Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length an... more Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length and tension throughout knee range of motion with transtibial, anteromedial (AM) portal, and all-epiphyseal drilling techniques with suspensory and apical femoral fixation. Methods The three different femoral tunnel drilling techniques using the same intra-articular starting point within the center of the femoral footprint were performed on fresh-frozen cadaveric specimens. All groups underwent standard tibial drilling in the center of the ACL tibial footprint. FiberWire (Arthrex Inc., Naples, FL) was used to simulate anatomic single bundle reconstructions. Changes in graft length and tension were measured at knee flexion angles of 0, 30, 60, 90, 120, and 135 degrees. Results Graft length and tension decreased from 0 through 60 degrees and subsequently increased from 90 to 135 degrees for all groups. The transtibial, AM portal suspensory, and apical fixation groups were similar. However, th...
Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length an... more Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length and tension throughout knee range of motion with transtibial, anteromedial (AM) portal, and all-epiphyseal drilling techniques with suspensory and apical femoral fixation. Methods The three different femoral tunnel drilling techniques using the same intra-articular starting point within the center of the femoral footprint were performed on fresh-frozen cadaveric specimens. All groups underwent standard tibial drilling in the center of the ACL tibial footprint. FiberWire (Arthrex Inc., Naples, FL) was used to simulate anatomic single bundle reconstructions. Changes in graft length and tension were measured at knee flexion angles of 0, 30, 60, 90, 120, and 135 degrees. Results Graft length and tension decreased from 0 through 60 degrees and subsequently increased from 90 to 135 degrees for all groups. The transtibial, AM portal suspensory, and apical fixation groups were similar. However, the all-epiphyseal tunnel with suspensory fixation had a significantly increased change in length (90, 120, and 135 degrees) and tension (120 and 135 degrees). Conclusion Transtibial and AM portal suspensory fixation and apical fixation demonstrate similar changes in length and tension throughout knee range of motion. The all-epiphyseal tunnel with suspensory fixation was associated with greater length and tension changes at higher degrees of knee flexion. All techniques demonstrated decreased graft length and tension with knee flexion to 60 degrees after which they increased with further knee flexion. Clinical Relevance ACL graft length and tension change throughout knee range of motion and also depend on femoral tunnel orientation and fixation type. The use of an all-epiphyseal tunnel with suspensory fixation should be studied further for evidence of graft elongation.
A single iliosacral screw placed into the S1 vertebral body has been shown to be clinically unrel... more A single iliosacral screw placed into the S1 vertebral body has been shown to be clinically unreliable for certain type C pelvic ring injuries. Insertion of a second supplemental iliosacral screw into the S1 or S2 vertebral body has been widely used. However, clinical fixation failures have been reported using this technique, and a supplemental long iliosacral or transsacral screw has been used. The purpose of this study was to compare the biomechanical effect of a supplemental S1 long iliosacral screw versus a transsacral screw in an unstable type C vertically oriented sacral fracture model. A type C pelvic ring injury was created in ten osteopenic/osteoporotic cadaver pelves by performing vertical osteotomies through zone 2 of the sacrum and the ipsilateral pubic rami. The sacrum was reduced maintaining a 2-mm fracture gap to simulate a closed-reduction model. All specimens were fixed using one 7.0-mm iliosacral screw into the S1 body. A supplemental long iliosacral screw was placed into the S1 body in five specimens. A supplemental transsacral S1 screw was placed in the other five. Each pelvis underwent 100,000 cycles at 250 N, followed by loading to failure. Vertical displacements at 25,000, 50,000, 75,000, and 100,000 cycles and failure force were recorded. Vertical displacement increased significantly (p < 0.05) within each group with each increase in the number of cycles. However, there was no statistically significant difference between groups in displacement or load to failure. Although intuitively a transsacral screw may seem to be better than a long iliosacral screw in conveying additional stability to an unstable sacral fracture fixation construct, we were not able to identify any biomechanical advantage of one method over the other. Does not apply-biomechanical study.
This study is a biomechanical analysis of intervertebral cage placement, using a biomechanical mo... more This study is a biomechanical analysis of intervertebral cage placement, using a biomechanical model that has the appropriate matching geometry of the lumbar spine at the level of L4-L5 based upon prior morphometric studies. The goal of this in vitro biomechanical analysis of interbody cages is to determine the effect of interbody cage position on the mechanics of posterior spinal instrumentation. This biomechanical analysis can potentially be used to guide surgical technique for placement of interbody cage devices. Lumbar interbody spinal fusion cages are increasingly being used to promote spinal fusion and improve sagittal alignment in patients with degenerative disk disease. The transforaminal approach for placement of these cages has become popular, although the actual position of the cage that will provide optimal mechanical support in the intervertebral space is not known. Leopard carbon fiber interbody cages (DepuySpine, Raynham, MA) were placed in a spinal fusion model simulating the L4-L5 disk space in one of 3 positions-anterior, middle, or anterolateral. We tested 5 constructs in each of the 3 positions, applying cyclic axial loads of 500 N at a rate of 4 Hz for 100,000 cycles. Strain on the posterior instrumentation and displacement of the cages was measured at periodic intervals. Load to failure of each construct was tested after 100,000 cycles were complete. Statistical analysis of biomechanical indicators show more strain in the anterolateral position as compared with the anterior position (P=0.002) and middle position (P=0.02). No difference was noted between anterior and middle positions (P=1.00). Interval analysis reveals differences in strain at 500 cycles in anterior versus anterolateral (P=0.01) and middle versus anterolateral (P=0.02). At 10,000 cycles, anterolateral strain was significantly higher (P=0.02) than anterior. No significant difference in strain was noted at 50,000 or 100,000 cycles between any of the positions. No significant differences were noted in displacement of the cages between each of the positions. Ultimate load to failure was lower (nonsignificant) in the anterolateral versus anterior position (P=0.06), but no difference was noted between anterior versus middle (P=0.57) or anterolateral versus middle (P=0.69) positions. Linear regression analysis of load-displacement curves shows significance at 500 cycles (P=0.02), approaching significance at 10,000 cycles (P=0.07), and no significant difference at 50,000 (P=0.28) or 100,000 (P=0.28) cycles. Positioning of interbody cages in an offset position shows higher strain upon posterior instrumentation than a central position, and quicker load to failure than an anteriorly placed cage. Biomechanical studies using shear loading, and testing of adjacent spinal levels, are necessary to further elucidate the biomechanical consequences of variable positioning of interbody cages.
