Hip and knee: these are two joints that really do influence each other, but around this link, things that have been proven circulate alongside things we repeat out of habit. In this article we separate the two: what the literature supports (referred pain, osteoarthritis, the adolescent case) and what has not passed the test of the facts (weak glutes as the cause of knee pain). And above all: how to use this information anyway.
⚠ Important: read this before continuing
The exercises and advice in this article are general indications and may not suit your situation. Everyone has a unique clinical history: what works for others could be counterproductive for you.
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First things first: the signs that should not be put off
The fact that the hip and knee can "talk to each other" is never a good reason to wait for months. See a doctor without delay if you recognise any of these situations.
- A child or adolescent has pain in the knee or thigh without an obvious trauma. (Among the typical causes at that age is transient synovitis of the hip.) This is the most insidious situation of all. Slipped capital femoral epiphysis (the slipping of the head of the femur, in English slipped capital femoral epiphysis) is the most frequent hip condition in pre-adolescence and adolescence, and the diagnosis often comes late precisely because the young person points to the knee or thigh rather than the hip. The delay has a cost: it increases the risk of necrosis of the femoral head. The guidance in the literature is clear: in a young person with leg pain this diagnosis must always be kept in mind, which means having the hip assessed and not only the knee.
- You cannot put weight on the leg, especially after a fall or in older age: a fracture needs to be ruled out.
- A hot, swollen, red knee, with fever or general malaise. This picture requires urgent assessment, not exercises: we discuss it in detail in the article on a hot, swollen knee.
- Night pain that does not change with position, rest pain that gradually worsens, unintended weight loss, or a personal history of cancer.
- Tingling, loss of strength or sensation along the leg, or pain that starts in the back: here the source may be lumbar, and the relationship between the hip and the back deserves an assessment of its own.
Outside these cases, you have time to think things through calmly. That is what we do in the rest of the article.
What is proven about the link between hip and knee
Let us lay out the three claims found everywhere, with their real scientific weight.
1. A diseased hip can cause knee pain. True and well documented. In a study of 60 patients waiting for a hip replacement, pain extended below the knee in 47% of cases, with a distribution consistent with the territory of the saphenous nerve. Pain in the groin and buttock was, by contrast, significantly more frequent in hip osteoarthritis than in lumbar stenosis. Curiously, in the same work 88.5% of orthopaedic trainees believed that hip pain could not travel below the knee. It is exactly the kind of belief that keeps people looking in the wrong place for years. In children and teenagers the trap is the same, but the causes to look for are different and change almost entirely with age: they are set out in what hurts the knee at 4, 9 or 14 years old.
2. An osteoarthritic hip overloads the knee on the other side. This is supported by measured data. In 62 patients with unilateral hip osteoarthritis and still asymptomatic knees, the peak dynamic loads and the bone mineral density of the medial compartment were higher in the contralateral knee than in the knee on the same side as the diseased hip. Asymmetries in loading, in other words, appear before symptoms. Be careful not to turn this into a self-fulfilling prophecy: these were people with established, unilateral hip osteoarthritis, not just any slightly stiff hip.
3. Weak glutes cause knee pain. Here the story changes, and it is worth giving it a whole paragraph.
Weak glutes and dynamic valgus: the most widespread explanation is also the most fragile
The chain of reasoning is familiar to anyone who frequents a gym or a physiotherapy clinic: weak gluteus medius → the pelvis drops on the opposite side when standing on one leg → the knee moves inwards (dynamic valgus) → the kneecap is loaded badly → pain. It is elegant, it is plausible, and it has one problem: when it was tested properly, it did not hold up.
The difference lies in study design. Cross-sectional studies (which photograph strength and pain at the same moment) do find that men and women with patellofemoral pain have lower isometric hip strength than people without pain. But prospective studies, which measure strength in healthy people and then wait to see who develops pain, find no association between isometric hip strength and the risk of developing patellofemoral pain. A systematic review with meta-analysis published in the British Journal of Sports Medicine puts the conclusion in black and white, while also noting that the available prospective studies are few: reduced hip strength may be a consequence of pain rather than its cause. In the same review, with limited evidence by its own definition, adolescents with patellofemoral pain did not show the same strength deficits as adults.
