture communicates with the skin surface and is at much higher risk of complications; a simple / closed fracture does not communicate with the surface.
Joint Involvement
- Look for involvement of the fracture through a joint, which may be associated with joint dislocation. If a fracture involves a joint, then it is identified as intra-articular; this suggests that the fracture is unstable and unlikely to heal without surgical intervention.
Growth Plate Involvement
- In children (whose bones are still growing), assess for whether the fracture involves the growth plate. Such fractures have the potential of interrupting the proliferative zone, halting bone growth. Higher grade fractures are at higher risk.
The method used for classifying these fractures is the Salter-Harris classification, which can be remembered using the mnemonic SALTR:
- IStraight through - fracture directly across the growth plate, not involving surrounding boneGood prognosis
- IIAbove - fracture across the growth plate and up through the metaphysis (most common)Good prognosis
- IIILower - fracture across the growth plate and down through the epiphysisPoor prognosis - interruption of the proliferative zone
- IVTransverse - fracture directly through the metaphysis, growth plate and epiphysisPoor prognosis - interruption of the proliferative zone
- VRuined / rammed - direct compression of the growth plateWorst prognosis
Bone Density
- Assess the density of the bone - whether it is increased or decreased.
- Types of reduction in bone density are:
- Generalised osteopaenia - an overall reduction in bone density. This suggests an imbalance in bone deposition and resorption, placing the bone at risk of pathologic fractures. This commonly occurs in post-menopausal women, in the elderly, as well as due to genetic, endocrine, nutritional, haematologic and drug causes.
- Periarticular osteopaenia - a reduction in bone density surrounding joints; this is classically a sign of rheumatoid arthritis.
- Lytic lesions - focal areas of bony hypodensity, which are classically a sign of multiple myeloma.
- Types of increased bone density are:
- Generalised osteosclerosis - an overall increase in bone density. This may be due to endocrine disease such as hypoparathyroidism; osteoblastic metastasis, or certain congenital diseases.
- Subchondral osteosclerosis - increased bone density surrounding a joint, in the subchondral layer. This is a classic radiologic sign of osteoarthritis.
Foreign Body
- Look for foreign bodies in or surrounding the bone. The patient may have plates, nails or other orthoses in situ from previous surgery. Shrapnel may also be present following trauma.
Assessment of Joints
Joint Position
Assess for subluxation or dislocation of the joints. This may affect one of many joints - in particular the:- Fingers - including the thumbs
- Elbows - most commonly dislocate posteriorly, particularly wih fractures of the radial head, olecranon or coranoid process.
- Shoulders - dislocate anteriorly in 95% of cases
- Hips - dislocate posteriorly in 90% of cases
- Patellae - tends to dislocate laterally
Note whether any dislocations are associated with a fracture, as this would be referred to as a complex dislocation, or fracture-dislocation.
Joint Effusions
- Look for fluid within the joint; also known as a joint effusion. This may be traumatic or associated with inflammation - such as with infection, osteoarthritis, autoimmune arthritis crystal arthropathy or malignancy.
To assess for an effusion of the knee, look for fluid within the suprapatellar pouch, as well as for fluid in Hoffa's triangle (anteriorly, between the femur and tibia).
To assess for an effusion of the ankle, look for a teardrop-shaped hyperdensity anterior to the ankle joint, due to displacement of the pretalar fat pad by fluid within the joint space.
Signs of Osteoarthritis
Four key signs suggest the presence of osteoarthritis:
- Reduced joint space - generally asymmetric
- Subchondral sclerosis: increased bone deposition surrounding the joint
- Subchondral cysts: cystic formations around the joint
- Osteophytes: bony projections along the joint line
Signs of Rheumatoid Arthritis
There are four key findings on x-ray that suggest a diagnosis of rheumatoid arthritis:- Reduced joint space - generally symmetric
- Articular surface erosions: discontinuities in the bone plate
- Periarticular osteopaenia: hypodensity of bone surrounding the joint
- Soft tissue swelling
Assessment of Soft Tissues
Air Within Soft Tissues
- Look for air within the soft tissues, especially around the site of a fracture. Presence of air is indicative of a compound fracture.
Foreign Body
- Look for foreign bodies within the soft tissues - particularly shrapnel which may have been deposited during penetrating injury.
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