A mechanical and chemical model of intervertebral disk (IVD) degeneration was developed by examin... more A mechanical and chemical model of intervertebral disk (IVD) degeneration was developed by examining the enzymatic degradation of the nucleus pulposus (NP), and a gelatin-based restoration study was performed. It was hypothesized that forced enzymatic degradation of the NP will mimic natural degeneration through the loss of disk height and that an injection of a gelatin solution will restore mechanical function. Collagen and proteoglycans are essential for normal NP function. Their chemical destruction, combined with light mechanical loading, will mimic degeneration. Previous studies have determined that collagenase and matrix metalloproteinase-3 are directly implicated in IVD degradation; therefore, these enzymes were used in this model. On the basis of preliminary testing, 0.5% collagenase, 1% collagenase, and 0.0025% metalloproteinase-3 in phosphate-buffered saline (PBS) were injected directly into the NP of various motion segments from a young bovine lumbar spine and subjected to light cyclic loading. To restore disk height and mechanical function, 20% gelatin in PBS at 70°C was injected into a degraded disk and subjected to the same loading conditions after an allotted hardening time. Mechanical testing showed statistically significant changes in disk height between control segments, 1% collagenase, and 0.5% collagenase. 0.5% collagenase had the most accurate appearance and loading pattern of degeneration upon disk transection postloading. A trend in restoration of disk function, given by the lessened loss of disk height upon loading, was observed with injection of gelatin after degradation with 0.5% collagenase. This study demonstrated the potential to create a degenerative model using enzymatic degradation of the NP and the possibility to restore function with an injectable therapy. Although gelatin is not a clinically viable option, it provides preliminary data for other injectable IVD therapies.
Although locked plating has been shown to have advantages for diaphyseal and metaphyseal fracture... more Although locked plating has been shown to have advantages for diaphyseal and metaphyseal fracture fixation, its benefits for pubic symphyseal disruption have not been established. With traditional plate fixation of the disrupted pubic symphysis, normal physiological symphyseal pelvic motion eventually results in plate breakage, screw breakage, and loosening of screws. A concern exists that common modes of locked plate construct failure could result in abrupt and complete loss of symphyseal fixation. The purposes of this study were to determine, using an open-book pelvic injury model, whether locked plating of the pubic symphysis 1) offers any advantage over standard unlocked plating; and 2) results in a potential increased risk of abrupt fixation failure. Twelve osteopenic cadaver pelvic specimens were acquired and dual-energy x-ray absorptiometry scans were obtained to ensure uniformity of the specimens' bone density. Sacrospinous, sacrotuberous, and anterior sacroiliac ligaments were released and the symphysis pubis was transected to simulate a partially stable open book (AO/Orthopaedic Trauma Association 61-B3.1) injury. Using a six-hole 3.5-mm plate specifically designed for the symphysis pubis with the capability of fixation in locked or unlocked mode, six pelvises were fixed with locked screws and six pelvises were fixed standard unlocked bicortical screws. There was no significant difference between these 2 groups with regard to bone density (P = 0.47). Two equally osteopenic pelvic specimens from each fixation group were selected for the purpose of obtaining failure data and determining an acceptable load for trialing. Both specimens failed at 1985 N. The remaining 10 pelvises were then mounted on a materials testing apparatus using the bilateral stance model as described by Tile. In accordance with the failure data, each pelvis was stressed at 440 N for a total of one million cycles (equivalent to 6.5 months of daily walking) or until fixation failure. All pelvic specimens in both fixation groups completed one million cycles without plate or screw failure. However, diastasis of the initial pubic symphysis reduction was found in all pelvises (mean, 2.45 mm; range, 1.5-4.0 mm) regardless of fixation method. This loss of reduction was not significantly different between the 2 fixation groups (P = 0.914). No abrupt failures occurred in either plating group. Consequently, any fear of catastrophic (ie, abrupt and complete) failure of locked symphyseal plates appears to be unfounded for open-book injuries treated in patients with low bone density. However, minor loss of the symphyseal reduction was evident in all pelvises regardless of the fixation method. Therefore, locked plating of the pubic symphysis does not appear to offer any advantage over the standard unlocked technique for an AO/Orthopaedic Trauma Association 61-B3.1 partially stable open-book pelvic injury pattern in osteopenic bone.
Varus failure is a well-known complication of open reduction internal fixation of proximal humera... more Varus failure is a well-known complication of open reduction internal fixation of proximal humeral fractures. The addition of tension reducing sutures from the plate to the rotator cuff may attenuate the deforming forces of the rotator cuff resulting in decreased varus failure. In this study, we investigate the biomechanical contributions of tension reducing sutures to a locked plate construct in a two-part proximal humerus fracture model. Two fixation techniques were tested in twelve matched fresh frozen humeri in which standard two-part fractures of the surgical neck were created with a gap simulating surgical neck medial comminution. In group 1, fractures were fixed with a standard proximal humerus locking plate. In group 2, the plate fixation was similar and additionally tension-reducing sutures were applied from the plate to the rotator cuff. Active abduction was simulated for 400 cycles with force applied through the rotator cuff tendons. Intercyclic fracture motion, change in displacement and load to failure were recorded. The addition of tension reducing sutures did not lead to significant differences in intercyclic fracture motion. The mean change in displacement and load to failure were similar in both groups. Failure typically occurred in both groups at the rotator cuff - testing clamp interface. Tension relieving rotator cuff sutures added to locking plate fixation did not lead to a change in fracture gap with cyclic loading or an increase in ultimate failure load in a two-part surgical neck proximal humerus fracture model without medial support.
