Smith Fracture

Smith fracture is a distal radius fracture with volar displacement and angulation of the distal fragment, the reverse of a Colles fracture. It is also called a reverse Colles fracture, and the wrist has a "garden spade" deformity.

It makes up about 3 to 5% of distal radius fractures. The usual mechanism is a fall on the flexed wrist or onto the dorsum of the hand, or a direct blow to the dorsal distal forearm. Both young adults (high energy) and older women (fragility) are affected.

The Thomas classification divides them into type I (extra-articular, transverse), type II (oblique, entering the joint, the commonest and the volar Barton equivalent) and type III (juxta articular oblique).

Complications are malunion with limited wrist extension, median nerve compression, finger stiffness, flexor tendon injury, complex regional pain syndrome and post-traumatic arthritis in intra-articular injuries.

Pathophysiology.

The distal fragment is driven volarly by the force and by pull of the pronator quadratus. Volar displacement leaves a bony deficit on the volar side that the usual cast cannot hold, so Smith fractures are inherently unstable.

Wrist pain, swelling and a garden spade deformity with a volar prominence of the distal fragment, and tenderness over the distal radius. Test the median nerve (thumb to ring finger numbness, thenar weakness) and the other nerves, and check pulses and skin. Examine the distal radioulnar joint, the snuffbox and the elbow.

• Radiographs: posteroanterior and lateral wrist. The lateral view shows volar tilt of the distal fragment (over the usual 11 degrees), volar displacement, and shortening.
• CT for intra-articular extension and for planning a volar buttress plate.
• Bone health tests in fragility fractures: calcium, 25-hydroxyvitamin D, creatinine and eGFR.

Differential diagnosis.

• Colles fracture and volar Barton fracture.
• Chauffeur fracture and scaphoid fracture.
• Radiocarpal dislocation and perilunate dislocation.
• Distal radioulnar joint injury.

Reduction. A haematoma block with lidocaine 1% (10 mg/mL) 5 to 10 mL into the fracture haematoma as a single administration (maximum 4.5 mg/kg of plain lidocaine and not exceeding 300 mg).

Precautions with the block:

• monitoring for toxicity (perioral numbness, tinnitus, drowsiness)
• avoiding with infection at the site or allergy
• reducing the volume in hepatic impairment

Traction with the forearm supinated, then pressure on the distal fragment toward dorsal, and hold the wrist in slight extension.

Long arm cast in supination for 6 weeks, because the supinated forearm relaxes the brachioradialis pull.

Surgery. Most Smith fractures are unstable, and cast treatment often fails, so surgery is the usual treatment: open reduction and fixation with a volar buttress or locking plate through the flexor carpi radialis approach. Kirschner wires (1.6 mm) can supplement fixation for small fragments. Cast treatment is limited to undisplaced stable fractures.

Analgesia.

• Paracetamol 1 g orally every 6 hours as needed for up to 5 to 7 days (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Ibuprofen 400 mg orally every 8 hours with food for up to 5 days (maximum 1200 mg daily); avoid with eGFR under 30 mL/min/1.73 m2, peptic ulcer, heart failure or anticoagulant use.
• Oral morphine 5 to 10 mg every 4 hours as needed for severe pain for up to 3 days (start 2.5 to 5 mg with age over 75 or eGFR under 30 mL/min/1.73 m2; avoid exceeding 60 mg in 24 hours without senior review); monitor sedation and respiration and prescribe a laxative.

Complex regional pain syndrome prevention. Vitamin C (ascorbic acid) 500 mg orally once daily for 50 days from the day of injury (maximum 500 mg daily; the evidence is moderate). Avoid with a history of oxalate kidney stones, and limit with eGFR under 30 mL/min/1.73 m2. No routine monitoring.

Secondary prevention after a fragility fracture. Alendronate 70 mg orally once weekly, fasting with a full glass of water and kept upright for 30 minutes, for 5 years then reassess (maximum 70 mg weekly); check calcium, 25-hydroxyvitamin D and creatinine before starting and yearly; avoid with eGFR under 35 mL/min/1.73 m2, uncorrected hypocalcaemia or oesophageal stricture.

Zoledronic acid 5 mg intravenously over at least 15 minutes once yearly (3 years then reassess) when oral therapy is not tolerated and eGFR is 35 mL/min/1.73 m2 or over, checking creatinine and calcium before each dose. Colecalciferol 800 to 2000 IU orally daily with dietary calcium to a total of 1000 to 1200 mg daily (maximum total 2000 mg daily); correct vitamin D deficiency first.

Monitoring. Radiographs at 1 week, 2 weeks and 6 weeks. Median nerve and finger movement at each visit. Complex regional pain syndrome signs at 2 to 6 weeks. Wrist range and grip at 3 months.

Referral and escalation. Refer every displaced Smith fracture to orthopaedics within 1 week, since surgery is usually needed. Same day referral for open fracture, skin compromise, acute median nerve compression, or neurovascular compromise.

Special groups.

• Children: most are buckle or greenstick injuries managed in a cast for 3 to 4 weeks.
• Older adults: fragility fracture needs bone health assessment.
• Kidney impairment: avoid ibuprofen and bisphosphonates at eGFR under 35 mL/min/1.73 m2; reduce morphine doses.
• Pregnancy: avoid bisphosphonates; use paracetamol and a cast.