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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4501_Библиотеки_им_академика_М_И_Перельмана
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70 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
THE OSSICULAR ARTICULATIONS (JOINTS)
The ossicular articulations are true articulations in the sense of uniting two
bones. The articulating surfaces are lined by cartilage and there may or may
not be an interarticular disc. Each articulation has a true capsule composed
of ligamentous fibers originating from the periosteum of the linked bones
and lined by a synovial membrane.
While the ossicular articulations are sufficiently strong to withstand
physiologic stresses, they are easily torn by direct trauma to the middle ear,
fracture of the temporal bone, or surgical manipulation (Fig. 59). The ossicles
may be partially luxated in which case only part of the capsule is torn and
ossicular displacement is partial, or luxated in which case the entire capsule
is torn and total disarticulation occurs.
The Incudomalleal Articulation
The incudomalleal articulation is a nonweight-bearing, synovial, diarthrodial articulation linking the malleus and incus (Fig. 60). It is generally
described as saddle-shaped, although Wolff and Bellucci (12) point out that
in vertical sections the opposing joint surfaces appear to present interlocking
jaw-like surfaces (Fig. 61). A capsule of elastic tissue surrounds the articular
margin and there is an interarticular disc. The capsule is trilaminar with: (1)
the synovial membrane lining the cavity, (2) the mucous membrane of the
middle ear, and (3) an intervening fibrous layer. The capsule is not uniform
in structure. At superior levels, the medial aspect of the capsule shows
greater length and density of the fibrous layer and is known as the medial
incudomalleal ligament (Figs. 62–64). At inferior levels, the lateral part of the
capsule is thicker and is known as the lateral incudomalleal ligament. These
regional variations in fiber length, density, and thickness all interact to
control the interdigitation of the two ossicles.
The articular cartilage is bilaminar. The deep layer, adjacent to ossicular
bone, demonstrates enchondral bone formation as well as direct osseous
transformation of its cartilaginous matrix. This latter process is characteristic
Figure 59
Here is shown a surgically induced
inward subluxation of the posterior
margin of the footplate of the stapes. A
modified radical mastoidectomy had
been performed 14yr before death. The
membranous labyrinth appears normal
and there was no postoperative
sensorineural hearing loss (female, age
60yr).
CHAPTER 3: THE MIDDLE EAR ■ 71
Figure 60
The normal incudomalleal articulation
is shown here (male, age 10wk).
72 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 62
The capsule of the incudomalleal articulation is thickened on its medial side
to form the medial incudomalleal ligament (male, age 9yr).
Figure 61
Both the incudomalleal and incudostapedial
articulations (joints) are seen in this vertical section. The space inferior to the lateral malleal ligament is Prussak’s space (male, age unknown).
CHAPTER 3: THE MIDDLE EAR ■ 73
Figure 63
At a level slightly inferior to that of
Figure 62 the capsule is thickened to
form the lateral incudomalleal ligament (male, age 9yr).
Figure 64
The anterior suspensory ligament of
the malleus is located superior to the
anterior malleal ligament. Mucosal
folds from the lateral epitympanic wall
transmit the vascular supply for the
ossicles (male, age 81yr).
of secondary or chondroid cartilage which derives from membrane bone (19).
The superficial layer is of primitive cartilage, a product of and maintained by
the synovial membrane; it is considered analogous to epiphyseal cartilage.
The Incudostapedial Articulation
The incudostapedial articulation (Fig. 65), also a nonweight-bearing,
synovial, diarthrodial articulation, joins the convex lenticular process of the
incus (Fig. 66) and the concave surface of the head of the stapes. The lenticular process may exist as an accessory bone. There is a joint space, but an
interarticular cartilage is not usually present. The fibers of the capsule are
longer than those of the incudomalleal articulation, but are of similar
thickness and variability of thickness (12). At the inferior aspect of the articulation, the posterior capsular fibers sometimes merge with those of the tendon of the stapedius muscle with the effect that contraction of the stapedius
muscle, in addition to pulling the head of the stapes posteriorly, also draws
the long process of the incus posteriorly.
