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LABO RATO RY
- The Lower Limb
- LIMB 4.1 BONES OF THE LOWER
- Pelvic Girdle
- Thigh
- Leg
- Foot
- LIMB 4.2 JOINTS OF THE LOWER
- Hip Joint
- Knee Joint
- Ankle Joint
- LIMB 4.3 INNERVATION OF THE LOWER
- The Lumbosacral Plexus
- Nerves to Muscles That Move the Thigh
- and Digits Nerves to Muscles That Move the Leg, Ankle,
- Courses of the Peripheral Nerves
- Dorsal Compartment Nerves
- Ventral Compartment Nerves
- LIMB 4.4 MUSCLES OF THE LOWER
- Muscles That Move the Thigh
- Iliopsoas Group Muscles
- Gluteal Group Muscles
- Lateral Rotator Group Muscles
- Adductor Group Muscles
- Muscles That Move the Leg
- Leg Flexors
- Leg Extensors
- Muscles That Move the Foot
- Plantarflexors
- Dorsiflexors
- Muscles That Move the Toes
- Extrinsic Flexors
- Extrinsic Extensors
- Intrinsic Muscles
- LIMB 4.5 BLOOD VESSELS OF THE LOWER
- Arteries
- Veins
- Deep Veins
- Superficial Veins
92 LABORATORY THE LOWER LIMB
4.1 BONES OF THE LOWER LIMB
The bones of the lower limb comprise two groups: (1) those that form the free part of the limb, and (2) those that attach it to the trunk. The latter form the pelvic girdle.
Pelvic Girdle
The bony pelvis is made up of the Sacrum and Coccyx and by the left and right Os Coxae. The os coxae links the free part of the lower limb and the axial skeleton. We have already studied the sacrum (laboratory 2, p. 30). Os coxae. This is a large, irregularly shaped bone. It is sometimes (erroneously) referred to as the innominate. Each os coxae consists of three bones that fuse in adulthood. The superior element is the Ilium. The posterior ele- ment is the Ischium. The anterior element is the Pubis. Prior to their fusion, these bones are separated by the Triradiate Cartilage in the Acetabulum , or hip socket. The pubis and ischium are separated by cartilage be- low the large Obturator Foramen. In life, the obturator foramen is covered by a tendinous membrane. Posteriorly, each os coxae articulates with the sacrum by the large, ear-shaped Auricular Surface. This articulation is bounded anteriorly and posteriorly by very strong Sacroiliac Ligaments. Anteriorly, the os coxae articulate with each other in the midline at the cartilaginous Pubic Symphysis.
The superior margin of the os coxae is known as the Iliac Crest. It projects ventrally as the Anterior Superior Iliac Spine.
Below the auricular surface, the ischium projects as a prominent Ischial Spine. Below this, the ischium broadens lat- erally as the Ischial Tuberosity.
Between the auricular surface and the ischial spine is the deep Greater Sciatic Notch. Between the ischial spine and ischial tuberosity is the shallow Lesser Sciatic Notch. In life, ligaments stretch across the posterior margins of both notches, transforming them into foramina.
The superior ramus of the pubis forms a sharp crest (the Pecten Pubis ) that runs posteriorly from near the symphysis to the ilium. The line of the crest continues on the inner surface of the ilium as a ridge, known as the Arcuate Line, to the sacroiliac joint. The pecten pubis and arcuate line separate the pelvis into two parts: the so-called False Pelvis above, and the True Pelvis, or Obstetrical Pelvis below.
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94 LABORATORY THE LOWER LIMB
Figure 4.2 Femur and Patella anterior and posterior views of right femur and patella
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Thigh
The thigh has a single bone: the femur. Suspended in a tendon between the front of the thigh and leg is a small bone, the patella. Femur****. At the proximal end is a hemispherical Head that articulates in the acetabulum of the os coxae. The head is connected to the shaft by a long Neck. At the top of the junction of the neck and shaft is the Greater Trochanter ; it has a deep fossa on its medial side. The Lesser Trochanter projects medially from the back of the shaft where it meets the neck. The trochanters are connected on the back of the shaft by a ridge, the Intertrochanteric Crest. Lateral to the lesser trochanter is a roughened area, the Gluteal Tuberosity, which con- tinues down the back of the shaft as a prominent ridge, the Linea Aspera. The medial and lateral margins of the linea aspera diverge distally around the slightly concave Popliteal Surface. The distal end of the femur has two articular surfaces—the Lateral Condyle and Medial Condyle —that articulate with the proximal end of the tibia. The condyles are separated posteriorly; anteriorly they merge to form a spool-shaped Patellar Surface over which the patella glides. The distal epiphysis is expanded above the articular surface to form Lateral and Medial Epicondyles. Patella****. This triangular sesamoid bone forms in the tendon of the Quadriceps femoris muscle. Most of its posterior sur- face articulates with the patellar surface of the femur.
