Lag screw principle to fix unstable sagittal fracture of infraorbital rim: A technical note

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Introduction
Fractures of upper midface bones have both direct and indirect effects on the function and aesthetics of face, especially the eyes.This part of facial bony skeleton has impact on globe, lower eyelid and cheek positions.Due to its anatomical position and biomechanics, orbital rim fractures are common in midface injuries (1).Proper reduction and fixation of these fractures are mandatory to achieve a good functional and aesthetic outcome.Rigid internal fixation is the gold standard for fixation of the craniomaxillofacial skeleton using miniplates (2).Low profile miniplates are preferred in the fixation of fractures around the orbit.These plates cannot withstand high forces; hence a stable anatomic reduction is needed before fixation.This is not possible in case of grossly displaced fractures especially those present in conjunction with other related fractures.Effective reduction and fixation of a grossly displaced infraorbital rim sagittal fracture using lag screw fixation (LSF) principle is discussed in this article.

Case Presentation
A young male patient diagnosed with pan facial fracture underwent open reduction and internal fixation of fractured segments in our tertiary care centre.These complicated fractures were approached through multiple facial incisions and exploring existing lacerations over the fractures.Majority of the fractures were fixed using the conventional method with titanium miniplates and screws.But left infra-orbital rim fracture was grossly displaced and required much stronger force than usual to reduce the fractured segments.Figure 1a shows the oblique fracture of the lateral segment of infraorbital rim associated with other multiple fractures of orbital rims.Even after manual reduction which was done by intra-oral elevation of the zygomatic bone using a long straight elevator, the segments were unstable and found to be impossible to fix it using low profile miniplates and screws.Hence, an unconventional method was followed to fix the fracture in a stable position.Once the reduction was achieved, a "gliding hole" was drilled on the proximal bone segment perpendicular to the surface, equivalent to the outer diameter of the screw, i.e. 2-mm.A coaxial "traction" hole was drilled in the distal bone fragment using a drill sleeve of 1.6 diameter which is equivalent to inner or core diameter of the screw.If the drilled hole is not coaxial, it may lead to fracture or shifting of the bone fragments or improper reduction.A 10-mm-long titanium screw of 2-mm diameter was glided through the "glide hole" passively to engage the "traction" hole on the distal fragment.Screw was tightened to compress the proximal fragment against the distal fragment, till a stable fixation was achieved.The proximal segment was held in place by the screw head (Figure 1b).Preoperative and post-operative computed tomographic images are shown in Figure 2a and 2b.Healing was uneventful and excellent post-operative outcome was achieved which was confirmed during regular follow up examinations.

Discussion
LSF has been described as the simplest of the rigid internal fixation techniques.It requires less implant material, limited surgical exposure and has minimal post-operative complications (3).Oblique fractures are the ideal ones to be fixed by this principle.Perpendicularly placed screw will permit maximal compression and minimal risk of shift of bone segments.At least two screws are advisable to reduce the torsional forces and displacement of the segments (4).But in our case, the medial fracture of the infra orbital rim was fixed using a miniplate, which will indirectly serve the function of the second screw.A stronger and evenly distributed compression force applied by lag screw will result in more stable fixation.Hence, it is a simple and effective method for repair of sagittal fractures of midface skeleton.It can be used alone or in combination with other rigid internal fixation devices, which will help in reducing the hardware's used and is an easier technique to achieve good post-operative results (3).

Conclusion
LSF provides excellent intra-fragmentary compression and restores the pre-morbid anatomic position of fractured fragments.The application of the technique following a proper method can help the surgeon in managing complicated displaced oblique fractures of maxillofacial skeleton.Our experience shows that LSF provides excellent stability and saves intra-operative time.

Figure 1 .Figure 2 .
Figure 1.(a) Clinical photograph showing oblique fracture of infraorbital rim.(b) Clinical photograph showing fracture segments fixed using lag screw principle