The Linea Aspera Is Located On The, A Technical Note

Paul Rea MBChB, MSc, PhD, MIMI, RMIP, FHEA, FRSA, in Essential Clinically Applied Anatomy of the Peripheral Nervous System in the Limbs, 2015

3.3.11.3 Accessory Obturator Nerve

The accessory nerve arises from either the third and fourth lumbar vertebrae or the second and third lumbar vertebrae. It is inconstant, but when present, emerges from the medial margin of the psoas major and enters the thigh anterior to the pubis. It communicates with the anterior branch of the obturator nerve, supplying branches to the pectineus, but also the hip joint. It may also supply the adductor longus, but its presence is not common (Akkaya et al., 2008).

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3.3.11.3.1 Adductor Longus

This muscle attaches from the body of the pubis below the pubic crest proximally, passing to the linea aspera of the femur, approximately in its mid-third portion.

3.3.11.3.2 Adductor Magnus

The adductor magnus has two parts to it – the adductor portion, and the hamstring part. The adductor portion attaches proximally to the inferior ramus of the pubis, and also the ramus of the ischium. The hamstring part arises from the ischial tuberosity.

The distal attachments vary depending on if it is the adductor or hamstring portion. The adductor part attaches distally to the linea aspera, the gluteal tuberosity on the femur and the medial supracondylar line on the distal femur. The hamstring portion attaches onto the femur at the adductor tubercle on the inferomedial portion of the bone.

3.3.11.3.3 Adductor Brevis

The adductor brevis attaches proximally to the body and also the inferior ramus of the pubis passing to the pectineal line and the linea aspera on the femur, but only its proximal portion.

3.3.11.3.4 Obturator Externus

The obturator externus attaches proximally to the obturator foramen margins and membrane and passes to attach distally onto the femur, at the trochanteric fossa. The obturator externus is responsible for adduction of the thigh and also aids medial rotation of the thigh.

3.3.11.3.5 Pectineus

The pectineus muscle attaches proximally to the pubis (superior ramus) passing distally to attach to the pectineal line on the upper medial aspect of the femur. Pectineus is responsible for adduction and flexion of the thigh, and helps somewhat in rotation of the thigh medially.

3.3.11.3.6 Gracilis

This long thin strap muscle attaches proximally to the inferior ramus of the pubis and its body passing to its distal attachment site at the upper medial portion on the tibia. Again, gracilis is responsible for adduction of the thigh, flexion of the leg, but also medial rotation of the thigh. The name gracilis comes from its Latin meaning of slender.

Attachments: From the inferior ramus of the pubis to the upper third of the medial lip of the linea aspera

Innervation: Obturator nerve (L2–4)

Muscle type: Postural (type 1), with tendency to shorten and tighten when chronically stressed

Function: Adducts and flexes thigh and has (controversial) axial rotation benefits, depending upon femur position

Synergists:For thigh adduction: remaining adductor group, gracilis and pectineusFor thigh adduction-flexion action: iliopsoas, remaining adductor group, pectineus and gracilis

For axial rotation of the thigh: depends upon initial position of the hip

Antagonists: To flexion: gluteus maximus, hamstrings, portions of adductor magnusTo adduction: gluteus medius and minimus, tensor fasciae latae, upper fibers of gluteus maximus.

For intact femora or proximal ends, the head is proximal and faces medially. The lesser trochanter and linea aspera are posterior.

For isolated femoral heads, the fovea is medial and displaced posteriorly and inferiorly. The posteroinferior head-neck junction is more deeply excavated than the anterosuperior junction.

For proximal femoral shafts, the nutrient foramen opens distally, and the linea aspera is posterior and thins inferiorly. The gluteal tuberosity is superior and faces posterolaterally.

For femoral midshafts, the nutrient foramen opens distally, the bone widens distally, and the lateral posterior surface is usually more concave than the medial posterior surface.

For distal femoral shafts, the shaft widens distally and the lateral supracondylar ridge is more prominent than the medial. The medial condyle extends more distally than the lateral.

For femoral distal ends, the intercondylar notch is posterior and distal, and the lateral border of the patellar notch is more elevated. The lateral condyle bears the popliteal groove, and the medial condyle bulges away from the line of the shaft. Relative to the shaft axis, the lateral condyle extends more posteriorly than the medial. The medial condyle extends more distally than the lateral because in anatomical position the femur angles beneath the body.

