Clinical imaging: Musculoskeletal and trauma imaging

• Principles: Principles of Musculoskeletal Imaging | Describing a Fracture | Children's Fractures and Safeguarding
• Fractures by region: Shoulder and Elbow | Wrist and Hand | Hip and Pelvis | Knee, Ankle and Foot | Thoracolumbar Spine
• Joints and bone disease: Arthritis on X-ray | Bone Tumours and Aggressive Lesions | Metastases, Myeloma and Metabolic Bone Disease | Bone and Joint Infection | The Child's Hip | Soft Tissue Imaging — Ultrasound and MRI
• Major trauma: Imaging in Major Trauma
• Revision: MSK and Trauma Imaging at a Glance | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🩻 Musculoskeletal and trauma imaging — page 5 of the Clinical Imaging chapter. Bone and joint X-rays are among the commonest films interpreted by front-line doctors — often in the ED before a radiologist sees them — and missed fractures (scaphoid, hip, posterior shoulder dislocation, cervical spine in older people) are a frequent source of harm. This page covers how to describe fractures, the decision rules that tell you who needs a film, the patterns of arthritis and bone disease, and imaging in major trauma.
Your four questions for every musculoskeletal image: Do I have two views at right angles, and the joints above and below? Is there a fracture or dislocation — and is it stable, open, or involving a joint or growth plate? If the film is normal but the clinical suspicion is high, what's the next test? Could this be a pathological fracture or non-accidental injury?

Principles of Musculoskeletal Imaging

• Plain X-ray first for most bone injuries and bone pain.
• Rule of twos:
  • Two views at right angles (e.g. AP and lateral) — a fracture or dislocation can be invisible on one view.
  • Two joints — include the joint above and below for long bone fractures (e.g. Maisonneuve, Monteggia, Galeazzi injuries).
  • Two sides — compare with the other side in children (ossification centres).
  • Two occasions — repeat films at 10–14 days for occult fractures (scaphoid), or use MRI.
• Clinical decision rules reduce unnecessary films — Ottawa ankle and knee rules, Canadian C-spine rule.
• CT — complex and intra-articular fractures (tibial plateau, calcaneus, acetabulum, pelvis), spine, surgical planning; occult fractures when MRI isn't available.
• MRI — occult fractures (hip, scaphoid, stress fractures), ligaments, menisci, cartilage, tendons, bone marrow (osteomyelitis, tumours, avascular necrosis), spinal cord.
• Ultrasound — tendons, muscles, joint effusions (guided aspiration), soft tissue lumps, foreign bodies, infant hips.
• Nuclear medicine — bone scan (metastases, stress fractures, occult fractures when MRI isn't possible); PET-CT (sarcoma staging, infection in selected cases).
• Look beyond the fracture — bone density, lytic lesions (pathological fracture), soft tissue swelling, joint effusion (fat pads, lipohaemarthrosis), foreign bodies.

Describing a Fracture

• Patient and film — name, date, views, side.
• Bone and location — which bone; diaphysis (shaft), metaphysis, epiphysis; proximal, middle or distal third; intra-articular or extra-articular.
• Pattern:
  • Transverse (direct blow), oblique, spiral (twisting — in a non-mobile child, consider NAI).
  • Comminuted (more than two fragments), segmental, butterfly fragment.
  • Avulsion (tendon or ligament pulls off bone — e.g. base of the fifth metatarsal).
  • Impacted, compression (vertebral body), stress fracture, pathological (through abnormal bone — tumour, metastasis, Paget's).
• Displacement — translation (as % of bone width), angulation (direction of the distal fragment's apex — e.g. dorsal angulation), rotation (often clinical), shortening, distraction.
• Joint involvement — intra-articular step, dislocation or subluxation.
• Open or closed — any wound over a fracture is open until proven otherwise (antibiotics within 1 hour, tetanus, photograph, cover — BOAST).
• Soft tissue and neurovascular status — document distal pulses, sensation and movement before and after manipulation.
• Example — "AP and lateral X-rays of the left wrist show a transverse extra-articular fracture of the distal radial metaphysis with dorsal angulation of 25° and dorsal displacement, consistent with a Colles' fracture."

