Pure Orbital Trapdoor Fractures in Adults: Tight Entrapment of Perimuscular Tissue Mimicking True Muscle Incarceration with Successful Results from Early Intervention

Abstract

Orbital trapdoor fractures (OTFs) entail entrapment of intraorbital soft tissues with minimal or no displacement of the affected bones and are almost exclusively seen in children. This article aimed to report the diagnosis and treatment of an OTF of the floor in an adult patient and to critically review the literature regarding the management aspects of this specific subset of orbital blowout fractures in adults. A 29-year-old man presented with limitations of vertical right eye movements owing to blunt orbital trauma. The patient mainly complained of double vision in upper gazes and some episodes of nausea. Neither floor defect nor significant bone displacement found on orbital computed tomography, while edema of inferior rectus muscle was apparent. The patient underwent surgical repair 5 days later; a linear minimally displaced fracture of the floor was recognized and complete release of the entrapped perimuscular tissues was followed. Within the first week postoperatively, full range of ocular motility was restored, without residual diplopia. This case was the only identified pure OTF over a 6-year period in our department (0.6% of 159 orbital fractures in patients >18 years). By reviewing the literature indexed in PubMed, a very limited number of either of isolated case reports or retrospective case series of pure OTFs has been reported in adults. Contrary to the typical white-eyed blowout fractures, the literature indicates that OTFs in adults seem to not always constitute absolute emergency conditions. Although such fractures need to be emergently/ immediately treated in children, in the absence of true muscle incarceration, adults may undergo successful treatment within a wider but either early or urgent frame of time. Adults frequently exhibit vagal manifestations and marked signs of local soft tissues injury.

Taking into consideration various terminologies, orbital fractures can be roughly subdivided into three groups: (1) orbital rim fractures, (2) comminuted orbital wall fractures, and (3) orbital trapdoor fractures (OTFs).[1] The latter are considered as “pure” (solitary) orbital wall fractures and their pattern entails entrapment of intraorbital soft tissues with minimal or no displacement of the affected bones.[1,2,3] Even though their occurrence is almost completely observed in pediatric populations,[4,5,6] there are a few reports in the literature which describe the diagnosis of OTFs in adult individuals. The objectives of this article were twofold: (1) to describe the diagnosis and treatment of an OTF of the floor in an adult with vertical eye globe movement limitation and (2) to highlight significant aspects of current literature concerning to this subset of orbital blowout fractures in adult patients.

Case Report

A 29-year-old male patient presented to the emergency department of Evaggelismos, General Hospital of Athens 3 hours after an assault-related injury. The patient mentioned that he suffered a blow to his right eye. He chiefly complained about orbital pain, periorbital edema, and double vision in upper gaze, in conjunction with nausea, faintness, one episode of vomiting, and dizziness within the 3-hour interval. His vital signs were within normal values and he was alert, fully orientated, and hemodynamically stable. Two electrocardiograms displayed sinus rhythm without any sign of arrhythmias, myocardial ischemia, or atrial and ventricular load. On clinical examination of maxillofacial region, limitation of upgaze and downgaze eye movements, traumatic dilation of right pupil, hyphema (grade I), subconjunctival hemorrhage, and small superficial lacerations in right lower eyelid and forehead were evident (Figure 1a). Palpation of infraorbital rim did not reveal any alteration of normal contour, while mild hypoesthesia in distribution of right infraorbital nerve (IN) was noted too. Visual acuity test showed no serious disturbances, intraorbital pressure in both eyes was measured normal, and horizontal eye movements were unaffected. The patient confirmed moderate alcohol use several hours before the injury. A computed tomography (CT) evidenced a minimally displaced and hinge-like trapdoor fracture of the right orbital floor, with minimal orbital content entrapment (Figure 1b). Other injuries were not detected, and previous medical history was not significant.

