Flat foot (pes planovalgus et abductus) and flat foot (pes planus)
The stability of the longitudinal arch of the foot is ensured by a strong, stabilising ligament along the sole of the foot, the plantar fascia (video Normal foot, Figures 1 + 2). Like a truss, the ligament prevents the overlying bony arch of the foot from flattening due to the force acting on the foot from above (red arrows).
Flat feet or fallen arches are characterised by a reduced longitudinal arch of the foot. The causes of this deformity are varied and lead to a disruption of the functional integrity between the bony arch, the joints involved and the plantar fascia. There is often a misalignment of individual foot joints, particularly the talonavicular joint or the first metatarsophalangeal joint, which „slip“ out of their physiological position. This misalignment reduces the tension in the bony arch and the plantar fascia, which ultimately leads to the arch of the foot dropping and the formation of a flat foot (see video Flatfoot, Figures 3 and 4).
Video Normal foot
Video Flatfoot
Figure 1: Lateral view of a normal foot skeleton with the plantar fascia in blue. The bony arch consists of several joints and is stabilised by the plantar fascia. The stabilising force exerted by the plantar fascia (blue arrows) counteracts the acting weight force (red arrows) and thus helps to maintain the longitudinal arch of the foot.
Figure 2: In the normal foot, the plantar fascia (blue) stretches in a fan shape along the sole of the foot and inserts into the individual phalanges. The bony arch of the foot lies above the plantar fascia and is stabilised by it.
Figure 3+4: In the case of flat foot (pes planovalgus et abductus), the 1st midfoot joint, the talonavicular joint, slips inwards (red arrow). This reduces the tension of the plantar fascia below the arch of the foot and the fascia turns outwards towards the lesser toe (blue arrow). These changes lead to instability of the longitudinal arch of the foot with consequent subsidence. As a result, the bony arch of the foot no longer lies completely over the plantar fascia, which compromises the structural integrity of the arch of the foot
Figure 5: Clinical picture of a flat foot (pes planovalgus et abductus), lateral view as in Fig. 4.
Figure 6: The longitudinal arch of the flat foot in Figure 4 was restored with a corrective fusion of the first midfoot and lower ankle joint.
Figure 7: The plantar fascia (blue) was brought back under the bony longitudinal arch of the foot by corrective fusion of the first midfoot and lower ankle joint.
In the surgical treatment of flat feet, care is taken to ensure that the bony arch of the foot is corrected again via the plantar fascia and that the tension in the plantar fascia is restored.
I had the underlying theory and the surgical procedure reviewed by experts in an international specialist journal and studied by over a thousand colleagues in foot and ankle surgery.
Read more:
Merian M, Kaim A
The Plantar Fascia Talar Head Correlation: A Radiographic Parameter With a Distinct Threshold to Validate Flatfoot Deformity and Its Corrective Surgery on Conventional Weightbearing Radiographs.
Foot & Ankle Int. 2022; 43(3): 414-425.
DOI: 10.1177/10711007211052258 PMID: 34802299