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4.1 BONES OF THE LOWER LIMB 95
Leg
The leg comprises two bones: the tibia (medial) and the fibula (lateral). Tibia****. The proximal end is expanded to form the Tibial Plateau, which articulates with the femur by separate Medial and Lateral Condyles. They are separated in the center of the plateau by the Intercondylar Eminence
. The shaft is triangular in cross section; its anterior edge (the “shin”) lies just below the skin. There is a rough- ened tuberosity on the front of the shaft just below the plateau where the tendon of the Quadriceps femoris muscle attaches. The medial side of the distal end of the bone projects as the Medial Malleolus. The talus articulates with the distal surface of the tibia, and with the lateral surface of the medial malleolus.
Fibula****. It has a slightly expanded proximal end, the Head , which articulates with a facet on the tibia just below its lateral condyle. The shaft is very slender, because the bone bears practically no weight. The slightly enlarged distal end is held tightly against a notch in the tibia by ligaments; it forms the Lateral Malleolus. Its medial sur- face articulates with the talus.
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Figure 4.3 Tibia and Fibula anterior and posterior views of right tibia and fibula
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4.1 BONES OF THE LOWER LIMB 97
Figure 4.4 Foot Bones superior and plantar (inferior) views of right foot
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The Arch of the Foot
A feature that is peculiar to humans is a foot with a plantar arch. An arched foot was present in our ancestral lineage at least 3.7 million years ago. We know this because humanlike footprints are preserved in a volcanic ash layer in Tanzania.
The arch resists the pressures of deformation that are generated during walking and running. In the latter part of the sup- port phase of locomotion, the body’s weight is borne by the front part of the foot. This would cause the foot to dorsiflex were it not for the arch.
A prominent Longitudinal Arch runs along the medial side of the foot between the tuberosity of the calcaneus (the heel) and the metatarsal-phalangeal joint (the ball). A footprint emphasizes this observation. There is also a transverse arch, but this is largely a by-product of the fact that the longitudinal arch is higher medially than laterally.
The arch is maintained by (1) the shapes and fit of the bones, (2) the ligaments that bind the tarsal bones, and (3) the plantar aponeurosis. Some of the intrinsic muscles of the foot also provide some support for the arch.
- Bones. When the foot is examined from its medial side, the bones are seen to form an arch. The Talus is its keystone. It is wedged between the Calcaneus and the Navicular. The back of the arch is formed by the calcaneus. The front of the arch is formed by the navicular, one of the three cuneiforms (principally the medial), and the more medial metatarsals (principally the first).
- Ligaments. The body’s weight is transmitted directly to the talus. This would cause the arch to collapse were it not for the fact that the tarsals are bound together by a number of strong ligaments. These provide a relatively rigid structure that is also capable of some degree of movement. The most important of these is the Spring Ligament. It arises from the edge of a medially projecting shelf of bone from the calcaneus (the Sustentaculum tali ), runs under- neath the talus, and inserts onto the navicular.
- Plantar Aponeurosis. Just deep to the superficial fascia of the sole of the foot is the thick, fibrous Plantar Aponeu- rosis. It arises from the tuberosity of the calcaneus, and fans out to insert onto the base of the proximal phalanx of each toe. The aponeurosis is tightened as the toes are dorsiflexed, and this causes the arch to be maintained. The Abductor hallucis muscle runs from the tuberosity of the calcaneus to the base of the proximal phalanx of the big toe. It also helps sustain the medial longitudinal arch during locomotion. We will study it later in this lab (p. 136).
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100 LABORATORY THE LOWER LIMB
4.2 JOINTS OF THE LOWER LIMB
In this section we will study the anatomy of the three lower limb joints: the hip, the knee, and the ankle.
Hip Joint
The deeply cupped Acetabulum of the os coxae and the hemispherical Head of the Femur form a snugly stable ball-and- socket joint.