The objective of this study was to test the stiffness and ultimate load to failure of new intrame... more The objective of this study was to test the stiffness and ultimate load to failure of new intramedullary (IM) nail proximal screw configurations as compared to a trochanteric reconstruction nail. Twenty-one synthetic composite femurs were mounted on a Material Testing System and tested in axial compression 5 times. The femurs had an 1 of 2 IM nail types inserted with 1 of 3 proximal screw configurations: a 3-screw configuration with 2 transverse screws and a screw angled into the femoral neck; a 2-screw design with a single transverse screw and a single screw angled into the femoral neck; 2 parallel screws angled into the femoral neck. There were 7 specimens in each group. An unstable fracture (OTA/AO 32-C3.2) was created. and the stiffness of these constructs was tested in compression 5 times. Each construct was then loaded to failure in compression. The 3-screw construct provided more axial stiffness (214 N/mm +/- 75) than either the 2-screw construct (123 N/mm +/- 32) or the trochanteric reconstruction nail (127 N/mm +/- 21) (P = 0.017 and 0.035 for 3-screw vs. 2-screw and recon respectively, P = 0.45 for 2-screw vs. recon). Load-to-failure testing demonstrated similarity among the different screw configurations (3-screw = 2230 N +/- 265, 2-screw = 2283 N +/- 260, Reconstruction nail = 2121 N +/- 156) (P = 1.0 all groups). The proximal 3-screw configuration provided more stiffness than either the 2-screw configuration or trochanteric reconstruction nail. The 2-screw configuration performed equally to a standard trochanteric reconstruction nail in stiffness testing. The ultimate loads to failure for the 3 tested constructs were not significantly different.
No study to date has evaluated cortical thickness as it relates to locking plate failure or screw... more No study to date has evaluated cortical thickness as it relates to locking plate failure or screw pullout in the proximal humerus. The purpose of this study is to determine the relationship between proximal humerus cortical thickness and locked plate hardware failure in a cadaveric proximal humerus fracture model. Twelve humerus specimens were placed into two groups based on the proximal humerus cortical thickness on an anteroposterior radiograph: less than 4 mm and greater than 4 mm. The specimens were plated with a six-hole proximal humerus locking plate and a 15-mm resection osteotomy at the surgical neck was performed. The specimens were tested in a materials testing machine at a displacement of 5 mm/min to failure. Load at failure, stiffness, maximum load, failure, and fracture gap closure were all statistically similar (P > 0.05) between the groups. Our biomechanical study used modern locked plate-screw construct fixation of a simulated two-part proximal humerus fracture. The mechanical strength was unaffected based on a threshold combined proximal humerus cortical thickness of 4 mm.
Historically, because of the magnitude of muscle forces exerted locally, as well as the commonly ... more Historically, because of the magnitude of muscle forces exerted locally, as well as the commonly associated comminution, subtrochanteric fractures have been difficult to treat. Tencer et al found intramedullary nail fixation to be superior to lateral plate constructs in axial compression and combined bending. In addition, reconstruction-type intramedullary nails of more recent design have been shown to provide strength and stiffness superior to that supplied by the earlier antegrade intramedullary implants. A relatively new reconstruction nail, the DePuy VersaNail Troch Entry Nail (DePuy Orthopaedics, Inc., Warsaw, IN, USA), is unique in that it allows for two different proximal two-screw configurations: (1) the common parallel cephalomedullary arrangement and (2) a novel crossed-screw pattern. Our hypothesis was that the crossed-screw configuration would be as strong in axial loading as the cephalomedullary screw configuration. Twenty composite femurs were instrumented using the DePuy VersaNail Troch Entry Nail in a subtrochanteric fracture model: 10 with the crossed proximal screw configuration and 10 with the traditional parallel screw configuration. These constructs were first loaded axially to calculate their stiffness and then axially loaded to failure. One specimen was rendered unusable for all calculations. Therefore, 19 constructs were evaluated: 9 parallel screw constructs, 10 crossed-screw constructs. The crossed-screw construct had a significantly higher stiffness than the parallel screw construct (347 +/- 73 N/mm and 261 +/- 42 N/mm, respectively; P = 0.01) and a significantly higher axial load to failure (2848 +/- 391 N vs. 2300 +/- 444 N; P = 0.01). This study shows that axial failure loads of the crossed-screw configuration were greater than those of the parallel screw configuration. Clinically, this provides the surgeon more options for stabilizing a subtrochanteric femur fracture. This decision may be made intra-operatively if necessary, facilitating fracture fixation and providing a stable construct.
To test the stability to axial loading of 2 new polyaxial locking screw-plate designs and analyze... more To test the stability to axial loading of 2 new polyaxial locking screw-plate designs and analyze different angles of screw insertion. The noncontact bridging (NCB) polyaxial locking plate (Zimmer) and the POLYAX plate (DePuy) were compared with a fixed-angle less invasive stabilization system (LISS; Synthes). Twenty-five synthetic femurs were divided into 5 groups and assigned fixation with the LISS plate (group I), POLYAX plate (groups IIA and IIB), or NCB plate (groups IIIA and IIIB). The polyaxial constructs were divided into parallel and crossed distal condylar screw configurations. Each construct was tested under axial loading and stressed to failure at a displacement rate of 5 mm/min with a preload of 100 N. Outcome measurements included stiffness, load to failure, peak force, and mode of failure. All LISS and POLYAX constructs failed by plastic deformation of the plate, whereas 9 of 10 NCB constructs failed by an intra-articular lateral condyle fracture. No failures occurred at the screw-plate interface in either polyaxial constructs. Load to failure of the LISS was 33% greater than the parallel POLYAX (P < 0.01) and 24% greater than the crossed POLYAX (P < 0.01). Load to failure of NCB (parallel and crossed) were 24% greater than the parallel POLYAX (P < 0.01 and P < 0.01, respectively) and 15% greater than the crossed POLYAX (P < 0.01 and P = 0.02, respectively). The POLYAX also had significantly lower stiffness and peak force compared with the LISS and NCB. There was no difference between the LISS and NCB with regard to stiffness, load to failure, and peak force. Parallel and crossed polyaxial constructs showed no difference in stiffness or failure loads. There were no failures of either polyaxial screw-plate interface despite large forces and screw angle did not affect the overall strength of these constructs, supporting the biomechanical soundness of both polyaxial device designs under axial loading. However, the POLYAX supported smaller loads compared with the LISS and NCB while under axial loading. In addition, the mode of failure of the NCB plate, creating an intra-articular fracture propagating from the distal posterior screw hole, may be of some concern. Additional testing is needed to determine the clinical importance of the demonstrated differences among these plate designs.
