Foot and Ankle

10


Foot and Ankle


Craig R. Lareau, Jason T. Bariteau, and Christopher W. DiGiovanni


I. Foot and Ankle Anatomy


1. Bones


• Twenty-six non-sesamoid bones of the foot: seven tarsals, five metatarsals, and 14 phalanges (Figs. 10.1, 10.2, 10.3, 10.4)


• Divided into hindfoot (calcaneus and talus), midfoot (navicular, three cuneiforms, and cuboid) and forefoot (metatarsals and phalanges) (Fig. 10.5)


a. Tarsal bones include all bones in the hindfoot and midfoot


• Calcaneus (Figs. 10.6 and 10.7)


a. Sustentaculum tali (the “constant fragment”) is the eminence on the anteromedial calcaneus that supports the medial talar body and forms part of the anterior and middle facets of the subtalar joint; also creates inferior groove for the flexor hallucis longus (FHL)


Constant fragment rarely moves with hindfoot pathology (e.g., calcaneal fracture) due to its strong ligamentous attachments to the talus



Reconstruct fracture fragments to the constant fragment in calcaneus fractures.


• Talus (Figs. 10.8 and 10.9)


a. Talar dome wider anteriorly; ankle more stable in dorsiflexion (DF)


b. No muscular attachments or tendon insertions; two thirds covered with cartilage


c. Primary blood supply to the talar body: artery of the tarsal canal (from the posterior tibial artery)


d. Secondary blood supply to the talar body: deltoid branch of the posterior tibial artery


e. The talar head and neck are supplied by the dorsalis pedis and peroneal arteries, which anastomose to form the artery of the tarsal sinus.


• Navicular


a. Medial plantar projection: attachment for the posterior tibial tendon


b. Tenuous centripetal blood supply


• Cuneiforms: medial, intermediate (middle), and lateral


• Cuboid: grooved on its plantar surface by the peroneus longus


• Metatarsals (MTs)


a. First MT has plantar cristae for articulation with the sesamoids contained within the flexor hallucis brevis (FHB)


b. Deep transverse intermetatarsal ligaments connect the MT heads


First interspace: ligament connects second MT head to fibular sesamoid


c. Phalanges (great toe has two phalanges, remaining toes have three)


• Accessory bones: os trigonum, os peroneum, accessory navicular, etc.


a. Os trigonum syndrome commonly occurs in dancers with symptoms at the “en-pointe” position and is treated with arthroscopic or open excision if conservative management fails.











2. Joints


• Tibiotalar (ankle) joint


a. The mortise, which articulates with the talus, is composed of the tibial plafond, medial malleolus, and lateral malleolus (Figs. 10.10, 10.11, 10.12).


b. Deltoid ligament: main stabilizer of the ankle during stance


Superficial deltoid: tibionavicular, anterior tibiotalar, and tibiocalcaneal ligaments




♦ Origin: anterior colliculus; resists valgus ankle force


♦ Crosses tibiotalar, subtalar, and talonavicular (TN) joints


Deep deltoid = anterior and posterior tibiotalar ligaments


♦ Origin = posterior colliculus


♦ Resists lateral talar translation and external rotation


c. Lateral ankle ligaments resist varus forces


Anterior talofibular ligament (ATFL): resists inversion with the ankle in plantarflexion (PF)


♦ Intracapsular, weakest of three ligaments


Calcaneofibular ligament (CFL): resists inversion with the ankle in neutral/DF


Posterior talofibular ligament (PTFL): strongest of three ligaments, rarely torn


• Inferior tibiofibular joint (syndesmosis): resists lateral talar translation


a. Convex medial distal fibula articulates with concave incisura fibularis


b. Composed of four ligaments: anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), transverse tibiofibular, and interosseous


PITFL is strongest, and often injured last


• Hindfoot joints include the subtalar (ST) and transverse tarsal (Chopart) joints


a. The ST joint is stabilized by medial, lateral, interosseous talocalcaneal, and cervical ligaments.


b. Transverse tarsal (midtarsal or Chopart) joints: TN and calcaneocuboid (CC) joints


c. The spring (plantar calcaneonavicular) ligament, which originates at the sustentaculum tali, is critical in maintaining the arch.


Rupture of this ligament can occur with or contribute to severe pes planovalgus deformity; seen on coronal magnetic resonance imaging (MRI)



• Midfoot joints include the naviculocuneiform (NC), intercuneiform, and tarsometatarsal (TMT; a.k.a. Lisfranc) joints


a. Lisfranc joints


No ligamentous connection between the bases of the first and second MT.


