Bennett's Fracture

Upper Limb

Overview

Bennett's fracture is an intra-articular fracture-dislocation of the base of the first metacarpal (thumb), characterized by a medial shaft fracture with dorsal displacement of the metacarpal head and thumb. This injury results from axial loading and flexion forces and requires prompt diagnosis and appropriate management to prevent chronic thumb instability and arthritis.

Pathophysiology

Bennett's fracture occurs when a longitudinal force is applied to the flexed thumb, typically from a punch or fall on a flexed thumb. The fracture involves the first carpometacarpal (trapeziometacarpal) joint: the anterior oblique ligament holds a small volar-ulnar fragment in place, while the metacarpal base and shaft are pulled dorsally, radially and proximally by abductor pollicis longus, with adductor pollicis adducting the shaft. This creates an unstable intra-articular fracture pattern. Disruption of the carpometacarpal joint biomechanics leads to malunion, chronic pain, loss of grip strength, and early osteoarthritis if inadequately reduced or maintained.

Patient Education

Bennett's fractures are serious injuries requiring early specialist referral; timely and accurate reduction is crucial to prevent permanent loss of thumb function and chronic pain.

Typical Presentation

Site

Base of thumb (first metacarpal), carpometacarpal joint region, often with swelling extending into wrist and hand

Quality

Sharp, throbbing pain at thumb base; potential clicking or locking sensation if involving intra-articular fragment

Intensity

Moderate to severe (often 6-8/10) with immediate onset; pain increases with any attempted thumb movement or gripping

Aggravating

Axial loading of thumb, thumb flexion/extension, gripping or pinching activities, direct palpation over fracture site, any attempt to oppose thumb to fingers

Relieving

Complete immobilization, elevation, ice application, analgesia; pain relief with hand at rest in supported position

Associated

Marked swelling at thumb base, bruising around CMC joint and wrist, loss of thumb mobility, inability to perform pinch or grip, possible visible deformity with thumb appearing abducted, sensory changes if associated nerve injury, audible crepitus or feeling of instability

Orthopaedic Tests

Test descriptions are written with AI assistance from standard clinical texts. Where a test lists Sources, its description has been checked against them; those sources are independent and do not endorse OsteoKit. Accuracy figures and grades (A–D) appear only when checked against the published study; tests without one are marked “No accuracy study”.

Further reading: full test procedures are described in standard clinical examination texts, e.g. Magee & Manske, Orthopedic Physical Assessment (7th ed.), and Cook & Hegedus, Orthopedic Physical Examination Tests: An Evidence-Based Approach (2nd ed.).

No accuracy study

Clinical Examination for Thumb CMC Joint Deformity

Procedure

Look at the thumb base for swelling, bruising and a prominence at the base of the first metacarpal, and palpate gently over the CMC joint.

Positive Finding

Swelling and localised tenderness at the thumb base, often with a visible prominence where the metacarpal has slipped.

Interpretation

Suggests a fracture or dislocation at the thumb base. In a Bennett's fracture the metacarpal shaft is pulled radially and dorsally, mainly by abductor pollicis longus, while a small palmar-ulnar fragment stays attached to the trapezium. It needs an X-ray, and these fractures usually need surgical referral.

Sources

No accuracy study

Thumb Axial Load Test (Metacarpal Compression)

Procedure

Only before imaging and if there is no obvious deformity: apply gentle pressure along the long axis of the thumb.

Positive Finding

Pain at the thumb base.

Interpretation

Pain on gentle axial loading supports a fracture at the thumb base and means X-ray. Stop if it is clearly painful; repeating it adds nothing.

Further reading

No accuracy study

Thumb Opposition and Adduction Strength Assessment

Procedure

Not for a suspected acute fracture. During rehabilitation, grade thumb opposition, abduction and adduction strength (0–5) and measure key pinch on both sides.

Positive Finding

Weakness or pain compared with the other thumb.

Interpretation

Tracks recovery after the fracture has been fixed or has healed. Weakness in the acute phase is mostly pain inhibition and does not help diagnosis.

Sources

No accuracy study

Thumb Hyperabduction Stress Test

Procedure

Do not stress a suspected Bennett's fracture. Only once a fracture has been excluded or has healed: stabilise the trapezium and gently stress the thumb CMC joint, comparing with the other side.

Positive Finding

Pain, or more laxity than on the other side.

Interpretation

Stressing an unstable intra-articular fracture can displace it further. Suspected instability at the thumb base needs imaging and hand surgery review.

