Tensile strength of a novel superficial suture pattern compared to traditional suture patterns in a cadaveric human skin model.

BACKGROUND: The suture material and pattern utilized to maintain the skin edges in proximity allows for successful primary wound healing. No prior studies have evaluated the tensile strength of different suture patterns on human cadaveric skin. This study evaluates the tensile strength of four single suture patterns: simple (S), horizontal-mattress (HM), vertical-mattress (VM), and a novel stich termed Lindeque locking (LL). METHODS: Four skin closure patterns were tested on human cadaveric skin using 3-0 nylon - S, HM, VM, LL - totaling four groups with twelve samples each. A tensioning device applied 1 N of force/second in a linear fashion. The primary outcome measures were: (i) wound dehiscence force, and (ii) ultimate load to failure. Statistics included one-way ANOVA with post-hoc Tukey tests. RESULTS: The LL stitch had the greatest dehiscence force (198.60 N) and ultimate load to failure force (211.13 N) but was only significantly greater on both outcomes versus HM (104.81 N; 95% confidence interval [CI], 65.7 to 121.9; p< 0.001) and (120.79 N; 95% CI, 63.5 to 117.2; p < 0.001), respectively. There was no significant difference between LL and S for dehiscence, nor for the ultimate load to failure (186.90 N and 195.08 N, respectively). The LL pattern was significantly greater for an ultimate load to failure, but not for dehiscence when compared to VM (173.9 N and 171.1 N, respectively). Of all patterns, HM had significantly less withstanding force. CONCLUSIONS: The Lindeque Locking stitch demonstrated the greatest dehiscence force and tensile strength. It may decrease the risk of wound dehiscence for high tension wounds.

The potential biomechanical advantage of lag by technique screw fixation of the posterior pelvic ring.

PURPOSE: Diastasis of the sacroiliac joint after pelvic ring injury is commonly reduced by lagging by design with partially threaded (PT) screws. There may be a biomechanical benefit to lagging by technique with fully threaded (FT) screws. The purpose of this study was to compare these two methods. METHODS: Twelve pairs of synthetic bone blocks were lagged together with 8.0-mm FT or PT screws. Maximum compressive and steady-state force was measured. Pullout force testing was performed. RESULTS: The maximum compressive force of FT and PT screws was not different [mean difference (MD) 32 Newtons (N), 95% confidence interval (CI) 124, 60)]; however, lagging by technique with FT screws resulted in significantly higher steady-state force (MD 83 N, 95% CI 165, 5) and pullout force (MD 634 N, 95% CI 778, 491). CONCLUSION: Lagging by technique with large diameter FT screws has a biomechanical advantage over lagging by design with PT screws.

The Role of Complete Posterior Cruciate Ligament Release in Flexion Gap Balancing for Total Knee Arthroplasty.

BACKGROUND: The sequence of posterior cruciate ligament (PCL) release in posterior-substituting designs, when performing gap balancing in total knee arthroplasty (TKA), is variable. We hypothesize that early complete PCL release during knee exposure will change the flexion balance to result in a uniform medial-lateral flexion gap symmetry at the time of implant placement. METHODS: Ten cadaveric knees were prepared for TKA using standard medial parapatellar approach. Medial and lateral flexion gaps were measured in the conditions of intact, partial (50%) resection, and full resection of PCL. Measurements were performed with both surgical navigation and a caliper. Flexion gap distances were reported for medial and lateral compartments in the 3 PCL conditions. RESULTS: Medial flexion gap increased after only complete release of the PCL (mean 3.94-5.05 mm). The lateral flexion gap increased as well (mean 4.17-4.67 mm). Complete PCL release resulted in a statistically significant increase in medial flexion gap compared to intact (P = .013) and partially released (P = .012) specimens. No significant differences were noted in lateral flexion gap change. Notable change in medial versus lateral gap (flexion gap symmetry) relationship occurred after just partial PCL release (P = .018). CONCLUSION: Among the 3 PCL states, changes in flexion gap distance were most conspicuous in the medial compartment. This suggests gap balancing performed with incomplete PCL release will not accurately reflect gap distance after eventual PCL removal, thus supporting the hypothesis. It is recommended that the PCL should be released to the fullest extent possible before ligament tensioning for femoral component rotation in posterior-stabilized TKA.

