Latarjet Procedure: Biomechanical Evaluation of 2 Screw Coracoid Fixation.

BACKGROUND: Coracoid nonunion is a relevant complication following the Latarjet procedure and is influenced by multiple factors, including the method of graft fixation. AIMS: The purpose of this study was to evaluate and characterize the biomechanical properties of various two-screw fixation constructs used for coracoid graft fixation in the Latarjet procedure. METHODS: Forty model scapulae (Sawbones Inc., Vashon, WA, USA) were used for this study. A 15 percent anterior inferior glenoid bone defect was created. The coracoid was osteotomized at the juncture of the vertical and horizontal aspects, transferred to the anterior-inferior edge of the glenoid, and fixed with either two 3.5 mm fully threaded cannulated cortical screws (FTCS), two 3.5 mm fully threaded solid cortical screws (FTSS), two 3.5 mm partially threaded cannulated screws (PTCS), or two 4.5 mm partially threaded malleolar screws (MS). Biomechanical testing was performed with an Instron materials testing machine (Instron Corp., Norwood, MA) by applying loads to the lateral aspect of the transferred coracoid graft. The constructs were preconditioned with non-destructive cyclical loading (0-20N) to determine construct stiffness. After 100 cycles of dynamic loading, the construct was loaded to failure to determine ultimate failure load, yield displacement, and mode of failure. RESULTS: All failures were associated with plastic deformation of the screws and coracoid graft fracture. There was a significantly lower initial stiffness for PTCS compared to MS (186±49.3 N/mm vs 280±65.5 N/mm, p=0.01) but no significant differences among the other constructs. There was no difference in ultimate failure load (p=0.18) or yield displacement (p=0.05) among constructs. CONCLUSION: Two screw coracoid fixation of the coracoid in a simulated classic Latarjet procedure with 3.5 mm fully threaded cortical and cannulated screws is comparable to 4.5 mm malleolar screws in strength, stiffness, and displacement at failure. On the other hand, partially threaded 3.5 mm cannulated screws provide inferior fixation stiffness and could potentially affect clinical outcomes.

Biomechanical Analysis of Pedicle Screw Fixation for Thoracolumbar Burst Fractures.

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

Biomechanical and Computed Tomography Analysis of Adjustable Femoral Cortical Fixation Devices for Anterior Cruciate Ligament Reconstruction in a Cadaveric Human Knee Model.

PURPOSE: To evaluate and compare two adjustable femoral cortical suspensory fixation devices used for anterior cruciate ligament reconstruction through a novel, direct computed tomography (CT) analysis metric and biomechanical laxity testing in a matched cadaveric human knee study. METHODS: Anterior cruciate ligament reconstructions with bovine tendon grafts were performed using two adjustable femoral cortical suspensory fixation devices (RigidLoop Adjustable [DePuy Synthes Mitek, Raynham, MA] and TightRope [Arthrex, Naples, FL]) in 12 knees (6 matched pairs). A mechanical testing series was used to determine each knee's laxity in the intact condition. After reconstruction, each specimen was again tested for laxity and also imaged with CT. The laxity testing and CT imaging were then repeated after 1,000 cycles of anteroposterior loading on each knee to compare changes in laxity for the two fixation devices and to visualize changes in button-to-graft distance migration through a three-dimensional CT imaging method. RESULTS: No significant differences were found between the two fixation groups' laxity measures after reconstruction (all P values ≥ .620) or after cycling (all P values ≥ .211) at any flexion angle. In addition, no significant differences were found between the two groups regarding button-to-graft distance migration (P = .773; mean, 0.61 ± 0.6 mm [95% confidence interval, -0.1 to 1.3 mm] in RigidLoop Adjustable group and 0.53 ± 0.6 mm [95% confidence interval, -0.1 to 1.2 mm] in TightRope group). CONCLUSIONS: There were no significant differences between the two femoral cortical suspensory adjustable-loop devices regarding laxity outcomes or loop displacement as measured by button-to-graft distance migration. CLINICAL RELEVANCE: Use of either of the adjustable-loop cortical suspensory devices in our analysis would appear to produce similar, acceptable laxity outcomes and minimal effects in terms of device-related loop displacement.

