1

Fig. 18. Coronal T1 fat-saturated image of focal grade 3 cartilage defect of superior acetabulum (white arrow).

and 77% to 89% for cartilage injury detection, respectively [4,62]. One of these studies showed an overreliance on secondary signs of osteoarthritis and chon-drosis (ie, increased signal intensity of subchondral marrow and osteophytes) resulted in false positive interpretation. These authors also had more difficulty assessing acetabular sided cartilage lesions. However, a more recent study using unilateral noncontrast MR described sensitivities from 86% to 93% and specificities from 72% to 88% [6]. Unpublished data from our institution evaluating MRI in professional golfers found that MRI underestimated the degree of articular cartilage injury when compared with arthroscopic findings. Traumatic lateral impact injuries associated with falls onto the ground with axial loading of femoral head can be associated with hip pain and chondral impaction injury. Subchondral marrow edema may be present, but MR findings can be minimal in these cases [63].

Capsular Laxity/Injury

The glenohumeral joint of the shoulder is the archetypal unstable joint, which relies on secondary soft tissues to confer static and dynamic stability because of the relative small bony contact of the humeral head and glenoid fossa. Unlike the shoulder, the hip is generally considered a statically stable joint due to large bony contact areas of the femoral head and acetabulum. Consequently, the concept of soft tissues to confer additional static and dynamic stability to the hip, particularly during rotation and extremes of motions associated with sporting activities, is relatively new [13]. Clinically, some patients without generalized laxity disorders (ie, Marfan or Ehler-Danlos syndromes) have exam findings of rotational instability of the hip thought to be related to laxity or dysfunction of the anterior capsule and iliofemoral ligament, which is amenable to surgical intervention via suture plication or thermal capsulorrhaphy [13,38]. Therefore, we thoroughly assess the joint capsule and iliofemoral ligament during MR arthrography. With MR arthrography, we have noticed a thick lateral margin of the anterior capsule (which corresponds to the iliofemoral ligament), along with irregularity of the undersurface on oblique axial images, correlates highly with clinical findings of capsular laxity, whereas a capsule with uniform thickness and a smooth undersurface was found in patients without capsular laxity (unpublished data) (Fig. 19). Anecdotally we have also noted an association of capsular laxity in patients with ligamentum teres hypertrophy suggesting recruitment of this ligament. Traumatic rupture to the iliofemoral ligament have been described in American football players in the setting of traumatic posterior hip subluxation, posterior acetabular rim fracture, and hemarthrosis [64]. Although much less commonly involved, posterior capsule injury may also occur.

Ligamentum Teres

Tears of the ligamentum teres have recently been associated with intra-articular hip pain and represented the third most common intra-articular problem in athletes. These injuries are usually diagnosed arthroscopically as either complete, partial, or degenerated tears [65,66]. In the past, preoperative imaging

Fig. 19. (A) Oblique axial T2 fat-saturated images with normal uniform thickness (from lateral to medial) of the anterior capsule/iliofemoral ligament with smooth undersurface (black arrowheads). (B) Lack of uniform thickness of the capsule with thickening of lateral aspect (black arrows) and relative thinning medially (black arrowheads). This latter finding correlated with clinical and surgical findings of capsular laxity. Also note cystic changes of the posterior capsule insertion medially indicative of prior injury (white arrow).

Fig. 19. (A) Oblique axial T2 fat-saturated images with normal uniform thickness (from lateral to medial) of the anterior capsule/iliofemoral ligament with smooth undersurface (black arrowheads). (B) Lack of uniform thickness of the capsule with thickening of lateral aspect (black arrows) and relative thinning medially (black arrowheads). This latter finding correlated with clinical and surgical findings of capsular laxity. Also note cystic changes of the posterior capsule insertion medially indicative of prior injury (white arrow).

studies of were of little value for detecting tears of the ligamentum teres. Bony avulsion of the femoral head has been associated with tears of ligamentum teres, but this is a very unusual finding [67]. There is almost no literature regarding the MR appearance of tears of the ligamentum teres [68].

