Relationship between the preoperative status of the inferior rectus muscle and recovery time of ocular symptoms in patients with inferior orbital blowout fractures using computed tomography

Abstract

Background

Inferior orbital blowout fractures (BOF) cause ocular symptoms like diplopia and extraocular muscle limitation, influenced by inferior rectus muscle (IRM) status. This study evaluated the relationship between preoperative IRM status on computed tomography (CT) and ocular symptom recovery time.

Methods

This retrospective study analyzed 127 patients with inferior BOF and ocular symptoms (2012–2024). Inclusion criteria included age 18–80 years and preoperative CT availability. IRM status was assessed for bone interruption, herniation extent, and swelling (short/ long axis ratio < 0.54 or ≥ 0.54). Recovery times were analyzed using t-tests and Kaplan-Meier survival analysis (p< 0.05).

Results

Of 127 patients (mean age, 35 years; 67.7% male), 66 (52.0%) recovered from ocular symptoms within 7 days, 53 (41.7%) within 30–90 days, and eight (6.3%) had diplopia that remained as a permanent sequela at the last follow-up. Diplopia recovery time was longer in IRM–bone contact (16.9± 5.5 days, n= 35) and bone-pierced IRM (29.4± 10.3 days, n= 15) groups versus no-contact (5.1± 4.2 days, n= 77; p= 0.02, t-test). Herniation and swelling showed no significant correlation (p> 0.05).

Conclusion

Preoperative CT-based assessment of the IRM–bone interface predicts diplopia recovery time, with bone-pierced IRM linked to prolonged recovery. Patients with bone-pierced IRM may require closer follow-up and careful consideration of timely surgical management.

INTRODUCTION

Orbital blowout fractures (BOF), often caused by blunt trauma to the orbital region, increase intraorbital pressure, leading to rupture of the orbital wall and prolapse of intraorbital soft tissue. These injuries may result in enophthalmos, diplopia, and extraocular muscle limitation, significantly impacting patients’ quality of life [1,2]. The incidence of orbital fractures has risen in recent decades, driven by increased traffic accidents, violent injuries, and sports-related trauma [3].

Diagnostic methods for orbital fractures include plain radiography and computed tomography (CT). Plain radiography is limited by overlapping anatomical structures and the thinness of orbital bones, making accurate diagnosis challenging. In contrast, CT is the gold standard for assessing fracture presence, size, location, extraocular muscle status, and soft tissue herniation, owing to its high resolution and ability to provide three-dimensional reconstructions [4].

Patients with inferior orbital BOF commonly experience ocular symptoms, including diplopia, limited extraocular muscle movement (EOM), periocular discomfort, and hypoesthesia [5]. These symptoms are influenced by factors such as fracture size, type, soft tissue herniation, time from trauma to surgery, and the status of the inferior rectus muscle (IRM) [6]. Among these, IRM status, particularly entrapment or swelling, is critical due to its role in ocular motility [7,8]. This study investigates the relationship between preoperative IRM status, assessed via CT, and the recovery time of ocular symptoms in patients with inferior orbital BOF.

METHODS

This retrospective study included patients diagnosed with isolated inferior orbital BOF who underwent surgery and presented with ocular symptoms between March 2012 and March 2024. Of 368 patients with inferior BOF, 127 with preoperative ocular symptoms were included. Exclusion criteria were concomitant facial fractures, age outside 18–80 years, or unavailable preoperative CT scans. Postoperative follow-up was conducted at 1, 3, 6, and 12 months after surgery. A retrospective analysis of medical charts was performed to evaluate factors related to ocular symptom recovery time. The study was approved by the Institutional Review Board of Yeungnam University Hospital (IRB No. YUMC 2025-09-007).

