Last Updated on May 27, 2025
Nail dynamization is an orthopedic intervention used to stimulate fracture healing in long bones treated by the interlocking nail procedure, where union is delayed.
It involves modifying a previously statically locked intramedullary nail by selectively removing one or more interlocking screws, thereby converting the fixation from static to dynamic (see explanation below).
This controlled mechanical adjustment promotes axial micromotion at the fracture site to encourage biological activity of healing.
Nail dynamization is most commonly employed in the femur and tibia. The procedure is considered a minimally invasive, cost-effective strategy for managing delayed union or early nonunion.
In this article, we explore the principles, indications, procedural steps, outcomes, and limitations of nail dynamization.
Static vs Dynamic Locking
Static Locking
When locking screws are inserted at both the proximal and distal ends of the intramedullary nail, both bone fragments are rigidly fixed to the nail. This creates a static relationship—there is no movement between the nail and the bone. The fracture site remains rigidly stable, with no telescoping or axial movement possible.
Dynamic Locking
If the nail is locked only at one end, only that fragment is fixed to the nail. The other end of the nail is free within the medullary canal. On weight bearing, the fixed fragment and nail move together, but at the free end, the nail can slide within the medullary cavity. This “telescoping” effect causes the nail to slide proximally until the fracture fragments are brought together, allowing controlled compression at the fracture site. This sliding movement repeats with every loading event, such as during walking.
This is an example of dynamic locking.
What is need for Dynamic Locking
In actual practice, the nails are locked in the static mode because it provides better fixation, rotational control, and better control over the fixed bone. However, it doesn’t allow the axial loading of the fracture.
Most of these fractures unite, but some of these fractures are slow to unite and may not show enough union by 8-12 weeks. At this point, it may be worthwhile to convert this static mode into a dynamic mode so that fracture surfaces contact with the loading and get a better chance of union.
This conversion from static to dynamic locking is termed nail dynamization.
Dynamization of femoral nail and the tibial nail is commonly done because these are weight-bearing bones and predictable loading behavior can be expected.
What is Nail Dynamization?
Nail dynamization refers to the process of converting a statically locked intramedullary nail into a dynamically loaded construct by removing one or more interlocking screws from one of the ends of the nail (proximal or distal).
History of Nail Dynamization
The concept of dynamization gained prominence in the late 1980s and early 1990s as a biologically favorable method to promote healing in fractures that showed sluggish progress after nailing [1].
Dynamization means different methods (i.e. applied cyclic micromotion and progressive axial loading) of altering the fixation of fractures during the bone healing process to improve external callus formation. [2]
This concept was introduced in a fixator but extended to interlock nails and called nail dynamization.
Early studies demonstrated that converting a nail from static to dynamic could lead to union without the need for more invasive interventions like bone grafting or exchange nailing. [2]
As we know that, there are two transverse screws slots on either end of the interlocking nail. Earlier, all the screw slots were circular and to dynamize both the screws were removed [or one if only one slot was used in the index surgery].
This provided dynamization but also left a fragment without any rotational control because there was no fixation to the bone on account of both screws being removed. This could lead to rotational malalignment.
It would be better if we could dynamize as well and retain the rotary control. This problem was solved by an oval slot for screws.
Modern nails have an oval slot or dynamic locking screw hole along with static locking screw hole or circular hole. See the image below. The nail used is a femoral nail.
When both the slots are filled by transverse screws, the nail is in static mode.
However, if we remove static locking screw or the crew from the circular slot, we get a dynamized nail which is fixed to bone and offers rotary control as well.
At the same time, it also allows the nail to move with loading, leading to desired dynamization.
Of course, the extent of dynamization is limited by the oval slot length, but then only a few millimeters of movement is required in most cases.
How Does Nail Dynamization Work?
Load Sharing and Axial Micromotion
The dynamization permits controlled shortening or movement of the fractured bone under physiological loads. This dynamic axial movement
- Enhances mechanical stimulation at the fracture site,
- Facilitates bridging callus formation,
- Transforms a biologically inactive fracture into an active healing environment.
Stress Transfer
In static nailing, the implant bears a significant portion of mechanical stress. This can delay the transition of load to the healing bone. Dynamization shifts some of this stress to the callus, encouraging remodeling and maturation.
Controlled Collapse/ Fracture End Contact
Dynamization allows controlled fracture collapse, reducing any residual gap between bone ends and improving surface contact—an essential condition for osteogenic activity and endochondral ossification.
Indications for Nail Dynamization
Nail dynamization is typically done in cases where fracture healing is delayed but the mechanical environment remains favorable.
The most common indication of nail dynamization is a delayed union, where the fracture is uniting slowly than usual. Nail dynamization is also effective in nonunions. [3]
Best results are obtained in fractures of the mid-diaphyseal region and no angular deformity, and the patient must be able to bear weight post-procedure to allow axial loading.
