Operative Treatment of Fractures — Principles of Osteosynthesis

Introduction

Operative osteosynthesis — the surgical fixation of fractures with internal or external metallic implants — is the foundation of modern fracture surgery and one of the great advances of 20th-century orthopedics. The principles articulated by the AO (Arbeitsgemeinschaft für Osteosynthesefragen) Foundation since the late 1950s — anatomical reduction, stable fixation, preservation of vascularity, and early functional rehabilitation — have transformed the outcomes of fractures that were historically managed by prolonged immobilization with high rates of stiffness and deformity. This chapter, synthesizing content from AO Principles of Fracture Management, Apley & Solomon’s, Miller’s Review, and Rockwood and Green’s, addresses the principles of osteosynthesis, the principal implant types (screws, plates, intramedullary nails, external fixators, cerclage wire and tension band), the biomechanical principles guiding their use, the specific indications and techniques, and the principles of implant removal.

Biomechanical Principles

The biomechanical environment created by fracture fixation determines the mechanism of healing. The fundamental distinction is between absolute stability (rigid fixation with no interfragmentary motion, producing direct/primary bone healing) and relative stability (controlled motion at the fracture site, producing indirect/secondary bone healing with callus). Each mechanical environment requires different implant choices and techniques. Absolute stability is achieved by lag screws (with or without protection plates), by compression plates applied with compression at the fracture site, and by tension band wiring at appropriate sites. The clinical indications for absolute stability are simple articular fractures (where anatomical reduction must be preserved through healing without any motion that could disrupt the cartilage) and certain simple diaphyseal fractures. Relative stability is achieved by bridging plates, by intramedullary nails, and by external fixators. The clinical indications are diaphyseal fractures (particularly comminuted patterns) where the natural healing with callus is preferred to direct healing. The concept of “load sharing” versus “load bearing” is also important. A load-sharing implant transmits some of the load through the bone fragments themselves; a load-bearing implant transmits the entire load through the implant. Locked plates and intramedullary nails can function as load-bearing implants when the fracture pattern does not permit reduction and direct bone contact; they function as load-sharing implants when the bone fragments are reduced and contribute to load transmission.

Implant Materials

The materials used in osteosynthesis are similar to those used in arthroplasty (see chapter on arthroplasty principles): stainless steel (316L grade for trauma implants); titanium and titanium alloys (Ti-6Al-4V); cobalt-chromium alloys for selected applications. The principal considerations include biocompatibility, corrosion resistance, mechanical properties (strength, ductility, fatigue resistance), and increasingly the imaging properties (with titanium being preferred for compatibility with MRI and CT). Biodegradable implants (polylactic acid, polyglycolic acid, and copolymers) have niche applications in selected fractures (particularly malleolar and small-fragment fractures); their use has been limited by the occasionally inadequate strength and by the inflammatory response to degradation products in some cases.

Screws

The screw is the most fundamental implant in fracture surgery. The principal types and applications include:

Screw Types Cortical screws: Designed for purchase in cortical bone. Typically 3.5 mm diameter for adult use (with smaller sizes for hand, foot, and pediatric applications), with fine threads providing purchase along the cortex of long bones. Cancellous screws: Designed for purchase in cancellous (trabecular) metaphyseal and epiphyseal bone. Typically 4.0 mm and 6.5 mm diameter for adult use, with coarser threads providing purchase in the trabecular bone. Available as fully threaded or partially threaded. Cannulated screws: Hollow screws inserted over a guidewire, allowing precise placement in difficult locations (femoral neck, talus, scaphoid). The hollow centre reduces strength compared with solid screws of similar outer diameter. Locking screws: Designed to lock into a corresponding plate hole, creating a fixed-angle construct. The screw thread engages corresponding threads in the plate hole rather than relying on screw-bone compression. Headless compression screws: Self-compressing screws with no head, designed to remain buried within bone (Herbert screw, Acutrak, others). Used for scaphoid fractures, talar fractures, osteochondral fragment fixation, and other applications where a prominent screw head would be problematic. Bioabsorbable screws: Made of degradable polymers. Useful in selected applications including malleolar fixation, syndesmosis fixation in some cases, and fragment fixation in the wrist.

