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Acetabular Canal. Part 2.

 

Acetabular CanalPart 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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