Femoral interference screw divergence as a result of anteromedial portal insertion and outside-in FlipCutter femoral tunnel drilling: A cadaveric study.

Aims and objectives: To investigate whether interference screw fixation through an anteromedial portal into an outside-in drilled femoral tunnel via a flip cutter results in acceptable hardware position. Materials & methods: 10 cadaveric knees underwent ACL-reconstruction with patellar BTB autograft. Femoral tunnel drilling was performed utilizing an outside-in flip cutter drill and interference screws for femoral fixation. Lateral and anterior-posterior (AP) fluoroscopic images were taken to measure screw divergence within the femoral tunnel. The means of AP and lateral divergence angles were compared using two-tailed t-tests. Results: Using the flip cutter, the AP and lateral divergence angles were 7.3° ± 4.5° and 9.3° ± 9.3°, respectively, while the total divergence angles were 16.6° ± 11.8°. Divergence angles using a cannulated reamer were found to be 14.4° ± 2.5° and 6.8° ± 2.8° for AP and lateral, respectively and 21.1° ± 5.2° for the total divergence. The AP divergence angles using the flip cutter were significantly less than those reported using a cannulated reamer (p = 0.001). Conclusions: The flip cutter method resulted in significantly reduced divergence angle between the screw and graft when compared to previous cadaveric studies in the coronal plane. There was no significant difference in divergence angle in the sagittal plane. Both methods appear to result in divergence angles below the threshold which would be considered to significantly decrease pull-out strength. Large standard deviations also reflect limited sample size but may also suggest more variability in divergence when compared to historical control set. This study clearly establishes the outside-in technique using a retrograde reamer as a viable independent femoral drilling solution for ACL reconstruction when using a BTB autograft with a femoral interference screw.

Interspinous-Interbody Fusion via a Strictly Lateral Surgical Approach: A Biomechanical Stabilization Comparison to Constructs Requiring Both Lateral and Posterior Approaches.

Objective Lumbar fusion performed through lateral approaches is becoming more common. The interbody devices are generally supported by supplemental posterior fixation implanted through a posterior approach, potentially requiring a second incision and intraoperative repositioning of the patient. A minimally invasive lateral interspinous fixation device may eliminate the need for intraoperative repositioning and avoid disruption of the supraspinous ligament. The objective of this in vitrobiomechanical study was to investigate segmental multidirectional stability and maintenance of foraminal distraction of a lateral interspinous fixation device compared to commonly used pedicle screw and facet screw posterior fixation constructs when combined with lumbar interbody cages. Methods Six human cadaver lumbar spine specimens were subjected to nondestructive quasistatic loading in the following states: (1) intact; (2) interspinous fixation device alone and (3) with lateral interbody cage; (4) lateral lumbar interbody cage with bilateral pedicle screws; (5) lateral lumbar interbody cage with unilateral pedicle screws; and (6) lateral lumbar interbody cage with facet screws. Multidirectional pure bending in 1.5 Nm increments to 7.5 Nm, and 7.5 Nm flexion-extension bending with a 700 N compressive follower load were performed separately with optoelectronic segmental motion measurement. Relative angular motions of L2-L3, L3-L4, and L4-L5 functional spinal units were evaluated, and the mean instantaneous axis of rotation in the sagittal plane was calculated for the index level. Foraminal height was assessed during combined flexion-extension and compression loading for each test construct. Results All implant configurations significantly restricted flexion-extension motion compared with intact (p < 0.05). No significant differences were found in flexion-extension when comparing the different posterior implants combined with lateral lumbar interbody cages. All posterior fixation devices provided comparable neuroforaminal distraction and maintained distraction during flexion and extension. Conclusions When combinedwith lateral lumbar interbody cages, the minimally invasive lateral interspinous fixation device effectively stabilized the spine and maintained neuroforaminal distraction comparable to pedicle screw constructs or facet screws. These results suggest the lateral interspinous fixation device may provide a favorable alternative to other posterior systems that require patient repositioning during surgery and involve a greater disruption of native tissues.

Does the Bone Mineral Density of the Lumbar Spine Correlate With Dual-Energy X-ray Absorptiometry T Score? A Cadaveric-Based Analysis of Computed Tomography Densitometry.

