Consequences
Why your knee suffers from FHL
The knee is the joint that suffers most from Functional Hallux Limitus. When the foot loses its synchrony, the knee becomes the biomechanical fuse of the entire chain. Patellofemoral pain syndrome, cruciate ligament tear, iliotibial band syndrome — three major conditions whose origin traces back to the big toe.
The cascade of FHL to the knee
The foot is not an isolated joint. It is part of a biomechanical chain in which each link influences the next. When FHL blocks the roll-through of the step, the tibia can no longer rotate correctly, the knee ends up poorly positioned, and the entire extensor apparatus is destabilized.
The biomechanical chain involved
The knee, biomechanical fuse of gait
To understand the involvement of FHL in knee pain, this joint must be placed in the overall context of the lower limb. The knee is a condylar joint which, during walking, is almost fixed in rotation by the contraction of the popliteus muscle at the moment the heel touches the ground. The rotational component is negligible during walking, and it is the hip upstream and the subtalar joint downstream that take on this function.
The subtalar joint and the hip are anatomically comparable. English speakers call them ball-in-the-socket joints. Professor Pisani named them coxa pedis and coxa femoris. These two joints are interdependent. When one locks, the other must follow the imposed direction of movement or resist through the strength of its stabilizers.
This is exactly what happens in FHL. The subtalar joint is locked by the tenodesis effect of the flexor hallucis longus tendon. The hip is drawn into internal rotation during stance (medial collapse) and then into external rotation during the heel-contact phase. The gluteal lever arm loses its effectiveness.
The knee, a sandwiched joint
Caught between a misaligned hip and a locked ankle, the knee bears the brunt. It is poorly positioned in rotation, its stabilizing muscles are desynchronized, and it becomes the target of compensations. It is most often the first to hurt.
Three areas of pain, three syndromes
FHL is responsible for three major painful syndromes of the knee, each localized to a specific area of the joint. Recognizing the painful area points to the corresponding syndrome.
Anterior aspect (patella) → patellofemoral syndrome. Lateral aspect → iliotibial band. Medial aspect → pes anserine tendinitis.
Patellofemoral pain syndrome
Patellofemoral pain syndrome is the most frequently encountered knee condition in sports medicine consultation. It is defined by mechanical pain felt at the anterior aspect of the knee, often described as anteromedial. Compressive demands — squatting, going up and down stairs, prolonged sitting — are triggering or aggravating factors.
The mechanism explained — FHL causes a desynchronization during walking that leads to a delayed contraction of the quadriceps when the foot lands on the ground. At that precise moment, the patella is not pressed against the lateral facet of the trochlea as it should be, but floats. It is then abruptly forced against the medial facet of the trochlea when the quadriceps finally contracts, too late. This repetition of pressure and shear stress causes a transient bone edema on the medial facet of the patella, which is the source of the pain.
The pain appears during exertion, particularly when running. It can be so severe that it forces the activity to stop. Rest from sport makes it disappear, but it recurs as soon as activity is resumed. No correlation has been established between cartilage lesions and the pain. The term patellar chondropathy is no longer used today to define this syndrome, which does not progress to osteoarthritis.
« By systematically looking for FHL for twenty years, I have observed that this entity is present and can be diagnosed in every case of patellofemoral pain syndrome. »
Dr Jacques Vallotton, Centre Orthopédique d’Ouchy
The associated peripheral pain
Alongside joint pain, pain can exist at the periphery of the knee, particularly on the tendons. The most exposed are the iliotibial band and the pes anserine tendons on the medial side of the tibial plateau. These tendons try to counter the excessive external rotation of the tibia associated with the excessive supination at foot impact induced by FHL. The forces involved are large because they act eccentrically, that is, braking the movement. Patients rarely complain of this pain, but it is found consistently on palpation.
The anterior cruciate ligament tear
Anterior cruciate ligament (ACL) injuries account for between 100,000 and 200,000 cases per year in the United States, according to a recent Harvard University study published in 2020. Three quarters of these injuries occur during non-contact trauma, in sports involving pivoting movements — ball sports, gliding sports, combat sports, gymnastics.
The injury mechanism — The injury typically occurs during an abrupt deceleration combined with a change of direction that unbalances the knee, or on landing from a jump followed by a buckling of the knee into valgus. This sudden movement is caused by a tipping of the foot into pronation that drags the knee into a vicious spiral of valgus and internal tibial rotation. This is what is called the medial collapse of the knee.
A discovery at the Centre du pied
The starting point of this sudden tipping of the foot into pronation is a characteristic of FHL, revealed by analysis of the foot’s ground-contact pattern during gait assessments on an instrumented treadmill. For populations at high risk of recurrence, we recommend combining a tenolysis of FHL with the ACL reconstruction to improve the prognosis of the knee.
A retrospective study of more than 120 cases is under way at the Centre du pied to evaluate the medium-term results of this combination of tenolysis plus ACL reconstruction.
Iliotibial band syndrome
Iliotibial band pain syndrome, also called windshield-wiper syndrome or Runner’s Knee, is the most visible expression of the interaction between the foot and the knee in movement. It appears mainly when running, hence its English name of runner’s knee. The pain is located electively on the lateral aspect of the knee, where a tendinous band rubs against the bony prominence of the femur (lateral condyle) and creates inflammation, a bursitis.
The origin: an altered heel strike — The iliotibial band is anatomically comparable to a blind strap three to four centimeters wide. It originates on the iliac crest and attaches distally on the lateral plateau of the tibia, functioning as a true lateral stay that stabilizes both the hip and the knee.
Certain morphologies predispose to the syndrome — knock knees or bow legs, natural hyperlaxity, lack of muscle flexibility, a prominent bony relief. But since this syndrome appears in movement, and especially when running or walking downhill, the biomechanical explanation is essential. FHL is present in every case of iliotibial band pain syndrome and plays a major role in the onset of the pain. Heel strike on the outer edge of the heel and the stronger impact put additional tension on the band.
Good news for runners
The conservative treatment offered for FHL is most often effective for iliotibial band syndrome. For regular runners, a movement analysis on a treadmill and a dynamic podiatric assessment make it possible to continue the activity under the best conditions.
Key scientific articles
Two publications from the Centre du pied, in collaboration with the orthopedic research team, document the involvement of FHL in knee conditions.
Article
Posterolateral pain after TKA
Olden T. R., Vallotton J., 2021, A rare etiology of posterolateral pain subsequent to a total knee arthroplasty.
Article
Endoscopic Tenolysis of FHL
Olden T. R., Vallotton J., 2020, Endoscopic Tenolysis of Flexor Hallucis Longus Tendon, Surgical Technique.
Understanding through video
Two lectures from the Congrès Medicol 2013 illustrate the biomechanical consequences of FHL and the interdependence between the subtalar joint and the hip, the two “coxa” described by Professor Pisani.
Biomechanical consequences of functional hallux limitus
Coxa pedis and coxa femoris: interdependence and complementarity
Do you recognize your pain?
Take stock of your situation
If the pain described matches what you feel, the mobility assessment at the Centre du pied makes it possible to objectively document any underlying FHL behind it.
At a glance
Joint
the most affected
Syndromes
3 main ones
Typical patient
young, athletic
Population
predominantly female
Imaging
usually normal
Progression to osteoarthritis
no
Going further
Other consequences and useful pages
Hip
The joint upstream of the knee, source of the rotational compensations linked to FHL.