5th Metatarsal Base Fracture - Foot & Ankle

SUMMARY

5th metatarsal base fractures are among the most common fractures of the foot.
Some fractures may be predisposed to poor healing due to the limited blood supply to the specific areas of the 5th metatarsal base.
Treatment can include protected weight bearing, immobilization or surgery depending on location of fracture, degree of displacement, and athletic level of patient.

SCIENCE

Epidemiology
- incidence
  - frequent injury encountered in primary care setting
  - base of 5th metatarsal fractures account for 25% of all metatarsal fractures
    - 90% are zone 1 fractures
- demographics
  - athletes, military recruits, and manual laborers
Pathophysiology
- mechanism of injury
  - plantarflexion and hindfoot inversion leads to zone 1 fractures
  - forefoot adduction leads to zone 2 fractures
  - repetitive microtrauma leads to zone 3 fractures
Associated conditions
- concomitant midfoot injuries (i.e. Lisfranc injury)
- lateral ankle ligamentous laxity
- cavus foot and varus hindfoot deformities

ANATOMY

Osteology
- divided into tuberosity, base, metadiaphysis, diaphysis, neck, and head
  - base and tuberosity
    - is primarily cancellous and highly vascularized
    - tuberosity flairs from base
      - site of peroneus brevis and lateral band of plantar fascia insertion
      - open apophysis or os peroneum may be confused for fracture (comparison radiographs warranted)
  - metadiaphyseal region
    - has no tendinous attachments and is vascular watershed
  - diaphysis
    - has dorsal curve in distal one third
    - peroneus tertius inserts on dorsal diaphysis
  - neck
    - distal metadiaphyseal region
    - more common site of fracture
  - head
    - articulates with proximal phalanx to form metatarsophalangeal joint
Blood supply
- blood supply provided by metaphyseal vessels and diaphyseal nutrient artery
- zone 2 (Jones fracture) represents a vascular watershed area, making these fractures prone to nonunion
Biomechanics
- fifth metatarsal forms lateral border of forefoot
- functions as a lever in gait during push-off

CLASSIFICATION

Torg Anatomic Classification
Class	Description	Images
Zone 1 (pseudo Jones fx)	Proximal tubercle avulsion Due to long plantar ligament, lateral band of the plantar fascia, or contraction of the peroneus brevis May extend into cubometatarsal joint Nonunion uncommon
Zone 2 (Jones fx)	Metaphyseal-diaphyseal junction Involves the 4th-5th metatarsal articulation Vascular watershed area Acute injury Increased risk of nonunion (15-30%)
Zone 3	Proximal diaphyseal fracture Distal to the 4th-5th metatarsal articulation Stress fracture in athletes Associated with cavovarus foot deformities or sensory neuropathies Increased risk of nonunion

Torg Radiographic Classification
Class	Fracture Age	Characteristics
Type I	Acute	Narrow fracture line without intramedullary sclerosis
Type II	Delayed Union	Widened fracture line with intramedullary sclerosis
Type III	Nonunion	Widened intramedullary canal with no callus

PRESENTATION

History
- antecedent pain in setting of stress fracture, rapid increase in workload or change in training regimen
Symptoms
- location
  - pain over lateral border of forefoot, especially with weight bearing
- aggravating/alieving factors
  - worse on weightbearing
Physical Exam
- inspection
  - rare skin tenting from zone 1 fractures
  - tenderness to palpation along bone at fracture site
  - varus hindfoot alignment during weightbearing
  - cavus foot deformity
  - excessive lateral wear pattern on shoe treads
  - fifth metatarsal head callosity
- motion
  - evaluate for lateral ligamentous instability and whether varus hindfoot is correctable
- provocative tests
  - pain with resisted foot eversion (indicates peroneal tendon weakness)

IMAGING

Radiographs
- recommended views
  - AP, lateral and oblique foot images
- findings
  - details fracture pattern and location
  - intramedullary sclerosis and lack of periosteal callus reaction indicative of chronicity
    - callus forms medially first and progresses laterally
  - plantar fracture gap lends poor prognosis for union with nonoperative treatment
  - plantarflexed first metatarsal and high Meary's angle indicating cavovarus deformity
Bone scan
- indications
  - suspicion for stress fracture with equivocal radiographs
- findings
  - uptake within diaphysis
CT
- indications
  - to evaluate degree of fracture healing in setting of delayed/nonunion or following surgical fixation
MRI
- indications
  - suspicion for stress fracture with equivocal radiographs or bone scan
- findings
  - high signal stress reaction and edema

