Download Musculoskeletal System

Musculoskeletal System
Parts of the Long Bone
Bones of the Body
Shoulder Girdle
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There are 7 true ribs, 5 false ribs, and 2 floating ribs.
Upper Extremeties
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Pelvis
Carpals- 8
Metacarpals- 5
Phalanges- 14 (Proximal, 5, Middle, 4, Distal, 5)
Lower Extremeties
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Tarsals- 7
Metatarsals- 5
Phalanges- 14 (proximal, 5, middle, 4, distal, 5)
Vertebral Column
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Cervical- 7
Thoracic- 12
Lumbar- 5
Sacral- 5 (Fuse to form the sacrum (1))
Coccygeal (2-4): fuse to form coccyx (1)
Congenital and Hereditary Diseases of the Bone
Achondroplasia
 AD
 Impairment of long bone formation, resulting in shorter bones.
 Most common cause of dwarfism (50%)
Osteogenesis Imperfecta
 Brittle Bone Disease
 Improper bone formation
o Defect in Type I collagen
 Genetic
 Fairly common
 Blue sclera
 Multiple fractures
Osteoporosis
 This is accelerated bone loss. Faster than normal
o Normal loss is about 1% per year after 35 years.
o Normal vertebral bone is square and dense.
o 1:2 females over 70 will have an osteoporotic fracture
 1 in 40 males
 Pathogenesis
o Microarchitectural deterioration of bone tissue leading to decreased bone
mass and bone fragility
 Classification
o Primary
 Simple, standard
o Secondary
 Due to other conditions (hyperparathyroidism, neoplasms, tumors,
malnutrition, iatrogenic, steroids)
 Risk Factors
o Females
o Age >70 years
o Caucasian or Asian races
o Early onset of menopause
 Estrogen protective
o Longer menopausal interval
o Inactivitiy, especially lack of weight bearing exercise
o Decreased calcium
o Smoking, alcohol
o Decreased exposure to sun, because of decreased levels of vitamin D.
 Consequences
o Fracture
 Hip (femoral neck)- most common
 Wrist
 Vertebrae
 Prevention Strategies
o Behavior modification
o Diet
 Calcium- 1,000 mg/day
 Vitamin D
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o Exercise
 Weight bearing
o Decrease smoking and excessive alcohol
o Inhaled vs. injested steroids
Treatment
o Calcium, Vitamin D (increase amounts)
o (Probably not) Estrogen
 More risk than a benefit
o Bisphonsphonates (Actonel, Fosamax)
 Inhibit osteoclasts that break bones
o Raloxifene (SERM, Evista)
 SERM- selective estrogen receptor modulators
 Increased side effects
o Calcitonin (Miacalin Nasal Spray)
 Hormone that decreases bone reabsorption
 Injection/nasal spray
Bone diseases Associated with Hyperparathyroidism
 Effects of parathyroid hormone
o Osteoclast activation with increased bone reabsorption and calcium
activation.
o Increased reabsorption of calcium by renal tubules
o Increased synthesis of active vitamin D by kidneys, which enhances
calcium absorption by the gut.
 Result is hypercalcemia
Osteomyelitis
 Bone infections
 Pyogenic
o Bacterial. Hematogenous spread or from direct surrounding.
o Most common
 Tuberculosus
o Rarer
o Usually just confined to the lungs.
o Pus forming (Gram + Staph/Strep)
o Treatment: surgical debridement
o Problem due to increased pressure.
o Pox Disease- Tuberculosis in the spine
 Diagnosis of Acute Osteomyelitis
o Pus on aspiration
o Positive bacterial culture from bone or blood
o Presence of classic signs and symptoms of acute osteomyelitis
o Radiographic changes typical of osteomyelitis.
 Two of the listed findings must be present for establishment of the
diagnosis
 Brodie’s Abcess
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o Pus caught in the bone.
o May need surgery if bad. Most do not.
Treatment
o Acute hematogenous osteomyelitis
 4-6 week course of appropriate antimicrobial therapy (via IV)
o Chronic osteomyelitis
 Treated with antibiotics and surgical debridement.
Paget’s Disease
 Aka Osteitis deformans
 Metabolic bone disease
 Elderly (3%)
 Subclinical
 In 1 or more bones
 Increased metabolism causes deformation
 Responds well to inhaled calcitonin
Bone tumors
 Nomenclature
 Bone forming tumors
o Benign
 Osteoma
 Slow-growing
 Asymptomatic
 Harmless if they do not obstruct anything
 Osteoid osteoma
 Tender, painful
 In long bones (children and young adults)
 See a “nidus” (<2cm) surrounded by reactive bone (causing
pain).
