Sarath Koruprolu

Biomechanical Analysis of Brostrom Versus Brostrom-Gould Lateral Ankle Instability Repairs:

Background: The traditional Brostrom repair and the modified Brostrom-Gould repair are 2 historically reliable procedures used to address lateral ankle instability. The purpose of this study was to evaluate the biomechanical stability conferred by the Brostrom repair as compared to the Brostrom-Gould modification in an unstable cadaveric ankle model. Methods: A total of 10 cadaveric specimens were placed in a Telos ankle stress apparatus in an anterior-posterior position and then in a lateral position, while a 170 N load was applied to simulate anterior drawer (AD) and talar tilt (TT) tests, respectively. In both circumstances, the ankle was held in 15 degrees of plantarflexion, neutral, and 15 degrees of dorsiflexion, while the movement of the sensors was measured using a video motion analysis system. Measurement of the translation between the talus and tibia in the AD test and the angle between the tibia and talus in the TT test were calculated for specimens in the (1) intact, (2) sectioned (division of the ATFL and CFL), (3) Brostrom repair and (4) Gould modification states. Results: When compared to both the repaired states and the intact states, the sectioned state demonstrated increased inversion and translation at all ankle positions during TT and AD testing. Furthermore, no significant differences were found between the intact state and either of the repaired states. Finally, no difference in the biomechanical stability could be identified between the traditional Brostrom repair and the modified Brostrom-Gould procedure. Conclusions: Our findings indicate that there is no significant biomechanical difference in initial ankle stability conferred by augmenting the traditional Brostrom repair with the Gould modification in this time-zero cadaveric model. Clinical Relevance: These data suggest that the additional reinforcement of an ankle’s lateral ligament complex repair of the ankle with the inferior extensor retinaculum may be marginal at the time of surgery.

Contribution of the Medial Malleolus to Tibiotalar Joint Contact Characteristics

Background. Isolated medial malleolus fractures are typically treated operatively to minimize the potential for articular incongruity, instability, nonunion, and posttraumatic arthritis. The literature, however, has not clearly demonstrated inferior outcomes with conservative treatment of these injuries. This study measured the effects of medial malleolus fracture and its resultant instability on tibiotalar joint contact characteristics. We hypothesized that restoration of anatomical alignment and stability through fixation would significantly improve contact characteristics. Methods. A Tekscan pressure sensor was inserted and centered over the talar dome in 8 cadaveric foot and ankle specimens. Each specimen was loaded at 700 N in multiple coronal and sagittal plane orientations. After testing fractured samples, the medial malleolus was anatomically fixed before repeat testing. Contact area and pressure were analyzed using a 2-way repeated-measure ANOVA. Results. In treated fractures, contact areas were higher, and mean contact pressures were lower for all positions. These differences were statistically significant in the majority of orientations and approached statistical significance in pure plantarflexion and pure inversion. Decreases in contact area varied from 15.1% to 42.1%, with the most dramatic reductions in positions of hindfoot eversion. Conclusions. These data emphasize the importance of the medial malleolus in maintaining normal tibiotalar contact area and pressure. The average decrease in contact area after simulated medial malleolar fractures was 27.8% (>40% in positions of hindfoot eversion). Such differences become clinically relevant in cases of medial malleolar nonunion or malunion. Therefore, we recommend anatomical reduction and fixation of medial malleolus fractures with any displacement. Level of Evidence: Therapeutic Level V—Cadaveric Study

Effect of Distal Interlock Fixation in Stable Intertrochanteric Fractures

The objective of this study was to evaluate the torsion stiffness of locked and unlocked distal fixation of long cephalomedullary nail constructs, in both a fresh fracture and healed, stable intertrochanteric fracture model. Samples were tested in both internal and external rotation (0±3 Nm) for a duration of 10 cycles. Each femur was tested without instrumentation (intact femur), with instrumentation and no fracture (healed intertrochanteric fracture), and with instrumentation with an osteotomy creating a stable intertrochanteric fracture (fresh fracture). All specimens were instrumented with a long cephalomedullary nail. A distal interlock was placed in the dynamic position in 1 femur, and the other femur of the matched pair was left unlocked. Mean external (ER) and internal (IR) rotation stiffness for intact femurs without instrumentation (ER, 2.1±0.5 Nm/degree; IR, 2.2±0.5 Nm/degree) was statistically stiffer (P<.05 for all) compared with fresh fractured locked (ER, 1.1±0.2 Nm/degree; IR, 1.1±0.3 Nm/degree) and fresh fractured unlocked (ER, 0.9±0.3 Nm/degree; IR, 1.0±0.2 Nm/degree) samples. Similarly, healed locked (ER, 2.5±0.2 Nm/degree; IR, 2.8±0.1 Nm/degree) and healed unlocked (ER, 2.5±0.5 Nm/degree; IR, 2.4±0.3 Nm/degree) samples had statistically higher stiffness compared with fresh fractured treatments. These results suggest that the unlocked distal constructs provide similar torsional strength compared with locked fixation in these models.

