External Rotation Loading Research Articles

Augmenting ACL Repair With Suture Tape Improves Knee Laxity: A Biomechanical Study.

Anterior cruciate ligament (ACL) repair is an alternative to reconstruction; however, suture tape support may be necessary to achieve adequate outcomes. To investigate the influence of suture tape augmentation (STA) of proximal ACL repair on knee kinematics and to evaluate the effect of the 2 flexion angles of suture tape fixation. Controlled laboratory study. Fourteen cadaveric knees were tested using a 6 degrees of freedom robotic testing system under anterior tibial (AT) load, simulated pivot-shift (PS) load, and internal rotation (IR) and external rotation loads. Kinematics and in situ tissue forces were evaluated. Knee states tested were (1) ACL intact, (2) ACL cut, (3) ACL repair with suture only, (4) ACL repair with STA fixed at 0° of knee flexion, and (5) ACL repair with STA fixed at 20° of knee flexion. ACL repair alone did not restore the intact ACL AT translation at 0°, 15°, 30°, or 60° of flexion. Adding suture tape to the repair significantly decreased AT translation at 0°, 15°, and 30° of knee flexion but not to the level of the intact ACL. With PS and IR loadings, only ACL repair with STA fixed at 20° of flexion was not significantly different from the intact state at all knee flexion angles. ACL suture repair had significantly lower in situ forces than the intact ACL with AT, PS, and IR loadings. With AT, PS, and IR loadings, adding suture tape significantly increased the in situ force in the repaired ACL at all knee flexion angles to become closer to that of the intact ACL state. For complete proximal ACL tears, suture repair alone did not restore normal knee laxity or normal ACL in situ force. However, adding suture tape to augment the repair resulted in knee laxity closer to that of the intact ACL. STA with fixation at 20° of knee flexion was superior to fixation with the knee in full extension. The study findings suggest that ACL repair with STA fixed at 20° could be considered in the treatment of femoral sided ACL tears in the appropriate patient population.

A Biomechanical Comparison of the LaPrade Technique Versus a Novel Technique for Reconstruction of Medial-Sided Knee Injuries

Background: Medial-sided knee injuries can lead to symptomatic valgus laxity or anteromedial rotatory instability and may require surgery, particularly in the setting of cruciate tears and tibial-sided medial collateral ligament (MCL) avulsions. The LaPrade (LP) technique utilizes 2 free grafts to reconstruct the superficial MCL (sMCL) and the posterior oblique ligament (POL). An alternative MCL reconstruction devised by the senior author comprises an anatomic single-bundle reconstruction using a free graft to reconstruct the sMCL with advancement and imbrication of the posteromedial capsule/POL (MCL anatomic reconstruction with capsular imbrication [MARCI] technique). These techniques have not been biomechanically compared with one another. Purpose: To identify if one of these reconstruction techniques better restores valgus and rotational medial knee stability throughout the range of motion. Study Design: Controlled laboratory study. Methods: A total of 20 fresh-frozen, male (mean age, 43.7 years [range, 20-63 years]), midfemur-to-toe-matched cadaveric knees were utilized. All reconstructions were performed by a single fellowship-trained sports medicine surgeon. Left and right specimens within matched pairs were randomized to 1 of the 2 treatment groups: LP or MARCI. Each specimen was tested in 3 phases: (1) intact knee, (2) destabilized (MCL and POL completely severed), and (3) reconstructed (post-LP or post-MARCI reconstruction). We quantified valgus angulation defined by medial joint line opening, as well as internal and external tibial rotation at 0°, 20°, 30°, 60°, and 90° of knee flexion under applied external moments/torques at each phase. Results: There were significant differences between the MARCI and LP reconstruction groups in valgus stability compared with the intact state (P = .021), with the MARCI reconstruction more closely approximating the intact knee. There was no overall difference between the MARCI and LP reconstruction techniques for internal rotation (P = .163), with both closely resembling the intact state. For external rotation, the effect of the reconstruction technique was dependent on the knee flexion angle (P < .001). At the highest angles, there were no differences between reconstructions; however, for lower knee flexion angles, the MARCI technique more closely resembled the intact state. Conclusion: Although both techniques improved knee stability compared with destabilized conditions, the MARCI technique better approximated intact stability during valgus at knee flexion angles from 0° to 90° and external rotation loads at knee flexion angles ≤30° in a cadaveric model. Clinical Relevance: The MARCI technique provides an alternative option to improve valgus stability throughout the range of motion. It utilizes a POL advancement without the potential limitations seen in the LP technique, such as multiple tunnel complexity and collision, particularly in the multiple ligament–injured knee.