The effects of distal interlocking screws on torsional stability in three-part intertrochanteric hip fractures.

OBJECTIVE: Many surgeons currently use long cephomedullary nails for the treatment of intertrochanteric fractures. The optimal indications for deploying distal interlocks are still debatable. This study examined the torsional biomechanical properties of 3-part intertrochanteric femur fractures in a cadaveric bone model using two different distal fixation strategies, an unlocked long cephalomedullary nail versus a dynamically locked nail. Our hypothesis is that a long cephalomedullary nail does not require distal locking fixation when used for treatment of a 3-part intertrochanteric fracture. METHODS: Five matched pairs of cadaveric femora were randomly assigned to one of two distal fixation treatment groups; a single distal interlock screw placed in the dynamic orientation or no distal fixation. A 3-part intertrochanteric fracture was produced. Specimens were potted and mounted in a double gimbal fixture facilitating unconstrained motion in the sagittal and coronal planes. Specimens were cyclically loaded dynamically in both internal and external rotation. Range of motion, internal and external rotation stiffness, torsion stiffness, torsion yield and ultimate torsion magnitude were calculated. RESULTS: The samples instrumented with a distal locking screw reported statistically greater external rotational stiffness than the unlocked samples in nondestructive testing. The results of the destructive data demonstrated no statistical difference between the locked and unlocked group with regard to yield torque (p = 0.282), peak torque (p = 0.340), stiffness (p = 0.220), displacement at yield torque (p = 0.0605), and displacement at peak torque (p = 0.280). CONCLUSION: Distal locking of a long cephalomedullary nail increases the stiffness of the nail-femur construct in a 3-part biomechanical fracture model. However, our testing illustrates that an unlocked construct will tolerate at least equal stress before catastrophic failure in a torsional loading model.

Isolating Suture Slippage During Cadaveric Testing of Knotless Anchors.

We evaluated a testing method designed to isolate and analyze the effectiveness of different suture-retention mechanisms in knotless suture anchors used for rotator cuff repairs. Six knotless PushLock implants (Arthrex) with a suture-retention mechanism dependent on a press-fit of suture between the anchor's outer diameter and surrounding bone were compared with 6 ReelX STT devices (Stryker) reliant on an intrinsic suture-locking mechanism. Suture slippage beyond minimal clinical failure thresholds, as well as ultimate failure load, were determined with a novel testing fixture that isolated suture slippage. Suture slippage was isolated from anchor-bone disengagement. Each PushLock exhibited suture slippage of more than 3 mm, and each ReelX exhibited slippage of less than 3 mm. The PushLock implants also exhibited significantly (P < .05) more interval and maximum slippage; 5 of these 6 implants failed via complete suture slippage before dynamic testing could be completed. All ReelX devices survived dynamic testing and ultimately failed via suture breakage. This novel axial load biomechanical testing technique isolated suture slippage in 2 uniquely designed knotless anchors. The press-fit PushLock implant was prone to slippage failure, whereas the ReelX device with its internal suture-locking mechanism exhibited minimal slippage.

Long head biceps tenodesis with a knotless cinch suture anchor: a biomechanical analysis.

PURPOSE: The purpose of this study was to evaluate the initial fixation strength of 3 techniques of arthroscopic tenodesis of the long head of the biceps (LHB). METHODS: Eighteen human cadaveric shoulders were randomly assigned to one of 3 simulated arthroscopic biceps tenodesis techniques-simple suture (SS), Krakow stitch (KS), or lasso loop (LL)-combined with a knotless fixation implant (3.5-mm Piton Anchor; Tornier, Minneapolis, MN). Biomechanical parameters were evaluated by cyclic loading and load to failure. RESULTS: The mean failure load (P = .007) was 158.3 ± 32.2 N, 109.8 ± 41.1 N, and 46.6 ± 3.8 N for the KS, SS, and LL techniques, respectively. Mean stiffness was greater (statistically significant) in the KS (21.4 ± 3.0 N/mm) and SS (20.7 ± 7.9 N/mm) treatment groups compared with the LL group (4.5 ± 1.5 N/mm) (P = .011). CONCLUSIONS: Biceps tenodesis performed with a more secure tendon suturing technique, such as the Krakow technique, provides superior ultimate and fatigue strength and thus may be more secure in clinical application and yield better clinical results. The mechanical properties of the LL technique were especially poor in comparison. CLINICAL RELEVANCE: Although more complex suturing techniques for arthroscopic biceps tenodesis can be technically challenging, more secure tendon fixation may improve clinical outcomes.

