Anatomical Thin Titanium Mesh Plate Structural Optimization for Zygomatic-Maxillary Complex Fracture under Fatigue Testing.

This study performs a structural optimization of anatomical thin titanium mesh (ATTM) plate and optimal designed ATTM plate fabricated using additive manufacturing (AM) to verify its stabilization under fatigue testing. Finite element (FE) analysis was used to simulate the structural bending resistance of a regular ATTM plate. The Taguchi method was employed to identify the significance of each design factor in controlling the deflection and determine an optimal combination of designed factors. The optimal designed ATTM plate with patient-matched facial contour was fabricated using AM and applied to a ZMC comminuted fracture to evaluate the resting maxillary micromotion/strain under fatigue testing. The Taguchi analysis found that the ATTM plate required a designed internal hole distance to be 0.9 mm, internal hole diameter to be 1 mm, plate thickness to be 0.8 mm, and plate height to be 10 mm. The designed plate thickness factor primarily dominated the bending resistance up to 78% importance. The averaged micromotion (displacement) and strain of the maxillary bone showed that ZMC fracture fixation using the miniplate was significantly higher than those using the AM optimal designed ATTM plate. This study concluded that the optimal designed ATTM plate with enough strength to resist the bending effect can be obtained by combining FE and Taguchi analyses. The optimal designed ATTM plate with patient-matched facial contour fabricated using AM provides superior stabilization for ZMC comminuted fractured bone segments.

Preoperative evaluation and surgical technique of functional and cosmetic aspects in zygomatic complex fracture patients.

The zygomatico-maxillary complex functions as the principle buttress of the face and is the cornerstone to an individual’s aesthetic appearance. Its fracture not only creates cosmetic deformities owing to its position and facial contour, but can also cause disruption of ocular and mandibular functions. The aim of this study was to evaluate the quality, efficacy and impact of internal fixation of zygomatic complex fractures on functional and cosmetic outcomes. A prospective study was carried out on 100 patients who were divided according to the classification and the severity of injury. Subjective evaluation was submitted based on the patient’s perception of signs and symptoms in the preoperative and postoperative periods. Intraoperative and postoperative assessment of bone reduction quality was made according to the type of the fracture and related difficulties; also, the difference between these groups was observed as functional and esthetic outcome. To optimize the treatment of zygomatic bone fractures, a pre-designed questionnaire was used for subjective evaluation of symptoms and treatment outcome. In 70% of cases, ophthalmologic consultation was taken and was most common in type VII fractures (100% cases). Neurosensory disturbance was the most common finding (60%), followed by diplopia (56R%), pain upon mouth opening (54%) and malar depression (50%). Out of all possible 400 fracture sites in 100 patients of zygomatic complex fractures, 266 (66.5%) fractures were detected by clinical examination, in contrast to 330 (82.5%) on radiological examination, which were highest at zygomatic-maxillary buttress (93%) followed by infraorbital rim (91%) and almost equal among fronto-zygomatic site (72%) and zygomatic arch (74%). The scores from the questionnaire for annoyance were significantly higher for paraesthesia (23%) than for trismus (10%), pain (8.5%), or deformity (8.25%). Residual deformity and pain significantly influenced the total satisfaction. Conclusively, there are many treatment modalities available for zygomatic complex fractures, and the preferred methods should be selected on the basis of fracture type, fracture severity, pre-operative signs and symptoms. Regarding the requirements of fracture site exposure and actual fixation, one priority should be to minimize postoperative complications, morbidity and residual deformities.

Does facial soft tissue protect against zygomatic fractures? Results of a finite element analysis.

