Keywords
Absorbable implants - Orbital fractures - Follow-up studies
INTRODUCTION
There are many different types of materials that can be used in the reconstruction
of the orbit. Surgeons can choose either autologous or alloplastic materials, and
each material has its own benefits and disadvantages [[1]]. Absorbable plates and screws have a few advantages over metal plates and screws.
These materials undergo biological degradation, and therefore they do not interfere
with normal growth and do not need to be removed. However, these materials usually
dissolve after 9 to 15 months following insertion and delayed enophthalmos may occur.
Also, the use of these materials may trigger a foreign body reaction or cyst formation
[[2]].
Al-Sukhun et al. [[3]] reported that absorbable implants are reliable for large (>2 cm2) inferior orbital wall bony defects. They concluded that absorbable materials provide
adequate strength to support the orbital contents during the period of bone healing.
However, we found that long-term follow-up computed tomography (CT) showed expanded
orbital volume without enophthalmos in some cases.
In this study, we report the two-year follow-up results of onlay implanting of absorbable
materials in the treatment of medial orbital wall fractures based on morphometric
studies of the orbital wall and morbidity due to enophthalmos. We focused on the following
two points: 1) morphometric analysis of the orbit, that is, the volumetric changes
in the orbit and the condition of the reconstructed medial orbital wall, and 2) the
postoperative clinical enophthalmos.
METHODS
Between May 2008 and October 2010, 44 patients were diagnosed with isolated medial
orbital wall fractures by CT scans. All of the patients had pure medial orbital wall
fractures. The patients who had impure orbital wall fractures or combined medial and
inferior orbital wall fractures were excluded from the study. Among these 44 patients,
35 were males. The mean age was 31.6 years (range, 15 to 56 years). All of the patients
underwent an operation by a single surgeon for reconstruction of the medial orbital
wall via retrocaruncular incision with absorbable mesh plates (Inion CPS mesh plate,
Inion, Tempere, Finland). Out of the 44 patients, 20 patients were followed up and
postoperative CT scans were taken for more than 2 years postoperatively. We calculated
the volume of the expanded orbital tissue from CT scans using simple linear measurements
[[4]]. The height of the medial orbital wall defect (a) was measured using the coronal
views, the length of the medial orbital wall defect (b) using the axial views, and
the degree of medial displacement of the herniated orbital tissue (c) using both the
axial and coronal views. The expanded orbital volume through the medial orbital wall
defect was measured using this formula (volume=πabc/6), assuming that the shape of
the dislocated tissue was hemi-ellipsoid ([Fig. 1]).
Fig. 1 Calculation of herniated orbital volume
(A, B) The herniated orbital volume through the medial orbital wall defect was measured
using the formula πabc/6, assuming that the shape of the dislocated tissue was hemi-ellipsoid.
a, the height of the medial orbital wall defect; b, the length of the medial orbital
wall defect; c, the degree of medial displacement of the herniated orbital tissue.
We compared the expanded orbital volume between the preoperative CT and postoperative
CT. Also, the presence of postoperative enophthalmos was assessed by performing a
photographic analysis by two different medical observers. Globe position was assessed
grossly by direct visual inspection of the preoperative and postoperative clinical
photographs. A worm's-eye view facilitated a gross determination of the axial globe
position. The photographs were horizontally compensated before analysis. The evaluation
scale consisted of four grades from 0 to 3, as follows: grade 0, no enophthalmos;
grade 1, mild enophthalmos; grade 2, moderate enophthalmos; and grade 3, severe enophthalmos.
If two medical observers had different opinions regarding the patient's grade, the
average score was used. Hertel's exophthalmometer was used as an ancillary method
to measure enophthalmos based on medical records of the ophthalmology department.
Analysis of preoperative clinical enophthalmos was not included in this study due
to post-traumatic swelling.
Statistical analysis
Statistical comparison between the preoperative expanded orbital volume and the postoperative
herniated orbital volume was performed using the Mann-Whitney U test. Statistical
significance was accepted at the 5% level.
RESULTS
None of the patients had complications related to the absorbable mesh plates such
as infection, palpable migration, or extrusions of mesh plates during long-term follow-up.
We compared the volume of expanded orbital tissue between the preoperative and postoperative
CT scans ([Table 1]). The mean expanded orbital volume was 1.36±0.88 mL and 1.32±0.94 mL in the preoperative
and postoperative CT scans, respectively. Among 20 patients, only one patient (patient
No. 2) showed mild enophthalmos postoperatively ([Table 2]). The expanded orbital volume decreased from 1.36 mL preoperatively to 1.32 mL postoperatively;
however, the difference was not statistically significant (P=0.118). The postoperative
CT scans showed a well healed medial orbital wall, and the integrity of the ethmoid
sinus was well preserved. However, there was an overall increase in the orbital volume
compared to the normal orbit, and the medial orbital wall was displaced medially ([Fig. 2]). Postoperative CT scans showed that the medial rectus muscle was located more symmetrically
compared to the preoperative CT scans. The medial rectus muscle was located almost
at the homologous position in the reconstructed orbit and the normal orbit. A vague
shadow of the scar band was observed between the medial rectus muscle and the reconstructed
medial orbital wall ([Fig. 2]).
