What is the influence of biomechanical variables on the Y balance test performance in recreational runners?

BACKGROUND

Asymmetries and poor Y balance test (YBT) performance are associated with an increased risk of injuries in athletes. The aim of this study was to investigate the association between YBT performance with biomechanical variables in runners.

METHODS

The runners underwent the YBT, followed by the assessment of center of pressure, plank position, muscle strength (MS) of hip flexors, extensors, abductors, and external rotators, knee extensors, ankle dorsiflexion range of motion (ROM), Q angle, forefoot alignment, and passive hip internal rotation. Associations between variables were examined using multiple linear regression models with the Bayesian Information Criterion.

RESULTS

122 cases were analyzed. The R2 values were 0.38; 0.05; 0.06; and 0.15 for the anterior, posteromedial, posterolateral and composite directions models, respectively. The anterior reach in the YBT was associated with ankle dorsiflexion ROM [Sβ 95%IC: 0.43 (0.32-0.55)], passive hip internal rotation [Sβ 95%IC: 0.35 (0.24-0.47)], MS of the hip extensors [Sβ 95%IC: 0.19 (0.07-0.31)] and forefoot alignment [Sβ 95%IC: 0.14 (-0.25-0.02)]. The posteromedial and posterolateral reach were associated with MS of the hip flexors [Sβ 95%IC: 0.23 (0.09-0.37) and 0.24 (0.11-0.38)], respectively. The composite score was associated with MS of the hip flexors [Sβ 95%IC: 0.31 (0.18-0.45)], ankle dorsiflexion ROM [Sβ 95%IC: 0.24 (0.10-0.37)] and Q angle [Sβ 95%IC: 0.18 (0.04-0.31)].

CONCLUSION

YBT performance in different directions demonstrated specific associations with key biomechanical factors.

Carpal instability after partial trapeziectomy, total trapeziectomy and the resection of the distal scaphoid pole: a cadaveric study

INTRODUCTION

Non-dissociative carpal instability (CIND) may lead to severe functional impairment. Destabilisation of the scapho-trapezial-trapezoidal (STT) ligament complex seems to result in a CIND.

MATERIALS AND METHODS

In one group with eight cadaver arms, distal scaphoid pole was resected with the adjacent ligaments. In the other eight cadavers, hemitrapeziectomy was performed followed by total trapeziectomy. CT scans were performed in different wrist positions, and the changed positions of the scaphoid, lunate and capitate were measured in comparison to non-operated wrists.

RESULTS

Mainly in clenched fist position, dissociation between proximal and distal row can be determined after total trapeziectomy and resection of distal scaphoid pole. Capitate rotates dorsally up to 24°, the scaphoid up to 17° and the lunate up to 7° compared to the non-operated wrists. Resection of the distal scaphoid pole results in dorsal rotation of capitate and scaphoid of about 14° and the lunate 8°. Relative scapholunate and capitolunate angle increased significantly after total trapeziectomy, especially in clenched fist position. After scaphoid pole resection, significant SL and CL angles changes could be seen in almost every wrist position.

CONCLUSION

Destabilisation of the STT ligament complex by total trapeziectomy or distal scaphoid pole resection results in dissociation of the proximal and distal carpal row without instability within the proximal or distal row, corresponding to a CIND.

LEVEL OF EVIDENCE

III.

Biomechanical comparison of two different compression screws for the treatment of odontoid fractures in human dens axis specimen

BACKGROUND

Lag screw osteosynthesis for odontoid fractures has a high rate of pseudoarthrosis, especially in elderly patients. Besides biomechanical properties of the different screw types, insufficient fragment compression or unnoticed screw stripping may be the main causing factors for this adverse event. The aim of the study was to compare two screws in clinical use with different design principles in terms of compression force and stability against screw stripping.

METHODS

Twelve human cadaveric C2 vertebral bodies were considered. Bone density was determined. The specimens were matched according to bone density and randomly assigned to two experimental groups. An odontoid fracture was induced, which were fixed either with a 3.5 mm standard compression screw or with a 5 mm sleeve nut screw. Both screws are certified for the treatment of odontoid fractures. The bone samples were fixed in a measuring device. The screwdriver was driven mechanically. The tests were analyzed for peak interfragmentary compression and screw-in torque with a frequency of 20 Hz.

