Runner’s Knee (Patellofemoral Pain): Causes and Rehabilitation

The kneecap moves in the groove of the thigh bone, and the force pressing it into the groove rises with knee flexion and load: going down stairs, deep squats, running downhill and jumping generate considerable loads on the patellofemoral joint. If the load exceeds the ability of the tissues to tolerate it — and the tissues around the kneecap (subchondral bone, fat pad, retinacula, tendons) are richly innervated — pain appears. In practical terms, PFPS is a mismatch between load and the joint’s capacity, not a “crooked kneecap” as a stand-alone cause.

The second layer is factors that change this match. The most often cited are a sudden increase in training volume or intensity (more kilometres, hills, descents, a new sport), weakness or reduced endurance of the quadriceps and hip muscles, the way of moving (e.g. excessive pelvic drop and thigh adduction during single-leg stance), and factors that are not visible on an image: fear of movement, irregular sleep, stress and overall activity level. Caution is warranted, however: the link between weak hip muscles and the onset of knee pain is ambiguous in the literature. A systematic review of studies in distance runners found that hip abductor weakness was associated with iliotibial band syndrome, whereas for patellofemoral pain it was unclear whether it is a significant factor in the development of symptoms.

PFPS is more often reported by people starting to run or suddenly increasing training volume, teenagers during rapid growth and people who do a lot of squatting and stair climbing at work. Diagnosis is clinical — it relies on history (pain at the front of the knee, aggravated by squats, stairs, running, prolonged sitting with bent knees) and physical examination, and imaging is usually not needed unless there are alarm symptoms. X-ray or MRI findings in many people without pain are “not ideal” and do not determine pain.

This is a practical division into “what to do and what not to expect”. The foundation is active rehabilitation, not passive treatments. At the same time the consensus honestly admits that for several popular methods — taping, bracing, dry needling, running retraining — the evidence is not enough for a clear recommendation; this does not mean they cannot help a particular patient, but that there is no solid evidence for it at the population level.

A lot of attention has been paid to the question of whether in PFPS it is better to strengthen the hip muscles (gluteus medius, abductors, external rotators) or the traditional quadriceps. A 2015 systematic review with meta-analysis covering 14 studies (7 of high quality) found that rehabilitation of the proximal (hip) muscles combined with quadriceps exercises is effective: strong evidence indicated reduced pain and improved function in the short term, moderate evidence in the medium term, and limited evidence suggested a greater effect of this combination than quadriceps rehabilitation alone, even at one year.

A later review comparing hip strengthening alone with traditional knee strengthening alone covered five comparative studies and showed no statistically significant differences in pain or function between the groups — the two approaches were equivalent, although in two studies pain decreased earlier in the hip group, and in two the hip group achieved greater hip abductor and extensor strength. Practical conclusion: there is no need to choose between hip and knee, and a combined programme is best justified. It is also important that patients improved in both approaches — that is, systematic strengthening itself matters.

A programme usually consists of several elements: strengthening the quadriceps (squats to a comfortable depth, lunges, Romanian deadlift, seated knee extension), strengthening the glutes and abductors (hip bridge, side-lying abduction, band exercises to the side), work on single-leg movement control and a gradual return to activity. A shared principle: the load should be large enough to be a real training stimulus but controlled enough not to aggravate symptoms beyond a moderate, tolerated level.

Load management in running is as important as exercise: weekly volume, the number of descents and hills, the amount of training on hard surfaces and recovery time affect whether the knee has time to adapt. The rule “one variable at a time” works similarly to other overuse injuries of runners, described in this series in the articles on the Achilles tendon and iliotibial band syndrome.

Foot orthoses are the only “additional” method that the consensus lists as recommended to improve pain and function; patellar taping and knee braces remain in the realm of uncertainty. In practice this means that taping or a brace may give temporary relief and make exercise easier, but they do not replace rehabilitation and have no strong evidence that they change the course of the condition. Joint mobilisations and physical modalities (ultrasound, electrotherapy) as stand-alone treatment are not recommended.

This is a pilot trial — 10 people per group, without a strengthening exercise group as a comparison — so it does not prove that gait retraining is better than strengthening; it shows only that in runners with PFPS a short intervention that changes the way of running (lower impact or higher cadence) can reduce pain during running. In the 2018 consensus gait retraining was still in the area of uncertainty; newer studies like this one point the direction but require larger trials.

One thing from the prognostic data is worth remembering: chronicity is not rare, and science is still learning what predicts it. A review mapping prognostic factors in PFPS included 10 cohort studies and 12 randomised trials; sociodemographic, anthropometric and symptom and function factors were studied most often, whereas biomechanical, behavioural, psychological and neurobiological factors were studied far less. It is a reminder that in treating PFPS the whole person matters — not only the muscles and the joint.

Runner’s knee is frustrating because it rarely has a single simple cause and rarely goes away after a week of rest. The good news is that there is a coherent course of action supported by expert consensus: active rehabilitation combining hip and knee exercises, sensible dosing of running and descents, and patience measured in weeks and months. Add-ons such as taping, a brace or gait retraining may help individually, but it is worth treating them as a complement, not a substitute for training.

If after several weeks of a consistent programme there is no improvement, do not look for another procedure; check whether the diagnosis is right and whether the loads are really matched. The wider importance of strength training for joints, tendons and bones is described in our knowledge-base entries on strength training and on sports recovery.