INTRODUCTION: Zygomatic fractures form a major entity in craniomaxillofacial traumatology. Few studies have dealt with biomechanical basics and none with the role of the facial soft tissues. Therefore this study should investigate, whether facial soft tissue plays a protecting role in lateral midfacial trauma. METHODS: A head-to-head encounter was simulated by way of finite element analysis. In two scenarios this impact - with and without soft tissues - was investigated to demonstrate the potential protective effects. To achieve realism, a transient simulation was chosen, which considers temporal dynamics and realistic material parameters derived from CT grey values. RESULTS: The simulation results presented a typical zygomatic fracture with all relevant fracture lines. Including soft tissues did not change the maximum bony stress pattern, but increased the time period from impact to maximal stresses by 1.3 msec. CONCLUSIONS: Although this could have clinical implications, facial soft tissues may be disregarded in biomechanical simulations of the lateral midface, if only the bony structures are to be investigated. Soft tissue seems to act as a temporal buffer only.

Electromyography assessment in zygomaticomaxillary complex fractures.

OBJECTIVE: The aim of this study was to assess the activity of the masseter and temporalis muscles using surface electromyography (EMG) in patients with zygomaticomaxillary complex (ZMC) fractures. PATIENTS AND METHODS: This prospective study was carried out on 25 patients who had ZMC fractures. Fifteen patients were managed by open reduction and rigid fixation (ORIF) using titanium miniplates. This study, using surface electromyography, analyzed the activity of the masseter and temporalis muscles of 25 patients with ZMC fractures; 15 of them were surgically treated under general anesthesia (GA). Evaluations were made before surgery and 6 weeks after surgery by recording the mean of muscle contraction of 20 motor unit action potential (MUAP) against resistance, and statistical analyses were performed. RESULTS: A significant EMG difference between the normal and ZMC fracture sides was found (P < 0.0001) for both masseter and temporalis muscles and was significantly improved after ORIF. However, postoperative EMV values of the repaired side was significantly less than measured postoperatively in the normal side (P < 0.0001) for both muscles. CONCLUSION: ZMC fractures significantly diminish muscular activity of the masseter and temporalis and even though significant recovery of muscle activity was revealed after 6 weeks, it is still less than normal activity, highlighting the importance of postoperative rehabilitation.

Biomechanical mechanisms of orbital wall fractures - a transient finite element analysis.

As the biomechanical mechanisms of orbital wall fractures are still under research, three different fracture mechanisms were tested in a finite element based investigation. In contrast to earlier studies, a finer skeletal model and a transient dynamic simulation were used to test pure hydraulic, pure buckling and a mixed force transmission. Results showed that each set-up led to different orbital fracture patterns, which correlate well with clinical findings. Therefore the conclusion is that different mechanisms may act together explaining the variety of clinical fracture situations. Biomechanical testing has proven to be appropriate in answering questions regarding fracture mechanisms.

Transient finite element analysis of a traumatic fracture of the zygomatic bone caused by a head collision.

Midfacial fractures rank first concerning maxillofacial traumatology. Collisions of two heads or head to object are the main causes for these fractures. An investigation based on a transient simulation using the finite element method was performed. A biomechanical head model was created and tested. A transient collision of two heads was simulated. The results were compared to a typical real patient case. This comparison revealed an identical fracture pattern, which can be interpreted as a clinical match of the simulation. The results of this study show the validity of biomechanical investigations, which may serve as a method to better understand maxillofacial fracture patterns. These results will be used for the optimization of fracture therapy or trauma prevention in the future.

Outcomes in pediatric facial fractures: early follow-up in 177 children and classification scheme.

