sequestration is the process by which a portion of tissue — most classically bone, but also lung or spleen — becomes separated from its surrounding healthy structure and loses its normal blood supply, forming an isolated, non-viable fragment. In its surgical/orthopedic sense, the resulting fragment is called a sequestrum, distinguished from an involucrum (the shell of new, living bone that forms around and encases the dead fragment) and from simple necrosis (cell death without physical separation from adjacent tissue). The underlying mechanism is loss of vascular supply to the affected segment — in bone, this typically follows chronic osteomyelitis, trauma, or radiation, where infection or ischemia strips the periosteal blood supply and the isolated fragment can no longer be resorbed or revascularized. sequestration can also describe a purely congenital, non-infectious process, as in pulmonary sequestration, where a mass of nonfunctioning lung tissue develops without normal connection to the tracheobronchial tree (Q33.2), or an acute hematologic process, as in splenic sequestration crisis in sickle cell disease, where blood becomes trapped in the spleen (D57 family). The term is most commonly confused with necrosis — necrosis is the death of tissue in place, while sequestration specifically implies that dead tissue has become anatomically separated from living tissue; it is also distinguished from abscess, which is a walled-off collection of pus rather than a fragment of dead tissue itself, though the two frequently coexist in chronic osteomyelitis.
The word entered English by the mid-14th century as the verb sequester, borrowed via Old French sequestrer, from Late Latin sequestrare (“to place in safekeeping, hand over to a trustee”), from Latin sequester — a neutral third party who holds disputed property until a dispute is resolved. The surgical noun sequestrum (the dead bone fragment itself) was adopted directly from the Latin neuter form and was established in English medical usage by the 18th century, describing a piece of bone “held apart” from the living tissue around it. The same root underlies the modern legal sense of sequester (isolating a jury) and connects, through the same Proto-Indo-European base, to words built on the idea of following or being placed in sequence, such as sequela (“that which follows,” a condition resulting from a prior disease or injury) and consequence.
🔀 ALIASES / ALTERNATE TERMS
Sequestrum / sequestra(noun — the physical fragment of dead tissue itself, most often bone; “sequestra” is the plural)
Sequestered(adjective/past-participle form — describes devitalized tissue that has become isolated from its blood supply, e.g., “sequestered bone fragment”)
Bronchopulmonary sequestration(clinical synonym for pulmonary sequestration; congenital, coded Q33.2)
Splenic sequestration crisis(acute hematologic form seen in sickle cell disease; life-threatening in pediatric patients — coded within the D57 family based on genotype)
🔗 RELATED TERMS
involucrum — the shell of new, viable bone that forms around a sequestrum in chronic osteomyelitis; distinguishes active chronic infection from a simple healed defect.
necrosis — shares the concept of tissue death but does not require physical separation from living tissue; sequestration is a more advanced, mechanically distinct process.
osteomyelitis — the most common underlying cause of bone sequestrum; chronic osteomyelitis with a draining sinus or sequestrum formation is the classic clinical picture coders will see on inpatient profee charts, especially jaw and skull-base cases in ENT/OMFS documentation.
debridement — the surgical mechanism, along with sequestrectomy, used to remove sequestered/necrotic tissue and promote healing.
avascular necrosis — related ischemic bone process, but typically involves a broader segment (e.g., femoral head) rather than a discrete separated fragment.
Sickle cell disease — the driving disease process behind splenic sequestration crisis; genotype (Hb-SS, Hb-SC, sickle-thalassemia, other) determines the correct D57 code family.
Osteoradionecrosis — a distinct etiologic pathway to jaw sequestrum, driven by radiation-induced vascular compromise rather than infection; still captured under M27.2.
⚠️ Coding Note:M27.2 has no 5th-character laterality subdivision — document mandible vs. maxilla and side in the operative note for surgical clarity, but the code itself doesn’t split by site or side, and it does not require sequencing behind a separate osteomyelitis code since it’s already a combination code covering osteitis, osteoradionecrosis, periostitis, and sequestrum together. Watch for undercoding when an op note documents “sequestrectomy of the jaw” or “removal of dead bone” without the word “osteomyelitis” spelled out — M27.2 still applies per its Includes note, and skipping it in favor of a vague symptom code is a common miss on inpatient profee claims. For splenic sequestration, the sickle cell genotype (Hb-SS, Hb-SC, sickle-thalassemia, or other) drives which D57 subfamily applies — confirm genotype in the H&P or hematology consult before finalizing, since these are combination codes capturing disease, crisis, and complication in one code and don’t need a separate crisis code appended. If osteoradionecrosis is the documented etiology for jaw sequestrum, an additional external cause code (W88–W90 or X39.0) is required per the “Use Additional Code” instruction under M27.2 — this is mandatory, not discretionary, and payers will kick claims missing it.