IRM status was assessed using preoperative CT scans (1-mm slice thickness, coronal and sagittal views). Bone involvement was classified according to the interface between the IRM and displaced bone fragments as follows: no contact with bone segment, pierced by bone segment, or contact without piercing (Fig. 1). This IRM–bone interface classification was devised by the authors based on the presumed severity of direct muscle injury on CT. The position of the IRM and herniated orbital soft tissue was categorized relative to a virtual fracture line drawn along the natural orbital floor: above the fracture line, at the fracture line (overlapping), or below the fracture line (Fig. 2). IRM swelling was quantified by the short-to-long axis ratio on coronal CT views, with a threshold of 0.54: <0.54 (less swelling) or ≥0.54 (more swelling) (Fig. 3), adopting the cutoff previously proposed by Kim et al. [5]. Recovery time for ocular symptoms (diplopia, EOM limitation, discomfort) was mea-sured from surgery to symptom resolution, based on patient reports and clinical exams.

Fig. 1.

Coronal computed tomography images showing the degree of IRM–bone interface. No contact with a displaced bone segment (A), IRM pierced by a bone segment (B), and contact without piercing (C). A virtual fracture line along the natural orbital floor is indicated (red dashed line). IRM, inferior rectus muscle.

Fig. 2.

Coronal computed tomography images showing the position of the IRM and herniated orbital soft tissue relative to a virtual fracture line (red dashed line) along the natural orbital floor. IRM located above the fracture line (A), at the fracture line (overlapping, B), and below the fracture line (C). IRM, inferior rectus muscle.

Fig. 3.

Short-to-long axis ratio of the inferior rectus muscle used to evaluate swelling on coronal computed tomography. Short axis indicated by white arrow; long axis indicated by yellow arrow.

Statistical analysis

Data were analyzed using descriptive statistics, chi-square tests, Kruskal-Wallis H tests, t-tests, Spearman correlation, Kaplan-Meier survival analysis, and binary logistic regression. Analyses were performed with SPSS version 28 (IBM Corp.). A p-value <0.05 was considered statistically significant. Power analysis confirmed an adequate sample size for detecting differences in recovery time (power>0.80).

Surgical procedure

All procedures were performed by a single surgeon under general anesthesia using a subciliary approach. Local infiltration of the inferior orbital rim was done with 0.5% lidocaine hydrochloride and 1:200,000 epinephrine. An incision was made 2 mm below and parallel to the lower eyelash using a No. 15 scalpel, incising the orbicularis oculi muscle and raising a combined skin-muscle flap to the inferior orbital rim. The orbital septum was followed below the tarsus to the orbital rim, where a periosteal incision was made on the anterior aspect to preserve the septum. Subperiosteal dissection was performed using a Freer periosteal elevator, with malleable retractors for exposure. Fracture margins and size were confirmed, and orbital floor reconstruction was achieved with titanium mesh, repositioning herniated soft tissue [9].

RESULTS

The demographic and clinical characteristics of the 127 patients are summarized in Table 1. The mean age was 35 years (standard deviation, ±10), with 67.7% male (n=86) and 32.3% female (n=41). Overall, 66 patients (52.0%) recovered from ocular symptoms within 7 days, 53 (41.7%) within 30–90 days, and eight (6.3%) had diplopia that remained as a permanent sequela at the last follow-up.

Table 1.

Demographic and clinical characteristics of patients with inferior orbital blowout fractures

Characteristic	Value (n=127)
Sex
Male	86 (67.7)
Female	41 (32.3)
Age (yr)
Mean±SD	35±10
Range	18–80
Distribution, No. (%)
18–30	63 (49.6)
31–50	44 (34.6)
51–80	20 (15.7)
IRM–bone involvement, No. (%)
No contact	77 (60.6)
Bone contact	35 (27.6)
Bone-pierced	15 (11.8)
IRM herniation extent, No. (%)
Above orbital floor	71 (55.9)
Middle of orbital floor	45 (35.4)
Below orbital floor	11 (8.7)
IRM swelling (short/long axis ratio), No. (%)
<0.54	63 (49.6)
≥0.54	64 (50.4)
Symptom, No (%)
Diplopia	84 (66.1)
EOM limitation	46 (36.2)
Discomfort	23 (18.1)

SD, standard deviation; IRM, inferior rectus muscle; EOM, extraocular muscle movement.

