Incomplete calcification of the first tissue (soft callus) that forms between two parts of a bone after a fracture, with the result that the two parts of the bone can still move relatively to each other. If a fracture heals normally the two parts of the bone are joined together by the soft callus, then growth takes place from the internal and external bone membranes to form bone and cartilage, and finally the joint is completed with bone tissue. The commonest cause of imperfect hardening of the callus is excessive mobility of the bone, caused by a loose splint or putting a load on the bone too soon. Other causes are deficiencies in the absorption of calcium, phosphate and certain vitamins. Conditions such as osteoporosis and osteomalacia may affect bone formation, and thus bone healing. Also muscle and connective tissue can be caught between the two parts of the bone when it is set (nonsurgical^), thus preventing proper callus formation. Inflammation, quite common after a complicated fracture, can prevent normal healing. Fortunately correction of these problems can lead to normal healing even after a long time. In serious cases, surgery is used to clean up the affected area and pin the bone.