Measuring Knee Joint Laxity in Three Degrees-of-Freedom In Vivo Using a Robotics- and Image-Based Technology.

Accurate and reliable information about three-dimensional (3D) knee joint laxity can prevent misdiagnosis and avoid incorrect treatments. Nevertheless, knee laxity assessments presented in the literature suffer from significant drawbacks such as soft tissue artifacts, restricting the knee within the measurement, and the absence of quantitative knee ligament property information. In this study, we demonstrated the applicability of a novel methodology for measuring 3D knee laxity, combining robotics- and image-based technology. As such technology has never been applied to healthy living subjects, the aims of this study were to develop novel technology to measure 3D knee laxity in vivo and to provide proof-of-concept 3D knee laxity measurements. To measure tibiofemoral movements, four healthy subjects were placed on a custom-built arthrometer located inside a low dose biplanar X-ray system with an approximately 60 deg knee flexion angle. Anteroposterior and mediolateral translation as well as internal and external rotation loads were subsequently applied to the unconstrained leg, which was placed inside a pneumatic cast boot. Bone contours were segmented in the obtained X-rays, to which subject-specific bone geometries from magnetic resonance imaging (MRI) scans were registered. Afterward, tibiofemoral poses were computed. Measurements of primary and secondary laxity revealed considerable interpersonal differences. The method differs from those available by the ability to accurately track secondary laxity of the unrestricted knee and to apply coupled forces in multiple planes. Our methodology can provide reliable information for academic knee ligament research as well as for clinical diagnostics in the future.

Comparison of Suture-Button Fixation with Suture-Tape Augmentation and Trans-Syndesmotic Screw Fixation for Syndemosis Injury: A Biomechanical Study

Category:Ankle; Basic Sciences/BiologicsIntroduction/Purpose:The treatment of syndesmotic injuries with ankle fractures is controversial. The purpose of this study was to compare the biomechanical properties of suture-button fixation with suture-tape augmentation with those of screw fixation.Methods:Ten matched pairs of human cadaver specimens were subjected to suture-button fixation with suture-tape augmentation or screw fixation. Each specimen underwent initial intact physiologic loading, consisting of 10 cycles of axial loading with peak of 750N, 10 cycles of external torsional loading with peak of 7.5Nm, and 10 cycles of combined axial and external torsional loading with peak of 750N and 7.5Nm at 0.05 Hz. Injuries of the anterior inferior tibiofibular ligament, tibiofibular interosseous membrane, posterior tibiofibular ligament and medial malleolar fracture were applied to each specimen. Postfixation cyclic loading consisted of 50 cycles of combinedaxial and external rotation loading with peak torques of 750 N and 7.5 Nm at a rate of 0.05 Hz. After postfixation loading, each specimen underwent failure loading by external rotation at 0.25 degrees/second. Failure torque and failure angle were measured.Results:Mean failure torques were 15.99 +- 8.88 Nm in the suture-button fixation with suture-tape augmentation and 17.10 +- 10.38 Nm in the screw group. There was no significant difference in average failure torque between two groups (p-value = 0.669)Average failure angle in screw-fixation group (39.37 +- 10.19 deg) was significantly lower than average failure angle suture- button fixation with suture-tape augmentation (56.64 +- 9.64 deg) (p-value = 0.001).Average rotational stiffness in screw-fixation group (0.53 +- 0.24 Nm/deg) was significantly higher than average rotational stiffness in suture-button fixation with suture-tape augmentation group (0.35 +- 0.19 Nm/deg) (p-value = 0.033).Conclusion:Suture-button fixation with suture-tape augmentation for ankle syndesmotic injury provides similar torsional strength to that of screw fixation and has lower stiffness than screw fixation. Therefore, Suture-button fixation with suture-tape augmentation can be considered as an alternative treatment option for syndesmosis injury.

