Device Lab 30

Prosthetic Limbs

The anatomical knee is intact, so the whole argument is the socket: 510 square centimetres of wall carrying a body weight that arrives with an offset, and a carbon keel that gives back some of what the step put into it.

Also called: Prosthetic Limb, Artificial Limb. Arabic: الأطراف الاصطناعية. Device Lab 30 of 69 in BMEssentia Medical City, 6 configurations.

Overview: the configurations

Transtibial prosthesis, total-surface-bearing socket and energy-storing foot

Transfemoral prosthesis, ischial-containment socket and polycentric four-bar knee

Everything the transtibial has, plus a knee with no muscle across it. Stance stability is bought with geometry alone: the four-bar puts its instantaneous centre 40 mm behind the load line and that offset is the entire safety margin.

Transfemoral prosthesis, microprocessor-controlled hydraulic knee

The same socket and the same load path, with the knee resistance modulated from sensed shank moment and knee angle rather than set at the bench. Damping goes as the inverse square of the valve orifice, so the controller has a very large authority over a very small aperture.

Transradial prosthesis, figure-of-nine harness and voluntary-opening hook

A stainless cable from a harness across the opposite shoulder to a voluntary-opening hook. Prehension is stored in rubber bands and the user pulls against them to open, so the command and the reaction travel the same wire.

How it works: the main parts

What each part does, from the Prosthetic Limbs lessons in the 3D Device Lab.

Roll-on interface liner: The liner is the only part of this device that touches skin, and it is the reason the rest of the load path is possible at all. It is a roll-on sleeve of silicone or a thermoplastic elastomer, a few millimetres thick, turned inside out and rolled on so that no air is trapped and no shear is dragged along ahead of it.
Hypobaric seal ring and expulsion valve: The seal ring and the one-way expulsion valve together are the suspension. Between them they turn the socket into a closed volume that atmospheric pressure holds on, and they are physically small out of all proportion to what they do.
Distal attachment collar and end pad: The distal attachment is where the socket stops being a shell and becomes part of a machine. It is a collar bonded or laminated into the closed end of the socket, carrying a standard four-screw interface on one face and, on the other, an end pad that decides whether the closed end touches at all.
Bench alignment and load jig: The alignment jig is a levelled bench with a slotted top, two uprights carrying reference lines, a clamp head and a dial gauge. It is the only instrument in the workshop that can hold a limb still enough for a measurement to mean anything, and it is a component of this family rather than furniture because alignment is not a property a limb has on its own.
Interface pressure-mapping array: The interface pressure-mapping array is a thin sensor film that lies between liner and socket wall, carrying a grid of sensing pads and a ribbon that leaves over the brim. It is the only instrument in this family that can see the quantity the whole device is about, and it is the only one that can show that a peak is somewhere other than where it was expected.
Modular pylon: The pylon is the tube between the socket and whatever meets the ground. It is a plain cylinder of aluminium alloy, titanium or carbon composite, thirty millimetres across, with a clamp at each end and a scale etched along it.
Four-screw pyramid adapter: The pyramid adapter is a truncated four-sided boss sitting in a matching receiver, held by four set screws at ninety degrees. It is the joint that lets a limb be angled, and it is the reason two identical sets of components can be assembled into two limbs that stand quite differently.
Energy-storing carbon keel: The energy-storing keel is a carbon-fibre leaf that runs from a clamp near the ankle forward to the forefoot and back to the heel. It is a spring, and it is the only component in a passive lower limb that gives anything back.

Common faults and what to check

Most reported device problems (FDA MAUDE)

Device problem	Reports
Mechanical Problem	170
Device Operates Differently Than Expected	82
Unintended System Motion	70
Device Handling Problem	40
Physical Resistance/Sticking	23
Break	14

Raw counts of adverse event reports for this device type (FDA product code ISW, ISY), all years. Not adjusted for the number of units in use, so they show what gets reported, not failure rates. Report text is never copied.

Planned maintenance checks

From the BMEssentia procedure library: every 12 months, about 30 minutes, electrical class II, applied part type BF.

Fitted and serviced by the prosthetist and the manufacturer; this covers the powered parts and the charger.

Check	Pass when
Socket, joints and electronics Inspect the socket, joints, electrodes and cables.	No damage; electrodes clean.
Diagnostics Run the manufacturer's diagnostic.	No fault codes.

Test instruments: Manufacturer's diagnostic software.

Recent FDA recalls

Recall	Product and reason
Z-1787-2024 2024-05-10	Ossur H / F: RKN130002, RHEO KNEE 2 YR WARRANTY, MD, CE, External lower limb prosthetic component Due to firmware issues with the prosthetic knee, there is the potential for unintended warnings and device shutdown which could result in patient falls. Root cause: Software design.
Z-1788-2024 2024-05-10	Ossur H / F: RKN130003, RHEO KNEE 3 YR WARRANTY, MD, CE, External lower limb prosthetic component Due to firmware issues with the prosthetic knee, there is the potential for unintended warnings and device shutdown which could result in patient falls. Root cause: Software design.
Z-1789-2024 2024-05-10	Ossur H / F: RKNXC0003, RHEO KNEE XC 3 YR WARRANTY, MD, CE, External lower limb prosthetic component Due to firmware issues with the prosthetic knee, there is the potential for unintended warnings and device shutdown which could result in patient falls. Root cause: Software design.
Z-1790-2024 2024-05-10	Ossur H / F: RKNXC0005, RHEO KNEE XC 5 YR WARRANTY, MD, CE, External lower limb prosthetic component Due to firmware issues with the prosthetic knee, there is the potential for unintended warnings and device shutdown which could result in patient falls. Root cause: Software design.
Z-0788-2024 2024-01-25	Ossur H / F: Power Knee, REF: PKA10001, and PKA10003 Knee batteries may need replacement with conforming batteries to ensure there isn't a failure to turn on the device, or an unexpected shutdown, which is a momentary loss of power to the knee where the user may experience. Root cause: Process control.

From the FDA recall database (openFDA), newest first, imported 2026-10-22. 27 recalls on record for this device type. Recall text is the FDA's public text; each recall links to the official record.

Learn it, see it in 3D, ask about it

Ask Essentia about the Prosthetic Limbs: answers from named sources, with the device open in its 3D Device Lab beside the answer.
The Prosthetic Limbs on the BMEssentia Platform: the Device Library course, 13 sections from physics to maintenance.
BMEssentia Medical City: Device Lab 30, the Prosthetic Limbs fully assembled in 3D, with lab tasks and the simulations.

Previous: Orthopedic Implants. Next: Cranial Drill. All 69 devices.

Ask about the Prosthetic Limbs

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