 Treatment: antiinflammatories or surgery
 Osteoblastoma
 “Giant Osteoid Osteomas”
 Typically found in vertebrae or pelvis and larger.
o Malignant
 Osteosarcoma
 Aka Osteogenic Sarcome
 Most common type of primary bone cancer
 This is a cancer of the osteoblasts
 The pathologist must see malignant cells making their own
osteoid.
 Associated with retinoblastoma (on same chromosome)
 Arise in the shaft of long bones
 Results in starburst fractures
 Starts at the metaphysis and goes to the cortex.
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 Usually around the knee
 Not too common
 Can extend to the soft tissue
 Most often seen in male adolescents.
Cartilaginous Tumors
o Benign
 Osteochondroma
 Aka “Exostosis”
 Outer branches growing off a bone
 Cartilage on end.
 Incidental finding
 Genetic
 No problem
 Chondroma
 (Enchondroma)
 Malignant more with genetics (Oiler’s Syndrome)
 Inside the bone
 Popcorn shaped cartilage in the bone
 In fingers, etc.
 Can occur with stress fractures
 Usually harmless
o Malignant
 Chondrosarcoma
 After osteosarcoma, this is the 2nd most common bone
tumor.
 Rare
 In pelvis of middle-aged men.
 Slow growing
 Painful
 See bone destruction, calcification, and tumor
Other tumors and tumor-like conditions
o Giant cell tumor
 Myeloma
 4th most common
 Aggressive
 Multibucleated giant cells
 Tumor of the osteoclasts (destructive cells)
 More lytic
 Also found near the knee
o Ewing’s Tumor
 3rd most common
 In cortex
 In diaphysis
 Younger population
 Aggressive
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 Fast/ painful
Almost only Caucasians
Can metastasize
With early detection, 5 year survival rate is 80%.
 Less with metastasis
Onion skinning- diagnostic
“Moth eaten”
Fibrous Dysplasia
 Bone replaced with fibrous tissue
 Abnormally decreased strength
Diseases of the Joints
 Anatomy
o These are between the bones
o Joint capsule
 Lined with synovium (has vasculature)
 Secretes hyaluronic acid (lube) and used as nutrition
 Fluid comes and goes very easily
 Osteoarthritis
o Most common joint disorder
o Clinical features
 Symptoms
 Joint pain
 Morning stiffness lasting less than 30 minutes
 Joint instability or buckling
 Loss of function
 Signs
 Bony enlargement at affected joints
 Limitation of range of motion
 Crepitus on motions- joints make noises
 Pain with motion and morning stiffness
 Malalignment and/or joint deformity.
 Heberdan’s Nodes
o On distal fingers
 Osteophyte formation restricts movement
 Pattern of Joint involvement
 Axial: cervical and lumbar spine
 Peripheral: distal interphalangeal joint, proximal
interphalangeal joint, first carpometacarpal joints, knees,
hips
 Avascular necrosis
 A cuase of secondary arthritis due to decreased blood
supply
 Death of tissue
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Gout
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o
o
 From trauma or steroids
 Because it is avascular, it is hard to repair.
Slowly progressive
Noninflammatory (just due to wear and tear)
Seen in weight-bearing joints and small joints of hands and feet.
Seen in an x-ray as a narrowing of the articular space (covers
bones/not seen on x-ray)
Treatment
 Nonpharmacologic management
o Patient education
o Exercise (stimulate synovium)
o Assistive devices (cane)
o Weight management
o Supplements (glucosamine)
 Surgery
 Pharmacologic Treatments
o Simple analgesics
 Tylenol
o NSAIDs
 Ibuprofen
o Local analgesics
 Menthol
 Intra-articular corticolsteroid injections
o Intra-articular injections of hyaluronic acid like
products
 Increased lubrication for 6 months
Deposition of uric acid crystals in joints
Increased serum uric acid levels, or can precipitate
Pain, redness, inflammation
Kidney stones
Classic location- the big toes
Monoarticular- involves 1 joint
Increased risk
 Males, overweight, follows alcohol intake, foods with nitrates
o Clinical presentation
 Acute gouty arthritis
 Red, hot, uncomfortable
 Interval gout (subacute)
 Tophaceous gout (uric acid globs in soft tissue, called tophi)
 Tophi seen on ligaments, tendons, and around joints.
