Medial Meniscus Tear: This is the most likely diagnosis given the location of the pain (along the medial joint line) and the history of trauma. Meniscus tears are common injuries that can occur from a sudden twisting motion or direct blow to the knee, and they often present with pain along the joint line.

Medial Collateral Ligament (MCL) Sprain: An MCL sprain can also cause medial knee pain, especially if the trauma involved a valgus stress (a force that bends the knee inward). The pain might be more diffuse than with a meniscus tear but can still be prominent along the medial joint line.
Osteochondritis Dissecans: This condition involves a piece of cartilage and bone becoming detached from the surrounding bone, often due to trauma. It can cause pain along the joint line and might not always have abnormal findings on a physical exam, especially in early stages.

Septic Arthritis: Although less likely, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. It can present with joint line pain and might not always have significant findings on physical exam early in the course, especially if the patient is able to ambulate without significant distress.
Osteonecrosis (Avascular Necrosis): This condition involves the death of bone tissue due to a lack of blood supply and can be precipitated by trauma. It might not have significant findings on a normal physical exam but is crucial to diagnose early to prevent further bone collapse.

Pellegrini-Stieda Syndrome: This is a rare condition characterized by ossification of the MCL, often following a traumatic injury. It can cause chronic medial knee pain and might not have specific findings on a routine physical exam.
Meniscal Cyst: A meniscal cyst is a rare condition where a fluid-filled cyst forms adjacent to a meniscus tear. It can cause localized pain and swelling but might not always be palpable or visible on a standard physical exam.