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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 5  |  Issue : 1  |  Page : 33-36

Hexapod orthogonal periarticular slack-wire stabilization technique: Surgical tip for accurate orthogonal metaphyseal frame mounting


Department of Surgical Sciences, Division of Orthopaedic Surgery, Faculty of Medicine and Health Sciences, Stellenbosch University, Tygerberg Campus, Tygerberg, South Africa

Date of Web Publication23-Aug-2019

Correspondence Address:
Dr. Henry Sean Pretorius
Department of Surgical Sciences, Division of Orthopaedics, Faculty of Medicine and Health Sciences, Stellenbosch University, Tygerberg Campus, Tygerberg
South Africa
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jllr.jllr_5_19

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  Abstract 

Introduction: The use of hexapod circular external fixators in the treatment of various orthopedic conditions has become more common in recent years. One of the principle mounting requirements is that the fixator is orthogonally aligned to the mechanical axis of the limb. This creates the optimal mechanical environment for bone formation as any forces exerted on the fixator are transmitted as axial forces to the limb while eliminating unwanted motions such as rotation and shear. We describe a method to reliably obtain orthogonal mounting of periarticular rings during hexapod circular external fixator application. The technique is fast, accurate, and uses components readily available on all hexapod external fixator systems. Methods: The “hexapod orthogonal periarticular slack-wire stabilization (HOPSS) technique” uses a untensioned/slack wire as the second fixation element following the transverse reference wire. A wire fixation bolt is attached to the ring, and a second wire (slack wire) is placed through the wire fixation bolt to allow insertion in an antero–posterior direction. The wire is advanced through the near cortex and onto the far cortex after which the wire fixation bolt can be tightened and a final image intensifier check can be done. The technique can be used for the application rings to the metaphysis of long bones. Discussion: Orthogonal mounting for Ilizarov all-wire frames has been a crucial part of the surgical technique and has long been accepted as it promotes axial micromotion that supports callus formation and union and eliminated parasitic motion at the bone ends. The described technique uses readily available instruments and components to assist with perfect orthogonal mounting. Conclusions: The hexapod orthogonal periarticular slack-wire technique is a simple method for obtaining more accurate orthogonal mounting. It is quick and effective and does not require any additional equipment.

Keywords: Circular external fixator, hexapod, orthogonal


How to cite this article:
Pretorius HS, Plessis RD, Ferreira N. Hexapod orthogonal periarticular slack-wire stabilization technique: Surgical tip for accurate orthogonal metaphyseal frame mounting. J Limb Lengthen Reconstr 2019;5:33-6

How to cite this URL:
Pretorius HS, Plessis RD, Ferreira N. Hexapod orthogonal periarticular slack-wire stabilization technique: Surgical tip for accurate orthogonal metaphyseal frame mounting. J Limb Lengthen Reconstr [serial online] 2019 [cited 2019 Sep 15];5:33-6. Available from: http://www.jlimblengthrecon.org/text.asp?2019/5/1/33/265360


  Introduction Top


The use of hexapod circular external fixators in the treatment of various orthopedic conditions has become more common in recent years. To achieve adequate correction of complex deformities through the use of these devices requires comprehensive preoperative planning, meticulous surgical technique, and a rigorous postoperative management strategy.[1],[2],[3]

One of the principle mounting requirements is that the fixator is orthogonally aligned to the mechanical axis of the limb. This creates the optimal mechanical environment for bone formation as any forces exerted on the fixator are transmitted as axial forces to the limb while eliminating parasitic motions such as rotation and sheer.[4],[5] Orthogonal mounting followed by perfectly aligned radiographs further ensures accurate analysis of deformity and frame mounting parameters to be inputted in the hexapod software.[6],[7]

