Ankylosing spondylitis and heterotopic calcification: a case from the Prehispanic population of Buenavista del Norte (Tenerife, Canary Islands)

Skeletal remains of an adult (estimated age at death ≈ 27-30 years) Prehispanic male with fusion in the sacroiliac joints showed a heterotopic ossification consisting of a flat, 10 × 5 cm bone formation covering the posterior aspect of the right sacroiliac joint. The bones were recovered from a burial cave containing remains of 4 individuals, located on the side of a ravine, in Buenavista del Norte (NW corner of Tenerife, Canary Islands), at ≈ 450 m altitude. This individual was probably affected by ankylosing spondylitis (AS) that led to bony fusion of the pelvic bones with the sacrum, but several unusual features prompted us to compare the pelvis with those belonging to two modern individuals affected by AS (20^th century) housed at the Department of Anatomy of the school of medicine (University of La Laguna, Tenerife). The Prehispanic individual possibly suffered a pelvic fracture that caused a hematoma which underwent ossification. Some features (periosteal reaction, formation of new foramina) may also suggest a superimposed infection. The fracture altered the pelvic structure, severely narrowing the right sciatic notch, possibly causing neural and/or vascular compromise of the lower limbs. Living in a steep mountainous environment, this individual (possibly a goatherder) probably suffered a fall, that caused the fracture complicated by a severe bleeding and pelvic deformation.