Macerated Labral Tear

in the anterosuperior labroacetabular junction is usually considered a small partial detachment, because when probed arthroscopically, it appears unstable. Third, there is, however, a small sublabral sulcus in the posterior inferior aspect of the labrum seen in many individuals that has been reported as normal findings, which our own clinical experience confirms [49]. Fourth, the labrum cartilage interface and zone of transition may have mild increased signal on nearly all sequences and should not be confused for a tear. This "cartilage undercutting" phenomenon is seen in the shoulder involving the glenoid labrum-cartilage interface as well [49,50]. Finally, nonarthro-gram imaging in asymptomatic volunteers described the absence of the ante-rosuperior labrum, particularly in older adults. In our experience in young adult athletes, this finding is markedly abnormal and indicative of a macerated torn labrum.

Classifications for labral tears exists that are based on MR signal intensity, tear morphology, or arthroscopic findings [5,51,52]. The utility of an MR classification scheme has been questioned due to the general acceptance of arthroscopic debridement as the definitive treatment for symptomatic tears. Although de-bridement produces good to excellent results for 85% to 90% of patients, long-term studies are forthcoming [38]. However, there is a strong relationship between acetabular labral tears and arthritis [53]. In the knee and shoulder it is well known that meniscal and glenoid labral resection can cause significant increase in joint contact pressures [54,55]. One should also keep in mind that several decades passed after Fairbank's classic 1948 description of post-meniscectomy arthritis was published before meniscal repair became the standard of care [56]. Therefore, although not proven in the hip, based on past history of injury to fibrocartilage bearing joints, it is reasonable to surgically attempt to restore biomechanical function of the hip using techniques similar to those used to repair menisci and the glenoid labrum to reduce the possibility of late onset arthritis. Consequently, emerging arthroscopic techniques emphasizing tissue preservation and biomechanical function are being developed to repair the labrum [38]. Therefore, to help guide surgical intervention, our MR assessment of tears has progressed from a yes or no evaluation for the presence of a labral tear to a descriptive evaluation emphasizing the amount of residual intact labral tissue, orientation of intrasubstance tears, and the presence of labro-

Fig. 12. Normal MR variants. (A) Oblique axial T2 fat-saturated image showing small cleft or recess (white arrow) under the anterior labroacetabular junction arthroscopically confirmed to be a partially detached unstable tear. (B) Oblique axial T2 fat-saturated image with small cleft between the posteroinferior labrum and acetabulum, which should not be confused with a detached tear (white arrow). (C) Coronal T1 fat-saturated image of mid-hip with normal appearing superior labrum and normal labral-cartilage interface with a mild increased signal that should not be confused with a labral tear (white arrow). (D) Oblique axial T2 fat-saturated images with near complete loss of the anterosuperior labrum (white arrow) consistent with a macerated tear rather than a normal variant.

acetabular detachment. Currently, we categorize tears into three major groups: detached, intrasubstance, and degenerated with combinations thereof.

Detached tears demonstrate separation of the labrum from its acetabular base, which can be complete or partial, and may be nondisplaced. Detached tears with displacement on MR arthrography demonstrate linear fluid or contrast signal gap interposed between the base of the labrum and bony acetabular rim, and are best seen on coronal images for superior predominant tears and oblique axial images for anterior predominant tears (Fig. 13). These tears may exist without displacement, in which case diagnosis can be difficult with the tear manifesting as only a thin line of fluid signal at the labroacetabular junction. Detachment injuries can be treated with suture anchor reattachment much like glenoid labral repair techniques in the shoulder.

Intrasubstance labral tears demonstrate intrasubstance fluid or contrast signal, usually extending to the articular side of the labrum (sometimes capsular side), which is often oblique or curvilinear in shape. However, signal may also be complex extending in multiple directions in the long and short axis of the labrum. These tears can be treated with intrasubstance suture bandings and thermal treatment to restore shape (Fig. 14).

A labrum with abnormal irregular contours and a thin morphology, with or without intrasubstance fluid or contrast signal extending to the free margin, is considered a degenerative type tear. These tears will likely undergo debridement or thermal treatment when necessary. In young athletes, it is not uncommon to have a combination of detached tears or intrasubstance tears with superimposed degenerative components. Treatments include a combina-

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