Imaging Findings

Based on the provided knee MRI images, the following key features are observed:

• A cystic signal shadow is visible near the lateral meniscus of the left knee, showing high signal intensity adjacent to the meniscal tissue.
• A suspicious horizontal or near-horizontal abnormal high-signal band in the local fibrous structure of the lateral meniscus, suggesting a meniscal tear.
• Mild swelling of the local soft tissue, with protrusion outside the joint capsule, consistent with a meniscal cyst protrusion on imaging.
• No significant pathological changes in the bone structure, and no obvious signs of cartilage surface damage.

Potential Diagnoses

Considering the patient's age (12 years), symptoms (lateral knee pain and swelling), and MRI findings, the following diagnoses can be considered:

1. Lateral meniscal cyst (with or without tear): Meniscal tears can allow joint fluid or mucoid material to enter the meniscus or joint capsule through the tear site, forming a cystic structure, most commonly in the lateral meniscus. The patient’s symptoms and MRI findings of a cystic lesion and tear signals are consistent with this diagnosis.
2. Other soft tissue cystic lesions (e.g., synovial cyst, Baker’s cyst): These are typically found in the posterior aspect of the knee or other characteristic locations, which does not fully match the lateral meniscus region in this case.
3. Meniscal developmental abnormality with cystic changes: In children and adolescents, it may be necessary to rule out congenital or developmental variations, although their imaging features generally differ from typical meniscal cysts.

Final Diagnosis

Taking into account the patient's clinical presentation (lateral knee pain and swelling), MRI findings (horizontal or near-horizontal tear in the lateral meniscus with cystic changes), and the relative rarity but possibility of such injuries in this age group, the most likely final diagnosis is:

Lateral meniscal cyst with horizontal tear (with mucoid degeneration).

Should further confirmation be necessary, an arthroscopic examination could be considered to directly visualize the meniscal tear and rule out other soft tissue lesions.

Treatment Plan and Rehabilitation Program

The following are recommendations for treatment and rehabilitation:

• Conservative Treatment:

  If symptoms are mild or intermittent, short-term conservative management can be adopted, including reduction of intense activity, use of a knee brace, local physical therapy, and appropriate anti-inflammatory and pain relief medication (e.g., NSAIDs). However, given the significant pain and lateral knee swelling, close monitoring of symptoms is needed.

• Surgical Treatment:

  In cases of persistent pain, restricted activity, or a significantly sized cyst impacting joint function, arthroscopic meniscal repair or partial meniscectomy is recommended. During surgery, the cyst can also be addressed to prevent recurrence.

• Rehabilitation and Exercise Prescription:

  Rehabilitation should follow the FITT-VP principles (Frequency, Intensity, Time, Type, Progression) and be tailored to the patient’s individual condition in a stepwise fashion:

  1. Preoperative/Conservative Treatment Phase:
     • Frequency: 3–4 times per week with low-intensity lower limb and core muscle training.
     • Intensity: Emphasize isometric exercises and half squats with light to moderate loads, avoiding significant knee twisting or impact.
     • Time: 20–30 minutes per session.
     • Type: Stability training (core exercises, static squats) and leg-focused muscle strengthening with minimal resistance.
  2. Postoperative/Mid Rehabilitation Phase:
     • Starting approximately 1–2 weeks after arthroscopy, gradually restore range of motion with passive and active exercises.
     • Frequency: 3–5 times per week.
     • Intensity: Gradually increase range of motion and incorporate more demanding stability exercises; progress from light to moderate resistance.
     • Time: 30–45 minutes per session.
     • Type: Under supportive protection, perform straight-leg raises, seated knee flexion/extension, and other light-to-moderate exercises.
  3. Later Exercise Progression:
     • Gradually return to running, jumping, and higher-level activities once the meniscus has adequately healed.
     • Frequency: 3–4 times per week, focusing on balancing strength and flexibility.
     • Intensity: From moderate to moderately high, adjusting according to the absence of significant knee pain or swelling.
     • Time: 45–60 minutes per session, combining aerobic exercises with strength training.

  Special reminder: As meniscal injuries can worsen with twisting, over-extension, and high-load activities, training techniques must be carefully monitored. Avoid sudden, high-intensity lower limb movements to prevent re-injury.

Disclaimer

This report is a reference analysis based on current medical imaging and medical history data. It is not a substitute for an in-person consultation or professional medical advice. Specific treatment plans should be determined based on the patient’s actual clinical condition under the guidance of a specialist.