Recall that the muscles of the hand are exclusively lying on the palmar region; the muscles of the foot are divided into dorsal region and the plan-tar region. At the dorsal region there are three muscles, the extensor digi-torum brevis, extensor hallucis brevis, and the musculus dorsal interossei.
The muscles of the plantar region are divided into a medial group (the big toe side); lateral group (the small toe side), which is also called in karate,
“sword foot” or “edge of the foot” (Sokuto in Japanese); and intermediate group, which is associated with the tendons that separate the medial and lateral groups.
The classification using anatomical regions is accurate; however, the correct classification is made by identifying their layers, first through fourth, which are seen during dissection. The first layer is the most superfi-cial and closest to the plantar fascia. It is composed of the musculus abduc-tor hallucis, flexor digiabduc-torum brevis, and abducabduc-tor digiti minimi. The second layer contains the musculus lumbricalis and quadratus plantae. The third layer contains the musculus flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis. The fourth layer contains the musculus interos-sei (plantar) and the tendons of the tibialis posterior and peroneus longus.
The above-mentioned foot muscles have their origin and insertion on the foot excluding the lumbricalis. There are other foot muscles, but they have the origins on the tibia or the fibula. These muscles have been described in the previous section, and they are: Flexor hallucis longus, extensor hallucis longus, flexor digitorum longus, and extensor digitorum longus. The muscles of the foot are short (brevis) muscles and there are different names for these short muscles.
3.13.1 First Layer (Plantar)
Musculus abductor hallucis is the most medial and superficial layer of the sole of the foot. It is the most powerful muscle from the plantar region.
Under this muscle lies the plantar fascia. Insertion: The origin is on the tuberosity of the calcaneus bone. Also an additional origin is on the plantar aponeurosis and on the flexor retinaculum. It distally inserts on the medial side of the base of the proximal phalanx of the big toe. Action: Its action is to assure a static position of the body. It is also the abductor and flexor of the toe. Innervation is assured by the medial plantar nerve (L4, L5, S1).
Musculus flexor digitorum brevis is equivalent to the flexor digitorum superficialis muscle of the arm. This muscle has four fasciculi with their tendons and is fixed to the middle phalanges of the second to the fifth toes.
Insertion: The origin is on the calcaneal tuberosity and plantar aponeu-rosis. It distally inserts on the middle phalanges of the second to the fifth toes. Action: It is the flexor of the second to the fifth toes. Innervation is assured by the medial plantar nerve (L4 and L5).
Musculus abductor digiti minimi is on the lateral side of the sole of the foot. Insertion: The origin is the same as for flexor digitorum brevis. It distally inserts on the lateral side of the proximal phalanx of the fifth toe.
Action: Its primary action is to serve the static position of the human and assure curvature of the plantar portion of the foot. It is the abductor of the fifth toe. Innervation is given by the lateral plantar nerve (S2, S3). The first and second layers are shown in Figure 3.21a and 3.21b. Some muscles of the third and fourth layer are noted in Figure 3.21b.
3.13.2 Second Layer (Plantar)
Musculus lumbricals are four muscles annexed to the tendon of the flexor digitorum longus. Insertion: The origin is on the tendons of the flexor digi-torum longus. It distally inserts on the medial side of the base of the proxi-mal phalanges of the second through the fifth toes. Action: It is the flexor of the metatarsophalangeal joints and the extensor of the interphalangeal
joints of the second through the fifth toes. Innervation is assured by medial plantar nerve (L4, L5, S1).