For intact femora or proximal ends, the head is proximal and faces medially. The lesser trochanter and linea aspera are posterior.

For isolated femoral heads, the fovea is medial and displaced posteriorly and inferiorly. The posteroinferior head–neck junction is more deeply excavated than the anterosuperior junction.

For proximal femoral shafts, the nutrient foramen opens distally, and the linea aspera is posterior and thins inferiorly. The gluteal tuberosity is superior and faces posterolaterally.

For femoral midshafts, the nutrient foramen opens distally, the bone widens distally, and the lateral posterior surface is usually more concave than the medial posterior surface.

For distal femoral shafts, the shaft widens distally and the lateral supracondylar ridge is more prominent than the medial. The medial condyle extends more distally than the lateral.

For femoral distal ends, the intercondylar notch is posterior and distal, and the lateral border of the patellar notch is more elevated. The lateral condyle bears the popliteal groove, and the medial condyle bulges away from the line of the shaft. Relative to the shaft axis, the lateral condyle extends more posteriorly than the medial. The medial condyle extends more distally than the lateral because in anatomical position the femur angles beneath the body.

Attachments: From the anterior and lower surfaces of the greater trochanter, intertrochanteric line of femur, gluteal tuberosity, lateral intermuscular septum and lateral lip of linea aspera to insert into the lateral border of the patella and continue distal to the patella (as the patellar tendon or patellar ligament) to attach to the tibial tuberosity. Some fibers merge into the lateral patellar retinaculum

Innervation: Femoral nerve (L2–4)

Muscle type: Phasic, prone to weakening under stress

Function: Extends the leg at the knee and draws the patella laterally

Synergists:For knee extension: rectus femoris, vastus medialis and vastus intermedius

Antagonists:To knee extension: biceps femoris, semi-membranosus, semitendinosus, gastrocnemius, popliteus, gracilis and sartorius

The pelvis or hip consists of paired innominate bones (Figure 7.21) that articulate with each other ventrally at the pelvic symphysis and with the sacrum dorsally. Examine a mounted specimen, and note the position and orientation of the innominate. Each innominate is composed largely from three bones, the ilium, ischium, and pubis, although a fourth center of ossification, the acetabular bone, makes a small contribution. These bones are firmly fused together in the adult. Examine an innominate bone in lateral view and note the large ventral opening, the obturator foramen. Locate the acetabulum, the deep socket that receives the head of the femur (see later).

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The ilium consists of a body, near the acetabulum, and an anterodorsally projecting wing. The iliac crest is the roughened, anterodorsal edge of the ilium. The rugose articular surface for the sacrum lies on the medial surface of the wing. The ischium extends posteriorly from the acetabulum and has an expanded termination, the ischial tuberosity. The pubis and the rest of the ischium are oriented ventromedially. Both bones contribute to the medial margin of the obturator foramen. Also, the ischium and pubis of the each side of the body meet to form, respectively, the ischial and pubic symphyses, which together form the pelvic symphysis. The acetabular bone forms the thin, medial part of the acetabulum.

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Femur

The femur (Figure 7.22) is the bone of the proximal part of the hind limb, or thigh. The head of the femur is a hemispherical surface that fits into the acetabulum of the innominate. The head is supported by the neck, which projects obliquely from the proximal end of the femur. Lateral to the head is the roughened, proximally projecting greater trochanter, which serves for attachments of hip musculature. The deep depression posteriorly between the trochanter and head is the trochanteric fossa. On the posterior surface of the shaft, just distal to the head, is the lesser trochanter. The intertrochanteric line connects the two trochanters, but is especially defined along the posterior edge of the greater trochanter. The most prominent muscular insertion site on the diaphysis is the linea aspera, the roughened ridge that extends diagonally along the posterior surface of the femur.

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The femur expands distally into the prominent and posteriorly projecting lateral and medial condyles. Each condyle bears a smooth, semicircular surface for articulation with the tibia. The intercondyloid fossa is the depression posteriorly between the condyles. The rugose areas for muscular attachment proximal to the condyles are the lateral and medial epicondyles. The patellar trochlea, for articulation with the patella, lies anteriorly between the condyles. It is a smooth, shallow trough oriented proximodistally.

