Fitting & Sizing



Completely undo Velcro straps #1, #3 and #4.


Pull up on the #2 Tendon Back Plate Cable Release Button above the Cable Tensioning Dial and pull out the #2 Tendon Back Plate as far as it will go. Then slide the X8 over your leg and center the Patellar Shell over your kneecap while bending your leg. The brace should fit snug on the sides of your knee. If it is loose or too snug, choose the appropriate, included Patellar Shell Pad to achieve a snug fit against the sides of your knee.


While holding the Tibial Shell firmly against your upper shin, attach Velcro Strap #1 locating the Tibial Strap Pad above your calf muscle and just below the crease behind your knee.


While holding the Tendon Back Plate against the back of your thigh and above the crease behind your knee turn the Cable Tensioning Dial clockwise until the cable is tight.

After adjusting the Cable Tensioning Dial to your desired amount of resistance, there should be between 0.10” (2 mm) and 1.00” (25 mm) of exposed Cable. If the distance is less than 0.10” (2 mm) or the Cable Tensioning Dial locks out, then try replacing the standard Tendon Back Plate pad with the included thicker Tendon Back Plate pads. If you still can’t achieve the proper tension in the cable, then you need a smaller brace. If the distance is more than 1.00” (25 mm) then you need a larger brace.


Attach Velcro Straps #3 and #4 and re-adjust Cable Tensioning Dial, if necessary, so that the Cable is as tight as you can make it without being too uncomfortable. The tighter you make the Cable the better knee protection you will have.

To remove the brace first remove Velcro Straps #1, #3, and #4. Then, while holding back the Cable Release Button pull the Femoral Shell away from your thigh until the cable is completely extended and remove the brace.


Everyone’s legs are different shapes and sizes and many people have different size legs. Mobius X8 Braces are completely customizable to accommodate different leg sizes and shapes.

Your braces come with two different optional thicknesses of Patellar Shell Pads so that you can get the brace to fit as snug as possible against the sides of your knees.

Many people have smaller or larger than normal upper legs and many people have smaller and larger than normal lower legs. To accommodate this Mobius offers Complete Pad Fit Kits for the X8 Braces.

For example: If you fit a Small or Medium brace, but your lower leg is relatively larger, then you could replace the Tibial Shell Pads with thinner pads from a Medium or Large Pad Fit Kit. And you could replace the lower Straps with larger Straps from a Medium or Large Strap Kit. The same can be done for the upper leg.

Your braces come with optional degrees of extension stops to limit full extension if desired. The extension stop installed on the brace is at 0 degrees, and included are 4, 8 and 12 degree stops.


Measure from the center point of the kneecap to 6 inches up the thigh. Measure the circumference of your thigh at that point. With this measurement, follow the size chart below.

• If you fall between two sizes, choose the smaller size.
• If the #2 Tendon Back Plate contacts the shells and will not tighten any further, the brace is too large for you. Using an X8 that is too large for you will not function as designed and will not protect you properly. It may also cause premature wear of the device and may void the warranty.

XS15”-17” (38-43cm)3.2”-3.8”(8.1-9.6cm)
S17”-19” (43-48cm)3.4”-4.4” (8.6-11.2cm)
M19”-21” (48-53cm)3.4”-4.4” (8.6-11.2cm)
L21”-23” (53-58cm)3.4”-4.4” (8.6-11.2cm)
XL23”-25” (58-63cm)4.2”-5.0” (10.7-12.7cm)
How to Measure the Knee


1. Injection Molded Shells

20% Glass Filled Nylon shells are designed to be flexible in places to allow the shells to conform to the users leg for better fit, comfort and stability, and designed to be rigid where necessary to resist excessive movement and provide impact resistance.

2. Forged Aluminum Parts

The Dial, Dial Fastener, Extension Stop, and Hinges are made of CNC Forged 6061 T-6 aluminum for maximum strength.

3. UHMWPE Cable

The cable is made with an Ultra High Molecular Weight Polyethylene Fiber. This material is being used in many advanced applications such as the aerospace industry and the military. It is the latest replacement material for Kevlar. It is known for its high tensile, bending and abrasion strength.

4. Tendon Back Plate

The Tendon Back Plate is uniquely designed to route the cable around the users leg in strategic locations to reinforce the main ligaments of the knee. The Tendon Back Plate is made from a special flexible Kraton material designed to grip the users leg and prevent migration.

5. Foam Padding

The Foam Padding is made from closed cell ethyl vinyl acetate (EVA) foam. The EVA foam pads are designed to conform to the users unique leg shape providing maximum comfort and control while gripping the users leg and preventing migration. Closed cell EVA Foam won’t absorb moisture (sweat), so they are odorless and easy to clean..

6. Straps

The velcro straps are designed to be comfortable and fully adjustable. Thermo Plastic Rubber (TPR) Pull Tabs are durable to make the straps easy to use and are numbered to prompt the user to tighten the straps in the correct order to ensure proper fit.

7. Extension Stops

The braces come with optional degrees of extension stops to limit full extension if desired. The extension stop installed on the brace is at 0 degrees, and included are 4, 8 and 12 degree stops.

Cable Replacement Kit


The cables of the X8 Knee Brace are fully replaceable. All of the necessary parts are included in our kit.

RX perscription