A 30-year-old female presents with a painful, swollen knee after falling onto it while rollerblading. She is unable to fully extend the knee. On examination, there is tenderness along the anterior aspect of the knee, and there's a positive Lachman's test. What is the likely diagnosis and the appropriate next steps?
This patient's presentation suggests a potential anterior cruciate ligament (ACL) sprain or tear, which is common after a direct blow or sudden deceleration and change in direction. The positive Lachman's test, which assesses the integrity of the ACL, further supports this diagnosis. An immediate plan of action should involve RICE therapy, use of a knee brace for support, and referral for imaging studies, typically an MRI, which is most sensitive for diagnosing ACL tears. Depending on the severity of the tear, the patient may need physical therapy or surgical intervention.