Sports Medicine: Just the Facts

CHAPTER 56 • MAGNETIC RESONANCE IMAGING: LOWER EXTREMITY 333

evaluate the integrity of the popliteal artery and

geniculate vessels (Potter et al, 2002).

• The cyclops lesion, a localized, often mass-like, form of
  arthrofibrosis seen postoperative ACL repair, has been
  demonstrated with high sensitivity and specificity on
  MR imaging (Bradley, Bergman, and Dillingham, 2000).


• Ganglion formation in ACL grafts, seen as thickening
  and hyperintensity of the graft without any other MR
  evidence for traumatic injury occurs not infrequently
  post-ACL reconstruction, especially noted with gra-
  cilis or semitendinosis autografts (Schatz et al, 1997).


• The meniscus is seen at MR imaging as a triangular
  hypointense focus of fibrocartilage on sagittal sequences.
  The posterior horn of the medial meniscus should be
  larger than the anterior horn on sagittal sequences. The
  lateral meniscus is less fixed to the tibia than the medial
  meniscus and therefore is less likely to be injured.


• The lateral meniscus is more circular in shape than the
  medial meniscus.


• Meniscal tears are diagnosed as abnormal linear
  hyperintense (fluid) signal reaching an articular sur-
  face as well as abnormal morphology. Wedge-shaped
  degenerative signal (sometimes classified as grade 2C
  signal) does not usually correlate with patient symp-
  tomatology (McCauley et al, 2002).


• When evaluating for meniscal tears, one should look
  for displaced meniscal fragments (Fig. 56-6). Bucket
  handle tears are a specific category of meniscal tears

in which the meniscus is cleaved in an anteroposterior

direction and the inner margin of the meniscus is dis-

placed into the intercondylar notch; this often results

in the “double PCL” sign whereby the paramidline

sagittal sequence demonstrates an additional

hypointense curvilinear density deep to and in addi-

tion to the posterior cruciate ligament.

• If a meniscal tear is found at MR imaging, the tear
  should be categorized as a horizontal, vertical, or
  radial split tear. In addition, the location of the tear
  with respect to the periphery in the anteroposterior
  dimension is important in determining repairability of
  the tear. The more in the periphery the tear is, the
  greater the vascular supply and therefore the greater
  likelihood of viability if the tear is repaired.


• Meniscal cysts, often encountered in cases of degener-
  ative tears of the menisci, have been reported to occur
  with greater frequency in the medial compartment than
  laterally (Campbell, Sanders, and Morrison, 2001).


• Postoperatively, recurrent meniscal tears can be diag-
  nosed with unenhanced MR imaging as well as MR
  arthrography. A slightly higher specificity for recur-
  rent meniscal tears has been demonstrated with direct
  MR arthrography compared with unenhanced mag-
  netic resonance imaging (78 vs. 67%); however, sen-
  sitivity is similar at 83 and 86% as well as positive
  predictive value of 90 versus 83%, respectively
  (White et al, 2002).


• There is a high accuracy of evaluating articular carti-
  lage abnormalities with appropriate MR pulse
  sequences. A prospective study evaluating 616 articu-
  lar surfaces in the knee with specific cartilage-sensi-
  tive pulse sequences found an accuracy of 92% of MR
  compared with arthroscopy (Potter et al, 1998).


• Surgical repair of articular cartilage defects can
  include microfracture, autologous chondrocyte
  implantation, fresh cadaver allografts, and mosaic-
  plasty (Minas and Nehrer, 1997; Kish, Modis, and
  Hangody, 1999), all of which can be imaged with MR
  post operatively.


• Some authors have suggested a correlation between
  the presence of subchondral bone marrow edema and
  clinical outcome in cases of chondral injuries (Rubin,
  Harner, and Costello, 2000).


• Osteochondral injuries can occur on any articular sur-
  face. The classic osteochondritis dissecanslesion is
  located on the nonweight bearing aspect of the medial
  femoral condyle.


• Mosaicplasty is a procedure where multiple osteo-
  chondral plugs are harvested from a nonweightbear-
  ing portion of the knee, usually in the patellofemoral
  joint and used to fill an osteochondral defect (Kish,
  Modis, and Hangody, 1999; Hangody et al, 1998;
  Berlet, Mascia, and Miniaci, 1999).

FIG. 56-6 Coronal fast spin echo MR image demonstrating a
tear of the medial meniscus (short thick white arrow) with a dis-
placed fragment of hypointense fibrocartilage into the inter-
condylar notch (long thin white arrow).