Hallux valgus, hallux rigidus, hammer toes, metatarsal arthrosis
In a normal foot, all metatarsophalangeal and forefoot joints are in balance and bear their share of the load on the foot. The plantar fascia, a strong ligament along the sole of the foot, stabilises and holds the entire foot together uniformly by originating from the heel and attaching to all five toes (video Normal foot, images 1 and 2).
Video Normal foot, image 1 and 2: Lateral view and top view of a foot skeleton. The plantar fascia is shown in blue. This strong band of connective tissue stabilises the longitudinal arch of the foot by stretching along the sole of the foot.
In the case of a splayfoot, the hallux valgus malposition in the metatarsophalangeal joint leads to a relaxation of the plantar fascia under the metatarsophalangeal joint and is therefore functionally less stressed. The resulting additional load is compensated for by the neighbouring second ray - in particular the second metatarsophalangeal joint or the second tarsometatarsal joint.
This compensatory overload can lead to overstretching or even a tear in the plantar fascia in the area of the second metatarsophalangeal joint. As a result, a hammer toe deformity of the second toe or arthrosis of the second tarsometatarsal joint can develop (see video splayfoot, images 3 and 4).
Video splayfoot
Figure 3: Pronounced hallux valgus deformity with hammer toe deformity of the second toe and digitus quintus varus (so-called tailor's bunion) of the fifth toe. The plantar fascia no longer runs under the metatarsophalangeal joint of the big toe and small toe, resulting in a lack of tension in these areas. The reduced stability leads to overloading of the second ray. This results in stretching or rupture of the plantar fascia under the second toe, which ultimately leads to the formation of a hammer toe.
Figure 4: The lateral view of the foot shown in Figure 3 clearly shows the pronounced deformity of the second toe, which lies over the big toe. The plantar fascia shown in blue runs along the sole of the foot. There was a tear in the plantar fascia in the area of the second toe, which led to a loss of stability in this ray and ultimately to the second toe deviating over the big toe.
The aim of surgical treatment is to restore the normal biomechanical functions of the foot. The bony structure above the plantar fascia is corrected so that it runs under the metatarsophalangeal joint of the big toe and small toe and is reconstructed or refixed in the area of the second metatarsophalangeal joint (see Figures 5 and 6).
I will soon be submitting the underlying biomechanical theory and the corresponding surgical procedure to an internationally recognised specialist journal for peer review, in the same way as I have already published a paper on flat feet and fallen arches.
Figure 5: Illustration of the same foot as in Figures 3 and 4 after surgical correction. The plantar fascia now runs under the metatarsophalangeal joint of the big toe and small toe again and can therefore resume its stabilising function in the longitudinal arch of the foot. At the same time, the hammer toe malposition of the second toe was corrected by reconstructing and refixing the previously torn plantar fascia in the area of the second metatarsophalangeal joint.
Figure 6: Lateral view of the same foot as in Figure 5 after surgical correction. The second toe is back in its anatomically correct position.