Hello and welcome to HCM, A bruise behind the knee with small lump formation can be due to a number of causes. Trauma is the most common possibility. Have you sustained trauma in recent past? If yes then trauma is the most probable cause. If trauma is not present the bruise can be due to connective tissue disorder, platelet disorders etc. The lump associated with bruise can cause compression of the nerves passing from that compartment. The numbness experienced in calf and toes can be due to the nerve compression caused by the lump. Since, the tests showing up some platelet abnormality, further platelet function tests need to be done to assess the cause of platelet dysfunction. Alkaline phosphatase is an enzyme which is released by liver, bone and placenta. The origin of the alkaline phosphatase enzyme has to be known to know the cause of its increase. Clinical correlation is also required. Thanks and take care Dr Shailja P Wahal