Amputation is often not required in -
Amputation may, very rarely, be preferred in a case with a long-standing discharging sinus, especially if the sinus undergoes a malignant change.

Amputation 

Amputation is a procedure where a part of the limb is removed through one or more bones.
Disarticulation is a procedure where the limb is removed through a joint.
Indications of amputation
Indications of amputations may be absolute or relative :-

A) Absolute indications

Gas gangrene
Diabetic gangrene
Irreparable loss of blood supply due to trauma or disease
Peripheral vascular disease (Burger's gangrene)

B) Relative indications

Trauma
Tumors
Severe loss of function of limb
Nerve injuries
Congenital anomalies


Overall most common cause of amputation is trauma (injury) to a limb.
Gas gangrene
Buerger's
Chronic osteomyelitis
Diabetic gangrene