Table 1 Expanded orbital volume on preoperative and postoperative computed tomography
scans
a)The difference was not statistically significant, P=0.118.
Table 2 The clinical degree of postoperative enophthalmos was evaluated by medical
observers. Hertel's exophthalmometer data was also analyzed
a)Only 1 patient showed mild enophthalmos.
Fig. 2 The location of the medial rectus muscle
The medial rectus muscle (white arrow) was located at the homologous position in the
reconstructed orbit and the normal orbit, and a vague shadow of the scar band (dotted
white arrow) was observed between the medial rectus muscle and the reconstructed medial
orbital wall.
Case 1
A 31-year-old female (patient No. 1) had a left medial orbital wall fracture. The
expanded orbital volume was calculated to be approximately 1.85 mL. Nine days after
trauma, the swelling improved and the patient showed mild enophthalmos. Medial wall
reconstruction with an absorbable mesh plate was performed. The 2-year follow-up CT
scan showed an asymmetric orbit but the enophthalmos was corrected ([Fig. 3]).
Fig. 3 Case 1, medial orbital wall reconstruction
(A) Preoperative computed tomography (CT) showed a medial orbital wall fracture on
the left side. (B) An immediate postoperative CT scan. The absorbable mesh plate was
located in an adequate position. (C) Postoperative CT at the 2-year follow-up showed
a well healed medial orbital wall, but both orbits showed asymmetry. (D) Nine days
after trauma, swelling subsided and mild enophthalmos was detected. (E) Clinical photograph
at the 2-year follow-up showed that enophthalmos was corrected.
Case 2
A 27-year-old male (patient No. 2) suffered blunt trauma and developed a right medial
orbital wall fracture. The expanded orbital volume was approximately 3.5 mL. Eight
days after trauma, the medial wall was reconstructed with an absorbable mesh plate.
The 2-year follow-up CT scan showed orbital asymmetry and grade 1 enophthalmos was
noted at the right side ([Fig. 4]). Hertel's exophthalmometry showed 2 mm of mild enophthalmos.
Fig. 4 Case 2, medial orbital wall reconstruction
(A) Preoperative computed tomography (CT) showed a medial orbital wall fracture on
the right side. (B) Postoperative CT at the 2-year follow-up showed a well healed
medial orbital wall, but both orbits showed asymmetry. (C) Eight days after trauma,
swelling had subsided and mild enophthalmos was detected. (D) Clinical photograph
at the 2-year follow-up showed mild enophthalmos of 2 mm, but the patient was satisfied
with the results.
DISCUSSION
Recently, the incidence of medial orbital wall fracture diagnosis has been increasing
due to the invention of diagnostic tools such as CT scans. The importance of surgery
for treating medial orbital wall fractures tends to be overlooked because crucial
clinical symptoms such as limitation of eye movement are rare. Moreover, it is difficult
to assess the degree of enophthalmos because of periorbital edema in the early post-traumatic
period. Yab et al. [[5]] concluded that a relatively good proportional relationship is found between enophthalmos
and medial displacement of the eyeball, but not between enophthalmos and inferior
displacement of the eyeball. Therefore, surgical correction of medial orbital wall
fractures is necessary.
Using autogenous materials for reconstruction is a good option; however, donor site
morbidity and prolonged operative time are the major concerns [[1]]. Absorbable materials have many advantages over metal or autologous materials.
They are used for pediatric craniofacial surgery because they do not interfere with
normal growth. They also do not need to be removed and can be easily contoured when
heated. However, the chief concern regarding absorbable materials is infection. Moreover,
they usually dissolve after 9 to 15 months of insertion and enophthalmos may occur
[[2]].
Various absorbable materials have been used, and most of the materials are composed
of monomers such as L lactide, D lactide, glycolide, and tri-methylene carbonate.
During the degradation phase, the monomers are metabolized into carbon dioxide and
water through the Kreb's cycle [[2]]. The characteristics and degradation rate depends on the proportion of monomers.