IRM–bone interface

In the bone contact group (n=35), mean recovery periods were 16.9±5.5 days for diplopia (n=84 total with diplopia), 1.0±0.8 days for EOM limitation (n=46 total), and 10.7±4.2 days for discomfort (n=23 total). In the bone-pierced group (n=15), these were 29.4±10.3 days, 6.0±3.5 days, and 17.0±7.1 days, respectively. In the no-contact group (n=77), recovery periods were 5.1±4.2 days, 1.6±1.2 days, and 5.3±3.8 days. Diplopia recovery was significantly longer in the bone-pierced group (p=0.02, t-test) (Table 2). Kaplan-Meier analysis confirmed prolonged diplopia persistence in bone-involved groups (p=0.03, log-rank test). Fig. 4 illustrates the Kaplan-Meier survival curves for diplopia recovery, demonstrating distinct separation be-tween groups, with the bone-pierced IRM group exhibiting the slowest resolution.

Table 2.

Symptom improvement by degree of bone interface

Symptom	Recovery times (day), mean± SD			p-value
	Bone contact	Bone-pierced	No contact
Diplopia (n=84)	16.9±5.5	29.4±10.3	5.1±4.2	0.02*
EOM limitation (n=46)	1.0±0.8	6.0±3.5	1.6±1.2	0.25
Discomfort (n=23)	10.7±4.2	17.0±7.1	5.3±3.8	0.06

SD, standard deviation; EOM, extraocular muscle movement.

^*Statistically significant (p<0.05).

Fig. 4.

Kaplan-Meier survival curves for diplopia recovery among inferior rectus muscle–bone interface groups. The bone-pierced group shows the slowest recovery (log-rank test, p=0.03).

IRM position relative to the fracture line

For IRM position relative to the fracture line, recovery times were: above the virtual fracture line (n=71)–diplopia 4.5±3.9 days, EOM limitation 2.0±1.5 days, discomfort 5.3±4.0 days; at the fracture line (overlapping, n=45)–22.0±9.8 days, 3.5±2.4 days, 17.0±8.2 days; and below the fracture line (n=11)– 7.4±5.1 days, 1.3±1.0 days, 4.5±3.2 days. No statistically significant differences were found (p>0.05, Kruskal-Wallis) (Table 3).

Table 3.

Symptom improvement by the extent of the inferior rectus muscle herniation

Symptom	Recovery times (day), mean± SD			p-value
	Above orbital floor	Middle of orbital floor	Below orbital floor
Diplopia (n=84)	4.5±3.9	22.0±9.8	7.4±5.1	0.06
EOM limitation (n=46)	2.0±1.5	3.5±2.4	1.3±1.0	0.67
Discomfort (n=23)	5.3±4.0	17.0±8.2	4.5±3.2	0.07

SD, standard deviation; EOM, extraocular muscle movement.

IRM swelling

For IRM swelling, recovery times in the <0.54 ratio group were 18.7±7.6 days for diplopia, 2.0±1.4 days for EOM limitation, and 11.2±5.3 days for discomfort. In the ≥0.54 group, these were 21.4±9.2, 5.0±3.1, and 16.0±6.8 days. No significant correlations were observed (p>0.05) (Table 4). All patients recovered from EOM limitation and periocular discomfort during follow-up, whereas diplopia remained as a permanent sequela in eight patients (6.3%).

Table 4.

Symptom improvement by degree of inferior rectus muscle swelling

Symptom	Short/long axis ratio, mean± SD		p-value
	< 0.54	≥ 0.54
Diplopia (n=84)	18.7±7.6	21.4±9.2	0.21
EOM limitation (n=46)	2.0±1.4	5.0±3.1	0.25
Discomfort (n=23)	11.2±5.3	16.0±6.8	0.09

SD, standard deviation; EOM, extraocular muscle movement.