So-called Lisfranc ligament connects the medial cuneiform to the second MT.


• Metatarsophalangeal (MTP) joints: primary stabilizer is the plantar plate


a. Also supported by the collaterals and plantar ligaments


3. Muscles (Figs. 10.13, 10.14, 10.15, and Table 10.1)


• Major tendons crossing the ankle joint into the foot (extrinsic muscles):


a. Anterior: tibialis anterior (TA), extensor hallucis longus (EHL), extensor digitorum longus (EDL), peroneus tertius






b. Lateral: peroneus longus (PL) and peroneus brevis (PB)


PB lies anterior and medial to the PL in the retromalleolar groove


c. Posterior: Achilles (confluence of the gastrocnemius and soleus muscles, strongest and largest tendon in the body)


Rotates ~ 90 degrees: soleus fibers insert on the medial aspect of the Achilles tendon footprint; gastrocnemius fibers insert on the lateral aspect (due to embryological limb bud rotation)


d. Medial: posterior tibialis (PT), flexor digitorum longus (FDL), and flexor hallucis longus (FHL)



From anterior to posterior: PT, FDL, Vein, Artery, Nerve, FHL; use mnemonic “Tom, Dick, and a Very Angry Nervous Harry”


♦ Posterior tibial vein and artery and tibial nerve


PT initiates hindfoot inversion during gait


In the ankle, the FDL is medial/anterior to the FHL; crosses in midfoot (knot of Henry) where FHL goes deep (dorsal) to FDL


e. Plantar foot muscles layers (Figs. 10.16, 10.17, 10.18 and Table 10.2)


Intrinsic muscles dominate the first and third layers


Extrinsic muscles contribute more to the second and fourth layers


Medial and lateral plantar nerves travel in the second layer





Deep plantar arch exists in the fourth layer


The lumbrical muscles are plantar to the transverse MT ligament, while the interossei are dorsal.


f. Extensor digitorum brevis (EDB): single dorsal intrinsic foot muscle


Originates from the superolateral calcaneus


Inserts at base of the proximal phalanges [except hallux: extensor hallucis brevis (EHB)]


Located lateral to EDL of each toe


g. Plantar calcaneal (heel) spurs occur in the flexor digitorum brevis (FDB) origin.


Table 10.2 Plantar Foot Muscles Layers
















First (most plantar)


AbH, FDB, ADM


Second


QP, Lumbricals, FDL, FHL


Third


FHB, AdH, FDMB


Fourth (most dorsal)


Dorsal and plantar interossei, PL, PT


Abbreviations: AbH, abductor hallucis; AdH, adductor hallucis; ADM, abductor digiti minimi; FDB, flexor digitorum brevis; FDL, flexor digitorum longus; FDMB, flexor digiti minimi brevis; FHB, flexor hallucis brevis; FHL, flexor hallucis longus; QP, quadratus plantae; PL, peroneus longus; PT, posterior tibialis.


4. Nerves (Figs. 10.19, 10.20, 10.21)


• Tibial nerve (Fig. 10.22)


a. Supplies all the intrinsic muscles of the foot except for the EDB (deep peroneal [DP] nerve)


b. Travels in tarsal tunnel beneath flexor retinaculum and splits into medial plantar nerve (MPN), lateral plantar nerve (LPN), and calcaneal sensory branch


MPN innervates the FHB, abductor hallucis (AbH), FDB, and first lumbrical muscle, and supplies sensation to the plantar medial 3½ digits.


LPN innervates the remaining intrinsics, and supplies sensation to the plantar lateral 1½ digits.


c. MPN runs deep to the AbH; LPN runs under the quadratus plantae (QP).


d. First branch of the LPN (Baxter’s nerve) supplies the abductor digiti quinti.


• Superficial peroneal (SP) nerve


a. The medial and intermediate dorsal cutaneous nerves of the SP nerve supply sensation to the dorsum of the foot except for the first web space.


b. The dorsal medial cutaneous nerve (branch of the SP nerve) supplies sensation to the dorsomedial aspect of the great toe and is at risk during hallux valgus correction surgery







• Deep peroneal (DP) nerve


a. Lateral terminal recurrent branch of DP nerve supplies the EDB


b. Medial terminal branch of DP nerve supplies sensation to first web space


• Saphenous nerve (posterior to greater saphenous vein)


a. All sensation to the foot is supplied by the sciatic nerve except for the medial foot (saphenous nerve is the termination of the femoral nerve).


