Infection - Potential to spread bugs around in a joint
Recent Unstable Fractures
Pregnancy - Hormone relaxin released causing abnormal laxity in ligaments and muscles etc
Infection in a bone - Osteomyelitis
DVT - Can be a risk to anyone who's been immobilised for a significant period or post surgery, essentially thrombosis in the veins. Movement can cause the clot to come loose and potentially get stuck in lungs (pulmonary embelism), heart or brain.