‘Hallux rigidus‘ is a condition in which the big toe (‘hallux’) is rigid (‘rigidus’) or less flexible than what is normally required for movement at the big toe joint (‘first metatarsophalangeal joint’) when walking. By far the most common cause of hallux rigidus is osteoarthritis of that joint. Osteoarthritis is such a common cause of hallux rigidus that you can often see the two terms, ‘osteoarthritis’ and ‘hallux rigidus’ used interchangeably. The condition is painful because of that limited range of motion in the joint is all used up when walking. As the joint is pushed to its end range of motion, that jamming becomes painful. This will cause pain and inflammation the joint.
One way to deal with a painful hallux rigidus is to use the the rigid carbon fibre inserts or insoles to restrict the motion about the joint by making the shoes stiffer. By making the shoes stiffer with these rigid inserts that are only 1.0-1.2mm thick, the big toe joint does not have to flex or bend as much reducing the pressure on the joint and helping with the symptoms. These carbon fiber plate are very rigid and flat and has only a small amount of flex or bend. The research evidence is that they do help improve the symptoms of a painful joint in those with hallux rigidus.
For those with hallux rigidus you can use either the Morton’s extension version or the full width version as both can help. The Morton’s extension version allows a more normal motion of the joints on the lateral side (the 2nd to 5th metatarsophalangeal joints) whereas the full width version does limit the motion of those lessor joints as well as the big toe joint.