Ideal absorbable materials should provide appropriate strength while degrading at
an adequate rate without causing any adverse reactions. The overall degradation of
Inion does not show the extreme degradation peak that is sometimes seen in products
made from one type of polymer ([Fig. 5]). Therefore, the likelihood of degradation-related inflammatory reactions is usually
lower than that in the fast-degrading homopolymers, and very low levels of adverse
tissue reaction (-0.1%) have been reported compared to incidences of up to 46% seen
in other materials [[6]]. Macrophages and giant cells are responsible for ultimate digestion of the polymeric
debris. This is associated with a transient foreign body reaction that is not clinically
evident [[7]]. An adequate degradation rate helps to transfer the load to the healing bone progressively
since the material degrades at a rate that coincides with bone healing. In our study,
the follow-up CT scans showed well-healed orbital bones, but asymmetric orbits. The
reconstructed orbit was expanded compared to the normal orbit on the postoperative
CT scan. There was no statistically significant difference between the preoperative
herniated orbital volume and the postoperative herniated orbital volume. However,
there was one patient who developed enophthalmos during the 2-year follow-up. Al-Sukhun
et al. [[3]] reported that resorption of the absorbable implants seems to take place at a reasonable
rate with respect to the bone healing rate in orbital wall fractures. The orbital
walls ossified during the follow-up period, and bone healing seemed to take place
along the bone fragments. The material showed adequate strength to stabilize the bone
segments during the critical period of bone healing, thereby preventing displacement
of the overlying orbital contents. Even after the dissolution of the implanted absorbable
plate, the medial rectus muscle was located at an almost homologous position in the
reconstructed orbit and the normal orbit ([Fig. 2]). We considered this a sign that the implanted absorbable plate finally provided
an adequate supportive scar to the orbital contents like a "hammock" even though the
medial bony shadow was displaced medially. On the postoperative follow-up CT scans,
increased density was detected like a thin septal pattern at the medial side of the
medial rectus muscle. As discussed above, the subclinical inflammatory reaction during
biodegradation of the absorbable implants or preserved periosteum may be associated
with the formation of a scar band or de novo thin septum.
Fig. 5 Degradation rate of absorbable materials
An Inion mesh plate degrades at an adequate rate compared to fast-absorbing polyglycolide
polymer and slow-degrading poly-L-lactide polymer material.
In our study, an immediate postoperative CT was not conducted in all of the patients.
The representative case 1 patient underwent immediate postoperative CT. The immediate
postoperative CT showed the absorbable mesh plate was in an adequate anatomical position
([Fig. 3]). The preoperative expanded orbital volume due to herniation was reduced. However,
the long-term follow-up CT showed expanded volume with a fibrous scar band. On long-term
follow-up CT, the orbital contents were supported by a fibrous scar band and orbital
tissue herniation was not detected. Therefore, absorbable mesh plates might work as
internal splints for a fractured orbital wall during their degradation and the bony
healing process.
In conclusion, the use of absorbable mesh plates has a number of advantages. The absorbable
mesh plate is in an anatomical location immediately after operation. During the absorption
of the absorbable material, a fibrous scar band is formed and the medial wall is healed.
Even though the volume of the reconstructed orbit is expanded, the reconstructed medial
wall prevents orbital tissue herniation and enophthalmos. If the bony buttress fracture
(superior medial wall of the maxillary wall) is combined with a medial orbital wall
fracture, we prefer to use more rigid materials such as titanium-embedded porous polyethylene
or titanium mesh over absorbable mesh plates ([Fig. 6]). If the bony buttress is collapsed, the supporting system is disrupted and the
orbital contents sustain severe injury. Therefore, in such cases more rigid materials
are needed [[8]].
Fig. 6 The bony buttress on coronal view
The bony buttress is identical to the superior medial wall of maxillary sinus. This
structure is the bony septum between the maxillary and the ethomoid sinus (arrow).
The bony buttress is an important structure to support the medial and inferior orbital
walls.
There were some points to consider in our study. First, nowadays, there are many computer
software programs that can calculate the expanded orbital volume from CT scans. However,
the ethmoid sinus is quite irregular, and unlike the inferior orbital wall, the border
of its mucosal surface is not definite. Therefore, to evaluate medial orbital wall
fractures, a simple linear measurement is more suitable and can eliminate the subjective
bias in measuring the extent of herniation. Second, we mainly used clinical medical
observers who graded the cases using photographic analysis to evaluate enophthalmos,
and we used Hertel's exophthalmometer as an ancillary method. There are many studies
that have used Hertel's exophthalmometer to evaluate enophthalmos. However, Hertel's
exophthalmometery is criticized for its low repeatability and low accuracy. Kim and
Choi [[9]] reported that the measurement of exophthalmometric parameters by orbital CT scan
could be helpful. However, in our study, we did not use this method. When this method
is applied, the axial view is commonly used; however, it is difficult to adjust the
midline on the natural head position. Third, further studies with a larger sample
of patients are required to establish the effect of absorbable materials with certainty.
Further studies using magnetic resonance imaging for follow-up imaging would be very
helpful [[10]].
The authors used the absorbable mesh plate to correct medial orbital wall fracture
and obtained fair results such as the following: 1) no major complications, 2) the
onlay implanting may provide a supportive scar or de novo septum to the orbital contents
even after the absorbable materials have dissolved completely. Absorbable mesh plates
could be another option for reconstruction of the medial orbital wall.