BACKGROUND: Pedicle screw loosening is a complication of spinal instrumentation in osteoporotic patients. Dual-energy x-ray absorptiometry scans are not able to detect variations in bone mineral density (BMD) within specific regions of vertebrae. The purpose of this study was to investigate whether spine T scores correlate with cortical and cancellous BMD of pedicles and other 6 anatomical regions of lumbar spine. METHODS: Eleven cadaveric spines with a mean age of 73 years were digitally isolated by applying filters for cortical and cancellous bone on computed tomography images. Eleven L5 vertebrae were separated into 7 anatomical regions of interest using 3-dimensional software modeling. Hounsfield units (HU) were determined for each region and converted to cortical and cancellous BMD with calibration phantoms of known BMD. Correlations between T scores and HU values were calculated using Pearson correlation coefficient. RESULTS: Mean vertebral T score was 0.15. Cortical BMD of pedicles was strongly correlated with T score (R 2 = 0.74). There was moderate correlation between T score and cortical BMD of lamina, inferior articular process (IAP), superior articular process (SAP), spinous process, and vertebral body. There was weak correlation between T score and cortical BMD of transverse process (R 2 = 0.16). Cancellous BMD of vertebral body was strongly correlated with T score (R 2 = 0.82). There was moderate correlation between T score and cancellous BMD of pedicles, spinous process, and transverse process. There was weak correlation between T scores and cancellous BMD of lamina, IAP, and SAP. CONCLUSIONS: There is a strong correlation between T scores and cortical BMD of lumbar pedicle. There is strong correlation between T scores and cancellous BMD of vertebral body. Cortical and cancellous BMD of transverse process and lamina were weakly correlated with T score and less affected by osteoporosis. CLINICAL RELEVANCE: Patients with osteoporosis may especially benefit from the development of extrapedicular fusion strategies due to the relatively higher bone density of these fixation sites.

Pyogenic spinal infections warrant a total spine MRI.

Study design: retrospective case series. Objective: the presenting clinical symptoms of spinal infections are often nonspecific and a delay in diagnosis can lead to adverse patient outcomes. The morbidity and mortality of patients with multifocal spinal infections is significantly higher compared to unifocal infections. The purpose of the current study was to analyse the risk factors for multifocal spinal infections. Methods: we conducted a retrospective review of all pyogenic non-tuberculous spinal infections treated surgically at a single tertiary care medical center from 2006-2020. The medical records, imaging studies, and laboratory data of 43 patients during this time period were reviewed and analysed after receiving Institutional Review Board approval. Univariate and multivariate analyses were performed to identify factors associated with a multifocal spinal infection. Results: 15 patients (35 %) had multifocal infections. In univariate analysis, there was a significant association with chronic kidney disease ( p = 0.040 ), gender ( p = 0.003 ), a white blood cell count ( p = 0.011 ), and cervical ( p < 0.001 ) or thoracic ( p < 0 .001) involvement. In multivariate analysis, both cervical and thoracic involvement remained statistically significant ( p = 0.001 and p < 0.001 , respectively). Conclusions: patients with infections in the thoracic or cervical region are more likely to have a multifocal infection. Multifocal pyogenic spinal infections remain a common entity and a total spine MRI should be performed to aid in prompt diagnosis.

C1-C2 Facet Joint Penetration by C2 Pedicle Screws: Influence of Local Anatomy, Bone Mineral Density, and Screw Length.

BACKGROUND: A challenge of C2 pedicle screw placement is to avoid penetration into the C1-C2 facet joint, as this may alter normal biomechanics and accelerate joint degeneration. Our objective was to clarify how local anatomy and surgical technique may relate to C2 pedicle screw penetration into the C1-C2 facet joint. METHODS: C2 pedicle screws were inserted using a fluoroscopically assisted freehand technique. Independent fellowship-trained spine surgeons blindly reviewed intraoperative fluoroscopic and postoperative computed tomography (CT) images for evidence of facet joint penetration (FJP). C2 pedicle morphometry, the sagittal angle of the facet joint, axial and sagittal pedicle screw angles, and screw length were measured on the relevant CT images. RESULTS: A total of 34 patients fulfilled the study criteria, and a total of 68 C2 pedicle screws were placed. Eight screws (16%) penetrated the C1-C2 facet joint. The mean sagittal angle of the C1-C2 facet joint was significantly lower in the FJP group compared with the non-FJP group. The mean sagittal angle of the screws was significantly higher in the FJP group compared with the non-FJP group. The mean screw length was significantly greater for screws causing FJP compared with the non-FJP group. The mean axial screw angle was significantly lower in the FJP group compared with the non-FJP group. Pedicle width, length, height, and transverse angle were not significantly associated with FJP. Independent reviewers were able to identify FJP on intraoperative fluoroscopic imaging in 2 out of 8 cases. CONCLUSION: Lower sagittal angle of the facet joint, higher sagittal angle of the pedicle screw, and screw length >24 mm are associated with higher risk of C1-C2 FJP. When placing C2 pedicle screws under these conditions, caution should be taken to avoid FJP. CLINICAL RELEVANCE: Several anatomical and technical factors may increase the risk of C1-C2 FJP during placement of C2 pedicle screws using a fluoroscopically assisted freehand technique, underscoring the importance of preoperative planning and limiting screw length.

