A new configuration of lateral-pin fixation for pediatric supracondylar humeral fracture: A biomechanical analysis

OBJECTIVE

The aim of this study was to biomechanically compare a new lateral-pinning technique, in which pins engage the medial and lateral columns of the distal humerus in a divergent configuration in both the axial and sagittal planes instead of the coronal plane, with the cross-pin, and with 2 and 3 coronally divergent lateral-pin techniques in a synthetic humerus model of supracondylar humerus fractures.

METHODS

Thirty-six identical synthetic models of the humerus simulating a standardized supracondylar humerus fracture were included in this study. They were divided into 4 groups based on the pin configuration of fixation: the new 3-lateral pin-fixation technique (group A), 2 crossed pins (group B), 3 divergent lateral pins (group C), and 2 divergent lateral pins (group D). Each model was subjected to combined axial and torsional loading, and then torsional stability and torsional stiffness (Nmm/°) were recorded.

RESULTS

Group A had greater rotational stability than groups C and D but had no statistically significant additional rotational stability compared with group B (P=.042, P=.008, P=.648, respectively), whereas group B had greater rotational stability than only group D (P=.020). Furthermore, group A demonstrated higher internal rotational stiffness compared with groups C and D (P=.038, P=.006, respectively). Group B had better internal rotational stiffness than group D (P=.015). There was no significant difference in internal rotational stiffness between groups A and B (P=. 542), groups B and C (P=.804), and groups D and C (P=.352). Although no statistically significant differences existed between groups A and B, the modified pin configuration exhibited the highest torsional stability and stiffness. Group D showed the lowest values in all biomechanical properties.

CONCLUSION

This study has shown us that this new lateral-pinning technique may provide torsional resistance to internal rotational displacement as strong as the standard technique of crossed-pin configuration of fixation. Furthermore, with this new pin configuration, greater torsional resistance can be obtained than with either the standard 2- or the standard 3-lateral divergent pin configuration. Cite this article as: Bilgili F, Demirel M, Birişik F, Balcı Hİ, Sunbuloglu E, Bozdag E. A new configuration of lateral-pin fixation for pediatric supracondylar humeral fracture: A biomechanical analysis. Acta Orthop Traumatol Turc., 2023 10.5152/j.aott.2024.21091 [Epub Ahead of Print].

An in-silico approach to modeling orthodontic tooth movement using stimulus-induced external bone adaptation

Bone remodeling process has been used in orthodontics to treat malposition of teeth in patients by applying stimuli outside of usual everyday loads to promote tooth movement by affecting equilibrium state of the surrounding bone tissue. Accurate modeling of long term orthodontic tooth movement (OTM) is crucial in the field of dental biomechanical research since it allows to predict the behavior and interaction of bone-tooth environment in a non-destructive way, and helps to gain more insight on how exactly tooth motion progresses over time. Existence of such predictive tools might help to avoid the adverse effects of OTM on teeth and the surrounding tissues during this clinical procedure. In this study a new numerical approach to simulating long-term OTM is proposed, that involves external bone adaptation with strain energy density of the bone taken as the stimulus parameter and bone adaptation modeled by nodal movements at the bone-tooth interface using Abaqus UMESHMOTION subroutine. Contrary to conventional re-meshing algorithms, where the mesh of resorbed-apposed bone region is constantly updated and element deletion/creation is performed for each increment, the proposed method only moves nodes without changing the initial mesh topology. For this study, a 3D model of right central maxillary incisor tooth and its surrounding maxillary bone was used for the modeling of OTM for a duration of 1 week. Two test cases were performed and the results from induced tooth motion were investigated. Results indicate tooth movement values that were quite close to clinical values provided in the literature and this method is easily applicable to validate various postulates of OTM via adapting the stimulus-adaption rate relation and patient-specific planning of orthodontic patients as well.

A New Mini-External Fixator for Treating Hallux Valgus: A Preclinical, Biomechanical Study

Proximal metatarsal osteotomy is the most effective technique for correcting hallux valgus deformities, especially in metatarsus primus varus. However, these surgeries are technically demanding and prone to complications, such as nonunion, implant failure, and unexpected extension of the osteotomy to the tarsometatarsal joint. In a preclinical study, we evaluated the biomechanical properties of the fixator and compared it with compression screws for treating hallux valgus with a proximal metatarsal osteotomy. Of 18 metatarsal composite bone models proximally osteotomized, 9 were fixed with a headless compression screw and 9 with the mini-external fixator. A dorsal angulation of 10° and displacement of 10 mm were defined as the failure threshold values. Construct stiffness and the amount of interfragmentary angulation were calculated at various load cycles. All screw models failed before completing 1000 load cycles. In the fixator group, only 2 of 9 models (22.2%) failed before 1000 cycles, both between the 600th and 700th load cycles. The stability of fixation differed significantly between the groups (p < .001). The stability provided by the mini-external fixator was superior to that of compression screw fixation. Additional testing of the fixator is indicated.

