A patient comes in with pain at the front of the knee when going downstairs or running. Examining the knee shows little. We ask them to stand on one leg and the problem appears: the pelvis drops towards the side in the air and the knee collapses inwards.
The pain is in the knee. The deficit is in the hip.
What the gluteus medius really does
Its best-known function is moving the leg away from the body, but that isn't what matters here. Its main job is stabilising: every time you stand on one leg, the gluteus medius on that leg stops the opposite side of the pelvis from dropping and keeps the femur aligned.
And we stand on one leg constantly. Every step when walking, every stride when running, every stair, every change of direction. In running, single-leg stance time is practically the whole cycle.
The chain of events when it fails
1. La pelvis se inclina
When control of the standing side is lost, the pelvis drops towards the free side. This is known as the Trendelenburg sign.
2. The femur rotates and turns inwards
Without the gluteus medius as a brake, the thigh drops into adduction and internal rotation.
3. The knee goes into dynamic valgus
The knee collapses towards the midline. It is the posture seen in recordings of squats or poorly controlled landings.
4. The kneecap stops gliding properly
It changes the path of the patellar tendon and increases pressure on the outer side of the joint.
5. Pain appears
Usually as patellofemoral pain, iliotibial band syndrome or patellar tendinopathy. All with the same mechanical origin.
This dynamic valgus is also described as a risk factor for anterior cruciate ligament injury, especially when landing and braking. That is why ACL prevention programmes always include hip work.
Why it weakens
After any knee injury or surgery there is a period of offloading, and the gluteus medius loses strength very quickly. But it also weakens without a previous injury: long hours sitting, little walking, and training focused on front-to-back movement planes that barely challenge it.
There is an important clinical detail: the gluteus medius may have enough strength when measured in isolation and still not activate in time during movement. It isn't just a strength problem, it's a motor control problem.
How we assess it
With functional tests, not just manual strength testing. Sustained single-leg stance, single-leg squat, controlled step-down, and running observation when the patient is a runner. We look at whether the pelvis stays level and whether the knee holds its alignment under load and fatigue.
How reconditioning works
Progression goes from isolating to integrating. Starting with isolated exercise makes sense when strength is very low, but staying there doesn't transfer to the real movement.
Activation phase
Unloaded exercises so the patient learns to feel and contract the muscle: side-lying abduction, bridge variations, controlled isometric work.
Loaded strength phase
Single-leg deadlift, Bulgarian split squat, box step-ups, abduction with external load. This is where real capacity is gained.
Single-leg control phase
All work moves to a single leg, with surfaces and perturbations that force constant correction of pelvic position.
Sport-specific movement phase
Jumps and landings, changes of direction, braking, running. We check that control holds even with speed and fatigue, which is when injuries happen.
Key takeaways
If a knee hurts without a clear structural cause, or if the pain returns every time training resumes, it is worth looking at the hip. Treating only the spot that hurts explains quite a few recoveries that stop halfway.