Children's Fractures and Safeguarding

• Children's bones are softer, with growth plates (physes) — different fracture patterns:
  • Buckle (torus) — bulging of the cortex (distal radius) — stable — removable splint, no routine follow-up X-ray (NICE NG38).
  • Greenstick — one cortex breaks, the other bends.
  • Plastic deformation — bowing without a visible fracture line.
• Salter–Harris classification (growth plate injuries) — "SALTR":

  Type	Description	Notes
  I — Straight	Through the physis only	X-ray may look normal (widened physis)
  II — Above	Physis plus metaphysis	Commonest; good prognosis
  III — Lower	Physis plus epiphysis (intra-articular)	Needs accurate reduction
  IV — Through	Metaphysis, physis and epiphysis	Growth disturbance risk
  V — Rammed	Crush of the physis	Often missed; worst prognosis

• Suspected physical abuse (non-accidental injury) — fractures suggesting abuse:
  • Any fracture in a non-mobile infant (not yet crawling or walking).
  • Metaphyseal corner ("bucket handle") fractures, posterior rib fractures (squeezing), scapular, sternal and spinous process fractures, complex skull fractures.
  • Multiple fractures of different ages (healing stages).
  • History inconsistent with the injury or developmental stage; delayed presentation.
• Imaging for suspected abuse (RCR/SCoR guidance) — skeletal survey in children under 2 (and selected older children), repeat limited survey at 11–14 days (healing fractures become visible); CT head in infants under 1 (and considered in under 2s) — subdural haematomas, skull fractures; ophthalmology (retinal haemorrhages); follow local safeguarding procedures.
• Differentials — osteogenesis imperfecta, rickets, birth injury, accidental injury, leukaemia.

Shoulder and Elbow

• Anterior shoulder dislocation (about 95%) — fall on an outstretched or abducted, externally rotated arm — humeral head lies anterior and inferior to the glenoid (below the coracoid) on AP; confirm on a lateral (Y or axial) view; associated Hill–Sachs lesion (humeral head impaction) and Bankart lesion (anterior glenoid labrum or bone); check axillary nerve (regimental badge sensation) before and after reduction; post-reduction X-ray.
• Posterior shoulder dislocation — seizures, electric shock, direct blow — often missed on AP: "lightbulb" sign (internally rotated humeral head), widened glenohumeral space, axial or Y view essential.
• Proximal humerus fractures — older people after falls (osteoporosis); clavicle fractures (middle third commonest); acromioclavicular joint injuries.
• Elbow:
  • Fat pad signs — a visible posterior fat pad (or a raised "sail-shaped" anterior fat pad) indicates an effusion — assume an occult fracture (adults — radial head; children — supracondylar).
  • Supracondylar fracture (children, fall on outstretched hand) — the anterior humeral line should pass through the middle third of the capitellum (passes anterior in extension-type fractures) — check brachial artery and median, radial and ulnar nerves (anterior interosseous nerve); compartment syndrome risk.
  • Ossification centres (approximate age in years) — "CRITOE": Capitellum 1, Radial head 3, Internal (medial) epicondyle 5, Trochlea 7, Olecranon 9, External (lateral) epicondyle 11 — an "ossification centre" seen out of order may be an avulsed medial epicondyle trapped in the joint.
  • Radiocapitellar line — a line along the radial shaft should pass through the capitellum on every view — if not, radial head dislocation.
  • Monteggia — proximal ulna fracture with radial head dislocation; Galeazzi — distal radius fracture with distal radioulnar joint dislocation ("MUGR" — Monteggia Ulna, Galeazzi Radius).
  • Pulled elbow (radial head subluxation — toddlers) — X-ray not needed if typical history and reduction works.

