The 51-year-old constable, who was on a single crew patrol, was called to the Ryebank area of Livingston at around 1.40pm on Wednesday when the collision occurred.
It is understood the officer was responding to a complaint about anti-social behaviour involving a motorbike in the area shortly before the incident unfolded.
It is understood that the PC has suffered extensive damage to his knee and tibia bone in his leg which will require him to undergo surgery.
A police source revealed his brave colleague may now face having to undergo knee replacement surgery in the future due to the extent of the damage.
Police Scotland yesterday (Thurs) confirmed they have arrested and charged an 18-year-old man with various road traffic offences.
Chief Inspector Alun Williams (cor), local area commander for West Lothian, said: “We have charged an 18-year-old man in connection with a number of road traffic offences after a police officer was seriously injured following a collision with an off-road motorbike on a footpath near the Ryebank area of Livingston at around 1.40pm on Wednesday April 10.
“I can confirm that a 51-year-old male officer was taken to the Forth Valley Hospital with serious leg injuries.
“The 18-year-old is expected to appear in court at a later date.”
He said: “During the school holidays and moving forward into the summer months, our local officers will continue to maintain a high-visibility presence in areas throughout West Lothian, notably where the anti-social use of motorcycles has been highlighted as a concern.
“With our partners, we continue to focus on a preventative approach, but we will actively target offenders and ensure those who commit such offences are reported to the courts.”