Biomechanical Analysis of Sagittal Plane Pin Placement Configurations for Pediatric Supracondylar Humerus Fractures

Anterior to posterior (AP) pinning is the recommended sagittal pin configuration in divergent lateral entry coronal pinning of pediatrics supracondylar fractures. However, there was still a lack of evidence regarding alternative sagittal pins configurations. We aimed to compare the construct stiffness of alternative sagittal pin configurations by using synthetic bone models. Sixty synthetic pediatric humeri were osteotomized to create a supracondylar fracture. After the fracture reduction, all specimens were fixed in the coronal plane with divergent lateral entry pin configurations in four different patterns in the sagittal plane: AP, crossed, divergent and parallel sagittal pin configuration. Each configuration was tested with five loading patterns. The AP sagittal pin had significantly lower construct stiffness than the divergent (p = 0.003) and the parallel sagittal pin configuration (p = 0.005) in external rotation loading tests. The divergent sagittal pin had the highest construct stiffness in extension, valgus, and external rotation loads, but the parallel sagittal pin had lower construct stiffness under extension load than the divergent and crossed sagittal pin configurations. The divergent sagittal pin configuration provides greater construct stiffness than other sagittal pin configurations due to the maximal pin spreading distance at the fracture site and the pin angle lock mechanism.

Comparison of Open Anterior Syndesmotic Repair Augmented With Suture-Tape and Trans-syndesmotic Screw Fixation: A Biomechanical Study

The treatment of syndesmotic injuries with ankle fractures is controversial. The purpose of this study was to compare the biomechanical properties of open anterior syndesmotic repair with those of screw fixation. Ten matched pairs of human cadaver specimens were subjected to open syndesmotic repair or screw fixation. Each specimen underwent initial intact physiologic loading, consisting of 10 cycles of external torsional loading with a peak torque of 7.5 Nm at 0.05 Hz. Injuries of the anterior inferior tibiofibular ligament, tibiofibular interosseous membrane, and deltoid ligament were applied to each specimen. Postfixation cyclic loading consisted of 50 cycles of combined axial and external rotation loading with peak torques of 750 N and 7.5 Nm at a rate of 0.05 Hz. After postfixation loading, each specimen underwent failure loading by external rotation at 0.25 degrees/second. Failure torque and failure angle were measured. The paired t test and Wilcoxon signed-rank test were used to analyze the data. Mean failure torques were 95.63 Nm in the open anterior syndesmotic repair augmented with suture-tape group and 108.61 Nm in the screw group. Mean failure angles were 34.93 degrees in the open anterior syndesmotic repair augmented with suture-tape group and 43.55 degrees in the screw group. These data were not statistically significantly different between the groups (p= .7682 and .4133, respectively). Open anterior syndesmotic repair augmented with suture tape for ankle syndesmotic injury provides similar torsional strength to that of screw fixation. Therefore, this technique can be considered as an alternative treatment option for syndesmosis injury.