Contribution of the medial malleolus to tibiotalar joint contact characteristics.

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

Cervical total disc replacement exhibits similar stiffness to intact cervical functional spinal units tested on a dynamic pendulum testing system.

BACKGROUND CONTEXT: The pendulum testing system is capable of applying physiologic compressive loads without constraining the motion of functional spinal units (FSUs). The number of cycles to equilibrium observed under pendulum testing is a measure of the energy absorbed by the FSU. OBJECTIVE: To examine the dynamic bending stiffness and energy absorption of the cervical spine, with and without implanted cervical total disc replacement (TDR) under simulated physiologic motion. STUDY DESIGN: A biomechanical cadaver investigation. METHODS: Nine unembalmed, frozen human cervical FSUs from levels C3-C4 and C5-C6 were tested on the pendulum system with axial compressive loads of 25, 50, and 100 N before and after TDR implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5°, resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and the bending stiffness (Newton-meter/°) was calculated and compared for each testing mode. RESULTS: In flexion/extension, with increasing compressive loading from 25 to 100 N, the average number of cycles to equilibrium for the intact FSUs increased from 6.6 to 19.1, compared with 4.1 to 12.7 after TDR implantation (p<.05 for loads of 50 and 100 N). In flexion, with increasing compressive loading from 25 to 100 N, the bending stiffness of the intact FSUs increased from 0.27 to 0.59 Nm/°, compared with 0.21 to 0.57 Nm/° after TDR implantation. No significant differences were found in stiffness between the intact FSU and the TDR in flexion/extension and lateral bending at any load (p<.05). CONCLUSIONS: Cervical FSUs with implanted TDR were found to have similar stiffness, but had greater energy absorption than intact FSUs during cyclic loading with an unconstrained pendulum system. These results provide further insight into the biomechanical behavior of cervical TDR under approximated physiologic loading conditions.

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

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

Biomechanical evaluation of the suture anchors used in open-door laminoplasty: a cadaveric study.

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

Is tip apex distance as important as we think? A biomechanical study examining optimal lag screw placement.

BACKGROUND: Intertrochanteric hip fractures pose a significant challenge for the orthopaedic community as optimal surgical treatment continues to be debated. Currently, varus collapse with lag screw cutout is the most common mode of failure. Multiple factors contribute to cutout. From a surgical technique perspective, a tip apex distance less than 25 mm has been suggested to decrease the risk of cutout. We hypothesized that a low-center lag screw position in the femoral head, with a tip apex distance greater than 25 mm will provide equal, if not superior, biomechanical stability compared with a center-center position with a tip apex distance less than 25 mm in an unstable intertrochanteric hip fracture stabilized with a long cephalomedullary nail. QUESTIONS/PURPOSES: We attempted to examine the biomechanical characteristics of intertrochanteric fractures instrumented with long cephalomedullary nails with two separate lag screw positions, center-center and low-center. Our first research purpose was to examine if there was a difference between the center-center and low-center groups in cycles to failure and failure load. Second, we analyzed if there was a difference in fracture translation between the study groups during loading. METHODS: Nine matched pairs of femurs were assigned to one of two treatment groups: low-center lag screw position and center-center lag screw position. Cephalomedullary nails were placed and tip apex distance was measured. A standard unstable four-part intertrochanteric fracture was created in all samples. The femurs were loaded dynamically until failure. Cycles to failure and load and displacement data were recorded, and three-dimensional (3-D) motion was recorded using an Optotrak(®) motion tracking system. RESULTS: There were no significant differences between the low-center and center-center treatment groups regarding the mean number of cycles to failure and mean failure load. The 3-D kinematic data showed significantly increased motion in the center-center group compared with the low-center group. At the time of failure, the magnitude of fracture translation was statistically significantly greater in the center-center group (20 ± 2.8 mm) compared with the low-center group (15 ± 3.4 mm; p = 0.004). Additionally, there was statistically significantly increased fracture gap distraction (center-center group, 13 ± 2.8 versus low-center group, 7 ± 4; p < 0.001) and shear fracture gap translation (center-center group, 12 ± 2.3 mm; low-center group, 6 ± 2.7 mm; p < 0.001). CONCLUSIONS: Positioning of the lag screw inferior in the head and neck was found to be at least as biomechanically stable as the center-center group although the tip apex distance was greater than 25 mm. CLINICAL RELEVANCE: Our findings challenge previously accepted principles of optimal lag screw placement.