Pelvic stability during simulated total hip arthroplasty motions: Comparing different hip positioners.

Introduction: Total hip arthroplasty (THA) requires forceful maneuvers that can cause the pelvis to shift from its original position. Various methods for stabilizing the pelvis in the lateral decubitus position exist, but there is limited data quantifying the relative stability of each hip positioner. We sought to quantify the pelvic movement that occurred in four commercially available hip positioners during surgeon induced motion of the hip. Methods: An infrared marker was attached to the ilium of a cadaver secured in the lateral decubitus position. Four commercially available hip positioners were used for positioning: Beanbag, Pegboard, Stulberg, and ExactFit. Rotation and translation was captured using an infrared marker and camera system while the hip was moved through six motions (Flexion, Extension, Internal Rotation, External Rotation, Push, and Pull). Results: The Beanbag had the greatest amount of rotation and translation of the pelvis, with maximum hip rotation of 41.5°. The Stulberg and Pegboard positioners showed intermediate stability, with a maximum rotation of 7.8° and 17.1°, respectively. The ExactFit hip positioner resulted in the least amount of motion of the pelvis, with a maximum rotation of the pelvis of up to 3.2°. Of the simulated motions performed, internal rotation and flexion of the hip led to the greatest changes in pelvic rotation and translation. Conclusion: The ExactFit positioner was associated with the smallest amount of pelvic motion during simulated motions of hip arthroplasty, followed by the Stulberg, Pegboard, and Beanbag positioners. Further studies are required to correlate this information with clinical outcomes following total hip arthroplasty.

Improving the Management of Patients with Osteoporosis Undergoing Spinal Fusion: The Need for a Bone Mineral Density-Matched Interbody Cage.

With an increasingly aging population globally, a confluence has emerged between the rising prevalence of degenerative spinal disease and osteoporosis. Fusion of the anterior spinal column remains the mainstay surgical intervention for many spinal degenerative disorders. However, decreased vertebral bone mineral density (BMD), quantitatively measured by dual x-ray absorptiometry (DXA), complicates treatment with surgical interbody fusion as weak underlying bone stock increases the risk of post-operative implant-related adverse events, including cage subsidence. There is a necessity for developing cages with advanced structural designs that incorporate bioengineering and architectural principles to tailor the interbody fusion device directly to the patient's BMD status. Specifically, lattice-designed cages that mimic the web-like structure of native cancellous bone have demonstrated excellent resistance to post-operative subsidence. This article provides an introductory profile of a spinal interbody implant designed intentionally to simulate the lattice structure of human cancellous bone, with a similar modulus of elasticity, and specialized to match a patient's bone status across the BMD continuum. The implant incorporates an open pore design where the degree of pore compactness directly corresponds to the patient's DXA-defined BMD status, including patients with osteoporosis.

Alternatives to Traditional Pedicle Screws for Posterior Fixation of the Degenerative Lumbar Spine.

