The "flap-shaft" prosthesis for insensate feet with Chopart or Lisfranc amputations.

Background: The inevitable detachment of tendons and the loss of the forefoot in Chopart and Lisfranc amputations result in equinus and varus of the residual foot. In an insensate foot these deformities can lead to keratotic lesions and ulcerations. The currently available prostheses cannot safely counteract the deforming forces and the resulting complications.

Methods: A new below-knee prosthesis was developed, combining a soft socket with a rigid shaft. The mold is taken with the foot in the corrected position. After manufacturing the shaft, the lateral third of the circumference of the shaft is cut away and reattached distally with a hinge, creating a lateral flap. By closing this flap the hindfoot is gently levered from the varus position into valgus. Ten patients (seven amputations at the Chopart-level, three amputations at the Lisfranc-level) with insensate feet were fitted with this prosthesis at an average of 3 (range 1.5 to 9) months after amputation. The handling, comfort, time of daily use, mobility, correction of malposition and complications were recorded to the latest followup (average 31 months, range 24 to 37 months after amputation).

Results: Eight patients evaluated the handling as easy, two as difficult. No patient felt discomfort in the prosthesis. The average time of daily use was 12 hours, and all patients were able to walk. All varus deformities were corrected in the prosthesis. Sagittal alignment was kept neutral. Complications were two minor skin lesions and one small ulcer, all of which responded to conservative treatment, and one ulcer healed after debridement and lengthening of the Achilles tendon.

Conclusions: The "flap-shaft" prosthesis is a valuable option for primary or secondary prosthetic fitting of Chopart-level and Lisfranc-level amputees with insensate feet and flexible equinus and varus deformity at risk for recurrent ulceration. It provided safe and sufficient correction of malpositions and enabled the patients to walk as much as their general condition permitted.