Comparison of Open Syndesmotic Repair and Trans-syndesmotic Screw Fixation: A Biomechanical Study

Category:Trauma; AnkleIntroduction/Purpose:We hypothesized that open syndesmotic repair for ankle syndesmotic injury would provide adequate strength. The purpose of this study was to compare the biomechanical properties of open syndesmotic repair with those of screw fixation.Methods:Ten matched pairs of human cadaver specimens were subjected to open syndesmotic repair or screw fixation. Each specimen underwent initial intact physiologic loading, consisting of 10 cycles of external torsional loading with a peak torque of 7.5 Nm at 0.05 Hz. Post-fixation cyclic loading consisted of 50 cycles of combined axial and external rotation loading with peak torques of 750 N and 7.5 Nm at a rate of 0.05 Hz. After post-fixation loading, each specimen underwent failure loading by external rotation at 0.25 degrees/second. Failure was defined as a sudden decrease in the torque-degree curve. Failure torque and failure angle were measured. The paired t-test and Wilcoxon signed-rank test were used to analyze the data.Results:Mean failure torques were 95.63 Nm in the open syndesmotic repair group and 108.61 Nm in the screw group. Mean failure angles were 34.93 degrees in the open syndesmotic repair group and 43.55 degrees in the screw group. These data were not statistically significantly different between the two groups (p = 0.7682 and 0.4133, respectively).Conclusion:Open syndesmotic repair for ankle syndesmotic injury provides similar torsional strength to that of screw fixation. Therefore, this technique can be considered as an alternative treatment option for syndesmosis injury.

Impact of Medial Meniscotibial Ligament Disruption Compared to Peripheral Medial Meniscal Tear on Knee Biomechanics.

Medial meniscotibial ligament (MTL) lesions may go unrecognized and untreated and have detrimental impact on knee biomechanics and joint pathology. Therefore, this study was designed to compare the biomechanical impact of midbody MTL disruption to corresponding peripheral medial meniscal (PMM) tears in anterior cruciate ligament (ACL) intact and ACL-deficient cadaveric knees. Cadaveric knees (n = 12; 6 matched pairs) were tested for laxity and ACL strain under anterior, valgus, and external rotation loading at 0, 30, and 90 degree of flexion. Knees were randomly assigned to ACL-intact (n = 6) or ACL-deficient (n = 6) groups. Large midbody MTL disruption or corresponding PMM tears were created (n = 3/group) and knees retested. PMM tears were repaired arthroscopically with inside-out suturing, and MTL lesions were repaired with suture anchors via an open approach. Knees were retested after repair. Biomechanical testing data were compared for statistically significant differences. Large MTL and PMM lesions were associated with significant increases in ACL strain, anterior laxity at 0, 30, and 90 degrees (p = 0.006), valgus laxity (p = 0.0012), and external rotation laxity (p = 0.0003) compared with intact knees. Repair of each lesion restored knee stability and reduced ACL strain to intact levels. In ACL-deficient knees, there was significantly increased anterior, valgus, and external rotation laxity compared with the ACL-intact state and MTL and PMM lesions further increased laxity at all angles. However, differences were not statistically significant and repair of meniscal lesions alone did not restore stability to ACL-deficient knees. These results highlight the need to recognize medial MTL injury and perform an appropriate repair procedure to restore knee stability and protect against excessive ACL strain.

Motion of the distal tibiofibular syndesmosis under different loading patterns: A biomechanical study.

The distal tibiofibular syndesmosis is an important structure for ankle stability. The objective of this study was to evaluate the motion of the syndesmosis under different loading patterns and determine the characteristics of the syndesmotic motion. Six fresh cadaveric lower extremity specimens with the knee reserved were tested in this study. The skin and muscles were removed with all ligaments around the syndesmosis and knee and ankle joint intact. An axial load of 600 N was applied to the specimens with the ankle joint in 10° dorsiflexion, neutral position, and 15° plantar flexion using a universal material testing machine. Then, with the ankle joint positioned neutrally, a combination of 600-N axial and 5-Nm torsional external rotation loading was applied to the specimens. The medial-lateral and anterior-posterior displacement and rotation of the distal fibula relative to the distal tibia were measured. Under the axial loading, the distal fibula tended to move medially and anteriorly and rotate internally with the ankle positioned from the neutral position to 15° plantar flexion. Meanwhile, when the ankle was positioned from the neutral position to 10° dorsiflexion, the distal fibula tended to move laterally and posteriorly and rotate externally. Under the combined loading, with respect to the isolated axial loading, the distal fibula tended to move medially and posteriorly, and rotate externally relative to the distal tibia. Micro motion existed in the syndesmosis. The relative motion of the syndesmosis was correlated to the ankle position and loading patterns.

