Radiographic Evaluation of the Forefoot & Midfoot

Radiographic Foot Analysis Overview

• Radiographic analysis focuses on the forefoot and midfoot.

Radiologic Report Terminology

• This terminology is not all-inclusive and acts as a suggestion for report writing.
• Term suggestions provided by Drs. Pratt & Razzante.

General Overview

• Images should be listed by right, left, or bilateral.
• Note the body part: ankle, foot, toes, tibia/fibula, etc.
• Include WB/NWB/stressed views.
• List x-ray views: AP, MO, LAT, calcaneal axial.
• For multiple views, "3 views WB left foot" can be used.
• Indicate skeletal maturity or immaturity, open growth plates, and if the patient is pediatric.
• Foot architecture can be described as Pes Planus/Cavus, Rectus, Amputation, Midfoot collapse, or Skew foot.
• In Pes Planus, the lateral view may show:
  • Anterior break of the cyma line.
  • Lack of visible sinus tarsi.
  • Curved talar dome.
  • Decreased calcaneal inclination angle.
  • Decreased cuboid visibility.
  • Flattened metatarsals.
  • Medial column sag/break/fault.
  • Decreased/negative Meary's Angle.
  • Increased talar declination angle.
• In Pes Planus, the AP view may show:
  • Increased talo-calcaneal angle (Kite's).
  • Talar head uncovering.
  • Increased CC angle.
• In Pes Cavus, the lateral view may show:
  • Posterior break of the cyma line.
  • Bullet-hole sinus tarsi.
  • Flattened talar dome.
  • Increased calcaneal inclination angle.
  • "Bell shaped" visible cuboid.
  • Vertically stacked metatarsals.
  • Posterior positioned fibula.
  • Increased/positive Meary's Angle.
• Decreased talo-calcaneal angle (Kite's) is observed in the AP view of Pes Cavus.
• Bone density can be osteopenic, osteoporotic, or WNL per the patient's age.
• Soft tissues can have pertinent findings such as:
  • Gas extending to or from a foreign body.
  • Decreased tissue volume/density, which may be related to a wound.
  • Calcifications.

Bones

• Bone position can be specified with CORA, fault, breach, sag, and collapse
• Bone form can be hypertrophic, atrophic, heterotopic, or abnormal in shape/size/length, and/or accessory bones.
• Bone architecture can show:
  • Cortical thickening.
  • Cortical erosions.
  • Periosteal reaction.
  • Osteolysis.
  • Cystic formation.
  • Radiolucent/radiopaque areas.
  • Sclerotic rim on lesion.
  • General sclerosis.
  • Cortical break.
• The 1st metatarsal head shape can be:
  • Round.
  • Squared.
  • Central ridge.

Joints

• Joint space can show symmetric or asymmetric narrowing, can be increased or decreased, and may have intra-articular osteophytes.
• Apposition can be well opposed, congruent, deviated, subluxed, or dislocated.
• Joint margins may have peri-articular lipping or osteophyte formation.
• The subchondral bone plate may show sclerosis or cyst formation.

Common Findings

Hallux Valgus

• Hallux valgus can be characterized by:
  • Increased 1-2 IMA.
  • Tibial sesamoid position.
  • Hallux abductus angle.
  • Sesamoid deviation (sesamoid axial).
  • Decreased metatarsal protrusion distance.
  • 1st MPJ space reduction.

Hallux Rigidus

• Hallux rigidus can be characterized by:
  • Increased subchondral sclerosis or cysts.
  • Osteophyte formation (peri-articular or dorsal).
  • Sesamoid sclerosis.
  • Decreased joint space (asymmetric or symmetric narrowing).

Charcot

• Charcot joints may show:
  • Subluxation/fragmentation at a joint/joint complex.
  • Sclerosis.
  • Consolidation.
  • Remodeling.
  • Malunion.
  • Midfoot collapse.
  • Plantarflexed talus/calcaneus.
  • Ankle position (varus/valgus).

Fracture

• Fracture terminology includes:
  • L.A.R.D. (Location, Angulation, Rotation, Displacement).
  • Intra-articular or extra-articular.
  • Head, neck, shaft, or base location.
  • Transverse, oblique, spiral, comminuted, or butterfly fragment type.
  • Description of alignment; well aligned, minimal/significant angulation (medial, lateral, etc.), dislocated, rotated, or shortened.

