The differential diagnosis for a patient presenting in an outpatient clinic with hip pain is relatively narrow. It’s been said that when you hear hoofbeats, think horses, not zebras. In other words, those hoofbeats you’re hearing are more likely to be coming from common things (horses) than uncommon things (zebras). That makes good sense and is practical, but just to be safe, we will cover both the “horses” and the “zebras” in this chapter. The horses (common conditions) are hip arthritis, greater trochanteric bursitis, and hip pain that is actually pain radiating down from the lumbar spine. These three hip conditions account for over 90% of the hip pain you are likely to encounter in an outpatient setting. The occasional patient with avascular necrosis (AVN) or a form of femoral-acetabular impingement (FAI), make up the other 10%—these are the zebras.
Let’s start with hip arthritis. As discussed in Chapter 1, in orthopedics, we consider arthritis to be a disease of the articular surfaces of the joint. Figure 3-1 shows a hip joint that has been dislocated to show the head of the femur and acetabular socket better. In a normal hip, both the surface of the femoral head and the surface of the socket are coated with a 2- to 4-mm thick layer of slick, numb articular cartilage. Most patients are familiar with this material because they have seen it on the ends of chicken bones (see the sidebar in Chapter 1, for more details). In arthritis, this material wears thin or, in some instances, is gone completely, exposing the underlying bone. Bone is not slick and slippery; it is rough and abrasive. It isn’t numb like articular cartilage either. It has a rich nerve supply and, as a result, is very sensitive and a poor bearing surface for a weight-bearing joint. Figure 3-2 shows an arthritic femoral head with a large area of worn cartilage and exposed bone.
The ball and socket of a normal hip joint.
A photograph of a femoral head that shows changes typical of arthritis. There is a large area where the articular cartilage has been worn off to expose the rough, abrasive, sensitive bone beneath it.
The most common cause of hip arthritis is osteoarthritis. In osteoarthritis, the articular cartilage simply wears away with time and use. For this reason, most patients with osteoarthritis of the hip are older. A history of “high mileage” is probably the single most important factor in a patient’s history that predicts osteoarthritis. High mileage can mean many decades of normal use or a few decades of heavy use. Patients with hip arthritis usually complain of groin pain and will often remark that ...