Biomechanical analysis between Orthofix\xae external fixator and different K-wire configurations for pediatric supracondylar humerus fractures

BackgroundClosed reduction and percutaneous fixation are considered as the optional treatments for displaced supracondylar humerus fractures. However, there was no published report about the biomechanical analysis in Orthofix® external fixator. In this study, we developed a model of supracondylar humerus fractures and compared the biomechanical analysis of external fixator and different K-wires configurations in order to evaluate the stability of external fixator in supracondylar humerus fractures.MethodsWe developed an anatomic humerus model by third-generation synthetic composite, and 60 synthetic humeris were osteotomized to simulate the humeral transverse supracondylar fracture. Those fractures were reduced and fixed by external fixator or K-wires, and then biomechanical analysis was performed in extension, varus, valgus, and internal and external rotation loading. A paired-sample t test was used to evaluate the distance at the fracture site between the external fixator and K-wire configurations.ResultsDuring all direction loading, there was a significant statistical difference between external fixator and K-wires (P < 0.001 for all pairwise comparisons). In extension and internal rotation loading, the external fixator and three crossed K-wires had no comparable stiffness values (P = 0.572; P = 0.795), and both were significantly greater than two crossed and lateral K-wires (P < 0.05). In external rotation loading, there was no significance between the external fixator and K-wire configurations except two lateral K-wires (P > 0.05). In valgus loading, the stability of the external fixator was less than that of three crossed K-wires (P = 0.001) but was not significantly different with those of two crossed or three lateral K-wires (P = 0.126; P = 0.564). In varus loading, the stability of the external fixator was larger than those of two and three lateral K-wires (P = 0.000; P = 007).ConclusionsExternal fixator could provide enough stability for pediatric supracondylar humerus fractures without the injury of the ulnar nerve. Besides, it could enhance the rotational stiffness of the construct in rotation loading to avoid the complication of cubitus varus.

Anatomic and non-anatomic anterior cruciate ligament posterolateral bundle augmentation affects graft function.

The purpose of this study is to compare knee laxity and graft function (tissue force) between anatomic and non-anatomic posterolateral (PL) bundle augmentation. Twelve (n=12) fresh-frozen mature, unpaired porcine knees were tested using a robotic testing system. Four knee states were compared: (a) intact anterior cruciate ligament (ACL), (b) deficient PL and intermediate bundles, (c) anatomic PL augmentation, and (d) non-anatomic PL augmentation. Anterior tibial translation (ATT), internal rotation (IR) and external rotation (ER), and the in situ tissue force were measured under an 89.0-N anterior tibial load and 4.0-Nm internal and external tibial torques. Both anatomic and non-anatomic PL augmentation restored the ER, IR, and ATT of the intact knee at all knee flexion angles (n.s.). Both anatomic and non-anatomic PL augmentation restored the in situ tissue force of the ACL during ER and IR loading and ATT loading at all knee flexion angles except at 60° of knee flexion, where the non-anatomic PL augmentation did not restore the in situ tissue force of the ACL during external rotation loading and the anatomic PL augmentation did not restore the in situ tissue force of the ACL during IR loading. Furthermore, there were no differences in ATT, IR, ER, and in situ tissue force under anterior tibial loading, IR and ER loading between the two reconstruction groups. There were no significant differences between anatomic and non-anatomic PL augmentation using the porcine knee model.