The patient was admitted to oral and maxillofacial clinic for further treatment. The symptom of nausea remained for approximately 10 hours after his presentation, but repeated awhile at 27 hours together with an isolated and short episode of bradycardia (49 bpm) and faintness. Although the patient initially informed about the need for immediate operation, he asked to postpone any surgical intervention as both ocular motility and diplopia showed some gradual improvement within the following hours/days. However, the forced duction tests, made under local anesthesia, were proved positive without eliciting hemodynamic instability and surgical repair was decided. The patient was operated under general anesthesia on the fifth day of his hospitalization, after substantial remission of regional edema.

A subciliary incision was selected for surgical access. After infiltration with a local anesthetic contained adrenaline, a skin–muscle flap was raised. The infraorbital rim was identified intact without evidence of fracture and surgical exploration of the orbital floor followed. A trapdoor-type fracture was identified (Figure 2a), confirming the radiographic findings. Once the recognition of the posterior margin of the fracture line was completed, both the entrapped sheath of inferior rectus and orbital fat were released by gentle manipulations and reduced back to the orbital cavity. Sudden hemorrhage from a branch of infraorbital artery arose during the release of herniated orbital tissues, but it was arrested a few minutes later once the responsible vessel was cauterized (Figure 2b). The small defect of periorbita and orbital floor was patched with placement of a collagen resorbable membrane (Figure 2c). The negative forced duction test intra- and postoperatively confirmed the absence of extraocular muscle movement limitation (Figure 2d). Intraoperatively, three instant episodes of bradycardia were provoked during orbital floor dissection, without the pulse rate to be dropped below 25 bpm. The wound closure was performed by absorbable sutures and nylon (skin) 6–0 sutures (Figure 2e). Steroid treatment was initiated before surgery and continued with tapered doses of methylprednisolone for 3 days postoperatively. Healing was uneventful without manifestations pertinent with raised vagal tone. The patient was discharged on third postoperative day.

Within 1 week after surgery, the patient exhibited complete resolution of diplopia at extremes of gaze as well as full range of ocular motility (Figure 3a). Hypoesthesia was absent on 2-month follow-up examination. One year later, traumatic dilation of pupil was significantly improved, but was not restored (Figure 3b–f).

Discussion

Soll and Poley[7] first described the trapdoor variety of orbital floor blowout fractures secondary to blunt trauma. Since then, OTFs has been also mentioned in the literature as “white-eyed blowout” fractures and “linear nondisplaced”[8] fractures.[1,8] The former term is introduced by Jordan et al considering that this pattern was associated with minimal periorbital trauma in pediatric patients. Contrary to open-door orbital fractures, there is minimal or no bony defect as well as small amount of herniated soft tissues. Therefore, enophthalmos or hypoglobus is unlikely to ensue.[1] The fracture lies only on the orbital floor, or less commonly on the medial wall, whereas the orbital rim or other adjacent bone structures remain intact.[9] The OTFs are almost always localized medial to the IN because this area represents the weakest part of the orbital floor.[9]

The mechanism of OTFs can be explained by two proposed theories, the hydraulic and the buckling.[10,11] The hydraulic implies that there is a blow to the eye globe and then its force is transmitted into orbital floor which lacks central bony support.[10,11] In the buckling theory, the energy of the force is first exerted on the orbital rim and is then transmitted to the orbital floor.[10,11] The medial wall trapdoor fractures may be more properly explained by the hydraulic theory because there is no sufficient medial orbital rim, while the buckling mechanism is more compatible to trapdoor fractures of the orbital floor.[12] A blow results acute increase in intraorbital pressure and the cracked bones are temporarily displaced to the maxillary or ethmoid sinus; as a consequence, the intraorbital soft tissues prolapse through the created gap. When the pressure subsides, the bones return back into their normal or near-normal position, but the prolapsed soft tissues are incarcerated within the fracture line. Thus, an extraocular muscle or its fascial attachments together with orbital fat may be entrapped. The amount of soft tissues that entrapped within the fracture line determines the limitation of ocular motility, given that OTFs may involve either muscle entrapment or not.[1] Taking into account CT findings, the inferior rectus is regarded prone to entrapment because of vicinity to the orbital floor and absence of sufficient periorbital fat for cushion.[13]

