The hip joint is a “ball and socket” joint located where the thigh bone (femur) meets the pelvic bone. The upper segment (“head”) of the femur is a round ball that fits inside the cavity in the pelvic bone that forms the socket, also known as the acetabulum. The ball is normally held in the socket by very powerful ligaments that form a complete sleeve around the joint capsule.
Both the ball and socket are covered with a layer of smooth cartilage, each about 1/8 inches thick. The cartilage acts as a sponge to cushion the joint, allowing the bones to slide against each other with very little friction. Additionally, the depth of the acetabulum (socket) is increased by a fibrocartilaginous rim called a labrum that lines the rim of the socket and grips the head of the femur, securing it in the joint. The labrum acts as an “o-ring” or a gasket to ensure the ball fits into the socket.
Anatomy of the hip
Femoroacetabular impingement occurs when the ball (head of the femur) does not have its full range of motion within the socket (acetabulum of the pelvis).
Impingement itself is the premature and improper collision or impact between the head and/or neck of the femur and the acetabulum. This causes a decreased range of hip joint motion, in addition to pain. Most commonly, Femoroacetabular impingement is a result of excess bone that has formed around the head and/or neck of the femur, otherwise known as “cam”-type impingement. Femoroacetabular impingement also commonly occurs due to overgrowth of the acetabular (socket) rim, otherwise known as “pincer”-type impingement, or when the socket is angled in such a way that abnormal impact occurs between the femur and the rim of the acetabulum.
A) Normal Hip B) Cam impingement C) Pincer impingement D) Combination of cam and pincer impingement
Source: Femoroacetabular Impingement Forms - Lavigne, et al.
When the extra bone on the femoral head and/or neck hits the rim of the acetabulum, the cartilage and labrum that line the acetabulum can be damaged.
The extra bone can appear on x-rays as a seemingly very small “bump.” However, when the bump repeatedly rubs against the cartilage and labrum (which serve to cushion the impact between the ball and socket), the cartilage and labrum can fray or tear, resulting in pain. As more cartilage and labrum is lost, the bone of the femur will impact with the bone of the pelvis. This “bone on bone” notion is most commonly known as arthritis.
Tears of the labrum can also fold into the joint space, further restricting motion of the hip and causing additional pain. This is similar to what occurs in the knee of someone with a torn meniscus.
The extra bone that leads to impingement is often the result of normal bone growth and development. Cam-type impingement is when such development leads to the bump of bone on the femoral head and/or neck.
Normal development can also result in the overgrowth of the acetabular rim, or pincer-type impingement. Hip trauma (falling on one’s hip) can also lead to impingement. The tears of the labrum and/or cartilage are often the result of athletic activities that involve repetitive pivoting movements or repetitive hip flexion.
MRI of a normal hip with an intact labrum
MRI of a hip with a torn labrum
Impingement can present at any time between the teenage years and middle age. Many people first realize a pain in the front of their hip (groin) after prolonged sitting or walking. Walking uphill is also found to be difficult.
The pain can be a consistent dull ache or a catching and/or sharp, popping sensation. Pain can also be felt along the side of the thigh and in the buttocks.
Medical imagery in the form of x-ray and magnetic resonance imaging (MRI) are crucial for diagnosing femoroacetabular impingement. X-ray can reveal an excess of bone on the femoral head or neck, and on the acetabular rim. An MRI can reveal fraying or tears of the cartilage and labrum.
Non-surgical treatment should always be considered first when treating femoroacetabular impingement. Femoroacetabular impingement can often be resolved with rest, modifying one’s behavior, and a physical therapy and/or anti-inflammatory regimen. Such conservative treatments have been successful in reducing the pain and swelling in the joint.
If pain persists, it is sometimes necessary to differentiate between pain radiating from the hip joint and pain radiating from the lower back or abdomen. A proven method for differentiating between the two is by injecting the hip with a steroid and analgesic.
The injection accomplishes two things: First, if the pain is indeed coming from the hip joint the injection provides the patient with pain relief. Secondly, the injection serves to confirm the diagnosis. If the pain is a result of femoroacetabular impingement, a hip injection that relieves pain confirms that the pain is from the hip and not from the back.