Biomechanical comparison of different external fixator configurations for stabilization of supracondylar humerus fractures in children

BackgroundCurrently, closed reduction and percutaneous pinning are considered the treatment of choice for displaced supracondylar humerus fractures. However, indications exist for the use of external fixation with Schanz screws. In this in vitro study, we evaluate the biomechanical properties of a new variation for external fixation and compare them to an established construct. MethodsTwenty distal cadaver humeri (10 pairs) were allocated to 2 groups. The humeri of the first group were fixed by an external fixator consisting of Schanz screws and an oblique K-wire inserted from the distal radial cortex of the humerus, those of the second group were fixed by a new variation with the oblique K-wire inserted from the distal ulnar cortex of the humerus. Displacement and stiffness in static loading in internal and external rotation, as well as in extension and flexion were evaluated and compared. FindingsThe variation of the external fixator of the second group proved to be statistically significantly superior to the variation of the first group in internal rotation loading (p>0.05). In sagittal loading conditions and external rotation loading, the variations were equally stable (p>0.05). There was no significant effect of the samples' bone density on displacement and stiffness values in any direction of loading. InterpretationIn cases of pediatric supracondylar humerus fractures when an external fixator is used for osteosynthesis, the insertion of an additional ulnarly inserted anti-rotation K-wire should be preferred to a radially inserted one as it reduces secondary displacement of the distal fragment.

Stress Distribution Within Rotator Cuff Tendons With a Crescent-Shaped and an L-Shaped Tear

Background: There are 2 representative shapes of full-thickness rotator cuff tears commonly observed: crescent-shaped and L-shaped tears. To date, the exact process of tear propagation in each shape remains unknown. Purpose: To determine the stress distribution pattern in rotator cuff tendons with a crescent-shaped tear and an L-shaped tear. Study Design: Descriptive laboratory study. Methods: The computed tomography (CT) data of a normal cadaveric shoulder from a 69-year-old man were used to develop a 3-dimensional finite element model of the rotator cuff tendons. Three different sizes (1.0-, 2.0-, and 3.0-cm widths) of crescent-shaped and L-shaped tears were created. Tensile load was applied to each cuff tendon that simulated shoulder abduction and external rotation in the hanging-arm position. Elastic analysis was performed, and distribution of the von Mises equivalent stress was calculated. Then, the stress distribution pattern was compared between the 2 tear shapes and among the 3 different tear sizes. Results: In the crescent-shaped tear models, stress concentration was seen in both the anterior and the posterior edges of the torn tendon stump. In the L-shaped tear models, stress concentration was seen in the posterior torn tendon edge as well as the bottom of the longitudinal tear. The areas with high stress concentration increased with increasing tear size. At the posterior torn tendon edge, a common site of delamination, the articular half represented a higher equivalent stress than the bursal half in all models. The highest equivalent stress increased with an increase in tear size for both the abduction and the external rotation loads. Conclusion: A high stress concentration was seen in both the anterior and the posterior tendon edge in crescent-shaped tears and in both the posterior tendon edge and the bottom of the longitudinal tear in L-shaped tears. Stress concentration inside the tendon increased with increasing tear size. Clinical relevance: Crescent-shaped tears may propagate in the anterior and posterior directions, whereas L-shaped tears may propagate in the posterior and medial directions. Tear propagation may accelerate with an increase in tear size.

Biomechanical analysis of pinning configurations for a supracondylar humerus fracture with coronal medial obliquity