BACKGROUND: Traditional pedicle screws are currently the gold standard to achieve stable 3-column fixation of the degenerative lumbar spine. However, there are cases in which pedicle screw fixation may not be ideal. Due to their starting point lateral to the pars interarticularis, pedicle screws require a relatively wide dissection along with a medialized trajectory directed toward the centrally located neural elements and prevertebral vasculature. In addition, low bone mineral density remains a major risk factor for pedicle screw loosening, pullout, and pseudarthrosis. The purpose of this article is to review the indications, advantages, disadvantages, and complications associated with posterior fixation techniques of the degenerative lumbar spine beyond the traditional pedicle screws. METHODS: Comprehensive literature searches of the PubMed, Scopus, and Web of Science databases were performed for 5 methods of posterior spinal fixation, including (1) cortical bone trajectory (CBT) screws, (2) transfacet screws, (3) translaminar screws, (4) spinous process plates, and (5) fusion mass screws and hooks. Articles that had been published between January 1, 1990, and January 1, 2020, were considered. Non-English-language articles and studies involving fixation of the cervical or thoracic spine were excluded from our review. RESULTS: After reviewing over 1,700 articles pertaining to CBT and non-pedicular fixation techniques, a total of 284 articles met our inclusion criteria. CBT and transfacet screws require less-extensive exposure and paraspinal muscle dissection compared with traditional pedicle screws and may therefore reduce blood loss, postoperative pain, and length of hospital stay. In addition, several methods of non-pedicular fixation such as translaminar and fusion mass screws have trajectories that are directed away from or posterior to the spinal canal, potentially decreasing the risk of neurologic injury. CBT, transfacet, and fusion mass screws can also be used as salvage techniques when traditional pedicle screw constructs fail. CONCLUSIONS: CBT and non-pedicular fixation may be preferred in certain lumbar degenerative cases, particularly among patients with osteoporosis. Limitations of non-pedicular techniques include their reliance on intact posterior elements and the lack of 3-column fixation of the spine. As a result, transfacet and translaminar screws are infrequently used as the primary method of fixation. CBT, transfacet, and translaminar screws are effective in augmenting interbody fixation and have been shown to significantly improve fusion rates and clinical outcomes compared with stand-alone anterior lumbar interbody fusion. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

In-vitro 3D Analysis of Sacroiliac Joint Kinematics: Primary and Coupled Motions.

STUDY DESIGN: An in-vitro biomechanical study of human cadaver sacroiliac joints. OBJECTIVE: Our study aimed to develop a more comprehensive understanding of the native motion of the SIJ within the context of spinal kinematics and spinal implant evaluation. SUMMARY OF BACKGROUND DATA: Increasing attention has been given to the sacroiliac joint (SIJ) as a source of low back pain, despite its limited range of motion. We sought to characterize the rotational and translational motion in each axis utilizing standard pure moment flexion-extension (FE), lateral bending (LB), and axial rotation (AR) testing. METHODS: Sixteen sacroiliac joints were evaluated from eight lumbosacral cadaver specimens (six females, two males) from subjects aged 28 to 57 years (mean age 46.8) with body mass index (BMI) 22 to 36 (mean BMI 30). Single leg stance was modeled by clamping the blocks on one ischium in a vise and letting the contralateral ischium hang freely. Pure moment loading was applied in FE, right/left AR, and right/left LB. Relative motions were collected with infrared markers. RESULTS: The on-axis ratio was significantly lower in LB than in FE (P = 0.012) and in AR (P = 0.017). The rotation deviation angle measured 13.9 ±â€Š9.1° in FE, 17.1 ±â€Š8.7° in AR, and 35.7 ±â€Š25.7° in LB. In LB the rotational deviation angle is significantly higher than both FE and AR (P = 0.003 and P = 0.011, respectively). In-plane translation was significantly higher (P = 0.005) in FE loading than in LB loading. CONCLUSION: A nontrivial amount of rotation and translation occurred out of the expected axis of motion. The largest amount of off-axis rotation was observed in lateral bending. Relative to resultant translation, in-plane translation was lowest in lateral bending. Our results indicate that rotation of the SIJ is not fully described with the in-plane metrics which are normally reported in evaluation of fusion devices. Future studies of the SIJ may need to consider including off-axis rotation measurements when describing SIJ kinematics.Level of Evidence: 5.

Pedicle Screws Challenged: Lumbar Cortical Density and Thickness Are Greater in the Posterior Elements Than in the Pedicles.

