Knee Pain

A 17-year-old female patient presents to your office complaining of left knee pain for one month. She states that the pain is localized to the front of her knee, is intermittent, and occurs with using stairs, prolonged sitting with the knee bent, and running while playing soccer. She does not recall a traumatic incident. She lives in a duplex apartment with her family, with eight stairs into the building and the entrance to her apartment. She plays soccer, and the team practices four times a week for 2 hours, with games on the weekends.

Examination:

• Past Medical History: unremarkable
• Medication: Advil
• Observation: Subtalar joint pronation in weight-bearing; Genu recurvatum
• Active Range of Motion: Within normal limits, pain at end-range flexion
• Passive Range of Motion: Same as for active
• Manual Muscle Testing: Within normal limits, except left quadriceps 4-/5, hip abductors 3+/5, and hip external rotators ⅘
• Special Tests: Positive left step-down test (pain and loss of eccentric control); positive left Clarke’s sign; positive left patellar grind test
• Other: Decreased left stance time

Address the following questions:

• Based on the subjective information only, what are the three most likely diagnoses? Give your rationales for your differentials.
• How can you confirm your differentials? 
• What are the causative agents?
• How would you treat this patient? Include diagnostics, medication, and dosing.