Patellofemoral Pain Syndrome: This condition is characterized by pain in the front of the knee, usually around the patella, and is often exacerbated by activities such as going down stairs. The feeling of the knee giving out is common due to pain and instability, rather than true mechanical instability.

Meniscal Tear: A tear in the meniscus, which is the cartilage that cushions the knee joint, can cause pain and a feeling of instability, especially when going down stairs. The lack of specific point tenderness does not rule out this diagnosis, as meniscal tears can be difficult to localize.
Ligamentous Sprain: A sprain of the ligaments around the knee, such as the medial or lateral collateral ligament, can cause pain and a feeling of instability. The mechanism of injury might not always be clear, and the absence of point tenderness does not exclude this diagnosis.
Osteoarthritis: Early stages of osteoarthritis can cause knee pain, especially with weight-bearing activities like going down stairs. The pain might be diffuse, and there might not be specific point tenderness.

Septic Arthritis: Although less likely, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. It can present with diffuse knee pain, swelling, and warmth, without specific point tenderness. Fever and systemic symptoms might be absent in the early stages.
Osteonecrosis: Osteonecrosis of the knee, also known as avascular necrosis, can cause knee pain and might not have specific point tenderness. It is crucial to diagnose early to prevent further damage to the joint.
Tumor: A bone or soft tissue tumor around the knee can cause pain and might not have specific point tenderness. Although rare, missing a diagnosis of a tumor could have significant consequences.

Complex Regional Pain Syndrome (CRPS): This is a rare condition characterized by chronic pain, inflammation, and hypersensitivity after an injury or trauma. It can cause diffuse pain in the knee without specific point tenderness.
Plica Syndrome: This condition involves inflammation of the synovial folds within the knee joint, which can cause knee pain, especially with activities like climbing stairs. It is less common and might not have specific point tenderness.
Bursitis: Inflammation of one of the bursae around the knee can cause pain and might not have specific point tenderness, although swelling and warmth over the affected bursa might be present.