Functions of Screws Screws perform three principal mechanical functions:

Compression: The classic “lag screw” technique uses a screw to compress two fragments together. The technique requires that the screw glide through the near fragment (gliding hole drilled larger than the screw thread) and engage threads in the far fragment, so that tightening the screw produces compression of the fragments. Lag screws are used for simple fracture patterns and for selected articular fractures. Position screws: A screw used to hold fragments in a specific position without producing compression. Used for syndesmosis fixation (where compression is undesirable), for ankylosis fixation in some cases, and for transfixation in some other situations. Plate fixation: Screws securing a plate to bone, providing the connection between the plate and the underlying bone.

Plates

Plates are flat metal devices applied to the surface of bone and secured by screws. The principal types and functions of plates include: Plate Types Conventional (non-locking) plates: Including the dynamic compression plate (DCP), the limited-contact dynamic compression plate (LC-DCP), the reconstruction plate, and the one-third tubular plate. These plates rely on screw-bone compression — the screw is tightened down to draw the plate against the bone surface, providing friction between plate and bone. Locking plates: A modern category in which the screw heads thread into the plate, creating a fixed-angle construct that does not require plate-bone compression for stability. The locking screw functions as a “monoaxial” external fixator pin within the bone. Locking plates are particularly useful for osteoporotic bone, periarticular fractures, and revision applications. Hybrid plates (locking compression plates, LCP): Plates with both locking and non- locking screw hole options, allowing the surgeon to select either function as appropriate to the specific fracture. Anatomical plates: Pre-contoured plates matching the anatomy of specific bones (proximal humerus, distal radius, proximal tibia, distal tibia, distal femur, etc.). The pre- contouring simplifies application and improves fit. Periarticular plates: Designed for fixation of intra-articular and periarticular fractures, with low-profile heads, multiple-angle screw options, and other features for difficult anatomy. Reconstruction plates: Highly malleable plates that can be contoured to complex anatomy (pelvic, acetabular, scapular reconstruction). Mini-fragment plates: Small plates for hand, foot, and selected pediatric applications.

Functions of Plates The mechanical function of a plate depends on the technique of application: Compression plate: Applied with eccentric drilling to produce interfragmentary compression at the fracture site as the screws are tightened. Used for absolute stability fixation of simple fracture patterns. Neutralization plate: Applied after lag screw fixation of the fracture, protecting the lag screw fixation from physiological forces during healing. Used for simple oblique and spiral fractures. Buttress plate: Applied to a metaphyseal fragment to prevent collapse under axial loading. Classical application is the medial tibial plateau fracture, where the plate resists displacement of the cortical fragment medially as the axial load is applied. Bridging plate: Applied across a comminuted fracture region without attempting anatomical reduction of intermediate fragments. The plate provides relative stability, with healing by callus formation. Used for comminuted diaphyseal fractures, the bridging plate principle preserves the soft-tissue envelope and the vascularity of intermediate fragments. Tension band plate: Applied to the tension side of a fracture, with the principle that physiological loading produces compression at the fracture site through the plate’s tension resistance. Classical application is the lateral femoral plate, where axial loading produces compression at the medial cortex through the tension band effect of the lateral plate.

Minimally Invasive Plate Osteosynthesis (MIPO) The MIPO technique, developed in the 1990s, applies plates through small incisions at either end of the fracture without direct exposure of the comminuted fracture zone. The plate is inserted in a submuscular tunnel and secured with percutaneous screws under image intensification. The technique preserves the soft-tissue envelope and the local vascularity, with documented benefits in healing rates and complication profiles for selected fractures (particularly metaphyseal and distal humeral, distal femoral, proximal tibial, and distal tibial fractures).

Intramedullary Nails

The intramedullary nail is a long implant inserted into the medullary canal of a long bone, providing internal splinting of the fracture. The principal applications are diaphyseal fractures of the femur, tibia, and humerus, with selected applications in metaphyseal fractures of these bones. Types of Intramedullary Nails Conventional (non-locked) nails: The historical type. Provides bending stability but limited rotational and axial stability. Largely replaced by locked nails in modern practice.

