Increased walking speed isn't uncommon in leg amputees using a prosthesis. A prosthesis is an artificial limb or part of a limb. Changing the walking speed may be a way to compensate for the uneven gait pattern that develops when using a prosthetic device. By walking faster, the person shortens the stride length and equals out both sides.
When walking, the person with a prosthesis tends to shift the weight over to the normal or intact leg. The problem with this strategy is that over time, the nonamputated knee absorbs the force and is at increased risk for osteoarthritis.
Gait training and/or adjusting the prosthesis may help your husband even out the load on both legs and avoid future injury. A physical therapist can help you with this problem.