Anterior Cruciate Ligament (ACL) Tear: This is one of the most common injuries in young, active individuals, especially those involved in sports that require sudden stops, changes in direction, or direct contact. The mechanism of injury often involves a non-contact twisting injury or a direct blow to the knee.

Meniscal Tear: The menisci are cartilage structures in the knee joint that can be damaged by a traumatic injury, leading to pain, swelling, and mechanical symptoms like locking or catching. The presentation can be similar to an ACL tear, with pain and instability.
Medial Collateral Ligament (MCL) Tear: This injury typically occurs from a valgus stress (a force from the outside of the knee) and can present with pain on the medial aspect of the knee and instability.
Ligament Sprains (including Posterior Cruciate Ligament (PCL) and Lateral Collateral Ligament (LCL)): While less common than ACL or MCL injuries, PCL and LCL sprains can occur from specific mechanisms like a direct blow to the front of the knee (PCL) or a varus stress (LCL).

Knee Dislocation: Although rare, a knee dislocation is a medical emergency that requires immediate reduction to prevent vascular and neurological complications. The presentation can include severe pain, deformity, and potentially diminished pulses in the affected limb.
Fracture (e.g., Tibial Plateau, Patella, or Femur): Fractures around the knee can be subtle on initial presentation but are critical to diagnose to prevent long-term complications. A high index of suspicion is necessary, especially with significant trauma or inability to bear weight.
Vascular Injury: Direct trauma to the popliteal artery or vein can lead to significant morbidity if not promptly addressed. Symptoms may include coldness, pallor, paresthesia, pain, paralysis, and pulselessness (the "6 Ps").

Osteochondritis Dissecans: A condition where a piece of cartilage and bone in the knee joint becomes damaged, leading to pain and swelling. It's more common in younger patients but can be seen in adults, especially after trauma.
Peroneal Nerve Injury: Direct trauma to the lateral aspect of the knee can injure the peroneal nerve, leading to foot drop or other neurological deficits.
Septic Arthritis: Although rare in the context of an acute traumatic injury, if the joint is penetrated or if there's a delay in seeking medical attention, bacterial infection of the joint (septic arthritis) can occur, presenting with severe pain, swelling, and systemic signs of infection.