Wrist and Hand

• Distal radius fractures:
  • Colles' — extra-articular distal radius fracture with dorsal angulation ("dinner fork") — fall on outstretched hand — postmenopausal women (osteoporosis).
  • Smith's — volar angulation (fall on a flexed wrist).
  • Barton's — intra-articular fracture of the dorsal or volar rim with carpal subluxation.
  • Assess radial height, inclination and volar tilt; DEXA and fracture liaison referral in older people.
• Scaphoid fracture:
  • Young adults — fall on outstretched hand — anatomical snuffbox tenderness, scaphoid tubercle tenderness, pain on axial thumb compression.
  • Scaphoid series (4 views) — up to 1 in 5 fractures are not visible initially.
  • Clinically suspected with normal X-rays — immobilise and arrange early MRI (preferred — RCEM/BSSH pathways) or CT; or repeat X-ray at 10–14 days.
  • Complications — avascular necrosis of the proximal pole (retrograde blood supply), non-union, arthritis.
• Carpal dislocations — lunate and perilunate dislocations — "spilled teacup" on the lateral view; median nerve symptoms — easily missed — urgent orthopaedics.
• Scapholunate dissociation — gap over 3 mm ("Terry Thomas" sign).
• Hand — boxer's fracture (fifth metacarpal neck — check for fight bite wounds over the knuckle — antibiotics and washout), Bennett's fracture (intra-articular base of first metacarpal — unstable), mallet finger (avulsion at the distal phalanx base), gamekeeper's thumb (ulnar collateral ligament — Stener lesion), volar plate avulsions.

Hip and Pelvis

• Hip fracture — older people after a fall — pain, inability to weight-bear, shortened and externally rotated leg.
  • X-rays — AP pelvis and lateral hip; look at Shenton's line (smooth arc from the inferior femoral neck to the superior pubic ramus — disrupted in displaced fractures), trabecular pattern, cortical outline.
  • Intracapsular (subcapital, transcervical — Garden I–IV) — blood supply to the head at risk — undisplaced: screw fixation (or arthroplasty in older people); displaced: hemiarthroplasty or total hip replacement.
  • Extracapsular (intertrochanteric, subtrochanteric) — dynamic hip screw or intramedullary nail.
  • Occult hip fracture — if suspected despite negative X-rays, MRI (NICE CG124); if MRI isn't available within 24 hours or is contraindicated — CT.
  • Surgery — on the day of or the day after admission (NICE CG124); also look for pubic rami and acetabular fractures.
• Pelvic fractures:
  • Low-energy (older people) — pubic rami fractures — often occult; CT or MRI if pain persists and X-rays are normal; associated sacral insufficiency fractures.
  • High-energy — the pelvis is a ring — usually breaks in two places; open-book (anteroposterior compression), lateral compression, vertical shear — major haemorrhage risk — pelvic binder before imaging in unstable patients; CT; interventional radiology (embolisation) or surgical packing.
  • Acetabular fractures — CT for planning.
• Hip dislocation — usually posterior (knee hits the dashboard) — leg shortened, flexed, adducted and internally rotated — sciatic nerve injury; reduce urgently (avascular necrosis risk).
• Avascular necrosis of the femoral head — steroids, alcohol, sickle cell disease, previous fracture — MRI (early), later X-ray (crescent sign, collapse).

Knee, Ankle and Foot

• Ottawa knee rule — X-ray if any of: age 55 or over, isolated patella tenderness, fibular head tenderness, inability to flex to 90°, inability to bear weight (4 steps) immediately and in the ED.
• Knee X-ray signs:
  • Lipohaemarthrosis — fat–fluid level on a horizontal-beam lateral — intra-articular fracture (e.g. tibial plateau — CT).
  • Segond fracture — small avulsion from the lateral tibial plateau — strongly associated with ACL rupture.
  • Patellar fractures (vs bipartite patella — superolateral, smooth, often bilateral).
• MRI knee — ligament (ACL, PCL, collaterals) and meniscal tears, bone bruising, cartilage; not needed for degenerative knee pain in older adults.
• Ottawa ankle rules — ankle X-ray if pain in the malleolar zone and any of: bone tenderness at the posterior edge or tip of the lateral or medial malleolus (distal 6 cm), or inability to bear weight both immediately and in the ED (4 steps). Foot X-ray if midfoot pain and tenderness at the base of the fifth metatarsal or the navicular, or inability to bear weight.
• Ankle fractures — Weber classification (lateral malleolus relative to the syndesmosis):
  • Weber A — below the syndesmosis — usually stable — boot and weight-bear.
  • Weber B — at the level of the syndesmosis — may be unstable (check medial clear space, medial malleolus, weight-bearing films).
  • Weber C — above the syndesmosis — syndesmosis disrupted — unstable — surgical fixation.
  • Bimalleolar and trimalleolar fractures, talar shift — unstable; fracture-dislocation — reduce immediately (skin and neurovascular compromise) before X-ray if limb-threatening.
  • Maisonneuve fracture — medial ankle injury with a proximal fibular fracture — examine and image the whole fibula.
• Foot — fifth metatarsal base (avulsion — usually heals well) vs Jones fracture (proximal diaphysis — poor healing), Lisfranc injury (tarsometatarsal — easily missed — weight-bearing films or CT), calcaneal fractures (falls from height — Böhler's angle under 20°; look for spinal fractures), stress fractures (metatarsals — MRI or repeat X-ray).
• Achilles tendon rupture — clinical (Simmonds' test); ultrasound if uncertain.

