The Hip: The Missing Link for Back and Knee Pain?

By Troy L. Grubb, P.T., O.C.S., A.T.C.

There is an old saying that one often can't see the forest for the trees. When it comes to addressing problems related to the joints in our bodies, it is easy to focus on the problem site only and not consider the influence that neighboring anatomical structures have upon the problem. This is often the case when dealing with complaints of knee pain or back pain; we overlook other areas of the body that are possibly contributing to the problem. One area in particular that is often overlooked is the influence that the hip joint and related anatomy have upon knee and low back pain.

The hip joint is one of the most anatomically stable and mobile joints in the body. It is capable of six degrees of motion, as it is considered a "ball-and-socket" joint. It has many powerful muscular and dense connective tissue attachments connecting the femur (thigh bone) to the pelvis enabling this movement and stability. It essentially serves as a biomechanical link between the lower extremity and the trunk, influencing motion above and below. Hence, any problems with the hip and related structures can contribute to orthopedic problems in the knee and low back.

HIP MUSCLES

Given the significant amount of motion capable in the hip joint, there are several important muscles - hip flexors, hip abductors, hip extensors and hip adductors - that help control the joint. The hip flexors are specifically the psoas ( sew-az ) and the iliacus and are collectively known as one unit, the iliopsoas, as they share a common attachment to the femur. They serve to flex the hip (and leg) forward as when raising the knee to climb a step. The hip abductors are the muscles that lie along the side of the hip and pelvis and are comprised of the gluteus medius, gluteus minimus and tensor fascia latae. They serve to move the hip and leg away from the body to the side. The hip extensors are primarily the gluteus maximus muscles, and, to a lesser extent, the hamstrings. The gluteus maximus is a very powerful extensor of the hip and functions to straighten the hip and leg from a bent position as when standing up from a sitting position. The hip adductors generally are the muscles of the groin and inner thigh that serve to pull the hip and leg inward as when crossing the legs. Finally, there are several small, deep muscles that help to internally and externally rotate the hip joint.

Although the muscles and their respective functions as described above generally relate to moving the free leg - technically known as open chain movement - many issues related to the influence of the hip joint on knee and low back pain involve the fixed leg, known as closed chain movement. Examples of this type of movement are ascending and descending stairs, squatting, cycling and walking/running (open and closed chain). These types of motion are present throughout locomotion of the body when encountering knee pain or low back pain.

KNEE PAIN

Regarding knee pain, the hip joint can influence the position of the knee as it guides the leg through motion involving bending and straightening the knee. Although the knee joint is generally considered a hinge joint, it operates in three dimensions due to its anatomy and the positions the joint achieves when operating as part of the movement of the entire leg as influenced by the hip. For example, when descending stairs, the knee bends like a hinge, but also bends and turns slightly inward toward the other knee. The angle formed between the femur and tibia that comprise the knee joint is known as the "Q-angle" and is generally about 15 degrees. The maintenance of the angle is often due to the musculature of the hip, contracting to maintain the appropriate alignment of the knee when bending. When the musculature of the hip is weak, especially in the extensors and the abductors, maintenance of the alignment of the knee can be compromised leading to an increase in the Q-angle of the joint and excessive internal rotation of the limb. This causes increased lateral (to the outside) pull of the patella, resulting in aberrant tracking. The result is poor distribution of forces under the patella and excessive localized contact pressure leading to premature excessive degradation and inflammation of the cartilage under the patella.

BACK PAIN

Regarding back pain, the hip can play a causative role. For example, when walking, the hip musculature serves to stabilize the pelvis allowing smooth reciprocal motion of the trunk and lower limbs, controlling the lower portion of the trunk when bearing weight upon one limb. Often, those with back pain have weak hip musculature that allows excessive tilting of the pelvis when walking. This leads to excessive, poorly controlled motion in the lumbar spine that can result in aberrant stress and inflammation to the joints of the spine. As well, compensatory changes can occur in the musculature of the spine as the body attempts to control this aberrant movement leading to flexibility and conditioning problems.

Although there are many factors that affect knee and back pain, the hip may often be overlooked as a contributing factor. Fortunately, determining the role the hip may have regarding these problems is generally not difficult, and treating these problems is relatively straightforward. Simple exercises may help to enhance the function of the hip, but those with problems of the knee or back should consult a physician or physical therapist for help to ensure that the overall scope of the problem is evaluated.

Troy L. Grubb, P.T., O.C.S., A.T.C., is a board certified orthopedic specialist in physical therapy and athletic trainer with the Kentucky Orthopedic Rehab Team. E-mail comments to TroyGrubbPT@insightbb.com.