Musculus quadratus plantae has the shape of a quadrilateral and is also annexed to the tendon of the flexor digitorum longus. Insertion: The ori-gin has two fascicules. The medial head has its oriori-gin on the medial side of the calcaneus. The lateral head has origin on the lateral border of the infe-rior surface of the calcaneus. It distally inserts on the middle and lateral border of the tendon of the flexor digitorum longus. Action: It is the flexor
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FIGURE 3.21 (a) First layer of the plantar muscles (flexors). 1. Calcaneus; 2. plan-tar aponeurosis (central portion); 3. abductor digiti minimi; 4. flexor digiti minimi brevis; 5. flexor digitorum brevis; 6. tendon of flexor hallucis longus; 7. adductor hallucis (transverse head); 8. flexor hallucis brevis (lateral and medial fasciculus);
9. abductor hallucis.
(b) Second layer of plantar muscles (flexors). 1. Flexor digitorum brevis (sec-tioned); 2. and 2a. abductor digiti minimi; 3. quadratus plantae; 4. tendon of the flexor digitorum longus; 5. tuberosity of the fifth metatarsal bone; 6. flexor digiti minimi brevis; 7. lumbricals; 8. tendon of flexor digitorum brevis; 9. tendon of the flexor hallucis longus; 10. and 10a. flexor hallucis brevis; 11. adductor hallucis (oblique head); 12. abductor hallucis.
of the distal phalanges of the second to fifth toes. Innervation is given by the lateral plantar nerve (S1, S2).
3.13.3 Third Layer (Plantar)
Musculus flexor hallucis brevis is situated under the abductor hallucis.
Insertion: The origin is on the medial part of the cuboid bone (plantar surface) and the lateral cuneiform bone. It is distally inserted with two fascicules. Both are on the base of the proximal phalanx of the big toe; the medial part is on the medial side and the lateral part is on the lateral side of the big toe. Action: It is the flexor of the big toe at the metatarsophalan-geal joint. Innervation is assured by the medial plantar nerve.
Musculus adductor hallucis is situated in the middle of the plantar region. It has two fasciculi. One is oblique the other is transverse. Insertion:
The oblique head has its origin on the base of the second, third, and fourth metatarsal and the sheath of the fibularis longus tendon. The transverse head has its origin on the metatarsophalangeal ligaments of the third, fourth, and fifth toes adjacent to the transverse metatarsal ligaments. It is distally inserted on the base of the proximal phalanx of the big toe. Action:
It is the adductor and flexor of the big toe at the metatarsophalangeal joint.
Innervation is given by the lateral plantar nerve.
Musculus flexor digiti minimi brevis. Insertion: The origin is on the plantar ligament and the base of the fifth metatarsal. It is distally inserted on the base of the proximal phalanx of the fifth toe. Action: It is the flexor of the little toe. Innervation is given by the lateral plantar nerve.
3.13.4 Fourth Layer (Plantar)
Musculus plantar interossei fill the space between the metatarsal bones.
There are three muscles. The plantar interossei are smaller than the dorsal interossei. Insertion: The origin is on the medial sides of the third, fourth, and fifth metatarsal bones. Distal insertion is on the medial sides and bases of the proximal phalanges of the third, fourth, and fifth toes. Action:
It is the flexor of the metatarsophalangeal joints and adductor of the toes.
Innervation is given by the lateral plantar nerve.
3.13.5 Dorsal Region
There are only two muscles in the dorsal region musculus dorsal interossei and extensor digitorum brevis (extensor hallucis brevis).
Musculus dorsal interossei consists of four muscles. Insertion: They are on adjacent sides of the metatarsal bones. They are distally inserted in
this way: The first insertion is on the medial side of the proximal phalanx of the second toe. The other insertion is between all the proximal pha-langes of the second to fourth toes. Action: They are abductors of the toes and they flex the toes. Innervation is assured by the lateral plantar nerve.
Musculus extensor digitorum brevis is connected to the four toes exclud-ing the little toe. Insertion: The origin is on the anterior part of the calca-neus bone. It is distally inserted on the base of the proximal phalanx of the big toe. Also connected to the second, third, and fourth toes as adjacent to the tendons of the extensor digitorum longus. Action: It is the extensor of the medial four toes. Innervation is assured by the deep fibular nerve L4, L5, and S1. The dorsal region is represented by Figure 3.22. Figure 3.23 shows the bones of the foot with the majority of the muscle insertions only.