Despite hundreds of studies of pinning configurations for transverse supracondylar humerus fractures, very few studies have investigated the optimal pin configurations in the treatment of supracondylar humerus fractures with coronal medial obliquity. The aim of this study was to develop a model of supracondylar humerus fractures with coronal medial obliquity and compare the stability of three various pin configurations to provide an acceptable pin placement. Oblique cuts were made in synthetic humeri at the level of the coronoid and olecranon fossae to simulate a humeral supracondylar fracture with coronal medial obliquity. Each fracture was reduced and fixed using two 0.062 inch K-wires in three different configurations, and sequentially tested in extension, varus, valgus, and internal and external rotations using an MTS 858 Minibionix materials testing load frame. We performed analysis of variance to compare construction stiffness of different pin configurations and the standard level of significant (P-value ≤ 0.05) was used indicate statistical significance. In resistance to extension and valgus loading, there was no statistical difference between all the three pin configurations (P=0.22 and 0.130, respectively). During the varus loading condition, the greatest stiffness values were obtained with the two crossed pin configuration, followed by the two medial pins, and the two lateral pin configuration showed the lowest values. For resistance in internal and external rotation testing, although there was no statistical difference between the two medial pins and the two crossed pins configurations (P=0.06 and 0.75, respectively), they were significantly greater than that of the two lateral pin configuration (P=0.003 and 0.004; P=0.001 and 0.02, respectively). In a synthetic humerus model of supracondylar humerus fractures with coronal medial obliquity, the two crossed pin configuration provided statistically greatest or comparable stability in the varus, and internal and external rotation loading conditions.

Biomechanical Analysis of Supracondylar Humerus Fracture Pinning for Fractures With Coronal Lateral Obliquity

Closed reduction and percutaneous pin fixation is the recommended treatment of displaced supracondylar humerus fractures. The optimal pin configurations in the treatment of supracondylar humerus fractures with coronal lateral obliquity remain controversial. The aim of this study was to compare the stability of various pin configurations in the treatment of lateral oblique supracondylar humerus fractures to provide an acceptable pin placement. Nine third-generation synthetic composite humeri were osteotomized to simulate a humeral supracondylar fracture with coronal lateral obliquity. Each fracture was reduced and fixed using 2 or three 1.6-mm (0.062 in) Kirschner wires (K-wire) in 3 different configurations, and sequentially tested in extension, varus, valgus, and internal and external rotations using an MTS 858 Minibionix materials testing load frame (MTS Corporation, Eden Prairie, MN). Each fracture was fluoroscopically imaged and the distance between the pins at the fracture site was also recorded. Analysis of variance was carried out to compare construct stiffness for different pin configurations. A paired-samples t test was used to evaluate differences in the distance between the pins for 2 different pin configurations. A level of P<0.05 was considered statistically significant. During extension and internal and external rotation loading conditions, the 2 lateral divergent pins had significantly greater stiffness values than 2 crossed pins. During the valgus loading condition, crossed pins were more stable than 2 lateral pins. During varus loading, there was no statistical difference between the 3 pin configurations (P>0.05). During all the 5 loading conditions, there was a trend for 3 lateral pins to have greater stiffness values than the 2 lateral pins, but this was not statistically significant. The distance between the pins at the oblique fracture site for the 2 lateral divergent pins was statistically greater than the 2 crossed pins. Two and 3 lateral pin configurations had comparable construct stiffness and both were greater than crossed pins, except in the valgus, where crossed pins had greater stiffness. Using these readily available landmarks, the treating surgeon can reproducibly provide appropriate pinning treatment for most of these fractures. In addition, this report represents a helpful reminder that the pinning configuration should be effective and if not, the pins are not positioned correctly.

Alterations in Knee Joint Laxity During the Menstrual Cycle in Healthy Women Leads to Increases in Joint Loads During Selected Athletic Movements

Background It has been speculated that the hormonal cycle may be correlated with higher incidence of ACL injury in female athletes, but results have been very contradictory. Hypothesis Knee joint loads are influenced by knee joint laxity (KJL) during the menstrual cycle. Study Design Controlled laboratory study. Methods Serum samples and KJL were assessed at the follicular, ovulation, and luteal phases in 26 women. Knee joint mechanics (angle, moment, and impulse) were measured and compared at the same intervals. Each of the 26 subjects had a value for knee laxity at each of the 3 phases of their cycle, and these were ordered and designated low, medium, and high for that subject. Knee joint mechanics were then compared between low, medium, and high laxity. Results No significant differences in knee joint mechanics were found across the menstrual cycle (no phase effect). However, an increase in KJL was associated with higher knee joint loads during movement (laxity effect). A 1.3-mm increase in KJL resulted in an increase of approximately 30% in adduction impulse in a cutting maneuver, an increase of approximately 20% in knee adduction moment, and a 20% to 45% increase in external rotation loads during a jumping and stopping task (P < .05). Conclusion Changes in KJL during the menstrual cycle do change knee joint loading during movements. Clinical Relevance Our findings will be beneficial for researchers in the development of more effective ACL injury prevention programs.