Locked nails: With locking screws (interlocking bolts) at the proximal and distal ends. Provides full mechanical stability including bending, axial, and rotational stability. The standard for diaphyseal fractures in modern practice. Reamed vs unreamed nails: Reamed nails involve sequential enlargement of the medullary canal with intramedullary reamers before insertion of a larger-diameter nail. Reaming improves fixation strength and the contact area between nail and bone, but releases reaming products (including potentially embolic fat and marrow contents) and disturbs the endosteal blood supply. Unreamed nails are inserted into the unprepared medullary canal, providing less mechanical fixation but with theoretical benefits in preserving endosteal vascularity. Modern practice generally favors reamed nails for most diaphyseal fractures, with unreamed nails reserved for selected indications (severe open fractures with concerns about infection, multiple traumas with concerns about reaming- induced fat embolism). Cephalomedullary nails: Specialized nails for proximal femoral fractures, with a proximal locking screw extending into the femoral head and neck. Used for pertrochanteric, subtrochanteric, and segmental femoral fractures. Retrograde nails: Inserted from the distal end of the bone (commonly used at the femur for distal femoral and certain shaft fractures, where antegrade insertion through the piriformis fossa or trochanter is difficult). Biomechanical Principles Intramedullary nails function as load-sharing devices when the fracture pattern permits cortical contact between fragments, and as load-bearing devices when comminution prevents cortical contact. The mechanical strength of the nail-bone construct depends on the nail diameter (which determines bending stiffness), the working length (the distance between the most proximal and distal fixation points), and the type and number of interlocking screws. Advantages and Disadvantages The advantages of intramedullary nailing include: preservation of the periosteal blood supply (the nail is inserted along the endosteum, which has lower vascular contribution than the periosteum for diaphyseal bone); biological fixation with healing by callus; the ability to start weight-bearing relatively early in many cases; cosmetic advantages over plate fixation; and lower rates of infection than open plate fixation in many settings. The disadvantages include: technical demands of the procedure (requirement for fracture table or appropriate positioning, image intensification, specialized instruments); the small but real risk of fat embolism syndrome with reaming, particularly in polytrauma; the potential for malreduction (the nail follows the medullary canal, which may not perfectly match the desired axis); and the limitations in metaphyseal regions where the nail provides less reliable fixation.

External Fixation

External fixation involves pins or wires inserted into bone above and below the fracture, with the pins connected externally by bars, rings, or frames. The principal types include: Linear (unilateral) external fixators: Pins inserted along one side of the limb, connected by external bars. Used for temporary stabilization of unstable fractures, definitive treatment of selected fractures, treatment of pelvic injuries, and other applications. Circular external fixators (Ilizarov, Taylor Spatial Frame): Thin wires or fine pins through bone in multiple planes, connected to circumferential rings. The configuration allows multiplanar correction and gradual adjustment. Used for limb deformity correction, limb lengthening, treatment of non-union, and complex fracture management. Hybrid fixators: Combining elements of linear and circular fixation, often with a ring at the periarticular region and linear bars in the diaphysis. Useful for periarticular fractures of the proximal and distal tibia. The principal indications for external fixation include: temporary stabilization of unstable fractures in polytrauma (“damage control orthopedics”); open fractures with extensive soft-tissue injury where internal fixation is contraindicated; pelvic ring injuries with hemodynamic instability; revision surgery with bone defects; complex non-union; deformity correction; and selected fracture types (paediatric femoral fractures in older children, certain tibial fractures with poor soft-tissue envelope). The complications of external fixation include pin-tract infection (the principal long-term concern, requiring meticulous pin-site care), pin loosening, malunion, joint stiffness, and patient discomfort with prolonged frame use.

Cerclage Wire and Tension Band Wiring

Cerclage wire is a length of wire passed around bone and twisted to compress fragments together. Used historically for transverse and oblique fractures, cerclage is now used principally as an adjunct to plate or nail fixation for specific applications (long oblique fragments, periprosthetic fractures around stems). Tension band wiring is a specific technique applied to fractures where physiological loading produces tension at one cortex and compression at the opposite cortex — most classically the olecranon and patella. The wire is applied to the tension side and converts the tensile force into compression at the fracture site. The two principal techniques are figure-of-eight tension band wiring (with two parallel K-wires through the fragment, and a figure-of-eight wire over them and around a screw or transverse pin distal to the fracture) and modified tension band wiring with various modifications.