Thoracolumbar Spine

• Osteoporotic vertebral fractures — the commonest osteoporotic fracture — often painless or minor trauma; anterior wedge or biconcave deformity, height loss, kyphosis; often unreported on chest X-ray or CT — FRAX, DEXA and bone protection; MRI (STIR) distinguishes acute from old fractures and from malignancy.
• Red flags for pathological fracture — cancer history, weight loss, night pain, posterior element involvement, soft tissue mass, involvement above T4 — MRI.
• Traumatic fractures:
  • Burst fracture — axial load (falls from height) — retropulsed fragments into the canal — CT and MRI.
  • Chance fracture — flexion-distraction (lap seatbelt) — horizontal fracture through the vertebra — associated abdominal (bowel, pancreas) injuries.
  • Three-column concept — injury to two or more columns is unstable.
  • Calcaneal fractures after falls — look for thoracolumbar fractures too.
• Ankylosing spondylitis and DISH — rigid spine fractures are unstable and easily missed — CT (whole spine) after any trauma.
• Spondylolysis and spondylolisthesis — pars defect ("Scottie dog collar" on oblique films) — adolescents in sport; slip grading.
• Discitis and vertebral osteomyelitis — MRI with contrast (see page 4).
• Non-specific back pain — no routine imaging (NICE NG59).

Arthritis on X-ray

• Early inflammatory arthritis — X-rays may be normal; ultrasound (synovitis, power Doppler) and MRI detect early disease.
• Knee OA in over-45s with typical symptoms — clinical diagnosis without imaging (NICE NG226); X-ray if atypical or before referral for surgery.

Bone Tumours and Aggressive Lesions

• Features of an aggressive (likely malignant) bone lesion:
  • Wide zone of transition (ill-defined margin) — permeative or moth-eaten bone destruction.
  • Aggressive periosteal reaction — Codman's triangle, sunburst (spiculated), "onion skin" (lamellated).
  • Cortical destruction and a soft tissue mass.
  • Rapid growth, pain at night.
• Benign features — narrow zone of transition, sclerotic rim, no or solid periosteal reaction, no soft tissue mass.
• Primary bone tumours:

  Tumour	Features
  Osteosarcoma	Teenagers (and older adults with Paget's); metaphysis around the knee; sunburst and Codman's triangle; lung metastases
  Ewing sarcoma	Children and teenagers; diaphysis of long bones and pelvis; "onion skin" periosteal reaction; fever and raised inflammatory markers (mimics infection)
  Chondrosarcoma	Older adults; pelvis, femur, shoulder; "rings and arcs" chondroid calcification
  Giant cell tumour	Young adults (20–40); epiphyseal, eccentric, lytic "soap bubble" lesion extending to the joint surface (around the knee)
  Osteoid osteoma	Young people; night pain relieved by NSAIDs; small lucent nidus with dense surrounding sclerosis — CT; radiofrequency ablation
  Simple bone cyst	Children; proximal humerus or femur; "fallen fragment" sign after pathological fracture
  Enchondroma	Hand bones; lytic with chondroid calcification; Ollier's disease (multiple)
  Non-ossifying fibroma	Children; eccentric metaphyseal lucency with a sclerotic border — benign "don't touch" lesion

• Suspected bone sarcoma (NICE NG12) — urgent X-ray within 48 hours for children and young people with unexplained bone swelling or pain; if the X-ray suggests sarcoma — very urgent referral (within 48 hours) to a specialist sarcoma service; don't biopsy outside the sarcoma centre (contaminates the surgical field).
• Night pain or persistent bone pain in a young person needs an X-ray — don't label it "growing pains" without examination.