Patella

The patella (Figure 7.22), or kneecap, is a small, tear-shaped sesamoid bone, with its apex directed distally. Its anterior surface is roughened. Posteriorly it bears a smooth, shallowly concave surface for articulation with the femur.

Tibia

The tibia (Figure 7.23) is the larger and medial bone of the crus, or middle segment of the hind limb. Its proximal surface bears lateral and medial condyles that articulate with the femur. Just distal to the lateral condyle, on the lateral surface and facing distally, is the small, nearly oval facet for the head of the fibula (see later). On the posterior surface of the tibia, between the condyles, is the popliteal notch. A small muscle, the popliteus, lies in the notch and is a flexor of the knee joint. The tibial tuberosity, for insertion of the patellar ligament, lies anteriorly. The tibial crest continues distally from the tuberosity along the shaft.

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The distal end of the tibia has two articular surfaces. The large surface on the distal surface, the cochlea tibiae, is for the astragalus, the tarsal bone with which the pes articulates with the hind limb. Note how this facet consists of two sulci separated by a median ridge. This structure restricts motion at the ankle almost entirely to a fore and aft direction, producing flexion and extension. If available, manipulate the tibia and pes to observe this. The small, nearly triangular fibular facet, for articulation with the fibula, faces posterolaterally and is contiguous with the lateral part of the cochlea tibiae. The medial malleolus is the distal extension of the tibia's medial surface. It forms the medial protrusion of the ankle.

Fibula

The fibula (Figure 7.23) is the slender, lateral, and shorter bone of the crus. The head is irregular and expanded. It bears a proximal facet for articulation with the tibia. The slender shaft widens distally. There are two distal facets, both toward the anterior half of the medial surface. The more proximal facet is for the distal articulation with the tibia. The distal facet articulates with the lateral part of the trochlea of the astragalus. The lateral malleolus projects distally from the posterolateral end of the fibula.

Pes

The pes (Figure 7.24) consists of tarsals, metatarsals, and phalanges. There are seven tarsals, but the two most proximal bones, the astragalus and calcaneum, are much larger than the others. The astragalus is the medial bone. It articulates proximally with the tibia and fibula. Note again the form of the surface, or trochlea tali, for articulation with the tibia. The trochlea tali consists of medial and lateral keeled surfaces separated by a sulcus. The astragalus articulates ventrally with the calcaneum, which lies laterally. It is about twice as long as the astragalus and projects posteriorly as the heel. Distally the astragalus articulates with the navicular, while the calcaneum articulates with the cuboid. The navicular articulates distally with the lateral, intermediate, and medial cuneiform bones, and laterally with the cuboid. Note how the articulations among the tarsals and metatarsals are arranged to produce interlocking joints that tend to restrict movement. For example, the lateral cuneiform articulates with metatarsal III distally, but its medial surface articulates with both the intermediate cuneiform and metatarsal II. There are five metatarsals. The first is strongly reduced to a small nub that articulates with the medial cuneiform. The phalanges for digit 1 have been lost in the cat. The remaining metatarsals are stout, elongated elements and each articulates with a series of three phalanges, the proximal, intermediate, and ungual phalanges.

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Robert Lewis Maynard, Noel Downes, in Anatomy and Histology of the Laboratory Rat in Toxicology and Biomedical Research, 2019

Muscles of the Pelvic Girdle

The muscles of the pelvic girdle present certain problems. In the distal hindlimb, the separation of muscle groups into ventral and dorsal (flexor and extensor) is obvious, but less so around the hip joint, although separation into ventral and dorsal is possible on the basis of the embryology of the muscles (Romer, 1970). It is tempting, but incorrect, to assume that are similarities between the muscles of the pelvic and pectoral girdles. A recent paper by Diogo and Molnar (2014), with the formidable title: ‘Comparative anatomy, evolution and homologies of tetrapod hindlimb muscles, comparison with forelimb muscles, and deconstruction of the forelimb-hindlimb serial homology hypothesis’ is available online, and is worth looking at, if only as an example of the level of scholarship still being applied to the study of comparative anatomy. Abandoning any attempt to homologise between the fore and hindlimbs musculature, we shall merely outline briefly the arrangement of muscles in the rat, and compare with man where possible.

