A four-year old black female was seen in the office with primary complaints of popping with discomfort in her right knee for the past year. This was associated with a slight limp. She denied fever. There was no family history of knee problems.

      Physical exam revealed repetitive clunking  of the knee in extension.  There was popping over the lateral joint line.  Mild effusion was noted.  Collateral ligaments were stable.  Lachman and posterior drawer at 90 were negative.  Patellar tendon and quadriceps tendon were nontender.
Patella glide  was 2+, patella tilt was 1+, and there was no significant tenderness in the patellofemoral joint.  X-rays including AP and Lateral of the knee joint were negative.  the impression was rule out discoid meniscus and an MRI scan was requested.  The MRI report revealed normal medial meniscus.  There was abnormal increased signal throughout the lateral meniscus and the meniscal tissue was thicker and more medially located than is the norm.  No definite Grade III tears were identified, but there were diffuse Grade II changed throughout the entire lateral meniscus.

      Arthroscopy and mini-arthrotomy were performed under general enesthesia using small 2.7mm instruments.  Prior to prepping and draping but with the patient asleep, the knee was put through a range of motion, again confirming subluxation of the discoid meniscus on near extension of the knee producing an audible clunk or pop.

      A tourniques was applied  to the knee, as well as a surgical knee assistant holder, and the knee was prepped and draped.  Routine arthroscopy portals were made.  The scope was introduced through the anteromedial portal visualizing the lateral knee joint.  The lateral meniscus was probed throughout its anterior, lateral, and posterior horns and found to be without tear.   There was adequate attachment throughout the periphery of the meniscus on both surfaces without defect.  The poplitues tendon was identified.  The lateral meniscus was discoid and did not have the typical half-moon shaped appearance.  In addition the lateral meniscus was much thicker than normal.   The remainder of the joint inspection was normal.

      Using the small joint arthroscopy instruments, a portion of the discoid meniscus was excised.  After this initial trimming of the meniscus, the instruments were removed and the knee was put through a range of motion with persistence of the clunking.  A mini arthrotomy was performed.  Kocher clamps (small), and a disposable fish-mouth arthroscopy blade were used to excise the central portion of the discoid meniscus.  The knee was put through a range of motion and it was felt that the clunking was eliminated.

     The wound was closed, patient was awakened from general anesthesia, carried to the recovery room and discharge to follow-up in the office.  The patient experienced no further clunking, had no demonstrable symptoms or limp and was overall improved from the procedure.

     TECHNICAL NOTES    The tissue was so thick that the small instruments could not grasp both sides of the the meniscus.  The joint was so small that large standard arthroscopy instruments would not be tolerated.  In retrospect, one could have used a banana disposable arthroscopy blade to create in effect a horizontal tear through the abnormal area  and then use a banana knife to create multiple vertical incision which would allow more easy resection of the meniscus tissue.

      Bellier, et al. 1 studied 19 lateral discoid menisci in 16 children, average age 10 years (5 to 15)  Arthroscopic menisectomy achieved excellent results in 18 of 19 cases.  Three children had bilateral surgery.  The period from first appearance of symptoms until treatment average six months (1mo to 2 years)

      Symptoms included snapping or locking in eight cases, locking with loss of hyperextension in 10 cases.  Both symptoms were seen in five cases.  There was lateral pain in 15 cases, but nonlocalized or medial (2 cases).  Quadriceps atrophy was constant, demonstrating the existence of anatomic pathology.  Two cases of locking @ 30 flesion suggesting a tear of the menisus.

      Plain x-ray findings included 12 of 19 normal though the lateral tibial space was enlarged (lateral and inferior oblique view) in five knees.  In two cases the lateral tibial eminence was blunted.  Also seen is a "squared" lateral femoral condyle, and "cupped" lateral tibial plateau.

     RESUSLTS      There was a complete lateral discoid meniscus in 14 knees, five knees were incomplete.  There were two thickenings of the intermediate segment, two posterior megahorns, one anterior megahorn.  No Wrisberg ligament type menisci were found (lacking the normal posterior tibial attachment, but with a femoral attachment by a meniscofemoral ligament).  A total of 12 lateral discoid menisci were torn (8 complete and 4 incomplete)  Eight tears were horizontal cleavage, and four were bucket handle.  No medial pathology was found.  There were 13 central partial minisectomies and one total menisectomy performed on 14 complete lateral discoid menisci.  Five incomplete discoid menisci were treated by partial menisectomy.

CLASSIFICATION OF DISCOID MENISCUS.

     A. Complete disc-shaped type with thinner center

     B. Incomplete semilunar type with concave or convex free edge.  Present in this case report.

     C. Hypermobile type (wrisberg) with no posterior attachment.

FREQUENCY     In 347 consecutive scopes for meniscal lesions, Dickhaut and DeLee found 18 lateral discoid meniscal lesions (5.2%).  A recent French study found bilaterality in 17 of 84 children  (20%).

REFERENCE       CALL  2548800