Value of washers in internal fixation of femoral neck fractures with cancellous screws: a biomechanical evaluation.

OBJECTIVE: The purpose of this study was to evaluate the maximum insertion torque of cancellous bone screws in osteoporotic proximal femurs with and without the use of washers. METHODS: Eight matched pairs of osteoporotic fresh-frozen human cadaveric femurs (age >70 years, all female) were used. Two screws were inserted in each femur either with or without a washer, and maximum insertion torque was measured using a 50 N·m torque transducer. The testing was performed using a customized device, which allowed the torque transducer to apply a constant axial force and rate of rotation to the screws. RESULTS: In 14 of 16 paired trials, the maximum screw insertion torque was higher when a washer was used. The average maximum torque with a washer was 5.1 N·m compared with 3.1 N·m without a washer (P < 0.01). CONCLUSIONS: The addition of washers increased the maximum insertion torque of cancellous screws in the proximal femur by 65% in this study. Washers prevent the screw heads from penetrating the lateral cortex at low insertion torque loads, and thereby provide for an improved purchase of the screws in the femoral head with a higher maximum insertion torque. We advocate for routine washer use and encourage future clinical studies to further understand the correlation between their use and improved outcomes in this patient population.

Sagittal balance and spinopelvic parameters after lateral lumbar interbody fusion for degenerative scoliosis: a case-control study.

STUDY DESIGN: Retrospective matched-cohort analysis. OBJECTIVE: To evaluate the change in radiographical parameters in patients undergoing interbody fusion and posterior instrumentation compared with posterior spine fusion (PSF) alone for degenerative scoliosis. SUMMARY OF BACKGROUND DATA: Little is known about the effect of lateral interbody fusion (LIF) on sagittal plane correction in the setting of degenerative scoliosis. We performed a retrospective study to investigate these changes compared with PSF. METHODS: Between 1997 and 2011, 33 patients had LIF at 181 levels between T8 and L5 vertebrae for the treatment of degenerative scoliosis (mean; 5 ± 2 levels). Of those, 23 patients had additional anterior lumbar interbody fusion (ALIF) at 37 levels between L4 and S1 vertebrae (mean; 1.6 ± 0.5 levels). A 1:1 matched control of patients who underwent PSF was performed. Patients were matched by age, sex, and diagnosis. Clinical and radiographical data were collected and compared between the matched cohorts. RESULTS: Lumbar lordosis (LL) was significantly restored in the LIF ± ALIF compared with PSF cohort (44° ± 14° vs. 36° ± 15°, P = 0.02). The segmental LL over the 102 LIF levels significantly improved from 12°± 10° to 21°± 13° postoperatively (P < 0.0001). However, the change over the 37 ALIF levels was not significant (from 30° ± 15° to 29° ± 9°, P = 0.8). Sagittal plane alignment was improved in the LIF ± ALIF compared with PSF cohort and trended toward but did not reach significance (3.8 ± 3.2 cm vs. 6.2 ± 5.7 cm, P = 0.09). Sacral slope was significantly higher in the LIF ± ALIF compared with PSF cohort (33° ± 11° vs. 28° ± 10°, P = 0.03). Pelvic tilt was lower in the LIF ± ALIF compared with PSF cohort and trended toward but did not reach significance (22° ± 10° vs. 26° ± 10°, P = 0.08). CONCLUSION: LL and sacral slope had mildly but statistically improved in the interbody fusion cohort compared with PSF cohort. Sagittal alignment and pelvic tilt trended toward but did not reach statistical significance. Segmental LL was improved at LIF levels more than at ALIF levels. LEVEL OF EVIDENCE: 3.

Periarticular raft constructs and fracture stability in split-depression tibial plateau fractures.

