Early degenerative changes of the hip are not an uncommon arthroscopic finding. Standard radiographic projections have poor diagnostic ability in detecting
FIGURE 8.3. The horseshoe-shaped appearance of the acetabulum.
precocious chondral damage. In a previous study,8 we reviewed records and radiographs of 234 hip arthro-scopies and compared intraoperative and radiographic findings. Sixty patients (32.2%) of the 186 with normal preoperative radiographs had evidence of os-teoarthritis at the time of surgery. This evidence makes initial osteoarthritis the most likely cause of hip symptoms in young patients (average age, 36 years) with normal radiographic findings.
One more interesting finding was the preponderance of female subjects (71% versus 29%) in the group with normal radiographic findings. Quantification of the damage was obtained by dividing the acetabulum and the femoral head in quadrants. Hips with normal radiographic findings but arthroscopic osteoarthritis were found to have less chondral damage (1.9 quadrants) compared with those with radiographically evident osteoarthritis (4.2) quadrants. Hips with normal
radiographic findings also were more likely to have only one side (60%) of the joint involved.
Hip osteoarthritis appears to begin on one of the two sides of the joint and not as a generalized disease. The hip, due to its peculiar ball-and-socket shape, is poorly studied with a conventional anteroposterior projection. Radiographic signs of osteoarthritis become evident only when degenerative changes are fairly widespread within the joint (4.2 quadrants).
When good distension of the joint is obtained, this portion of the acetabulum can be safely seen. However, often a fat pad lies within the fossa and can expand into the cavity and obscure the view. Usually, the fossa has a flattened superior margin and anterior and posterior borders. From the posteroin-ferior part of the fossa arises the ligamentum teres. Superiorly, the fossa is lined by dense fibroconnec-tive tissue, lacking a synovial lining. The lower part of the fossa is occupied by adipose tissue; this appears well vascularized and is usually mobile when suction on the outflow is applied. Sometimes the adipose tissue can behave like a pedunculated structure within the joint. It is said to contain numerous proprioceptive nerve endings. When it becomes compressed, it partially extrudes from the acetabu-lar fossa beneath the transverse ligament.
A thickened band of fibrous tissue, the transverse ligament (Figure 8.6), closes the lowest portion of the acetabular fossa. This structure bridges the open end of the horseshoe-shaped acetabulum and can occasionally be probed with a hook. It divides the acetab-ular fossa from the inferior recess. Close to the transverse ligament, synovial tissue from the inferior recess encroaches on and passes beneath the ligament into the fossa. The inferior recess is a frequent hiding place for loose bodies, although it is unlikely they cause any great harm in such a position.
The acetabular labrum (Figure 8.7), or labrum gle-noidale, gives permanent stability to the hip joint by deepening the acetabular cavity. The labrum is triangular in cross section with the apex forming the free thin edge. The diameter of this free edge is smaller than its fixed edge and is somewhat less than the maximum diameter of the femoral head. It provides coverage and support to the anterior, superior, and posterior surfaces of the femoral head.
As with the glenoidal labrum in the shoulder, it produces a valve effect that significantly increases the stability of the joint. Takechi and coauthors4 have measured the intraarticular pressure both inside and outside the labrum in a hemipelvectomy specimen. They found that the pressure within the inner part of the joint, inside the labrum, was almost double that outside the labrum. This explains why it is so difficult to obtain a satisfactory distraction of the hip without injecting saline or air into the joint.9
Histologically, the fibrocartilaginous labrum is connected with the acetabular articular cartilage through a 1- to 2-mm zone of transition. A consistent projection of bone extends from the bony acetabulum into the substance of the labrum that is attached via a zone of calcified cartilage with a well-defined tidemark.10
At the time of arthroscopy, the labrum appears to overlap the hyaline cartilage around the perimeter of the acetabular cup. It continues downward into the transverse ligament of the acetabulum. This structure is usually regarded as the anatomic extension of the labrum across the notch. Sometimes, at the margins of the acetabular fossa, the labrum does not directly continue into the transverse ligament. In such cases, an area of acetabular articular cartilage intervenes between the two structures. No instability of the labrum seems to be associated with this finding.
The labrum is the first structure that the arthro-scopic surgeon can damage. To avoid it, proper identification of the joint line must be made. If, on the image intensifier, the guidewire is too close to the bony margin of the cup, it is possible to disrupt the labrum during the insertion of the trochar. In this case, it is better to reposition the guidewire before the introduction of instruments.
Once entered, with a 70-degree arthroscope, it is possible to visualize the majority of the circumference of the labrum and the transverse ligament. In its anterior, superior, and posterior portions, it has a meniscus-like consistency and it is indentable with a probe. In the inferior part, the transverse ligament, it no longer has a fibrocartilaginous structure and consists of strong, flattened fibers, which cross the acetabular fossa. The labrum blends with the margins of the ac-etabulum, except inferiorly. Here it is usually separated from the hyaline cartilage by a distinct groove, the labral groove (Figure 8.8). Commonly, the labrum is inverted, although it may be everted, and sometimes mobile. In a review of 37 cases operated for labral pathology,11 2 cases of unstable acetabular labra have been reported; both were teenaged girls with generalized ligamentous laxity. At the time of arthroscopy, the labrum subluxed during internal and external rotation of the limb. The absence of a trauma in the history of these 2 patients suggests this finding could be a peculiar congenital feature of labral development of ligament laxity.
Average width of the acetabular labrum is reported to be 5.3 mm (SD, 2.6 mm).12 It enlarges significantly the size of the acetabulum. Tan and coauthors12 reported an increase of acetabular surface area from 28.8 cm2 without the labrum to 36.8 cm2 (P < 0.0001) with the labrum. The volume of the acetabulum without the labrum is 31.5 cm3; with the labrum, it is 41.1 cm3 (P < 0.0001).
Although the labral cross section is almost con-
stantly triangular, its thickness varies in different portions. It is larger and thicker in the posterosuperior region and thinner in the anteroinferior region. Hypertrophy of the labrum combined with elongation of the ligamentum teres, and eburnation around the ac-etabular notch, have been reported in proven cases of hip dysplasia.13
On arthroscopic observation, in the young adult, the labrum has an avascular, meniscus-like, elastic appearance, whereas in the elderly it can appear yellow and degenerate. Suzuki and coauthors14 have described hypervascularity of the labrum as a striking finding in every stage of Legg-Calve-Perthes disease.
Within the joint, the acetabular labrum divides the peripheral portion lined with synovia from the in-traarticular portion. Three distinct gutters are identified outside the articular portion of the joint: the perilabral sulcus (Figure 8.9), the anterior gutter (Figure 8.10), and the posterior gutter.
FIGURE 8.8. The labral groove.
The anterior gutter.
FIGURE 8.8. The labral groove.
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