Foot and Ankle Anatomy and Biomechanics

1. Foot and AnkleAnatomy and Biomechanics Dr. M. Creech Drs. Brunet, Lalonde and Butterwick 2012

2. I would like to thank those whose that came before us staff and residents as our understanding has evolved and what we now know is because ‘we are standing on the shoulders of giants’ • (John of Salisbury and Isaac Newton among others)

3. Essential Functions of the foot to provide a structural supporting platform for the body to absorb shock from the ground reaction forces to be able to adjust to different terrains to convert transverse torque from the lower extremity to become a rigid lever capable of forward propulsion

4. Ankle Made up of the tibia, fibula and talus Primary motion • dorsifexion(extension) and plantarflexion (flexion) Normal ROM (AAOS) • Extension 18 • Flexion 48 Bimalleolar axis • Coronal plane: 82˚(+/- 4) • Axial plane: 13 – 18˚ external rotation Triplane motion (subtalar joint) • Discussed later so stay awake

5. Ankle Talar body - wedge shaped, wider anteriorly than posteriorly Mortise “put on stretch” during dorsiflexion • Ankle more stable Fibula ascends, increased wt transmission (10 – 15% axial load) Plantarflexed – mortise more reliant on ligamentous restraints - sprains

6. Ankle SYNDESMOSIS • AITF ligament • anterolateral tibia tubercle (Chaput) • anterior tubercle of fibula (Wagstaff) • Interosseous ligament • Continuation of IOM • PITF ligament • posterior tubercle of tibia (Volkmann) • inserts on posterior fibula

7. Normal X-ray alignment of the ankle joint • Talocrural angle • (8-15° on mortise view) • Medial clear space • (£ 4mm on mortise view) • Tibiofibular clear space • (£ 6mm on AP and mortise views)

8. Syndesmotic radiological assessmentContinued • >6mm on AP and >1mm on mortise • Tibiofibular overlap

9. ANKLE • Lateral fibular ligaments **weaker** than Deltoid ligament • ATFL • Weakest, intracapsular thickening • CFL • longest, narrow cord, covered by PB/PL • PTFL • Deepest, strongest • Position of ankle critical when testing lateral ligament complex • PF tightens ATFL • Inversion in 0deg flexion tightens CFL

10. ANKLE • Medial Ligament Complex = Deltoid Ligament • 2 layers • Superficial • Tibionavicular & tibiocalcaneal ligaments • Deep • Anterior & posterior tibiotalar ligaments

11. OsteologyFOOT • 26 bones • 7 tarsal bones • 5 metatarsals • 14 phalanges • Plus sesamoids (FHB) • Hindfoot • Calcaneus, talus • Midfoot • cuboid, navicular, cuneiforms • Forefoot • Metatarsals, phalanges

12. Osteology—Hindfoot • Calcaneus • Anterior, middle, and posterior articular facets • The middle articular facet is supported by what calcaneal structure? • Sustentaculum tali • Bohler’s angle = 20-40 degree • Angle of Gissane = 95-105 degree of Gissane

13. Osteology—Hindfoot • Talus • Consists of a body, neck, and head • What proportion of the surface is cartilaginous? • 60% • How many muscles attach to the talus? • None • What is the name of the posterolateral process that may be nonunited (and what attaches to it)? • Os trigonum (posterior talofibular ligament)

14. Blood SupplyTALUS • 3 sources: • Posterior Tibial Artery = Artery of the Tarsal Canal • deltoid branch • calcaneal branches • **primary blood supply • DorsalisPedis Artery • medial tarsal branches • Artery of the Tarsal Sinus • Peroneal Artery • contributes to artery of Tarsal Sinus

15. Osteology—Midfoot • Cuboid • Has a groove on its undersurface that receives which tendon? • Peroneus longus • Navicular • Cuneiforms • Medial, middle, and lateral cuneiforms • The middle cuneiform does not extend as far distally, allowing the 2nd MT to “key” into place

16. Osteology—Forefoot • In general, the metatarsals and phalanges are similar in shape and function to those in the hand • Sesamoids beneath the 1st MT head are buried within which tendon? • Flexor hallucis brevis • What muscle attaches to the base of the 5th MT? • Peroneus brevis

17. Basic Alignment • Calcaneal inclination = angle between the ground & inferior aspect of the calcaneus • N=18-22 degree • Distal calcaneus tilted upward = pescavus • Horizontal orientation = pesplanus

18. Basic Alignment • Meary’s alignment = between long axis of talus and 1st MT on weight-bearing lateral • Angle > 4 degree is abnormal

19. Basic Alignment • Lateral talocalcaneal angle = bisecting angle between long axis of talus and calcaneal inclination • Normal 25-45 degrees • > 45 degree suggest hindfoot valgus

20. Basic Alignment • Kite’s angle = bisecting line from head of talus & parallel line lateral surface of calcaneus • Normal is 15-30 degree • > 30 degree suggest hindfoot valgus

21. Basic Alignment • Sinus tarsi see-through sign • Indicates external rotation of hindfoot • Often seen with varus and forefoot adduction in cavovarus deformities

22. Basic Alignment • Hallux valgus angle = axis of 1st MT to 1st proximal phalanx • N < 15 degree

23. Basic Alignment • Intermetatarasal angle (IMA) = angle between longitudinal axis of 1st and 2nd ray • N< 9 degrees

24. Arthrology—Ankle • What structure attaches to the anterolateral tibia and is responsible for a Tillaux avulsion fragment? • Anterior inferior tibiofibular ligament • What structure attaches to the posterolateral tibia and is responsible for posterior malleolus fractures? • Posterior inferior tibiofibular ligament