Post-Operative

• Post-operative status should include:
  • Hardware assessment to determine if the hardware is intact/broken/backing out/in place, surrounding radiolucency, implant well aligned/deviated.
  • Operative site assessment, including callus formation, trabeculation visible across the fusion/fracture site, mal-aligned or adequately aligned, and distracted joint/fusion sites.

Views to Order

• Standard 3 views include AP, MO, and LAT.
• Sesamoid axial views are also important.
• Imaging should be full weight-bearing to properly evaluate angles.

Angles

• Sesamoid/Plantar Axial: for evaluation of sesamoids and crista.
• Lateral view is for evaluation of the relationship between 1st and 2nd metatarsals.
• AP View:
  • Hallux Interphalangeus Angle (HIA) / Hallux Abductus Interphalangeus Angle (HAIA)
  • Distal Articular Set Angle (DASA)
  • Hallux Abductus Angle (HAA)
  • Proximal Articular Set Angle (PASA) / Distal Metatarsal Articular Angle (DMAA)
  • Metatarsal Protrusion Distance (MPD)
  • Tibial Sesamoid Position (TSP)
  • Intermetatarsal Angle (IMA)
  • Metatarsus Adductus Angle (MAA)

HIPA/HAIA

• Measures the relationship between long axis of distal and proximal phalanx.
• Deformity is centered at the joint, with center of rotation of angulation (CORA).
• Normal value is <10 degrees.

DASA

• Measures the intrinsic deformity of proximal phalanx and the relationship of proximal phalanx shaft to base.
• Normal value is <8 (7.5) degrees.
• Corrected via Akin procedure.

HAA

• Bisection of proximal phalanx and 1st metatarsal
• The measurement of hallux is abnormal in every hallux valgus.
• Normal is <15 degrees.

MPD

• Measurement from the end of 1st and 2nd metatarsal
• Normal is +/- 2mm.
• Positive if 1st met is longer.
• Negative if 1st met is shorter.

PASA

• Measures the articular cartilage surface on 1st metatarsal head compared to metatarsal shaft bisection.
• Normal value is <8 (7.5) degrees
• Reliability is questionable

TSP

• Measures the position of the sesamoid along axis of 1st metatarsal.
• Normal measurement is 1-4.
• More tibial sesamoid lateralization indicates a higher number.

IMA

• Measures the angle created from bisection of 1st and 2nd metatarsals.
• Normal measurement is up to 8-12 degrees and 8-10 degrees.
• Factor in MAA when increased.

MAA

• Measures the relationship of bisection of 2nd metatarsal and line perpendicular to bisection of lesser tarsus.
• Normal measurement is 5 - 17 degrees.
• True IMA = IMA + MAA - 15

Engle's Angle

• Measures the relationship of bisection of intermediate cuneiform and bisection of 2nd metatarsal.
• Normal = <24 degrees.

Misc Radiographic Findings

• Soft tissue of the foot: Bursa and Gout/Tophi.
• Elevated 1st metatarsal can be parallel or divergent.
• Sesamoid Axial evaluations in relation to the crista:
  • Evaluate the sesamoids
  • Evaluate the crista
    • The crista can be present as an entire metatarsal
    • The crista can be eroded away
    • Lateral translation of sesamoids
• Medial eminence hypertrophy.
• Subchondral cysts.
• Subchondral sclerosis.
• Atavistic cuneiform.
• Joint congruity.
• 1st met head shape/width.
• Cortical difference of 1st vs 2nd metatarsals.
• Ancillary findings like hammertoes, Pes Planus, etc.
• Cortical thickness 1 vs 2: Wolf's Law says bone will adapt to areas where increased load is present.
• Rheumatoid Arthritis:
  • Lateral (fibular) deviation of lesser digits at MPJs.
  • Diffuse osteopenia present.
  • More radiolucent met heads.
  • Contracted digits.
  • 5th is spared.

Joint Congruity and Spacing

• May be seen w/ osteophyte formation and/or loose bodies
• Joint space narrowing can be symmetric or asymmetrical
• Deviation → Subluxation → Dislocation is a gradient

Gout

• Increased soft tissue volume & density
• Tophi
• Osteolysis
• Rat bite erosions
• Martel sign

1st Metatarsal Head Shape & Size

• Round
• Central ridge
• Square
• More narrow head width allow less lateral translation for distal metatarsal osteotomies

Postoperative Imaging

• Views and procedures should be noted.
• Hardware should be evaluated.
• Look for signs of hardware complications.
• Note alignment or malalignment.
• Assess the joint/fracture site for trabeculation, gapping, and joint space visibility.
• Note other abnormal findings.

