Determining the cause of hip pain usually starts with a visit to the family doctor, internist, or orthopedist. In many cases, the physician can make a diagnosis and recommend a course of treatment based on a patient history and a physical exam.
But for some patients, imaging studies may be recommended in order to precisely determine the source of the pain, make a diagnosis, and gain important information about the condition.
“Hip pain can come from a lot of different places,” explains Douglas N. Mintz. MD, formerly a radiologist at Hospital for Special Surgery (HSS), “including the spine, the pelvis, or even the knee.”
Imaging technologies used at HSS to diagnose hip pain include x-ray, MRI (magnetic resonance imaging), CT (computed tomography), and ultrasound. The orthopedist determines which method to use based on the suspected disease or injury, the specific type of information needed and, in some cases, the age or general condition of the patient.
“If we see a ball player who injured their hip or hamstring, we don’t expect to see a bone abnormality, so we are probably going to use an ultrasound first,” says Gregory R. Saboeiro, MD, Chief of Interventional Radiology and CT at HSS. “In an older patient we are likely to begin with x-rays of the hip.”
X-ray, also known as plain films or conventional radiographs, are often the first choice for obtaining images. While bony structures can be viewed clearly on x-ray, in some cases, the orthopedist may also want to see whether injury to surrounding soft tissues are contributing to the patient’s pain. To obtain this information, an MRI may be necessary.
Magnetic Resonance Imaging (MRI) involves a large apparatus containing a high strength magnet which surrounds the platform on which a patient lies during the examination. MRI produces cross-sectional, multiplanar images that allow the orthopedist to evaluate anatomic stuctures– including various types of cartilage, tendons, ligaments, and bones.
Because MRI can be noisy, at HSS every patient is given a pair of earplugs or MRI-compatible headphones and offered a wide range of music to help them relax and protect their ears during the exam. Most MRI exams for hip pain take about 45 minutes.
“MRI can also be important in diagnosing a hip fracture that is not clearly visible on x-ray or CT scan,” says Dr. Saboeiro. “For example, a patient may fracture a hip and, despite some pain, may not be severely disabled by the injury. MRI can reveal edema, or swelling within the bone, information that can help confirm diagnosis of a subtle fracture or injury.”
MRI uses no radiation and most people can undergo the process without any difficulty, according to Dr. Mintz. For the small percentage of patients who may experience claustrophobia, a mild sedative can make them more comfortable. Individuals with cardiac pacemakers and a few metal implants are not candidates for MRI.
Ultrasound images are obtained using high frequency sound waves which are sent and received through a small hand-held device known as a transducer. Images obtained with ultrasound show details of soft tissues around joints, tendons, and muscles.
However, because the ultrasound images don’t offer clear pictures of the cartilage and some of the other structures that MRI can, their use in diagnosis of hip pain is restricted to specific conditions and abnormalities, according to Dr. Saboeiro. These abnormalities are near the surface - on the outside of the joint, making them readily visible to an ultrasound probe that is put on the skin overlying the structure. These conditions include:
Ultrasound can also be used to guide procedures such as injections, allowing the doctor doing the procedure to guide a needle exactly where it should go, whether it is a cyst to aspirate, a tendon sheath to inject, or the hip joint itself.
In some cases, ultrasound is used to guide cortisone or hyaluronic acid injections (viscosupplementation administered with an anesthetic), an effective treatment for some kinds of hip conditions, such as arthritis.
Injections may also be used diagnostically. “If the patient responds to a hip injection, it indicates that the pain arises from the hip.,” explains Dr. Mintz. Conversely, if the patient does not get pain relief from the injection, the problem may be from a tendon or muscle around the hip, or another area entirely, such as the back.
The time needed to complete ultrasound images varies depending on the application of this technology. For diagnostic imaging, patients can expect to spend between 30 and 45 minutes.
On an average day roughly 35 diagnostic ultrasounds are performed - with an additional 15 ultrasound guided injections - for the treatment of hip pain.
CT scans, also known as CAT scans, is an imaging study in which a series of digital images are obtained as the patient moves through a doughnut-shaped machine that houses a thin x-ray beam. This method provides more detailed information than is available on conventional x-ray; however, its usefulness in the diagnosis of hip pain is limited because of the multiple structures that are present in the hip - including different forms of cartilage and tendons - that are difficult to visualize on a CT examination.
CT scans may be used to obtain pre-surgical measurements for a certain hip conditions, including femoroacetabular impingement (a condition in which the ball and socket of the hip joint rub together abnormally, thereby damaging the cartilage that lines the ends of the bones) or osteoid osteoma (a benign tumor).
Patients who will be undergoing CT or MR imaging can expect to meet with a radiologist who will conduct a brief patient history and describe the procedure.
At HSS, all imaging is supervised and interpreted by the nation’s top musculoskeletal Board Certified radiologists, who work closely with the nation’s top experts in orthopedic conditions involving the hip.
According to Dr. Mintz, “One of the strengths of HSS is that a patient can come in for an assessment of their pain and receive the necessary work-up, including all imaging they need at the same facility, by world renowned physicians, often on the same day.”
Summary by Nancy Novick, interview by Mike Elvin