Arthroscopy of the hip joint was first described in the 1970s and then further refined in the late 1980s and early 1990s. Recent advances in the development of surgical equipment have allowed orthopedic surgeons to treat conditions that were traditionally either ignored or treated with an open procedure. The procedure has been popular in Europe since the early 1990s, but gained popularity in the United States more recently, in the late 1990s and early 2000s.
Because of its lack of popularity in the United States, few orthopedic surgeons have advanced training in hip arthroscopy. However, as the procedure is becoming more accepted and more popular, more and more surgeons are becoming trained in this area of orthopedic surgery.
The hip arthroscopy procedure has been slower to evolve than arthroscopy of other joints (such as the knee and shoulder) because the hip is much deeper in the body and therefore less accessible. Furthermore, because the hip is a “ball and socket”-type joint, it is necessary to employ traction so as to expose the joint enough to fit the surgical instruments inside the joint without causing further damage to the cartilage and labrum.
Hip arthroscopy, or a “hip scope,” is a minimally-invasive procedure. The use of an arthroscope means that the procedure is done using 2-3 small incisions (approximately 1/4-1/2 inch long) rather than a more invasive “open” surgery that would require a much larger incision. These small incisions, or “portals", are used to insert the surgical instruments into the joint.
Aiding other advances in arthroscope technology, the flow of saline through the joint during the procedure provides the surgeon with excellent visualization. The surgeon is also aided by fluoroscopy, a portable x-ray apparatus that is used during the surgery to ensure that the instruments and arthroscope are inserted properly.
A patient being set up for traction
The location of the incisions and instruments for the procedure
The instruments include an arthroscope, which is a long thin camera that allows the surgeon to view the inside of the joint, and a variety of “shavers” that allow the surgeon to cut away (debride) the frayed cartilage or labrum that is causing the pain. The shaver is also used to shave away the bump(s) of bone that are responsible for the cartilage or labral damage.
In addition to removing frayed tissue and loose bodies within the joint, occasionally holes may be drilled into patches of bare bone where the cartilage has been lost. This technique is called "microfracture" and promotes the formation of new cartilage where it has been lost.
The procedure is normally done as an “outpatient” surgery, which means the patient has the surgery in the morning and can go home that same day. Normally, the patient is under regional anesthesia. Under regional anesthesia, the patient is numbed only from the waist down and does not require a breathing tube.
Following the procedure, patients are normally given crutches to use for the first 1-2 weeks to minimize weight-bearing. A post-operative appointment is normally held a week after the surgery to remove sutures. Following this appointment, the patient normally begins a physical therapy regimen that improves strength and flexibility in the hip.
After six weeks of physical therapy, many patients can resume normal activities, but it may take 3-6 months for one to experience no soreness or pain following physical activity. As no two patients are the same, regular post-operative appointments with one’s surgeon is necessary to formulate the best possible recovery plan.
Following a combination of physical and diagnostic exams, patients are deemed suitable for hip arthroscopy on a case-by-case basis. Patients who respond best to hip arthroscopy are active individuals with hip pain, where there exists an opportunity to preserve the amount of cartilage they still have. Patients who have already suffered significant cartilage loss in the joint may be better suited to have a more extensive operation, which may include a hip replacement.
Studies have shown that 85-90% of hip arthroscopy patients return to sports and other physical activities at the level they were at before their onset of hip pain and impingement. The majority of patients clearly get better, but it is not yet clear to what extent the procedure stops the course of arthritis. Patients who have underlying skeletal deformities or degenerative conditions may not experience as much relief from the procedure as would a patient with simple impingement.
As with all surgical procedures, there remains a small likelihood of complications associated with hip arthroscopy. Some of the risks are related to the use of traction. Traction is required to distract and open up the hip joint to allow for the insertion of surgical instruments. This can lead to post-surgery muscle and soft tissue pain, particularly around the hip and thigh. Temporary numbness in the groin and/or thigh can also result from prolonged traction. Additionally, there are certain neurovascular structures around the hip joint that can be injured during surgery, as well as a chance of a poor reaction to the anesthesia.
Hip arthroscopy is indicated when conservative measures fail to relieve symptoms related to femoroacetabular impingement, a condition that has been poorly understood and under-treated in the past. Advances have made hip arthroscopy a safe and effective alternative to open surgery of the hip, a tremendous advantage in treating early hip conditions that ultimately can advance to end-stage arthritis. Hospital for Special Surgery hip surgeons have the special training and high volume of experience to perform hip arthroscopy skillfully and with documented successful outcome.