To achieve this alignment, the classic Ilizarov technique uses ring blocks with tensioned fine wires that are perpendicular to the mechanical axes of the respective limb segments, resulting in an orthogonal frame, where the long axis of the frame is aligned with the long axis of the limb.[2],[4] Hexapod circular external fixators are usually constructed with a single ring attached to each limb segment proximal and distal to a fracture or osteotomy. This is either done with an initial reference wire or half pin followed by a second fixation point in another plane. This technique requires careful placement of the second fixation point to not lose the orthogonal alignment. Using half pins as the initial reference, the fixation point has the advantage of providing more stability to the ring than a reference wire. When ring placement to a short periarticular segment is required, accurate placement of the reference half pin can be demanding, especially in the sagittal plane. Most surgeons would, therefore, use a reference wire, where a tensioned transverse wire is placed parallel to the joint line in the coronal plane. When this wire is connected to the ring, it creates an axis that the ring can rotate around. This often makes it difficult to align this ring with the mechanical axis in the sagittal plane and maintaining the alignment while placing a second fixation element can be difficult.

We describe a method to reliably obtain orthogonal mounting of periarticular rings during hexapod circular external fixator application. The technique is fast, accurate, and uses components readily available on all hexapod external fixator systems.


  Methods Top


The “hexapod orthogonal periarticular slack-wire stabilization technique”

The hexapod orthogonal periarticular slack-wire stabilization technique uses an un-tensioned/slack wire as the second fixation element following the transverse reference wire. The technique can be used with the application of full or partial rings to the distal femur, distal humerus, proximal tibia, and distal tibia.

Ring application starts with the placement of a transverse reference wire, parallel to the joint surface in the coronal plane. The ring is mounted on the wire, and the wire is tensioned as prescribed. The fluoroscopy machine is then placed in the medial-lateral plane. The limb is positioned that the fluoroscopy beam is orthogonal to the ring in the sagittal plane. The ring is then rotated on the transverse wire axel and aligned perpendicular to the mechanical axis of the bone segment in the sagittal plane [Figure 1]. A wire fixation bolt is attached to the ring and a second wire (slack wire) is placed through the wire fixation bolt to allow insertion in an antero–posterior direction [Figure 2]. The wire is advanced through the near cortex and onto the far cortex after which the wire fixation bolt can be tightened, and a final image intensifier check can be done. The ring is now aligned in both the sagittal and coronal planes which makes it possible to carefully add fixation elements from any acceptable angle without losing the position of the ring [Figure 3] and [Figure 4]. At this stage, the fixation is tenuous and excess force should not be applied to the ring as this may lead to bending of the wires and loss of orthogonal alignment. Frame application can now be completed as per the standard operative technique.
Figure 1: Lateral radiograph showing orthogonal alignment of a ring to the distal tibia

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Figure 2: Periarticular slack-wire placed in antero–posterior direction through the anterior cortex of the proximal tibia

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Figure 3: Proximal ring position maintained with hexapod orthogonal periarticular slack-wire stabilization technique

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Figure 4: Lateral radiograph and the clinical picture showing orthogonal alignment of a ring to the distal humerus

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  Discussion Top


Hexapod fixators are often used in patients with tumors, trauma, and limb reconstruction, which makes periarticular fixation inevitable.[8],[9],[10],[11] The application techniques that are used for these problems all require a stable orthogonal frame with some notable exceptions (e.g., frames for joint contractures, where one ring of the frame cannot be applied orthogonally due to extreme deformity). In obese patients, especially orthogonally mounted frames can be difficult to achieve (e.g., Blount's disease).

Orthogonal mounting for Ilizarov all-wire frames has been a crucial part of the surgical technique and has long been accepted as it promotes axial micromotion that supports callus formation and union and eliminated parasitic motion at the bone ends. Although Ilizarov all-wire frames have shown better mechanobiology than frames with hybrid fixation, both devices have less parasitic movements at the bone ends compared to monoliteral fixators.[2],[5]

The advent of hexapod circular fixators has not negated the need to accurate orthogonal mounting of the fixator to the axis of the relevant bone segment. Data acquisition for hexapod deformity correction mandates accurate mounting and perfect subsequent radiographs. When this is achieved, all radiographic deformity and mounting measurements are “in plane” with the bone and minimizes errors due to forced perspective and Pythagorean parallax. Imaging strategies such as the “Silhouette technique” have been described to assist with improving postoperative radiographs for the planning of correction, but the accuracy of intraoperative mounting still lags behind.[6] The described technique uses readily available instruments and components to assist with perfect orthogonal mounting and has become the standard technique to periarticular hexapod ring mounting at our institution.