Indications for Operative Treatment

The principal indications for operative fixation, summarized from the AO principles and other sources, include:

Articular fractures with displacement requiring anatomical restoration of the joint surface (>1-2 mm of step-off or gap). Unstable fractures that cannot maintain reduction with closed methods. Fractures with vascular injury requiring concurrent vascular repair. Open fractures of Gustilo-Anderson Grade II or higher (with selected Grade I fractures also requiring fixation). Polytrauma where rapid stabilization permits early mobilization and reduces complications. Pathological fractures through tumor or metabolic bone disease. Failed conservative treatment with non-union or malunion. Specific fracture patterns known to have poor outcomes with conservative management. Patient factors including the requirements for early mobilization, the need to avoid prolonged casting, and patient preference.

Damage Control Orthopedics

The concept of “damage control orthopedics” (DCO), developed in the 1990s, applies to the polytrauma patient in whom prolonged operative procedures may exacerbate the physiological insult of the original injury. The principle is to provide minimal initial fracture stabilization (typically external fixation), allow physiological recovery and resuscitation, and undertake definitive fracture fixation when the patient’s condition permits. The classical example is the femoral shaft fracture in a polytrauma patient with chest injury, where early definitive intramedullary nailing has been associated with worsening of pulmonary injury through fat embolism and the inflammatory cascade; instead, external fixation provides initial stabilization, with conversion to intramedullary nailing once the patient is physiologically stable. The decision between DCO and early total care (ETC, with immediate definitive fixation of all fractures) is based on the patient’s overall physiological status, with the “borderline” patient — neither clearly stable nor clearly unstable — being the principal focus of clinical decision-making.

Implant Removal

The decision to remove orthopedic implants after fracture healing is one of the more controversial areas of fracture surgery. The principal indications for removal include: Symptomatic hardware: Prominent or palpable implants producing pain or skin irritation. Particularly common with subcutaneous implants (tibial plates, olecranon hardware, malleolar hardware).

Infection: Implants colonized by biofilm-forming bacteria require removal for effective infection treatment. Patient request: Particularly in younger patients with concerns about long-term effects of implant retention. Imaging requirements: Ferromagnetic implants that interfere with MRI in patients requiring this imaging. Pediatric patients: Implants spanning physes that may impair growth. Plates spanning joints: That may produce arthritis or other long-term problems. The principal arguments against routine removal include: the risk of complications from a second operation (infection, neurovascular injury, refracture); the substantial cost and patient inconvenience; and the lack of clear evidence that retention causes long-term problems in most cases. Modern practice generally favors selective rather than routine removal, with the decision based on the specific implant, the location, the patient’s symptoms, and the patient’s preference after appropriate counseling. Specific situations warranting routine removal include: subcutaneous plates (particularly the proximal tibial, olecranon, malleolar, distal radius), particularly in young active patients; pediatric implants spanning physes; syndesmotic screws (timing debated, with current trend toward selective rather than routine removal); and infected implants.

Summary and Take-Home Points

Operative osteosynthesis is the foundation of modern fracture surgery, with the AO principles of anatomical reduction, stable fixation, preservation of vascularity, and early functional rehabilitation guiding all decisions. The biomechanical environment created by fixation — absolute stability for primary bone healing or relative stability for callus healing — must be matched to the specific fracture and clinical situation. The principal implants — screws (cortical, cancellous, cannulated, locking, headless compression), plates (compression, neutralization, buttress, bridging, tension band, with locking and non- locking options), intramedullary nails (reamed vs unreamed, with locking technology), external fixators (linear, circular Ilizarov, hybrid), cerclage wire and tension band wiring — each have specific applications and biomechanical principles. The indications for operative treatment include articular fractures requiring anatomical restoration, unstable fractures, open fractures, fractures with vascular injury, polytrauma, pathological fractures, and selected other situations. Damage control orthopedics provides initial stabilization in the unstable polytrauma patient. Implant removal is selective in modern practice, with specific indications including symptomatic hardware, infection, and certain anatomical or imaging considerations. Across all aspects of osteosynthesis, the principles of biological preservation, appropriate mechanical environment, and meticulous surgical technique produce the best outcomes.