A comprehensive study of adverse outcomes after pediatric facial fractures has not been published. This study aimed to determine the incidence and classify adverse outcomes after facial fractures in children while reporting our early results. A retrospective chart review was performed on facial fracture patients identified in the Craniofacial Trauma Database of the Children's Hospital of Pittsburgh and seen in follow-up from 2003 to 2007. An Adverse Outcome Classification Scheme was developed: type 1, outcomes resulting from the fracture; type 2, outcomes resulting from fracture treatment; and type 3, outcomes resulting from the interaction between the fracture, its treatment, and subsequent growth and development. Fisher exact or χ analyses were completed. A total of 177 pediatric facial fracture patients were identified with 13.3 months of average follow-up. Mean age was 9.8 years (range, 0.4-18.7 y). Of these patients, 41.8% underwent surgery and 57 patients (32.2%) had adverse outcomes (type 1, 14.1%; type 2, 11.3%; and type 3, 15.8%); 26.3% of these had multiple adverse outcomes. Isolated fractures resulted in fewer adverse outcomes and fewer multiple adverse outcomes compared with combined fractures (26.6% versus 45.3%, P = 0.015; 4% versus 18.9%, P = 0.002). Patients treated operatively exhibited more types 1, 2, and 3 and multiple adverse outcomes compared to those treated conservatively (P < 0.01). In our pediatric cohort, 32.2% of patients had an adverse outcome. With longer follow-up and growth and development studies, we will likely see an increase in the incidence of type 3 adverse outcomes. We recommend, whenever possible, conservative treatment of pediatric facial fractures.

Bite force, electromyography, and mandible mobility during the 6-month period after surgical treatment for isolated fractures of the zygomatico-orbital complex.

OBJECTIVE: The aim of this study was to identify the behavior of masticatory muscles after fractures of the zygomatico-orbital complex (ZOC) and subsequent surgical treatment, by using analyses of bite force, electromyography (EMG), and mandible mobility during a 6-month period after surgery. STUDY DESIGN: Five patients with fractured ZOCs treated surgically by using an intraoral approach and fixation exclusively in the region of the zygomaticomaxillary buttress were evaluated. The control group included 12 other patients. During postoperative follow-up, bite force, mandible mobility, and EMG analysis of the masticatory muscles were evaluated. RESULTS: There was an increase in bite force with time, but a decline in EMG activity during the same period. In the mandible mobility analysis, only maximum mouth-opening values increased significantly after the surgical treatment. CONCLUSIONS: The masticatory musculature, according to bite force and EMG, returned to its normal condition by the second month after surgery, and maximum mouth opening was observed after the first month.

[Forensic medical criteria for the assessment of severity of harm to the health in subjects with zygomatic bone fractures].

Expert reports concerning subjects with zygomatic bone fractures were analysed and comprehensively evaluated using investigatory, clinical and anamnestic data. A total of 704 forensic medical reports were available for the purpose including 225 (32%) isolated and 479 (68%) combined fractures. It was shown that most complications of zygomatic fractures develop late in the post-traumatic period which requires repeated examination of the patients within at least one month after the injury. It is emphasized that such examination must involve neuropathologist, ophthalmologist, and maxillofacial surgeon to adequately evaluate harm to the health in patients with isolated zygomatic fractures. The main causes of discrepancy between results of estimation of harm to the health during primary and subsequent forensic medical examination of subjects with zygomatic fractures are considered.

Experimental evaluation of relapse-risks in operated zygoma fractures.

OBJECTIVES: Prevention of relapse, or postoperative dislocation, of the fixed zygoma is necessary to achieve optimal results in the treatment of zygoma fractures. Assuming that the occurrence of intensified stresses on mastication at the screw-bone interface (SBI) constitutes the essential cause of the relapse, we evaluated the stresses for three different fixation methods-fixation at the frontal process (FP), inferior orbital rim (IOR), and zygomatico-maxillary buttress (ZMB). METHODS: We used 10 computer-aided design (CAD) models simulating zygoma fractures in the experiment. For each CAD model, we fixed the fractured zygoma with four screws and one mini-plate at the FP, IOR, or ZMB. After applying a 5.5kg force simulating mastication, we calculated the intensity and distribution patterns of the stresses occurring at the SBIs of the fixation screws using the finite element method. Thereby, we evaluated dynamic stability of the fixed zygoma for each of the three fixation methods. RESULTS: Greater stresses occur at the SBIs with IOR fixation than at those with FP and ZMB fixation. Although the stresses occurring at the SBIs on mastication demonstrated evenly distributed patterns with the FP and ZMB fixation, the stresses demonstrated concentration on one screw with the IOR fixation. CONCLUSIONS: The fixed zygoma is more likely to cause relapse with the IOR fixation than with the FP or ZMB fixation. Hence, in performing zygoma fixation at the IOR, care should be taken to minimize the likelihood of postoperative relapse that is caused by skewed distribution of the stresses on the fixation screws.