Based on intraoperative findings and CT scan features, Gerbino et al[14] classified the coronal views of the OTFs into two subgroups. The first named type 1a and included linear fractures parallel to the IN groove with the degree of bone displacement not exceeding the orbital floor thickness.[14] Type 1b was OTFs which displayed hinged pattern with medial bone displacement exceeding the orbital floor thickness.[14] The type 1a was significantly more common in patients younger than 12 years, while type 1b had better prognosis in terms of residual diplopia and was seen more frequently in patients near the age of 16 years.[14] The orbital CT of our patient revealed a type 1b fracture.

Despite the variations in diagnostic definitions used for OTFs, when critically reviewing the current literature, there are a few of cases/case series of pure OTFs that have been reported in adult patients (

Table 1. Case reports/series of OTFs in adult patients ≥ 20 years old.

Abbreviations: IR, inferior rectus; MR, medial rectus; OTFs, orbital trapdoor fractures.

).[9,12,15,16,17,18,19,20] The age of oldest patient suffered from an OTF was 53 years.[9] Also, isolated cases of adult patients encountered in retrospective studies whose almost all of their patients are children. Among 589 adult patients with orbital wall fractures, Chi et al[5] found that only one (0.2%) presented the trapdoor pattern. Also, Parbhu et al[21] evaluated a series of patients submitted to primary repair of an orbital floor fracture and found 2 out of 31 adult patients who were aged 23 and 25 years. The study by Kwon et al[22] included 24 adult patients (age ≥ 17 years; 44% of the adult group) with trapdoor fractures, but the authors did not clarify which of these fractures were pure. One retrospective study from New Zealand contained five cases of adult patients with orbital floor fractures and activation of the oculocardiac reflex (OCR).[23] Nevertheless, the author did not mention which of these fractures exhibited trapdoor pattern. Kakizaki et al[24] described a case of a 20-year-old patient with a OTF which caused incarceration of the inferior oblique muscle branch of the oculomotor nerve; the OTF was not solitary as well as the authors did not identify muscle incarceration during surgical exploration. In our department, between January 2010 and December 2015, we managed 159 orbital wall fractures (35 pure; 124 impure) among 144 patients with age >18 years. After the evaluation of CT coronal views and intraoperative data of all these patients, the presented case was proved as the only diagnosed pure OTF over a 6-year period (0.6% of all orbital fractures).

The reasons that OTFs are more commonly diagnosed in children than in adults involve differences in bone structure and histology. The bones of children demonstrate greater elasticity, increased thickness of periosteum, open sutures lines, and less quantity of calcified osseous tissue.[22,25] These features make children’s bones more bendy and prone to sustain greenstick fractures. In contrast, the pure orbital floor fractures in adult patients usually show open-door or comminuted/crashed patterns with large defects.[21,22]

In case of OTFs, it is important for clinicians to take into account that the entrapment of orbital tissues may provoke the occurrence of OCR.[8] Orbital trauma, which is accompanied by bradycardia, nausea, vomiting, orbital pain, syncope, and abdominal pain, is likely to indicate extraocular muscle entrapment.[26] One study, which contained children with orbital floor fractures, found that if there is a diagnosed OTF, the positive predictive value of nausea and vomiting for inferior rectus entrapment is estimated 83.3%.[27] The patient of the presented case experienced episodic manifestations of OCR (one episode of mild bradycardia) during the first 24 hours after his admission. The symptom of nausea might be attributed to combined effect of medications and alcohol. Persistent or prolonged stimulation of OCR is an indication for immediate surgical repair for avoidance of fatal hemodynamic instability.[28]