The effect of strut allograft and its position on Vancouver type B1 periprosthetic femoral fractures: a biomechanical study

The aim of this study is to assess the biomechanical advantage of adding strut allograft and the effect of its position on the construct in Vancouver type B1 fractures. Fifteen forth-generation synthetic femurs were used and created a fracture model at the tip of prosthesis, and subsequently fixated with a lateral plate only, lateral plate and medial strut, lateral plate and anterior strut. Rotational and axial tests were performed. In all loading tests, the plate with medial strut group was stiffer than the other constructs and had higher failure load values and had less displacement in the fracture site. A combination of a plate with a medial strut allograft provides more mechanical stability on periprosthetic femoral fractures near the tip of a total hip arthroplasty.

Stress analysis of a complete maxillary denture under various drop impact conditions: a 3D finite element study

Complete maxillary dentures are one of the most economic and easy ways of treatment for edentulous patients and are still widely used. However, their survival rate is slightly above three years. It is presumed that the failure reasons are not only due to normal fatigue but also emerge from damage based on unavoidable improper usage. Failure types other than long-term fatigue, such as over-deforming, also influence the effective life span of dentures. A hypothesis is presumed, stating that the premature/unexpected failures may be initiated by impact on dentures, which can be related to dropping them on the ground or other effects such as biting crispy food. Thus, the behavior of a complete maxillary denture under impact loading due to drop on a rigid surface was investigated using the finite element method utilizing explicit time integration and a rate-sensitive elastoplastic material model of polymethylmethacrylate (PMMA). Local permanent deformations have been observed along with an emphasis on frenulum region of the denture, regardless of the point of impact. Contact stresses at the tooth-denture base were also investigated. The spread of energy within the structure via wave propagation is seen to play a critical role in this fact. Stress-wave propagation is also seen to be an important factor that decreases the denture's fatigue life.

In vitro comparison of two different materials for the repair of urethan dimethacrylate denture bases

PURPOSE

The purpose of this in vitro study was to investigate the flexural properties of a recently introduced urethane dimethacrylate denture base material (Eclipse) after being repaired with two different materials.

MATERIALS AND METHODS

Two repair groups and a control group consisting of 10 specimens each were generated. The ES group was repaired with auto-polymerizing polymer. The EE group was repaired with the Eclipse. The E group was left intact as a control group. A 3-point bending test device which was set to travel at a crosshead speed of 5 mm/min was used. Specimens were loaded until fracture occurred and the mean displacement, maximum load, flexural modulus and flexural strength values and standard deviations were calculated for each group and the data were statistically analyzed. The results were assessed at a significance level of P<.05.

RESULTS

The mean "displacement", "maximum load before fracture", "flexural strength" and "flexural modulus" rates of Group E were statistically significant higher than those of Groups ES and EE, but no significant difference (P>.05) was found between the mean values of Group ES and EE. There was a statistically significant positive relation (P<.01) between the displacement and maximum load of Group ES (99.5%), Group EE (94.3%) and Group E (84.4%).

CONCLUSION

The more economic and commonly used self-curing acrylic resin can be recommended as an alternative repair material for Eclipse denture bases.

The impact of frenulum height on strains in maxillary denture bases

PURPOSE

The midline fracture of maxillary complete dentures is a frequently encountered complication. The purpose of this study was to assess the effect of frenulum height on midline strains of maxillary complete dentures.

MATERIALS AND METHODS

A removable maxillary complete denture was fabricated and duplicated seven times. Four different labial frenulum heights were tested for stresses occurring on the palatal cameo surface. The strains were measured with strain gauges placed on 5 different locations and the stresses were calculated. To mimic occlusal forces bilaterally 100 N of load was applied from the premolar and molar region.

RESULTS

A statistically significant association between the height of the labial frenulum and the calculated stresses and strains was shown (P<.05) predominantly on the midline and especially on the incisive papilla. The results showed that stress on the anterior midline of the maxillary complete denture increases with a higher labial frenulum.

CONCLUSION

Within the limitations of this in vitro study, it can be concluded that the stress on the anterior midline of the maxillary complete denture increases with a higher labial frenulum. Surgical or mechanical precautions should be taken to prevent short-term failure of maxillary complete dentures due to stress concentration and low cycle fatigue tendency at the labial frenulum region.