A biomechanical evaluation of locked plating for distal fibula fractures in an osteoporotic sawbone model.

BACKGROUND: Supination external rotation (SER) injuries are commonly fixed with a one third tubular neutralization plate. This study investigated if a combination locked plate with additional fixation options was biomechanically superior in osteoporotic bone and comminuted fracture models. METHODS: Using an osteoporotic and a comminuted Sawbones model, SER injuries were fixed with a lag screw for simple oblique fibula fractures, and either a one third tubular neutralization plate or a locking plate. Samples were tested in stiffness, peak torque, displacement at failure, and torsion fatigue. RESULTS: There was no statistically significant difference in biomechanical testing for fractures treated with a lag screw and plate. For comminuted fractures, locked plating demonstrated statistically significant stiffer fixation. CONCLUSION: A combination locked plate is biomechanically superior to a standard one third tubular plate in comminuted SER ankle fractures. There was no biomechanical superiority between locked and one third tubular plates when the fracture was amenable to a lag screw.

Mechanical properties of revision ACL reconstruction.

The aim of this study is to evaluate the mechanical properties of a revision anterior cruciate ligament (ACL) reconstruction after redrilling the original tibial bone tunnel through a retained composite screw compared with initial soft tissue graft fixation. A total of 24 porcine tendons were fixed to porcine tibial tunnels with a 10 × 35 mm composite interference screw. Following the pullout test, a revision tunnel was drilled through the first interference screw and a second graft was fixed in the bone tunnel using a larger composite screw (11 × 35 mm). Following insertion of the revision screw, the graft was reloaded as described for the primary reconstruction. Load versus displacement data were recorded for each test. There were no significant differences between the primary and revision reconstruction constructs for yield load (p = 0.62), linear stiffness (p = 0.18), maximum failure load (p = 0.57), and yield displacement (p = 0.46). These results indicate that the mechanical properties of tibial fixation for ACL reconstruction with a composite screw following a revision provide similar fixation compared with initial reconstruction in this model. Revising a failed composite ACL construct by means of overdrilling and reinstrumenting may provide fixation equivalent to the initial reconstruction.

Long-term clinical outcomes, motion, strength, and function after total claviculectomy.

