The medial collateral ligament (MCL) is the most commonly injured knee ligament. Such injuries in children are rare due to the relative thickness of the articular cartilage and physes that can absorb energy. Traumatic MCL entrapment into the medial knee joint in a child has not yet been reported. This article presents a case of intra-articular MCL entrapment in a 9-year-old boy with characteristic findings on magnetic resonance imaging showing the interposition of the MCL between the medial meniscus and medial tibial plateau. During arthroscopic surgery, the MCL tear pattern was visualized underneath the medial meniscus. A medial knee incision was performed and the MCL was retrieved from the knee joint. The meniscotibial ligaments and medial meniscus were repaired to the tibial plateau. The torn ends of MCL were reapproximated and sutured. One year postoperatively, the patient is back to full activities including sports without limitations. This article should help raise awareness about the possibility of such injuries to avoid a delay in diagnosis. Although it is true that children would injure their physes more often than their ligaments due to their relative weakness, this article describes the possibility of a serious ligament injury without physeal involvement.
The medial collateral ligament (MCL) is the most commonly injured knee joint ligament.1 However, MCL entrapment into the medial knee joint is rare. This article presents a case of intra-articular MCL entrapment in a child with findings on magnetic resonance imaging (MRI) and intraoperatively.
A 9-year-old boy presented with a right knee injury after a fall while jumping on a trampoline. As he fell, his right knee was caught between the trampoline spring and the frame. He had immediate pain and was unable to ambulate. He was seen in the emergency department where conventional radiographs showed only medial soft tissue swelling with no fracture or dislocation. The right knee was placed in an immobilizer and the patient was discharged with crutches.
Clinical examination 2 days later showed a knee effusion, tenderness on the medial side of the knee joint, and a medial joint space opening of approximately 5 mm, with valgus stress at 30° of knee flexion, compared to the contralateral knee. There was no significant medial joint space opening with the knee in extension. Range of motion (ROM) was painful. The Lachman test showed approximately 3 mm of increased anterior translation with a firm end point, compared to the contralateral side. The pivot shift test was negative.
The patient underwent MRI evaluation of the right knee 2 days after the injury. The findings included a complete avulsion of the distal aspect of the superficial MCL and the meniscotibial portion of the deep MCL. The distal MCL was interposed beneath the body of the medial meniscus and the medial tibial plateau (Figure 1, 2A). There were bone bruises of the lateral femoral condyle and posterolateral tibial plateau, and poorly delineated fibers of the anterior cruciate ligament (ACL) suggesting a partial tear. A moderate joint effusion was also seen.
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|Figure 1: Coronal T2-weighted image of the right knee showing the distal aspect of the MCL (arrow) interposed between the medial meniscus (dotted arrow) and the medial tibial plateau. There is abundant edema in the soft tissues medial to the knee joint. A lateral femoral bone marrow edema (asterisk) is also seen (A). The sagittal proton density image shows the interposed MCL (arrow) beneath the medial meniscus (dotted arrow) (B). |
The findings on the preoperative MRI were confirmed at knee arthroscopy. The medial meniscus was detached from the medial tibial plateau with meniscotibial ligament tears. A distal portion of superficial MCL was interposed between the medial meniscus and the medial tibial plateau. Fibers of ACL, although hemorrhagic, appeared to be intact. As in the initial clinic evaluation, the right knee subluxated approximately 3 mm anteriorly with the Lachman test, but there was a firm endpoint. After diagnostic arthroscopy, a 5-cm incision was placed on the medial side of the knee overlying the MCL, with one-third of the incision above and two-thirds below the joint line. A transverse MCL tear was identified, and with valgus stress, the proximal end of the distal part of the torn MCL was extracted from the knee joint. The medial meniscus and the torn edges of the meniscotibial ligaments of the joint capsule were identified. The meniscus was repositioned and the meniscotibial ligaments were repaired using size 2-0 Ethibond (Ethicon, Inc, Somerville, New Jersey) sutures in a horizontal mattress fashion (Figure 2B). The torn ends of the superficial MCL were then approximated, end to end, with size 0 Fiberwire (Arthrex, Naples, Florida) sutures using the Mason-Allen technique. The repair was reinforced with number 0 Vicryl (Ethicon, Inc) sutures. The posterior oblique ligament was imbricated with the posterior aspect of superficial MCL using number 0 Vicryl (Ethicon, Inc) sutures. A standard closure was then performed in layers. Knee arthroscopy confirmed proper position of the meniscus and its attachment to the joint capsule. The knee was placed in a hinged postoperative brace.
