INTRODUCTION AND EPIDEMIOLOGY
Every practicing emergency physician over their career will see hundreds of patients with complaints of hip or knee pain that are unrelated to major trauma or an acute fracture. Discomfort and limitations to normal use in these areas are typically related to the minor trauma that occurs on a repetitive basis from performing routine daily functions or exercising. Athletes of all varieties are especially prone to these maladies, where strenuous activity transmits forces that are equivalent to three to five times the body weight directly to these joints. Conversely, the problem of obesity similarly contributes to joint and supporting structural stress and pain.
However, be alert to the various catastrophic processes that can mimic more mundane etiologies, including ruptured abdominal aortic aneurysm, epidural abscess, and septic joint (among others). Pay close attention to historical points, specific risk factors, abnormal vital signs, and physical findings to avoid making a life- or limb-threatening misdiagnosis.
PATHOPHYSIOLOGY AND ANATOMY
The hip is a ball-and-socket joint (enarthrosis), allowing motion in all directions. The hip is similar to the shoulder in this capacity but is much more stable and relatively resistant to dislocation. The bones of the joint (femoral head, pelvic acetabulum) are strongly reinforced with a fibrocartilaginous labrum, a joint capsule, overlying ligaments, and numerous muscles.
The knee is the largest synovial joint in the body and is relatively complicated in structure, comprising two distinct articulating groups: the tibiofemoral and patellofemoral joints. The patella floats above the main joint, attaching to the femur superiorly by the quadriceps tendon and inserting into the tibia inferiorly by the patellar ligament. The knee is stabilized internally by the anterior and posterior cruciate ligaments, and externally by the medial and lateral collateral ligaments. In addition, distal to the main joint, the fibular head attaches by ligaments to the proximal lateral tibia. The medial and lateral menisci are interposed between, and protect, the femoral and tibial condyles. Numerous muscles, tendons, bursa, and additional ligaments add to the complexity of the joint and serve as potential sources for pain and dysfunction (Figures 281-1 and 281-2).
Anterior view of the knee. [Reproduced with permission from Simon RR, Sherman SC, Koenigsknecht SJ: Emergency Orthopedics: The Extremities, 5th ed. © 2007, McGraw-Hill, Inc., New York.]
Medial view of the knee. [Reproduced with permission from Simon RR, Sherman SC, Koenigsknecht SJ: Emergency Orthopedics: The Extremities, 5th ed. © 2007, McGraw-Hill, Inc., New York.]
NERVES OF THE UPPER LEG AND REFERRED PAIN
The femoral and sciatic nerves are the major nerves within the thigh (Figure 281-3). The femoral nerve is the largest branch of the lumbar plexus, and ...