 Renal manifestations
o Diagnose with fluid extraction
 Aspirated synovial fluid looks like crystals. No bacteria is seen.
o Treatment
 Acute gouty arthritis
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 NSAIDs
 Colchicines
 Corticosteroids
 Prevention of recurrent attacks
 Uricosuric Drugs (Probenicid)
o Makes you pee out all of the uric acid.
 Decrease uric acid production
o Allopurinol
 Colchicine
 The goal is to decrease serum uric acid levels. This
prevents kidney problems, tophi, and bone destruction.
Infective arthritis
o Septic/suppurative
o Due to trauma, gonorrhea, hematogenous spread, etc.
o Bacteria changes the cartilage quickly, so aspiration and diagnosis should
be done fast.
Rheumatoid Arthritis
 Autoimmune, inflammatory arthritis
 Abrupt onset
 Associated with Sjogren’s Syndrome, episcleritis, carditis, pleuritis, hepatitis, and
vasculitis
 Swan deformity with RA
 Boutonniere’s Deformity- opposite of swan neck
 Diagnostic criteria (Need 4)
o Morning stiffness lasting longer than 1 hour before improvement
o Arthritis involving 3 or more joints (and other systems)
o Arthritis of the hand, particularly involvement of the proximal
interphalangeal (PIP) joints, metacarpophalangeal (MCP) joints, or wrist
joints.
o Bilateral involvement of joint areas (ie both wrists, symmetric PI P and
MCP joints
o Positive serum rheumatoid factor (RF)
 Not seen immediately
o Rheumatoid nodules
o Radiographic evidence of RA
 Destruction/deformation of bone
Soft Tissue Tumors
 Very rare
 Tumors of Adipose Tissue
o Lipoma
 Most common
 Benign
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 Slow
 Mature fat cells in subcutaneous tissue
 Nonmobile (skin around it moves)
 Normally 1-2cm
 Treatment: removal.
o Liposarcoma
 Rapid, fixed, painful
Tumors of fibrous tissue
o Nodular fascitis
o Fibromatoses
o Fibrosarcomas
Fibrohistiocytic tumors
o Fibrous histiocytoma
o Dermatofibrosarcoma Protuberans
o Malignant Fibrous Histiocytoma
 2nd most common
Neoplasms of skeletal muscle
o Rhabdomyosarcoma
Synovial sarcoma
The Skull
 The skull consists essentially of 2 principal parts
o The cranial portion which forms the brain case
o The facial portion forming the framework for the eyes, nose, and mouth.
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Cranial Bones
o Frontal- front and upper part of the forehead
o Parietal- forms roof and sides of the cranium
o Occipital- forms dorsal part of the cranium
o Temporal- forms sides and part of floor of cranium
o Sphenoid- forms anterior floor of cranium
 Body- sella turcica
 Greater wing
 Foramen rotundum
 Foramen ovale
 Foramen spinosum
 Lesser wing- anterior clinoid processes
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o Ethmoid- posterior to the lacrimal bone, medial.
Facial Bones
o Nasal- forms upper portion of nose
o Lacrimal- anterior medial wall of orbit
o Palatine- forms upper palate of the mouth
o Zygomatic- forms cheekbone
o Mandible- forms lower jaw
o Maxillae- forms upper jaw
o Inferior nasal conchae- forms part of lateral wall of nasal cavity
o Vomer- forms lower posterior part of nasal septum
Sutures
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o
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o
o
o
o
Fossa
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Coronal- frontal and parietal
Sagittal- parietal to parietal
Squamousal- parietal to temporal
Lambdoidal- parietal to occipital
Bregma- junction of coronal and sagittal sutures
Lambda- junction of sagittal and lambdoidal sutures
o Temporal fossa
 Bound above and behind by the temporal bones, in front by frontal
and zygomatic bones, and below by infratemporal crest.
 Houses the temporalis muscle.
 Communicates inferiorly with infratemporal fossa
 Pterion
 Sutural landmark
 Intersection of squamosal and parietosphenoid sutures.
o Infratemporal fossa
 Bound in front by maxilla, above by great wing of the sphenoid,
and below by the border of the maxilla.
 Inferior to temporal fossa and posterior to zygomatic arch.