The most obvious difference between the pelvic and pectoral girdles is that the pectoral girdle lies outside the body wall (outside the ribs), whereas the pelvic girdle forms a part of the body wall itself. No muscles run from within the chest to the forelimb, but a number of muscles run from the ventral surfaces of the lumbar vertebrae to the hindlimb. In man, psoas runs from the ventral surfaces of lumbar vertebrae where it is joined by iliacus, running from the inner surface of the ilium, to form a joint tendon that inserts into the lesser trochanter of the femur. Both act as flexors of the hip joint. Obturator internus also arises inside the pelvis and runs out to the femur.

Rats, unlike men, have tails for which seven muscles that move the tail have been described (Hebel and Stromberg, 1976). The ilioischiopubo-coccygeus (as Romer said: ‘what names these muscles have’) is the largest and runs from the inner surfaces of the three bones of the pelvic girdle to the vertebrae of the tail. This muscle, rather surprisingly as men have no tails, is of interest to human anatomists as it slips down the inner walls of the pelvis and forms the levator ani muscle, the important muscle of the pelvic floor.

Muscles Arising From the Pelvis and Causing the Hindlimb to Move at the Hip JointExtensors of the Hip Joint

Extension of the hip joint, defined as occurring when the hindlimb is pulled back, is a key movement of locomotion: as the limb is pressed back against the ground, the body is propelled forwards. The gluteal muscles run from the outer surface of the ilium to the great trochanter of the femur, and extend the leg at the hip joint. The mechanical advantage of these muscles is small because the site of insertion is close to the hip joint, but these are powerful muscles in man, though rather less so in the rat. In the rat, gluteus maximus blends with another muscle, tensor fasciae latae, which is attached to the strong fascia running down the outer side of the thigh.

Muscles of the Thigh

These muscles can be divided into the hamstrings (behind), the extensors of the knee (in front) and the adductors of the hip joint (on the inner or medial aspect). Some cross both the hip and knee joints and therefore act on both.

The Hamstrings

These comprise three muscles, biceps femoris, semimembranosus and semitendinosus. All run from the ischial tuberosity to the lower, posterior, surface of the femur and the upper posterior surfaces of the tibia and/or fibula. In the rat, there are small medial and lateral fabellae (sesamoid bones) lying behind the knee into which the hamstrings insert en route to the bones of the second segment of the limb. The rat also has a caudo-femoralis muscle associated with biceps that inserts across the lower posterior surface of the femur from the medial fabella to the lateral fabella (Greene, 1935). All these muscles extend the hip and flex the knee.

Muscles of the Anterior Aspect of the Thigh

Four muscles; rectus femoris, vastus lateralis, vastus intermedius and vastus medialis, make up the muscle usually referred to as the quadriceps femoris. All arise from the upper end of the femur (rectus femoris also arises from the pubis) and are inserted into the patella. The patella is a sesamoid bone that develops in the tendon of the quadriceps. The part of the tendon below the patella, the patellar ligament, is attached to the upper anterior part of the tibia. Although all these muscles mainly extend the knee joint, rectus is also a weak flexor of the hip joint.

Muscles of the Medial Aspect of the Thigh

There are adductors, longus, magnus and brevis (long, large and short) and gracilis (thin) that run from the pubis and from the shaft of the femur to the tibia. The attachment to the shaft of the femur is long, and in man is marked by the linea aspera (roughened line) on the posterior surface of the bone.

In addition, there are the lateral rotators piriformis, obturator externus and internus, quadratus femoris or gemelli; short muscles that run from the pelvis to the upper end of the femur and rotate the femur and stabilise the hip joint.

Muscles of the Second Segment of the Hindlimb

Human anatomists make a great song and dance about reserving the term ‘leg’ for the second segment of the hindlimb, and ‘arm’ for the first segment of the forelimb. When thinking about rats we all know that they have four legs. The muscles of the second segment (hindlimb understood) are arranged as extensors and flexors of the ankle joint.