Horizontal suture placement influences meniscal repair fixation strength

PURPOSE

This in vitro biomechanical study investigated the influence of horizontal suture placement distance from the medial meniscal lesion repair site on fixation characteristics during submaximal cyclic and load to failure test conditions.

METHODS

Eighteen cadaveric (20-45 years of age) medial menisci with intact joint capsules were harvested within 24-48 h after death and divided into two groups of 9 specimens each for biomechanical testing. A 2.0-cm-long antero-posterior vertical longitudinal lesion was created with a #15 scalpel 2.0-3.0 mm from the outer edge of each meniscus. Menisci were repaired using #2-0 suture material with two horizontal suture loops placed either 1.0 mm (Group 1) or 3.0 mm (Group 2) from the lesion site. Following repair, the lesion was extended completely through the meniscal horns so that no tissue secured the repair, only the two horizontal suture loops representing a "worst-case" testing scenario. Following repair, specimens were placed in a servo hydraulic device using a pair of 1.2-mm-diameter steel wire loops and underwent submaximal cyclic loading between 5 and 50 N (1 Hz) for 500 cycles prior to load to failure testing (5 mm/min crosshead speed, 20 Hz data collection). An alpha level of P < 0.05 was selected to indicate statistical significance.

RESULTS

Five of nine (55.6 %) Group 1 specimens did not complete submaximal cyclic testing. All Group 2 specimens completed submaximal cyclic testing (Fisher's exact test P = 0.029). Statistically significant mean group differences were not observed for displacement during submaximal cyclic loading (Group 1 = 5.0 ± 1.5 mm and Group 2 = 5.7 ± 1.6 mm) or for construct stiffness during load to failure testing (Group 1 = 50.1 ± 6.3 N/mm and Group 2 = 52.6 ± 11.9 N/mm). Group 2 displayed greater mean load at failure (112.1 ± 40.8 N vs. 72.7 ± 11.2 N, P = 0.02) and mean displacement at failure (11.1 ± 2.2 mm vs. 7.6 ± 1.4 mm, P = 0.03) than Group 1.

CONCLUSIONS

Horizontal sutures placed slightly farther away from the meniscus lesion displayed superior repair fixation than sutures placed closer to the lesion. The superior biomechanical meniscal repair fixation provided by capturing greater tissue volume may enable safe earlier participation in functional exercise activities. Studies are needed to verify these findings in vivo.

Experimental parameter estimation method for nonlinear viscoelastic composite material models: an application on arterial tissue

This study is aimed at setting a method of experimental parameter estimation for large-deforming nonlinear viscoelastic continuous fibre-reinforced composite material model. Specifically, arterial tissue was investigated during experimental research and parameter estimation studies, due to medical, scientific and socio-economic importance of soft tissue research. Using analytical formulations for specimens under combined inflation/extension/torsion on thick-walled cylindrical tubes, in vitro experiments were carried out with fresh sheep arterial segments, and parameter estimation procedures were carried out on experimental data. Model restrictions were pointed out using outcomes from parameter estimation. Needs for further studies that can be developed are discussed.

A comparison of percutaneous and mini-open techniques of Achilles tenotomy: an experimental study in rats

PURPOSE

To investigate the effect of Achilles tenotomy performed percutaneously and by mini-open methods on tendon healing and final strength.

MATERIALS AND METHODS

In two groups, each consisting of 14 rats, percutaneous and mini-open techniques in Achilles tenotomy were compared in terms of biomechanical, histological and gross properties.

RESULTS

In the gross evaluation, it was observed that an obvious thickening and adhesion to the subcutaneous tissue of the healing tendon were observed in nearly all rats in which the mini-open technique was performed. In the biomechanical analysis, there was no significant difference between percutaneous and mini-open groups and between operated and intact Achilles tendons in both groups, in terms of tendon strength (P > 0.05). In the histological evaluation, irregularity in the parallel pattern of the collagen fibres, emergence of a non-specific collagenous tissue formation and infiltration of mild mononuclear inflammatory cells were reported. These changes were more marked in the rats in which the percutaneous technique was performed.

CONCLUSION

Mini-open technique for Achilles tenotomy may be considered as an alternative method of treatment to apply the tenotomy technique in a secure way.