Metastases, Myeloma and Metabolic Bone Disease

• Bone metastases — far more common than primary bone tumours in adults:
  • Lytic — kidney, thyroid, lung, breast, melanoma; sclerotic — prostate, breast (often mixed), carcinoid.
  • Sites — spine, pelvis, ribs, proximal femur and humerus.
  • Imaging — bone scan (sensitive for sclerotic metastases — prostate, breast), CT, MRI (spine, marrow), PSMA or FDG PET-CT.
  • Impending pathological fracture — lytic lesion over 2/3 of cortical width, pain on weight-bearing (Mirels' score) — prophylactic fixation and radiotherapy.
• Myeloma — multiple lytic "punched-out" lesions (skull — "pepper pot"), diffuse osteopenia, vertebral collapse; bone scan is often normal ("cold") — use whole-body low-dose CT or whole-body MRI (NICE NG35).
• Paget's disease — older adults; raised ALP with normal calcium; X-ray — thickened cortex, coarse trabeculae, bone enlargement, "cotton wool" skull, osteoporosis circumscripta, bowed tibia; bone scan — intense uptake; complications — deafness, fractures, osteosarcoma (rare); IV zoledronic acid for bone pain.
• Osteoporosis — DEXA (T-score −2.5 or less; −1 to −2.5 osteopenia); X-ray osteopenia is unreliable.
• Osteomalacia and rickets — Looser's zones (pseudofractures — lucent bands perpendicular to the cortex — pubic rami, femoral neck, scapula); rickets — cupping and fraying of metaphyses, widened growth plates, bowed legs, "rachitic rosary".
• Hyperparathyroidism — subperiosteal resorption (radial side of middle phalanges), "salt and pepper" skull, brown tumours, chondrocalcinosis.
• Renal osteodystrophy — "rugger jersey" spine (sclerotic end plates), vascular calcification.
• Sickle cell disease — avascular necrosis, bone infarcts, "H-shaped" vertebrae, osteomyelitis (Salmonella).

Bone and Joint Infection

• Septic arthritis — hot, swollen, painful joint with restricted movement — joint aspiration before antibiotics (ultrasound-guided for the hip and deep joints) — don't delay for imaging; X-ray is often normal early but provides a baseline (and excludes fracture or chondrocalcinosis).
• Acute osteomyelitis:
  • X-ray changes appear after 10–14 days (periosteal reaction, lytic destruction, sequestrum and involucrum in chronic disease) — a normal early X-ray doesn't exclude it.
  • MRI is the most sensitive and specific test (marrow oedema, abscess, extent); bone scan or white cell scan if MRI isn't possible.
  • Children — haematogenous spread to metaphyses (Staph aureus, Kingella in under-4s).
• Diabetic foot osteomyelitis (NICE NG19) — X-ray first; MRI if osteomyelitis is suspected and X-ray doesn't confirm it; probe-to-bone test; bone biopsy for microbiology.
• Prosthetic joint infection — X-ray (loosening, lucency), aspiration (orthopaedic team), nuclear medicine in selected cases.
• Necrotising fasciitis — surgery shouldn't wait for imaging; CT may show gas in the soft tissues and fascial fluid.
• Foreign bodies — glass and metal are usually visible on X-ray; wood and plastic often aren't — ultrasound.