25. ArthrologyFOOT Ankle joint – talocrural joint Subtalar joint Talonavicular Calcaneocuboid Intertarsal joints Tarsometatarsal joints Interphalangeal joints

26. Transverse tarsal joint (Chopart) Made up of the calcaneocuboid and talonavicular Permits rotation in the sagittal plane (sup/pro) Adduction/abduction in the coronal plane

27. Medial cuneiform Arthrology—TMT • Lisfranc’s (TMT) joint • Immobile • The base of the 2nd MT is recessed between the 3 cuneiforms • Lisfranc’s ligament is plantar and joins the 2nd MT base to the medial cuneiform

28. Foot and Ankle Questions • What tendon runs beneath the sustentaculum tali? • FHL • Is the plantaris tendon medial or lateral to the Achilles tendon at the ankle? • Medial • What is the root innervation of EHB? • L5

29. Foot and Ankle Questions • A complete common peroneal nerve injury at the level of the fibular head would result in loss of sensation to which area? • Entire dorsum of the foot • Following ORIF of a calcaneal fracture through a lateral approach, the patient complains of numbness along the lateral border of the foot. What sensory nerve has been injured? • Sural nerve

30. Subtalar joint Gliding joint Entire body, part of talar head rests on anterior 2/3 of calcaneus Three articular facets • Posterior, middle and anterior

31. Subtalar joint Provides basis inversion/eversion • Calcaneus moving under talus ROM (AAOS) • Inversion 33 • Eversion 18

32. Subtalar Joint Supination and pronation Tri-plane motion

33. Arthrology—Subtalar • What is the sinus tarsi? • It is an anatomical space that is medially continuous with the much narrower tarsal canal • What are the boundaries of the sinus tarsi? • Superior: Talus • Inferior: Calcaneus • Anterior: Talocalcaneonavicular joint • Posterior: Posterior facet of the subtalar joint

34. Arthrology—Midtarsal & TMT • The hindfoot is connected to the midfoot through which joint? • Chopart’s joint (TTJ) • The midfoot is connected to the forefoot through which joint? • Lisfranc’s joint (TMT)

35. Tarsometatarsal and midfoot joints Little motion occurs through the intercuneiform and naviculocuneiform joints. The fourth and fifth TMT joints are the most mobile, with a range of 5° to 20° of motion. The second TMT is the least mobile, with 1° of motion

36. Talus Navicular 1st Cuneiform Calcaneus 1st Metatarsal Phalanges Medial Arch Formed by • Calcaneus, Talus, Navicular, Cuneiforms 1-2-3, MT 1-2-3 Elastic (talonavicular is weakest point) Calcaneonavicular ligament (Spring ligament) which blends with the deltoid aids in support supported by tib post, plantar fascia, muscles in the sole of the foot, tib ant, peroneus longus

37. Medial Arch Toe extension: Tightens the plantar fascia. Raises arch, inverts calcaneus Stiffens foot in preparation for push off/ propulsion

38. Lateral Arch • Formed by • Calcaneus, Cuboid, 4th & 5th metatarsal • Less elastic than medial • Supported by two strong ligaments • long plantar lig • plantar calcaneocuboidlig Cuboid Calcaneus 4th & 5th Metatarsals

39. Weight Distribution Lateral Arch Medial Arch Anterior Pillar : Posterior Pillar = 1:1 Anterior Pillar • Medial Arch : Lateral Arch = 2:1

40. Transverse Arches Series of transverse arches • strengthened by the interosseous, plantar, and dorsal ligaments, by the muscles of the 1st 5th toes add. hallucis, peroneus longus Combination of arches gives rise to the tripod stance concept

41. Gait "loose bag of bones" as it flies through the air toward the ground. During that brief time on the ground, those loose bones, along with the attendant muscles, tendons, and ligaments of the foot have to organize and transform into a rigid lever to lift you into the next period of flight Hansen et al 2011

42. Gait Cycle Three dynamic functions required • Flexible foot to accommodate variations in the environment • Semi-rigid foot act as spring/lever arm @ push off • Rigid foot to ensure body wt carried with stability

43. Gait cycle Heel strike • Foot supinated (locked) • Tibia IR 5˚, ankle neutral to slight PF • Compression of heel pad (posterolateral corner) Foot Flat • Foot undergoes controlled decent to floor via eccentric contraction of ant muscle grp • Tibia continues to IR, transmitting forces through mortise (foot PF, less stability), causing adduction of fore foot • Foot begins quick pronation (10˚ first 8% stance phase) • Axis of transverse tarsal joint aligned, unlocking the transverse tarsal joint = cushioning

44. Subtalar & transverse tarsal interaction Subtalar pronation causes the TTJ axes to become more parallel often referred to as unlocking. Subtalar supination causes the TTJ axes to become non-parallel and locked

45. Gait cycle Midstance • Foot fixed on ground, lower limb begins to ER • Foot begins to supinate • Stability increases • Body begins to pass over foot - DF Heel rise • Ankle begins to PF • Forces MTP into extension • Causes windlass effect – further increasing stability • Rigid lever arm ready for push off Push off • Leg goes back to IR • Foot goes into pronation, unlocking it to allowing flexible foot during swing phase

46. Force Distribution 4 x body weight walking 12 x body wt running

47. Muscle Actions • Anterior to ankle = DF • Posterior to ankle = PF • Lateral to STJ = everter • Medical to STJ = inverter

48. Muscle activity during gait