Fracture Fixation: Plates, Screws, and Intramedullary Nails

Fracture fixation encompasses the surgical methods used to stabilize broken bones through the implantation of metal hardware, allowing controlled healing in proper anatomical alignment. The three principal constructs — bone plates, cortical and cancellous screws, and intramedullary (IM) nails — address different fracture patterns, bone segments, and patient demands. Understanding the mechanical logic behind each device clarifies why orthopedic surgeons select one approach over another, and how the broader regulatory and standards landscape governing orthopedic implants shapes the devices themselves. This page covers definitions, operative mechanisms, clinical indications, and the decision boundaries that guide implant selection.

Definition and Scope

Fracture fixation hardware constitutes a class of implantable medical devices regulated in the United States by the Food and Drug Administration (FDA) under 21 CFR Part 888, which governs orthopedic devices. Plates, screws, and IM nails each fall within Class II or Class III device classifications depending on their intended use and novelty, typically requiring 510(k) premarket notification or, for novel devices, premarket approval (PMA) before clinical use (FDA Device Classification Database, 21 CFR §888).

Bone plates are flat or contoured metal strips fixed to the outer cortex of bone with screws. They span a fracture site and resist bending, shearing, and rotational forces.

Bone screws are threaded fasteners used independently or in conjunction with plates. Cortical screws feature fine, uniform threads for dense diaphyseal bone; cancellous screws use wider, coarser threads to purchase softer metaphyseal or epiphyseal bone.

Intramedullary nails are rods inserted longitudinally through the hollow medullary canal of a long bone, typically locked at both ends with interlocking screws to control length, rotation, and alignment.

All three categories are primarily fabricated from titanium alloy (Ti-6Al-4V) or stainless steel (316L), materials evaluated against ASTM International standards — specifically ASTM F136 for surgical-grade titanium and ASTM F138 for implant-quality stainless steel (ASTM International, Committee F04).

Fractures of the type that require fixation are discussed in greater depth at Fractures: Types, Healing, and Complications, which contextualizes the injury spectrum feeding into surgical decision-making.

How It Works

Each construct achieves stability through a distinct mechanical principle:

Plates and Screws

A plate applied to bone surface can function in four main modes:

1. Neutralization — the plate shields the fracture from torsional and bending loads while a lag screw provides primary compression across the fracture line.
2. Compression — using a dynamic compression plate (DCP) or limited-contact DCP, the screw insertion angle generates interfragmentary compression, promoting primary (direct) bone healing without a visible callus.
3. Bridging (biological plating) — the plate spans a comminuted zone without attempting anatomic reduction of every fragment, preserving the periosteal blood supply and encouraging indirect (callus-based) healing.
4. Buttressing — a plate positioned perpendicular to the collapse force prevents axial displacement in metaphyseal fractures, such as tibial plateau splits.

Locking plates, in which screws thread into the plate hole itself rather than relying on plate-to-bone friction, are particularly indicated in osteoporotic bone. Locking screw torque is governed by manufacturer-specified insertion protocols, typically in the range of 1.5–4.0 Nm depending on screw diameter, to prevent stripping of the locking mechanism.

Intramedullary Nails

An IM nail exploits the natural tubular geometry of long bones. The nail is introduced through a carefully placed entry portal — the piriformis fossa or greater trochanter for femoral nails, the patellar tendon interval for tibial nails — and advanced across the fracture under fluoroscopic guidance without exposing the fracture site itself (closed nailing technique). Interlocking screws placed through drill-guide-aligned holes in the proximal and distal nail control rotation and prevent shortening. Static locking locks both ends; dynamic locking leaves one end free to allow controlled axial compression during weight bearing, used in certain diaphyseal fractures to stimulate callus formation.

Common Scenarios

Implant choice correlates strongly with fracture location and energy pattern:

The AO Foundation maintains the internationally recognized AO/OTA Fracture and Dislocation Classification, which assigns alphanumeric codes to fracture patterns and guides implant selection logic across these and other scenarios.

Decision Boundaries

The choice among plates, screws, and IM nails is governed by a structured set of criteria rather than surgeon preference alone:

Patient-Level Factors

1. Bone quality — Dual-energy X-ray absorptiometry (DEXA) T-scores below −2.5 indicate osteoporosis (National Osteoporosis Foundation), which shifts preference toward locking constructs or cephalomedullary devices with greater cortical purchase.
2. Soft-tissue envelope — Significant open fractures (Gustilo-Anderson Type III) or crush injuries may preclude plating over contaminated zones; IM nailing or external fixation staged with delayed definitive fixation is preferred.
3. Age and activity demand — Pediatric patients with open physes require implants that avoid growth plate traversal, directing surgeons toward flexible nails (e.g., TENS — titanium elastic nails) rather than rigid locked nails. Pediatric orthopedic principles are addressed at Pediatric Orthopedics.
4. Comorbidities — Vascular disease, diabetes, or prior infection at the operative site elevates the risk of hardware failure and nonunion, catalogued by the American Academy of Orthopaedic Surgeons (AAOS) clinical practice guidelines.

Fracture-Level Factors

1. Location within the bone — Diaphyseal fractures favor IM nails; metaphyseal and articular fractures favor plates because IM nails cannot adequately control short periarticular segments.
2. Fracture pattern — The AO/OTA classification distinguishes Type A (simple), Type B (wedge), and Type C (complex/comminuted) patterns. Type C fractures at joint surfaces require open reduction and internal fixation (ORIF) with plates to restore articular congruence to within 2 mm, the generally accepted threshold for acceptable joint-surface step-off.
3. Stability after reduction — An inherently stable fracture pattern after closed reduction may be managed with functional bracing or casting, reserving hardware for patterns that cannot be held by external means. Bracing and casting as non-operative alternatives are detailed at Bracing, Casting, and Splinting.

Implant-Level Factors

Surgeons must operate within implant-specific technique guides validated through FDA clearance. Deviation from cleared indications — such as using a nail outside its approved diameter range — constitutes off-label use, a category tracked by the FDA's Medical Device Reporting (MDR) system under 21 CFR Part 803. Hardware failure events are reportable through MedWatch (FDA MedWatch Program).

Post-operative outcomes tracking increasingly relies on registries such as the American Joint Replacement Registry (AJRR) operated by AAOS, which captures revision and complication data across enrolled institutions, and the broader context of orthopedic practice covered across the orthopedics reference overview.

References

• U.S. Food and Drug Administration — 21 CFR Part 888: Orthopedic Devices
• FDA MedWatch Safety Reporting Program
• ASTM International — Committee F04 on Medical and Surgical Materials and Devices
• [AO Foundation — AO/

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