DISCUSSION

This study evaluated the prognostic value of preoperative CT findings in predicting ocular symptom recovery in patients with inferior orbital BOF, focusing on IRM status [6]. Fractures occur via hydraulic or buckling mechanisms, leading to muscle/soft tissue damage and symptoms like diplopia due to altered orbital anatomy [10,11]. Orbital fat atrophy and fibrosis further impair motility, especially with IRM entrapment [12,13]. We found that IRM–bone interruption, particularly in the bonepierced group, significantly prolonged diplopia recovery (29.4± 10.3 days vs. 5.1±4.2 days in the no-contact group; p=0.02), likely due to severe muscle trauma, hematoma, or ischemia [1,14-16]. We propose that bone-pierced IRM represents a distinct CT pattern associated with more severe direct muscle trauma than conventional entrapment, which may partially explain the prolonged diplopia in this subgroup. Kaplan-Meier curves confirmed delayed resolution in the bone-pierced group (log-rank p=0.03) (Fig. 4).

Preoperative CT assessment of IRM–bone interruption, herniation, and swelling guides surgical timing and strategy [2,4]. The bone-pierced group (n=15) had the longest recovery across symptoms, with diplopia being statistically significant (Table 2). Although EOM limitation (6.0±3.5 days) and discomfort (17.0±7.1 days) trended longer, the differences were not significant (p=0.25, p=0.06), possibly due to smaller sample sizes (n=46, n=23). Diplopia appears more sensitive to IRM–bone interruption due to its impact on binocular vision [6,8].

IRM position relative to the fracture line and swelling (short/long axis ratio >0.54) did not significantly affect recovery (Tables 3, 4). Middle-floor herniation showed longer diplopia re-covery (22.0±9.8 days; p=0.06), and swelling trended toward delay (21.4±9.2 days; p=0.21), but lacked significance. This contrasts with prior studies linking swelling to prolonged recovery [5,16], possibly due to qualitative swelling assessment, younger patient demographics (49.6% aged 18–30) (Table 1) with better tissue resilience, or retrospective design limitations [4,5].

Persistent diplopia occurred in 6.3% (8/127), lower than reported rates up to 30% in delayed cases [17,18]. Five of eight cases were in the bone-pierced group, underscoring its prognostic weight [1,6]. Early surgery (within 2 weeks) likely reduced complications like fibrosis or malunion [19,20]. In our cohort, most patients underwent surgery within 2 weeks; however, we did not directly compare outcomes according to injury-to-surgery interval, and our data cannot prove a causal benefit of earlier intervention in the bone-pierced IRM subgroup. Therefore, any recommendation for timely surgery in these patients should be interpreted as a theoretical consideration based on the presumed risk of progressive fibrosis rather than a definitive conclusion from our dataset. However, persistent symptoms in bone-pierced cases highlight the need for meticulous muscle release and advanced reconstruction materials [7,9,21].

Limitations include retrospective design with potential selection bias, subjective diplopia assessment without quantitative tools (e.g., Hess charts) [22], single-center setting with male (67.7%) and young (18–30 years; 49.6%) predominance (Table 1), and lack of intraoperative data (e.g., adhesion, hematoma) [9,14]. In addition, the IRM–bone interface classification used in this study was devised by the authors and has not been externally validated, so our findings should be interpreted with caution and confirmed in further studies. Future studies should adopt prospective, multicenter designs with quantitative motility testing, advanced imaging (three-dimensional CT and magnetic resonance imaging), and stratification by injury-to-surgery interval [12,13,23].

Clinically, CT-based IRM assessment identifies high-risk patients who may benefit from closer observation and consideration of timely intervention to reduce the likelihood of persistent symptoms [2,4]. Standardized CT protocols and postoperative monitoring are recommended [24]. Long-term studies and rehabilitation strategies may further optimize outcomes [15].

Preoperative CT assessment of the IRM–bone interface predicts diplopia recovery time in inferior orbital BOF. Bonepierced IRM is associated with significantly longer recovery. Patients with bone-pierced IRM may warrant closer observation and consideration of timely surgical intervention to minimize the risk of persistent diplopia. IRM position relative to the fracture line and swelling did not show a significant impact on recovery. Prospective, multicenter studies with objective motility measurements are needed to validate these findings and to clarify the effect of injury-to-surgery interval.

Abbreviations

BOF

blowout fractures

CT

computed tomography

EOM

extraocular muscle movement

IRM

inferior rectus muscle