STUDY DESIGN: Controlled laboratory study. OBJECTIVE: To measure the total bone mineral density (BMD), cortical volume, and cortical thickness in seven different anatomical regions of the lumbar spine. METHODS: Using computed tomography (CT) images, 3 cadaveric spines were digitally isolated by applying filters for cortical and cancellous bone. Each spine model was separated into 5 lumbar vertebrae, followed by segmentation of each vertebra into 7 anatomical regions of interest using 3-dimensional software modeling. The average Hounsfield units (HU) was determined for each region and converted to BMD with calibration phantoms of known BMD. These BMD measurements were further analyzed by the total volume, cortical volume, and cancellous volume. The cortical thickness was also measured. A similar analysis was performed by vertebral segment. St Mary's Medical Center's Institutional Review Board approved this study. No external funding was received for this work. RESULTS: The lamina and inferior articular process contained the highest total BMD, thickest cortical shell, and largest percent volumes of cortical bone. The vertebral body demonstrated the lowest BMD. The BMDs of the L4 and L5 segments were lower; however, there were no statistically significant differences in BMD between the L1-L5 vertebral segments. CONCLUSION: Extrapedicular regions of the lumbar vertebrae, including the lamina and inferior articular process, contain denser bone than the pedicles. Since screw pullout strength relies greatly on bone density, the lamina and inferior articular processes may offer stronger fixation of the lumbar spine.

Non-Pedicular Fixation Techniques for the Treatment of Spinal Deformity: A Systematic Review.

BACKGROUND: In recent years, the use of pedicle screws has become the gold standard for achieving stable, 3-column fixation of the spine. However, pedicle screw placement may not always be ideal, such as in adolescent idiopathic scoliosis, because of pedicle morphology. An understanding of the alternatives to pedicle screw fixation is therefore important in the treatment of patients with spinal deformity. The purpose of this article is to review the indications, advantages, disadvantages, and complications associated with non-pedicular fixation techniques of the thoracolumbar spine. METHODS: Comprehensive literature searches of PubMed, Scopus, and Web of Science databases were performed for 10 methods of non-pedicular fixation. Articles published between January 1, 1990, and June 1, 2019, were considered. Non-English-language articles and studies involving fixation of the cervical spine were excluded from our review. RESULTS: After reviewing >1,600 titles and abstracts pertaining to non-pedicular fixation, a total of 213 articles met our inclusion criteria. Non-pedicular fixation may be preferred in certain cases of spinal deformity and may provide stronger fixation in osteoporotic bone. The use of non-pedicular fixation techniques is often limited by the inability to place multilevel constructs on intact posterior elements. Additionally, some methods of non-pedicular fixation, such as spinous process tethering, primarily have utility for the end of constructs to minimize junctional problems. CONCLUSIONS: Pedicle screws remain the anchor of choice in spinal deformity surgery because of their ability to engage all 3 columns of the spine and provide safe correction in all 3 planes. Nevertheless, non-pedicular fixation may be useful in cases in which pedicle screw placement is extremely difficult. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Anterior Lumbar Interbody Fusion May Provide Superior Decompression of the Foraminal Space Compared with Direct Foraminotomy: Biomechanical Cadaveric Study.

OBJECTIVE: The objective of this cadaveric biomechanical study was to compare the area of the foraminal space during motion in the intact condition, after direct decompression via foraminotomy, and after indirect decompression via anterior lumbar interbody spacer insertion. METHODS: Eight (8) L5-S1 cadaver specimens were used for testing. Each specimen was tested in the intact state, after posterior foraminotomy, and after standalone anterior lumbar interbody fusion (ALIF). Each specimen was 3-dimensional imaged under neutral loading, flexion, and extension. The 3-dimensional images were analyzed for changes in the foraminal area under each loading scenario. A repeat-measures design was used. Outcome measures from testing included the frequency in which an increase in cross-sectional area was observed, as well as the percent increase of the foraminal area for each surgical group and loading direction. RESULTS: Direct foraminotomy and ALIF maintained the foraminal space during initial distraction under no loading with areas 99.7% and 96.5% of the native foraminal area, respectively (P = 0.955 and P = 0.455). Direct foraminotomy increased the foraminal area significantly during flexion to 112.2% of the area before motion (P = 0.008) while ALIF did not. Direct foraminotomy significantly decreased the foraminal area during extension to 89.2% of the area before motion (P = 0.006). ALIF, however, maintained its initial distraction during extension with 98.2% of the area before motion (P = 0.808). CONCLUSIONS: ALIF maintains the foraminal area in extension while direct posterior foraminotomy does not.

