System, including method and apparatus, for applying traction to a patient's limb using constant-force springs. The constant-force springs may include one or more main springs that apply a base tractive force and at least one supplementary spring that can apply a supplementary tractive force to the limb. The at least one supplementary spring may be changeable reversibly between uncoupled and coupled configurations while the base tractive force is applied continuously to the limb and without repositioning the limb, thereby providing discrete adjustment of traction force while the limb remains in traction.