The most striking trend observed in both the arthroscopic and cadaveric data is the overwhelming preponderance of lesions involving the anterior labral-cartilage junction. The most common location for labral tears was unequivocally the anterior articular margin. There are several hypothetical explanations for this phenomenon. These include: This region of the labrum may possess inferior intrinsic mechanical properties compared to other portions of the labrum; this region may be subjected to higher mechanical demands; or the region may be relatively hypovascular, and hence disproportionately vulnerable to wear and degeneration due to resultant compromise in remodeling and healing capacity.
The cadaveric investigation failed to detect a structural diathesis, which could support a morphologic explanation for the preponderance of anterior lesions. The normal transition between the labrum and the articular cartilage appeared smooth around the entire perimeter of the acetabulum, and there was no evidence of localized anterior structural frailty. Similarly, the analysis of labral vascularity by itself does not account for the asymmetric distribution of labral pathology. Microangiography and immunohistochemical staining both confirmed that intraosseous vessels within the bony acetabu-lum and the joint capsule were present on the capsular surface and reached the interface with the fibrocartilaginous labrum, but did not seem to penetrate the body of the labrum to any significant extent. The labrum itself contained no intrinsic vessels. Despite the hypovascularity of the body of the labrum, this vascular pattern was consistent around the entire acetabular rim. That is, it was not disproportionately deficient in any specific region.
The hip symptoms in a high percentage of patients were associated with athletic activities that involve strenuous, repetitive twisting and pivoting motions (such as ballet, football, soccer, basketball, and place-kicking). It is conceivable that certain recurrent torsional maneuvers preferentially subject the anterior portion of the articular-labral junction to recurrent microtrauma and eventual mechanical attrition. This scenario would be exacerbated by the diffuse suboptimal blood supply within the body of the labrum.
Two significant differences exist between the author's arthroscopic patients and the cadaveric specimens. First, the chronological age of the cadaveric acetabula was considerably greater than the age of the arthroscopy patients. Second, the patients in the arthroscopic branch of this investigation were inherently subjected to bias due to the fact that they were selected on the basis of their symptoms. The cadaveric donors, on the other hand, were not selected on the basis of symptoms. In fact, many of the donors (and perhaps the majority of them) may have had minimal hip symptoms or may not have been active enough for the pathology within their hips to cause significant difficulty. It is impressive to note that, in spite of these discrepancies, the relative frequency of junc-tional anterior labral tears noted in the arthroscopy group was corroborated by the cadaveric investigation.
Both the arthroscopic and cadaveric populations demonstrated that the majority of labral tears and cartilage lesions were located in the anterior quadrant of the acetabulum. Moreover, this was the most common location for lesions of the acetabular articular cartilage. Furthermore, the prevalence of severe (grade IV) articular lesions was greater anteriorly that in any other region of the acetabulum.
It should be noted that the only type of articular lesion that did not predominantly affect the anterior aspect of the ac-etabulum was labral fraying, without associated local labral tearing. The prevalence of this form of pathology was roughly equivalent in the three locations (anteriorly, posteriorly, and laterally). We attribute this finding to our belief that labral fraying is more likely to progress to frank labral disruption in this region. This contention is supported by the fact that the prevalence of frank labral tears was greatest anteriorly.
Of supreme interest is that fact that the arthroscopic data demonstrate an association between progression of labral pathology and progression of anterior acetabular articular cartilage lesions. Specifically, both the frequency and the severity of acetabular articular degeneration was dramatically higher in patients with labral pathology than in those in whom the labrum was neither frayed nor torn. While the presence of a statistically significant association between labral and chondral pathology does not prove that the two are causally related, this conclusion seems inescapable in many cases where cartilage degeneration and delamination are observed directly in continuity with preexisting labral lesions. Specifically, both the frequency and the severity of acetabular articular degeneration were augmented among patients who had true anterior labral tears versus those with anterior labral fraying alone.
Additional evidence can be found in the incidence of each type of lesion as a function of the age of the patient. However, as both chondral and labral lesions become more common with aging, it is not possible to prove unequivocally that the increase in incidence of labral lesions in one age-group decade leads to the increased frequency of joint degeneration a decade later. Nonetheless, the data do demonstrate that labral lesions leading to arthroscopic treatment are most common beyond middle age, and not in younger patients who undergo extreme activities. This speaks to the degenerative, chronic nature of labral pathology and the need for improved methods of earlier detection and diagnosis.
These observations suggest that acetabular labral pathology may indeed be a contributing factor in the evolution and progression of osteoarthritis of the hip. Anterior labral discontinuity could conceivably disrupt the stability of the hip, and hence disrupt the congruence of the hip articulation under dynamic torsional loading conditions. In this sense, the labral lesion could act as a nidus for further intra-articular degeneration. Although the weightbearing function of the intact labrum under normal loading conditions has recently been called into question by Konrath and colleagues, it remains plausible that loss of the putative stabilizing and weightbear-ing roles of the labrum at the extremes of motion (where the labrum would be anticipated to exert its most significant effect) could predispose the hip to further degeneration.20
Alternatively, lesions of the anterior labrum may represent a final common pathway of deterioration in hips with a wide variety of primary pathology. These concepts are concordant with clinical arthroscopic experience, which has yielded the impression that this process progresses in the following sequence: first, fraying of the articular margin of the anterior labrum; second, frank tearing along the articular margin of the anterior labrum; third, delamination of the articular cartilage from the articular margin adjacent to the labral pathology; and finally, more global labral and articular cartilage degeneration.
In summary, the arthroscopic and anatomic observations support the concept that labral disruption and degenerative joint disease are frequently part of a continuum of joint pathology that consists of the following sequence of events: first, excessive loading of the labrum, through traction or impingement, at the extremes of joint motion; second, fraying of the articular margin of the anterior labrum; third, frank tearing along the articular margin of the anterior labrum; fourth, delamination of the articular cartilage from the articular margin adjacent to the labral pathology; and finally, more global labral and articular cartilage destruction. Future research is needed to elucidate the processes that connect each of these events leading to failure of the articulation.
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