BACKGROUND: Total excision of the clavicle is rarely performed. No previous study has documented long-term outcomes with objective measurements of strength, motion, and patient-centered outcomes. We present the long-term consequences of total claviculectomy on shoulder girdle function, global upper extremity function, and overall general health. METHODS: Five total claviculectomy patients were evaluated at 2 time points (2005 and 2010, mean 4.8 and 9.4 years postoperatively) by use of the DASH, SF-36, Simple Shoulder Test, ASES, UCLA, HSS, and Constant shoulder scores. Isokinetic strength, clinical range of motion, and kinematic analysis were performed on each limb pair. RESULTS: All clinical scores allowing side-to-side comparison were poorer for the aclaviculate side, with significance reached for 2005 ASES scores and 2010 ASES, UCLA, HSS, and Constant scores. DASH scores and SF-36 scores were not significantly inferior to age- and sex-matched population norms. Deficits in strength were present in the aclaviculate limbs, with significance reached for adduction in 2005 and for forward flexion and external rotation in 2010. Kinematic and clinical range of motion analysis revealed scapular dyskinesis and significant deficits in external rotation in the aclaviculate limb. CONCLUSIONS: We found that the clavicle contributes to the strength, coordinated scapulohumeral rhythm, and overall range of motion of the shoulder girdle. Patients compensate for loss of the clavicle with minimal functional deficit. With time, patients gradually lose some compensatory ability as evidenced by deteriorating limb-specific, patient-centered outcome measures, diminished strength in certain planes of shoulder motion, and scapular dyskinesis at long-term follow-up. Despite objective deficits, these patients continue to have normal self-perceptions of overall health and global upper extremity function.

Redefining the Economics of Geriatric Orthopedics.

INTRODUCTION: The heath care system in the United States is in the midst of a transition, in large part to help accommodate an older and more medically complex population. Central to the current evolution is the reassessment of value based on the cost utility of a particular procedure compared to alternatives. The existing contribution of geriatric orthopedics to the societal burden of disease is substantial, and literature focusing on the economic value of treating elderly populations with musculoskeletal injuries is growing. MATERIALS AND METHODS: A literature review of peer-reviewed publications and abstracts related to the cost-effectiveness of treating geriatric patients with orthopedic injuries was carried out. RESULTS: In our review, we demonstrate that while cost-utility studies generally demonstrate net society savings for most orthopedic procedures, geriatric populations often contribute to negative net society savings due to decreased working years and lower salaries while in the workforce. However, the incremental cost-effective ratio for operative intervention has been shown to be below the financial willingness to treat threshold for common procedures including joint replacement surgery of the knee (ICER US$8551), hip (ICER US$17 115), and shoulder (CE US$957) as well as for spinal procedures and repair of torn rotator cuffs (ICER US$12 024). We also discuss the current trends directed toward improving institutional value and highlight important complementary next steps to help overcome the growing demands of an older, more active society. CONCLUSION: The geriatric population places a significant burden on the health care system. However, studies have shown that treating this demographic for orthopedic-related injuries is cost effective and profitable for providers under certain scenarios.

Is distal locking of long nails for intertrochanteric fractures necessary? A clinical study.

BACKGROUND: Few clinical studies have examined the utility of distal interlocking nails when fixing intertrochanteric fractures with intramedullary devices. In this study we performed a retrospective analysis comparing fixation method of intertrochanteric fractures with either a long unlocked cephalomedullary nail versus a long locked cephalomedullary nail. Our hypothesis was there would be no difference in device related failures or complications in stable intertrochanteric fractures treated with long locked or long unlocked cephalomedullary nails. METHODS: A retrospective chart review was performed of all stable intertrochanteric fractures treated with a long cephalomedullary nail between 2006 and 2012 at our institution. Clinical history as well as perioperative radiography was carefully reviewed for all subjects. AO classification, the use of locked or unlocked technique, and failure status was recorded. RESULTS: Overall, a device related failure rate of 1.8% (2/107) was observed for stable intertrochanteric fractures treated with long cephalomedullary nails. No statistical difference in failure rate was found between locked and unlocked nails within our studied population (0% long locked (0/56) versus 3.9% long unlocked (2/51), p = 0.224). CONCLUSION: This clinical study supports our hypothesis that long cephalomedullary nails do not need to be locked for stable intertrochanteric fractures. We found no difference in failure rates between the two approaches across 107 patients.

Effect of distal interlock fixation in stable intertrochanteric fractures.

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

Effectiveness of low-profile supplemental fixation in anterior cruciate ligament reconstructions with decreased bone mineral density.