Investigation of infraorbital nerve injury following zygomaticomaxillary complex fractures.

The aim of this study was to investigate the severity of infraorbital nerve injury following zygomaticomaxillary complex fractures and to estimate the treatment methods facilitating its functional recovery. A total of 478 patients with unilateral zygomaticomaxillary complex fractures were treated. Infraorbital nerve sensory disturbances were diagnosed in 64.4% of the patients. Injury of the infraorbital nerve was expressed as asymmetry index, which was calculated as a ratio between the affected side and the intact side electric pain detection thresholds at the innervation zone skin before treatment and 14 days, 1, 3, 6 and 12 months postoperatively. A mean asymmetry index of 0.6 +/- 0.03 and 1.9 +/- 0.5 was registered for 57 (11.9%) patients with hyperalgesia and for 251 (52.5%) patients with hypoalgesia, respectively. As a result of retrospective analysis of infraorbital nerve sensory disturbances and its functional recovery, infraorbital nerve injury severity was classified as mild, moderate and severe. It was found that the dynamics and outcome of the functional infraorbital nerve recovery depend on the severity of the injury and the presence of infraorbital canal damage. Function was completely recovered within 3 months after treatment in cases with mild nerve injury. In moderate cases, complete recovery was seen within 6 months and in 34.6% of the severe cases, within a 12-month period after treatment when infraorbital nerve decompression was performed according to the stated indication. Treatment based on infraorbital nerve injury classification offers a better prognosis for complete recovery of the infraorbital nerve function.

Direct orbital manometry in normal and fractured orbits of Chinese patients.

PURPOSE: This study measured direct orbital tension (DOT) in normal and fractured orbits of Chinese patients before and after orbital fracture repair, to investigate the changes in DOT and intraocular pressure (IOP) after surgery and to evaluate any correlation between them. MATERIALS AND METHODS: DOT was directly measured by a specially designed orbitonometer before and after orbital fracture surgery in 40 cases of unilateral orbital fractures, using the contralateral eyes as a control group. All of the patients were submitted to orbital fracture repair and globe repositioning. IOP and ocular function were recorded preoperatively and postoperatively. RESULTS: DOT was 5.0 +/- 1.3 mm Hg (mean +/- SD) in the normal orbits. DOT was positively correlated with IOP (r = 0.56; P < .01). DOT and IOP were significantly decreased (s = 81, P = .01 and s = 49.5, P = .02, respectively) on the fractured orbit side. Postoperative DOT and IOP were significantly increased (s = 410, P < .01 and s = 390, P < .01, respectively). The preoperative to postoperative changes in both DOT and IOP were positively correlated (r = 0.54; P < .01). CONCLUSIONS: DOT can be measured safely using an orbital manometer in normal and fractured orbits. DOT and IOP increased significantly after orbital fracture surgery. DOT was well-correlated with IOP both preoperatively and postoperatively.

Intraocular pressure variations during zygomatic fracture reduction and fixation: a clinical study.

BACKGROUND: The reduction of midface fractures has been associated with the rare but devastating complication of blindness. An increase in intraocular pressure is important in the mechanism of blindness in this setting. In this study, the authors assessed the intraocular pressure in patients who underwent zygomatic fracture reduction (with or without fixation). METHODS: Using applanation tonometry, 29 patients underwent intraocular pressure measurements before, during, and after fracture fixation. The contralateral pressures were measured and used as the control. RESULTS: There were 29 patients with a mean age of 35 years, and the mean time to surgery was 5 days. Preoperatively, all patients had normal intraocular pressures and normal visual acuity. All patients underwent a Gillies lift and 18 patients required open reduction and fixation of the frontozygomatic suture (n = 4) or the infraorbital margin (n = 2), and the remainder (n = 12) required fixation of both points. There was no statistically significant increase in the intraocular pressures following the reduction of uncomplicated zygomatic fractures. Statistically significant pressure reductions were noted immediately after reduction and fixation. CONCLUSIONS: The surgical reduction of uncomplicated zygomatic fractures has no adverse effect on the intraocular pressure. It is the authors' opinion that adjunctive measures to reduce the pressures are unnecessary.