Motion Preservation at All Costs? Multilevel Hinge Nonunion, Plate Breakage, and Intradural Plate Migration After Cervical Laminoplasty: A Case Report and Literature Review.

BACKGROUND: Cervical laminoplasty is a motion-preserving procedure that addresses spinal cord compression and avoids postlaminectomy kyphosis associated with cervical laminectomy. The most common complications include C5 nerve palsy, axial neck pain, hinge nonunion, and premature closure. Plating is a relatively newer method of laminoplasty fixation that may provide greater stabilization postoperatively and reduce the risk of laminoplasty closure compared with less rigid (e.g., suture) fixation techniques. Although prior studies have reported low rates of laminar/lateral mass screw back out, plate breakage and migration have not been previously described in the literature. The purpose of this paper is to present a case of multilevel hinge nonunion, plate breakage, and plate fragment migration. Although rare, plate failure may result in a dural tear and spinal cord injury/compression. CASE DESCRIPTION: In this case, a 61-year-old man with a history of cervical spondylotic myelopathy treated with C3-7 laminoplasty 7 years prior presented to our hospital with severe headaches and electrical-type pain through the left upper and lower extremities. Imaging studies revealed several broken laminoplasty plates and intradural migration of a fragment of the C7 plate. CONCLUSIONS: We provide recommendations for preventing hinge nonunion because resultant micromotion likely contributed to the plate breakages observed in this patient.

High Prevalence of Multifocal Spine Infections Involving the Cervical and Thoracic Regions: A Case for Imaging the Entire Spine.

OBJECTIVE: Pyogenic spinal infections account for 2%-4% of orthopaedic infections. They are often difficult to diagnose, resulting in a delay in diagnosis. Risk factors for orthopaedic and spinal infection are well-documented in the literature, yet there is a paucity of studies examining risk factors specifically for multifocal spinal infections. The objective of this study was to identify predictors of multifocal spinal infections in comparison to unifocal spinal infections. METHODS: The medical records, imaging studies, and bacteriology data of 20 patients treated surgically for pyogenic spinal infection over 6 years at a tertiary referral center were reviewed and analyzed after receiving Institutional Review Board approval. Univariate and multivariate analyses were performed to identify factors associated with a multifocal spinal infection. RESULTS: Seven patients (35%) had multifocal infections. Three were bifocal, and 4 were trifocal. Patients with surgically treated cervical or thoracic spinal infections had a high rate of concomitant multifocal spinal infections (71% and 83%, respectively). Other potential predictors (e.g., patient age, body mass index, magnetic resonance image findings, etc.) did not reach statistical significance. Each of the multifocal infections involved the lumbar spine. CONCLUSION: In this study, the spinal region was the only statistically significant risk factor for multifocal infection. Patients who are diagnosed with a spinal infection that requires operative treatment should have their entire spine evaluated with magnetic resonance imaging to detect multifocal involvement promptly.

Biomechanical Comparison of Ulnar Collateral Ligament Reconstruction With a Modified Docking Technique With and Without Suture Augmentation.

BACKGROUND: Throwing athletes with ulnar collateral ligament (UCL) injury and symptomatic valgus instability can expect to return to the same or higher level of play. Reconstruction with tendon graft is the dominant method of surgical treatment. Recent evidence suggests that spanning the joint with a suture anchored on both sides is biomechanically equivalent to reconstruction, with faster time to return to play. The authors developed a hybrid UCL reconstruction technique augmented with a suture brace to improve joint stability. PURPOSE/HYPOTHESIS: The purpose of this study was to biomechanically evaluate a hybrid reconstruction technique and compare its performance to reconstruction without augmentation. The authors hypothesized that (1) both groups would lose stability after the simulated tear and regain stability with treatment, (2) the suture augmentation would improve stability, and (3) the addition of the suture anchors near the bone tunnels would not decrease the strength of the hybrid reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: Ten matched pairs of cadaveric arms were dissected to expose the UCL. Each elbow was mounted on a test frame at 90° of flexion. A cyclic valgus rotational torque was applied to the humerus with the UCL in its intact state and repeated in its surgically torn state. Finally, each specimen received either a hybrid reconstruction with suture brace or a reconstruction and was again put through the cyclic protocol, followed by a valgus rotation load-to-fail protocol. RESULTS: Gap formation in the torn state for the reconstruction and hybrid reconstruction groups (0.9 ± 0.1 mm and 0.8 ± 0.1 mm, respectively) was significantly higher ( P = .009 and P = .0002) than in the intact state (0.6 ± 0.2 mm and 0.6 ± 0.3 mm, respectively). After the procedures, the hybrid group showed greater resistance to gapping ( P = .017) as compared with the reconstruction group (0.4 ± 0.2 mm and 0.6 ± 0.1 mm). During load to failure, no hybrid reconstructions failed from bone fracture or screw pullout. No statistical differences were found for failure torque ( P = .058) and stiffness ( P = .101). Gap at 10 N·m was significantly lower ( P = .014) for the hybrid reconstruction group than for the reconstruction group. CONCLUSION: The current study showed that hybrid reconstruction with suture bracing replicated the time-zero strength of traditional UCL reconstruction and may be more resistant to joint gapping during low cyclic load and load to failure. The combination of the bone tunnels and fixation screw holes did not appear to weaken the construct. CLINICAL RELEVANCE: This study demonstrated that reconstruction with suture bracing has important time-zero stability and strength as compared with the gold standard of UCL reconstruction. This technique may be useful for throwing athletes who need UCL reconstruction.

