Acetabular Canal. Part 2
S.V. Arkhipov, Independent Researcher, Joensuu, Finland
Abstract
This article describes the space where the ligamentum capitis femoris (LCF) attaches and functions. See also Part 1 and Part 3.
Topography of the Acetabular Canal
The
acetabular canal has two powerful walls. On the outside, it is the
bone-cartilaginous mass of the femoral head, which separates the contents of
the acetabular canal from the cervical part of the hip joint, surrounding
muscles, fatty tissue and synovial bags. On the medial side, the acetabular
canal is separated by the pelvic bone from the pelvic organs, fatty tissue,
muscles, large vessels and nerves.
 |
| Figure 1. Entrance to the right acetabular canal under the transverse
ligament of the acetabulum (indicated by the arrow); legend: 1 — pubic bone, 1'
— spine. — 2 — ischium. — 3 — ilium. — 4 — acetabulum, 4' — acetabular rim. — 5 — capsule,
resected at the level of the labrum. — 6 — obturator membrane, 6' — accessory
bundle. — 7 — subpubic ligament. — 8 —obturator canal. — 9 — openings occupied
by fat lobules. — 10 — ischiopubic foramen (from 1904TestutL). |
We
differentiate between the peripheral and central sections of the acetabular
canal. The entry opening into the peripheral section is formed by the outer
edges of the acetabular notch and the transverse ligament of the acetabulum.
Toward the center of the acetabular fossa, the space in the peripheral section
of the canal initially narrows. We propose to call the initial segment of the
peripheral section "external" or "ligamentous". It is
bordered by the inferior surface of the transverse ligament of the acetabulum,
as well as the floor and walls of the acetabular notch covered by periosteum
and the fibers of the portions of the LCF. The contents of the acetabular canal
here include: portions of LCF from dense organized connective tissue, white
adipose tissue, loose unstructured connective tissue, nerves, arteries, veins,
and lymphatic vessels. Normally, the outer segment has no communication with
the acetabular fossa and is not washed by synovial fluid, being tamponed with
adipose tissue.
 |
| Figure 2. Subsynovial parts of the sections of the acetabular canal
(schematically); red indicates the external (subligamentous) segment of the
peripheral section; blue indicates the internal (extrasynovial) segment of the
peripheral section; purple indicates the central section; green star - anterior
bay-shaped expansion, blue star - posterior bay-shaped expansion of the central
section of the acetabular canal (specimen from the Zoological Museum of Moscow
State University, photograph by the author). |
Approximately
in the middle third, the peripheral section of the acetabular canal begins to
widen. We have designated this segment as "internal" or
"extraligamentous". It is limited by the bottom and walls of the
acetabular notch, as well as the cartilaginous surface of the femoral head. The
extraligamentous segment is divided by the synovial membrane into two tiers.
One, conventionally located below, we have called the "subsynovial
part". The second tier, located above, we have called the
"suprasynovial part". Unlike the subsynovial part, the suprasynovial
part communicates with the acetabular fossa and contains synovial fluid. The
walls of the suprasynovial part include: the hyaline cartilage of the femoral
head, specifically its periosteum; the edges of the hyaline coating of the
lunate surface; the synovial membrane covering the walls of the acetabular
notch; the synovial membrane surrounding the LCF; and the bases of the synovial
folds. In the subinovial part of the internal segment of the peripheral section
of the acetabular canal contains: portions of LCF from dense formed connective
tissue, white adipose tissue, loose unformed connective tissue, nerves,
arteries, veins and lymphatic vessels. The upper wall of the subsynovial part
is the inferior surface of the synovial membrane surrounding the base of the
LCF. The lower wall is the floor of the acetabular notch. The posterior wall is
the edge of the lunate surface of the ischium. The anterior wall is the edge of
the lunate surface of the pubic bone. The floor and walls of the acetabular
notch here are covered with periosteum and fibers of the LCF portions.
The
peripheral section of the acetabular canal resembles an hourglass in shape.