Accuracy of plain radiographs versus 3D analysis of ankle stress test.

Background: Radiographic stress testing using both the anterior drawer (AD) and talar tilt (TT) technique is a widely accepted means of assessing ankle instability. The purpose of this study was to investigate the accuracy of plain film radiography in measuring translation of the talus during the AD test and the rotation of the talus during TT stress testing. In addition to determining the true accuracy of radiologic assessment in two planes, our goal was to further define instability in the sagittal, coronal and transverse planes. Methods: Twenty lower extremity specimens were placed in a Telos ankle stress apparatus, and respective lateral and AP radiographs were taken during simulated AD and TT testing. Positional measurements were calculated from the films. Next, a three-dimensional tracking system was used to calculate these displacements. The anterior talofibular ligament and calcaneofibular ligament were sectioned to simulate an unstable ankle, followed by repeat measurement using both methods. Movement calculated using the three dimensional system was compared to that of plain radiographs using a paired t-test. Results: Mean positional changes determined by plain film radiographs were found to be significantly lower than those calculated by the three-dimensional system in both AD and TT tests in the intact and sectioned states (p< 0.001). Conclusion: Radiographic stress testing assessment of ankle instability appears to be much less accurate than previously believed. Clinical Relevance: Compared to values calculated with the 3D system, radiographic measurements may underestimate the true magnitude of TT and AD changes which could influence clinical decision making.

A biomechanical comparison of locked and unlocked long cephalomedullary nails in a stable intertrochanteric fracture model.

Objectives: This study compared the torsional properties of stable intertrochanteric femur fractures in a cadaveric bone model using 2 different distal fixation strategies: unlocked long cephalomedullary nailing versus dynamically locked nailing. Methods: Fourteen matched pairs of cadaveric femora were randomly assigned to 1 of 2 distal fixation treatment groups: a single distal interlock screw placed in the dynamic orientation or no distal screw fixation. A stable 2-part intertrochanteric fracture was produced. Specimens were potted and mounted in a double gimbal fixture, facilitating unconstrained motion in the sagittal and coronal planes. Specimens were cyclically loaded dynamically in both internal and external rotation. Range of motion, internal and external rotation stiffness, torsion stiffness, torsion yield, and ultimate torsion magnitude were calculated. Results: The samples instrumented with a distal locking screw reported statistically significantly greater internal (1.54 ± 0.81 N·m per degree vs. 1.08 ± 0.35 N·m per degree; P = 0.026) and external rotational stiffness (1.42 ± 0.72 N·m per degree vs. 0.86 ± 0.36 N·m per degree; P = 0.009). Samples with locked distal fixation were statistically stiffer and displayed statistically less displacement at the yield and peak torque. The yield torque was statistically significantly higher in the samples without distal fixation (14.2 ± 3.3 N·m per degree vs. 10.6 ± 3.8 N·m per degree; P = 0.037). The peak torque was comparable between locked and unlocked samples (15.0 ± 4.6 N·m per degree vs. 16.2 ± 4.2 N·m per degree; P = 0.492). Conclusions: Distal locking of femoral intramedullary nails increases the stiffness of the nail–femur construct. Unlocked samples displayed statistically significant higher yield torque while maintaining comparable peak torque as the locked samples. This study indicates that treating stable intertrochanteric fractures with unlocked long intramedullary nails may be an acceptable option, although further clinical study will be needed to test this assertion.

Dynamic biomechanical examination of the lumbar spine with implanted total disc replacement using a pendulum testing system.