PURPOSE: The purpose of this study was to compare anterior cruciate ligament (ACL) fixation using a bioabsorbable interference screw (BIS) and a supplemental low-profile suture anchor (PushLock 4.5-mm polyetheretherketone anchor; Arthrex, Naples, FL) with a standard BIS fixation to determine if fixation methods were dependent on tibial bone mineral density (BMD). METHODS: Ten matched pairs of fresh-frozen human female knee specimens (20 total) were harvested with specimen ages ranging from 40 to 65 years. The BMD for each specimen was determined with a dual-energy x-ray absorptiometry scanner. The specimens were divided into 2 groups, 1 with a BIS and the other with a BIS plus a PushLock. Tibial-sided ACL fixation with hamstring tendon grafts was performed on all the specimens. Then, load to failure and stiffness were biomechanically tested. RESULTS: The BIS-plus-PushLock specimens had a significantly higher mean yield load compared with specimens with the BIS alone (702 N v 517 N, P = .047). However, in samples with lower bone density, there was no statistically significant difference in failure loads between fixation techniques (P = .8566 at BMD of 0.5 g/cm(2)). As the bone density of the samples increased, the failure loads increased for both techniques (P < .0001 for PushLock and P = .0057 for BIS). This BMD-associated increase was greater for the PushLock (P = .0148), resulting in a statistically significant difference in failure load at the upper range tested (P = .0293 at BMD of 0.9 g/cm(2)). CONCLUSIONS: Supplemental fixation of ACL reconstructions with a PushLock is beneficial in persons with a normal BMD of the proximal tibia, but at a lower BMD, there was no difference in our study. CLINICAL RELEVANCE: Individuals with normal BMDs may benefit from this supplemental fixation. However, caution should be used in postmenopausal women or individuals with chronic ACL injuries when using this fixation strategy.

Wound hematoma after anterior cervical spine surgery: in vitro study of the pathophysiology of airway obstruction.

Airway obstruction by wound hematoma is a serious adverse event associated with anterior cervical spine surgery. Although intrinsic airway edema is the most plausible pathophysiologic mechanism of obstruction, we hypothesized that extrinsic compression of the trachea by a hematoma can result in airway occlusion at an angle to the sagittal plane. A silicone indenter and a servohydraulic test frame were used to apply pressure to the ventral neck of 7 human cadaveric specimens. Increasing pressure was applied in the anteroposterior (AP) and oblique planes until the trachea collapsed, as visualized with fluoroscopy. A paired t test was used to determine any statistically significant differences in maximum pressure or indenter displacement at tracheal occlusion between the 2 test modes. Mean (SD) pressure required to cause complete tracheal collapse was 227.9 (54.8) mm Hg in the AP test mode and 135.6 (73.4) mm Hg in the oblique test mode. The difference was statistically significant (P = .004). Indenter displacement was significantly higher in the AP mode than in the oblique mode (P = .031). The trachea can collapse from external force within a physiologic pressure range when pressure is applied in an oblique orientation. The mass effect of a wound hematoma appears to be a viable mechanism of airway occlusion.

Effect of insertion of a single interference screw on the mechanical properties of porcine anterior cruciate ligament reconstruction grafts.

The objective of this study was to evaluate the mechanical properties of soft-tissue grafts following a single interference screw insertion of 4 different commercially available bioabsorbable interference screws. Twenty-four bovine proximal tibiae (12 matched pairs) were prepared and sagittally split to make 48 bone samples for testing. Tibiae were prepared for a 9 mm porcine tendon graft and were instrumented with 1 of 4 commercially available 10 x 35 mm composite screws, each with a different thread design. The samples were tensile loaded to failure at 200 mm/min and values for yield load, maximum load, and stiffness were recorded to quantify any differences on the function of the grafts. No graft showed macroscopic evidence of laceration following screw insertion and there were no statistically significant differences for yield load (P = .41), maximum load (P = .35), or stiffness (P = .68) among the different screw types. There is no significant difference in the mechanical properties of an anterior cruciate ligament graft following insertion of the 4 bioabsorbable screws tested in this study, in terms of yield load, stiffness, or failure load.