• Sural nerve: supplies sensation to the lateral aspect of the foot


• Digital nerves course plantar to the transverse MT ligaments (interdigital).



• Morton’s neuromas develop here, most commonly in second or third interspace


5. Vessels (Figs. 10.20 and 10.23)


• Dorsalis pedis artery: continuation of the anterior tibial artery of the leg (Fig. 10.24)


a. Largest branch, the deep plantar artery, runs between the first and second MTs and contributes to the plantar arch (implicated in foot compartment syndrome)


• PT artery (Fig. 10.25)


a. Divides into medial and lateral plantar branches beneath the AbH muscle


b. The larger lateral branch receives the deep plantar artery and forms the plantar arch in the fourth layer of the plantar foot.


6. Surgical approaches (Figs. 10.26, 10.27, 10.28 and Table 10.3)


7. Arthroscopy (Table 10.4)







Table 10.3 Surgical Approaches




















































Approach


Interval


Risks


Anterior approach to the ankle (Fig. 10.29)


Between EHL (DP nerve) and EDL (DP nerve)


Anterior NV bundle (retract medially)


Anteromedial approach to the ankle (Fig. 10.29)


Medial to tibialis anterior (DP nerve)


Saphenous nerve


Anterolateral approach to the ankle (Fig. 10.29)


Lateral to EDL (DP nerve)


SP nerve (anterior)


Approach to the medial malleolus (Fig. 10.30)


No internervous plane


Saphenous nerve
Long saphenous vein


Posteromedial approach to the ankle (Fig. 10.31)


Achilles and posteromedial aspect of tibia


Posterior tibial artery Tibial nerve


Posterolateral approach to the ankle (Fig. 10.29)


Between peroneals (SP nerve) and FHL (tibial nerve)


Peroneal artery
Sural nerve


Lateral approach to the lateral malleolus (Fig. 10.29)


Subcutaneous


Sural nerve (posterior)
SP nerve (anterior)


Extensile lateral approach to the calcaneus (Fig. 10.32)


Between peroneals (SP nerve) and Achilles (tibial nerve)


Sural nerve


Lateral approach to the hindfoot (sinus tarsi approach) (Fig. 10.32)


Between peroneus tertius (DP nerve) and peroneals (SP nerve)


Lesser saphenous vein Sural nerve


Medial utility incision (approach to talus and talonavicular joint) (Fig. 10.31)


Between tibialis anterior (DP nerve) and tibialis posterior (tibial nerve)


Saphenous vein and its branches


Lisfranc (midfoot) approach (centered dorsally over first TMT joint) (Fig. 10.30)


EHL (DP nerve) tendon sheath incised and tendon retracted laterally


Dorsalis pedis artery and DP nerve lie lateral to the EHL


Abbreviations: DP, deep peroneal; EDL, extensor digitorum longus; EHL, extensor hallucis longus; FHL, flexor hallucis longus; NV, neurovascular; SP, superficial peroneal; TMT, tarsometatarsal.






Table 10.4 Arthroscopy (Fig. 10.33)






















Portal Location


Risks


Anterolateral (Figs. 10.33 and 10.34)


Dorsal intermediate cutaneous branch of SP nerve


Anteromedial (Figs 10.33 and 10.35)


Saphenous nerve and greater saphenous vein


Anterocentral (not recommended) (Fig. 10.33)


Dorsalis pedis artery


Posteromedial (Figs. 10.35 and 10.36)


Posterior tibial artery and tibial nerve


Posterolateral (Fig. 10.36)


Sural nerve


Abbreviation: SP, superficial peroneal.






II. Foot and Ankle Biomechanics


1. Ankle


• Responsible for most sagittal plane motion of the foot and ankle


• Some contribution to inversion/eversion and rotation


2. Syndesmosis


• Fibula rotates ~ 2 degrees in the incisura during gait


• With DF, the distal fibula externally rotates and translates proximally.


3. Hindfoot and midfoot


• Transverse tarsal joints


a. Provide stability of the hindfoot/midfoot; rigid lever at heel-rise


b. During heel-strike (hindfoot valgus, forefoot abduction, and ankle DF), the axes of the transverse tarsal joints are parallel and supple, allowing them to adapt to uneven ground (Fig. 10.37).


c. During toe-off (hindfoot varus, forefoot adduction, and ankle PF), the axes of these joints diverge. This causes these joints to lock, creating a rigid lever arm during push-off.