Veterinary anatomists refer to the knee joint as the stifle joint, and to the ankle joint as the tarsal joint or hock. This confusing terminology led Dr. Johnson astray when he defined the pastern of a horse as the knee (the pastern is the proximal phalanx). His contempt for such trifles is recorded in his reply to the lady who asked him why he had done this: ‘Ignorance, Madam, sheer ignorance’ But movement of the ankle joint also presents what Winston Churchill would no doubt have called further terminological inexactitudes. If you think of your own ankle, it seems logical to call a downward movement of the foot extension, and an upward movement as flexion. To the anatomist this is incorrect, because flexion means the approximation of the flexor or volar surfaces (the sole of the foot and the back of the leg), so an upward movement of the foot is a further extension of an already extended joint, and a downward movement is flexion. Clinicians, not being obsessed with anatomical correctitude (the Johnsonian style is catching), define the movements as plantar-flexion (foot moved down) and dorsi-flexion (foot moved up). By these definitions, gastrocnemius and soleus are plantar-flexors, although Hebel and Stromberg defined them as extensors of the ankle joint, and combined them as triceps surae.

Muscles of the Posterior Aspect of the Second Segment

These include gastrocnemius, soleus, tibialis posterior and a group of long flexors of the digits. Gastrocnemius arises as two heads from the medial and lateral femoral epicondyles and fabellae, and soleus by a slender tendon from the head of the fibula (Greene, 1935). Gastrocnemius lies superficial to soleus, and together they combine to produce a single tendon (of Achilles) that is inserted into the calcaneum, from where they plantar-flex (or flex) the ankle. The rat has a long hindfoot, so the calcaneus projects well behind the ankle joint, providing good leverage when the digits are pressed to the ground, as in running. Tibialis posterior (Geene, using human anatomy as a basis for describing rat muscles, uses this term, Hebel and Stromberg prefer tibialis cranius and add tibialis caudalis as a separate muscle), flexor halluicis longus and flexor digitorum longus arise from the upper posterior surfaces of the tibia and fibula, run down on the medial side of the ankle joint, and on into the sole of the foot to reach bones of the tarsus (in the case of tibialis posterior) or of the digits. This is another area of confusion. In man, there is a large superficial muscle called flexor digitorum brevis in the sole of the foot, but in the rat, the equivalent of this muscle occurs with the long flexors described as flexor digitorum superficialis (see above) or plantaris (see below), and is shown by Hebel and Stromberg as a large muscle of the posterior aspect of the second segment. Table 6.2 may help.

ManRatRat
Greene (1935) Hebel and Stromberg (1976)
Flexor digitorum longus Flexor digitorum longus and flexor hallucis longus Flexor digitorum profundus and flexor digiti primi
Flexor hallucis longus
Flexor digitorum brevis (in the sole) Plantaris: fusing with flexor digitorum brevis in the sole of the foot Flexor digistorum superficialis: fusing with flexor digitorum brevis in the sole of the foot

Although Hebel and Stromberg make no mention of plantaris, it is mentioned in works on human anatomy, and like palmaris in the forelimb, is said to be a remnant of a superficial flexor of the digits that fails to reach beyond the sole or the palm.

Muscles of the Lateral Aspect of the Second Segment

This group is formed by peroneus longus and brevis, and two muscles not described in man, peroneus digiti quarti and peroneus digiti quinti. Each arises from the fibula (p. longus also arises from the lateral condyle of the tibia) and run to metatarsals having passed around the lateral side of the ankle joint and entered the sole of the foot. They lift the lateral edge of the foot (eversion) and plantar flex the ankle joint.

Muscles of the Anterior Aspect of the Second Segment

Here, we find the extensors of the ankle joint and digits: tibialis anterior, extensor digitorum longus and extensor hallucis longus. The major origins of all three muscles are from the anterior surfaces of the tibia and fibula, but extensor digitorum longus also arises in part from the lateral epicondyle of the femur. Tibialis anterior runs to the first (medial) cuneiform bone and to the first metatarsal and the long extensors run to the distal phalanges.

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Short Muscles of the Foot

Interest in these small muscles is likely to limited, not just among toxicologists. They are similar to those of the hand, but in the rat, unlike man, flexor digitorum brevis is a small muscle. In the rat the second digit has its own adductor (not the case in man), and there are no dorsal interossei in the rat hindfoot (Parsons, 1896). The plantar (ventral) interossei are well-developed muscles, and as in the forelimb, the rat has no opponens muscles for the hallux or fifth digit (Greene, 1935).

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