What interlock nailing means in fixation
Interlock nailing, more often described in orthopaedic literature as interlocking intramedullary nailing, is an internal fixation method in which a metal nail is inserted through the medullary canal of a long bone and locked with screws above and below the fracture. The nail shares load along the bone axis, while the locking screws help control rotation, shortening, and angular deformity. For many adult femoral and tibial shaft fractures, it is a core treatment option because it provides strong internal support with less exposure of the fracture site than wide open plating. It is not, however, a universal solution. Fracture location, soft tissue injury, canal size, growth plates, infection risk, and surgeon experience all influence whether nailing, plating, external fixation, or staged treatment is appropriate.
The phrase interlock nailing is often used as search shorthand. In clinical papers, surgical references, and implant technique guides, readers will also see terms such as locked intramedullary nail, interlocking nail, interlocking intramedullary nail, and IM nail with proximal and distal locking screws. The common principle is controlled fixation from inside the bone, with screws passing through the nail to resist motion that a simple unlocked rod cannot reliably control. For broader background on fracture stabilization methods, see the site’s fixation section.
How locking screws changed intramedullary fixation
Early intramedullary devices could align a shaft fracture and share axial load, but they provided limited control of rotation and length in many fracture patterns. Locking screws changed that mechanical relationship. When screws pass through holes in the nail and through the bone cortex, the bone segments are linked to the implant. This is why modern interlock nailing is especially relevant for unstable, comminuted, segmental, and length-unstable shaft fractures.
AO Surgery Reference describes several principles that remain important in daily practice. A nail can help restore axial alignment and prevent angulation after reduction, but rotational stability usually requires proximal and distal interlocking screws. Multifragmentary fractures are not length stable, so proximal and distal locking are used to reduce shortening. In proximal or distal metaphyseal areas, where the canal is wider and the nail may have less cortical guidance, additional planning is often needed to prevent translation or angular displacement.
| Fixation element | Main role | Practical implication |
|---|---|---|
| Intramedullary nail | Shares load along the long axis of the bone | Nail length, diameter, curvature, and entry point must match patient anatomy |
| Proximal locking screws | Control rotation and segment position near the entry side | Useful in both length-stable and length-unstable patterns, depending on configuration |
| Distal locking screws | Prevent rotation, shortening, and distal segment migration | Often require fluoroscopic targeting because insertion can slightly deform the nail |
| Dynamic locking option | Allows limited axial motion in selected length-stable patterns | May support controlled compression, but it is not suitable for every fracture |
| Blocking or Poller screws | Narrow the effective canal and guide the nail path | Most relevant in metaphyseal or widened canal areas where alignment is difficult |
Where interlock nailing is commonly used
The most established indications are adult long bone shaft fractures, especially in the femur and tibia. AAOS OrthoInfo states that femoral shaft fractures are almost always treated surgically and that intramedullary nailing is the method most surgeons use for femoral shaft fractures. It also describes the nail as a rod inserted into the femoral canal, with screws above and below the fracture to maintain alignment during healing. For tibial shaft fractures, AAOS patient education similarly identifies intramedullary nailing as a common surgical method and notes that screws stabilize the nail at both ends.
In the femur, interlock nailing is used for many shaft fractures caused by high-energy trauma in younger adults and lower-energy injuries in older patients with weaker bone. In the tibia, it is often considered for displaced shaft fractures, open fractures after appropriate wound management, fractures with multiple fragments, and cases where nonsurgical treatment is unlikely to maintain alignment. These are broad patterns, not automatic indications. Patient condition, contamination, vascular status, compartment concerns, and soft tissue coverage may change both timing and technique.
Other anatomic regions require more caution. Humeral shaft nailing is used in selected cases, but it competes with plating and nonoperative care depending on fracture pattern and patient factors. Adult forearm interlocking nails have been studied, but forearm fractures place high demands on rotational restoration, so indications are narrower and technique sensitivity is high. In children and adolescents, rigid intramedullary implants must be considered carefully because growth plates can be at risk; flexible nailing or other approaches may be preferred depending on age, bone, and fracture morphology.