Locked plates provide greater stiffness, possibly at the expense of fracture healing. The purpose... more Locked plates provide greater stiffness, possibly at the expense of fracture healing. The purpose of this study is to evaluate construct stiffness of distal femur plates as a function of unlocked screw position in cadaveric distal femur fractures. Osteoporotic cadaveric femurs were used. Four diaphyseal bridge plate constructs were created using 13-hole distal femur locking plates, all with identical condylar fixation. Constructs included all locked (AL), all unlocked (AUL), proximal unlocked (PUL), and distally unlocked (DUL) groups. Constructs underwent cyclic axial loading with increasing force per interval. Data were gathered on axial stiffness, torsional stiffness, maximum torque required for 5-degree external rotation, and axial force to failure. Twenty-one specimens were divided into AL, AUL, PUL, and DUL groups. Axial stiffness was not significantly different between the constructs. AL and PUL demonstrated greater torsional stiffness, maximum torque, and force to failure than AUL and AL showed greater final torsional stiffness and failure force than DUL (P < 0.05). AL and PUL had similar axial, torsion, and failure measures, as did AUL and DUL constructs. All but 2 specimens fractured before medial gap closure during failure tests. Drop-offs on load-displacement curves confirmed all failures. Only the screw nearest the gap had significant effect on torsional and failure stiffness but not axial stiffness. Construct mechanics depended on the type of screw placed in this position. This screw nearest the fracture dictates working length stiffness when the working length itself is constant and in turn determines overall construct stiffness in osteoporotic bone.
Iliosacral screw fixation into the first sacral body is a common method for pelvic ring fixation.... more Iliosacral screw fixation into the first sacral body is a common method for pelvic ring fixation. However, this construct has been shown to be clinically unreliable for the percutaneous fixation of unstable Type C zone II vertically oriented sacral fractures with residual fracture site separation. The objective of this study was to biomechanically compare a locked transsacral construct versus the standard iliosacral construct in a Type C zone II sacral fracture model. A Type C pelvic ring injury was created in ten embalmed cadaver pelves by performing vertical osteotomies through zone II of the sacrum and the ipsilateral pubic rami. The sacrum was then reduced maintaining a 2 mm fracture gap. Five specimens were fixed using two 7.0-mm iliosacral screws into the S1 body; the other 5 were fixed using one 7.0-mm iliosacral screw and one 7.0-mm transsacral screw exiting the contralateral ilium with a nut placed on its end, creating a locked construct. Each pelvis underwent 100,000 cycles at 250 N and was then loaded to failure using a unilateral stance testing model. Vertical displacements at 25,000; 50,000; 75,000 and 100,000 cycles and failure force were recorded for each pelvis. The locked transsacral construct performed significantly better than the iliosacral construct at all 4 measurement points (P = 0.009) and in force to failure (P value = 0.02). Fixation of unstable zone II sacral fractures using the combination of an iliosacral screw and a locked transsacral screw resists deformation and withstands a greater force to failure as compared to fixation with 2 standard iliosacral screws. This locked transsacral construct may prove advantageous, especially when a percutaneous technique is used for a Type C zone II vertically oriented sacral fracture injury pattern, which can result in residual fracture site separation.
The purpose of this study was to test the biomechanical properties of locking and nonlocking plat... more The purpose of this study was to test the biomechanical properties of locking and nonlocking plates using one-third tubular and periarticular plate designs in an osteoporotic distal fibula fracture model. Twenty-four cadaveric specimens, whose bone mineral densities were obtained using dual x-ray absorptiometry scans, were tested. The fracture model simulated an OTA 44-B2.1 fracture. The constructs included (1) nonlocking one-third tubular plate, (2) locking one-third tubular plate, (3) nonlocking periarticular plate, and (4) locking periarticular plate. The specimens underwent axial loading followed by torsional loading to failure. Statistical analysis was performed using Kruskal-Wallis testing and further analysis with Mann-Whitney testing. The periarticular plates had greater rotational stiffness compared with the one-third tubular plates (P = 0.04). The nonlocking plates had greater torque to failure than the locking plates (P = 0.01). The nonlocking one-third tubular plate had greater torque to failure than the locking one-third tubular plate (P = 0.03). No significant differences were found in any of the comparisons regarding axial stiffness. In biomechanical testing using an osteoporotic model of OTA 44-B2.1 fractures, periarticular plates were superior to one-third tubular plates in rotational stiffness only. Locking plates did not outperform their nonlocking counterparts. Periarticular plates should be considered when treating osteoporotic distal fibula fractures, but one-third tubular plates and nonlocking plates provide adequate fixation for these injuries.
Techniques such as varying screw insertion angles and the use of locked plating have been shown t... more Techniques such as varying screw insertion angles and the use of locked plating have been shown to improve the strength of fixation in bone. The effects of these methods is less clearly understood in bone of exceedingly poor quality. Forty plate-bone constructs were assembled and divided into four groups of ten. Perpendicularly placed screws were placed in one group, convergently placed crossing screws were placed in a second group, an oblique end screw was placed in a third group, and a fourth group utilized perpendicularly placed locking screws in a locking plate. All test subjects were mounted and loaded in cantilever bending to the point of failure. Stiffness, initial load to failure, and maximal load tolerated were all analyzed. All four groups demonstrated evidence of failure at similar loads (21.8-26.1N). The locked group was able to tolerate significantly higher loads overall (37.3N, P=.044). All three non-locked groups demonstrated similar failure patterns and load to failure. Locking constructs demonstrated a distinctly different failure pattern. No significant differences were detected with regard to screw orientation and load to failure. The group with an oblique end screw was significantly less stiff than the other three constructs (P=.017). In a severely osteoporotic model, failure in cantilever bending at low forces will take place regardless of fixation methods used. The mechanism of failure is different in locked constructs compared to traditional constructs. The added benefit of oblique screw placement observed in healthy bone is not observed in osteoporotic bone.
Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length an... more Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length and tension throughout knee range of motion with transtibial, anteromedial (AM) portal, and all-epiphyseal drilling techniques with suspensory and apical femoral fixation. Methods The three different femoral tunnel drilling techniques using the same intra-articular starting point within the center of the femoral footprint were performed on fresh-frozen cadaveric specimens. All groups underwent standard tibial drilling in the center of the ACL tibial footprint. FiberWire (Arthrex Inc., Naples, FL) was used to simulate anatomic single bundle reconstructions. Changes in graft length and tension were measured at knee flexion angles of 0, 30, 60, 90, 120, and 135 degrees. Results Graft length and tension decreased from 0 through 60 degrees and subsequently increased from 90 to 135 degrees for all groups. The transtibial, AM portal suspensory, and apical fixation groups were similar. However, th...
Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length an... more Purpose The purpose of this study was to compare anterior cruciate ligament (ACL) graft length and tension throughout knee range of motion with transtibial, anteromedial (AM) portal, and all-epiphyseal drilling techniques with suspensory and apical femoral fixation. Methods The three different femoral tunnel drilling techniques using the same intra-articular starting point within the center of the femoral footprint were performed on fresh-frozen cadaveric specimens. All groups underwent standard tibial drilling in the center of the ACL tibial footprint. FiberWire (Arthrex Inc., Naples, FL) was used to simulate anatomic single bundle reconstructions. Changes in graft length and tension were measured at knee flexion angles of 0, 30, 60, 90, 120, and 135 degrees. Results Graft length and tension decreased from 0 through 60 degrees and subsequently increased from 90 to 135 degrees for all groups. The transtibial, AM portal suspensory, and apical fixation groups were similar. However, the all-epiphyseal tunnel with suspensory fixation had a significantly increased change in length (90, 120, and 135 degrees) and tension (120 and 135 degrees). Conclusion Transtibial and AM portal suspensory fixation and apical fixation demonstrate similar changes in length and tension throughout knee range of motion. The all-epiphyseal tunnel with suspensory fixation was associated with greater length and tension changes at higher degrees of knee flexion. All techniques demonstrated decreased graft length and tension with knee flexion to 60 degrees after which they increased with further knee flexion. Clinical Relevance ACL graft length and tension change throughout knee range of motion and also depend on femoral tunnel orientation and fixation type. The use of an all-epiphyseal tunnel with suspensory fixation should be studied further for evidence of graft elongation.
A single iliosacral screw placed into the S1 vertebral body has been shown to be clinically unrel... more A single iliosacral screw placed into the S1 vertebral body has been shown to be clinically unreliable for certain type C pelvic ring injuries. Insertion of a second supplemental iliosacral screw into the S1 or S2 vertebral body has been widely used. However, clinical fixation failures have been reported using this technique, and a supplemental long iliosacral or transsacral screw has been used. The purpose of this study was to compare the biomechanical effect of a supplemental S1 long iliosacral screw versus a transsacral screw in an unstable type C vertically oriented sacral fracture model. A type C pelvic ring injury was created in ten osteopenic/osteoporotic cadaver pelves by performing vertical osteotomies through zone 2 of the sacrum and the ipsilateral pubic rami. The sacrum was reduced maintaining a 2-mm fracture gap to simulate a closed-reduction model. All specimens were fixed using one 7.0-mm iliosacral screw into the S1 body. A supplemental long iliosacral screw was placed into the S1 body in five specimens. A supplemental transsacral S1 screw was placed in the other five. Each pelvis underwent 100,000 cycles at 250 N, followed by loading to failure. Vertical displacements at 25,000, 50,000, 75,000, and 100,000 cycles and failure force were recorded. Vertical displacement increased significantly (p < 0.05) within each group with each increase in the number of cycles. However, there was no statistically significant difference between groups in displacement or load to failure. Although intuitively a transsacral screw may seem to be better than a long iliosacral screw in conveying additional stability to an unstable sacral fracture fixation construct, we were not able to identify any biomechanical advantage of one method over the other. Does not apply-biomechanical study.
This study is a biomechanical analysis of intervertebral cage placement, using a biomechanical mo... more This study is a biomechanical analysis of intervertebral cage placement, using a biomechanical model that has the appropriate matching geometry of the lumbar spine at the level of L4-L5 based upon prior morphometric studies. The goal of this in vitro biomechanical analysis of interbody cages is to determine the effect of interbody cage position on the mechanics of posterior spinal instrumentation. This biomechanical analysis can potentially be used to guide surgical technique for placement of interbody cage devices. Lumbar interbody spinal fusion cages are increasingly being used to promote spinal fusion and improve sagittal alignment in patients with degenerative disk disease. The transforaminal approach for placement of these cages has become popular, although the actual position of the cage that will provide optimal mechanical support in the intervertebral space is not known. Leopard carbon fiber interbody cages (DepuySpine, Raynham, MA) were placed in a spinal fusion model simulating the L4-L5 disk space in one of 3 positions-anterior, middle, or anterolateral. We tested 5 constructs in each of the 3 positions, applying cyclic axial loads of 500 N at a rate of 4 Hz for 100,000 cycles. Strain on the posterior instrumentation and displacement of the cages was measured at periodic intervals. Load to failure of each construct was tested after 100,000 cycles were complete. Statistical analysis of biomechanical indicators show more strain in the anterolateral position as compared with the anterior position (P=0.002) and middle position (P=0.02). No difference was noted between anterior and middle positions (P=1.00). Interval analysis reveals differences in strain at 500 cycles in anterior versus anterolateral (P=0.01) and middle versus anterolateral (P=0.02). At 10,000 cycles, anterolateral strain was significantly higher (P=0.02) than anterior. No significant difference in strain was noted at 50,000 or 100,000 cycles between any of the positions. No significant differences were noted in displacement of the cages between each of the positions. Ultimate load to failure was lower (nonsignificant) in the anterolateral versus anterior position (P=0.06), but no difference was noted between anterior versus middle (P=0.57) or anterolateral versus middle (P=0.69) positions. Linear regression analysis of load-displacement curves shows significance at 500 cycles (P=0.02), approaching significance at 10,000 cycles (P=0.07), and no significant difference at 50,000 (P=0.28) or 100,000 (P=0.28) cycles. Positioning of interbody cages in an offset position shows higher strain upon posterior instrumentation than a central position, and quicker load to failure than an anteriorly placed cage. Biomechanical studies using shear loading, and testing of adjacent spinal levels, are necessary to further elucidate the biomechanical consequences of variable positioning of interbody cages.