The articular surface of the acetabulum is a horseshoe-shaped surface known as the Lunate Surface. It is open infe- riorly (because it bears no weight here), but its two horns are connected by the Transverse Acetabular Ligament. This completes the socket, which is deepened further by a fibrocartilaginous Acetabular Labrum.
Almost the entire head of the femur is covered by an articular surface except for a small pit known as the Fovea Capitis through which blood vessels enter the head. A short ligament fans out from this pit to attach to the horns of the lunate surface and the transverse acetabular ligament. This is known as the Ligament of the Head of the Femur (= Ligamentum Teres). It helps secure the stability of the joint. The ligament of the head of the femur is covered by Synovial Membrane , and runs through the synovial cavity of the hip joint.
The Joint Capsule is attached medially to the acetabular labrum, and laterally to the base of the femoral neck. The fibrous part of the capsule is very thick over most of its coverage. Because its fibers have different orientations, three sep- arate ligaments can be identified.
The first is the Iliofemoral Ligament. It arises from the anterior edge of the ilium between the acetabulum and ante- rior inferior iliac spine, and fans out to insert along a line on the front of the femur between the greater and lesser trochanters called the Intertrochanteric Line. This very strong ligament prevents overextension of the lower limb during standing.
The second is the Ischiofemoral Ligament. It arises from the back of the acetabulum adjacent to the ischial tuberos- ity, and runs laterally to attach onto the back of the femoral neck. This ligament also limits extension of the lower limb.
The third is the Pubofemoral Ligament. It arises from the superior pubic ramus, and fans out laterally to insert along the lower part of the intertrochanteric line on the front of the femoral neck. This weak ligament probably limits abduc- tion of the lower limb.
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4.2 JOINTS OF THE LOWER LIMB 101
Figure 4.6 Structure of the Hip Joint (a) lateral view with femur rotated out of joint; (b) coronal section; (c) posterior view; (d) anterior view.
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4.2 JOINTS OF THE LOWER LIMB 103
Figure 4.7 Structure of the Knee Joint (a) anterior view of right knee in flexion; (b) posterior view of right knee in extension; (c) sagittal section (lateral to midline); (d) superior view of right tibial plateau.
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Ankle Joint
Strictly speaking, the ankle joint involves only the articulation between the talus and the tibia and fibula. It permits dor- siflexion and plantarflexion of the foot. Other movements of the foot—eversion, inversion and rotation—are provided by joints between the tarsal bones. Because these intertarsal joints are involved together with the ankle in the principal movements of the foot, they will be considered together under the rubric of the “ankle.” Both sets of joints are centered around the talus as the keystone of movement.
The Talocrural ( Ankle) Joint involves the articulation of the body of the Talus with the tibia and fibula. In dorsiflexion and plantarflexion, the superior surface of the talus glides over the distal surface of the tibia. The medial and lateral sides of the body of the talus articulate with the Medial malleolus and the Lateral malleolus , which pre- vent side-to-side movement and rotation of the talus.
The talocrural joint has a single joint capsule. It is stabilized by ligaments that prevent the talus from moving anteriorly and posteriorly, and from being abducted or adducted. Three ligaments fan out from the medial malleolus to insert onto the talus and Calcaneus. This fan is known as the Deltoid ligament. Three ligaments also radiate from the lateral malleolus to insert onto the talus and calcaneus. These three— Anterior talofibular, Calcaneofibular, and Posterior talofibular — form what is referred to as the Lateral collateral ligament^7.
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The ankle is the most frequently injured joint of the body. The lateral collateral ligament is commonly damaged because it is much weaker than the deltoid ligament. A sprained ankle results from twisting the talus within the tibiofibular mortise, and it nearly always involves inversion, with consequent damage to the weaker lateral collateral ligament.
The Intertarsal Joints involve articulations between the talus and calcaneus, and between them and the Navicular and Cuboid. Two articulations (anterior and posterior) between the talus and calcaneus comprise the Subtalar Joint. Articulations between the talus and navicular and between the calcaneus and cuboid constitute the Transverse Tarsal Joint. The anterior subtalar joint relates the talus to both the calcaneus and navicular in a single capsule; thus, it is part of both the subtalar and transverse tarsal joints.
The subtalar and transverse tarsal joints are reinforced by a series of ligaments. The two most significant of these run on the plantar aspect between the calcaneus and cuboid (laterally) and between the calcaneus and navicular (medially). The latter is known as the Spring Ligament —its significance was noted earlier in the discussion of the arch of the foot (p. 98).
