Bennett's Fracture
Upper LimbOverview
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 metacarpocapitellar joint, with the anterior oblique ligament remaining attached to the medial fragment while the metacarpal head is displaced dorsally and radially by the action of the abductor pollicis longus and extensor pollicis longus muscles. 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
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.
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.
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.
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.
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.
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.
⚠ 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
Region
First metacarpal and carpometacarpal joint
Technique
Rationale
Gentle passive articulation within pain-free range promotes synovial fluid distribution, maintains joint mobility, and assists proprioceptive input to guide accurate fracture healing alignment during early mobilization phase
Region
Forearm (extensors and flexors), wrist
Technique
Rationale
Addresses myofascial tension in forearm muscles that may perpetuate stress through CMC joint or contribute to loss of hand function; reduces pain-guarding patterns that inhibit early rehabilitation
Region
Wrist and second-fifth metacarpals
Technique
Rationale
Maintains function of adjacent joints during thumb immobilization period; prevents secondary stiffness and maintains overall hand proprioception for coordinated grip patterns during eventual thumb integration
Region
Cervical spine and shoulder (ipsilateral)
Technique
Rationale
Addresses compensatory restrictions developing from protective posturing of injured hand and upper limb; restores normal kinetic chain function essential for coordinated hand use in rehabilitation
Region
Hand and thumb lymphatic system
Technique
Rationale
Facilitates drainage of post-fracture edema through gentle lymphatic pumping techniques; reduces swelling that restricts joint mobility and perpetuates inflammation during healing phase
Region
Thumb intrinsic muscles and surrounding fascia
Technique
Rationale
Gentle soft tissue release of first dorsal interosseous, adductors, and thenar eminence muscles reduces muscular guarding patterns that may splint the fracture site but also restrict necessary early micromotion for healing
Rehabilitation Exercises
Thumb Interphalangeal Joint Active Flexion-Extension (Early Phase)
Thumb Metacarpophalangeal Flexion-Extension (Post-Immobilization)
Thumb Opposition to Fingertips (Progressive)
Thumb Web Space Passive Stretch
Thumb Isometric Abduction Against Resistance
Thumb Opposition with Resistance Band
Progressive Grip Strengthening with Therapy Putty
Pinch Strength Training (Lateral, Tip, Palmar Pinches)
Shoulder Posture and Scapular Stabilization Exercises
Fine Motor Coordination Tasks (Picking Up Small Objects, Threading Beads)
Upper Body Aerobic Activity (Stationary Cycling with Arm Movements)
Wrist and Forearm Pronation-Supination (Maintained During Thumb Recovery)
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