A 35-year-old man comes to the office for evaluation of left knee pain that is worse when kneeling and when walking up or down stairs. Medical history is significant for type 1 diabetes mellitus and vitamin D deficiency. In high school, the patient had reconstruction of the left anterior cruciate ligament. He works as a software engineer and rarely exercises. He drinks 1 or 2 beers a night but does not use tobacco or illicit drugs. Temperature is 36.7 C (98 F), blood pressure is 120/70 mm Hg, pulse is 76/min, and respirations are 14/min. BMI is 24 kg/m². On examination, the left knee has full range of motion. There is mild tenderness at the medial joint line, and the Lachman test is negative. There is no clicking, locking, or swelling. Laboratory studies show a low serum vitamin D level and a hemoglobin A1c of 8%. Which of the following is the most significant contributor to this patient's knee pain?

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11ec25c8_d2ec_96ae_bc81_97001147380d_MD0003_00 This patient most likely has osteoarthritis (OA) of the knee, presenting with monarticular arthritis that is worse with joint loading during kneeling and negotiating stairs. OA is very common in patients with prior joint injury or surgery (secondary OA); contributing factors include altered joint mechanics and both acute and chronic inflammation, which lead to altered expression of matrix metalloproteinases and accelerated chondrocyte death. OA develops within 10 years in most patients with anterior cruciate ligament injury, and the risk is increased whether or not the tear is surgically corrected. Other causes of secondary OA include joint infection, inflammatory disorders (eg, rheumatoid arthritis), congenital or acquired bony deformities, and neuromuscular weakness. (Choice A) Alcohol use can contribute to the degradation of articular cartilage. Heavy alcohol intake (>3 drinks/day) is associated with a significant increase in the risk for OA of the knee; however, moderate intake, as in this patient, has only a minor effect on risk. (Choice B) Physical inactivity is associated with an increased risk for primary OA, likely due to abnormal joint loading from muscular weakness or associated obesity. However, in the absence of trauma or other secondary causes of OA, the risk of primary OA is low before age 40. (Choice C) Chronic hyperglycemia can accelerate the progression of OA, likely due to the glycosylation of components of articular cartilage. However, this patient's hemoglobin A1c is only slightly elevated and likely has little effect on his OA risk. (Choice E) Vitamin D deficiency can lead to osteomalacia manifesting with bone pain, muscle weakness, disordered gait, and increased risk of fracture; subclinical deficiency is associated with osteoporosis. It does not cause monarthritis of the knee. Educational objective: Osteoarthritis is common in patients with prior joint injury (especially anterior cruciate ligament injury) or surgery. Other secondary causes of osteoarthritis include infection, inflammatory disorders, bony deformities, and neuromuscular weakness. References: Treatment for acute anterior cruciate ligament tear: five year outcome of randomised trial. (http://www.ncbi.nlm.nih.gov/pubmed/23349407)

A 35-Year-Old Man Comes to the Office for Evaluation of Left