The Child's Hip

• Developmental dysplasia of the hip (DDH) — risk factors (breech presentation, first-degree family history) or abnormal examination (Barlow, Ortolani) — ultrasound in infants under about 4–5 months (NIPE screening — by 6 weeks if risk factors, within 2 weeks if abnormal examination); X-ray once the femoral head ossifies (after about 4–6 months).
• Transient synovitis (irritable hip) — age 3–8, after a viral illness, well child, limp — ultrasound shows effusion but can't distinguish from septic arthritis.
• Septic arthritis of the hip — fever, unable to weight-bear, raised CRP and WCC (Kocher criteria) — urgent ultrasound-guided aspiration and orthopaedics.
• Perthes disease — boys aged 4–8 — avascular necrosis of the femoral head — limp, hip or knee pain — X-ray: flattened, fragmented, sclerotic femoral head; MRI early.
• Slipped upper femoral epiphysis (SUFE) — overweight adolescent boys (10–15), hip or knee pain, limp, loss of internal rotation — AP and frog-leg lateral X-rays of both hips — Klein's line (along the superior femoral neck) fails to intersect the epiphysis; bilateral in up to a third — urgent surgical pinning.
• Knee pain in a child — always examine (and image if needed) the hip.
• Other — Osgood–Schlatter (tibial tuberosity — clinical), osteomyelitis, leukaemia (bone pain, cytopenias), bone tumours.

Soft Tissue Imaging — Ultrasound and MRI

• Ultrasound:
  • Rotator cuff tears and tendinopathy, subacromial bursitis — and guided injections.
  • Tendon ruptures (Achilles, quadriceps, biceps), muscle tears and haematomas.
  • Joint effusions and synovitis; guided aspiration.
  • Soft tissue lumps — lipoma, ganglion, Baker's cyst (and rupture — mimics DVT; scan both), abscess, foreign bodies, Morton's neuroma.
  • Soft tissue sarcoma (NICE NG12) — urgent direct-access ultrasound (within 2 weeks) for adults with an unexplained lump that is increasing in size; refer on a suspected cancer pathway if the scan suggests sarcoma or is uncertain; red flags — over 5 cm, deep to fascia, growing, painful, recurrent after excision.
• MRI:
  • Knee — menisci, cruciate ligaments, cartilage, bone bruising.
  • Shoulder — labral tears (MR arthrogram), rotator cuff.
  • Hip — labral tears, femoroacetabular impingement, avascular necrosis, occult fractures.
  • Wrist — occult scaphoid fractures, ligament injuries.
  • Bone marrow — stress fractures, bone bruises, osteomyelitis, tumour infiltration.
  • Inflammatory — sacroiliitis in axial spondyloarthritis, myositis (guides biopsy), enthesitis.
  • Soft tissue masses — characterisation and sarcoma staging.
• Imaging isn't always needed — most soft tissue injuries and degenerative joint pain are clinical diagnoses.

Imaging in Major Trauma

• Primary survey first (<C>ABCDE) — control catastrophic haemorrhage; imaging must not delay life-saving treatment.
• Adjuncts to the primary survey:
  • Chest X-ray (supine) — haemothorax, pneumothorax, widened mediastinum, tube positions.
  • Pelvic X-ray — pelvic ring injury (if not going straight to CT).
  • eFAST — free fluid in the abdomen (hepatorenal, splenorenal, pelvis), pericardial fluid, pneumothorax — a positive FAST in an unstable patient supports going to laparotomy; a negative FAST doesn't exclude injury (retroperitoneal bleeding, hollow viscus).
• Whole-body CT (NICE NG39) — for adults with blunt major trauma and suspected multiple injuries — vertex to toes (or mid-thigh) — rapid, comprehensive; reported immediately (provisional "hot" report).
• Patients too unstable for CT — straight to theatre or interventional radiology (damage control); don't take unstable patients to CT unless the trauma team leader decides the benefit outweighs the risk.
• Children — targeted imaging (not routine whole-body CT) to reduce radiation; ultrasound and clinical assessment; CT head and c-spine by specific criteria.
• Key CT findings:
  • Active contrast extravasation ("blush") — ongoing bleeding — interventional radiology (embolisation of spleen, liver, kidney, pelvic arteries) or surgery.
  • Solid organ injury grading (spleen, liver, kidney) — many managed non-operatively.
  • Traumatic aortic injury, diaphragmatic rupture, bowel injury (free fluid without solid organ injury), pneumothorax, spinal fractures.
• Penetrating trauma — CT in stable patients; unstable patients go to theatre.
• Tertiary survey within 24 hours — re-examination for missed injuries (fingers, toes, ribs).
• Major trauma networks — major trauma centres with 24/7 CT and interventional radiology.

MSK and Trauma Imaging at a Glance