Finite element analysis of the foot: model validation and comparison between two common treatments of the clawed hallux deformity.
BACKGROUND
Clawed hallux is defined by first metatarsophalangeal joint extension and first interphalangeal joint flexion; it can increase plantar pressures and ulceration risk. We investigated two corrective surgical techniques, the modified Jones and flexor hallucis longus tendon transfer.


METHODS
A finite element foot model was modified to generate muscle overpulls, including extensor hallucis longus, flexor hallucis longus and peroneus longus. Both corrective procedures were simulated, predicting joint angle and plantar pressure changes.


RESULTS
The clawed hallux deformity was generated by overpulling: 1) extensor hallucis longus, 2) peroneus longus + extensor hallucis longus, 3) extensor hallucis longus + flexor hallucis longus and 4) all three together. The modified Jones reduced metatarsophalangeal joint angles, but acceptable hallux pressure was found only when there was no flexor hallucis longus overpull. The flexor hallucis longus tendon transfer reduced deformity at the metatarsophalangeal and interphalangeal joints but may extended the hallux due to the unopposed extensor hallucis longus. Additionally, metatarsal head pressure increased with overpulling of the extensor hallucis longus + flexor hallucis longus, and all three muscles together.


CONCLUSIONS
The modified Jones was effective in correcting clawed hallux deformity involving extensor hallucis longus overpull without flexor hallucis longus overpull. The flexor hallucis longus tendon transfer was effective in correcting clawed hallux deformity resulting from the combined overpull of both extensor and flexor hallucis longus, but not with isolated extensor hallucis longus overpull. An additional procedure to reduce the metatarsal head pressure may be required concomitant to the flexor hallucis longus tendon transfer. However this procedure avoids interphalangeal joint fusion.
RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering, Department of Veterans Affairs, Seattle, WA, USA.
Vara
V
Isvilanonda
Evan
E
Dengler
Joseph M
JM
Iaquinto
Bruce J
BJ
Sangeorzan
William R
WR
Ledoux
D000328:Adult; D001835:Body Weight; D002102:Cadaver; D002356:Cartilage / Q000473:pathology; D020342:Finite Element Analysis; D005528:Foot / Q000033:anatomy & histology / Q000601:surgery*; D037801:Hammer Toe Syndrome / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D008022:Ligaments / Q000473:pathology; D008297:Male; D008422:Materials Testing; D008683:Metatarsophalangeal Joint / Q000601:surgery; D008962:Models, Theoretical; D009985:Orthopedics / Q000379:methods; D011312:Pressure; D013709:Tendon Transfer / Q000379:methods; D013710:Tendons / Q000473:pathology; D013718:Tensile Strength