A mechanical and chemical model of intervertebral disk (IVD) degeneration was developed by examin... more A mechanical and chemical model of intervertebral disk (IVD) degeneration was developed by examining the enzymatic degradation of the nucleus pulposus (NP), and a gelatin-based restoration study was performed. It was hypothesized that forced enzymatic degradation of the NP will mimic natural degeneration through the loss of disk height and that an injection of a gelatin solution will restore mechanical function. Collagen and proteoglycans are essential for normal NP function. Their chemical destruction, combined with light mechanical loading, will mimic degeneration. Previous studies have determined that collagenase and matrix metalloproteinase-3 are directly implicated in IVD degradation; therefore, these enzymes were used in this model. On the basis of preliminary testing, 0.5% collagenase, 1% collagenase, and 0.0025% metalloproteinase-3 in phosphate-buffered saline (PBS) were injected directly into the NP of various motion segments from a young bovine lumbar spine and subjected to light cyclic loading. To restore disk height and mechanical function, 20% gelatin in PBS at 70°C was injected into a degraded disk and subjected to the same loading conditions after an allotted hardening time. Mechanical testing showed statistically significant changes in disk height between control segments, 1% collagenase, and 0.5% collagenase. 0.5% collagenase had the most accurate appearance and loading pattern of degeneration upon disk transection postloading. A trend in restoration of disk function, given by the lessened loss of disk height upon loading, was observed with injection of gelatin after degradation with 0.5% collagenase. This study demonstrated the potential to create a degenerative model using enzymatic degradation of the NP and the possibility to restore function with an injectable therapy. Although gelatin is not a clinically viable option, it provides preliminary data for other injectable IVD therapies.
Although locked plating has been shown to have advantages for diaphyseal and metaphyseal fracture... more Although locked plating has been shown to have advantages for diaphyseal and metaphyseal fracture fixation, its benefits for pubic symphyseal disruption have not been established. With traditional plate fixation of the disrupted pubic symphysis, normal physiological symphyseal pelvic motion eventually results in plate breakage, screw breakage, and loosening of screws. A concern exists that common modes of locked plate construct failure could result in abrupt and complete loss of symphyseal fixation. The purposes of this study were to determine, using an open-book pelvic injury model, whether locked plating of the pubic symphysis 1) offers any advantage over standard unlocked plating; and 2) results in a potential increased risk of abrupt fixation failure. Twelve osteopenic cadaver pelvic specimens were acquired and dual-energy x-ray absorptiometry scans were obtained to ensure uniformity of the specimens' bone density. Sacrospinous, sacrotuberous, and anterior sacroiliac ligaments were released and the symphysis pubis was transected to simulate a partially stable open book (AO/Orthopaedic Trauma Association 61-B3.1) injury. Using a six-hole 3.5-mm plate specifically designed for the symphysis pubis with the capability of fixation in locked or unlocked mode, six pelvises were fixed with locked screws and six pelvises were fixed standard unlocked bicortical screws. There was no significant difference between these 2 groups with regard to bone density (P = 0.47). Two equally osteopenic pelvic specimens from each fixation group were selected for the purpose of obtaining failure data and determining an acceptable load for trialing. Both specimens failed at 1985 N. The remaining 10 pelvises were then mounted on a materials testing apparatus using the bilateral stance model as described by Tile. In accordance with the failure data, each pelvis was stressed at 440 N for a total of one million cycles (equivalent to 6.5 months of daily walking) or until fixation failure. All pelvic specimens in both fixation groups completed one million cycles without plate or screw failure. However, diastasis of the initial pubic symphysis reduction was found in all pelvises (mean, 2.45 mm; range, 1.5-4.0 mm) regardless of fixation method. This loss of reduction was not significantly different between the 2 fixation groups (P = 0.914). No abrupt failures occurred in either plating group. Consequently, any fear of catastrophic (ie, abrupt and complete) failure of locked symphyseal plates appears to be unfounded for open-book injuries treated in patients with low bone density. However, minor loss of the symphyseal reduction was evident in all pelvises regardless of the fixation method. Therefore, locked plating of the pubic symphysis does not appear to offer any advantage over the standard unlocked technique for an AO/Orthopaedic Trauma Association 61-B3.1 partially stable open-book pelvic injury pattern in osteopenic bone.
Varus failure is a well-known complication of open reduction internal fixation of proximal humera... more Varus failure is a well-known complication of open reduction internal fixation of proximal humeral fractures. The addition of tension reducing sutures from the plate to the rotator cuff may attenuate the deforming forces of the rotator cuff resulting in decreased varus failure. In this study, we investigate the biomechanical contributions of tension reducing sutures to a locked plate construct in a two-part proximal humerus fracture model. Two fixation techniques were tested in twelve matched fresh frozen humeri in which standard two-part fractures of the surgical neck were created with a gap simulating surgical neck medial comminution. In group 1, fractures were fixed with a standard proximal humerus locking plate. In group 2, the plate fixation was similar and additionally tension-reducing sutures were applied from the plate to the rotator cuff. Active abduction was simulated for 400 cycles with force applied through the rotator cuff tendons. Intercyclic fracture motion, change in displacement and load to failure were recorded. The addition of tension reducing sutures did not lead to significant differences in intercyclic fracture motion. The mean change in displacement and load to failure were similar in both groups. Failure typically occurred in both groups at the rotator cuff - testing clamp interface. Tension relieving rotator cuff sutures added to locking plate fixation did not lead to a change in fracture gap with cyclic loading or an increase in ultimate failure load in a two-part surgical neck proximal humerus fracture model without medial support.