Typical radiographic findings are not essential to be evident in case of OTFs, especially of those being linear with extraocular muscle entrapment. It has been documented that radiologists may not interpret barely noticeable findings,[29] though abnormal ocular mobility might be apparent in clinical examination. Special emphasis should be paid in recognition of tissue teardrop formed on the roof of maxillary antrum and small air pockets close to affected orbital wall; inferior rectus muscle should be checked for round-shaped configuration, absence, and inferior displacement.[30,31]

Many authors advocated that OTFs in children constitute an emergent situation needing surgical repair as soon as possible.[1,8,25,28,29,32,33] It is assumed that a prolonged time of extraocular muscle entrapment may result in increased likelihood for permanent postsurgical diplopia due to various pathologic events such as muscle contusion, scar development within and around the orbital fibrous sheath network, nerve contusion, hemorrhage, edema, and tissue incarceration within fracture line.[34] Providing that the muscle ischemia is irreversibly established within few hours,[35,36] it may be proved impossible to timely perform the operation before the definitive diagnosis. Permanent restriction of extraocular muscle movement might be inevitable for orbital fractures with severe muscular injuries exceeding a critical threshold, even secondary to a timely operation.[19] Iliff et al[34] showed that muscle contusion and fibrosis or incarceration affecting the muscular fascial network are probably the main causes of diplopia rather than compartmental ischemic necrosis. Contrary to what is recommended for children, the literature data report that OTFs in adults, not treated in emergency basis, showed to have successful repair after a more extended window of time than 48 hours (Table 1). This difference between adults and children might be explained by the fact that both type 1b pattern (better prognosis) and periorbital edema (limited ductions) are more common in adults. Thus, the severity of “true” muscle entrapment may be more in children. It should be also noted that there is vague evidence for which specific type of tissue (fat, septa, periosteum, nerve, or muscle) is responsible for the motility disorders[37] and if/ how it is associated with the patients’ age. Yano et al[38] underscored the emergency status for the specific sign of true “missing rectus” on coronal CT slice, that is, minimal or no inferior rectus muscle density above the floor and any concrete floor fracture, which denotes muscle strangulation (firmly and tightly entrapped muscle) and needs for immediate surgery to avoid irreversible fibrosis. In linear OTFs, the rare occurrence of muscle entrapment only impacts restricted areas of the muscle, without harming more than half of its belly (absence of “missing rectus”).[35,39] However, such fractures without “missing rectus” less commonly present spontaneous healing and full recovery;[19] surgery is usually unavoidable even if it can be postponed for a few days for resolution of edema.[38]

In their retrospective study, Kwon et al[22] concluded that OTFs in adults should be optimally repaired within the first 5 days after the injury, even if favorable outcomes in recovery were achieved for patients operated within 2 weeks posttraumatically. Yang et al[40] found that the time between orbital injury and surgery did not significantly influence the muscle recovery in pediatric patients. The authors underscored the importance of complete release of the entrapped orbital soft tissues in the success of outcome. Yano et al[19] showed that full recovery was achieved in the surgical group of 14 young patients (age 6.9–24.3 years), with linear-type blowout fractures and limitation of gazes who operated within the first 5 days after injury. The severity of injury (missing rectus) and time of surgery (>8 days) were considered important factors for residual diplopia. In another retrospective study, Kasaee et al[41] demonstrated that maximum interval between trauma and surgery for isolated pure blowout fractures is 4.5 days to avoid diplopia and motility disorders.