Planning choices that influence reduction and fixation quality
Good interlock nailing starts before the nail is opened. Planning should identify the fracture pattern, canal diameter, deformity, existing implants, open wounds, contamination, and whether the patient can tolerate definitive fixation immediately. In polytrauma or severe soft tissue injury, temporary external fixation may be used first to restore length and provide provisional stability until definitive internal fixation is safer. AAOS patient education describes external fixation as a temporary stabilizing frame in many severe femur fracture situations, especially when a longer operation is not yet appropriate.
Reduction quality is a major determinant of outcome. The nail cannot correct every deformity by itself, and a small entry-point error can translate into malalignment along the shaft. AO teaching emphasizes restoring length, angulation, and rotation before reaming and nail insertion. Closed reduction is often preferred when achievable because it can preserve fracture biology and soft tissue attachments. However, closed reduction is not always successful, particularly in delayed cases, proximal or distal fractures, or when a fragment is incarcerated in the canal. In those circumstances, limited open or mini-open reduction may be needed.
A 2023 systematic review and meta-analysis of adult femoral shaft fractures compared open versus closed reduction with intramedullary nailing. It included 12 studies and 1,346 nailing cases. The review found better union outcomes and lower nonunion and infection results in the closed-reduction group, while malalignment was lower in the open-reduction group. The authors also cautioned that findings should be interpreted in context because of confounding and a lack of high-quality studies. The practical message is balanced: preserve biology where possible, but do not accept poor alignment simply to keep the procedure closed.
Technique variables and adjuncts that matter
Several technical decisions shape the mechanical and biological behavior of an interlocked nail construct. Entry point selection is one of the most important. A suboptimal entry point can push the nail into the wrong path, increase fracture displacement, or create cortical stress. Nail diameter and length must be selected to achieve stable fixation without forcing an implant that does not match the patient’s canal or bow. AO materials specifically warn that mismatch between nail choice and long-bone anatomy can contribute to iatrogenic fracture, especially in bones with deformity or pronounced sagittal bow.
Reaming is another important variable. Reaming can allow a larger nail and may improve cortical contact, but it also affects the intramedullary environment and may not be desirable in every clinical scenario. Unreamed nails may be considered in selected indications, including certain open fracture or soft tissue situations, depending on surgeon preference and implant system. Evidence comparing reamed and unreamed techniques varies by fracture type and study design, so the choice should not be reduced to a single rule.
Locking configuration also deserves attention. Static locking is commonly used when a fracture is length unstable, comminuted, or at risk of shortening. Dynamic locking can allow limited axial compression in selected length-stable fractures, but it may be inappropriate where shortening or translation is likely. Some systems provide multiplanar or fixed-angle options to improve control in short segments. Distal locking often requires precise fluoroscopic imaging because guide attachments from the proximal end may not remain accurate after nail insertion.
Blocking screws, also called Poller screws, are useful when the metaphyseal canal is wide relative to the nail. By narrowing the available path, a blocking screw can guide the nail centrally and increase construct stiffness. A systematic review of Poller screw augmentation in long bone nailing reported low rates of several complications in the included studies, including nonunion, coronal plane malunion, deep infection, superficial infection, and secondary procedures. Because the evidence base included varied fracture types and study designs, Poller screws should be viewed as a targeted alignment tool rather than a universal add-on. See also: Implants.
Complications and evidence that deserve attention
Interlock nailing is widely used, but it still carries meaningful risks. Common concerns include malalignment, malrotation, delayed union, nonunion, infection, implant irritation, screw breakage, hardware failure, neurovascular injury, compartment syndrome in tibial trauma, and pain around the entry region. Some risks relate to the original injury rather than the implant alone. Open wounds, high-energy trauma, comminution, smoking, vascular compromise, diabetes, and delayed soft tissue coverage can all influence healing and infection risk.
