Bone bank in Orthopaedics

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Bone Bank in Orthopaedics

Definition

A bone bank is an organized system for the procurement, processing, testing, storage, and distribution of bone tissue (allografts) for use in orthopaedic and other surgical procedures. Bone banking began several decades ago when surgeons first stored surgical discard bone — primarily femoral heads from joint replacement surgery — for use in spinal fusions and other procedures. Early practices were informal (unmonitored freezers, no donor testing, no consent). Today, bone banks are registered and accredited facilities that operate under strict regulatory and quality standards.

Sources of Bone for a Bone Bank

Source	Details
Surgical discard (living donors)	Femoral heads removed during total hip arthroplasty — most common source; donor is screened, tested, and must give informed consent
Deceased donors (cadaveric)	Provide a wider range of bone types including whole bones, osteoarticular grafts

Processing of Banked Bone

Both surgical discard and deceased donor bone undergo similar processing:

Removal of extraneous tissue — blood, marrow, and soft tissue removed by high-pressure pulse washing
Antibiotic soaking — tissue soaked in antibiotic solutions
Bacteriologic culturing — at collection, during processing, and before freezing
Lipid removal — ethanol soaks used to remove lipid content (for demineralized/lyophilized preparations)
Sterilization — most bone is sterilized by low-dose irradiation; ethylene oxide has been eliminated due to adverse recipient reactions
Preservation — by freezing (−60°C to −150°C) or freeze-drying (lyophilization)

Note: Ethylene oxide for end-sterilization has been largely abandoned after reports of adverse reactions in recipients.

Types of Allograft Bone from a Bone Bank

1. Fresh Allograft

Highest immunogenicity — greatest risk of disease transmission
BMP preserved → osteoinductive
Rarely used due to risks

2. Fresh-Frozen Allograft

Less immunogenic than fresh
BMP preserved → osteoinductive
Stored at −60°C to −150°C
Most commonly used structural allograft form

3. Freeze-Dried (Lyophilized) Allograft — "croutons"

Least immunogenic — lowest risk of disease transmission
Least structural integrity
BMP depleted → purely osteoconductive
Lyophilization also reduces immunogenicity and infectivity

4. Demineralized Bone Matrix (DBM)

Produced by acid extraction of inorganic components
Retains proteins and growth factors (BMP-2, BMP-7)
Minimally osteoinductive, osteoconductive — but no structural support
Variability in BMP content between batches/manufacturers leads to inconsistent clinical results

Bone Graft Properties

Three mechanisms by which bone grafts stimulate healing:

Mechanism	Definition
Osteoinduction	Recruits, proliferates, and differentiates host mesenchymal stem cells into osteoblasts (BMP-dependent)
Osteoconduction	Acts as a passive scaffold for host cells; structural framework
Osteogenesis	Direct formation of new bone by cells within the graft material

Autograft provides all three properties. Allograft from a bone bank typically provides osteoconduction primarily; some osteoinduction if BMP is preserved (fresh/fresh-frozen).

Immunogenicity of Allograft Bone

Bone possesses antigens primarily from cell surface glycoproteins
Classes I & II cellular antigens in allograft are recognized by host T-lymphocytes
Primary rejection mechanism is cellular (not humoral)
Cellular components contributing to antigenicity:
- Marrow cells — incite the greatest immunogenic response
- Endothelium, reticular activating cells
Extracellular matrix antigens: type I collagen (stimulates both cell-mediated and humoral responses), proteoglycans, osteopontin, osteocalcin
Hydroxyapatite does NOT elicit an immune response
Because processing removes blood, marrow, and extraneous tissue: ABO matching is not required
Exception: Large osteoarticular grafts may contain residual RBCs → Rh-compatible tissue recommended for Rh-negative females of childbearing age

Disease Transmission Risk

Route	Approximate Risk
Blood transfusion (HIV)	~1 per 500,000 units
Frozen bone allograft (HIV)	< 1 per 1 million

Donor screening is the most important factor in preventing viral transmission
No cases of HIV from fresh-frozen bone allograft have been reported since 2001
Most sensitive screening test: Nucleic Acid Amplification Testing (NAAT)
Allografts screened for: HB surface antigen, HB core antibody, HCV, HIV

Clinical Indications for Banked Bone (Allograft)

Fracture surgery — filling voids after elevation of depressed articular segments (tibial plateau, calcaneal, pilon, posterior acetabular wall fractures)
Structural support — e.g., fibular strut allograft along calcar in proximal humeral fractures to prevent screw penetration/collapse
Revision arthroplasty — replacement of failed prosthetic joints; impaction bone grafting techniques
Spinal fusion surgery
Bone cyst packing (benign lesions)
Maxillofacial and alveolar bone reconstruction
Tumor surgery — replacement of resected bone in osteosarcoma
Nonunion treatment — usually combined with autograft (not used in isolation, as osteoinductive stimulus is insufficient)
Ligament/tendon reconstruction — tendon and cartilage allografts for knee repair

Autograft vs. Allograft (Bone Bank) Comparison

Feature	Autograft	Allograft (Bone Bank)
Osteogenic potential	High	Absent
Osteoinductive	Yes	Variable (fresh/fresh-frozen)
Osteoconductive	Yes	Yes
Donor site morbidity	Yes (increased blood loss, pain)	None
Disease transmission	None	Rare but possible
Immunogenicity	None	Low (after processing)
Supply	Limited	Unlimited
Surgical time	Longer	Shorter
Incorporation	Faster	Slower

Accreditation and Quality Standards

Modern bone banks operate under accreditation bodies (such as the American Association of Tissue Banks — AATB in the USA). Requirements include:

Informed consent from all donors
Serological and microbiological testing of all donors
Controlled storage conditions (monitored temperature)
Traceability — detailed records of source donor and recipient for follow-up
Validated processing and sterilization protocols

Sources:

Rockwood and Green's Fractures in Adults, 10th ed. 2025 — Chapter on Bone Graft and Bone Graft Substitutes
Miller's Review of Orthopaedics, 9th Edition
Henry's Clinical Diagnosis and Management by Laboratory Methods — Musculoskeletal Tissues

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