ConditionBones, joints & muscles
Dynamic Knee Valgus (Knees Caving In)
Dynamic knee valgus is the inward collapse of the knee during movements such as squatting, landing from a jump, running or cutting. The thigh turns in and the knee drops toward the midline while the foot stays planted, creating a "knock-kneed" position under load. It is a movement pattern, not a fixed deformity, and usually comes from weak hip muscles, poor control, stiff ankles or flat feet. It is linked to ACL injuries and kneecap pain, and it can be improved with targeted strength and movement training.
Also called: Knee valgus collapse, inward knee collapse, medial knee collapse, knees caving in
At a glance
- What it is
- The knee moving inward during weight-bearing movement, a combination of hip turning in, thigh moving inward and foot flattening.
- Main causes
- Weak hip abductors and external rotators, poor neuromuscular control, limited ankle mobility and foot pronation.
- Linked problems
- ACL tears (especially in female athletes), patellofemoral pain and IT band pain.
- How it is assessed
- Single-leg squat, drop-jump landing and step-down tests.
- Fix
- Hip and core strengthening, landing and squat technique training, and ankle mobility work.
When to get help
See a doctor within a day or two
- A pop in the knee during a landing or pivot, followed by swelling within hours and a knee that gives way (possible ACL tear)
- A knee that locks, cannot straighten or is too painful to bear weight
Book a routine appointment
- Knee pain at the front of the knee with squats, stairs or sitting for long periods
- Knees that visibly cave in during squats, jumps or running, especially in a young athlete
- Knee pain that persists for more than a few weeks despite rest
- Knock knees that are worsening, one-sided, or still present after age 7 to 8 in a child
Usually safe to manage at home
- Knees that cave in slightly during exercise with no pain or instability, which can be worked on with strength and technique training
What dynamic knee valgus looks like
From the front, during a squat, lunge, step-down or landing:
- the knees move toward each other or inside the line of the big toe
- the thigh rotates inward
- the hip drops on the opposite side (in single-leg movements)
- the foot arch collapses (pronation)
- the trunk may lean sideways
This is different from static genu valgum (knock knees), where the legs are angled even when standing still. Static knock knees are normal in children aged about 2 to 7 and usually straighten by around age 8.
Causes and contributing factors
Hip weakness and control
The gluteus medius and hip external rotators hold the thigh in line. When they are weak or slow to activate, the thigh drops into internal rotation and adduction, pulling the knee inward. This is the most common and most trainable factor.
Poor landing and movement technique
Landing with stiff, straight knees, letting the knees drift inward and landing on one foot with the trunk to the side increase load on the knee. Fatigue makes it worse, which is why injuries often happen late in games.
Ankle and foot factors
- Limited ankle dorsiflexion (stiff calves or ankle joints) forces the knee to move inward to get depth in a squat.
- Flat feet and excessive pronation let the shin rotate inward.
Other factors
- Sex: female athletes show more valgus on landing on average, linked to anatomy, hormonal factors and training differences.
- Growth spurts: rapid growth temporarily affects coordination.
- Previous injury: ankle or knee injuries change movement patterns.
Why it matters
ACL injuries
Most ACL injuries happen without contact, during landing, cutting or decelerating. Dynamic valgus combined with rotation and a relatively straight knee places high strain on the ACL. Female athletes have a 2 to 8 times higher rate of non-contact ACL injury in some sports, partly explained by these movement patterns.
Patellofemoral pain
Valgus alters how the kneecap tracks in its groove, increasing pressure on its outer side. Patellofemoral pain syndrome causes aching at the front of the knee with stairs, squats, running and sitting with bent knees.
Other conditions
- iliotibial band syndrome in runners
- patellar tendinitis
- possible contribution to medial knee and meniscus stress over time
How it is assessed
A physical therapist, athletic trainer or sports medicine doctor will observe:
- single-leg squat and step-down tests
- drop vertical jump or tuck jump landing
- hip strength testing (abduction, external rotation)
- ankle dorsiflexion (knee-to-wall test)
- foot posture
Video analysis, sometimes in slow motion, helps show valgus and track progress. Imaging is not needed unless an injury is suspected.
How to fix dynamic knee valgus
Programs usually run 2 to 3 times a week for at least 6 to 8 weeks.
Hip and core strengthening
- side-lying hip abduction and clamshells
- banded side steps (monster walks)
- side planks
- glute bridges and single-leg bridges
- single-leg Romanian deadlifts
Movement retraining
- squats with a light resistance band around the knees, cueing "knees over toes"
- step-downs from a low box with the knee kept in line
- lunges and split squats with mirror feedback
- landing practice: land softly on both feet, knees bent, hips back, knees in line with toes
Ankle mobility and foot control
- calf stretches and knee-to-wall ankle mobilization
- short-foot exercises to strengthen the arch
- supportive footwear or orthotics for marked flat feet
Injury prevention programs
Structured neuromuscular warm-ups, such as FIFA 11+ and similar programs that combine strength, balance, plyometrics and landing technique, reduce ACL injuries in youth and female athletes when done regularly.
Frequently asked questions
What is dynamic knee valgus?
Dynamic knee valgus is when the knee collapses inward during movements like squatting, landing or running. It reflects how the hip, knee and foot are controlled under load, rather than a fixed bone shape, and it is linked to knee pain and ACL injuries.
What causes knees to cave in during squats?
Common causes are weak hip muscles (especially the gluteus medius), poor movement control, stiff ankles that limit squat depth, and flat feet. Fatigue and heavy loads make it worse. Strengthening and technique training usually help.
Does knee valgus cause ACL tears?
Dynamic knee valgus is one of the main movement risk factors for non-contact ACL tears, especially when combined with rotation and landing with straight knees. Neuromuscular training programs that reduce valgus lower ACL injury rates.
Can dynamic knee valgus be fixed?
Yes, in most people. Hip and core strengthening, landing and squat technique training and ankle mobility work improve knee alignment within weeks to months. Progress is best tracked with video or a physical therapist's assessment.
Is knee valgus the same as knock knees?
Not exactly. Knock knees (genu valgum) is a static alignment seen when standing. Dynamic knee valgus happens only during movement. A person can have straight legs standing but still show dynamic valgus when landing or squatting.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Orthopaedic Surgeons: Anterior cruciate ligament (ACL) injuries
- National Athletic Trainers' Association: Prevention of anterior cruciate ligament injury position statement
- Journal of Orthopaedic & Sports Physical Therapy: Patellofemoral pain clinical practice guideline
- American Academy of Pediatrics: Prevention of ACL injuries in youth athletes
- American College of Sports Medicine: Neuromuscular training resources