Common Foot Pathologies

Adductovarus

• Adduction and varus of the 5th toe. Additional notes include:
  • Can also be seen in the 3rd and 4th toes.
  • Transverse and coronal plane deformity.
  • Nail plate will be rotated.
  • Apex of deformity can be at the DIPJ or PIPJ.
  • Less common to have contracted in the sagittal plane.

Synostosis

• Most common location in the foot is the 5th DIPJ. Additional notes include:
  • Congenital union of intermediate and distal phalanx.
  • May present with or without deformity.

MPJ Subluxation

• Medial or lateral subluxation. Additional notes include:
  • Transverse plane deformity.
  • Dorsal contracture at MPJ is referred to dorsal dislocation.

MPJ Dislocation

• Usually a sagittal plane deformity. Additional notes include:
  • Can be transverse plane deformity due to post-op complications.

Freiberg's Disease

• Collapse of metatarsal head, usually of the 2nd metatarsal. Additional notes include:
  • Early stage flattening.
  • Late stage collapse.
  • Joint space narrowing.
  • Fragmentation.

Stress Fracture

• Early stages do not show radiographic changes. Additional notes include:
  • May see cortical thickening.
  • Eventually will see callus formation. Refrain from using tumor descriptive terms to describe.
  • May or may not see transverse fracture line.
• Alignment needs to be commented on when healed.

Tailor's Bunion

• 3 types described include:
  • Enlarged 4-5 IMA.
  • Increased lateral deviation angle (lateral bowing).
  • Enlarged 5th met head (dumbbell shaped met head).
  • Some consider type 4 as a mix of the above 3 types, with any combination of the above

Osteomyelitis

• Cortical erosion may be present. Additional notes include:
  • Presence of osteolysis.
  • Identify the bones affected.
  • Determine if gas is present.
  • Remember pertinent negatives

HT Implant:

Cannulated & Metallic

- Allows placement of guide wire (small K-wire) which may be retained to stabilize while the bone is healing.
- Radio-opaqueness increases the chance for the implant to be identified on X-rays

Non-Metallic

- Will appear radiolucent
      - Absorbable materials
            -Bone pegs
      - Non-absorbable plastic/polymer
           -May or may not be cannulated
           - Plastic can be absorbable or not

Solid & Metallic

-Completely internal device, does not allow for K-wire
    -Not able to pin across MPJ
    -Can be static or dynamic (Open after being thawed out of nitinol release)

Procedure Selection

• Hallux valgus procedures should be selected based on their ability to correct abnormal angles.

Post-Op Amputations

Partial Toe Amputation

• Only part of the toe is taken
• Named as a generic procedure to be anatomically specific
• Can be cut through bone or disarticulation at DIPJ or PIPJ

MPJ Disarticulation

• Entire digit is removed at MPJ
• Also referred as toe amputation (total or entire)
• There is no resection of metatarsal

Complete Ray Resection

• Digit and part of the metatarsal has been removed.

Metatarsal Head Resection

• Only the metatarsal head is removed.
• The digit remains.

Transmetatarsal Amputation (TMA)

• All 5 digits and partial metatarsals resected.
• Important to monitor long term for adequate stump parabola.
• The possibility of hypertrophic ossification should be monitored.
• Ulcers can present at distal or plantar stump

Post-Op PIPJ Arthrodesis

• Look for good trabeculation across PIPJ
• Was hardware retained or a K-wire removed?
• Well aligned arthrodesis site or malaligned?

Post-Op IPJ Arthroplasty

• Resection of proximal phalanx head.
• Assess overall alignment.
• Inspect hypertrophic ossification.
• If the whole phalanx was removed is referred to as phalangectomy

Met Osteotomy: Screws

• Usually 2.0-2.7
• Headed, headless, snap-off
• Usually cannulated as are small

PMMA Spacer

• Polymethylmethacrylate-Contains antibiotics to help fight inside an infection. Appears radiopaque -Should be noted on Xrays with surrounding issues (migrate/movement) or bone erosion

Hypertrophic Ossification

• Extra bone grows out of where bone was resected/ Amputation site.
• Appears as normal healing post-op
• Monitor amputations moving forward, can be source of ulcerations