ISSN 2398-2942      

Fracture fixation: interlocking nail


Synonym(s): Locking nail, locked nail


  • Interlocking nail (ILN) fixation is a method of fracture repair that capitalizes on the inherent strengths of intramedullary (IM) pin fixation. From an overall biomechanical standpoint, a fixation device is strongest when it follows the central axis of the long bone. As the device is moved away from the central axis, the device is less able to withstand cyclic bending loads and is more susceptible to fatigue failure. Bone plates Fracture fixation: plate and, to a greater extent, external skeletal fixators Fracture fixation: external skeletal fixator , because they are distant to the center of the bone, have increased loads placed on them and are therefore biomechanically less stable. Obviously there are techniques that allow those devices to be used successfully but the weakness, nevertheless, exists.
  • Intramedullary pin fixation Fracture fixation: pin effectively counters bending forces; however, rotational and shear forces are not neutralized by IM pins, necessitating the use of supplemental devices such as cerclage wires Fracture fixation: wire , or external skeletal fixators. Cerclage wiring requires an open approach to the fracture site and are applicable only to simple fracture configurations that can be anatomically reconstructed. External skeletal fixators present their own set of problems including issues with pin placement and postoperative maintenance. An ILN combines the inherent strength of a centrally located device with rotational and shear control provided by locking screws or bolts placed transversely through holes in the proximal and distal ends of the nail.
  • Interlocking nails are indicated for fractures of the diaphysis of the humerus, tibia, and femur Femur: head and neck fracture fixation. Simple and comminuted fractures can be repaired using ILN technology. Interlocking nails can be used for treatment of fracture nonunions but attention must be given to other aspects of fracture nonunion management such as debridement of fibrous tissue and cancellous bone grafting. The use of ILN fixation for treatment of open or infected fractures is somewhat controversial but if other aspects of open fracture management, eg debridement, bacterial culturing, and antibiotic therapy are addressed, ILN fixation can be used effectively. On the other hand, ILN fixation should be avoided if a fracture is grossly infected and cannot be converted into a healthy wound prior to fracture stabilization, if a segmental fracture pattern is present, or if there is significant vascular and/or soft tissue injury. Such fractures are better treated with external fixation as the definitive method of stabilization.
  • Numerous ILN systems have been developed for use in human beings. None of these systems are practically applicable to dogs and cats due to size of nails and cost restraints. One commercially available system exists in the United States that is specifically designed for veterinary patients; more are offered in other countries. The system consists of the nail that is a modified Steinman pin, bolts, and instrumentation to implant the nail. The nail has a trocar point on one end, a key-lock connection on the opposite end, and is made of surgical stainless steel Interlocking nail fixation 01: key lock combination and trochar point. One or two transverse holes are present on each end of the nail to allow bolts or screws to pass through the bone and nail to control rotation and shear. Nails with one hole are used when the fracture site is so close to the metaphysis that two bolts cannot be placed without a bolt entering the fracture site. Interlocking nails are currently manufactured in four diameters (4.0, 4.7, 6.0, and 8.0 mm) and varying lengths.
  • Instrumentation for placing the nail consists of reamers Interlocking nail fixation 02: reamer , extensions Interlocking nail fixation 03: extensions , alignment guides Interlocking nail fixation 04: alignment guides , guide sleeves Interlocking nail fixation 05: guide sleeves , and instruments for placing bolts or screws. The use of bolts has largely replaced the use of screws in the nail, the screws were prone to breaking or bending and as they do not form a tight fit with the nail they allowed a significant amount of rotation. The bolts form a much tighter fit in the nail hole and in addition they have a larger core diameter so they are significantly stronger and therefore less prone to complication. The reamers are used to prepare the medullary canal for placement of the nail. Long and short extensions are made for coupling the nail to the alignment guide and the guide is used to allow precise placement of the locking screws. Placement of the bolts is achieved using a trocar; various guide sleeves; and a drill and screwdriver. Additionally a tap is provided if standard bone screws are used in place of bolts.
  • It should be remembered that with closed approaches or open approaches where the fracture has been minimally disturbed, anatomic reconstruction is not the goal but rather functional bone alignment. Some surgeons advocate anatomic reconstruction of the fracture with supplemental fixation devices such as cerclage wire prior placement of the nail. In general, this approach defeats one advantage of ILN, minimal disruption of the fracture site. Additionally, ILN are very strong and mechanically sound and the need for anatomic reconstruction is generally unnecessary.


  • Interlocking nails are useful for diaphyseal fractures of the femur, tibia, and humerus.


  • Biomechanically rigid fixation:
    • Relatively inexpensive implant costs.
    • Can be placed through closed or limited open approaches.
  • Useful for some open fractures and nonunion fractures.


  • Expensive instrumentation:
    • Use limited to diaphyseal fractures of the humerus, femur, and tibia.
    • Steep learning curve for use.


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  • The prognosis for healing is generally very good and dictated primarily by the factors associated with the fracture.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Nanai B & Basinger R R (2005) Use of a new investigational interlocking nail supplement in the repair of comminuted diaphyseal tibia fractures in two dogs. JAAHA 41 (3), 203-208 PubMed.
  • Basinger R R & Suber J T (2004) Two techniques for supplementing interlocking nail repair of fractures of the humerus, femue, and tibia: results in 12 dogs and cats. Vet Surg 33 (6), 673-680 PubMed.
  • Duhautois B (2003) Use of veterinary interlocking nails for diaphyseal fractures in dogs and cats: 121 cases. Vet Surg 32 (1), 8-20 PubMed.
  • Dueland R T, Johnson K A, Roe S C et al (1999) Interlocking nail treatment of diaphyseal long-bone fractures in dogs. J Am Vet Med Assoc 214 (1), 59-66 PubMed.
  • Roush J K, McLaughlin R M (1999) Using interlocking nail fixation to repair fractures in small animals. Vet Med 94 (1), 46-52 VetMedResource.

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