The objective of this study was to test the stiffness and ultimate load to failure of new intrame... more The objective of this study was to test the stiffness and ultimate load to failure of new intramedullary (IM) nail proximal screw configurations as compared to a trochanteric reconstruction nail. Twenty-one synthetic composite femurs were mounted on a Material Testing System and tested in axial compression 5 times. The femurs had an 1 of 2 IM nail types inserted with 1 of 3 proximal screw configurations: a 3-screw configuration with 2 transverse screws and a screw angled into the femoral neck; a 2-screw design with a single transverse screw and a single screw angled into the femoral neck; 2 parallel screws angled into the femoral neck. There were 7 specimens in each group. An unstable fracture (OTA/AO 32-C3.2) was created. and the stiffness of these constructs was tested in compression 5 times. Each construct was then loaded to failure in compression. The 3-screw construct provided more axial stiffness (214 N/mm +/- 75) than either the 2-screw construct (123 N/mm +/- 32) or the trochanteric reconstruction nail (127 N/mm +/- 21) (P = 0.017 and 0.035 for 3-screw vs. 2-screw and recon respectively, P = 0.45 for 2-screw vs. recon). Load-to-failure testing demonstrated similarity among the different screw configurations (3-screw = 2230 N +/- 265, 2-screw = 2283 N +/- 260, Reconstruction nail = 2121 N +/- 156) (P = 1.0 all groups). The proximal 3-screw configuration provided more stiffness than either the 2-screw configuration or trochanteric reconstruction nail. The 2-screw configuration performed equally to a standard trochanteric reconstruction nail in stiffness testing. The ultimate loads to failure for the 3 tested constructs were not significantly different.
No study to date has evaluated cortical thickness as it relates to locking plate failure or screw... more No study to date has evaluated cortical thickness as it relates to locking plate failure or screw pullout in the proximal humerus. The purpose of this study is to determine the relationship between proximal humerus cortical thickness and locked plate hardware failure in a cadaveric proximal humerus fracture model. Twelve humerus specimens were placed into two groups based on the proximal humerus cortical thickness on an anteroposterior radiograph: less than 4 mm and greater than 4 mm. The specimens were plated with a six-hole proximal humerus locking plate and a 15-mm resection osteotomy at the surgical neck was performed. The specimens were tested in a materials testing machine at a displacement of 5 mm/min to failure. Load at failure, stiffness, maximum load, failure, and fracture gap closure were all statistically similar (P > 0.05) between the groups. Our biomechanical study used modern locked plate-screw construct fixation of a simulated two-part proximal humerus fracture. The mechanical strength was unaffected based on a threshold combined proximal humerus cortical thickness of 4 mm.
Historically, because of the magnitude of muscle forces exerted locally, as well as the commonly ... more Historically, because of the magnitude of muscle forces exerted locally, as well as the commonly associated comminution, subtrochanteric fractures have been difficult to treat. Tencer et al found intramedullary nail fixation to be superior to lateral plate constructs in axial compression and combined bending. In addition, reconstruction-type intramedullary nails of more recent design have been shown to provide strength and stiffness superior to that supplied by the earlier antegrade intramedullary implants. A relatively new reconstruction nail, the DePuy VersaNail Troch Entry Nail (DePuy Orthopaedics, Inc., Warsaw, IN, USA), is unique in that it allows for two different proximal two-screw configurations: (1) the common parallel cephalomedullary arrangement and (2) a novel crossed-screw pattern. Our hypothesis was that the crossed-screw configuration would be as strong in axial loading as the cephalomedullary screw configuration. Twenty composite femurs were instrumented using the DePuy VersaNail Troch Entry Nail in a subtrochanteric fracture model: 10 with the crossed proximal screw configuration and 10 with the traditional parallel screw configuration. These constructs were first loaded axially to calculate their stiffness and then axially loaded to failure. One specimen was rendered unusable for all calculations. Therefore, 19 constructs were evaluated: 9 parallel screw constructs, 10 crossed-screw constructs. The crossed-screw construct had a significantly higher stiffness than the parallel screw construct (347 +/- 73 N/mm and 261 +/- 42 N/mm, respectively; P = 0.01) and a significantly higher axial load to failure (2848 +/- 391 N vs. 2300 +/- 444 N; P = 0.01). This study shows that axial failure loads of the crossed-screw configuration were greater than those of the parallel screw configuration. Clinically, this provides the surgeon more options for stabilizing a subtrochanteric femur fracture. This decision may be made intra-operatively if necessary, facilitating fracture fixation and providing a stable construct.
To test the stability to axial loading of 2 new polyaxial locking screw-plate designs and analyze... more To test the stability to axial loading of 2 new polyaxial locking screw-plate designs and analyze different angles of screw insertion. The noncontact bridging (NCB) polyaxial locking plate (Zimmer) and the POLYAX plate (DePuy) were compared with a fixed-angle less invasive stabilization system (LISS; Synthes). Twenty-five synthetic femurs were divided into 5 groups and assigned fixation with the LISS plate (group I), POLYAX plate (groups IIA and IIB), or NCB plate (groups IIIA and IIIB). The polyaxial constructs were divided into parallel and crossed distal condylar screw configurations. Each construct was tested under axial loading and stressed to failure at a displacement rate of 5 mm/min with a preload of 100 N. Outcome measurements included stiffness, load to failure, peak force, and mode of failure. All LISS and POLYAX constructs failed by plastic deformation of the plate, whereas 9 of 10 NCB constructs failed by an intra-articular lateral condyle fracture. No failures occurred at the screw-plate interface in either polyaxial constructs. Load to failure of the LISS was 33% greater than the parallel POLYAX (P < 0.01) and 24% greater than the crossed POLYAX (P < 0.01). Load to failure of NCB (parallel and crossed) were 24% greater than the parallel POLYAX (P < 0.01 and P < 0.01, respectively) and 15% greater than the crossed POLYAX (P < 0.01 and P = 0.02, respectively). The POLYAX also had significantly lower stiffness and peak force compared with the LISS and NCB. There was no difference between the LISS and NCB with regard to stiffness, load to failure, and peak force. Parallel and crossed polyaxial constructs showed no difference in stiffness or failure loads. There were no failures of either polyaxial screw-plate interface despite large forces and screw angle did not affect the overall strength of these constructs, supporting the biomechanical soundness of both polyaxial device designs under axial loading. However, the POLYAX supported smaller loads compared with the LISS and NCB while under axial loading. In addition, the mode of failure of the NCB plate, creating an intra-articular fracture propagating from the distal posterior screw hole, may be of some concern. Additional testing is needed to determine the clinical importance of the demonstrated differences among these plate designs.
