In a below-knee prosthesis, the SACH (Solid Ankle Cushion Heel) foot is the most basic energy-storing prosthetic foot. Its key limitation compared to a dynamic energy-return (carbon fibre) foot is:

• A Higher incidence of socket skin breakdown
• B Reduced proprioceptive feedback to the residual limb
• C Inability to accommodate terrain changes and higher metabolic cost at fast walking speeds ✓
• D Excessive ankle plantar flexion causing back knee gait

Explanation

The SACH foot absorbs heel strike via a compliant heel wedge but returns very little energy during push-off (no stored elastic energy release). This limits performance at higher walking speeds and on uneven terrain. Dynamic energy-return feet (Flex-Foot, Seattle foot) store energy in carbon fibre keel during midstance and release it at toe-off, reducing the metabolic cost of walking by 15–25% and improving cadence. SACH feet remain appropriate for elderly, sedentary K1–K2 ambulators where cost and simplicity outweigh performance benefits.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.