Clinical analysis of isolated zygomatic arch fractures.

PURPOSE: The purpose of this study is to analyze the characteristics of isolated zygomatic arch fractures and to evaluate the functional and radiological outcomes of the treatment. PATIENTS AND METHODS: Forty patients with isolated zygomatic arch fractures were analyzed clinically. RESULTS: The patients were 25 males and 15 females with an average age of 42 years. The cause of injury was traffic accident in 26, followed by fall in 8, sports in 3, and assault in 3. The left side was involved in 25 cases. Fractures were classified into 5 types according to the degree of displacement and loss of bone contact. Reduction was performed in 31 patients, 26 treated by the Gillies temporal approach. Conservative treatment was chosen in 9 patients. The reduction status was excellent in 12 cases, good in 17 cases, and fair in 2 cases. There was no difference in the reduction status in terms of the fracture types or the interval between reduction and injury. Interincisal distance (IID) at maximal mouth opening recovered from 33.4 to 43.8 mm by excellent reduction, from 26.2 to 42.2 mm by good reduction, from 27.5 to 40 mm by fair reduction, and from 41 to 46.6 mm by conservative treatment. CONCLUSIONS: Good functional and radiological outcomes were obtained in isolated zygomatic arch fractures. Reduction status was not influenced by either the fracture type or the interval between reduction and injury, and recovery of IID was similarly achieved by excellent, good, and fair reduction.

Predicting zygoma fractures from baseball impact.

The purpose of this study is to develop injury risk functions that predict zygoma fracture based on baseball type and impact velocity. Zygoma fracture strength data from published experiments were mapped with the force exerted by a baseball on the orbit as a function of ball velocity. Using a normal distribution, zygoma fracture risk functions were developed. Experimental evaluation of these risk functions was performed using six human cadaver tests and two baseballs of different stiffness values. High speed video measured the baseball impact velocity. Post test analysis of the cadaver skulls was performed using CT imaging including three-dimensional reconstruction as well as autopsy. The developed injury risk functions accurately identify the risk of zygoma fracture as a result of baseball impact. The experimental results validated the zygoma risk functions at the lower and upper levels. The injuries observed in the post test analysis included fractures of the zygomatic arch, frontal process and the maxilla, zygoma suture, with combinations of these creating comminuted, tripod fractures of the zygoma. Tests with a softer baseball did result in injury but these had fewer resulting zygoma bone fragments and occurred at velocities 50% higher than the major league ball.

Biomechanical analysis of the rigid fixation of zygoma fractures: an experimental study.

In this experimental study, the goal was to test the sufficiency of actual fixation plates in zygomatic complex fractures and the efficiency of a modified plate at the zygomaticofrontal suture in a suitable model, which was designed for biomechanical study. To address this issue, a zygomatic fracture model produced by using a cadaveric cranium was simulated and the fractures were fixed by the actual and modified fixation materials. The force simulating masseter muscle pull was applied with the Lloyd material testing apparatus, and the rotation of the zygoma was determined using displacement transducers. In this study, there were three different experimental groups. Although miniplates at the zygomaticomaxillary buttress and microplates at the infraorbital rim were used in all three groups, three different plates (miniplate, microplate, and modified plate) were used at the frontozygomatic suture in these groups. Rotational displacement of the zygoma with the effects of simulated masseter muscle force was determined. According to the results obtained, microplates are not effective in stabilizing the frontozygomatic suture when the masseter muscle forces are within physiological range. Although miniplates stabilize zygomatic complex fractures, it was shown that modified microplates, which have no ondulation along the plate border, have a higher resistance to rotation than that of the conventional plates. The rotation angle at the instant of fracture with microplates was 4.59 degrees, and that with miniplates was 1.26 degrees. The maximum rotation angle with modified microplates was 0.32 degrees. Modified microplates designed for the fixation of fractures in the zygomatico-orbital region have been shown to be suitable in a well-designed experimental model and might be appropriate for clinical use.