FINDINGS

The maximum fragment compression was significantly higher with screw with sleeve nut at 346.13(SD ±72.35) N compared with classic compression screw at 162.68(SD ±114.13) N (p = 0.025). Screw stripping occurred significantly earlier in classic compression screw at 255.5(SD ±192.0)° rotation after reaching maximum compression than in screw with sleeve nut at 1005.2(SD ±341.1)° (p = 0.0039).

INTERPRETATION

Screw with sleeve nut achieves greater fragment compression and is more robust to screw stripping compared to classic compression screw. Whether the better biomechanical properties lead to a reduction of pseudoarthrosis has to be proven in clinical studies.

Rate-dependent adhesion together with limb collaborations facilitate grasshoppers reliable attachment under highly dynamic conditions

Dynamic attachment is indispensable for animals to cope with unexpected disturbances. Minor attention has been paid to the dynamic performance of insects' adhesive pads. Through experiments pulling whole grasshoppers off a glass rod at varying speeds, surprising findings emerged. The feet did not always maintain contact but released and then reconnected to the substrate rapidly during leg extension, potentially reducing the shock damage to pads. As the pulling speeds increased from 1 to 400 mm/s, the maximum forces of single front tarsus insects and entire tarsi insects were nearly proportional to the 1/3 power of pulling speeds by 0.11 and 0.29 times, respectively. The force of some individuals could be even 800 times greater than their weight, which is unexpectedly high for smooth insect pads. This work not only helps us to understand the attachment intelligence of animals but is also informative for artificial attachment in extreme situations.

Influence of carbonated acid beverage on fracture resistance and marginal gap formation in different restorative approaches to non-carious cervical lesions

OBJECTIVE

This study is to evaluate fracture resistance, failure mode, and gap formation at the restorative interface of unrestored or restored non-carious cervical lesions (NCCLs) submitted to a short-term erosive environment.

MATERIALS AND METHODS

Artificial NCCLs were produced in vitro in bovine incisors, and were randomly divided into four restorative resins groups (n = 22): nanohybrid-NR; bulk-fill-BR; flow with a nanohybrid layer-FNR; bulk-fill with a nanohybrid layer-BNR; and a group unrestored-UR (n = 16). Half of the specimens were submitted to an erosive challenge (per 5 min, 3 × a day for 7 days, before and after restoration), and the other half, was immersed in artificial saliva. After, all teeth undergone thermal (5 ºC, 37 ºC, and 55 ºC, 3600 cycles) and mechanical (50 N, 2 Hz, 300,000 cycles) aging. Eighty teeth were subjected to compressive loading, and resistance and failures were analyzed, while 24 teeth were evaluated for gaps by microcomputed tomography. Statistical tests were performed (p < 0.05).

RESULTS

The restorative approaches affected fracture resistance (η2p = 0.14, p = 0.023), and gap formation (η2 = 0.18, p = 0.012) and so did the immersion medium (fracture η2p = 0.09, p = 0.008; gap η2 = 0.09, p = 0.017). BNR showed the highest resistance, while UR the lowest. FNR showed the highest gaps in both immersion media. Neither the resin groups nor the immersion media were associated with failure mode.

CONCLUSIONS

The erosive immersion medium based in acid beverages has been shown to affect NCCLs with or without restoration, but when Bulk-Fill resin is covered by nanohybrid resin, the performance is good.

CLINICAL RELEVANCE

Erosion negatively affects restorations, but unrestored NCCL shows worse biomechanical performance in stress-bearing situations.

[Translated article] Comparative clinical and biomechanical study of different types of osteosynthesis in the treatment of distal femur fractures

INTRODUCTION AND OBJECTIVES

Distal femoral fractures represent a problem due to their high number of complications. The aim was to compare the results, complications and stability achieved with retrograde intramedullary nailing and the angular stable plate in the treatment of distal femoral diaphyseal fractures.

MATERIAL AND METHOD

A clinical and experimental biomechanical study was carried out using finite elements. The results of the simulations allowed us to obtain the main results related to the stability of osteosynthesis. For clinical follow-up data, frequencies were used for qualitative variables, and Fisher's exact test and χ2 test were used to evaluate the significance of the different factors, with the condition of P<.05.

