Hip joint internal rotation (sometimes also called medial rotation) occurs when the femur rotates within the hip joint, toward the mid-line of the body. It also occurs in standing when the lower limb is fixed and the pelvis rotates — so the left side ASIS moves in front of the right side, for example, or vice versa on the other side.

A "normal" value for hip internal rotation is 45 degrees, although few individuals get anywhere near that level of movement and a minimum of 35 degrees is considered sufficient for most people.

Why do we need all this IR?

Many people — runners, coaches and physical therapists — are aware of the need for sufficient hip extension during the gait cycle, in both walking and running. A lack of extension can cause big problems, for sports people and the nonsporting alike.

One large issue is the link between reduced hip extension and gluteal muscle inhibition. Inactive glutes increase the strain on the hamstrings and lumbar spine to name just a couple of knock-on effects.

However, what a lot of people don't know is that in order to sufficiently extend the hip toward the end of the gait cycle, there has to be enough hip internal rotation. Without sufficient internal rotation, the pelvis cannot move as far forward over the stance leg, and we instinctively shorten our stride.

In fact, without full internal rotation, the body employs various compensatory techniques to get by. In the end, these cause problems of their own that inevitably, somewhere along the chain, lead to injury.

The most common compensations seen in those with a hip internal rotation deficit (HIRD) include overpronation at the feet, a knee valgus, reduced step length, external rotation of the foot toward terminal stance phase and increased lumbar and knee extension. As you can imagine, such varied compensations can result in numerous injuries, from the ankle to the shoulder.

Where a hip internal rotation deficit becomes even more troublesome is in those sports and activities that require either deep hip flexion (such as squatting) or rotation — through the hip, pelvis, lumbar and thoracic spine in particular. Golf is a great example.

How can you assess a HIRD?

Assessment can be undertaken a number of ways, and it's a good idea to employ at least two of these techniques when testing the hip joint.

The joint should be assessed in both hip flexion and extension as the change in position affects muscle function of some of the prime movers here — namely gluteus minimus and piriformis, which switch between internally and externally rotating the hip, depending on the degree of flexion the joint is in. Assessing in flexion also removes any additional restriction coming from the external rotators that cross the hip joint at the front (e.g. iliopsoas, sartorius, pectineus and adductors brevis and magnus).

Finally, the hip should also be assessed actively and passively. This can really help you determine the cause of any deficit. An increase in range on passive motion suggests weakness or inhibition in the internal rotators is more responsible than tight external rotators, and vice versa.

• Seated: Usually on the edge of a treatment couch so the feet are dangling free, with the knee and hip flexed to 90 degrees. The patient is asked to keep the knees together as they move the ankles apart. The therapist may then apply some overpressure for a passive test.
• Prone: With the knees together and flexed to 90 degrees, the ankles are allowed to fall apart. Again, overpressure can be used for a passive test.
• Supine: With the knee extended, the leg is rotated inward from the hip. This one is perhaps a little less sensitive, although good for rotational athletes as the hip and knee are both extended in a more functional position.
• Gait observation: Watching the patient walk or run (using video software) is also a great indicator of a possible hip internal rotation deficit. While actually seeing the reduction in rotation is unlikely due to the small movements we are talking about here (4-6 degrees in the minimum requirement in walking), it can highlight other, possibly compensatory movement patterns.

How can you reduce a HIRD?

In order to increase the range of motion at a joint, you need to focus on reducing muscle tension in the opposing muscle group — in this case the external rotators, as well as strengthening the internal rotators themselves.

Here are a couple of stretches:

• Knee to knee: Start laying flat on the back with both knees bent and feet on the floor. Take the feet wide — wider than the hips — and then allow the knees to fall inwards toward each other, thus internally rotating the hip.
• Knee to shoulder: Again lying on the back, grasp the knee with both hands and pull it across the body in the direction of the opposite armpit.

Both stretches should be held for 30 seconds and repeated 2-3 times for maximal effect. This should be repeated 2-3 times a day.

And a couple of strengthening exercises:

• Reverse clam: Start in a side-lying position with both knees bent to 90 degrees and feet in line with the spine. Keep the knees together and raise the top foot away from the bottom one. Ensure the pelvis stays static throughout. For additional difficulty, add a resistance band tied around the ankles.
• Straight-leg IR: Start with the left leg by looping a band around the left mid-foot and a sturdy object like a table leg. Lie on your back with the table leg on your left side, legs straight and heel of the left foot on the floor. Keep the knee straight as you twist the leg (using the heel as a pivot) so that the toes point inward toward the other leg. Ensure the movement is coming from the hip and not the foot.

Perform strengthening exercises once a day at around three sets of 15 reps. Always work both sides evenly to avoid imbalances.

There you have it. Hip internal rotation deficits are a lot more common than you might imagine and can set off a long chain of dysfunction which at some point will result in pain, injury and performance deficits. So, if you don't already, check your athletes' range of hip rotation.