18 1 2
3 17 4
16 15 14 13 12 11
3b 10 9 8 3a 4a 7 6 5
FIGURE 3.22 Dorsal muscles of the foot. 1. Tibia; 2. triceps surae; 3., 3a., and 3b. extensor hallucis longus; 4. and 4a. tibialis anterior; 5. medial malleolus;
6. inferior extensor retinaculum; 7. extensor hallucis brevis; 8. extensor digito-rum brevis; 9. ligaments (extensor digitodigito-rum longus); 10. interossei; 11. fibularis tertius; 12. tuberosity of fifth metatarsal bone; 13. fibularis brevis; 14. lateral mal-leolus; 15. superior extensor retinaculum; 16. fibularis longus; 17. fibularis brevis;
18. extensor digitorum longus.
3.13.6 The Plantar and the Transverse Arch of the Foot
The plantar arch or plantar vault controls the longitudinal or sagittal direc-tion of the foot. The transverse arch represents the transverse curvature of the sole of the foot. The firmness or stability of both arches is maintained by anatomical stabilizers which can be active or passive. The muscles and some of the tendons of the leg which act on the foot are considered to be active stabilizers while some ligaments and the plantar aponeurosis are considered to be passive stabilizers.
The active stabilizers of the longitudinal arch of the foot are abductor hal-lucis, flexor hallucis brevis, flexor digitorum brevis, quadratus plantae, and abductor digiti minimi. These are the short muscles of the foot. The primary
18 1
2 3 4 5 6
8 7
9 10
11 17
15a
16
15 14
13 12
FIGURE 3.23 Muscle insertions on the plantar view of the right foot. 1. Flexor hallucis longus; 2. flexor digitorum brevis; 3. flexor hallucis brevis; 4. abductor hallucis; 5. adductor hallucis; 6. tibialis anterior; 7. fibularis longus; 8. tibialis pos-terior; 9. medial cuneiform bone; 10. navicular bone; 11. triceps surae; 12. cuboid bone; 13. lateral cuneiform bone; 14. fibularis brevis; 15. and 15a. abductor digiti minimi; 16. metatarsal bones; 17. flexor digiti minimi; 18. flexor digitorum lon-gus. The shaded area represents the intermediate cuneiform bone.
passive stabilizers are the plantar aponeurosis, the long plantar ligament, and the plantar calcaneonavicular (spring) ligament. The flexor hallucis longus and the flexor digitorum longus are the secondary passive stabilizers.
3.13.7 The Movements of the Foot
In sagittal direction dorsiflexion is when the dorsal part of the foot approaches the leg. Another movement is the plantarflexion when the sole of the foot descends to the ground and the heel ascends toward the leg. In lateral direction the foot everts approximately 10° (the outer edge of the foot is lifted up from the ground). In medial direction the foot inverts approximately 20° (the inner edge of the foot is lifted up from the ground). When the inversion is strained, then the action is named supination.
From Figure 3.23, two tiny cartilage bones (sesamoids) are not rep-resented. The representations of these two bones are on the area of the abductor hallucis.
Demonstration by the author: how to break five sheets of glass. It is very impor-tant to know the angle of the punching arm and where to hit the glass (refer to Chapter 11 for more detail).
3.13.8 Summary
At the beginning of this part of the book the division of the human body movement is explained. The bone structure and composition, different types of joints and the complexity of different types of muscles and their roles in the movement of the human body has been described.
In this part of the book, the focus has been on the human anatomy, particularly the joints and muscles of the body part. Part I also describes the muscle insertions, their primary mechanical actions, and the innerva-tions of the muscles.
Some of the chapters described the biomechanics of the specific mus-cular region, for example, biomechanics of the knee and other body parts.
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