 Communicates with orbit via inferior orbital foramen.
 Houses the mastication muscle.
o Pterygopalatine fossa
 Bound above by body of the sphenoid, in front by maxilla, and
behind by the greater wing of sphenoid.
 Located inferior and posterior to apex of orbit.
 Communicates directly with orbit via inferior orbital foramen.
 Communicates with the middle cranial fossa via the foramen
rotundum and foramen lacerum.
o Interior Skull Cranial Fossa
 Anterior Cranial Fossa
 Bound anteriorly and laterally by the frontal bone and
posteriorly by the lesser wing of the sphenoid.
 Middle Cranial Fossa
 Bound anteriorly and laterally by the frontal bone and
posteriorly by the greater wing of sphenoid.
 Posterior Cranial Fossa
 Bound anteriorly by the dorsum sellae and occipital bone
laterally by the parietal bone.
 Jugular Fossa
 Anterior and temporal to the occipital condyle
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 Foramina
Foramen
Anterior Ethmoid
Cribiform Plate
Posterior Ethmoid
Optic Canal
Pituitary Fossa (Hypophyseal Fossa)
 Within the pituitary gland.
Cranial Fossa
Anterior
Anterior
Anterior
Middle
Superior Orbital Fissure
Middle
Foramen Rotundum
Foramen Ovale
Middle
Middle
Foramen Spinosum
Middle
Foramen Lacerum
Middle
Carotid Canal
Internal Acoutic Meatus
Middle
Posterior
Jugular Foramen
Posterior
Hypoglossal Canal
Foramen Magnum
Posterior
Posterior
Stylomastoid Foramen
Posterior
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Temporo-Mandibular Joint
Contents
Anterior ethmoidal A, V, N
Olfactory nerve bundles
Posterior ethmoidal A, V, N
Optic Nerve (II)
Ophthalmic A
Ocularmotor N (III)
Trochlear Nerve (IV)
Lacrimal branch of V1
Frontal branch of V1
Nasociliary branch of V1
Abducens N (VI)
Superior ophthalmic
Maxillary N
Mandibular N (V3)
Accessory Meningeal A
Lesser petrosal N
(occasionally)
Middle meningeal A and V
Meningeal branch of V3
Internal Carotid A
Internal carotid N plexus
Internal Carotid
Facial N (VII)
Vestibulocochlear N (VIII)
Int. auditory A
Inf. Petrosal sinus
Glossopharyngeal N (IX)
Vagus N (X)
Accessory N (XI)
Sigmoid sinus
Post. Meningeal A
Hypoglosal N (XII)
Medulla oblongata
Meninges
Vertebral As
Meningeal branch of
vertebrals
Spinal roots of accessory N
Facial N
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o Joint by which the mandible is connected to the skull.
o Only synovial joint in the skull.
o Enclosed in an articular capsule. Has an articular disc that divides the joint
into two cavities. A synovial membrane surrounds each cavity.
o Support to the joint is via special ligaments.
Surface of the Cranium
o The bones which form the roof and walls of the cranium are marked off by
well-defined sutures.
o The frontal bone forms the forehead, and the part forming the eyebrows is
known as the supraorbital margin. The bone contains a hollow, air-filled
space, the frontal sinus, which communicates with the cavity of the nose.
o The parietal bones (considered to be bilaterally paired) form the principal
part of the roof and sides of the brain case. They are divided from the
frontal bone by the coronal suture.
o The occipital bone forms the posterior wall. On its inferior aspect it
contains a large opening, the foramen magnum, through which the spinal
cord passes. On either side of this opening is a pair of smooth articulating
surfaces, the occipital condyles, which rest on the vertebral column.
o On the sides of the skull, inferior to the parietals, and between the frontal
and occipital bones, lie the paired temporal bones. The inner and middle
ear are imbedded in this bone, which presents a prominent opening, the
external auditory meatus for the passage of the ear canal. Posterior to this
opening, is a prominent projection, the mastoid process, whose spongy
interior is sometimes the site of infection. The concavity into which the
lower jaw articulates is the mandibular fossa. The slender arch which
passes from this articulation to the orbit is the zygomatic arch, whose
posterior portion is formed by the zygomatic process of the temporal bone.
