ISSN 2398-2950      

Fracture fixation: interlocking nail


Synonym(s): ILN


  • 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 is 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 mid diaphyseal fractures of femur Femur: fracture, tibia and humerus. Simple and comminuted fractures can be repaired using ILN technology but their use if particularly suited to a mid diaphyseal comminuted fracture. 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, 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.
  • There are several commercially available ILN systems that are specifically designed for veterinary patients. The systems generally consist of the nail that is modified Steinman pin, bolts and instrumentation to implant the nail. The Innovative Animal Products Interlocking nail is the system that has been used most widely in the cat with published results. 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 pin . One or two transverse holes are present on each end of the nail to allow bolts 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. The sizes of Interlocking nails that are suitable for cats are currently 4.0, 4.7 mm diameter 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 guide , 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 to 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 most useful for diaphyseal fractures of the femur in the cat. They can also be used for tibial fractures in large cats, and proximal humeral fractures in large cats.

Feline femur

  • The use of interlocking nails for stabilization of cat femoral fractures has been described (Endo1998, Larin 2001, Duhatois 2003), Basinger 2004). The interlocking nail has been used with more frequency in the femur compared to all the other long bones in the cat. It is an ideally shaped bone being straight and with a fairly uniform diameter. In one study the most common length of interlocking nail used in the cat was 91 mm (with a range from 79 mm to 101 mm), the 4.7 mm nail was used in 11 cats and the 4.0 mm in only one, however the 4.0 mm nail was only introduced towards the end of the study (Larin 2001). It was also noted that it was significantly easier to place the 4.0 mm nail compared to the 4.7 mm when the isthmus was intact, so the latter may be a better option for the cat (Larin 2001). Only one implant complication occurred in this series, this involved a broken proximal screw and resulted in a functional non-union.

Feline humerus

  • The use of a n interlocking nail for stabilization of cat humeral fractures has been described (Moses, Lewis 2001, Duhatois 2003). Due to the narrow size and lack of intramedullary canal in the distal humerus of the cat this implant is mainly useful for proximal to mid diaphyseal fractures. There should be room to place two screws distal and proximal to the fracture, with the middle screws placed a minimum distance, equivalent to one screw diameter, from the fracture line.

Feline tibia

  • The use of an interlocking nail for stabilization of six feline tibial fractures has been described by Duhatois (2003) as part of a large retrospective study involving nail use in dogs and cats. From the information obtained from the study no complications occurred with the use of interlocking nails in the feline tibia. When compared to its use in other long bones the interlocking nail has been used relatively infrequently in the tibia in the cat. This is most likely related to size as although the feline tibia is a relatively straight bone it narrows distally, so with the current range of interlocking nail sizes the nail can only be used in large cats with fractures involving the mid to proximal third diaphysis.


  • 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 femur, tibia and humerus.
    • Steep learning curve for use.


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


  • 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.
  • Díaz-Bertrana M C, Durall I, Puchol J L et al (2005) Interlocking nail treatment of long-bone fractures in cats: 33 cases (1995-2004). Vet Comp Orthop Traumatol 18 (3), 119-126 PubMed.
  • 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.
  • Moses P A, Lewis D D, Lanz O I et al (2002) Intramedullary interlocking nail stabilization of 21 humeral fractures in 19 dogs and one cat. Aust Vet J 80 (6), 336-343 PubMed.
  • Larin A, Eich C S, Parker R B et al (2001) Repair of diaphyseal femoral fractures in cats using interlocking intramedullary nails: 12 cases (1996-2000). JAVMA 219 (8), 1098-1104 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 PubMed.
  • Endo K, Nakamura K, Maeda H et al (1998) Interlocking intrameduulary nail method for the treatment of femoral and tibial fractures in cats and small dogs. J Vet Med Sci 60 (1), 119-122 PubMed.

Related Images

Want more related items, why not
contact us

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field

 Security code