Home Functional Hallux Limitus Knee ACL tear
The knee
The anterior cruciate ligament tear
Most often without contact, during a pivot or on landing from a jump, the ACL tear arises from a sudden collapse of the knee into valgus. The starting point of this “medial collapse” lies in the foot, in the tilt into pronation characteristic of Functional Hallux Limitus.
A frequent injury, most often without contact
Knee ligament injuries involving the ACL account for between 100,000 and 200,000 cases per year in the United States, according to a Harvard University study published in 2020. 75% of these injuries occur through non-contact trauma, in sports involving pivoting movements: ball sports, snow and board sports, combat sports or gymnastics.
The injury occurs during a sudden deceleration combined with a change of direction that throws the knee off balance, or on landing from a jump followed by the knee giving way into valgus. This abrupt movement is due to the foot tilting into pronation, dragging the knee into a spiral of valgus and internal tibial rotation, the “medial collapse.”
Key concept
The medial collapse
A medial collapse of the knee into valgus, combined with internal tibial rotation, triggered by a sudden tilt of the foot into pronation. This is the mechanism behind most anterior cruciate ligament tears occurring without contact.
The mechanism on video
The sequence below illustrates the mechanism of the pivoting injury and the collapse of the knee into valgus as the foot plants.
The mechanism of the pivoting injury
The decisive role of FHL
The starting point of this sudden tilt of the foot into pronation is a hallmark of FHL, revealed by analyzing the footprint on the ground during our gait assessments on an instrumented treadmill.
Today, for a population at high risk of recurrence, we recommend combining an FHL tenolysis with the ACL reconstruction in order to improve the knee’s prognosis. A retrospective study of more than 120 cases is under way to assess the medium-term results of this combined approach.
Key scientific articles
Two publications from the Centre du pied document the link between FHL and knee conditions, as well as the endoscopic tenolysis technique.
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.
Pivoting sport, knee at risk?
Assess your biomechanical risk
If you play a pivoting sport or have already suffered a knee injury, the mobility assessment at the Centre du pied can objectively identify a possible FHL and evaluate your risk profile for recurrence.
At a glance
Cases per year (USA)
100,000 to 200,000
Non-contact
75% of cases
Sports
pivoting
Mechanism
medial collapse
Underlying cause
Functional Hallux Limitus
Approach
FHL tenolysis + reconstruction
Further reading
Related pages
Knee overview
The three zones and the knee syndromes linked to FHL, from the patellofemoral syndrome to the ACL.