MKSAP Quiz: aching knee pain and stiffness
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EDITOR’S NOTE: ACP InternistWeekly now features questions from MKSAP 15. See the Answer and Critique for this question for important information about MKSAP 15.
A 37-year-old woman is evaluated for a 2-week history of bilateral anterior knee pain. The pain is described as aching in nature; it worsens when she descends steps or kneels, and requires her get up from her chair at work every few hours to relieve stiffness and discomfort. The patient runs several times a week but has not had any traumatic injury to the knees. She has no other medical problems.
On physical examination, there is no swelling, warmth, redness, or instability of the knees. Pressing the patella against the femur and moving it inferiorly and superiorly reproduces the pain.
Which of the following is the most likely cause of this patient's knee pain?
A. Osteoarthritis
B. Patellofemoral pain syndrome
C. Pes anserine bursitis
D. Prepatellar bursitis
MKSAP Answer and Critique
The correct answer is B) Patellofemoral pain syndrome. This item is available online to MKSAP 15 subscribers in the General Internal Medicine section, Item 132.
This patient's history and physical examination are typical of the patellofemoral pain syndrome (chondromalacia patellae), the most common cause of knee pain in active adults younger than 45 years. The exacerbation of the pain by going down steps and the development of knee stiffness and pain at rest when the knee is flexed for an extended period are clues to the diagnosis. Reproducing the pain by firmly moving the patella along the femur confirms the diagnosis. Patellofemoral pain syndrome is self-limited and responds to rest and NSAIDs.
The patient has no history of worsening pain over the course of the day that is typical for osteoarthritis. Patients with knee osteoarthritis may have crepitus with joint movement and bone tenderness and enlargement. The absence of these signs and symptoms excludes the diagnosis of osteoarthritis in this patient.
Pes anserine bursitis is another common overuse injury characterized by tenderness directly over the pes anserine bursa on the medial aspect of the leg just below the knee. This patient's presentation is consistent with patellofemoral pain syndrome rather than anserine bursitis.
Prepatellar bursitis is nearly always unilateral and often asymptomatic. Typically, there is a history of knee trauma or repetitive or extended kneeling preceding the knee pain. On palpation, there is tenderness over the entire bursal sac and a collection of fluid directly over the patella; these findings are absent in this patient, excluding this diagnosis.
Key Point
- The typical patient with patellofemoral pain syndrome is an active young woman with anterior knee pain worsened by going down steps.