Dual-Motion Ankle Support Joint
by Lecturer Nattapong Polharn, CPO, Sirindhorn School of Prosthetics and Orthotics
Patients with hemiplegia often face mobility challenges, such as foot drop and equinovarus (inward ankle twisting), resulting in instability while walking, increased energy expenditure, and a higher risk of falls—particularly on uneven surfaces. Conventional ankle-foot orthoses (AFOs) partially address these issues but lack the flexibility for natural movement.
This research introduces a newly developed, patented ankle joint capable of bi-planar motion, allowing movements in both the sagittal plane (dorsiflexion/plantarflexion) and the frontal plane (inversion/eversion). The device is further enhanced with an internal shock-absorbing system to improve stability on uneven terrains. This innovative design aims to restore stable and natural-like walking for hemiplegic patients.
Importance of Bi-Planar Motion and Shock Absorption
Lateral ankle movement plays a critical role in maintaining balance on uneven surfaces. Restricted motion in this plane increases torque on the knee and hip joints, leading to higher energy demands, greater instability, and an elevated fall risk. Additionally, shock absorption during the heel-strike phase of walking is crucial for reducing joint stress and ensuring smooth gait transitions.
Traditional AFOs, such as Tamarack joints and AFOs with oil dampers, have limitations in supporting bi-planar movement and providing adequate shock absorption in all scenarios. These constraints make walking, especially on uneven surfaces, challenging for users of these devices.
Features and Design of the Patented Joint
The patented joint incorporates dual-axis rotation, enabling motion in both sagittal and frontal planes. It also includes an adjustable spring-based shock absorption system tailored to patient needs. Constructed from high-quality stainless steel, the joint offers durability for long-term use.
Performance testing compared the patented joint to conventional AFOs by evaluating parameters such as walking speed, center of gravity (COG) movement, and ground reaction force (GRF) patterns on both even and uneven surfaces.
Impressive Results
The patented joint demonstrated superior performance, significantly enhancing stability and walking speed. Key findings include:
- COG Movement: The new joint ensured smooth and balanced COG shifts between left and right sides.
- Walking Speed: Patients achieved the highest walking speeds using the new joint, with average speeds on uneven surfaces exceeding those with other devices.
- Shock Absorption: The internal spring system effectively reduced impact forces during heel strikes, resulting in smoother gait transitions and minimized stress on other joints.
This groundbreaking development offers a promising solution for hemiplegic patients, enabling more stable and natural mobility across diverse terrains.
