Which of the following are considered additive pathologies in the skeletal system?

Additive pathologies in the skeletal system refer to conditions that increase the density or mass of bones, typically requiring an increase in exposure during radiological imaging. Among the options presented, additive osteopetrosis and Paget's disease both fit this definition, as they lead to an increase in bone density.

Osteopetrosis is characterized by excessive deposition of bone, resulting in abnormally dense but fragile bones. This condition generally requires higher radiographic exposure due to the increased bone density. Paget's disease involves the abnormal remodeling of bone, which also leads to areas of increased density interspersed with areas that may be weakened, presenting a mixed pattern on imaging, yet still typically increasing overall density in affected bones.

In contrast, other listed conditions such as destructive osteoporosis and osteomalacia involve a reduction in bone density, leading to a need for lower exposure settings on imaging. Osteomyelitis and ligament injuries relate more to inflammation or associated soft tissue changes rather than changes in bone density, while fractures and bone cysts also signify bone loss or structural weaknesses rather than additive changes. Thus, the correct identification of additive pathologies rests clearly with osteopetrosis and Paget's disease.