There is a second element that is rarely reported. A masterclass paper published in the Brazilian Journal of Physical Therapy points out that several clinical studies achieved a significant improvement in symptoms by strengthening the glutes without changing the kinematics of the movement: if the pain improves but the knee still falls inwards as before, the explanation "we have corrected the mechanical cause" wobbles. For fairness, not all the data point in the same direction: the meta-analysis on proximal rehabilitation we mention shortly also reports, with very limited evidence, a reduction in knee valgus variability during running. The overall picture is still far from the certainty with which the theory is usually presented.
What do you do with this information? Three very concrete things:
- Do not let anyone tell you that you have "a crooked knee" and that this is your destiny. Dynamic valgus has not been proven as a cause, and not everyone with patellofemoral pain shows it.
- Be wary of programmes that strengthen only the glutes on the grounds that "the problem is there anyway": you are skipping the knee, which has the most solid role in the evidence.
- Do not give up hip exercises. They work, as we see now, but only for reasons different from the ones we used to tell ourselves.
An important point: before trying these exercises, make sure you have received a correct diagnosis. People often assume they have one problem, but the real cause of the pain is something else. Doing the wrong exercises can make the situation worse rather than better.
Why working on the hip helps all the same
This is the part that is often lost in the debate. The fact that hip weakness has not been shown to be a cause takes nothing away from the effectiveness of the treatment.
A systematic review with meta-analysis assessed the rehabilitation of the proximal muscles (hip and pelvis) in patellofemoral pain and found strong evidence that proximal work combined with quadriceps work reduces pain and improves function in the short term, with moderate evidence in the medium term and, here with limited evidence, a benefit for pain that holds at one year compared with quadriceps work alone. Along the same lines, the international consensus statement on patellofemoral pain recommends therapeutic exercise and, in particular, the combination of hip exercises and knee exercises. The same consensus is equally clear about what should not be used on its own: mobilisation of the kneecap, the knee or the lumbar spine in isolation, and physical modalities.
In practical terms: the hip enters the programme because the complete programme works, not because we have found the culprit. It is a difference that changes the way you work: less hunting for postural faults, more progressive loading across the whole limb.
Hip stiffness: a good diagnostic sign, a cause not proven
That a stiff hip forces the knee to compensate is a reasonable biomechanical hypothesis, but I have not found solid evidence that limited internal rotation of the hip causes knee pain in people who have no hip problems. What the reduced movement does very well is something else, just as useful: signalling that the hip itself is diseased.
A systematic review in the Rational Clinical Examination series of JAMA assessed which clinical signs are most associated with radiographic hip osteoarthritis. Among patients who come to their GP with hip or groin pain, about a third do have radiographic signs of osteoarthritis. The most useful findings for identifying it were pain at the back evoked by squatting, groin pain on passive abduction or adduction, weakness of the abductors and reduced passive adduction or internal rotation, measured with a goniometer or compared with the healthy leg. And the mirror-image finding: normal passive hip adduction is the finding that makes hip osteoarthritis most unlikely. These, however, are measurements taken by a clinician, not a test to do at home.
Note that in the same review a personal history of knee osteoarthritis was also associated with a higher probability of hip osteoarthritis. The two joints often become ill together, which does not mean that one causes the other: they share age, weight, load and genetics.
How to find your way between hip and knee: an honest self-assessment
There is no home test that establishes with certainty where the pain comes from, and anyone who promises one is oversimplifying. There are, however, clues that shift the probabilities, and knowing what they are lets you arrive at the professional with useful information.
Clues that point towards the hip:
- pain in the groin, the buttock or the front of the thigh, even if the worst point is felt at the knee;
- pain that appears climbing stairs or hills;
- difficulty putting on socks, crossing your legs or getting out of a car;
- passive hip movements that are clearly more limited than on the healthy side, particularly adduction and internal rotation;
- a knee that, on examination, is not tender at any precise point and is not swollen.
