A painful and stiff knee with locking.
The plain radiograph appeared to be within normal limits.
MR imaging demonstrated a displaced horizontal tear of the left lateral meniscus, with a truncated anterior horn (figs 1 and 2). The lateral meniscal root remained intact, but the displaced fragment had migrated through the popliteal hiatus and could be seen posterior to the popliteal tendon (fig 3).
Background: Traumatic tears of the menisci within the knee are the most common soft tissue injury of the knee [1]. Unlike degenerative meniscal tears, where there is controversy over the need for surgical management [2], traumatic tears are still regarded as being best treated surgically. There are a variety of approaches ranging from suturing the tear itself to partial meniscectomy; however, the arthroscopic technique is not a comprehensive review of all joint compartments [3] but centres on removing any loose bodies and attempting to restore a smooth articular surface.
Imaging perspectives: As can be seen from this case, aberrant fragments do not always lie within the larger joint compartments, and the surgeons will find it particularly valuable to be directed toward unusual positions. It therefore relies upon the radiologist to perform a thorough search for the missing portion of the meniscus, and a sound knowledge of knee joint anatomy will aid us in constructing a comprehensive search pattern. The lateral meniscus is attached to the tibia by the meniscofemoral ligaments, but two fascicles of the meniscus separate to create an approximately 1cm gap through which the popliteal tendon passes [4]. This gap is the popliteal hiatus and represents a normal anatomic weakness in the posterior knee capsule. It is usually of little clinical relevance, and is not included in a normal arthroscopy [3] so can easily be overlooked.
Teaching point: it is essential that radiologists are comfortable identifying and describing detailed anatomy of the knee to aid the surgeons when treating displaced cartilage fragments.
Horizontal left lateral meniscal tear, with displacement through popliteal hiatus.
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
The patient in this case is a 40-year-old male complaining of knee pain, stiffness, and locking symptoms.
From the provided MRI images (coronal and sagittal sequences), the following can be observed:
1. A high-signal tear in the lateral meniscus, with disrupted signal in the posterior horn, suggesting a meniscal tear.
2. Abnormal small pieces of soft tissue or meniscal fragments can be seen within the joint cavity, with certain fragments located around the popliteus tendon in the posterolateral area of the knee (near the popliteus tendon hiatus), indicating possible free or displaced meniscal fragments.
3. No clear large defect is noted on the articular cartilage surface, but attention should be paid to localized irregularities or mild wear of the cartilage.
4. No obvious bone contusion signals or signs of significant ligament rupture are observed; most ligament structures remain generally intact.
5. No significant edema or muscle tear is noted in the surrounding soft tissues.
Combining the patient’s age, symptoms (locking, pain, restricted mobility), clinical examination, and MRI findings, the most likely diagnosis is a traumatic tear of the lateral meniscus with fragments displaced near the popliteus tendon hiatus.
Further verification of fragment size, location, and reparability may be conducted via arthroscopic exploration or direct observation during surgery.
Treatment Guidelines:
1. Surgical Treatment: For traumatic meniscal tears with significant locking and impaired activity, arthroscopic surgery is a primary option, including meniscal repair or partial meniscectomy. If the fragment is large or repairable, meniscal suturing is preferred to preserve meniscal function as much as possible.
2. Conservative Treatment: If symptoms are mild and the tear does not cause severe mechanical locking, conservative management can be attempted first (e.g., using a knee brace, reducing weight-bearing activities, acupuncture, and physiotherapy), with close monitoring of any changes.
Rehabilitation/Exercise Prescription:
To help the patient regain function promptly post-treatment, follow the FITT-VP principle (Frequency, Intensity, Time, Type, Volume, Progression):
1. Early Postoperative Period (1–2 weeks):
• Frequency: 2–3 times/day
• Intensity: Primarily passive range-of-motion activities and leg lifts without causing increased pain or swelling
• Time: Each session 5–10 minutes, can be gradually increased based on tolerance
• Type: Straight leg raises, ankle pump exercises, icing for reducing swelling, etc.
• Progression: As pain is brought under control, gradually increase weight-bearing activities and range of motion
2. Intermediate Postoperative Period (2–6 weeks):
• Frequency: 3–5 times/week (guided functional training)
• Intensity: Maintain low-to-moderate intensity functional activities and begin muscle strengthening (e.g., using elastic bands or light resistance)
• Time: 20–30 minutes per session, paying close attention to knee response
• Type: Seated or supine knee flexion and extension, light squats, etc.
• Progression: Gradually increase the range of motion and resistance according to swelling and pain status
3. Late Postoperative Period (6 weeks and beyond):
• Frequency: 3–4 times/week
• Intensity: Gradually return to moderate- or high-intensity exercise, such as jogging or cycling
• Time: At least 30 minutes each session, adjusted according to individual tolerance
• Type: Stability training (e.g., balance board), progressive strength training (squats, lunges), etc.
• Progression: Increase exercise difficulty gradually, ensuring stable knee function and minimal pain
Throughout rehabilitation, knee swelling, pain, and range of motion should be continuously monitored. If any unusual pain or functional regression occurs, a medical professional should be consulted promptly to adjust the rehabilitation plan or treatment.
Disclaimer: This analysis report is for reference only and cannot replace a physician’s in-person diagnosis and treatment. If you have any questions or experience changes in your condition, please consult a professional orthopedic or sports medicine doctor promptly.
Horizontal left lateral meniscal tear, with displacement through popliteal hiatus.
