Differential Diagnosis for Hyperextended Knee
- Single most likely diagnosis
- Anterior Cruciate Ligament (ACL) tear: The mechanism of injury (hyperextension) and symptoms (sharp pain, loss of knee motion, inability to fully straighten the knee) are consistent with an ACL tear, which is a common injury in activities that involve sudden stops, changes in direction, or direct blows to the knee.
- Other Likely diagnoses
- Meniscal tear: The menisci are cartilage structures in the knee that can be damaged with twisting or hyperextension injuries, leading to pain, swelling, and mechanical symptoms such as locking or catching.
- Posterior Cruciate Ligament (PCL) tear: Although less common than ACL tears, PCL injuries can occur with hyperextension, especially if there's a direct blow to the front of the tibia.
- Knee dislocation: While less likely, a knee dislocation could result from a severe hyperextension injury, leading to significant instability and potentially severe complications if not promptly addressed.
- Do Not Miss diagnoses
- Vascular injury (e.g., popliteal artery injury): A severe knee injury could potentially damage the blood vessels behind the knee, leading to ischemia or even limb loss if not promptly diagnosed and treated.
- Peroneal nerve injury: The peroneal nerve wraps around the lateral aspect of the knee and can be injured in severe knee trauma, leading to foot drop or other neurological deficits.
- Fracture (e.g., tibial plateau, patella): While the primary complaint is soft tissue in nature, it's crucial to rule out fractures, especially in the setting of significant trauma or if there's point tenderness over bony structures.
- Rare diagnoses
- Osteochondritis dissecans: A condition where a piece of cartilage and bone in the knee joint becomes damaged, leading to pain and mechanical symptoms. It's less likely in the acute setting of a hyperextension injury but could be considered in the differential if other diagnoses are ruled out.
- Spontaneous osteonecrosis of the knee (SONK): A rare condition characterized by the sudden onset of knee pain due to a loss of blood supply to the bone, typically affecting the weight-bearing portion of the knee.