RESULTS

In the biomechanical study, the retrograde intramedullar nails demonstrated superiority, obtaining lower values in terms of global displacement, maximum tension, torsion resistance, and bending resistance. In the clinical study, the rate of consolidation of the plates was lower than nails (77% vs. 96%, P=.02). The factor that most influenced the healing of fractures treated with plate were the central cortical thickness (P=.019). The factor that most influenced the healing of nail-treated fractures was the difference between the diameter of the medullary canal and the nail.

CONCLUSIONS

Our biomechanical study shows that both osteosynthesis provide sufficient stability, but biomechanically behaves differently. Nails provide greater overall stability being preferable the use of long nails adjusted to the diameter of the canal. Plates form less rigid osteosynthesis, with little resistance to bending.

Comparative clinical and biomechanical study of different types of osteosynthesis in the treatment of distal femur fractures

INTRODUCTION AND OBJECTIVES

Distal femoral fractures represent a problem due to their high number of complications. The aim was to compare the results, complications and stability achieved with retrograde intramedullary nailing and the angular stable plate in the treatment of distal femoral diaphyseal fractures.

MATERIAL AND METHOD

A clinical and experimental biomechanical study was carried out using finite elements. The results of the simulations allowed us to obtain the main results related to the stability of osteosynthesis. For clinical follow-up data, frequencies were used for qualitative variables, and Fisher's exact test and χ2 test were used to evaluate the significance of the different factors, with the condition of P<.05.

RESULTS

In the biomechanical study, the retrograde intramedullar nails demonstrated superiority, obtaining lower values in terms of global displacement, maximum tension, torsion resistance, and bending resistance. In the clinical study, the rate of consolidation of the plates was lower than nails (77% vs. 96%, P=.02). The factor that most influenced the healing of fractures treated with plate were the central cortical thickness (P=.019). The factor that most influenced the healing of nail-treated fractures was the difference between the diameter of the medullary canal and the nail.

CONCLUSIONS

Our biomechanical study shows that both osteosynthesis provide sufficient stability, but biomechanically behaves differently. Nails provide greater overall stability being preferable the use of long nails adjusted to the diameter of the canal. Plates form less rigid osteosynthesis, with little resistance to bending.

Does pin configuration matter in modified tension band wiring for transverse patellar fracture? A biomechanical study

BACKGROUND

Modified tension band wiring has been widely used for the treatment of transverse patellar fractures. The optimal position of a Kirschner wire (K-wire) in modified tension band wiring, however, has not yet been determined. The purpose of the present study was to evaluate biomechanically the effect of K-wire position in a modified tension band wiring technique.

METHODS

Forty-two polyurethane foam patellae with a midway transverse fracture were assigned to six different fixation groups regarding different pin configurations in tension band wiring. The depth or sagittal position of the K-wire was divided into anterior and posterior. The coronal position of the K-wire was divided into central, medial and lateral. A specially designed set up simulated a knee with 60° flexion. All specimens were tested under axial traction. Loads at 2 mm and 4 mm fracture displacement and at the failure of the construct were recorded.

RESULTS

At 2 mm fracture displacement, anterolateral (AL) placement of K-wires revealed significantly less durability when compared with five other groups (P < 0.001). At 4 mm fracture displacement, the AL group also revealed inferior biomechanical strength when compared with other groups. Posteromedial (PM) K-wire placement group revealed more durability when compared with the posterolateral (PL) group (P < 0.05). At failure of the osteosynthesis, anteromedial (AM) and anterocentral (AC) groups revealed superior biomechanical strengths (P < 0.05).

CONCLUSIONS

The coronal and sagittal position of K-wire affects the biomechanical characteristics of modified tension band wiring. Anterolateral placement of K-wires revealed inferior strength to all other constructs in modified anterior tension band wiring.

Biomechanical performance of short and long cephalomedullary nail constructs for stabilizing different levels of subtrochanteric fracture

INTRODUCTION

The aim of this study was to assess biomechanical performance of short and long Cephalomedullary nail constructs consisting of different number of distal screw for stabilizing different levels of subtrochanteric fracture.

MATERIALS AND METHODS

The femur obtained from computed tomography scanner was used to create a transverse fracture at 15 mm (level A), 35 mm (level B), and 55 mm (level C) below the lesser trochanter. Short and long Cephalomedullary nails were virtually inserted to the fractured femur. Four-node tetrahedral element was used to build up finite element (FE) models for biomechanical analysis. The analysis focused on post-operative stage of partial weight-bearing.