Study Design. Biomechanical cadaver investigation. Objective. To examine dynamic bending stiffness and energy absorption of the lumbar spine with and without implanted total disc replacement (TDR) under simulated physiological motion. Summary of Background Data. The pendulum testing system is capable of applying physiological compressive loads without constraining motion of functional spinal units (FSUs). The number of cycles to equilibrium observed under pendulum testing is a measure of the energy absorbed by the FSU. Methods. Five unembalmed, frozen human lumbar FSUs were tested on the pendulum system with axial compressive loads of 181 N, 282 N, 385 N, and 488 N before and after Synthes ProDisc-L TDR implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5º resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and bending stiffness (N·m/º) was calculated and compared for each testing mode. Results. In flexion/extension, the TDR constructs reached equilibrium with significantly (P < 0.05) fewer cycles than the intact FSU with compressive loads of 282 N, 385 N, and 488 N. Mean dynamic bending stiffness in flexion, extension, and lateral bending increased significantly with increasing load for both the intact FSU and TDR constructs (P < 0.001). In flexion, with increasing compressive loading from 181 N to 488 N, the bending stiffness of the intact FSUs increased from 4.0 N·m/º to 5.5 N·m/º, compared with 2.1 N·m/º to 3.6 N·m/º after TDR implantation. At each compressive load, the intact FSU was significantly stiffer than the TDR (P < 0.05). Conclusion. Lumbar FSUs with implanted TDR were found to be less stiff, but absorbed more energy during cyclic loading with an unconstrained pendulum system. Although the effects on clinical performance of motion-preserving devices are not fully known, these results provide further insight into the biomechanical behavior of these devices under approximated physiological loading conditions.

The Effect of C-Arm Position on Radiation Exposure During Fixation of Pediatric Supracondylar Fractures of the Humerus

BACKGROUND Closed reduction and percutaneous pinning of a pediatric supracondylar fracture of the humerus requires operating directly next to the C-arm to hold reduction and perform fixation under direct imaging. This study was designed to compare radiation exposure from two C-arm configurations: with the image intensifier serving as the operating surface, and with a radiolucent hand table serving as the operating surface and the image intensifier positioned above the table. METHODS We used a cadaveric specimen in this study to determine radiation exposure to the operative elbow and to the surgeon at the waist and neck levels during simulated closed reduction and percutaneous pinning of a pediatric supracondylar fracture of the humerus. Radiation exposure measurements were made (1) with the C-arm image intensifier serving as the operating surface, with the emitter positioned above the operative elbow; and (2) with the image intensifier positioned above a hand table, with the emitter below the table. RESULTS When the image intensifier was used as the operating surface, we noted 16% less scatter radiation at the waist level of the surgeon but 53% more neck-level scatter radiation compared with when the hand table was used as the operating surface and the image intensifier was positioned above the table. In terms of direct radiation exposure to the operative elbow, use of the image intensifier as the operating surface resulted in 21% more radiation exposure than from use of the other configuration. The direct radiation exposure was also more than two orders of magnitude greater than the neck and waist-level scatter radiation exposure. CONCLUSIONS Traditionally, there has been concern over increased radiation exposure when the C-arm image intensifier is used as an operating surface, with the emitter above, compared with when the image intensifier is positioned above the operating surface, with the emitter below. We determined that, although there was a statistically significant difference in radiation exposure between the two configurations, neither was safer than the other at all tested levels. CLINICAL RELEVANCE In contrast to traditional teaching regarding radiation exposure, neither C-arm configuration-with the image intensifier serving as the operating surface or with the image intensifier positioned above a radiolucent hand table-was shown to be clearly safer for pediatric supracondylar humeral fracture fixation.

Biomechanical Analysis of Pedicle Screw Fixation for Thoracolumbar Burst Fractures.