Further reading

No accuracy study

Radiographic Assessment (Plain Films Required)

Procedure

True AP (Robert's view) and true lateral views of the thumb CMC joint, plus standard hand views.

Positive Finding

An intra-articular fracture at the base of the first metacarpal with a small palmar-ulnar fragment and the shaft displaced radially and dorsally.

Interpretation

Confirms the diagnosis and shows displacement. Comminuted three-part (Y- or T-shaped) fractures at this site are Rolando fractures, which carry a worse outlook.

Sources

No accuracy study

Computed Tomography (CT) for Comminution Assessment

Procedure

CT of the thumb CMC joint with multiplanar reconstructions, when requested by the treating team.

Positive Finding

Detailed view of fragment size, displacement, the step in the joint surface and any comminution.

Interpretation

Used for surgical planning when X-rays do not show the fracture pattern clearly, especially with comminution. Not needed to make the diagnosis.

Sources

⚠ Red Flags

  • •Acute high-energy mechanism with severe trauma suggesting additional injuries
  • •Neurovascular compromise: absent radial pulse, colour changes, numbness in thumb or radial digits
  • •Open fracture with break in skin overlying fracture site
  • •Compartment syndrome signs: severe pain out of proportion, pain on passive thumb extension, paresthesia
  • •Associated injuries: multiple fractures, crush injuries, or polytrauma requiring emergency department evaluation
  • •Signs of infection in open fracture: wound contamination, foreign material
  • •Severe angulation or obvious malposition requiring urgent reduction to prevent skin tension necrosis

⚡ Yellow Flags

  • •Delayed presentation (>2 weeks) suggesting acceptance of functional loss and potential chronicity
  • •Work-related injury with compensation claim creating secondary gain incentives
  • •History of substance abuse potentially affecting pain perception and rehabilitation compliance
  • •Significant pain catastrophizing or fear-avoidance behaviour limiting early mobilization attempts
  • •Poor social support or unstable housing affecting ability to attend follow-up care and rehabilitation
  • •History of non-compliance with treatment in previous injuries
  • •Pending litigation affecting motivation for functional recovery

Osteopathic Techniques

Refer first

A Bennett fracture (an intra-articular fracture at the base of the thumb metacarpal) needs X-ray and hand surgeon management, with the aim of restoring joint congruity and alignment at the thumb CMC joint. Refer before using manual techniques on the thumb.

Rehabilitation Exercises

Thumb Interphalangeal Joint Active Flexion-Extension (Early Phase)

Range of MotionBeginner

Thumb Metacarpophalangeal Flexion-Extension (Post-Immobilization)

Range of MotionBeginner

Thumb Opposition to Fingertips (Progressive)

Range of MotionIntermediate

Thumb Web Space Passive Stretch

StretchingBeginner

Thumb Isometric Abduction Against Resistance

StrengtheningIntermediate

Thumb Opposition with Resistance Band

StrengtheningIntermediate

Progressive Grip Strengthening with Therapy Putty

StrengtheningIntermediate

Pinch Strength Training (Lateral, Tip, Palmar Pinches)

StrengtheningAdvanced

Shoulder Posture and Scapular Stabilization Exercises

PosturalIntermediate

Fine Motor Coordination Tasks (Picking Up Small Objects, Threading Beads)

BalanceAdvanced

Upper Body Aerobic Activity (Stationary Cycling with Arm Movements)

CardiovascularIntermediate

Wrist and Forearm Pronation-Supination (Maintained During Thumb Recovery)

Range of MotionBeginner

Referral Criteria

  • •Immediate referral to hand surgeon or orthopedic specialist for assessment and possible operative intervention (closed reduction and percutaneous pinning or open reduction internal fixation are gold standard treatments)
  • •Neurovascular compromise requiring urgent vascular surgery assessment
  • •Open fracture requiring emergency department care, tetanus prophylaxis, and wound management
  • •Intra-articular fracture >30% involvement of CMC joint articular surface meeting surgical criteria
  • •Fracture-dislocation not achieving anatomic reduction after closed reduction attempts
  • •Failure to maintain reduction after conservative treatment, requiring surgical stabilization
  • •Post-reduction imaging showing malalignment or persistent subluxation
  • •Signs of complex regional pain syndrome developing during rehabilitation requiring specialist pain management
  • •Persistent CMC joint pain or instability at 8-12 weeks post-union suggesting early arthritis, requiring consideration of arthroscopic debridement or CMC arthroplasty