Summary

FHL induces an hyperpronation in late stance synchrone with a screw home mechanism in the knee that predispose to ACL injuries. HL induces an hyperpronation in late stance synchrone with a screw home mechanism in the knee that predispose to ACL injuries.

Abstract

Functional Hallux Limitus (FHL) is often involved in ACL injuries in non contact injuries.
The mechanism combines a sudden shift of the foot to hyper pronation in late stance, together with a medial collapse of the knee. The screw-home effect is explained by the inter-articular synchronism between pronation and internal tibial rotation. ACL is then suddenly put in extreme tension and this is when a rupture could occur.
FHL is a clinical entity diagnosed by specific clinical tests and can also be detected on foot scan platforms because of its specific pathognomonic footprint. Its relevant biomechanical consequences for foot and knee stability in movement should prompt us to look for it in ACL tears.
In our experience of more than 400 consecutive ACL tears in non-contact injuries, FHL was present in more than 90% of cases (unpublished data).
FHL involvement in recurrent ACL injuries and/or residual laxity after ACL reconstruction has to be considered too.
FHL can be managed conservatively by a specific rehabilitation protocol or treated surgically by tenolysis of the Flexor Hallucis Longus tendon.

The purposes of this presentation are :
- to detail with several examples the mechanisms of ACL tears by a foot-knee approach in biomechanics
- and to present reliable diagnostic and therapeutic solutions.

The background of the discussion is based on Gait Analysis implemented pre- and post-operatively (16 months meantime follow up) by Win track platform, in a prospective cohort of 150 patients with an ACL rupture and a positive Stretch test for the diagnosis of FHL. ACL reconstructions were performed simultaneously with an endoscopic tenolysis of the Flexor Hallucis Longus tendon.

Results

showed significant changes between the pre-and post-op footprints with improvement of balance, better repartition of the load, reloaded first metatarsal head and resynchronization in pro-supination.

Conclusion

FHL disrupts the stability mechanisms of the foot with serious consequences to the knee. This new paradigm leads to a better understanding of ACL injuries and opens new horizons in terms of clinical, surgical and therapeutic approaches.