OBJECTIVES: To evaluate relative fracture stability yielded by screws placed above a lateral plate, as well as locking and non-locking screws placed through a plate in a split depression tibia plateau fracture model. METHODS: Cadaver tibia specimens (mean age 74.1 years) were randomised across 3 groups: Groups 1: raft-construct outside the plate, 2: non-locking raft screws through the plate, and 3: locking raft screws through the plate. Displacement of the depressed fragment was recorded with force values from 400N to 1600N in increasing 400N increments. The force required to elicit lateral plateau fragment displacement of 5mm, 10mm, and 15mm was also recorded. RESULTS: None of the mechanical testing results demonstrated statistical significance with p-values of <0.05. Cyclic testing of Groups 1, 2, and 3 at 400N revealed displacements of 0.54mm, 0.64mm, and 0.48mm, respectively. At 800N, displacements were 1.36mm, 1.4mm, and 1.4mm, respectively. At 1200N, displacements were 2.4mm, 1.9mm, and 2.1mm, respectively. At 1600N, displacements were 2.8mm, 2.5mm, and 2mm, respectively. Resistance to displacement data demonstrated the mean force required to displace the fracture 5mm in Groups 1, 2, and 3 were 250N, 330N, and 318N, respectively. For 10mm of displacement, forces required were 394N, 515N, and 556N, respectively. For 15mm of displacement, forces required were 681N, 853N, and 963N, respectively. Compared to combined groups using screws through the plate, Group 1 demonstrated lower displacement ≤800N, but demonstrated greater displacement >800N. Group 2 demonstrated greatest resistance to plateau displacement of 5mm compared to Group 1 or 3, while Group 3 was most resistant to greater displacement. The combined group using screws through the plate (Groups 2+3) was consistently more resistant than Group 1 at all levels of displacement. CONCLUSIONS: Designs utilising screws through the plate trended towards statistically significant improved stability against plateau displacement relative to utilising screws outside the plate. Our study also suggests that there is no significant benefit of locking screws over non-locking screws in this unicondylar tibia plateau fracture model.

An in vitro analysis of an anatomical medial knee reconstruction.

BACKGROUND: An anatomical medial knee reconstruction has not been described in the literature. HYPOTHESIS: Knee stability and ligamentous load distribution would be restored to the native state with an anatomical medial knee reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: Ten nonpaired cadaveric knees were tested in the intact, superficial medial collateral ligament and posterior oblique ligament-sectioned, and anatomically reconstructed states. Each knee was tested at 0 degrees , 20 degrees , 30 degrees , 60 degrees , and 90 degrees of knee flexion with a 10-N.m valgus load, 5-N.m external and internal rotation torques, and 88-N anterior and posterior drawer loads. A 6 degrees of freedom electromagnetic motion tracking system measured angulation and displacement changes of the tibia with respect to the femur. Buckle transducers measured the loads on the intact and reconstructed proximal and distal divisions of the superficial medial collateral ligament and the posterior oblique ligament. RESULTS: A significant increase was found in valgus angulation and external rotation after sectioning the medial knee structures at all tested knee flexion angles. This was restored after an anatomical medial knee reconstruction. The authors also found a significant increase in internal rotation at 0 degrees , 20 degrees , 30 degrees , and 60 degrees of knee flexion after sectioning the medial knee structures, which was restored after the reconstruction. A significant increase in anterior translation was observed after sectioning the medial knee structures at 20 degrees , 30 degrees , 60 degrees , and 90 degrees of knee flexion. This increase in anterior translation was restored following the reconstruction at 20 degrees and 30 degrees of knee flexion, but was not restored at 60 degrees and 90 degrees . A small, but significant, increase in posterior translation was found after sectioning the medial knee structures at 0 degrees and 30 degrees of knee flexion, but this was not restored after the reconstruction. Overall, there were no clinically important differences in observed load on the ligaments when comparing the intact with the reconstructed states for valgus, external and internal rotation, and anterior and posterior drawer loads. Conclusion An anatomical medial knee reconstruction restores near-normal stability to a knee with a complete superficial medial collateral ligament and posterior oblique ligament injury, while avoiding overconstraint of the reconstructed ligament grafts. CLINICAL SIGNIFICANCE: This anatomical medial knee reconstruction technique provides native stability and ligament load distribution in patients with chronic or severe acute medial knee injuries.

Mapping of scapular fractures with three-dimensional computed tomography.

