The leg shortening can be reduced by a raised shoe. Shortening itself usually does not provoke back pain but when it is as marked as you describe it can. Even reducing the shortening by half will help significantly. However the pain at rest will not be addressed by reducing limb shortening. The lumbar spine itself needs to be investigated. You may have incurred a crush fracture at the time of the accident. If the pain persists in spite of the above, you need to attend a pain management programme. Taking strong painkillers over a long time reduce their effect and after a while can actually increase your vulnerability to pain. Other approaches should then be explored.