Lateral meniscal root tear: Important association with ACL injury
What is the meniscal root?
The menisci are C-shaped structures inside the knee joint that act as shock absorbers. The menisci distribute the weight of the body evenly throughout knee joint.
The meniscus is attached at the front and back of the joint by the “root” attachments. The root attachments serve as anchor points for the meniscus.
Why is the meniscal root important?
The shape of the normal meniscus cups the femur and supports it. Given the root attachments are the anchor points for the meniscus, their integrity is vital in providing a cushioning effect for the femur bone. If the root attachments are torn, this support is lost. This will put more pressure on the cartilage surfaces[1] and cause cartilage wear, or arthritis, much quicker.
The menisci also provide more stability within the knee. A lateral meniscus root tear will make the instability found in ACL tears worse[2]. An attempt must be made to repair the root during an ACL reconstruction in order to restore more stability to the knee.
How is this injury diagnosed?
A lateral meniscus root tear has an association with an ACL tear[3]. In this setting, an MRI scan of the knee is performed to confirm the ACL tear. Lateral meniscal root injuries can be difficult to diagnose on MRI, even with an experienced musculoskeletal radiologist reviewing the images.
A high index of suspicion needs to be maintained when performing an arthroscopy during an ACL reconstruction. The lateral meniscal root tear can look deceptively intact on first inspection during an arthroscopic assessment. With ACL tears, it is typical for the lateral root to be detached from the insertion of the tibia at the back of the knee. It usually has healed back to the capsule in an abnormal position. When the root is stressed using an arthroscopic probing tool, it is apparent that it has detached, and a root repair should be performed.
How is it repaired?
A root repair is usually performed at the same time as the ACL reconstruction. A common technique of repairing it is to pass high-strength sutures into the torn meniscal root[4]. These sutures are passed through a bony tunnel in the tibia. This tunnel starts at the origin of the posterior lateral meniscal root and passes out through the front of the tibia. This allows to lateral meniscal root to ‘dock’ into the tunnel and re-anchor itself. The sutures are usually tied over a small metallic button or passed into the tibia bone using a suture anchor.
What are the implications of a missed injury?
A missed lateral meniscal root avulsion injury has two main implications in an ACL reconstruction:
- Accelerated arthritis in the lateral compartment of the knee due to a defunctioned meniscus
- A higher risk of ACL graft failure (i.e. reinjury of the reconstructed ACL graft) as the lateral meniscus has lost its function as a secondary stabiliser of the knee
Summary
Lateral meniscal root tears occur with ACL injury and can be easily missed on MRI. These injuries should be repaired to restore the normal function of the meniscus, prevent accelerated cartilage wear and to provide additional stability to the ACL reconstruction.
References
1. Schillhammer CK, Werner FW, Scuderi MG, Cannizzaro JP. Repair of lateral meniscus posterior horn detachment lesions: a biomechanical evaluation. Am J Sports Med. 2012;40(11):2604-2609. doi:10.1177/0363546512458574 ↩
2. Shybut TB, Vega CE, Haddad J, et al. Effect of Lateral Meniscal Root Tear on the Stability of the Anterior Cruciate Ligament–Deficient Knee. Am J Sports Med. 2015;43(4):905-911. doi:10.1177/0363546514563910 ↩
3. Brody JM, Lin HM, Hulstyn MJ, Tung GA. Lateral Meniscus Root Tear and Meniscus Extrusion with Anterior Cruciate Ligament Tear. Radiology. 2006;239(3):805-810. doi:10.1148/radiol.2393050559 ↩
4. LaPrade RF, LaPrade CM, James EW. Recent Advances in Posterior Meniscal Root Repair Techniques. JAAOS - J Am Acad Orthop Surg. 2015;23(2):71–76. doi:10.5435/JAAOS-D-14-00003 ↩
Schillhammer CK, Werner FW, Scuderi MG, Cannizzaro JP. Repair of lateral meniscus posterior horn detachment lesions: a biomechanical evaluation. Am J Sports Med. 2012;40(11):2604-2609. doi:10.1177/0363546512458574 ↩
Shybut TB, Vega CE, Haddad J, et al. Effect of Lateral Meniscal Root Tear on the Stability of the Anterior Cruciate Ligament–Deficient Knee. Am J Sports Med. 2015;43(4):905-911. doi:10.1177/0363546514563910 ↩
Brody JM, Lin HM, Hulstyn MJ, Tung GA. Lateral Meniscus Root Tear and Meniscus Extrusion with Anterior Cruciate Ligament Tear. Radiology. 2006;239(3):805-810. doi:10.1148/radiol.2393050559 ↩
LaPrade RF, LaPrade CM, James EW. Recent Advances in Posterior Meniscal Root Repair Techniques. JAAOS - J Am Acad Orthop Surg. 2015;23(2):71–76. doi:10.5435/JAAOS-D-14-00003 ↩
Read more about:
ACL injuries - Why they are common & what to do about them.
ACL surgery - How the surgery is performed and what graft options there are.
Meniscal tears - A common association with ACL injuries.
Meniscal repair - How a torn meniscus is repaired.
Return to play testing - Decreasing the risk of reinjury to your ACL graft.