Differential Diagnosis for Left Knee Pain after Fall

Single Most Likely Diagnosis

• Medial collateral ligament (MCL) sprain: This is a common injury after a fall, especially if the knee was twisted or bent during the incident. The MCL is a ligament that connects the femur (thigh bone) to the tibia (shin bone) and provides stability to the inner aspect of the knee.

Other Likely Diagnoses

• Meniscal tear: The meniscus is a cartilage structure in the knee joint that can be damaged during a fall, especially if the knee was twisted. Symptoms may include pain, swelling, and locking or catching of the knee.
• Anterior cruciate ligament (ACL) sprain: The ACL is another ligament that provides stability to the knee joint. It can be injured during a fall, especially if the knee was bent or twisted.
• Osteoarthritis flare-up: If the patient has pre-existing osteoarthritis, a fall can cause a flare-up of symptoms, including pain and swelling.
• Contusion or bruising: A fall can cause direct trauma to the knee, resulting in a contusion or bruising.

Do Not Miss Diagnoses

• Fracture (e.g., tibial plateau, femoral condyle): A fracture can occur after a fall, especially if the patient has osteoporosis or other underlying conditions that weaken the bones. It is essential to consider this diagnosis to avoid missing a potentially serious condition.
• Septic arthritis: If the patient has a compromised immune system or a history of joint injections, septic arthritis (infection of the joint) is a possibility, especially if the patient has a fever, redness, or swelling.
• Vascular injury (e.g., popliteal artery injury): A fall can cause damage to the blood vessels in the knee, leading to a vascular injury. This is a medical emergency that requires prompt attention.

Rare Diagnoses

• Osteonecrosis: This is a rare condition where the bone tissue dies due to a lack of blood supply. It can occur after a fall, especially if the patient has a history of steroid use or other underlying conditions.
• Spontaneous osteochondritis dissecans: This is a rare condition where a piece of cartilage and bone becomes detached from the surrounding bone. It can occur after a fall, especially if the patient has a history of repetitive trauma to the knee.
• Neurogenic pain (e.g., peroneal nerve injury): A fall can cause damage to the nerves in the knee, leading to neurogenic pain. This is a rare but possible diagnosis that should be considered if other causes of pain have been ruled out.