Abstract
Traditional medial canthopexy techniques require transnasal access, periorbital skin incision, and/or direct canthal suturing, often yielding unpredictable outcomes. The transcaruncular canthal barb and miniplate technique is a simplified method of canthopexy that avoids these manoeuvres. 10 transcaruncular medial canthopexies were performed on cadavers with simulated naso-orbito-ethmoid (NOE) injury. Differences in mean pre-injury and post-canthopexy intercanthal distance (ICD) and palpebral aperture width (PAW) measurements were compared using a matched paired t test. Reliability between pre-injury and post-injury intercanthal distance and PAW was compared with intraclass correlation coefficients. Canalicular distortion and final implant position were assessed with post-canthopexy computed tomography (CT). There was no difference in mean palpebral aperture width (32.32 and 32.43 mm) or mean intercanthal distance (29.18 and 29.06 mm) between pre-injury and post-canthopexy groups (both p > 0.05). All intercanthal distance and PAW intraclass correlation coefficients were >0.97 ( p < 0.05). Post-canthopexy, CT scans showed canaliculus distortion in 4/10 of upper and 0/10 of lower canaliculi with all canthal barbs in the correct position relative to the plate. In a cadaver telecanthus model, medial canthopexy using the transcaruncular barb and miniplate technique reliably reduces the medial canthus and did not distort the lower lacrimal canaliculus, but may distort the upper canaliculus.
Effective repair of traumatic telecanthus has challenged surgeons for decades. Achieving an optimal outcome is difficult because, in the intercanthal region of the face, even minor shortcomings are readily perceived by others. Following medial canthal tendon (MCT) avulsion, the typical deformity of traumatic telecanthus is caused by increased intercanthal distance (ICD), shortening of the palpebral aperture width (PAW) and rounding of the medial palpebral angle ( Fig. 1 ). After disruption of the MCT attachment, contraction of the orbicularis oculi muscle may even worsen the telecanthus and palpebral deformity over time. As these structures deform, epiphora and other functional changes may result.
The goals of medial canthopexy are to restore normal canthal position along the lacrimal crest, reestablish normal palpebral shape, and preserve normal palpebral function. Since the early 20th century, the medial canthopexy technique has steadily evolved as surgeons gained better understanding of the regional anatomy and the pathophysiology of naso-orbito-ethmoid (NOE) injury ( Table 1 ). Today most canthopexies are performed with some combination of transnasal suturing and external skin bolsters popularized in the 1960s, despite their known limitations: external skin bolsters do not directly reposition the MCT ( Fig. 2 ) and can cause skin necrosis, and transnasal suturing requires dissection of the MCT as well as transnasal access to the opposite orbit. In recognition of these limitations, a variety of devices have been developed which anchor the MCT to the medial orbit, but these are difficult to use when the bone around the lacrimal fossa is fractured and unstable.
| Year reported/author | Approaches required | Laterality | Device/technique |
|---|---|---|---|
| 1946 Callahan | Cutaneous (lynch) | Unilateral | MCT wired to holes drilled in lacrimal crest |
| 1966 Mustarde, Converse and Smith, Tessier, McCarthy et al. | Coronal/cutaneous | Bilateral transnasal | Wired MCT captured and reduced with a transnasal awl |
| 1992 Shore et al., Howard et al. | Coronal/cutaneous | Unilateral | MCT sutured to miniplate placed along medial orbital wall |
| 1996 Anotnyshyn et al. | Coronal/cutaneous | Unilateral | MCT sutured to Mitek anchor inserted into ethmoid |
| 1995 Hammer | Coronal/cutaneous | Unilateral | Barb engaging MCT wired to miniplate placed along medial orbital wall |
| 2011 Engelstad | Coronal/conjunctival | Unilateral | Barb introduced through conjunctiva/caruncle |
The authors describe transcaruncular canthopexy using a barb and miniplate, which is a minor modification of a technique previously described by Hammer. This technique has two main advantages over established techniques. First, a simple barb is used to capture and reduce the MCT, eliminating the need for canthal dissection from the thin surrounding tissues. Second, because the canthus is reduced toward a miniplate or mesh that has been fixed on the medial orbital wall, this technique can be used even when there is no stable bone remaining in the NOE region.
The anatomical rationale for canthopexy can be explained as follows. The MCT ( Fig. 3 ) is the medial extent of the tarsal apparatus. It defines the normal almond shape of the palpebral fissure and it acts as a hinge for lid function, keeping the eyelids curved against the globes during lid movement. Positioned in the same plane as the orbital septum, the tarsal apparatus extends from the lateral canthus at Whitnall’s tubercle, runs through the upper and lower tarsi, then flows into the MCT where it attaches to bone surrounding the lacrimal sac and fossa. In this position, the MCT structurally supports the lacrimal drainage pathways and promotes the movement of fluid through the lacrimal system during blinking.