On the floor of the cranium, between the anteriorly directed extensions of
the occipital and temporal bones, lies an elongated irregularly shaped
opening, the jugular foramen, through which pass the sinuses draining into
the jugular vein, and the 9th and 10th cranial nerves as well. Just lateral to
this is a projection, the base of the long slender styloid process which is
usually broken off. Just anterolateral to the jugular foramen, at the base of
the styloid process, is a large foramen directed anteriorly, the aperture of
the carotid canal, through which the internal carotid passes on its way to
the brain. This canal turns medially and courses through the petrous
portion of the temporal bone emerging above the foramen lacerum in the
interior. Just posterior to the styloid process and just medial to the mastoid
process, is the small stylomastoid foramen which transmits the facial
nerve as it emerges from the cranium. Anterior and medial to the styloid
process is the small foramen spinosum. A straight line can be drawn
through the stylomastoid foramen, styloid process and foramen spinosum.
o The central portion of the floor of the crainium is formed by the rather
complicated sphenoid (wedge-shaped) bone. It has a pair of “greater
wings” (alisphenoid) which may be seen on the lateral surface extending
superiorly up to the border of the parietal bone, and thus separating the
temporal bone from the frontal bone. Its central “body” lies on the floor of
the cranium in the mid-line, where processes from the temporal and
occipital bones extend forward to meet it. Its pterygoid processes (lateral
and medial) are a pair of prominent, inferiorly directed projections,
extending from the root of the “wings” down to the roof of the mouth
(palate). Between these lies the posterior choanae through which the nasal
passages pass to communicate with the pharynx.
o The septum dividing these opening s (nasal septum) is comprised largely
of the vomer (plowshare) bone, whose base extends back between the
pterygoid processes, thus compressing the body of the sphenoid into a
relatively narrow strip at its interior surface.
o The vomer conceals the bone forming the floor of the cranium along the
anterior mid-line. This is the ethmoid bone which forms the roof and most
of the walls of the nasal cavity.
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o On the roof of the orbit, on either side of the ethmoids along their
posterior border, may be seen another pair of anterior extensions from the
sphenoid bone, the lesser “wings,” which make up the remainder of the
floor of the crainium. The optic foramen passes through these processes. It
carries the ophthalmic artery as well as the optic nerve, into the orbit. The
large space between the greater and lesser wings of the sphenoids
constitute the supra-orbital fissure, which extends inferiorly into the infraorbital fissure.
Interior of the Cranium
o The composition of the walls of the cranium should be further clarified by
studying its surface from the interior. On the superior surface will be seen
a prominent shallow mid-line groove between the parietals which marks
the position of the superior sagittal venous sinus of the dura mater. On the
posterior surface of the cranium the superior saggital venous sinus leads to
a straight groove, the transverse sinus which leads to an s-shaped groove,
the sigmoid sinus and the to the jugular foramen. Other grooves indicate
the position of arteries supplying the membranous covering of the brain.
Prominent ridges on the floor of the cranium make it divisible into three
principal fossae.
 The anterior cranial fossa contains the frontal lobes of the brain. Its
posterior boundary is marked by the posterior edge of the lesser
wings of the sphenoids, which form the prominent sphenoidal
ridge. The large sphenoid sinus is contained within the body of this
portion of the sphenoid bone. In the mid-line, anterior to the
phenoid, lies the superior surface of the ethmoid bone. The
numerous perforations for the filaments to the olfactory nerve
(passing from the nasal membranes to the olfactory bulbs), have
given this surface the name of cribiform plates, separated in the
mid-line by a projection known as the crista galli (Cock’s comb).
Directly anterior to this process is an opening which usually ends
blindly, the foramen caecum.
 The middle cranial fossa contains the temporal lobes and the
anterior portion of the brain stem. The central raised portion in the
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mid-line is the sella turcica containing the fossa hypophysea which
is the repository for the pituitary gland. Anterior to the ridge of this
saddle-shaped structure is a flat, smooth surface, the jugum of the
sphenoid, which extends laterally on either side as the slender
anterior clinoid processes, tapering out along the inferior surface of
the lesser wings of the sphenoid. The optic foramina lie between
these two processes of the sphenoid. A groove is seen on the
anterior surface of the sella turcica. This is the chiasmatic groove.
The superior orbital fissure may be easily identified between the
wings of the sphenoid.