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|Figure 2: Arthroscopic image shows the interposed MCL (arrow) between the medial meniscus (dotted arrow) and the medial tibial plateau (A). Intraoperatively, the MCL (arrow) was retrieved from the knee joint. The infrapatellar branch of the saphenous nerve (dotted arrow) is protected intraoperatively (B). |
Rehabilitation included physical therapy beginning on postoperative day 2. This involved cryotherapy, static quadriceps strengthening exercises, gentle ROM in a figure-of-8 position, and toe-touch weight bearing with crutches. Physical therapy was advanced as pain and swelling was controlled. The knee brace and crutches were used for 6 weeks. The patient was released to full activities with a functional ACL brace 4 months postoperatively. The patient used the brace for approximately 6 months before discontinuing it because he felt confident and his involved knee felt no different from his contralateral knee. At 1-year follow-up, the patient was back to full activities with no restrictions or symptoms.
A review of the literature reveals several case reports of soft tissue structures entrapped in physeal fractures around the knee joint.2-4 Few published articles in the English literature describe the intra-articular entrapment of the MCL into the knee joint. Müller5 described various possible patterns of medial capsuloligamentous lesions around the knee joint. Although entrapment of MCL in the joint was addressed as a frequent form of incarceration of the torn distal end of the ligament, there were no reported patients or results of this entity. Patel6 described the MRI findings of MCL entrapment in the knee joint in a 47-year-old man, which was confirmed intraoperatively. To our knowledge, there have been no reports of intra-articular entrapment of the MCL in a child.
Irreducible posterolateral knee dislocation is a severe form of injury with entrapment of MCL in the joint being part of a wider spectrum of injury. Griswold7 reported 4 patients with irreducible posterolateral knee dislocation with button-holing of the medial femoral condyle through the medial joint capsule. Both interposition of the MCL and joint capsule between the femur and the tibia were noted and surgical intervention was required in all patients. Quinlan8 reported on 6 patients with posterolateral knee dislocation with button-holing of the medial femoral condyle with similar intraoperative findings. Tsiagadigui et al9 described the MRI findings in an adult with irreducible posterolateral knee dislocation and interposition of capsuloligamentous structures, although these were preoperatively mistaken for a medial meniscal tear. Thus MCL entrapment in the knee joint, in all reported cases of irreducible posterolateral dislocation, is an associated finding, and cannot be considered a distinct entity.
Warren and Marshall10 described 3 layers of the medial aspect of the knee. Layer 1 is the deep fascia, layer 2 is the superficial MCL, and layer 3 comprises the medial joint capsule and deep MCL. Posterior to the superficial MCL, layers 2 and 3 merge to form the ligaments of the posteromedial corner. In our patient, both the superficial and deep portions of the MCL were torn and the superficial part was interposed between the medial meniscus and the medial tibial condyle. In our patient, we postulate the mechanism of injury to be a severe abduction force on a nonweight bearing limb with the knee extended, resulting in a torn MCL. An associated partial tear of the ACL allowed further mobility and opening of the medial side of the joint, which closed again when the force was released. This mechanism might have resulted in a transient knee subluxation that reduced spontaneously. The medial opening allowed the intra-articular entrapment of the MCL. Such MCL tears, with no posterolateral knee dislocation, are transverse tears, as opposed to the vertical tears that occur with rotation in the posterolateral knee dislocation.11
Magnetic resonance imaging findings of MCL injury have been well described in the literature.12 The superficial portion of the MCL (also termed the tibial collateral ligament on imaging) is the most consistently seen on MRI. The abnormalities evident on MRI range from adjacent soft tissue edema and internal ligament abnormal signal, to morphologic disruption and fiber discontinuity, as in this patient. The lateral compartment bone bruises identified are consistent with valgus stress and associated ACL injury. On sagittal imaging, the hypointense signal of the interposed MCL should not be confused with a medial meniscal tear.
