1. Imaging Findings

Based on the provided MRI sequences of the knee joint, an enlarged and protruding fat pad can be observed in the area anterior to the suprapatellar bursa (above the femoral condyle of the right knee) and posterior to the quadriceps tendon. On T1WI, its signal is focally or diffusely irregular compared to the surrounding subcutaneous fat, and on T2WI, it appears as high signal intensity (indicating edema). On the sagittal view, the anterior-posterior diameter of the fat pad measures approximately 12.2 mm, exceeding the upper normal limit reported in the literature (6±2 mm), along with posterior protrusion into the suprapatellar bursa, and mild joint effusion is noted locally. No obvious extensive destruction or tear signs are seen on the articular surface and cartilage, but the edges of the adipose tissue in the affected region are thickened with edema signals, consistent with inflammatory or impingement changes caused by mechanical or repeated minor trauma.

2. Possible Diagnoses

1. Suprapatellar Fat Pad Impingement Syndrome (SPIS)
   Based on typical imaging features such as thickening of the fat pad, edema signals, and posterior protrusion into the joint capsule—especially in correlation with anterior knee pain—SPIS is highly likely.
2. Patellofemoral Pain Syndrome
   Common in younger individuals, potentially associated with patellar cartilage degeneration or abnormal patellar tracking. On MRI, it often shows cartilage signal changes or patellofemoral malalignment, or cartilage lesions.
3. Patellar Tendon–Lateral Femoral Condyle Impingement Syndrome
   Mainly occurs at the site of abnormal friction between the patellar tendon and the lateral femoral condyle. Imaging may reveal obvious edema or fibrosis in the superolateral portion of the Hoffa fat pad. Since the main changes here involve the suprapatellar fat pad, this diagnosis is less likely.
4. Quadriceps Tendinitis/Tendinopathy
   There would be structural abnormalities and increased signal in the quadriceps tendon itself. In this case, the primary abnormality is in the fat pad, without clear signs of tendon damage, so this is not the primary consideration.

3. Final Diagnosis

Taking into account the patient’s age (24 years, female), history of anterior knee pain (recurrent for 6 months), accompanied by clicking/popping during movement and limited range of motion, and the MRI findings of an enlarged suprapatellar fat pad with edema and protrusion into the suprapatellar bursa, the most likely diagnosis is:

Suprapatellar Fat Pad Impingement Syndrome (SPIS).

If further confirmation is required, ultrasound examination or observation of symptom relief following diagnostic interventions (such as ultrasound-guided local injections) may be considered.

4. Treatment Plan and Rehabilitation

4.1 Treatment Strategies

• Conservative Treatment:
  • Avoid activities that increase anterior knee load, such as deep squats and vigorous running or jumping. Pay special attention to correcting any biomechanical issues arising from leg length discrepancy (right leg being shorter).
  • Physical therapy (heat therapy, ultrasound, shock wave, etc.) can help reduce local edema and inflammation.
  • NSAIDs can be used short-term during acute exacerbations to alleviate pain and local inflammation.
• Local Injection:
  Under ultrasound guidance, a small dose of corticosteroids can be injected into the thickened fat pad to reduce edema and inflammation. Some patients achieve significant pain relief through this approach.
• Surgical Indications:
  If long-term conservative treatment is ineffective, and symptoms significantly affect daily activities, arthroscopic partial resection or release of the thickened fat pad may be considered. However, this should be carefully evaluated, and conservative measures should be attempted first.

4.2 Rehabilitation Training and Exercise Prescription (Following the FITT-VP Principle)

Once pain subsides and acute inflammatory responses are under control, start targeted, gradual rehabilitation exercises:

1. Type of Exercise:
   • Joint mobility training: Knee flexion-extension exercises in a seated or supine position, avoiding ranges where pain is severe.
   • Low-impact aerobic activities: Such as brisk walking on level ground, cycling, or elliptical training to reduce anterior knee stress.
   • Core and lower-limb stability work: Bridge exercises, gluteal strengthening (e.g., banded hip abduction), and isometric quadriceps contractions.
2. Frequency of Exercise:
   • 3–5 times per week, adjusted according to pain threshold and recovery status.
3. Intensity of Exercise:
   • Begin with a lower intensity (e.g., RPE 2–3) that is tolerable with minimal pain, and gradually increase.
4. Duration of Exercise (Time):
   • Each session can last 20–30 minutes, and may be broken into segments. Rest and use ice to reduce edema and pain as needed.
5. Progression of Exercise (Progression):
   • As pain decreases and range of motion improves, gradually increase weight-bearing and resistance (e.g., incrementally add dumbbells or use heavier resistance bands).
   • Correct lower-limb alignment, and consider using a heel lift or custom orthotic if the 1.5 cm discrepancy in right leg length impacts gait and load distribution.
6. Volume of Exercise (Volume):
   • Evaluate progress in stages based on individual response. If pain or swelling significantly worsens after exercise, reduce the volume or pause training.

Monitor joint load during training. If swelling recurs or pain intensifies significantly, seek medical attention or adjust the training plan promptly.

Disclaimer: The above report and suggestions serve as medical reference information only and cannot replace an in-person consultation or professional medical advice for diagnosis and treatment. Patients should consider their own situation and communicate fully with their primary physician to develop or adjust treatment and rehabilitation plans.