Treatment of unstable thoracolumbar burst fractures remains controversial. Long-segment pedicle screw constructs may be stiffer and impart greater forces on adjacent segments compared with short-segment constructs, which may affect clinical performance and long-term out come. The purpose of this study was to biomechanically evaluate long-segment posterior pedicle screw fixation (LSPF) vs short-segment posterior pedicle screw fixation (SSPF) for unstable burst fractures. Six unembalmed human thoracolumbar spine specimens (T10-L4) were used. Following intact testing, a simulated L1 burst fracture was created and sequentially stabilized using 5.5-mm titanium polyaxial pedicle screws and rods for 4 different constructs: SSPF (1 level above and below), SSPF+L1 (pedicle screw at fractured level), LSPF (2 levels above and below), and LSPF+L1 (pedicle screw at fractured level). Each fixation construct was tested in flexion-extension, lateral bending, and axial rotation; range of motion was also recorded. Two-way repeated-measures analysis of variance was performed to identify differences between treatment groups and functional noninstrumented spine. Short-segment posterior pedicle screw fixation did not achieve stability seen in an intact spine (P<.01), whereas LSPF constructs were significantly stiffer than SSPF constructs and demonstrated more stiffness than an intact spine (P<.01). Pedicle screws at the fracture level did not improve either SSPF or LSPF construct stability (P>.1). Long-segment posterior pedicle screw fixation constructs were not associated with increased adjacent segment motion. Al though the sample size of 6 specimens was small, this study may help guide clinical decisions regarding burst fracture stabilization. [Orthopedics. 2016; 39(3):e514-e518.].

Biomechanical Evaluation of the Suture Anchors Used in Open-door Laminoplasty: A Cadaveric Study

Study Design. A cadaveric study. Objective. To determine whether the use of suture anchors is warranted in cervical laminoplasty. Summary of Background Data. The use of suture anchors to stabilize elevated laminae has been popularized in laminoplasty. However, the validity of using suture anchors in laminoplasty has not been determined. Methods. Six intact fresh frozen cadavers were used. Open-door laminoplasty with a hinge on the cadavers left side was performed on levels C3–C7. Elevated laminae were stabilized by suture anchors equipped with strain gauges, which were placed on C3, C5, and C7 left lateral masses. After surgery, the cervical spine was manually loaded passively, and the mechanical loads on each suture anchor during each motion were measured. Finally, the incision was opened again, and the failure loads of the suture anchors were also measured. Results. After cervical loading, all elevated laminae were confirmed to be intact without dislodgement or failure of the suture anchors. The loads during left rotation and left bending were significantly higher than those during the respective motion to the right at all levels, except in rotation at C3. The loads on the C5 anchors in flexion and left rotation and on the C7 anchors in extension were relatively high. The maximum load obtained in the present study was 14.9 N, which was one order of magnitude lower than the mean failure load of the suture anchors (131.7 N). Conclusion. Biomechanical laterality was demonstrated, reflecting the asymmetrical nature of open-door laminoplasty. The maximum load on the suture anchors was much lower than the failure load and was consistent with the stability of the suture anchors encountered in clinical cases. This may support the validity of using suture anchors in laminoplasty, although the loads during active motion may be higher than our results. Level of Evidence: N/A

Dynamic Biomechanical Examination of the Lumbar Spine with Implanted Total Spinal Segment Replacement (TSSR) Utilizing a Pendulum Testing System

Background Biomechanical investigations of spinal motion preserving implants help in the understanding of their in vivo behavior. In this study, we hypothesized that the lumbar spine with implanted total spinal segment replacement (TSSR) would exhibit decreased dynamic stiffness and more rapid energy absorption compared to native functional spinal units under simulated physiologic motion when tested with the pendulum system. Methods Five unembalmed, frozen human lumbar functional spinal units were tested on the pendulum system with axial compressive loads of 181 N, 282 N, 385 N, and 488 N before and after Flexuspine total spinal segment replacement implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5°; resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and bending stiffness (N-m/°) was calculated and compared for each testing mode. Results The total spinal segment replacement reached equilibrium with significantly fewer cycles to equilibrium compared to the intact functional spinal unit at all loads in flexion (p<0.011), and at loads of 385 N and 488 N in lateral bending (p<0.020). Mean bending stiffness in flexion, extension, and lateral bending increased with increasing load for both the intact functional spinal unit and total spinal segment replacement constructs (p<0.001), with no significant differences in stiffness between the intact functional spinal unit and total spinal segment replacement in any of the test modes (p>0.18). Conclusions Lumbar functional spinal units with implanted total spinal segment replacement were found to have similar dynamic bending stiffness, but absorbed energy at a more rapid rate than intact functional spinal units during cyclic loading with an unconstrained pendulum system. Although the effects on clinical performance of motion preserving devices is not fully known, these results provide further insight into the biomechanical behavior of this device under approximated physiologic loading conditions.