However, in cross-section, this space is not round but close to ellipsoid. The
width of the peripheral section of the acetabular canal exceeds the height,
which is slightly less than the length. The long axis of the peripheral section
coincides with the longitudinal axis of the acetabular notch, which corresponds
to the sagittal axis of the acetabulum. Some studies indicate that in the
sagittal plane, it is tilted forward by 15° (1997КорниловНВ_ЭпштейнГГ). More
precise values for measuring the acetabulum are provided by H. Witte et al.
(1997).
Table: Morphometric
Parameters of the Acetabulum (from 1997WitteH_RecknagelS)
| ε (°) frontale | δ (°) horizontale | φ (°) sagittale |
Male pelvis | 66.0±4.1 | 40.2±5.3 | 18.7±6.1 |
Female pelvis | 65.5±5.5 | 40.2±3.2 | 21.4±5.7 |
General data | 65.7±4.7 | 40.2±4.3 | 20.0±6.0 |
The peripheral section smoothly transitions into the central section of the acetabular canal. The space between the femoral head and the acetabular fossa expands in the anteroposterior direction and upwards. The central section of the acetabular canal is close in shape to a concave-convex lens. Meanwhile, one, and more often two bay-shaped expansions are observed in the upper part. The first is located on the border of the ischium and ilium, and the second is in front, namely, "on the territory" of the ilium exclusively.
 |
| Figure 3. Suprsynovial subunit of the acetabular canal, marked by us (from 1867GrayH). |
In
the central section of the acetabular canal, we distinguish: the external
edges, medial wall, lateral wall, anteroinferior wall, and posteroinferior
wall. We believe it is useful to differentiate between the subsynovial and
suprasynovial parts in the central section. These parts are continuations of
the corresponding sections of the internal part of the peripheral section of
the acetabular canal. Accordingly, it is appropriate to speak of the presence
of a single subsynovial subunit and a common suprasynovial subunit in the
acetabular canal. The contents of the suprasynovial part of the central part of
the acetabular canal include: synovial fluid, folds of the synovial membrane,
and LCF covered with synovial membrane. The contents of the subsynovial part of
the central part include: portions of LCF from dense organized connective
tissue, white adipose tissue, loose unstructured connective tissue, nerves,
arteries, veins, and lymphatic vessels.
The
outer edges of the central section of the acetabular canal coincide with the
inner boundary of the cartilage covering the lunate surface of the acetabular
fossa. Here, the external boundaries of the subsynovial and suprasynovial parts
of the central section meet, separated by the synovial lining of the walls of
the acetabular fossa.
 |
| Figure 4. Central section of the acetabular canal (horizontal scan); the shadow of the LCF is indicated by an arrow; on the left is the medial wall, specifically the bottom of the acetabular fossa; on the right is the lateral wall, specifically the femoral head (CT, author's observation). |
The
lateral wall of the central section of the acetabular canal is formed by the
femoral head. Most of it is covered by perichondrium with an underlying layer
of hyaline cartilage proper, and deeper is the spongy substance. The lateral
wall has a depression – the fovea of the femoral head. Its bottom is a
perforated plate of compact bone tissue. It is covered by synovial tissue,
white adipose tissue, and dense organized connective tissue from LCF. Most of
the lateral wall of the central section of the acetabular canal is the outer
boundary of the suprasynovial part. Only the area of the fossa of the femoral
head where the distal end of the LCF attaches is the subsynovial part of the
central section of the acetabular canal.
The
anteroinferior wall of the central section of the acetabular canal is a
continuation of the anterior edge of the lunate surface of the pubic bone and
the edge of its cartilage coating. The anteroinferior wall is mainly covered by
the synovial membrane, with partial fibers of the pubic portion of LCF made of
dense organized connective tissue. The edge of the hyaline cartilage of the
lunate surface is covered with perichondrium.
