Differential Diagnosis for Right Lateral Inferior Pain to Knee
The patient presents with right lateral inferior pain to the knee, faint swelling, ecchymosis, sensitivity to touch, and no movement restriction but full range of motion (ROM). Based on these symptoms, the following differential diagnoses are considered:
Single Most Likely Diagnosis
- Contusion or Bruise: This is the most likely diagnosis given the presence of ecchymosis (bruising) and sensitivity to touch without significant limitation in movement or ROM. The mechanism of injury could be a direct blow to the area, leading to soft tissue damage.
Other Likely Diagnoses
- Lateral Meniscus Tear: Although the patient has full ROM, a lateral meniscus tear could cause pain and swelling, especially if the tear is small or not significantly impacting knee mechanics. The pain's location and the presence of faint swelling support this possibility.
- Iliotibial (IT) Band Syndrome: This condition, common in runners or cyclists, causes pain on the lateral aspect of the knee due to friction between the IT band and the lateral femoral condyle. However, it typically presents with activity-related pain and might not fully explain the ecchymosis.
- Lateral Collateral Ligament (LCL) Sprain: An LCL sprain could result from a varus stress (inward bending force) on the knee, leading to pain, swelling, and potentially ecchymosis on the lateral side. The absence of significant instability might suggest a mild sprain.
Do Not Miss Diagnoses
- Fracture (e.g., Tibial Plateau or Lateral Condyle): Although less likely given the full ROM and absence of significant swelling or deformity, a fracture must be considered, especially if there was a high-impact mechanism of injury. Missing a fracture could lead to improper healing and long-term disability.
- Septic Arthritis: This is an infection within the joint space, which can present with pain, swelling, and decreased range of motion. While the patient has full ROM, the presence of pain, swelling, and sensitivity to touch warrants consideration of this potentially serious condition, especially if there's a history of recent infection or immune compromise.
- Deep Vein Thrombosis (DVT): Although DVT typically presents with swelling, warmth, and discoloration of the entire leg, it's a critical condition to consider due to the risk of pulmonary embolism. The lateral location of symptoms might be less typical but should not rule out this diagnosis entirely.
Rare Diagnoses
- Osteonecrosis of the Lateral Femoral Condyle: A rare condition where the bone tissue dies due to lack of blood supply. It could present with knee pain but is less likely without specific risk factors (e.g., long-term steroid use, excessive alcohol consumption).
- Ganglion Cyst: A lump or mass that can occur on the lateral side of the knee, potentially causing pain and swelling. However, it would typically be more localized and might not fully explain the ecchymosis and sensitivity to touch.
- Neoplastic Processes: Tumors, either benign or malignant, could cause localized pain, swelling, and potentially ecchymosis if they erode into nearby structures. These are rare and would typically have a more gradual onset.