The Foot & Its Arches

Joints of the Foot

• Large joints
• Talocrural
• Subtalar
• Midtarsal

• Also note presence of series of typical synovial plane joints between adjacent tarsal bones (Intertarsal joints):-
• Cuneo-navicular
• Intercuneiform
• Cuneocuboid
  (reinforced by dorsal, plantar and interosseous ligaments)

Tarsometatarsal Joints

• Bases of metatarsal articulate with…
• Medial cuneiform (1^st MT)
• 2^nd MT is held in a mortise made by all 3 cuneiform (most stable)
• Lateral cuneiform (3^rd MT)
• Cuboid (4^th and 5^th MT)
• Series of plane joints that collectively form an irregular joints line
• Series of capsules and ligaments forming a variable number of joint cavities

Intermetatarsal Joints

• Typical synovial plane joints between bases of the 2^nd to 5^th metatarsals
• Reinforced by dorsal, plantar and interosseous ligaments

Metatarsophalangeal Joints

• Typical synovial condyloid joints between rounded head of metatarsal (larger articular surface to allow greater movement of  plantarflexion) and concave base of proximal phalanx (cf hand)
• Note lax capsule on inferior aspect and support from collateral ligament – from tubercles on MT head pass obliquely to sides of proximal phalanges
• Also note presence of plantar ligament (volar plate) and transverse ligament

Interphalangeal Joints

• Typical synovial hinge joints
• Named according to their position
• Between distal end of one phalanx and proximal end of the next
• Simple capsule, lined with synovial membrane
• Reinforced by collateral ligaments

Arches of the Foot

• Bones of foot arranged to form a vault
• Bounded by the:-
• Medial longitudinal arch
• Lateral longitudinal arch
• Transverse arch (anterior and posterior parts)

• Support is offered from static and dynamic structures (keystone, staples, bowstrings and suspension)
• Allows foot to fulfil its functions as a mobile adaptor and rigid lever

Medial Longitudinal Arch

• Formed by
• Calcaneum
• Talus (keystone)
• Navicular
• 3 cuneiform
• Medial 3 metatarsals
• Supports from
• Spring ligt, Short and long plantar ligt (important static stabilisers)
• Medial ½ of plantar aponeurosis (dual role)
• Long tendons of tibialis posterior and anterior, FDL, FHL and intrinsic muscles of the foot (more important in dynamic situations)

Lateral Longitudinal Arch

• Formed by the calcaneum, cuboid (keystone) lateral 2 metatarsals
• Less stable than MLA
• Support from
• Long and short plantar ligaments
• Plantar ligaments of related joints
• Peroneus longus (sling) and brevis, lateral part of FDL and intrinsic muscles of the foot

Transverse Arches

• 2 Parts:
• Posterior formed by 3 cuneiform and cuboid (only complete with both feet together) – support from ligaments and shape of bones
• Anterior – 5 MT heads – support from transverse head of adductor hallucis

Role of the Arches of the Foot

• Dynamic stability – change shape to allow foot to meet requirements as a rigid lever
• Dynamic mobility – adapting to shapes of surfaces
• Shock absorption/weight dissipation – see trabecular arrangement of bones

Intrinsic Muscles of the Foot

• Muscles with proximal and distal attachments within the boundaries of the foot
• Single muscle on dorsum of foot
• Extensor digitorum brevis
• O: Roughened area on anterior part of calcaneus
• I: Medial part to base of proximal phalanx, remainder blend with tendon of EDL at DDE
• Remaining muscles arranged in layers:
• Layer 1 (most superficial – deep to plantar aponeurosis)
• Abductor hallucis
• Flexor digitorum brevis
• Abductor digiti minimi
  
  
• Layer 2
• Flexor accessorius
• Lumbricals (compare with those of hand) – note complex action of lumbricals
  
  
• 3^rd layer
• Adductor hallucis – note 2 heads – oblique and transverse
• Flexor hallucis brevis – note presence of sesamoid bones in distal tendons
• Flexor digiti minimi
  
  
• 4^th layer
• Dorsal and plantar interossei
• Axis of motion of toes defined about longitudinal axis of 2^nd MT
• Dorsal interossei – Abduct 2^nd, 3^rd and 4^th toes
• Bipennate from adjacent sides of MT shafts
• 1 and 2 insert into 2^nd prox. Phalanx
• 3^rd into PP of 3^rd toe
• 4^th into PP of 4^th toe
• Plantar interossei – Adduct 3^rd, 4^th and 5^th toes
• Unipennate
• From medial side of 3^rd, 4^th and 5^th MT
• To medial side of proximal phalanges of 3^rd, 4^th and 5^th toes

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