The common medial canthus has two major limbs anterior and posterior, and a minor superior limb ( Fig. 3 ). The prominent anterior limb of the MCT has a broad attachment to the anterior lacrimal crest and nasal bone. The posterior limb, which is the most pertinent to this technique, was not even described until 1970; it attaches along the posterior lacrimal crest and medial orbital wall.
In any medial canthopexy, the goal is to reduce the MCT medially as well as posteriorly. Simply pulling the right and left canthi toward one another will reduce telecanthus, but an additional posterior vector reduction is needed to position the lids correctly against the curvature of the eyeball.
Transcaruncular canthopexy uses the caruncle as the main external reference point for engaging the MCT. The caruncle is a transitional tissue that contains elements of both skin and conjunctiva. Anatomic studies demonstrate that the lacrimal canaliculi and the posterior limb of the MCT are both located within 3 mm of the caruncle. For this reason, a needle and wire that is directed medially and posteriorly through the caruncle should pass through the posterior limb of the MCT; and when a barb is attached to the wire, that barb should firmly engage the MCT’s posterior limb. Also, because the posterior limb is posterior to the lacrimal system, the authors hypothesized that a medial canthopexy technique that engages only the posterior limb should have minimum impact on lacrimal canaliculi shape and position.
A cadaver-based study was performed to answer the following clinical questions: ‘In a simulated MCT injury/detachment model, does transcaruncular medial canthopexy with a barb and wire restore normal palpebral dimension and canthal position?’ and ‘Does this technique alter the shape of the lacrimal canaliculi?’ Study outcomes were: palpebral (PAW and ICD) measurements; radiographic signs of significant upper or lower lacrimal canaliculi distortion; and final canthal barb and plate position. The authors hypothesized that in cadavers undergoing MCT detachment, PAW and ICD dimensions in the pre-injury and post-canthopexy groups would be similar; they also hypothesized that this canthopexy technique would not significantly affect the shape of the lacrimal canaliculi.
Materials and methods
10 medial canthopexies were performed on both sides of five fresh frozen cadaver heads ( Table 2 ). Pre-injury PAW and ICD were measured with a calliper in mm at the palpebral angles and compared to post-canthopexy dimensions. In order to assess the shape and position of the lacrimal canaliculi after canthopexy, standard bicanalicular lacrimal intubation was performed with a single silicone crawford bicanalicular intubation tube (Freda Corp, Henan, China) that would later be filled with radiopaque dye. Institutional review board approval was obtained for this study.
| Cadaver number | Gender | Age |
|---|---|---|
| 1 | F | 72 |
| 2 | F | 57 |
| 3 | F | 69 |
| 4 | F | 69 |
| 5 | M | 55 |
A standard coronal approach was made for surgical exposure of the NOE region, including the nasal bones, lacrimal crests, and medial orbit. To simulate severe NOE injury and telecanthus, all three branches of the MCT were sharply detached from bone and the lamina papyracea was fractured with a blunt instrument (Type 3 injury). Medial canthopexy was performed via a transcaruncular approach using the barb ( Fig. 4 ) and miniplate technique ( Figs 5–11 ).
Transcaruncular medial canthopexy with barb and miniplate
Two implants are required, one to engage the MCT and one to provide a stable point of reduction. The first, to engage the MCT, is a wire or suture attached to a straight needle on one end and a canthal barb on the other ( Fig. 4 ). This barb (Synthes Corporation, Paolo, PA, USA) is a low profile micro anchor-like device designed to engage the MCT. The barb is commercially available attached to a 28-gauge titanium wire and straight needle (Synthes Corporation, Paolo, PA, USA). A small Mitek anchor with suture could also be used, but its anchor may be significantly larger than a canthal barb.
The second implant, to provide a stable point of reduction, is a titanium miniplate (or orbital mesh) adapted to the contour of the medial orbital wall and stabilized to frontal bone. Once it is fixed along the orbital wall, 2.0 mm miniplate (Synthes Corporation, Paolo, PA, USA) acts as a solid point toward which the barb and MCT is reduced as the wire is pulled. The miniplate must be sturdy enough to resist deformation as the wire is pulled through it, so a thicker plate is recommended ( Fig. 12 ).
Post-canthopexy PAW and ICD dimensions were compared to pre-injury dimensions. To assess the immediate stability of the canthal reduction, a bow-string test was performed by grasping the lateral canthus with a hook and pulling laterally with a force sufficient to displace the lateral canthus lateral to the lateral orbital rim while the medial canthus was observed for displacement or loss of reduction (not pictured). The nasolacrimal tubes (crawford bicanalicular intubation tubes) were injected with contrast dye and 0.5 mm slice axial computed tomography (CT) scans with three-dimensional (3D) reconstructions were obtained ( Fig. 13 ). Radiological outcome measures were presence/absence of significant distortion or kinking of the upper or lower lacrimal canaliculi as well as position and integrity of the canthal barb and plate.
