We used finite element analysis to study the mechanical displacements at three planes of the second through fourth hammertoes during the push-off phase of gait using a new neutral or 10° angled memory alloy intramedullary implant (FDA K070598) used for proximal interphalangeal joint arthrodesis.
After geometric reconstruction of the foot skeleton from computed tomographic images of a 36-year-old man, an intramedullary implant was positioned in the virtual model at the neutral and 10° angled positions at the proximal interphalangeal joints of the second through fourth hammertoes during the push-off phase of gait. The obtained displacement results in three planes were compared with those derived from the nonsurgical foot model using finite element analysis.
These results support the successful use of either a neutral or angled implant for proximal interphalangeal joint arthrodesis, with the neutral implant yielding slightly better results.
The neutral implant reduced vertical displacement to a greater extent than did the angled implant. We also highlight the potential risk of iatrogenic curly toe when performing a proximal interphalangeal joint arthrodesis using an angled implant specifically at the fourth toe.
The first metatarsal bone is a viable source for autologous bone grafting in foot and ankle surgery and may serve as another convenient graft site to correct a flail toe deformity. We aimed to determine how progressive bone removal from the first metatarsal affects the mechanical redistribution of the foot and whether this bone removal increases the risk of fracture.
A three-dimensional finite element model developed from computed tomographic images obtained from a healthy man were used to evaluate traction stresses on the first metatarsal bone as a function of applied loads on the talus and Achilles tendon at two phases of the gait cycle (and according to the depth of bone removal).
Simulations indicated that when maximum load was applied to the Achilles tendon, tensile stress increased from 2.049 MPa in the intact foot to 5.941 MPa in the area of maximum bone harvest during the stance phase. Furthermore, as the volume of bone extracted from the first metatarsal increased, there was a redistribution of stress that differed significantly from that of the intact foot.
Although the maximum stress on the first metatarsal was not significantly affected by increasing the volume of bone harvested, the ankle should be splinted in plantarflexion during the postoperative period to eliminate the stance phase of gait and reduce the risk of metatarsal fracture.