Patient presents with complaints of medial knee pain following a valgus stress injury to the left knee.  Onset of pain occurred while playing basketball three days ago.  The patient describes the pain as sharp and localized over the medial aspect of the left knee, exacerbated by weight-bearing and valgus stress.  He denies any popping or locking sensation.  Physical examination reveals tenderness to palpation along the medial joint line, with mild swelling and ecchymosis present.  Valgus stress testing at 0 and 30 degrees of flexion elicits pain and laxity compared to the contralateral knee, consistent with a medial collateral ligament sprain.  McMurray's test is negative for meniscal tear.  Lachman's test and anterior drawer test are negative, indicating no anterior cruciate ligament instability.  Posterior drawer test is negative.  Range of motion is limited due to pain, with flexion to 110 degrees and extension to 0 degrees.  Diagnosis of medial collateral ligament sprain, left knee, is made.  Treatment plan includes RICE protocol (rest, ice, compression, elevation), NSAIDs for pain management, and referral to physical therapy for rehabilitation.  Patient education provided regarding activity modification and bracing.  Follow-up scheduled in two weeks to assess progress and adjust treatment plan as needed.  Differential diagnoses considered include medial meniscus tear and pes anserine bursitis.  ICD-10 code S83.411A assigned for sprain of medial collateral ligament of left knee, initial encounter.