CLINICAL RELEVANCE

There are two basic advantages of Achilles tenotomy performed by the mini-incision open technique: (1) a complete tenotomy is guaranteed, as it has to be in the original Ponseti technique, (2) iatrogenic neuro-vascular injury risk is nearly completely avoided due to the subparatenon exploration of the tendon and direct visual observation during the transection. The mini-open technique may only be used in cases in which a vascular compromise is clinically suspected or confirmed by Doppler ultrasonography and/or arteriography. On the other hand, the technique may be performed in all cases routinely by the choice of the surgeon.

Biomechanical analysis of multilevel discectomy and excision of posterior longitudinal ligament: an in vitro study in sheep

AIM

This experimental biomechanical study was performed to determine the effects of multilevel anterior cervical discectomy and excision of posterior longitudinal ligament (PLL) to stabilize the cervical spine using an in vitro animal model.

MATERIALS AND METHODS

Fifty fresh cadaveric C3-C6 sheep spine specimens were divided into five experimental groups: Group A was the control group; Group B, one-level discectomy; Group C, two- level discectomy, Group D, three-level discectomy, and Group E, three-level discectomy and excision of PLL, respectively. The specimens were subjected to non-destructive loads cycled from zero to five Newton-meter for flexion, extension, right and left lateral bending, and axial rotation on an electrohydraulic test machine. Load displacement curves were obtained via collected data using strain gauges. The values were obtained for all five groups, statistical differences were determined respectively (P<0.05, ANOVA).

RESULTS

One-level discectomy was less stable than the control group, two-level discectomy was less stable than one-level discectomy and three-level discectomy was less stable than two-level discectomy, respectively (P<0.05). Excision of PLL did not seem to affect stability (P>0.05).

CONCLUSION

Our data suggested that cervical discectomy decreases stability of sheep spine pieces.

A comparison of single-versus double-row suture anchor techniques in a simulated repair of the rotator cuff

We compared time-dependent changes in the biomechanical properties of single-and double-row repair of a simulated acute tear of the rotator cuff in rabbits to determine the effect of the fixation techniques on the healing process.

A tear of the supraspinatus tendon was created in 80 rabbits which were separated into two equal groups. A single-row repair with two suture anchors was conducted in group 1 and a double-row repair with four suture anchors in group 2. A total of ten intact contralateral shoulder joints was used as a control group. Biomechanical testing was performed immediately post-operatively and at four and eight weeks, and histological analysis at four and eight weeks.

The mean load to failure in group 2 animals was greater than in group 1, but both groups remained lower than the control group at all intervals. Histological analysis showed similar healing properties at four and eight weeks in both groups, but a significantly larger number of healed tendon-bone interfaces were identified in group 2 than in group 1 at eight weeks (p < 0.012).

The ultimate load to failure increased with the number of suture anchors used immediately post-operatively, and at four and eight weeks. The increased load to failure at eight weeks seemed to be related to the increase in the surface area of healed tendon-to-bone in the double-row repair group.

Effect of antibiotic loading on the shear strength at the stem-cement interface (Shear strength of antibiotic loaded cement)

The purpose of this study was to investigate the effects of addition of antibiotics into cement powder on the shear properties of the cement-metal interface. The approach involved adding 800 mg of teicoplanin to 40 g bone cement powder in the t-800 group, 1,600 mg teicoplanin in the t-1,600 group, and no antibiotic in the control group. Industrially prepared bone cement containing 500 mg of gentamicin was used as group g-500. Each group consisted of ten samples. Cement-metal interfaces were produced using metal discs with porous surfaces (1 microm) and templates at the third minute. Shear stability of specimens was measured in a material testing machine. The ANOVA test was used for comparison between the mean shear results of each group. Results showed that mean shear stress to failure values were 12.28+/-3.35 MPa for the control group, 11.72+/-3.09 MPa for the t-800 group, 13.25+/-2.36 MPa for the t-1,600 group and 13.09+/-2.58 MPa for the g-500 group. No statistically significant differences were found between results of the groups. Results of the study have proven that addition of 1,600 mg of teicoplanin or 500 mg gentamycin in 40 g of bone cement does not decrease the shear strength at the cement-metal interface significantly on the day of application.

