RUNNER'S KNEE

Watching all the amazing athletes at the Tokyo Olympics I am sure has inspired many to get off the couch during the most recent COVID-19 lockdown and get back into a bit more exercise. With the Melbourne Marathon now less than 9 weeks away, those who have registered should be well into their training program in the build up to the big day (fingers crossed it can go ahead and isn’t a virtual event again this year!). Whether you’re training for a marathon or just wanting to go for a 5km run to work off those COVID kg’s, load management is the key to minimising the risk of injury. One common injury that Physiotherapists tend to see as people start running or increasing their distance is “Runner’s Knee”, or Patellofemoral Pain Syndrome (PFPS).

WHAT IS PFPS?

PFPS is anterior knee pain due to overload and irritation of the patellofemoral joint (the articulation of the knee cap and thigh bone). The joint can become irritated when load is increased too quickly, such as ramping up the km’s when training for a marathon. However, other factors can contribute, such as lack of strength around the hip causing the femur (thigh bone) to internally rotate and adduct during the stance phase of running or walking, impacting the load on the PFJ. Strength and neuromuscular control (or lack thereof) of muscles around the knee can also impact the PFJ. It is also important to consider technique or form with running, and whether this is contributing to an overloaded PFJ. Putting all this into the biopsychosocial model of Physiotherapy management, we also need to consider the “psychosocial” factors that contribute to someone’s pain (anxiety, stress etc).

Women tend to have a higher rate of PFJP, which is thought to be due to the differences in biomechanics to men, with increased adduction of the leg during the stance phase of walking and running, which can put more load on the PFJ.

MANAGING PFPS

Complete rest is NOT the answer to managing PFP, as this will only lead to further weakness. However, if you’re currently running 5-6km with no pain during or after exercise, but when you try to push it to 8-10km then I’d recommend stick to the 5-6km runs while working on strength and running technique, then gradually building up the km’s over time. Non-running days are also important to manage load, where the focus is on strength and control exercises. Generally the recommendations are that if you can run with less than 3/10 pain that doesn’t linger once you stop running, then it is ok to continue at that distance and frequency of runs per week. Once the pain is more than 3/10 during or after a run, or if the pain limits you with functional activities such as going up and down stairs for the rest of the day or the next day, then you should reduce the running load.

There are a couple of key changes to running gait that can reduce the load on the knee. One is to “run softly” - that is to land lightly more on the forefoot, rather than heel strike or land with a heavy flat foot. However, to do this you must have sufficient calf strength, otherwise there is the risk of overloading the Achilles Tendon. Therefore, calf strength and plyometric exercises (such as jumping, hopping and skipping) should be incorporated into a home program to ensure there is sufficient calf strength and endurance to transition to a forefoot landing pattern.

Increasing the cadence (step rate) has also shown to be an effective way of reducing load on the PFJ, and should naturally encourage more of a mid-foot to forefoot strike, as the “pick up, put down” of the foot will be more under the body, rather than ahead of the trunk. As a guide, for long-distance running an ideal cadence is usually around 170-180 steps/minute. However, if you are currently running at 140-150 steps/minute, this will be too big a jump to go up to 170+ straight away. Building in some interval training of 2-3minutes at a 5-10% increased cadence (i.e. 155-160 steps/minute) will help to build your fitness for an increased step rate, as well as allow the body to adjust to different loading patterns to minimise risk of injury to other structures, such as the Achilles.

Aside from strengthening the calf, other muscle imbalances should also be addressed. For example, it is common in clinical practice to see a weakness in the glutes on the same side as the knee pain. This can be a deficit in the gluteus medius (lateral glute muscle) and/or the gluteus maximus (primary hip extensor). When there is a weakness in the gluteus medius, the femur is more likely to internally rotate and adduct (knee drops across midline) during the stance phase, putting more strain through the PFJ. Weakness of the gluteus maximums can lead to less efficient hip extension during the drive phase, increasing the work for the hip flexors to swing the leg through, leading to tightness in the front of the leg which again can put more load through the PFJ. Having a comprehensive muscle strength and functional assessment with a Physiotherapist can help you address potential muscle imbalances that are contributing to your PFJ pain. Isolated strength should then be progressed to addressing neuromuscular control around the hip and knee, i.e. the form you hold with a single leg squat, step-up or step-down, all of which are functional strength and control exercises appropriate for running rehabilitation.

Following an assessment of running gait and foot biomechanics, it may also be recommended that you either change your running shoe to one with more arch support to reduce the pronation of the foot and subsequent load on the PFJ, or consider an orthotic for your runners to again help improve alignment during the stance phase of running.

SUMMARY

• Patellofemoral pain is caused by overload of the anterior knee joint.

• Load / activity modification is the key to managing PFJP.

• Addressing underlying muscle imbalances can help you to increase running load safely and avoid injury.

• Increasing cadence (step rate) can reduce the load on the PFJ, but should be done gradually.