Historically, ligamentous injuries around the knee in children were considered rare. The reasons cited were the relative thickness of the articular cartilage and growth cartilage, which can absorb the energy, thus sparing the ligaments. Also, the ligaments are stronger than growth plates, leading to epiphyseal separations rather than ligamentous disruptions.13 However, with greater participation in sports and recreational activities, increased awareness, and elevated competitiveness, as well as with the advent of MRI and arthroscopy, the incidence and recognition of ligamentous knee injuries in children is on the rise.
- Kaeding CC, Pedroza AD, Parker RD, Spindler KP, McCarty EC, Andrish JT. Intra-articular findings in the reconstructed multiligament-injured knee. Arthroscopy. 2005; 21(4):424-430.
- McAnally JL, Eberhardt SC, Mlady GW, Fitzpatrick J, Bosch P. Medial collateral ligament tear entrapped within a proximal tibial physeal separation: imaging findings and operative reduction. Skeletal Radiol. 2008; 37(10):943-946.
- Whan A, Breidahl W, Janes G. MRI of trapped periosteum in a proximal tibial physeal injury of a pediatric patient. AJR Am J Roentgenol. 2003; 181(5):1397-1399.
- Ciszewski WA, Buschmann WR, Rudolph CN. Irreducible fracture of the proximal tibial physis in an adolescent. Orthop Rev. 1989; 18(8):891-893.
- Müller W (Trans. T. G. Tegler). Injuries of the Ligaments and Capsule. The Knee: Form, Function and Ligament Reconstruction. New York City, NY: Springer-Verlag Berlin Heidelberg; 1983:148-154.
- Patel JJ. Intra-articular entrapment of the medial collateral ligament: radiographic and MRI findings. Skeletal Radiol. 1999; 28(11):658-660.
- Griswold AS. Irreducible dislocations of the knee joint. J Bone Joint Surg Am. 1951; 33(3):787-791.
- Quinlan AG. Irreducible posterolateral dislocation of the knee with button-holing of the medial femoral condyle. J Bone Joint Surg Am. 1966; 48(8):1619-1621.
- Tsiagadigui JG, Sabri F, Sintzoff S, Schuind F. Magnetic resonance imaging for irreducible posterolateral knee dislocation. J Orthop Trauma. 1997; 11(6):457-460.
- Warren LF, Marshall JL. The supporting structures and layers on the medial side of the knee: an anatomical analysis. J Bone Joint Surg Am. 1979; 61(1):56-62.
- Quinlan AG, Sharrard WJ. Postero-lateral dislocation of the knee with capsular interposition. J Bone Joint Surg Br. 1958; 40(4):660-663.
- Schweitzer ME, Tran D, Deely DM, Hume EL. Medial collateral ligament injuries: evaluation of multiple signs, prevalence and location of associated bone bruises, and assessment with MR imaging. Radiology. 1995; 194(3):825-829.
- Rang M. Children are not just small adults. In: Wenger DR, Pring ME, Rang M, eds. Childrens Fractures. Philadelphia, PA: JB Lippincott Company; 1974:1-5.
Drs Desai and Parikh are from the Department of Orthopedics, and Dr Laor is from the Department of Radiology, Cincinnati Childrens Hospital, Cincinnati, Ohio.
Drs Desai, Parikh, and Laor have no relevant financial relationships to disclose.
Correspondence should be addressed to: Shital Parikh, MD, Cincinnati Childrens Hospital, 3333 Burnet Ave, ML 2017, Cincinnati, OH 45229-3039 (firstname.lastname@example.org).