Knock-on

A knock-on (pseudoarthrosis) is characterized as a disorder of fracture healing, when bone fragments do not fuse together even in a time twice as long as the normal course of healing (until then, we are only talking about prolonged healing ). The fracture line is filled with fiber and surrounded by a fibrous sheath, that contains fluid.

Classification according to clinical findings

 * weak: unstable, with great pathological mobility, cannot bear loads
 * strong: without pathological momentum, withstands loads



Classification according to Čech and Weber

 * 1) Vital – insufficient stabilization and immobilization of the fracture, sufficient blood supply and tendency to healing.
 * 2) * Hypertrophic;
 * 3) * Normotrophic – occurs mostly in unstable osteosyntheses;
 * 4) * Oligotrophic – usually arises from overextended skeletal traction.
 * 5) Vital – insufficient blood supply, sclerotization or osteoporosis of bone ends.
 * 6) * Dystrophic;
 * 7) * necrotic;
 * 8) * defective;
 * 9) * atrophic.

The most serious form is an infected joint – it occurs in all the above-mentioned forms and can lead to limb amputation. A special example is the tibial joint in fractures of the lower leg, where the fibula heals earlier and acts as a spacer (similarly, earlier healing of the ulna acts in fractures of the radius).

related articles

 * Fracture of healing disorders
 * Malunion
 * Prolonged healing