In general, the indications and optimal time of orbital floor reconstruction are controversial issues.[37] The systematic literature review of Dubois et al[37] concluded that the age significantly affects the appropriate time frame of surgical repair. When there is no emergent or urgent indication for surgery, other parameters such as patient’s general condition, fracture close to the only seeing eye, local standards, time availability of the operating room, as well as legal and insurance issues may influence the surgeon’s choice concerning the time of orbital reconstruction.[37] Taking into account the recommendations of Burnstine’s systematic review,[28] immediate orbital reconstruction is required in case of nonresolving OCR, the “white-eyed” blowout fracture, and early enophthalmos or hypoglobus with sight-threatening emergency. Symptomatic diplopia with positive forced ductions in conjunction with signs of entrapped muscle or perimuscular soft tissue entrapment on CT scan may be treated within 2 weeks after injury, “as soon as reasonably possible” (Figure 4).[28,42,43] According to Burnistine’s recommendations, the presented case did not necessarily require emergent treatment; indeed, the orbital floor reconstruction was successfully performed within the early frame of 5 days, allowing for some improvement of ocular motility and substantial resolution of edema. As periorbital edema subsides, better surgical exposure can be achieved and the risk of postoperative orbital compartment syndrome is substantially lessened.[44] Except for the above-mentioned recommendations, Yano et al[38] classified the severity of CT findings for inferior rectus injury into three categories: strangulation, incarceration, and entrapment (Figure 5). A true “missing rectus” indicates strangulation and, therefore, OTFs should be emergently treated. If patients with linear OTFs exhibit diplopia and severe restriction in vertical movements but not apparent missing rectus on CT images, immediate orbital reconstruction is more advisable to be applied.[19] Besides, Liu et al[45] documented that orbital blowout fractures, where the distortion of herniated tissue is disproportionate to the configuration of surrounding bone fragments (type B), are better to be treated within 7 days after the injury.

Of note, a positive forced traction test during the acute phase of injury may be derived from hemorrhage and/or edema within and around the fibrous septae which attach both the inferior rectus and inferior oblique muscles to the periorbita.[46] Although a forced duction test is performed, the acute phase of trauma (edema, hemorrhage) may also prevent the reliable differentiation of eye mechanical restriction from oculomotor nerve palsy (inferior division to the inferior oblique muscle).[46] Consequently, notwithstanding the forced duction test, orbital pain during various ductions, and CT scan may all contribute to accurate diagnosis, none of them achieves 100% sensitivity or specificity.[47]

On surgical exploration of the orbital floor, it is crucial for surgeons to ascertain the more posterior border of the fracture line. Nevertheless, care should be taken to avoid bleeding injury and incomplete hemostasis of the branch of the inferior orbital artery, which is found medial and above to IN.[48] The branch is located in a mean distance of 16.6 mm from the inferior orbital rim, and should be always identified and not confused with avascular bands of connective tissue.[49] The vessel must be carefully cauterized (with bipolar cautery) during subperiosteal floor dissection; otherwise, even vision-threatening complications may arise due to uncontrolled intraorbital hemorrhage.[50]

The release of the entrapped soft tissues may require widening of the fracture line; this may be facilitated with depression of fractured parts of the orbital floor.[14,43] Patching of the orbital floor with a graft material is recommended by several authors for avoidance of recurrent herniation of the entrapped tissues.[14,36] A collagen absorbable membrane was selected to patch the defect in our case; collagen membranes have proved efficient means to reconstruct small size orbital floor defects, by promoting bone regeneration under the membrane in some cases.[51]

Conclusion

Neither patient’s age nor radiographic findings constitute absolute criteria to rule out the trapdoor pattern of a pure orbital fracture. Intraoperative findings document that the trapdoor variety of blowout orbital fractures do occur in adult patients. Although many authors recommend immediate (<24 hours) repair of such fractures in children, it can hypothesized that adults with OTFs sustain less severe injuries of extraocular muscles and, in the absence true muscle incarceration, may undergo successful treatment in a more reasonably wide (urgent or early) frame of time, and not necessarily in emergent basis. We advocate that an adult patient diagnosed with an orbital blowout fracture, eye mechanical restriction, and diplopia should be operated as soon as possible, but taking into account all the associated clinical parameters, benefits, and risks. Vagal signs and symptoms are commonly evident in adults too, and indicate immediate surgical intervention as long as they are severe and not resolved within the first 24 hours after orbital trauma. Adult patients with OTFs usually present marked signs of orbital soft tissues injury in contrast to white-eyed blowout fractures.