What is this?

Periosteal reaction, or periostitis, is an inflammatory response that produces new bone formation and is due to nonspecific bacterial infections or traumatic injury (Weston et al. 2009) 

What causes this?

Periostitis is non-specific in that it can arise from a number of local infections or trauma (Weston 2009). It is most common in the tibia due to the thin barrier between the bone and skin. Even though it is non-specific, it is a useful indicator of community health; high prevalence within a population is generally indicative of unhealthy living conditions associated with dense population, poor hygiene and/or poor sanitation practices (Larsen 2015).  

How do bioarchaeologists study this?

Periosteal reactions leave lesions on the outerlayer of long bones called the periosteum of long bones. Periosteal reactions were scored as absent (1) or present (2) for each individual, and on a scale on each long bone from one to seven depending on the severity of the lesion. For example, a score of one indicates no lesions present, a score of two indicates a mild lesion marked by longitudinal striations and a score of six indicates periostitis with associated pus-draining holes (Steckel et al. 2005).

Periostitis Scoring Method (Steckel et al. 2005)

Scoring methods for periostitis (Shackel et al. 2005).