Mechanical Testing of Epiphysiodesis Screws.

Epiphysiodesis is performed to treat leg-length discrepancies and angular deformities in children. However, when placed across a physis to modulate growth, screws can bend or break postoperatively. This study evaluated the mechanical properties of 3 different screw designs commonly used when performing an epiphysiodesis. Six 4.0-mm cannulated, fully threaded; six 4.0-mm cannulated, partially threaded; and six 4.0-mm noncannulated, partially threaded cancellous screws underwent cantilever bending and tension testing in a simulated physis. All screws were tested in simulated cancellous bone foam blocks. All testing was performed using a servo-hydraulic testing machine to determine stiffness and ultimate load. For statistical analysis, one-way analysis of variance with Tukey's honestly significant difference test in post hoc analysis was used to assess significant differences among groups (P<.05). The noncannulated, partially threaded screws had a significantly lower stiffness than the 2 cannulated screw types in the tension test (P<.001) and bending test (P<.001). Additionally, the noncannulated, partially threaded screws had significantly higher ultimate load to failure than the 2 cannulated screw types in the tension test (P<.001) and the cannulated, partially threaded screws in the bending test (P=.045). The results indicate that noncannulated, partially threaded screws have a higher ultimate load capacity and are less stiff than both cannulated, partially threaded screws and cannulated, fully threaded screws. Surgeons should take into consideration that noncannulated, partially threaded screws are less likely to fail following epiphysiodesis. [Orthopedics. 2018; 41(2):e240-e244.].

Epiphysiodesis Screw Bending.

Percutaneous epiphysiodesis using transphyseal screws is a common method for treatment of limb length discrepancy and angular deformity. The authors report 3 cases of a previously unreported complication following treatment with percutaneous epiphysiodesis using transphyseal screws: bending of the transphyseal screw. In each case, this rare complication was associated with difficult removal of the screw. This retrospective case report accessed the medical records of 3 children, 2 boys and 1 girl, 9 to 14 years old. All of the children had 4.0-mm cannulated stainless steel screws ranging from 40 to 50 mm in length. Two of the patients had partially threaded and 1 had fully threaded screws with bending noted a minimum of 6 months following implantation. Additionally, each of the screws bent near the physis of the bone, which was not located at the center of the screw in every case or at the transition from threaded to nonthreaded portions in each partially threaded screw. To the authors' knowledge, these are the first reported cases of cannulated screw bending following transphyseal tibial or femoral placement for the correction of leg length or angular deformity in a pediatric population. Although the true incidence rate is unknown, screw bending following percutaneous epiphysiodesis presents complications in the hardware removal process. Further biomechanical tests should be conducted to determine the best screw design to minimize bending of transphyseal screws from physiologic growth. [Orthopedics. 2017; 40(4):e717-e720.].

Biomechanical comparison of traditional anchors to all-suture anchors in a double-row rotator cuff repair cadaver model.

BACKGROUND: To further reduce the invasiveness of arthroscopic rotator cuff repair surgery the all-suture anchor has been developed. The all-suture anchor requires less bone removal and reduces the potential of loose body complications. The all-suture anchor must also have adequate biomechanical strength for the repair to heal. The hypothesis is there is no significant difference in the biomechanical performance of supraspinatus repairs using an all-suture anchor when compared to traditional solid-body suture anchors. METHODS: Using nine shoulders per group, the supraspinatus tendon was dissected from the greater tuberosity. The four different double row repairs tested were (medial row/lateral row): A: ICONIX2/ICONIX2; B: ICONIX2/Stryker ReelX 3.9mm; C: ICONIX2/Stryker ReelX 4.5mm; D: Arthrex BioComposite CorkScrew FT 4.5mm/Arthrex BioComposite SwiveLock 4.75mm. The ICONIX2 was the only all-suture anchor tested. Tendons underwent cyclic loading from 10 to 100N for 500 cycles, followed by load-to-failure. Data was collected at cycles 5, 100, 200, 300, 400, and 500. One-way ANOVA analysis was used to assess significance (P≤0.05). FINDINGS: The anchor combinations tested did not differ significantly in anterior (P>0.4) or posterior (P>0.3) gap formation, construct stiffness (P>0.7), ultimate load (P=0.06), or load to 5mm gap formation (P=0.84). INTERPRETATION: The all-suture anchor demonstrated comparable biomechanical performance in multiple double-row anchor combinations to a combination of traditional solid-body anchors. Thus it may be an attractive option to further reduce the invasiveness of rotator cuff repairs.