Risks and benefits

Benefits

  1. Orthogonal ring mounting is achieved
  2. As the frame is mounted orthogonally, a final X-ray check needs only to be done when all the fixation elements have been placed. This saves time and minimizes radiation exposure
  3. Simple technique that uses equipment that is available on the set and does not require specialized equipment
  4. Low cost – the use of a single k-wire.


Risks

  1. With overzealous drilling of the slack wire, the posterior (or anterior cortex in the setting of the distal humerus) could be breached with potential damage to neurovascular structures
  2. Excessive traction on the frame may bend the slack wire, with loss of orthogonal alignment
  3. The slack wire may be placed through the joint capsule, but as this is temporary, it should not cause any long-term complications.



  Conclusions Top


The hexapod orthogonal periarticular slack-wire technique is a simple method for obtaining more accurate orthogonal mounting of periarticular hexapod circular external fixator rings. It is quick and effective and does not require any additional equipment.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Watson JT, Gold S, Louie K. Circular external fixation for pilon fractures. Tech Orthop 2015;30:132-41.  Back to cited text no. 1
    
2.
Lenarz C, Bledsoe G, Watson JT. Circular external fixation frames with divergent half pins: A pilot biomechanical study. Clin Orthop Relat Res 2008;466:2933-9.  Back to cited text no. 2
    
3.
Ferreira N, Aldous C. The pathogenesis of tibial non-union. Journal of Orthpaedics 2016;15:51-9.  Back to cited text no. 3
    
4.
Gessmann J, Citak M, Jettkant B, Schildhauer TA, Seybold D. The influence of a weight-bearing platform on the mechanical behavior of two Ilizarov ring fixators: Tensioned wires vs. half-pins. J Orthop Surg Res 2011;6:61.  Back to cited text no. 4
    
5.
Bronson DG, Samchukov ML, Birch JG, Browne RH, Ashman RB. Stability of external circular fixation: A multi-variable biomechanical analysis. Clin Biomech (Bristol, Avon) 1998;13:441-8.  Back to cited text no. 5
    
6.
Wright J, Sabah SA, Patel S, Spence G. The silhouette technique: Improving post-operative radiographs for planning of correction with a hexapod external fixator. Strategies Trauma Limb Reconstr 2017;12:127-31.  Back to cited text no. 6
    
7.
Ferreira N, Birkholtz F. Radiographic analysis of hexapod external fixators: Fundamental differences between the taylor spatial frame and trueLok-hex. J Med Eng Technol 2015;39:173-6.  Back to cited text no. 7
    
8.
Menon DK, Dougall TW, Pool RD, Simonis RB. Augmentative Ilizarov external fixation after failure of diaphyseal union with intramedullary nailing. J Orthop Trauma 2002;16:491-7.  Back to cited text no. 8
    
9.
Ferreira N, Marais LC, Aldous C. Mechanobiology in the management of mobile atrophic and oligotrophic tibial nonunions. J Orthop 2015;12:S182-7.  Back to cited text no. 9
    
10.
Ferreira N, Marais LC, Serfontein C. Two stage reconstruction of septic non-union of the humerus with the use of circular external fixation. Injury 2016;47:1713-8.  Back to cited text no. 10
    
11.
Tomić S, Bumbasirević M, Lesić A, Mitković M, Atkinson HD. Ilizarov frame fixation without bone graft for atrophic humeral shaft nonunion: 28 patients with a minimum 2-year follow-up. J Orthop Trauma 2007;21:549-56.  Back to cited text no. 11
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]



 

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