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 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

Inspect the thumb at the carpometacarpal joint for visible deformity, swelling, and loss of thumb opposition. Palpate the CMC joint base for tenderness and subluxation.

Positive Finding

Visible posterior subluxation of the thumb metacarpal base, swelling over the CMC joint, tenderness on palpation, and loss of thumb opposition or adduction

Sensitivity / Specificity

Unknown / Unknown

Interpretation

Clinical signs suggestive of Bennett's fracture; however, imaging is required for definitive diagnosis. Loss of opposition indicates neuromuscular or structural compromise.

Thumb Axial Load Test (Metacarpal Compression)

Procedure

Apply axial longitudinal compression through the thumb metacarpal along its long axis while observing for pain, crepitus, or subluxation at the CMC joint.

Positive Finding

Pain at the CMC joint, audible or palpable crepitus, or reproduction of the patient's primary complaint

Sensitivity / Specificity

Unknown / Unknown

Interpretation

Suggests fracture or CMC joint pathology; helps localize injury to the thumb basilar region and assess fracture stability.

Thumb Opposition and Adduction Strength Assessment

Procedure

Test the patient's ability to oppose the thumb to each finger and assess thumb adduction strength against resistance (primarily assessing the adductor pollicis). Grade strength using manual muscle testing (0–5 scale).

Positive Finding

Weakness or inability to oppose/adduct the thumb (grade <4/5), or reproduction of pain with resisted adduction

Sensitivity / Specificity

Unknown / Unknown

Interpretation

Weakness may indicate associated nerve injury, muscle injury, or pain inhibition from fracture. Loss of adductor function is common with posterior subluxation.

Thumb Hyperabduction Stress Test

Procedure

Gently apply a varus (abduction) stress to the CMC joint while the thumb is in extension and abduction. Assess for pain or increased laxity compared to the contralateral side.

Positive Finding

Increased CMC joint laxity, pain with varus stress, or apprehension of instability

Sensitivity / Specificity

Unknown / Unknown

Interpretation

Indicates possible CMC ligament disruption or fracture-related instability; helps differentiate Bennett's fracture from isolated ligament injury.

Radiographic Assessment (Plain Films Required)

Procedure

Obtain posteroanterior (PA), lateral, and thumb-specific oblique radiographs of the hand. Review for an intra-articular fracture at the thumb CMC joint base with a characteristic '–piece' fragment and posterior subluxation of the metacarpal.

Positive Finding

Intra-articular fracture at the CMC joint base; posterior subluxation of the thumb metacarpal shaft; typically a small volar-ulnar fragment remains with the trapezium

Sensitivity / Specificity

Unknown / Unknown

Interpretation

Definitive radiographic diagnosis of Bennett's fracture. Plain films establish fracture pattern, degree of subluxation, and comminution—essential for treatment planning.

Computed Tomography (CT) for Comminution Assessment

Procedure

Obtain high-resolution CT imaging with multiplanar and 3D reconstructions of the thumb CMC region to evaluate fracture geometry, comminution, and articular surface involvement.

Positive Finding

Clear visualization of fracture lines, degree of comminution, posterior subluxation, and cartilage involvement at the CMC joint

Sensitivity / Specificity

Unknown / Unknown

Interpretation

CT provides superior detail for surgical planning, particularly when comminution or marginal fractures (Rolando fracture) are suspected. Guides decisions about open reduction versus conservative management.

⚠ 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

Articulation

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

Soft Tissue

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

Articulation

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

Articulation

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

Lymphatic

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

Soft Tissue

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

Add-On Approaches

Chinese Medicine

Acupuncture at LI-4 (Hegu), LI-10 (Shousanli), and local tender points may reduce pain perception and inflammation; moxibustion supports qi circulation and tissue healing during immobilization phase

Chiropractic

Cervical and thoracic spine manipulation to address any compensatory restrictions; gentle metacarpal articulations once fracture healing is established to restore joint mechanics

Physiotherapy

Progressive active-assisted range of motion exercises starting week 2-3 post-reduction; graded gripping and pinching exercises; scar tissue management once bony union is confirmed radiographically

Remedial Massage

Cross-friction techniques to forearm extensors post-immobilization to address myofascial restrictions; gentle massage to surrounding musculature to reduce compensatory tension patterns

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