Bone induction capacity of the periosteum and neonatal dura in the setting of the rat zygomatic arch fracture model.

OBJECTIVES: Osteogenic properties of the dura and periosteum are thought to contribute to the regenerative capacity of membranous bone tissue. The purpose of this investigation was to elucidate (1) whether dura without underlying neural tissues can induce osteogenesis, (2) to what extent the periosteum participates in membranous bone healing, and (3) the difference between dura-induced and periosteum-induced osteogenesis. METHODS: A standardized 2-mm defect was created within the middle portion of each zygomatic arch in 30 Wistar albino rats. The rats were divided into 3 groups, 10 animals in each group. In group 1, the periosteum was removed and neonatal dura grafts were transplanted onto the zygomatic arch bone defect circumferentially. In group 2, the overlying periosteum was preserved. In group 3, the periosteum was removed. At 3 and 10 weeks, animals from each group were killed, and specimens were obtained. Data were collected from the 3-dimensional computed tomographic scans and histologic studies to compare the extent of bony repair. RESULTS: Fracture sites demonstrated osteogenesis associated with chondrogenesis in groups 1 and 2 and only limited osteogenesis with no chondrogenesis in group 3. In some animals in group 3, cortical bone ends underwent resorption. In groups 1 and 2, bone defects were obliterated by the formation of the mature compact bone at 10 weeks postoperatively. The difference between bone regeneration in these groups was not significant (P =.16). In group 3, the defects failed to heal by bony union, and in most of the samples the fibrous union was observed instead. The difference between groups 1 and 3 was significant (P =.03). The difference between groups 2 and 3 was not significant (P =.09). CONCLUSIONS: The trend toward significance is in agreement with the current clinical practice of preserving periosteum in the manipulations of the membranous bone defects. Newborn dura can exert a potentiating effect on osteogenesis.

The sphenozygomatic suture as a key site for osteosynthesis of the orbitozygomatic complex in panfacial fractures: a biomechanical study in human cadavers based on clinical practice.

The aims of this study were to determine the forces required for fracturing the intact orbitozygomatic complex and to evaluate the strength of the orbitozygomatic complex-fixation, especially with regard to the sphenozygomatic suture as a fixation point. In severe midfacial and panfacial fractures, the sphenozygomatic suture is routinely used in the authors' practice as a key site for fixation of the orbitozygomatic complex, thus establishing a stable outer frame as a basis for subsequent reconstruction. However, this has never been formally described, nor has it been biomechanically tested. Eight human cadaver heads were subjected to forces applied in a standard fashion to the orbitozygomatic complex on both sides (n = 16) using a servohydraulic testing machine. The force required to break the intact orbitozygomatic complex was measured on both sides. Subsequently, fracture patterns were noted and each orbitozygomatic complex (n = 16) was assigned to one of four groups: four-point fixation (zygomatic arch, frontozygomatic suture, infraorbital rim, zygomaticomaxillary buttress) using a 1.3/2.0-mm titanium system (group 1) and a 2.0-mm bioresorbable system (group 3); or three-point fixation (zygomatic arch, frontozygomatic suture, sphenozygomatic suture) using 1.3/2.0-mm titanium system (group 2) and a 2.0-mm bioresorbable system (group 4). Forces for failure of the constructs were measured. The force for failure of the intact orbitozygomatic complex was 1826 +/- 852 N. The mean force required for failure of the reconstructed orbitozygomatic complex was 504 +/- 178 N for group 1, 620 +/- 304 N for group 2, 93 +/- 22 N for group 3, and 133 +/- 31 N for group 4. The titanium constructs provided 27.7 percent (four-point fixation) and 31.7 percent (three-point fixation) of the intact breaking strength of the orbitozygomatic complex, which was significantly higher (p < 0.05) compared with 5.4 percent (four-point fixation) and 7.7 percent (four-point fixation) for the bioresorbable system. Plate bending (91 percent) was the primary cause for failure in the titanium plating system, whereas plate and screw breakage (57 percent) was responsible for failure of the resorbable system. The fixation of the sphenozygomatic suture was a key site in the fixation of the orbitozygomatic complex, which could be demonstrated with superior results in the three-point fixation group compared with the four-point fixation group. The bioresorbable system showed the lowest values in this cadaver study. Further experimental and clinical studies might determine whether the bioresorbable materials are sufficient for the treatment of complex fractures of the orbitozygomatic complex.

