Anatomy of the Hip Joint
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 and Hip Mobility
What is femoroacetabular impingement?
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.
What happens inside a hip joint that has impingement?
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.
How does femoroacetabular impingement occur?
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
What are the common symptoms associated with impingement?
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.
How is impingement diagnosed?
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.
Hip Arthroscopy in Treating Femoroacetabular Impingement
What happens during a hip arthroscopy?
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.
What is the recovery time associated with hip arthroscopy?
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.
Who will benefit from hip arthroscopy and what are the possible complications?
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.