Presence of healing signs like early bridging callus, no signs of implant loosening (peri-implant radiolucency), and absence of end resorption will favor the success.
Contraindications to Nail Dynamization
- Active Infection or Osteomyelitis
- Segmental Bone Loss or Critical Gap
- Malalignment or Angular Deformity
- Implant Failure or Loosening
- Fracture Too Close to Interlocking Hole
- Noncompliant Patients
How is Nail Dynamization Performed?
Preoperative Planning
- Timing: Dynamization is routinely not required. It is considered only for fractures that are healing slowly.
Dynamization should be carried out only if the fracture is not showing signs of consolidation between 8-12 weeks. There is no known role of dynamization after 6 months. - Assessment: Confirm absence of infection, implant failure, or deformity. Evaluate fracture location, alignment, callus formation, and screw position.
Spiral, long oblique, and comminuted fractures are at risk of shortening by dynamization. The dynamization is more suited to transverse fractures.
- Weight-Bearing Ability: Ensure the patient can mobilize post-procedure to generate dynamic loading.
- Choosing Which Screw to Remove
- Midshaft fractures: usually the proximal screw
- Distal third fractures: the proximal screw (screw from longer fragent is removed. A shorter unscrewed fragents is difficult to control and may lead to deformity)
- Proximal third fractures: the distal screw
Operative Technique
- Performed under fluoroscopic guidance.
- A small incision is made over the selected screw.
- The screw is carefully removed using standard instrumentation.
- Confirm screw removal and retained nail position radiographically.
Postoperatively, weight-bearing is begun immediately in local surgeries and after the effect of regional anesthesia is over.
Outcomes of the Dynamization of nail
When carefully selected and appropriately timed, nail dynamization has demonstrated favorable results in long bone diaphyseal fractures managed with intramedullary nails.
Reported union rates after dynamization vary from 54%, though different studies have reported the efficacy of nail dynamization to be 19-82 %.[3] Another study has reported a union rate of 66 %.[4]
Highest success is observed in mid-diaphyseal femoral and tibial fractures with early signs of delayed healing but no significant bone loss or malalignment.
The radiological union is reported to take about 5 months from index surgery in case of dynamization [4]
Exchange nailing generally offers higher union rates overall (84%) but is comparable to dynamization.
However, nail dynamization is minimally invasive and is generally the preferred first choice in case of delayed union/nonunion that fits its selection criteria.
Complications
Malalignment
Removing interlocking screws may lead to angular deformity or rotational malalignment, particularly in fractures with inadequate cortical contact.
This is more common when the fracture was borderline stable even before dynamization.
Limb Shortening
In fractures with a residual gap or comminution, dynamization may allow overcollapse, resulting in limb length discrepancy, especially in femoral shaft fractures.
Nail Migration
Without adequate screw control, proximal or distal nail migration may occur. This can irritate nearby soft tissues or joints, and occasionally necessitate revision surgery.
Nonunion Despite Dynamization
Not all cases of nail dynamization proceed to union. Some will fail to unite and require additional surgeries like exchange nailing, bone grafting, or augmentative plating, may be required.
Hardware Failure
Prolonged weight-bearing after screw removal can lead to concentration of mechanical load on the remaining hardware, increasing the risk of implant fatigue or nail breakage, particularly in large or heavy patients.
Recent Advances
A recent study has reported that the addition of shock wave therapy in dynamized nails increases the chances of union. Shock wave therapy consists of acoustic waves.
Some modern intramedullary nails include slots or dynamization holes that permit controlled sliding without needing screw removal. Other nails with elescopic mechanisms or dynamizable locking bolts are able to provide fracture compression while maintaining alignment. These allow surgeons to plan for dynamization at the time of initial nailing, reducing the need for a second surgery.
References
- De Bastiani G, Aldegheri R et al. 1984. The treatment of fractures with a dynamic axial fixator. J Bone Joint Surg; 66B: 535-45.
- Orthofix. (n.d.). The concept of dynamization. Orthofix ABS. Retrieved May 26, 2025, from https://abs.orthofix.it/blog/the-concept-of-dynamization/
- Vaughn J, Gotha H, Cohen E, Fantry AJ, Feller RJ, Van Meter J, Hayda R, Born CT. Nail Dynamization for Delayed Union and Nonunion in Femur and Tibia Fractures. Orthopedics. 2016 Nov 1;39(6):e1117-e1123. [PubMed]
- Vaughn JE, Shah RV, Samman T, Stirton J, Liu J, Ebraheim NA. Systematic review of dynamization vs exchange nailing for delayed/non-union femoral fractures. World J Orthop. 2018 Jul 18;9(7):92-99. [PubMed]
- Stolberg-Stolberg J, Fuchs T, Lodde MF, Roßlenbroich S, Garcia P, Raschke M, Everding J. Addition of shock wave therapy to nail dynamization increases the chance of long-bone non-union healing. J Orthop Traumatol. 2022 Jan 8;23(1):4. [PubMed]