BACKGROUND: Fractures of the scapula involve a unique and challenging set of considerations, which must be understood to provide optimal treatment. The primary goal of this study was to create a frequency map of a series of surgically treated scapular fractures that specifically involved the scapular body and/or neck. METHODS: A prospective database was used in the collection of consecutive radiographic imaging studies of patients undergoing operative treatment of scapular fractures. Scanned three-dimensional computed tomography images were superimposed and oriented to fit a model scapular template. Size dimensions were normalized by aligning specific scapular landmarks. Fracture lines were identified and traced over the combined three-dimensional computed tomography model to create a scapular fracture map. RESULTS: Of ninety fractures that met the criteria for inclusion, 68% involved the inferior aspect of the glenoid neck and 71% involved the superior vertebral border. Seventeen percent of the patterns included articular extension, and 22% of the fractures entered the spinoglenoid notch. Of fractures involving the inferior aspect of the glenoid neck at the lateral scapular border, 84% traversed medially to exit just inferior to the medial extent of the scapular spine, and 59% of these inferior neck fractures also had propagation to the inferior third of the vertebral border. Among the fractures involving the spinoglenoid notch, the most common pattern was demonstrated by coexisting fracture lines; 60% of the fractures of the spinoglenoid notch exited just inferior to the glenoid, 65% extended to the superior-medial vertebral border, and 45% extended to the inferior-medial vertebral border. In contrast, articular fractures did not follow predictable patterns; they demonstrated the greatest variability in trajectory, which was almost random, and there was a wide distribution of exit points along the vertebral border. CONCLUSIONS: Surgically treated scapular fractures display very common patterns. The most common pattern is the lateral border fracture immediately inferior to the glenoid, which extends to the superior vertebral border in more than two-thirds of cases. A smaller proportion of scapular fractures enter the spinoglenoid notch or the articular surface. There is great variation in the patterns of fractures involving the articular surface.

Medial knee injury: Part 2, load sharing between the posterior oblique ligament and superficial medial collateral ligament.

BACKGROUND: There is limited information regarding directly measured load responses of the posterior oblique and superficial medial collateral ligaments in isolated and multiple medial knee ligament injury states. HYPOTHESES: Tensile load responses from both the superficial medial collateral ligament and the posterior oblique ligament would be measurable and reproducible, and the native load-sharing relationships between these ligaments would be altered after sectioning of medial knee structures. STUDY DESIGN: Descriptive laboratory study. METHODS: Twenty-four nonpaired, fresh-frozen adult cadaveric knees were distributed into 3 sequential sectioning sequences. Buckle transducers were applied to the posterior oblique ligament and the proximal and distal divisions of the superficial medial collateral ligament; 10 N.m valgus moments and 5 N.m internal and external rotation torques were applied at 0 degrees , 20 degrees , 30 degrees , 60 degrees , and 90 degrees of knee flexion. RESULTS: With an applied valgus and external rotation moment, there was a significant load increase on the posterior oblique ligament compared with the intact state after sectioning all other medial knee structures. With an applied external rotation torque, there was a significant load decrease on the proximal division of the superficial medial collateral ligament from the intact state after sectioning all other medial knee structures. With an applied external rotation torque, the distal division of the superficial medial collateral ligament experienced a significant load increase from the intact state after sectioning the posterior oblique ligament and the meniscofemoral division of the deep medial collateral ligament. CONCLUSION: This study found alterations in the native load-sharing relationships of the medial knee structures after injury. Sectioning both the primary and secondary restraints to valgus and internal/external rotation of the knee alters the intricate load-sharing relationships that exist between the medial knee structures. CLINICAL SIGNIFICANCE: In cases in which surgical repair or reconstruction is indicated, consideration should be placed on repairing or reconstructing all injured medial knee structures to restore the native load-sharing relationships among these medial knee structures.

The 1:1 versus the 2:2 tunnel-drilling technique: optimization of fixation strength and stiffness in an all-inside double-bundle anterior cruciate ligament reconstruction--a biomechanical study.

BACKGROUND: Double-bundle anterior cruciate ligament (ACL) reconstructions involve drilling 2 tibial tunnels separated by a narrow 2-mm bone bridge. The sequence of reaming and drilling the tibial tunnels for double-bundle ACL reconstructions has not been defined. HYPOTHESIS: Fixing a graft in the posterolateral ACL tibial tunnel before reaming the anteromedial tibial tunnel will reduce the number of complications, as compared with drilling both the anteromedial and posterolateral tunnels before graft fixation, when performing double-bundle ACL reconstructions. STUDY DESIGN: Controlled laboratory study. METHODS: Twelve porcine tibias were divided into 2 groups of 6 specimens. Fresh bovine extensor tendons grafts were fixed in 7-mm tunnels reamed using an inside-out method. Grafts were fixed in a retrograde fashion with 7-mm bioabsorbable retrograde screws. The tibias in group 1 were reconstructed by reaming and reconstructing the posterolateral tunnel before reaming and securing the graft for the anteromedial tunnel (ie, 1:1 method), whereas those in the second group were reconstructed by reaming both tunnels before graft fixation in either (ie, the 2:2 method). The specimens were biomechanically tested with cyclic and load-to-failure parameters. RESULTS: Cyclic testing revealed no significant difference between the 2 methods in displacement or stiffness. In load-to-failure testing, the 1:1 group withstood significantly higher initial failure loads and ultimate loads. Pullout displacement was significantly higher for the 1:1 group. Whereas no tibias in the 1:1 group sustained fractures, 4 from the 2:2 group demonstrated a bone bridge fracture. CONCLUSION: Soft tissue ACL grafts fixed in the tibia with the 1:1 method withstood significantly higher initial and ultimate failure loads and were stiffer than the grafts fixed with the 2:2 method. Tibias fixed with the 1:1 method were also less susceptible to bone bridge fracture. CLINICAL RELEVANCE: The potential for a lower complication rate and greater pullout strength seen with the 1:1 method may prove useful to surgeons performing anatomic double-bundle ACL reconstructions, in addition to other procedures involving reconstructing 2 closely positioned tunnels, including anatomic posterolateral corner and medial collateral reconstructions.

