Variations of meniscus morphology have been described. The Watanabe classification (1979) has been widely used to classify discoid variants. In 1998, Monllau et al1 described the ring-shaped lateral meniscus and proposed an addition to the Watanabe classification to include the ring-shaped lateral meniscus as a fourth variant discoid lateral meniscus. Since publication of the findings of Monllau et al, multiple authors have sought to characterize the epidemiology of the described discoid meniscus variants, including the ring-shaped lateral meniscus. The incidence of the ring-shaped variant was reported to be 0.9% to 2.4% in an Asian population, with the overall incidence of discoid menisci reported to be 13%.2,3 The incidence among Caucasians is not known. Morphologic variations of the lateral meniscus can present both diagnostic and therapeutic challenges to treating physicians.
This article describes a ring-shaped lateral meniscus without an anterior horn attachment in a patient with an anterior cruciate ligament (ACL) rupture.
A 15-year-old previously healthy boy sustained a left knee ACL rupture while playing soccer. Magnetic resonance imaging confirmed ACL rupture and what was initially thought to represent a possible bucket handle meniscus tear (Figure 1).
Coronal (A) and sagittal (B) PD T2 FS magnetic resonance images showing the lateral meniscus tissue near the intercondylar notch (arrows).
The patient underwent left knee arthroscopic ACL reconstruction using quadriceps tendon autograft approximately 1 month following the injury.
Arthroscopic inspection of the lateral meniscus revealed that it was ring shaped. The anterior horn of the lateral meniscus was found to insert into the ACL with no direct bony attachment (Figure 2). Preparation of the tibial tunnel for ACL reconstruction resulted in destabilization of the anterior horn of the lateral meniscus.
Arthroscopic view from the anterolateral portal with a 30° arthroscope demonstrating confluence of the anterior horn of the lateral meniscus with the anterior cruciate ligament.
Anterior cruciate ligament reconstruction tunnels were prepared using commercially available guides. The femoral tunnel was created with a guide placed through the anteromedial arthroscopy portal. The tibial tunnel was created using a barrel reamer over a guide pin that was placed using a commercially available tibial ACL guide. The anterior horn of the lateral meniscus was repaired using a double-loaded biocomposite suture anchor (Corkscrew; Arthrex) placed through the anteromedial arthroscopy portal (Figure 3).
Arthroscopic view from the anterolateral portal with a 30° arthroscope following repair of the anterior root of the lateral meniscus and reconstruction of the anterior cruciate ligament with quadriceps tendon autograft.
The suture anchor was placed at the anatomic attachment site of the anterior horn of the lateral meniscus. Suture limbs from the anchor were passed through the anterior horn of the lateral meniscus using a self-retrieving suture-passing device (Knee Scorpion; Arthrex). Sutures were tied in a horizontal mattress configuration.
Meniscal tissue bridging the anterior and posterior horns was left in situ. The ACL was reconstructed uneventfully using standard techniques.
Postoperatively, the patient was kept in a hinged knee brace with limited weight bearing and range of motion from 0° to 60° for 4 weeks. He participated in a standardized physical therapy program. At most recent follow-up, the patient had achieved full extension. A nonpainful clicking sensation was noted in early follow-up but had resolved by 6 months.
A ring-shaped lateral meniscus can present several challenges to treating physicians. It may be mistaken for an incomplete discoid lateral meniscus or a bucket handle meniscus tear.3,4 Esteves et al5 reported a case in which a ring-shaped meniscus was associated with a hypoplastic ACL and identified several magnetic resonance imaging findings that may help define a ring meniscus.
To the best of the authors' knowledge, this is the first report of a ring-shaped lateral meniscus that was rendered unstable during ACL reconstruction due to the absence of an anterior meniscotibial attachment. The treatment of choice in this case was arthroscopic repair using a suture anchor placed through the anteromedial portal. This repair used standard arthroscopy techniques and led to stability. Suture anchor fixation of meniscal root tears has been previously described and has been found to be biomechanically suitable.6,7 Meniscus repair did not interfere with the ability to reconstruct the ACL in the standard fashion. Indications for treatment of the meniscal bridge with resection vs retention have not been described. In the current case, the bridge was left in situ because it was not thought to interfere with knee function.
The authors recommend careful evaluation of preoperative imaging studies and thorough dynamic arthroscopic evaluation of the meniscus prior to and following reconstruction of the ACL. Consideration should be given to stabilization of the anterior root of the lateral meniscus when a significant portion of it is confluent with the ruptured ACL.
- Monllau JC, León A, Cugat R, Ballester J. Ring-shaped lateral meniscus. Arthroscopy. 1998;14(5):502–504. doi:10.1016/S0749-8063(98)70079-9 [CrossRef]. PMID:9681543
- Ryu K, Iriuchishima T, Oshida M, et al. Evaluation of the morphological variations of the meniscus: a cadaver study. Knee Surg Sports Traumatol Arthrosc. 2015;23(1):15–19. doi:10.1007/s00167-013-2612-y [CrossRef]. PMID:23873345
- Kim Y-G, Ihn JC, Park SK, Kyung HS. An arthroscopic analysis of lateral meniscal variants and a comparison with MRI findings. Knee Surg Sports Traumatol Arthrosc. 2006;14(1):20–26. doi:10.1007/s00167-005-0629-6 [CrossRef]. PMID:15905996
- Pandey V, Dinesh KV, Acharya KK, Rao PS. Ring meniscus mistaken for incomplete discoid meniscus: a case report and review of literature. Knee Surg Sports Traumatol Arthrosc. 2010;18(4):543–545. doi:10.1007/s00167-009-0924-8 [CrossRef]. PMID:19784627
- Esteves C, Castro R, Cadilha R, Raposo F, Melão L. Ring-shaped lateral meniscus with hypoplastic anterior cruciate ligament. Skeletal Radiol. 2015;44(12):1813–1818. doi:10.1007/s00256-015-2197-2 [CrossRef]. PMID:26178136
- Tapasvi SR, Shekhar A, Patil SS. Knotless medial meniscus posterior root repair. Arthrosc Tech. 2018;7(5):e429–e435. doi:10.1016/j.eats.2017.11.002 [CrossRef]. PMID:29868415
- Robbins CM, Murphy CP, Daney BT, Sanchez A, Provencher MT. Knotless suture anchor repair of anterolateral meniscus root after iatrogenic injury. Arthrosc Tech. 2018;7(8):e875–e879. doi:10.1016/j.eats.2018.04.012 [CrossRef]. PMID:30167368