The posterior boundary of the middle cranial fossa is marked by
the enlarged petrous portion of the temporal bone, which houses
the inner ear. At the inferior edge of the anterior surface of this
prominence is an obliquely situated irregularly shaped opening, the
foramen lacerum, over which passes the internal carotid artery,
after it emerges from the carotid canal. In life the foramen lacerum
is filled with cartilage. The internal carotid passes along either side
of the sella turcica in the carotid grooves and then turns superiorly
within a groove on the posterior surface of the anterior clinoid
process (this groove is occasionally completely closed over to
surround the artery), and thereupon enters into the foramen of the
circle of Willis around the stalk of the pituitary
The large foramen passing directly through the floor of the fossa is
the foramen ovale, and transmits the mandibular branch of the
trigeminal nerve. Anterior and medial to the foramen ovale, and
just inferior to the supra-orbital fissure, is the anteriorly directed
foramen rotundum, which carries the maxillary branch of the
trigeminal nerve.
 The posterior cranial fossa contains the cerebellum and the
medulla. The position of the pons is indicated by the portion of the
occipital bone lying anterior to the foramen magnum. Note again
the foramen magnum and the jugular foramen. In addition, note the
prominent internal auditory meatus on the posterior surface of the
petrous temporal. Both the 7th and 8th nerves leave the cranium by
way of this opening. After passing laterally for a short distance, the
7th turns abruptly posteriorly into the facial canal (imbedded in the
bone and therefore not visible from the surface) which emerges
through the stylomastoid foramen.
Facial Portion of the Cranium
o The facial portion of the skull consists of the bones which surround four
principal cavities, the two orbits, the nose, and the mouth.
o The orbit is formed by parts of the seven different bones. Its roof and
superior margin is formed by the frontal bone. The supraorbital margin
present a notch or foramen of the same name (for the passage of vessels
and nerves of the same name). Sometimes a second less marked notch is
present, medial to the supraorbital, the frontal notch. The medial portion of
the supraorbital margin is smoothly rounded along the nasal part of the
frontal bone. This portion of the supraorbital margin may present on its
inner surface, the small fovea trochlearis (occasionally a small spine),
marking the site of the cartilaginous pulley for the tendon of the superior
oblique muscle. Laterally, the supraorbital margin is sharp and extends
along the strong prominent zygomatic process of the frontal bone. Under
o
o
o
o
the lateral edge of this margin, within the orbit, is the shallow lacrimal
fossa for the lacrimal gland. It may be best identified by touch.
The roof of the orbit is formed by the thin orbital plates of the frontal
bones (which also form the floor of the anterior cranial fossa). Hold the
skull up to the light to see the thinness of the roof. Posteriorly, the roof of
the orbit is formed by the lesser wing of the sphenoid, through which the
optic foramen passes.
The lateral wall of the orbit is formed anteriorly by the zygomatic bone
(cheek bone), and posteriorly by the greater wing of the sphenoid. The
zygomatic bone, together with the zygomatic process of the temporal
bone, forms the zygomatic arch through which passes the temporal
muscle. The zygomatic bone articulates superiorly with the zygomatic
process of the frontal bone, forming a strong protective bulwark on the
most exposed area of the orbit. Slightly below the fissure of articulation,
within the orbit, is the variable lateral orbital tubercule, for the attachment
of muscle and ligaments. In the middle of its orbital surface is the
zygomatico-facial foramen, and on the surface within the arch is the
zygomatico-temporal foramen. Posteriorly the zygomatic bone articulates
with the greater wing of the sphenoid which forms the remainder of the
lateral wall of the orbit, separating the orbit from the middle cranial fossa.
Medially, the zygomatic bone contributes to the floor of the orbit and
articulates with the maxillary bone, the fissure between the two bones
running laterally at a sharp angle.
The medial wall of the orbit is made up of the paper thin lamina papyracea
of the ethmoid bone and the lacrimal bones. The lamina papyracea
separates the orbit from the sinusoidal air cells of the ethmoid bone. Along
the fissure between the lamina papyracea and the orbital plates of the
frontal bone may be a series of openings, the most prominent of which are
the anterior and posterior ethmoid canals. The lamina papyracea
articulates posteriorly with the body of the sphenoid, inferiorly with the
maxilla, and anteriorly with the lacrimal bone. The latter is the smallest
and most fragile bone of the skull. The posterior part of the lacrimal bone
forms the lacrimal groove, bounded posteriorly by the posterior lacrimal
crest of the lacrimal bone. The lacrimal groove is continuous anteriorly
with the lacrimal notch of the maxillary, bounded anteriorly by the
anterior lacrimal crest. Together, the lacrimal groove and the lacrimal
notch form the lacrimal fossa which contains the lacrimal sac and deepens
as it passes inferiorly into the nasolacrimal duct. superiorly, the lacrimal
bone articulates with the frontal bone, anteriorly with the frontal process
of ther maxilla, and inferiorly with the orbital plate of the maxilla and with
the lacrimal process of the inferior nasal conchae. There may be a small
lacrimal tubercle on the infra-orbital margin just below the lacrimal fossa.
