Knee cap injury is generally the result of a tripping fall while walking. The sudden loss of balance unlocks the knee from the straight position. Thus, while falling the knee cap is the first to strike the ground. The knee cap can also be injured by the impact of the dashboard of a car during a vehicular accident. Other than this certain sports also result in knee cap injuries if adequate protective gear is not worn. Knee cap injuries cause severe pain (knee cap pain), especially during bending of the knee for activities like walking or squatting. It is quite surprising how injury to such a small bone can cause so much disability !

Knee Cap Injury Types

Patella fracture or broken knee cap (Picture 1) can be simple or complex depending on the resulting pieces of the bone. A simple patella fracture is generally with 2 or 3 parts, which remain close to each other. This can be treated with a plaster cast from thigh to the ankle with the knee in extension or straight. Since the pieces are not displaced the fracture heals in 4-6 weeks. Sometimes, if the pieces of bone are displaced far apart from each other, it is treated by surgically holding the pieces of bones together using a steel wire. This is called tension band wiring (Picture 2).

Picture 1: Patella Fracture

(Source: Wikimedia Commons)

Picture 2: Patella Fracture Surgery

(Source: Wikimedia Commons)

A complex patella fracture is when the knee cap breaks into several small pieces, which cannot be reconstituted surgically. In this case, the pieces of broken patella have to be surgically removed from the body. This surgery is called patellectomy, and is associated with weakness during kicking movement called as extensor lag.

Patella dislocation occurs due to a sideways force on the knee cap, which breaks the restricting ligaments of patella and displace it sideways. The reflex forceful contraction of the quadriceps muscle locks it in this position and prevents it from coming back to its normal position. This is a highly painful condition and has to be treated immediately. A delay in treatment causes accumulation of blood in the knee joint, with resulting destruction in knee joint soft tissues (cartilage and ligaments) and restriction of knee movements. Even after the knee cap is brought in the normal position, the leg has to be kept in a plaster cast from thigh to ankle with the knee straight. This helps in healing of the injured ligaments and prevention of further episodes of knee dislocation. If this is not done the knee cap remains vulnerable to unrestricted and haphazard movement (patellar maltracking), which leads to recurrent dislocations and later degenerative disease of the patella like chondromalacia patellae or runner’s knee.

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Article reviewed by Dr. Greg. Last updated on October 6, 2010