Comparison of a Novel FiberWire-Button Construct versus Metallic Screw Fixation in a Syndesmotic Injury Model

There is minimal experience with less rigid syndesmotic fixation devices which may approximate the normal distal tibio-fibular mechanics during healing. This study evaluates the ability of a FiberWire-button implant (Arthrex, Naples, FL) to maintain syndesmotic reduction as compared with a metallic screw. Ten matched fresh-frozen cadaveric ankle pairs with intact ligaments were tested (12.5 Nm external rotation force) to establish physiologic syndesmotic diastasis. The same force was applied to the ankles after sectioning of the syndesmotic and deltoid ligaments. Within the pairs, each limb was randomized to receive a FiberWire-button implant or a metallic screw (Synthes, Paoli, PA); the ankles were tested for syndesmotic diastasis with progressive external rotation force, from 2.5 Nm to 25 Nm (or failure). There was no significant difference in diastasis amongst pairs with intact or sectioned syndesmosis (p=0.64 and p=0.80, respectively). There was a significantly greater diastasis in the FiberWire-button group at all external rotation loads (p<0.0001). Nine of the ten pairs failed (all through fracture of the distal fibula). There were no hardware failures. The metallic screw group failed at a lower load (mean 15 Nm) compared to the FiberWire-button group (mean 18 Nm, p=0.0004). The metallic screw group maintained syndesmotic reduction up to 5 Nm of force. The FiberWire-button was unable to maintain syndesmotic reduction of the ankles at any of the forces applied. The ankles fixed with the FiberWire-button demonstrated significantly greater widening of the syndesmosis compared to the screw, at all loads. The FiberWire-button implant may not maintain adequate ankle syndesmotic reduction in the immediate post-operative period relative to a metallic screw.

Force Measurements on the Fibular Collateral Ligament, Popliteofibular Ligament, and popliteus Tendon to Applied Loads

Background Little information is known about the forces seen on the main individual structures of the posterolateral knee to applied loads. This information is needed to determine which structures should be reconstructed and also the relative strengths needed for reconstruction grafts. Purpose To determine in vitro forces in the fibular collateral ligament, popliteofibular ligament, and popliteus tendon for various posterolateral knee loading conditions. Study Design Cadaveric study. Results The fibular collateral ligament was loaded in varus, internal rotation, and external rotation. The highest amount of force seen on the fibular collateral ligament was at 0° of knee flexion with external rotation, with the mean load response to external rotation significantly less at 90°. Fibular collateral ligament varus load response at 0°, 30°, and 60° was fairly constant, with a significant decrease at 90° compared to 30° of knee flexion. The popliteus tendon and popliteofibular ligament were loaded with an external rotation moment and were noted to have similar loading patterns. The mean load response on both the popliteus tendon and the popliteofibular ligament peaked at 60° of knee flexion. The mean popliteus tendon and popliteofibular ligament load response at 0° was significantly less than the mean load response at 30°, 60°, and 90° of knee flexion. Conclusions High relative loads were seen on the fibular collateral ligament with varus and external rotation and on the popliteus tendon and popliteofibular ligament, with external rotation. A reciprocal relationship of load sharing in external rotation depending on knee flexion angle was revealed that has not been previously reported. The force on the fibular collateral ligament with external rotation loads was higher than the load on the popliteus complex at lower flexion angles, with the popliteus complex having higher load sharing at 60° and 90° of knee flexion. These results provide a measure of the potential for failure of these structures with joint loading and guidelines for both graft strength requirements for surgical reconstructions and postoperative rehabilitation protocols.