A recent article in the New York Times addressed the significant number of hip injuries reported by yoga practitioners. Yoga is very popular and considered benign by millions of women and men, but this is not the truth. There are very real, underlying anatomical reasons accounting for many of these hip injuries.
Our anatomy is not identical. We do not come off an automotive assembly line, and this is especially true of the hip, a ball and socket joint. The hip's socket is deep but still allows a great deal of motion. The socket is surrounded by a cartilage ring (acetabular labrum) that is easiest to imagine as a picket fence around the socket. The ball is connected to the thigh bone by a slightly narrowed area known as the femoral neck. Some people have extra bone at the junction of the ball and femoral neck. This extra bone formation can impact against the roof of the socket and cause an impingement in the joint. This impingement can chip off fragments of cartilage that lines the joint, and it can tear the cartilage ring around the socket. Known clinically as a CAM femoroacetabular impingement (FAI) and acetabular labral tear, these injuries cause pain in many, but not all, patients, as a 2012 research article reported (Register B, et. al. Am J Sports Med 2012).
The injuries described above occur when the hip's range-of-motion is pushed. Yoga can certainly lead to femoroacetabular impingement and acetabular labral tears. One of the key goals of hatha yoga is to improve flexibility. A patient with a CAM-type FAI will have less ability to reach a commonly accepted level of hip range of motion due to the bony anomaly. The only way to know if a patient has impingement is to have a clinical examination of the hip. If the symptoms and the subtle loss of specific ranges of motion suggest FAI, special X-rays can measure the degree of the bony anomaly. An MRI known as an MR arthrogram can also reveal the bony anomaly, as well as ball-and-socket cartilage damage, and cartilage ring tear(s).
While these pathologies may be the cause of hip pain, again, not everyone with such MRI findings has hip pain. The pain may be caused by other structures in the hip, such as inflammation of the capsule/ligaments, the lining of the capsule (synovium), bursitis or tendinitis. In the end, the clinical exam is most important, and the patient should be treated, not the images. It is important to have a surgical opinion, but you should try a bout of conservative care first.
Those who practice yoga need to realize that our differing anatomies mean every yoga position is not for every person. Injuries may be reduced considerably if both instructors and students are more patient in pushing the body's physical limits. That said, a hip impingement may not necessarily be able to be "stretched out" and further stretching could cause more harm.
Try to be very honest with yourself. If you have hip joint discomfort during a yoga exercise, stop the exercise. The concept of "no pain, no gain" is invalid. This expression was only meant to address the brief, temporary discomfort of a lack of oxygen in a muscle along with a lactic acid peak. Joint pain is a different matter.