Vibration characteristics of grafts for the tympanic membrane

Perforation of the tympanic membrane occurs frequently as a result of infection, external trauma, and high-level impulsive sound pressure, such as that associated with an explosion. Many different surgical techniques can be used to repair the tympanic membrane and ossicles. Clinical operations such as tympanoplasty are undertaken to repair the damaged tympanic membrane and ossicles, thus improving hearing and reducing the chance of infection. The membrane is repaired or replaced with the use of graft materials, either from the patient's body or from artificial sources. The selection of graft material is very important because, as much as possible, it must exhibit the same dynamic behavior as the natural membrane. To compare various allograft materials, investigators developed a model of the ear on which different graft materials can be replaced. Three different membrane materials - irradiated allograft dura (Tutoplast Dura; IOP Inc., Costa Mesa, Calif), irradiated allograft fascia lata (Tutoplast Fascia Lata; IOP Inc.), and irradiated allograft fascia temporalis (Tutoplast Fascia Temporalis; IOP Inc.) - were used. Vibration responses of these membrane materials produced by defined sound signals with different frequencies were recorded by a small strain gauge; the spectra of sound for various corresponding input signals were recorded, and the results were compared with those of the sample graft material. Tutoplast Fascia Lata accomplished the best dynamic performance in vitro. Additional clinical and experimental data are needed, however, to determine which of these materials provides the best audiological and clinical performance.

Time-dependent changes in failure loads of 3 biceps tenodesis techniques: in vivo study in a sheep model

BACKGROUND

Failure load of the tendon-fixation material-bone unit has a crucial importance for the rehabilitation protocol after tenodesis procedures.

PURPOSE

To investigate and compare the time-dependent changes in fixation strengths of 3 proximal biceps tenodesis techniques.

STUDY DESIGN

Controlled laboratory study.

METHODS

Two intraosseous techniques (suture sling and tenodesis screw) and 1 extraosseous technique (2 suture anchors) were investigated. Biceps tenodesis was performed on 45 shoulders of 26 sheep, 15 shoulders for each technique. Twelve similar cadaveric sheep shoulders (4 for each technique) provided the day 0 results. Sheep were sacrificed at 3, 6, and 9 weeks, and specimens were tested for the failure load of the tenodeses.

RESULTS

All 3 tenodesis techniques were found to have similar failure loads at all time intervals tested. All 3 curves remained below the failure load of the intact tendon (862 +/- 96 N) and above their day 0 results for the study period; similarly, at each time interval, results tended to be better compared to the previous test. The tenodesis screw group exhibited significantly higher failure loads at week 3 (419 +/- 53 N) compared to day 0 values (164 +/- 45 N) (P = .009). The same level of significance was observed at week 6 in the remaining 2 groups.

CONCLUSION

Tenodesis of the biceps tendon on the proximal humerus at an extra-articular site does not weaken after surgery. The tenodesis screw group had a significantly higher increase in the fixation strength within the first 3 weeks.

CLINICAL RELEVANCE

No significant differences could be found between the failure loads of all 3 investigated tenodeses for the first 9 weeks.

Tensile strength of ligaments after thermal shrinkage depending on time and immobilization: in vivo study in the rabbit

The effects of immobilization on healing collagenous tissue treated with thermal shrinkage are investigated in an in vivo rabbit model. Thermal shrinkage was performed on 45 of 50 medial collateral ligaments in 25 mature New Zealand rabbit knees. In half of the knees, the joints were immobilized. Animals were killed at 0, 3, 6, and 9 weeks postoperatively. Failure loads of ligaments were determined, and morphologic changes were evaluated by electron microscopy. The failure load of shrunken ligaments was significantly lower than that of the intact ligaments on the day of operation (P<.05). Shrunken ligaments reached their highest failure loads in the third week within the first 9 weeks. The immobilized ligaments remained weaker than the mobile group, but this difference was statistically significant only in the ninth week (P<.05). Immobilization seems to have negative effects on the healing ligament. Ideal timing for remobilization is still controversial, and abandoning immobilization protocols for longer than 3 weeks should be considered.

Effect of Decortication on Laminar Strength During Sublaminar Wiring

Eighty lumbar segments from 16 female sheep were used to investigate the effect of laminar decortication on the strength of the lamina during sublaminar wiring procedure. Sheep were 12-14 months old. Forty vertebrae from eight animals were decorticated before loading with sublaminar wire to failure, and 40 vertebrae from the remaining eight sheep were tested with the same procedure but intact. The effects of bone mineral density (BMD) and laminar dimensions on laminar strength in both decorticated and nondecorticated groups were also investigated. The failure force values of the laminae for decorticated and nondecorticated groups were 881.15 +/- 36.86 and 298.48 +/- 21.99 N, respectively (P < 0.001). There was a positive linear relationship between BMD and laminar strength in an intact lamina. In a decorticated lamina, no significant relationship existed between these variables. There was a negative linear relationship between mediolateral length of hemilamina and laminar strength in both intact and decorticated vertebra. Laminar strength after decortication was positively related to dorsoventral length of the remaining portion of the lamina. Decortication leads to a statistically significant decrease in laminar strength.