TREATMENT

Nonoperative
- protected weight bearing in stiff soled shoe, boot or cast
  - indications
    - zone 1 fracture without rotational displacement
  - outcomes
    - union achieved by 8 weeks, fibrous unions are infrequently symptomatic
    - early return to work but symptoms may persist for up to 6 months
- non-weight bearing short leg cast for 6-8 weeks
  - indications
    - zone 2 fracture in recreational athlete
    - zone 3 fracture
  - outcomes
    - high non-union rate and risk of re-fracture approaching 33% in zone 2 fractures
Operative
- intramedullary screw fixation
  - indications
    - zone 1 fractures with rotational displacement or skin tenting
    - zone 2 (Jones fracture) in elite or competitive athletes
      - minimizes possibility of nonunion or prolonged restriction from activity
    - zone 3 fractures in athletic individuals, cavovarus alignment, or with sclerosis/nonunion (Torg Types 2-3)
  - outcomes
    - bony union rates approaching 100% in most series
- open reduction internal fixation with plate and screws
  - indications
    - same as intramedullary screw fixation
    - salvage for nonunion following intramedullary screw fixation
  - outcomes
    - early data show plate and screw construct has equivalent strength to intramedullary fixation

TECHNIQUES

Protected weight bearing in stiff soled shoe, boot, or cast
- technique
  - advance weight bearing as tolerated by pain
  - union achieved by 8 weeks, fibrous unions are infrequently symptomatic
  - early return to work but symptoms may persist for up to 6 months
Non-weight bearing short leg cast for 6-8 weeks
- technique
  - advance weight bearing with signs of radiographic callus (around 4-6 weeks)
  - zone 3 fractures often require 6-7 weeks of non-weight bearing immobilization
  - reports of extracorpeal shock wave with similar union rates as internal fixation for zone 3 stress fractures
Intramedullary screw fixation
- approach
  - patient supine with bump under hip and fluoroscopy immediately available
  - percutaneous/ limited open approach
  - short longitudinal incision proximal to tuberosity, parallel with plantar surface
- soft tissue
  - blunt dissection past sural nerve branches to tuberosity, between peroneus longus and brevis tendons
  - using fluoroscopy, K-wire starting position superior and medial on tuberosity ("high and inside" position)
    - k-wire does not need to be passed further than the metatarsal curvature
- reduction
  - k-wire placed intramedullary, fluoroscopy to confirm location
  - soft tissue protector placed and wire may be removed or cannulated drill used to open canal and drill pilot hole
  - sequentially tap to be able to place screw larger than 4mm diameter
- instrumentation
  - tap can be used to measure appropriate length screw
  - 4.5mm, 5.5mm, or 6.5mm diameter partially-threaded screw placed
    - recommended to use the largest diameter screw that can be accommodated
  - fluoroscopy must be used to confirm all threads cross fracture site and no distal cortical perforation
  - if fracture gap persists or in cases of nonunion/revision, bone graft material may be added at fracture site
- rehabilitation
  - short period of non-weight bearing (1-3 weeks) followed by protected weightbearing and beginning therapy focusing on range of motion and non-impact aerobic exercises
  - running and impact activities commenced at 6 weeks if surgical site pain-free and signs of radiographic callus
Open reduction with plate and screw internal fixation
- approach
  - longitudinal incision centered over proximal 5th metatarsal
- bone work
  - typical plantar fracture gap and/or rotational displacement able to be reduced
- instrumentation
  - 3mm plate bent to contour to plantar-lateral surface of bone to compress fracture

COMPLICATIONS

Nonunion
- incidence
  - nonunion rates for Zone 2 injuries are as high as 15-30%
- risk factors
  - zone 2 and zone 3 fractures due to vascular supply
  - smaller diameter screws (<4.5mm) associated with delayed or nonunion
  - nutritional (vitamin-D) or hormonal (thyroid) deficiencies
- treatment
  - revision intramedullary screw fixation with use of bone grafting
Failure of fixation
- risk factors
  - elite athletes
  - return to sports prior to radiographic union
  - fracture distraction or malreduction due to screw length
    - screws that are too long will straighten the curved metatarsal shaft or perforate the medial cortex
    - screw that is too short will not compress fracture
- treatment
  - revision internal fixation
Refracture
- incidence
  - 33% of zone 2 fractures following nonoperative treatment
- risk factors
  - cavovarus foot deformity, stress fractures, vitamin-D insufficiency, removal of intramedullary screw
- treatment
  - internal fixation with surgical correction of cavovarus deformity if present
  - leave screw in place until end of patient's athletic career
Painful hardware
- incidence
  - rare complication following intramedullary screw fixation
- risk factors
  - screw head left prominent can irritate sural nerve branches
- treatment
  - modified shoewear
Sural nerve injury
- risk factors
  - direct trauma during screw insertion
  - prominent screw head impinging on nerve branches
    - dorsolateral branch of sural nerve within 2-3 mm of tuberosity
- treatment
  - prevented by using tissue protector during procedure and sinking screw head
Chronic pain
- uncommon, result of zone 1 fracture nonunion after initial conservative treatment
- treatment
  - fragment excision and reattachment of peroneus brevis tendon