Biomechanical Comparison of First Tarsometatarsal Arthrodesis Constructs Over Prolonged Cyclic Testing.

BACKGROUND: Traditionally, a lengthy period of nonweightbearing is required following arthrodesis of the first tarsometatarsal (TMT) joint in order to provide a stable healing environment for the bones. The goal of this research was to determine the resistance to plantar gapping of 2 locked intramedullary devices and a medial plate with crossing screw, all specifically designed for hallux valgus correction, and compare them to traditional 2-crossing screw fixation under a cyclic testing protocol. We hypothesized the locked intramedullary devices and the medial plate with crossing screw would better resist plantar gapping. METHODS: Forty cadaver specimens received 1 of 4 operative treatments: a locked intramedullary device with 2 points of fixation in the cuneiform, a locked intramedullary device with 1 point of fixation in the cuneiform, a medial plate with crossing screw, or 2 crossing screws. We applied dorsiflexion bending forces to the first TMT joint using a cadaveric fatigue model for 20 000 cycles. The plantar gap between the metatarsal and cuneiform was measured at the beginning and end of cyclic testing. Thirty-six specimens were included in the final data set. RESULTS: Both locked intramedullary device groups and the medial plate with crossing screw group exhibited significantly less gap widening compared to the 2-crossing screw group (vs 3-hole intramedullary device, P = .014; vs 4-hole intramedullary device, P = .010; and vs medial plate with crossing screw, P = .044). The intramedullary device groups were the most stable during the cyclic fatigue test, exhibiting the smallest gap widening. The medial plate with crossing screw fixation was also more stable than crossing screws in the cyclic fatigue model. CONCLUSIONS: The locked intramedullary devices and medial plate with crossing screw resisted plantar gapping better than 2 crossing screws when used for first TMT arthrodesis. CLINICAL RELEVANCE: These results indicate that locked intramedullary devices and medial plates with crossing screws may promote superior bone healing and may better tolerate early weightbearing compared with 2 crossing screws.

Assessment of Biomechanical Changes After Sacroiliac Joint Fusion by Application of the 3-Dimensional Motion Analysis Technique.

BACKGROUND: Sacroiliac (SI) joint motion is complex and is poorly understood overall. In this study we evaluated a new biomechanical method developed to provide more insight into SI joint movement and to elucidate biomechanical changes after SI joint fusion surgery in a one-leg standing model. METHODS: Eight lumbosacral cadaver specimens (L5-pelvis specimens, age 28-57 years, 6 female and 2 male) were used in this experiment. We analyzed the changes in range of motion (ROM) in single-plane motion and mobility in 3 groups of patients: intact, unilateral fusion, and bilateral fusion groups. For statistical analysis, we used repeated-measures analysis of variance to compare SI joint ROM among the 3 groups. iFuse implants were prepared using the standard posterior placement technique. Pure-moment multidirectional bending tests were performed in each direction (nutation and counternutation, axial rotation, and lateral bending). RESULTS: Average ROM in single-plane motion and mobility of the intact SI joint were 4.5 ± 3.3° and 4.8 ± 3.4°, respectively in nutation-counternutation; 2.9 ± 2.1° and 3.3 ± 2.3°, respectively, in axial rotation; and 1.5 ± 1.5° and 2.8 ± 2.5°, respectively, in lateral bending. We observed statistically significantly (P = 0.05) greater mobility in lateral moment testing than in single motion testing. Comparisons among the intact, unilateral fusion, and bilateral fusion groups showed statistically significant differences in the lateral moment test. CONCLUSIONS: This study suggests that our new biomechanical method for SI joint evaluation may provide improved insight into SI joint movement and biomechanical changes after SI joint fusion surgery in a one-leg standing model.