Are conventional reconstruction plates equivalent to precontoured locking plates for distal humerus fracture fixation? A biomechanics cadaver study.

BACKGROUND: The optimal plate type and configuration for distal humerus fracture fixation has yet to be defined. Available biomechanical studies show conflicting results. No existing studies compare conventional reconstruction plates to newer precontoured distal humerus locking plates in both parallel and perpendicular configurations. METHODS: Three groups of humerus specimens were compared via biomechanical testing in a cadaver model simulating metaphyseal comminution. Group 1 consisted of conventional reconstruction plates in a perpendicular configuration. Group 2 used precontoured locking plates in a perpendicular configuration. Group 3 used precontoured locking plates in a parallel configuration. Each group was tested for stiffness in anterior bending, posterior bending, axial compression, and torsion. The specimens then underwent cyclic loading followed by single load to failure in posterior bending. FINDINGS: There was no significant difference between the three groups for anterior bending, posterior bending, axial compression, or torsional stiffness. There was no significant difference in load to failure for any of the three groups. Screw loosening was significantly higher in Group 1 when compared to Groups 2 and 3 after cyclic loading. INTERPRETATION: In the early postoperative period, less expensive perpendicular conventional reconstruction plate constructs provide similar stiffness and load to failure properties to newer precontoured locking plate systems regardless of plate configuration.

Cancellous bone adaptation to in vivo loading in a rabbit model.

Biophysical stimuli are important to the development and maintenance of cancellous bone, but the regulatory mechanisms need to be understood. We investigated the effects of mechanical loading applied in vivo to native cancellous bone in the rabbit on bone formation and trabecular realignment. A novel device was developed to apply controlled compressive loads to cancellous bone in situ. The effect of loading on cancellous bone volume fraction and architecture was quantified. A 4-week experiment was performed in rabbits with devices implanted bilaterally. Cyclic 1 MPa pressures were applied daily to the right limb for 10, 25, or 50 cycles at 0.5 Hz, and the left limb served as the control without any applied loading. Microcomputed tomography and histomorphometry were used to characterize the cancellous tissue within a 4-mm spherical volume located below the loading core. In vivo cyclic loading significantly increased the bone volume fraction, direct trabecular thickness, mean intercept length, and mineral apposition rate in the loaded limbs compared with contralateral limbs. Insufficient evidence was found to demonstrate an effect of number of cycles on the cancellous adaptation between loaded and control limbs. Using a rabbit model, we demonstrated that mechanical loading applied to cancellous bone in situ increased bone formation and altered trabecular morphology. This in vivo model will allow further investigation of cancellous functional adaptation to controlled mechanical stimuli and the influence of mechanical loading parameters, metabolic status, and therapeutic agents.

Spectroscopically determined collagen Pyr/deH-DHLNL cross-link ratio and crystallinity indices differ markedly in recombinant congenic mice with divergent calculated bone tissue strength.

Whole bone strength can be partitioned into structural and material components. In three-point bending tests of 6-month-old female humeri from the HcB/Dem recombinant congenic series, strains HcB/8 and HcB/23 differed markedly in calculated failure stress but not ash percentage. Fourier transform infrared spectroscopic imaging was used to determine whether differences in the ratio of pyridinoline (pyr; nonreducible) to dehydrodihydroxynorleucine (de-DHLNL; reducible) collagen cross-links (XLR), mineral crystallinity, or spatial ordering could account for the strains' differing biomechanical performance. HcB/8 had significantly higher XLR and significantly higher crystallinity than HcB/23. XLR and crystallinity were highly and similarly correlated in both strains. There were no significant differences between the strains' one-dimensional spatial correlation functions, suggesting no difference in short-range order between them. The strong correlation between XLR and crystallinity reflects the interdependence of the protein and mineral elements of bone. The data illustrate the importance of material properties in addition to mineral quantity to bone tissue strength.