LATERAL MENISCAL TEAR

Definition:    A lateral meniscal tear involves a disruption in the lateral fibrocartilage of the knee. There is also an normal variant of the lateral meniscus where the meniscus forms a circle/or disc and is called a discoid meniscus.   There are several different types of tears ranging from longitudinal, horizontal, radial, parrot beak, flap tears, bucket handle and degenerative tears (Figures 1 – 8).
Figure 1 – Bucket Handle Tear       Figure 2 – Degenerative Tear

Figure 3 – Discoid Meniscus            Figure 4 – Flap Tear

Figure 5 – Horizontal Tear                Figure 6 – Longitudinal Tear

Figure 7 – Parrot Beak Tear          Figure 8 – Radial Tear

Patients may complain of specific lateral-sided or posterolateral knee pain, swelling, giving way, difficulty bending knee, difficulty extending knee, locking, and possibly instability. It may be associated with a pop. Acute tears can occur in all age groups. Degenerative tears are more common in older populations in association with signs of osteoarthritis. The pain is usually made worse with squatting and twisting.
Anatomy of the lateral meniscus:
Variants such as discoid (see above)
The outer/peripheral 1/3 of the meniscus is referred to as the red zone with increased vascularity and probability of healing for repair considerations.1

Figure 9 – Crossection of Meniscus and Red Zone

Injury Mechanism: Can occur from a twisting motion of the knee with the foot planted, or squatting and twisting. May be associated with ACL tears and pivoting.

Differential Diagnoses:   ACL rupture, LCL tear, Pes Anserine Bursitis, Lateral Compartment osteoarthritis (OA), Patellofemoral osteochondrosis/PFPS/PFOA, Biceps femoris strain/tear, Osteochondritis dissecans, iliotibial band friction syndrome.
Exam:
Assess for an effusion, lateral joint line tenderness. Pain with flexion located in the lateral joint.
Test active and passive range of motion to rule out locking of the knee (block from full extensions) as this can occur with bucket handle tears and are a surgical urgency.
Special tests for Meniscal tests include:

• McMurray – flexion, valgus and external rotation with opposite hand over joint line. A positive test for meniscal tear includes pain in lateral compartment +- clunk.
• Thessaly – with patient standing on only the affected leg with knee flexed at 20 degrees, hold the patients hands and have them twist side to side over their knee. A positive test would be reproduction of lateral sided knee pain
• Ebe’s test – Have patient squat in valgus. A positive test would be pain in the lateral compartment.
• Appley Grind test – with patient lying prone, flex knee and apply axial pressure into bed along with rotation. A positive test will reproduce lateral-sided pain

Finally it is important to test remaining ligaments and lateral meniscus as there may be associated injuries with other ligaments in conjunction with the medial meniscus tear depending on the mechanism of injury.

Investigations:
Xrays – AP, Lat, WB, Skyline, Tunnel views– may assess for lateral OA, osteochondral defect, patellofemoral OA.
MRI – Very sensitive for picking up tears in the meniscus
Management:

Management is highly dependent on type of tear, pre-existing degeneration in the joint, patient expectations, and patient symptoms (location of symptoms and mechanical symptoms [buckling, catching, locking]).  The question of age is one that has been raised in relation to decision making but is not exclusive of other patient factors.  It is also important given the previously discussed numerous tear types as well as patient factors not to generalize results of studies on meniscal arthroscopy.   However a recent randomized study performed in Finland did question the benefit of menisectomy in patients over the age of 35 compared to patients who had arthroscopy without menisectomy for meniscal tears.4

Conservative Goals: Decrease swelling, decrease pain, improve range of motion.  Avoid repetitive deep squats and twisting.

Physiotherapy, quadriceps activation (straight leg raises, supine knee extensions into bed), icing, knee sleeve/bracing/compression bandage.
Surgical: For acute or unstable meniscal tears – arthroscopy is recommended for either repair, partial or full menisectomy depending on location, type, and extent of tear and patient type.
Surgical repair is more amenable for peripheral longitudinal tears and acute reducible bucket handle tears.2,3

Dr. Neil Dilworth  (November 14, 2014)

References:

1) Fox AJ, Wanivenhaus F, Burge AJ, Warren RF, Rodeo SA. The human meniscus: A review of anatomy, function, injury, and advances in treatment. Clin Anat. 2014 Aug 14. doi: 10.1002/ca.22456.

2) Laible C1, Stein DA, Kiridly DN. Meniscal repair. J Am Acad Orthop Surg. 2013 Apr;21(4):204-13. doi: 10.5435/JAAOS-21-04-204.

3) Miller, M Review of orthopaedics. 5th ed. ed. Philadelphia: Saunders / Elsevier; 2008.

4) Sihvonen R1, Paavola M, Malmivaara A, Itälä A, Joukainen A, Nurmi H, Kalske J, Järvinen TL; Finnish Degenerative Meniscal Lesion Study (FIDELITY) Group.  Arthroscopic partial meniscectomy versus sham surgery for a degenerative meniscal tear. N Engl J Med. 2013 Dec 26;369(26):2515-24. doi: 10.1056/NEJMoa1305189.