The
posteroinferior wall of the central section of the acetabular canal is a
continuation of the posterior edge of the lunate surface of the ischial bone
and the edge of its cartilage coating. It is also primarily covered by the
synovial membrane and fibers of the pubic portion of LCF made of dense
organized connective tissue. The edge of the hyaline cartilage of the lunate
surface is covered with perichondrium.
 |
| Figure 5. Lateral wall of the central part of the left acetabular canal, the macerated left femoral head (view from the medial side, author's observation). |
The
medial wall of the subsynovial part of the central section of the acetabular
canal is the bottom of the acetabular fossa and the inner edges of the
semilunar surface of the acetabulum. The medial wall is made of compact bone
tissue from the bodies of the pubic, ischial, and iliac bones. The medial wall
of the suprasynovial part of the central section is the synovial membrane and
its folds. Their lower surface forms the lateral wall of the subsynovial part
of the central part of the acetabular canal.
In
terms of the structure of the walls, the acetabular canal should be classified
as fibrous-bony-cartilaginous in adults. In children in the first years of
life, it is fibrous-cartilaginous due to the cartilaginous structure of the
acetabular fossa and femoral head. The acetabular canal exists only when the
articular surfaces of the hip joint are connected. It represents an open
slit-like space between the acetabular fossa and the femoral head. The overall
configuration of the acetabular canal resembles a tennis racket with a concave
face and a shaped handle.
The
long axis of the acetabular canal coincides with the sagittal axis of the
acetabular fossa. It starts from the center of the acetabular fossa and extends
forward, downward, and outward. According to our measurements, the sagittal
axis of the acetabular fossa is tilted forward in the sagittal plane by
approximately 20-25°, whereas literature data indicate a tilt of 15-26° (1997КорниловНВ_ЭпштейнГГ; 1997WitteH_RecknagelS).
Dimensions of the Acetabular Canal
The
depth of the acetabular fossa, i.e., the depth of the central part of the
acetabular canal, in young individuals is 10-12 mm, with an average of 11.1±0.5
mm. With age, the depth decreases. In elderly individuals, it is 5-12 mm, with
an average of 7.5±0.37 mm, and in senile age, it is 3.5±0.25 mm (1972ПодрушнякЕП). According to our measurements from X-rays, the depth of the
acetabular fossa in young and middle-aged individuals is, on average, 7.89 mm
in women, 8.99 mm in men, and 8.38 mm in both sexes (2004Архипов-БалтийскийСВ).
According to К.П. Минеев & К.К. Стэльмах (1996), the height of the
slit-like space, i.e., the depth of the acetabular canal, is 4-8 mm. The
average diameter of the acetabular fossa is 25-26 mm (1972ПодрушнякЕП).
This corresponds to the diameter of the central section of the acetabular
canal. The width of the lunate surface of the acetabular fossa in the area of
the acetabular notch is about 12.5 mm (1932ВоробьевВП). In other words, this
is the length of the peripheral section of the acetabular canal. The width of
the acetabular notch, i.e., the width of the peripheral section of the
acetabular canal, is 20-25 mm (1996МинеевКП_СтэльмахКК). The dimensions
of its external segment can be estimated based on the size of the transverse
ligament of the acetabulum. Its length is on average 20 mm, and width is 4-9
mm. In senile age, the width is 5-7 mm, with a length of 14-18 mm (1972ПодрушнякЕП).
References
Witte H, Eckstein F, Recknagel S. A Calculation of the Forces Acting on the Human Acetabulum during Walking. Cells Tissues Organs. 1997;160(4)269–80.
Архипов-Балтийский С.В. Рассуждение о морфомеханике. Норма: В 2-х томах. Калининград, 2004.
Воробьев В.П. Анатомия человека: Руководство и атлас для студентов и врачей. В 3 томах, Т.1. Москва: Медгиз, 1932.
Корнилов НВ, Войтович АВ, Машков ВМ, Эпштейн ГГ. Хирургическое лечение дегенеративно-дистрофических поражений тазобедренного сустава. Санкт Петербург: ЛИТО Синтез, 1997.
Минеев К.П., Стэльмах К.К. Лечение тяжелых повреждений таза и позвоночника. Ульяновск: Симбирская книга, 1996.
Подрушняк ЕП. Возрастные изменения суставов человека. Киев: Здоров‘я, 1972.
Keywords
ligamentum capitis femoris, ligamentum teres, ligament of head of femur, acetabular canal, anatomy, attachment
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