The Knee-Hip Connection: Muscles and movement

This article is part of a series discussing the biomechanical connections between the feet, ankles, knees and hips and how they all impact knee health.

The knee-hip connection

Healthy hips are able to perform a diverse range of movements (see diagram right). All of these movements and their associated muscles have a direct impact on the knee.

If any of the hip muscles are weak, tight or both, they can affect the alignment of the knee joint at rest and in movement. The best approach for hip and knee health is a regimen that balances mobility with stability, or stretch with strength.

Front side – flexion

Whether working at your desk, driving your car, or watching your favorite show, every time you sit for an extended period your hip flexors get tight and your buttock muscles get weak. Both of these issues affect how your hips function and move.

Tight hip flexors, especially when combined with weak buttocks, can pull the pelvis forward into an anterior tilt. This can cause your thigh bones to internally rotate, leading to excess pressure on the inner knee. An anterior pelvic tilt also affects the biomechanics of walking, again leading extra pressure being loaded onto the knees.

Weak hip flexors also present a problem when it comes to knee health. The two major hip flexors are the rectus femoris, the most superficial of the quadriceps muscles, and the iliopsoas, a deep muscle that connects from the thigh to the spine.

The deeper iliopsoas muscle is the hip flexor most likely to be weak on  people with knee pain. Because the illopsoas also acts as a secondary hip extensor, it helps prevent excessive inward rotation of the thigh and pronation of the foot. It also helps track the knee cap in place over the joint. The illiopsoas needs to be both long and strong if it’s going to support a healthy and durable knee joint.

The recuts femoris on the other hand is usually relatively stronger on most people. In fact, when it works overtime to make up for a weak illopsoas, it has the ability to overpower the knee and push the joint back into hyperextension.

Check here for yoga poses for strong, long hip flexors

Backside – extension

Standing up, sitting down, walking, running, all require strong hip extensors. The hip extonsor muscles are the gluteus maximus (the largest buttock muscle) and the hamstrings (the long back thigh muscles).

As mentioned above, the buttocks can become weak from prolonged sitting and begin to vacate their job of extending the leg back in space. When that happens the hamstrings end up picking up the extra workload and become tight in the process. Both of these issues affect your walking gait and exert extra pressure further down the kinetic chain at the knee joint.

When the gluteus muscles become tight they can pull the thigh bone into excessive external rotation and pull the knee along with it. This puts unnecessary stress on the knee, and of course, affects how you walk and run.

Outside – abduction

The movement of the leg away from the midline is called abduction. The muscles responsible for this action, the gluteus medius, gluteus minimus and the deep gluteals, are located at the outer hips and in the deep buttocks. The abductors are important walking and balance muscles, which prevent the hips from swaying too far out to the sides as you walk.

Just like the gluteus maximus (see above) the abductors can get weak and tight from too much sitting.  This can lead to patellofemoral pain syndrome and iliotibial band syndrome, both painful knee conditions.

Inside – adduction

The hip adductors bring the leg back to the midline. The muscles responsible for this action, the adductors longus, brevis and magnus, and the pectineus and gracillis, are located at the inner thighs. Again, like all the other hip muscles, they should be long and strong so they support healthy knee functioning.

Of note, one of the adductor muscles, the gracillus, shares a tendon with the sartorius (a hip flexor) and the semitendinosus (an inner hamstring muscle). The tendon is called the pes anserinus and it attaches to the shin bone at the inner knee. Overuse of the three muscles (usually from bicycling or running) can cause the tendon become tender and inflamed resulting in pain at the inner knee. Stretching to reduce tightness of the three connected muscles can help.

Turning in – internal rotation

Internal or medial hip rotation is the action of turning the thigh towards the midline. This appears as a “knock kneed” look at the knee joint. Normal internal rotation is required for a healthy walking gait. However, when it’s caused by weak hip muscles, it can lead to pronation (a collapse at the inner foot) and excessive pressure at the inner knee.

The muscles involved in internal hip rotation are the gluteus medius and minimus (both buttocks muscles), and the semitendinosus and semimembranosus (both inner hamstring muscles).

Turning out – external rotation

External or lateral hip rotation is the action of turning the the thigh away from the midline. Normal external rotation is also required for a healthy walking gait. However, when it’s caused by tight hip muscles it can lead to supination of the foot, which puts too much pressure on the outer foot. This twists the knee out from the midline and again can cause an imbalance of pressure in the knees.

The muscles responsible for external hip rotation are the biceps femoris, gluteus maximus, and the deep gluteals

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