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106 LABORATORY THE LOWER LIMB
4.3 INNERVATION OF THE LOWER LIMB
There is a pattern to the innervation of the lower limb muscles. The key to remembering the nerves that supply the mus- cles is to appreciate this developmental pattern.
The muscles in the thigh, leg, and foot occupy one of two compartments. One is dorsal; the other is ventral. From your experience with the upper limb, and your knowledge of anatomical terminology, you might expect that the dorsal com- partment would occupy the posterior aspect, and that the ventral compartment would be on the anterior side of the lower limb. This is not the case! Rather, the situation is exactly the reverse of what you might expect.
In the lower limb, the Dorsal Division Muscles occupy the anterior and lateral aspects of the thigh and leg; the Ven- tral Division Muscles occupy the posterior and medial aspects of the thigh and leg, and the sole of the foot.
How does this seemingly bizarre situation come to be? The explanation lies in the fact that the lower limb undergoes rotation and repositioning during embryonic development. This mimics the changes that took place during the course of evolution.
In the exercise that follows on pages 108–109, we will relive our embryonic development (and recapitulate our evolu- tionary heritage) to better understand the pattern of lower limb innervation. The rotation and repositioning of the lower limb is essentially a four-stage process. Follow this by performing each exercise.
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4.3 INNERVATION OF THE LOWER LIMB 107
Figure 4.9 Muscle Compartments of the Lower Limb Schematic transverse sections through a left thigh, leg, and foot. (Fe femur, Fi fibula, T tibia, 1m first metatarsal) Color the ventral compartments blue, and the dorsal compartments red.
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4.3 INNERVATION OF THE LOWER LIMB 109
Stage Three Your trunk is still vertical, but now your lower limb is flexed, and your knee and toes point forward. ( Again, color the stippled cross section red, and the open cross section blue. )
Now, simply extend your thigh and leg. This brings you to stage 4.
Stage Four This is the Anatomical Position. ( Again, color the stippled cross sections red, and the open cross sections blue. )
Note how the Dorsal Division Muscles that arise from the ilium and run onto what was originally the dorsal surface of your thigh have come to occupy its anterior surface. Note how the muscles that run from the dorsal surface of the thigh onto the lateral aspect of your leg now occupy its anterior surface. Note that the muscles that run from the lateral surface of the leg onto the top of the foot still occupy its dorsal surface.
Observe the changes to the Ventral Division Muscles.
110 LABORATORY THE LOWER LIMB
The Lumbosacral Plexus
The muscles of the lower limb are served by the ventral rami of seven spinal nerves (L2–S3) via the lumbosacral plexus. The lumbosacral plexus actually has nine roots, but spinal nerves T12 and L1 do not provide fibers to lower limb mus- cles. Recall that a peripheral nerve that emerges from a plexus has axons from more than one ventral ramus.
Each ventral ramus carries fibers that will serve a ventral compartment muscle, and fibers that will serve a dorsal com- partment muscle.
Two nearly separate entities, known as the Lumbar Plexus (T12–L4), and the Sacral Plexus (L5–S3), are connected by a single twig between L4 and L5, the Lumbosacral Trunk.
The lumbosacral plexus differs from the brachial plexus in that there are no trunks or cords. Instead, the ventral and dor- sal compartment fibers of each root split off from one another and then combine directly to form the peripheral nerves.
Peripheral Nerves
Ventral compartment fibers from L2–L4 form: Obturator nerve Dorsal compartment fibers from L2–L4 form:
These two nerves serve only hip and thigh muscles.
Femoral nerve
Ventral compartment fibers from L4–S3 form: Tibial nerve Nerve to Obturator Internus Nerve to Quadratus Femoris Dorsal compartment fibers from L4–S3 form: These six nerves serve hip and thigh muscles, and all muscles Common Fibular nerve* below the knee. Superior Gluteal nerve Inferior Gluteal nerve
The Tibial nerve and Common Fibular nerve run together in a single sheath through much of the thigh as the Sciatic Nerve. Thus, the sciatic nerve carries both ventral and dorsal compartment fibers.
*Note that older anatomy texts refer to the Peroneal nerve (i.e., Common Peroneal and its branches, the Deep Peroneal and Super- ficial Peroneal nerves). The term Peroneal has undergone a formal change to Fibular.