Anatomically, the ligamentum teres arises inferiorly predominantly from the transverse ligament where it is trapezoid in shape and becomes progressively round or oval in shape (and somewhat banded or bilobed in appearance) [65]. It inserts in the fovea of the femoral head. In our MR experience, the normal ligamentum teres generally appears homogenous with dark signal intensity on T1- and T2-weighted images. At its inflection where it crosses 55°, magic angle phenomena can be noted on short TE sequences. We rely heavily on oblique axial images during MR arthrography for assessment, as there is too much partial volume averaging with sagittal and coronal images for consistent evaluation. We look for discontinuity, fraying, and intrinsic signal changes to assess for injury (Fig. 20). Adjacent inflammation and edema of the cotyloid fossa may also be present and contribute to symptoms. A recent unpublished retrospective review from our institution found that MR arthrography offered good correlation with arthroscopic evaluation for partial tears of the ligamentum teres, which can aid preoperative planning and treatment. Our definition of a tear in this study included abnormal T2 signal and morphology of the ligament when the cross-sectional thickness was determined to be normal. The criteria were less stringent in cases of a hypertrophied ligamentum teres (defined as extending more than 2 mm beyond foveal insertion on oblique axial images) where only abnormal T2 signal or morphologic irregularity was considered a partial tear.

Fig. 20. (A) Oblique axial T2 fat-saturated image with normal size and signal of proximal aspect of ligamentum teres (white arrows). (B) A different patient with a hypertrophic ligamentum teres with normal signal and contour without a superimposed tear (white arrows). (C) Demonstrates a hypertrophic ligamentum teres with abnormal contour and bright T2 signal indicating a partial tear posteriorly that was arthroscopically debrided (black arrows).

Fig. 20. (A) Oblique axial T2 fat-saturated image with normal size and signal of proximal aspect of ligamentum teres (white arrows). (B) A different patient with a hypertrophic ligamentum teres with normal signal and contour without a superimposed tear (white arrows). (C) Demonstrates a hypertrophic ligamentum teres with abnormal contour and bright T2 signal indicating a partial tear posteriorly that was arthroscopically debrided (black arrows).

The significance of a hypertrophied ligamentum teres is unclear, but may represent a chronic process with reactionary changes of the ligament from overloading (ie, rotational instability) and could be an abnormal finding by itself. Interestingly, a recent study of high level runners noted a hypertrophic change of the ligamentum teres during arthroscopy, and suggested a relationship with chronic instability [69].

POSTOPERATIVE EVALUATION OF THE HIP

Initial radiographs should assess for overall anatomic alignment, bony contours, and mineralization with comparison to preoperative studies. Postoperative changes involving arthroscopic osteochondroplasty, open resection osteoplasty, or acetabular realignment should assess for any residual FAI. Plain films may detect postoperative myositis ossificans, which can be a rare postoperative complication. However, when clinically indicated, symptomatic postoperative evaluation primarily involves analysis of the labrum searching for recurrent labral tears or detachments (Fig. 21). Although no published data exists, evaluation of the postoperative labrum can be difficult. It is essential that the interpreting physician is familiar with the original surgical technique to properly diagnosis recurrent problems. Intrasubstance suture or granulation tissue may mimic tear, much like postoperative MR appearance of meniscal repair. In our experience, if bioabsorbable suture anchors are used they are rarely seen postoperatively. Postoperative scarring or fibrosis can occur and symptomatic labral adhesions have been seen (Fig. 22). Anecdotally, pre- and postoperative synovitis may be occult with MR arthrography, and there may be a role for intravenous contrast in this scenario to better assess for synovitis. It is not uncommon to see enlargement of the iliofemoral ligament/anterior

Fig. 21. Division 1 college running back with two prior labral debridement surgeries with persistent pain. Axial T2 fat-saturated image showed attenuated anterosuperior labrum (white arrowhead ), which on close scrutiny was detached from the acetabular rim (white arrow) causing entrapment that was confirmed arthroscopically.

Fig. 21. Division 1 college running back with two prior labral debridement surgeries with persistent pain. Axial T2 fat-saturated image showed attenuated anterosuperior labrum (white arrowhead ), which on close scrutiny was detached from the acetabular rim (white arrow) causing entrapment that was confirmed arthroscopically.

Fig. 22. Oblique axial T2 MR arthrogram image demonstrating surgically proven postoperative labral adhesions (black arrow) between the anterior capsule and capsular side of the anterior labrum. (From Armfield DR. Clinical evaluation of the hip: radiologic evaluation. Oper Tech Orthop 2005;15(3):182-90, with permission.)

capsule after surgery when suture plication or thermal capsulorrhaphy has been performed.

FUTURE DIRECTIONS

Future evaluation of intra-articular hip pathology will be largely influence by stronger MR magnetic fields (3T and greater), improved coil technology, and expanding knowledge base. The ultimate goal will be to create an easily reproducible noninvasive test with conspicuity of abnormal findings. We are currently evaluating the role of stress positioning and kinematic imaging to assess for biomechanical soft tissue dysfunction of the capsule, labrum, and ligamentum teres. We are evaluating computer-generated bone collision detection to help predict and visualize femoroacetabular impingement to aid surgical planning.

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