Locked plates provide greater stiffness, possibly at the expense of fracture healing. The purpose... more Locked plates provide greater stiffness, possibly at the expense of fracture healing. The purpose of this study is to evaluate construct stiffness of distal femur plates as a function of unlocked screw position in cadaveric distal femur fractures. Osteoporotic cadaveric femurs were used. Four diaphyseal bridge plate constructs were created using 13-hole distal femur locking plates, all with identical condylar fixation. Constructs included all locked (AL), all unlocked (AUL), proximal unlocked (PUL), and distally unlocked (DUL) groups. Constructs underwent cyclic axial loading with increasing force per interval. Data were gathered on axial stiffness, torsional stiffness, maximum torque required for 5-degree external rotation, and axial force to failure. Twenty-one specimens were divided into AL, AUL, PUL, and DUL groups. Axial stiffness was not significantly different between the constructs. AL and PUL demonstrated greater torsional stiffness, maximum torque, and force to failure than AUL and AL showed greater final torsional stiffness and failure force than DUL (P < 0.05). AL and PUL had similar axial, torsion, and failure measures, as did AUL and DUL constructs. All but 2 specimens fractured before medial gap closure during failure tests. Drop-offs on load-displacement curves confirmed all failures. Only the screw nearest the gap had significant effect on torsional and failure stiffness but not axial stiffness. Construct mechanics depended on the type of screw placed in this position. This screw nearest the fracture dictates working length stiffness when the working length itself is constant and in turn determines overall construct stiffness in osteoporotic bone.
Iliosacral screw fixation into the first sacral body is a common method for pelvic ring fixation.... more Iliosacral screw fixation into the first sacral body is a common method for pelvic ring fixation. However, this construct has been shown to be clinically unreliable for the percutaneous fixation of unstable Type C zone II vertically oriented sacral fractures with residual fracture site separation. The objective of this study was to biomechanically compare a locked transsacral construct versus the standard iliosacral construct in a Type C zone II sacral fracture model. A Type C pelvic ring injury was created in ten embalmed cadaver pelves by performing vertical osteotomies through zone II of the sacrum and the ipsilateral pubic rami. The sacrum was then reduced maintaining a 2 mm fracture gap. Five specimens were fixed using two 7.0-mm iliosacral screws into the S1 body; the other 5 were fixed using one 7.0-mm iliosacral screw and one 7.0-mm transsacral screw exiting the contralateral ilium with a nut placed on its end, creating a locked construct. Each pelvis underwent 100,000 cycles at 250 N and was then loaded to failure using a unilateral stance testing model. Vertical displacements at 25,000; 50,000; 75,000 and 100,000 cycles and failure force were recorded for each pelvis. The locked transsacral construct performed significantly better than the iliosacral construct at all 4 measurement points (P = 0.009) and in force to failure (P value = 0.02). Fixation of unstable zone II sacral fractures using the combination of an iliosacral screw and a locked transsacral screw resists deformation and withstands a greater force to failure as compared to fixation with 2 standard iliosacral screws. This locked transsacral construct may prove advantageous, especially when a percutaneous technique is used for a Type C zone II vertically oriented sacral fracture injury pattern, which can result in residual fracture site separation.
The purpose of this study was to test the biomechanical properties of locking and nonlocking plat... more The purpose of this study was to test the biomechanical properties of locking and nonlocking plates using one-third tubular and periarticular plate designs in an osteoporotic distal fibula fracture model. Twenty-four cadaveric specimens, whose bone mineral densities were obtained using dual x-ray absorptiometry scans, were tested. The fracture model simulated an OTA 44-B2.1 fracture. The constructs included (1) nonlocking one-third tubular plate, (2) locking one-third tubular plate, (3) nonlocking periarticular plate, and (4) locking periarticular plate. The specimens underwent axial loading followed by torsional loading to failure. Statistical analysis was performed using Kruskal-Wallis testing and further analysis with Mann-Whitney testing. The periarticular plates had greater rotational stiffness compared with the one-third tubular plates (P = 0.04). The nonlocking plates had greater torque to failure than the locking plates (P = 0.01). The nonlocking one-third tubular plate had greater torque to failure than the locking one-third tubular plate (P = 0.03). No significant differences were found in any of the comparisons regarding axial stiffness. In biomechanical testing using an osteoporotic model of OTA 44-B2.1 fractures, periarticular plates were superior to one-third tubular plates in rotational stiffness only. Locking plates did not outperform their nonlocking counterparts. Periarticular plates should be considered when treating osteoporotic distal fibula fractures, but one-third tubular plates and nonlocking plates provide adequate fixation for these injuries.
Techniques such as varying screw insertion angles and the use of locked plating have been shown t... more Techniques such as varying screw insertion angles and the use of locked plating have been shown to improve the strength of fixation in bone. The effects of these methods is less clearly understood in bone of exceedingly poor quality. Forty plate-bone constructs were assembled and divided into four groups of ten. Perpendicularly placed screws were placed in one group, convergently placed crossing screws were placed in a second group, an oblique end screw was placed in a third group, and a fourth group utilized perpendicularly placed locking screws in a locking plate. All test subjects were mounted and loaded in cantilever bending to the point of failure. Stiffness, initial load to failure, and maximal load tolerated were all analyzed. All four groups demonstrated evidence of failure at similar loads (21.8-26.1N). The locked group was able to tolerate significantly higher loads overall (37.3N, P=.044). All three non-locked groups demonstrated similar failure patterns and load to failure. Locking constructs demonstrated a distinctly different failure pattern. No significant differences were detected with regard to screw orientation and load to failure. The group with an oblique end screw was significantly less stiff than the other three constructs (P=.017). In a severely osteoporotic model, failure in cantilever bending at low forces will take place regardless of fixation methods used. The mechanism of failure is different in locked constructs compared to traditional constructs. The added benefit of oblique screw placement observed in healthy bone is not observed in osteoporotic bone.
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