In surgical procedures for otosclerosis, the head and crura of the stapes
are usually removed preparatory to fenestrating the fixed footplate. The
74 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 65
The incudostapedial articulation of a 10-wk-old
male infant is shown here. The articular facet of
the lenticular process is convex and that of the
head of stapes is concave. The lenticular process
normally contains islands of fibrous tissue; perhaps this fibrous component underlies the susceptibility of the lenticular process to resorption
in chronic otitis media.
CHAPTER 3: THE MIDDLE EAR ■ 75
Figure 66
The lenticular process of the incus is
shown as it rests in the concavity of the
head of the stapes. The facial recess is
located directly posterior to the incudostapedial articulation (male, age
58yr).
incudostapedial articulation is fragile enough that downward pressure on
the head in the direction of the promontory causes separation of the joint
without luxating the incus; thus fracture-dislocation of the head and crura is
easily performed.
The Stapediovestibular Articulation
The stapediovestibular articulation is the junction between the stapes
footplate and the oval window. This articulation is one of the sites of
predilection for otosclerosis and has been the focus of detailed study. It has
been variously labeled as a syndesmosis, an amphiarthrosis, and a
“half-joint.” The annular ligament holds the footplate of the stapes in the
oval window; peripherally, its connective tissue fibers fuse with periosteum
and endosteum. Wolff and Bellucci (12) have identified fibers which span the
entire distance from the endosteal surface of the footplate to the periosteum
of the tympanic aspect of the bony labyrinth; moreover, they have documented that “posteroinferiorly, . . . endosteal ligamentous fibers are continuous with those of the spiral ligament of the basal turn of the cochlea.”
Spaces within the stapediovestibular articulation (Fig. 67) were recognized
as long ago as 1873 (327) but later were attributed to artifact (329). In a more
recent study of morphology of the stapediovestibular articulation, Bolz and Lim
(20) found such spaces in 70% of adult temporal bones, usually in the posterior
pole of the articulation (Fig. 67). Because no such spaces were found in the
temporal bones of children, they hypothesized that these spaces represent
adventitious bursae developing in response to friction, pressure, or trauma.
Changes of Aging in the Articulations
Both the incudomalleal and incudostapedial joints show pathologic changes of
aging in which chondroid cartilage undergoes a change to a chondro–osseous
matrix (19).
76 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 68
The incudomalleal articulation of a 16-yr-old
female illustrates grade I changes of aging.
Figure 67
Small spaces (bursae) are found in the
posterior part of the stapediovestibular
articulation in 70% of adult temporal
bones (female, age 61yr).
CHAPTER 3: THE MIDDLE EAR ■ 77
Figure 69
The incudomalleal articulation of this
34-yr-old female shows narrowing of
the joint space, hyalinization of cartilage, and deposition of hyalin within
the articular cartilage characteristic of
grade II changes of aging.
Etholm and Belal (21) describe three grades of degenerative change.
Grade I shows fraying (Fig. 68), vacuolization, and fibrillation of the articular cartilage. Grade II changes show narrowing of the joint space, rarefaction
and calcification of the articular cartilage, and hyaline deposition in the
capsule and disc (Figs. 69 and 70). Grade III changes include obliteration of
the joint space, as well as calcification of the articular cartilage, capsule, and
disc (Figs. 71–73).
Fibrous fixation or bony ankylosis of the incudomalleal and/or incudostapedial articulations appears to have little or no effect on hearing (21),
and therefore is of minor pathologic significance.
78 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 70
The incudostapedial articulation of this
59-yr-old man shows grade II changes
consisting of hyalinization of the joint
capsule, as well as hyalinized deposits
and narrowing of the joint space.
Figure 71
The incudomalleal articulation of this 60-yr-old
female demonstrates grade II changes with narrowing of the joint space, calcification, and
hyalinization.
CHAPTER 3: THE MIDDLE EAR ■ 79
Figure 72
The incudomalleal articulation of this
65-yr-old male shows severe (grade III)
arthritic changes. The joint space is
obliterated laterally, while medially
there are scattered calcium deposits.
There is irregular thinning and calcification of the articular cartilage. The
joint capsule shows atrophic changes.
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