Tibial nailing shows why complication counseling must be specific. A 2020 systematic review of 8,110 patients treated with intramedullary nailing for tibial shaft fractures reported anterior knee pain as the most frequent complication at 23%, followed by nonunion at 11%. It also reported that 18% of patients required at least one subsequent surgery, with screw removal for pain or discomfort reported in 9% and dynamization to promote union reported in 8%. These figures should not be applied mechanically to every patient, but they show that a technically successful nail insertion does not eliminate the need for follow-up and possible secondary procedures.
Femoral shaft fractures have a different complication profile. Union rates are generally favorable with modern nailing, but malrotation, limb length discrepancy, nonunion, and infection remain important. AAOS patient information notes that many femoral shaft fractures take 3 to 6 months to heal completely, and some take longer, particularly open or highly comminuted fractures and cases involving tobacco use. For industry readers, this matters because implant performance is only one part of fracture care. Reduction technique, biology, rehabilitation, patient factors, and surveillance are inseparable from the outcome.
| Issue | Why it happens | Risk-control focus |
|---|---|---|
| Malalignment | Entry point error, poor reduction, wide metaphyseal canal, short segment control | Preoperative planning, fluoroscopic checks, blocking screws when indicated |
| Malrotation | Rotational alignment not fully controlled before locking | Compare limb rotation, cortical profile, and intraoperative landmarks before final locking |
| Delayed union or nonunion | Biology, fracture gap, instability, infection, smoking, high-energy injury | Appropriate locking strategy, follow-up imaging, dynamization or revision when indicated |
| Infection | Open injury, contamination, soft tissue damage, systemic risk factors | Debridement, antibiotics, soft tissue management, staged fixation when necessary |
| Hardware symptoms | Prominent screws, entry-site irritation, local soft tissue sensitivity | Implant positioning, screw length accuracy, selective removal only after medical assessment |
How interlock nailing compares with plates and external fixation
Interlock nailing, plating, and external fixation are not competing slogans; they are tools for different mechanical and biological situations. Nailing places the main implant inside the medullary canal, which can provide full-length internal support through smaller approaches in many shaft fractures. Plating places the implant on the bone surface and may be preferred when a fracture extends into a joint, when precise articular reconstruction is required, when the canal is unsuitable, or when nail entry would create unacceptable risk. External fixation is valuable for temporary stabilization, severe soft tissue injury, contamination, and selected definitive indications.
The decision is often clearest at the ends of bones. Diaphyseal femur and tibia fractures frequently fit the mechanical strengths of interlocking nails. Proximal and distal fractures can still be nailed in selected cases, but they require careful control of the short segment and may benefit from modern multiplanar locking or blocking screws. Fractures that extend into the hip, knee, or ankle joint often require direct articular reduction and may be better treated with plates, screws, or combined methods. The implant choice should follow the fracture, not the other way around.
Frequently asked questions
Is interlock nailing the same as intramedullary nailing?
Interlock nailing is a locked form of intramedullary nailing. A simple intramedullary nail sits inside the medullary canal, while an interlocking nail is fixed to the bone with screws through the nail. Those screws improve control of rotation, alignment, and shortening.
Is closed reduction always better than open reduction?
No. Closed reduction can preserve soft tissue and fracture biology and is often preferred when it gives acceptable alignment. However, open or limited open reduction may be necessary when closed methods fail, when a fragment blocks the canal, or when alignment cannot otherwise be restored.
When are locking screws or nails removed?
Routine removal is not always required. AO educational materials state that intramedullary nails generally do not need removal unless the patient is symptomatic, and that removal should usually wait until the fracture has definitely united unless urgent removal is indicated. Individual decisions depend on pain, union, infection, implant position, and patient goals.
Can patients bear weight after interlock nailing?
Weight-bearing instructions depend on bone, fracture pattern, stability, soft tissue injury, implant configuration, and surgeon judgment. Some simple fractures stabilized with intramedullary fixation may allow earlier weight bearing, while comminuted, open, segmental, or biologically compromised fractures may require restrictions.
What is the main takeaway for fixation planning?
The key value of interlock nailing is its ability to combine intramedullary load sharing with screw-based control of rotation and length. Its success depends on matching the implant to anatomy, achieving reduction before final locking, protecting soft tissue biology, and monitoring for complications after surgery.