Force measurements on the posterior oblique ligament and superficial medial collateral ligament proximal and distal divisions to applied loads.

BACKGROUND: There is limited information regarding load responses of the posterior oblique and superficial medial collateral ligaments to applied loads. HYPOTHESES: The degree of knee flexion affects loads experienced by the posterior oblique ligament and both divisions of the superficial medial collateral ligament. The posterior oblique ligament provides significant resistance to valgus and internal rotation forces near knee extension. Different load responses are experienced by proximal and distal divisions of the superficial medial collateral ligament. STUDY DESIGN: Descriptive laboratory study. METHODS: Twenty-four nonpaired, fresh-frozen cadaveric knees were tested. Buckle transducers were applied to the proximal and distal divisions of the superficial medial collateral and posterior oblique ligaments. Applied loads at 0 degrees, 20 degrees, 30 degrees, 60 degrees, and 90 degrees of knee flexion consisted of 10 N m valgus loads, 5 N.m internal and external rotation torques, and 88 N anterior and posterior drawer loads. RESULTS: External rotation torques produced a significantly higher load response on the distal superficial medial collateral ligament than did internal rotation torques at all flexion angles with the largest difference at 90 degrees (96.6 vs 22.5 N). For an applied valgus load at 60 degrees of knee flexion, loads on the superficial medial collateral ligament were significantly higher in the distal division (103.5 N) than the proximal division (71.9 N). The valgus load response of the posterior oblique ligament at 0 degrees of flexion (19.1 N) was significantly higher than at 30 degrees (10.6 N), 60 degrees (7.8 N), and 90 degrees (6.8 N) of flexion. At 0 degrees of knee flexion, the load response to internal rotation on the posterior oblique ligament (45.8 N) was significantly larger than was the response on both divisions of the superficial medial collateral ligament (20 N for both divisions). At 90 degrees of flexion, the load response to internal rotation torques reciprocated between these structures with a significantly higher response in the distal superficial medial collateral ligament division (22.5 N) than the posterior oblique ligament (9.1 N). CONCLUSION: The superficial medial collateral ligament experienced the largest load response to applied valgus and external rotation torques; the posterior oblique ligament observed the highest load response to internal rotation near extension. CLINICAL RELEVANCE: This study provides new knowledge of the individual biomechanical function of the main medial knee structures in an intact knee and will assist in the interpretation of clinical knee motion testing and provide evidence for techniques involving repair or reconstruction of the posterior oblique ligament and both divisions of the superficial medial collateral ligament.

Vulnerable neurovasculature with a posterior approach to the scapula.

Anatomic studies have described areas where there is no direct threat of inadvertent suprascapular nerve injury; however, these studies did not describe danger zones during open reduction and internal fixation of the fractured scapula. We therefore sought to define the topographic distribution in which these vulnerable structures most commonly are found, thus establishing danger zones. Twenty-four nonpaired cadaveric specimens were dissected. The infraspinatus and teres minor musculature were elevated off the posterior scapula body to reveal critical areas where the suprascapular neurovasculature and circumflex scapular artery were vulnerable to injury. We established radial coordinates to determine this relation to osseous landmarks. The mean distance from the spinoglenoid notch to the inferior border of the danger zone was 2.4 cm (range, 1.2-3.8 cm). The mean distance from the medial extent of the scapular spine to the medial border of the danger zone was 4.3 cm (range, 3.0-6.7 cm). The entry of the ascending branch of the circumflex scapular artery was located at the lateral border 5.6 cm (range, 4.5-7.0 cm) inferior to the spinoglenoid notch. These danger zones can aid the surgeon in determining the risk for suprascapular nerve injury, specifically with scapula fractures involving the spinoglenoid notch and/or lateral border.