27-year-old female with sports-related injury a week before; presently with left knee pain and limited movement when bending.
Sagittal MR images of the knee show a normal infrapatellar plica (ligamentum mucosum).
Plicae are embryologic remnants of synovium that may be obstructive during arthroscopic intervention or produce symptoms such as knee pain on certain positions of the knee [1-2].
The suprapatellar plica located at the border between the suprapatellar bursa and knee joint cavity runs obliquely downward from the anterior aspect of the femoral metaphysis to the posterior aspect of the quadriceps tendon. The medial patellar plica which originates from the medial wall of the knee joint also courses obliquely downward and inserts into the synovium covering the infrapatellar fat pad. The lateral patellar plica is the least common plica, and originates in the lateral wall above the popliteus hiatus before attaching to the infrapatellar fat pad [3].
The infrapatellar plica, or ligamentum mucosum is the most common plica in the knee and is found at approximately 8th-12th weeks gestation. It has a narrow femoral origin in the anterior part of the intercondylar notch, with a wider appearance as it descends anteriorly and inferiorly through the infrapatellar fat pad before attaching distally to the inferior pole of the patella. On sagittal MR images, it appears as a low signal intensity structure located anterior and parallel to the anterior cruciate ligament. Its close association with the anterior portion of the ACL may lead to an incorrect diagnosis of a partial ACL tear. Furthermore, this normal synovial fold can also be mistaken for focal nodular synovitis, post-operative changes or an intra-articular body [4-5].
Conservative options for symptomatic plicae include activity restriction, NSAIDs and physical therapy. Nonresponse to these modalities may warrant its arthroscopic resection [2].
Infrapatellar plica (Ligamentum mucosum)
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Based on the provided knee MRI images, there is a low-signal band-like structure seen in the anterior aspect of the knee joint, adjacent to the anterior cruciate ligament (ACL) and near the infrapatellar fat pad. It extends from the anterior portion of the femoral intercondylar notch down to the area near the inferior pole of the patella, consistent with the typical morphology of the infrapatellar plica or “ligamentum mucosum.” In different sequences, there is no clear sign of ACL fiber disruption or tear, nor any obvious meniscal tear signal. Mild edema is noted in the surrounding soft tissue, which may be related to recent sports-related injury or inflammatory factors.
This low-signal band-like structure matches the typical MRI appearance of an infrapatellar plica. When the knee joint moves, the plica can become irritated or impinged, causing pain or limited range of motion.
In certain views, the infrapatellar plica may be mistaken for partial tearing of the ACL fibers. However, based on the overall signal and anatomical course, there is no prominent evidence of ACL rupture or edema. Still, partial ACL injury should be considered in the differential diagnosis.
If the plica appears thickened or degenerated on MRI, it may need to be differentiated from pathological synovial proliferation or pigmented villonodular synovitis. These conditions typically present with more pronounced synovial thickening and soft tissue abnormalities.
Combining the patient’s recent exercise history (increased ankle and knee load due to sports injury), clinical symptoms (anterior knee or peripatellar pain, sense of blockage when flexing or extending), and the MRI findings, the most likely diagnosis is “Symptomatic Infrapatellar Plica.”
1. Conservative Management
• Local Rest and Avoidance of Excessive Flexion/Extension Stress: Temporarily reduce or eliminate activities that may irritate the infrapatellar plica (e.g., deep squats, running, jumping).
• Nonsteroidal Anti-inflammatory Drugs (NSAIDs): If no contraindications exist, a short course of oral or topical NSAIDs can help relieve pain and inflammation.
• Physical Therapy: This may include cold or heat therapy, along with ultrasound, kinesiology taping, or other modalities to reduce local irritation and inflammatory response.
• Joint Mobilization and Flexibility Training: Under the guidance of a professional therapist, perform stretching of the hamstring, quadriceps, and iliotibial band to improve joint stability and flexibility.
2. Rehabilitation Exercise Prescription (FITT-VP Principle Example)
• Frequency: Approximately 3-4 sessions per week, progressively increasing to 5 sessions/week depending on pain tolerance.
• Intensity: Exercise should be pain-free or cause only mild discomfort, using light to moderate resistance with bands or machines.
• Time: Each session lasts about 20-30 minutes, adjusted according to individual tolerance.
• Type: Includes phased training:
• Initial Phase: Static quadriceps isometric exercises, seated leg raises, straight leg raises, and other low-impact activities.
• Intermediate Phase: Progression to seated stretching and flexion-extension exercises with resistance bands, light walking on flat ground, or elliptical training.
• Advanced Phase: Once symptoms substantially improve, gradually add light squats, step-ups, or closed-chain exercises to strengthen the quadriceps and the overall lower limb muscles.
• Progression: Gradually increase resistance (bands or devices), add single-leg support or balance exercises, and ensure continuous progression without provoking significant pain.
3. Surgical Intervention
If conservative treatment fails and symptoms persist, arthroscopic plica excision may be considered, but only upon evaluation by a specialist.
Disclaimer:
This report is based solely on the provided images and history and is for reference only. It cannot replace in-person consultation or professional medical advice. If you experience persistent or worsening pain, or any other discomfort, please seek immediate medical attention or consult a specialist.
Infrapatellar plica (Ligamentum mucosum)