Biomechanics of unilateral and bilateral sacroiliac joint stabilization: laboratory investigation.

OBJECTIVE Bilateral symptoms have been reported in 8%-35% of patients with sacroiliac (SI) joint dysfunction. Stabilization of a single SI joint may significantly alter the stresses on the contralateral SI joint. If the contralateral SI joint stresses are significantly increased, degeneration may occur; alternatively, if the stresses are significantly reduced, bilateral stabilization may be unnecessary for patients with bilateral symptoms. The biomechanical effects of 1) unilateral stabilization on the contralateral SI joint and 2) bilateral stabilization on both SI joints are currently unknown. The objectives of this study were to characterize bilateral SI joint range of motion (ROM) and evaluate and compare the biomechanical effects of unilateral and bilateral implant placement for SI joint fusion. METHODS A lumbopelvic model (L5-pelvis) was used to test the ROM of both SI joints in 8 cadavers. A single-leg stance setup was used to load the lumbar spine and measure the ROM of each SI joint in flexion-extension, lateral bending, and axial rotation. Both joints were tested 1) while intact, 2) after unilateral stabilization, and 3) after bilateral stabilization. Stabilization consisted of lateral transiliac placement of 3 triangular titanium plasma-sprayed (TPS) implants. RESULTS Intact testing showed that during single-leg stance the contralateral SI joint had less ROM in flexion-extension (27%), lateral bending (32%), and axial rotation (69%) than the loaded joint. Unilateral stabilization resulted in significant reduction of flexion-extension ROM (46%) on the treated side; no significant ROM changes were observed for the nontreated side. Bilateral stabilization resulted in significant reduction of flexion-extension ROM of the primary (45%) and secondary (75%) SI joints. CONCLUSIONS This study demonstrated that during single-leg loading the ROMs for the stance (loaded) and swing (unloaded) SI joints are significantly different. Unilateral stabilization for SI joint dysfunction significantly reduces the ROM of the treated side, but does not significantly reduce the ROM of the nontreated contralateral SI joint. Bilateral stabilization is necessary to significantly reduce the ROM for both SI joints.

Stand-alone anterior interbody fusion for substitution of iliac fixation in long spinal fixation constructs.

INTRODUCTION: The use of distal sacral anchorage solely, in long spinal fusions, may lead to substantial complications. Extending the fixation down to the ilium and the addition of anterior column support are both used to facilitate construct stability and improve fusion rates. In the current study, we aimed to determine whether supplementation of long thoracolumbar fixation constructs with stand-alone anterior interbody fusion (ALIF) cage with embedded screws can eliminate the biomechanical need for iliac screws fixation biomechanically. METHODS: Seven lumbopelvic human cadavers (L1-full pelvis) were used. All specimens were tested with the following fixation constructs: bilateral L1-S1, bilateral L1-S1 with unilateral iliac screw, and bilateral L1-S1 with bilateral iliac screw. The three constructs were tested with and without the addition of stand-alone ALIF cage. We evaluated the multidirectional rigidity and the axial S1 screw strain. RESULTS: The addition of an ALIF cage solely did not affect rigidity and resulted in mixed S1 screw strain results. One iliac screw was superior to ALIF in rigidity and inferior in S1 screws strain. Bilateral iliac fixation produced similar rigidity and lower S1 screws strain than unilateral iliac fixation. When ALIF was combined with bilateral iliac screws, it resulted in equal rigidity and lower S1 screws strain. CONCLUSION: Our results do not support stand-alone ALIF cage as a substitute for iliac fixation in in long posterior lumbosacral fusion. They do support the use of stand-alone ALIF for the supplementation of bilateral iliac fixation in long lumbosacral fusions.