Experimental trauma to the malar eminence: fracture biomechanics and injury patterns.

OBJECTIVES: To document patterns of facial fractures after trauma to the malar eminence and to elucidate biomechanical factors relevant to the injury patterns. STUDY DESIGN AND SETTING: Studies were conducted on 14 cadaver heads. Study variables included impact velocity, contact area, impact force, and zygomatic skin thickness. Bony fractures and clinical injury patterns were documented. A fracture severity rating scale was devised and statistically correlated to the study variables using regression ANOVA analysis. RESULTS: A broad spectrum of facial fracture patterns was found. Skin thickness and surface area did not correlate with fracture severity (P = 0.67, P = 0.83, respectively). Impact force demonstrated a trend toward significance (P = 0.14). Velocity was most correlative with fracture severity (P = 0.07). A critical threshold velocity (3.5 m/s) was found to correlate with the most severe fracture patterns. CONCLUSIONS: A broad spectrum of facial fracture patterns was demonstrated after experimental trauma to the malar eminence. Contact surface area and zygomatic skin thickness were not found to be significant factors in fracture severity. Velocity, rather than impact force, was most correlative with fracture severity. The most severe fracture patterns were elicited by velocities above 3.5 m/s.

Intraocular and intraorbital compartment pressure changes following orbital bone grafting: a clinical and laboratory study.

Visual loss is an uncommon but catastrophic complication after intraorbital bone grafting for the reconstruction of acute traumatic defects or long-standing enophthalmos. Increased intraocular or intraorbital compartment pressure may be pathogenic in this setting. A two-part study was designed to test the null hypothesis that intraocular and intraorbital compartment pressure values remain constant despite orbital volume reduction with graft material. Laboratory study: Intraocular and intraorbital compartment pressures were measured during sequential orbital volume reduction in New Zealand White rabbits that had been randomized to one of three groups: intact orbits (n = 10), acute orbital wall defects (n = 8), and chronic (3 months) orbital wall defects (n = 11). Intraocular pressure was significantly (p<0.05) elevated in all three groups of orbits undergoing orbital volume reduction compared with control, nonoperated orbits. Intraorbital compartment pressure values did not change significantly from control levels throughout the grafting sequence. Although no significant differences existed between groups in the maximum levels of intraocular pressure attained, the chronic group demonstrated a greater rate of rise and slower rate of decline. Clinical study: Using applanation tonometry, intraocular pressure was measured before and serially after orbital floor exploration and intraorbital placement of split calvarial bone grafts in 19 patients who presented with orbital-zygomatic complex fractures that required surgery. A separate group of 16 patients with orbital-zygomatic complex fractures that required exploration of the orbital floor but not bone grafting was used for comparison. A significant (p<0.05) elevation of intraocular pressure was observed immediately after bone grafting compared with nongrafted orbits, but values returned to normal within 30 minutes and remained stable through the third postoperative day. There were no cases of visual impairment in any patients in either group as the result of surgical treatment. These data indicate that orbital volume reduction with graft material results in significant, temporary elevation of intraocular pressure. No significant elevations of intraorbital compartment pressure were detected in the rabbit orbits. Data from this study may have direct relevance in defining guidelines for "tolerable" changes in orbital tissue and globe pressures after surgery.