Failure of the PT tendon to lock the transverse tarsal joints in patients with posterior tibial tendon insufficiency (PTTI) results in an inability to perform single-limb heel-rise.


• The foot is divided into three columns:


a. Medial column: first MT, medial cuneiform, navicular


Least sagittal plane motion, rigid lever-arm during push-off


b. Intermediate column: second and third MTs, middle and lateral cuneiforms


c. Lateral column: fourth and fifth MTs and cuboid


Most sagittal plane motion; helps foot adapt to uneven ground


• Ligamentous stability of the midfoot is provided by the longitudinal and transverse ligaments on the plantar and dorsal surfaces of each joint.


a. Plantar ligaments are thicker and stronger than dorsal ligaments.


b. Primary stabilizer of the longitudinal arch: interosseous ligaments


c. Secondary stabilizer of the longitudinal arch: plantar fascia


• Lisfranc joint complex is stable due to bony and ligamentous architecture


a. Middle cuneiform ends more proximally so that the second MT is recessed proximally (“keystone” providing bony stability) (Fig. 10.38)


b. The cuneiforms and medial three MT bases are trapezoidal (wider dorsally than plantarly), allowing for sagittal plane stability with weight bearing.


c. Dorsal and plantar ligaments extend from the second MT to cuneiforms


Largest/strongest of these ligaments is the Lisfranc ligament, which connects the base of the second MT to the medial cuneiform.



Injury to the Lisfranc ligament leads to Lisfranc joint instability.




4. Forefoot


• All structures distal to the TMT joints


• First MT bears 50% of the weight during gait.


• The second MT is usually the longest and experiences more stress than the other lesser metatarsals by virtue of its length and stability (constraint).


• Intrinsic tendons pass plantar to the MTP joint axis proximally (flexion force) and dorsal to the axis distally (extension force).


a. Weil osteotomy can lead to plantar migration of this center of rotation, and cause a “cock-up” (“floating toe”) toe deformity (tendons become dorsal to the MTP axis and hence extend).


• Loss of intrinsic function from hereditary motor sensory neuropathy (HMSN) [e.g., Charcot-Marie-Tooth (CMT) disease] leads to claw toes.


5. Foot positions versus foot motions


• Foot positions: varus/valgus (hindfoot), abduction/adduction (midfoot), equinus/calcaneus (ankle)


• Foot motions (defined in three axes of rotation) (Fig. 10.39)


a. Sagittal plane motion: DF/PF


b. Coronal plane motion: inversion/eversion


c. Transverse plane motion: forefoot/midfoot adduction/abduction, ankle/hindfoot internal/external rotation


d. Triplanar motion


Supination: adduction, inversion, PF


Pronation: abduction, eversion, DF


e. If the heel is in a subtalar neutral position, the forefoot should be parallel with the floor to meet the ground flush (plantigrade).


If the first ray is elevated, the forefoot is in varus (supination); if the first ray is flexed, the forefoot is in valgus (pronation).


In a long-term flatfoot deformity, the forefoot compensates by supinating to attempt to achieve a plantigrade foot.



III. Physical Examination of the Foot and Ankle


1. Inspection


• Alignment


a. Cavovarus: elevated longitudinal arch with hindfoot varus and plantarflexed first ray (Fig. 10.40)


b. Pes planus: flat longitudinal arch with hindfoot valgus (Fig. 10.41)


2. Vascular examination


• If DP and PT pulses are not palpable, consider noninvasive studies


• Predictive for healing:


a. Ankle-brachial index (ABI) > 0.5 (normal range, 0.9 to 1.3)


b. Toe pressure > 40 mm Hg


c. Transcutaneous oxygen pressure (Tcpo2) > 40 mm Hg


3. Neurologic examination


• Sensory examination


a. Assess all five cutaneous nerves supplying the foot (Fig. 10.42).


b. Inability to sense a Semmes-Weinstein 5.07 monofilament is most predictive of development of foot ulceration in patients with neuropathy (tests for protective sensation).


• Motor examination


a. Keep in mind the location of the tendon in relation to the axis of the ankle.


b. The following muscles should be tested:


Tibialis anterior (L3–4): ankle DF


Extensor hallucis longus (L4–5): great toe DF



PL and PB (L5-S1): hindfoot eversion


Posterior tibialis (L4–5): hindfoot inversion


Gastrocnemius-soleus (S1): ankle PF


c. Neurologic deficits can be secondary to more proximal etiology


Jun 28, 2018 | Posted by in ORTHOPEDIC | Comments Off on Foot and Ankle
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