Clues that point towards the knee:
- a precise point of tenderness that you can point to with one finger;
- swelling, crepitus, locking or giving way;
- pain that appears going down stairs, sitting for long periods with the knee bent, or squatting: the typical picture of anterior knee pain;
- pain that appeared after a sudden increase in running or training, as described in the article on knee pain in running.
One further practical criterion: if a knee treated well for weeks does not improve at all, it is worth having the hip and the lumbar spine checked before persisting with the same programme. Not because it is likely, but because it is the only way to catch the case in which we are treating the wrong place.
What to do in practice
A sensible programme does not choose between the two joints: it trains both, with judgement.
For the knee. It is the joint with the strongest evidence in patellofemoral pain: progressive quadriceps work, in open and closed kinetic chains, dosed so that the pain stays tolerable and does not worsen in the following days (this is a practical dosing criterion, not a threshold measured by a study).
For the hip. Strengthening of the abductors and extensors (clamshells, side-lying abduction, single-leg bridge, lateral steps with a band), and mobility work when it is reduced: stretching of the hip flexors, rotations, figure-4 stretch. You will find a broader progression in the hip mobility and strengthening exercises. Remember that here the goal is the capacity to load, not "correcting" an alignment.
For the whole movement. Controlled squats, lunges and step-ups bring the hip, knee and ankle back together into the movement you actually need.
If there is osteoarthritis. The Dutch KNGF physiotherapy guideline for hip and knee osteoarthritis focuses on two things: education and self-management on one side, and personalised, appropriately dosed therapeutic exercise on the other, in line with the physical activity recommendations for the general population, ranging from simple advice to longer supervised exercise, depending on the profile. The same guideline explicitly asks that warning signs be sought during assessment. Targeted reading: hip osteoarthritis for the hip and knee osteoarthritis for the knee.
What does not make sense to do: chase dynamic valgus with continual corrections of movement, suspend all activity while waiting for "the alignment to sort itself out", or be promised that knee pain will disappear as soon as your glutes are strong.
Online physiotherapy
Much of what this pathway requires can be done well remotely: taking the history, understanding where and when it hurts, watching how you move, testing hip mobility against the healthy side, setting and correcting exercises and, not least, recognising the cases where an in-person examination is needed.
Ri-Hub offers online physiotherapy sessions for 29,90€ with physiotherapists who assess the hip and knee together, rather than treating only the point that hurts.
In summary
The link between hip and knee exists, but it is not the one usually described. It is solid for the referred pain from a diseased hip (even reaching below the knee), it is documented for the overloading of the contralateral knee in advanced hip osteoarthritis, and it is a genuine emergency that must not be missed in the adolescent with knee pain. It is, however, much weaker than commonly believed in the "weak glutes, knee collapsing inwards" version: prospective studies do not confirm it.
The good news is that the practical conclusion does not change much: the hip and knee are trained together because the combined programme is what works. What changes is how it is explained, and above all how much time you lose looking for a fault that may not be your problem.
Sources
- Hip osteoarthritis: where is the pain?, Annals of the Royal College of Surgeons of England, 2004
- Is hip strength a risk factor for patellofemoral pain? A systematic review and meta-analysis, British Journal of Sports Medicine, 2014
- Proximal muscle rehabilitation is effective for patellofemoral pain: a systematic review with meta-analysis, British Journal of Sports Medicine, 2015
- Do hip muscle weakness and dynamic knee valgus matter for the clinical evaluation and decision-making process in patients with patellofemoral pain?, Brazilian Journal of Physical Therapy, 2018
- 2018 Consensus statement on exercise therapy and physical interventions to treat patellofemoral pain, British Journal of Sports Medicine, 2018
- Does This Patient Have Hip Osteoarthritis? The Rational Clinical Examination Systematic Review, JAMA, 2019
- Asymmetric loading and bone mineral density at the asymptomatic knees of patients with unilateral hip osteoarthritis, Arthritis & Rheumatism, 2011
- Slipped Capital Femoral Epiphysis, StatPearls, 2023
- A clinical practice guideline for physical therapy in patients with hip or knee osteoarthritis, Musculoskeletal Care, 2020
Last source check: August 2026.
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