The floor of the orbit is mostly made up of the orbital plate of the maxilla,
also receiving a contribution laterally from the zygomatic bone. The
orbital plate of the maxilla is relatively thin, and separates the orbit from
the large maxillary sinus (antrum of Highmore). Below the infraorbital
margin, the prominent infraorbital foramen is located. Its posterior
continuation may reappear in the floor of the orbit as the infraorbital
groove. The posterior corner of the floor of the orbit is formed by the
orbital process of the palatine bone, which extends superiorly between the
maxilla and the pterygoid processes of the sphenoid to reach to the orbit.
The lateral part of the infraorbital margin is formed by the zygomatic
bone. Its medial part is formed by the maxilla, principally by its superiorly
directed frontal process. Most of the structures mentioned in the margins
and inner rim of the orbit can be palpated with the finger tip.
o Posteriorly, the orbit receives blood vessels and nerves through two large
slits. The supraorbital fissue, roughly comma-shaped, lies vertically
between the greater and lesser wings of the sphenoid, and contains
structures passing from the middle cranial fossa to the orbit (the branches
of the ophthalmic division of the 5th nerve, the nerves to the eye muscles,
the ophthalmic vein, and some small arteries). About midway along its
lateral margin may be found the small spine of the lateral rectus.
o The infraorbital fissure, lying horizontally between the greater wing of the
sphenoid, the orbital plate of the maxilla, its expanded anterior portion
being bounded by the zygomatic. It contains structures passing to the orbit
from the infratemporal fossa (just below the wing of sphenoid) and the
pterygo-palatine fossa (between the pterygoid process of the sphenoid and
the orbital process of the palate). These include the infra-orbital artery and
vein, the infraorbital and zygomatic branches of the maxillary nerve, and
branches from the inferior ophthalmic vein.
o The mouth cavity is formed by the upper and lower jaws and the palate.
The lower jaw consists of the mandible, which has a horizontal body
which bears the teeth, and a posterior ramus for muscle attachment and
articulation with the skull. A noticeable process, the coronoid process
extends superiorly from the ramus. On the inner surface of the angle
where body and ramus join is the mandibular foramen which receives the
inferior alveolar branch of the mandibular nerve. This nerve emerges at
the front of the chin through the mental foramen.
o The upper jaw is formed by the maxilla. The maxilla has an alveolar
process which bears the teeth, and the anterior facial surface, zygomatic
and frontal processes, an orbital surface, a palatine process, and a nasal
surface. The palatine processes of the maxillary and palatine bones form
the roof of the mouth and the floor of the nasal cavities.
o The anterior part of the roof of the nasal cavity slanting downward,
consists of the two small flat nasal bones, situated on either side of the
midline between the frontal processes of the maxillary bone. They
articulate superiorly with the frontal bone, which sends a sharp spine
between them on the inner surface of the nasal cavity.
o The middle horizontal portion of the roof of the nasal cavity is formed by
the cribiform plate of the ethmoid. Posteriorly, the roof again slants
downward, being formed by the body of the sphenoid principally and
small parts of the adjacent bones (vomer, palatine). The lateral walls are
formed anteriorly by the maxilla and lacrimal bones, in the middle by the
ethmoid superiorly, and the maxilla inferiorly, and posteriorly by the
vertical part of the palatine bones and the pterygoid processes of the
sphenoid. The medial septum is formed superiorly by the vertical plate of
the ethmoid, and inferiorly by the vomer. The lateral walls give rise to the
three conchae or turbinates, the superior and middle arising from the
ethmoid and fusing anteriorly, the inferior deriving from the maxilla and
becoming a separate bone. Beneath each turbinate lies an air passage, the
superior, middle, and inferior meatus respectively, and it is into the latter
that the nasolacrimal duct opens, after passing through the maxillary bone.
The nasal cavity communicates with the paranasal air sinuses of the
sphenoid, maxillary, ethmoid, and frontal bones.