RESULTS

Stress on the implant localized at the surface between lag screw/nail and distal screw/nail. Short Cephalomedullary nail exhibited higher stress than long Cephalomedullary nail. The stress in short Cephalomedullary nail could be reduced by using two distal screws fixation and the fracture at level A produced less stress than that of level B and C. Either short or long nail with two distal screws is sufficient to withstand the stress magnitude produced from the physiologic load. When single dynamic distal screw was used, stress on implant, elastic strain at fracture gap, and bone stress reached the high values. Elastic strain of the fracture gap at level C were less than that of level A and B, but no statistically significant difference. There was no proximal cancellous bone damage observed from the FE analysis.

CONCLUSIONS

Long Cephalomedullary nail with at least two distal locking screws remains a proper implant for subtrochanteric fracture fixation in overall locations. However, short Cephalomedullary nail with two distal screws may be a candidate for a high subtrochanteric fracture. Single dynamic screw insertion is strongly not recommended with either short or long nail regarding implant failure.

Functionalization of screw implants with superelastic structured Nitinol anchoring elements

Background

Demographic change is leading to an increase in the number of osteoporotic patients, so a rethink is required in implantology in order to be able to guarantee adequate anchoring stability in the bone. The functional modification of conventional standard screw implants using superelastic, structured Ti6Al4V anchoring elements promises great potential for increasing anchoring stability.

Methods

For this purpose, conventional screw implants were mechanically machined and extended so that structured-superelastic-positionable-Ti6Al4V anchoring elements could be used. The novel implants were investigated with three tests. The setup of the anchoring elements was investigated in CT studies in an artificial bone. In a subsequent simplified handling test, the handling of the functional samples was evaluated under surgical conditions. The anchorage stability compared to standard screw implants was investigated in a final pullout test according to ASTM F543—the international for the standard specification and test methods for metallic medical bone screws.

Results

The functionalization of conventional screw implants with structured superelastic Ti6Al4V anchoring elements is technically realizable. It was demonstrated that the anchoring elements can be set up in the artificial bone without any problems. The anchorage mechanism is easy to handle under operating conditions. The first simplified handling test showed that at the current point of the investigations, the anchoring elements have no negative influence on the surgical procedure (especially under the focus of screw implantation). Compared to conventional standard screws, more mechanical work is required to remove the functional patterns completely from the bone.

Conclusion

In summary, it was shown that conventional standard screw implants can be functionalized with Ti6Al4V-structured NiTi anchoring elements and the new type of screws are suitable for orthopedic and neurosurgical use. A first biomechanical test showed that the anchoring stability could be increased by the anchoring elements.

Effects of local application of the ankaferd blood stopper on osseointegration in three different surface titanium implants

Objective

Researchs of the effects of ankaferd blood stopper (ABS) on bone healing metabolism have revealed that it affects bone regeneration positively. The exact mechanism by which this positive effect on bone tissue metabolism is not known. The aim of this study is to biomechanic and biochemical analysis of the effects of the local ABS application on osseointegration of 3 different surfaced titanium implants.

Material & Methods

Spraque dawley rats were divided machined surfaced (MS) (n ​= ​10), sandblasted and large acid grid (SLA) (n ​= ​10) and resorbable blast material (RBM) (n ​= ​10) surfaced implants. ABS applied locally during the surgical application of the titanium implant before insertion in bone sockets. After 4 weeks experimental period the rats sacrificed and implants with surrounding bone tissues were removed to reverse torque analysis (Newton), blood samples collected to biochemical analysis (ALP, calcium, P).

Results

Biomechanic bone implant contact ratio detected higher in SLA surfaced implants compared with the RBM and controls (P ​< ​0,05). Phosphor levels detected lower in RBM implant group compared with the controls and SLA (P ​< ​0,05). Additionally; phosphor levels detected highly in controls compared with the RBM implants.

Conclusion

According the biomechanical parameters ABS may be more effective in SLA and RBM surfaced implants when locally applied.

The T-pod is as stable as supraacetabular fixation using 1 or 2 Schanz screws in partially unstable pelvic fractures: a biomechanical study

INTRODUCTION

Unstable fractures of the pelvis remain the predominant cause of severe hemorrhage, shock and early death in severely injured patients. The use of pelvic binders has become increasingly popular, particularly in the preclinical setting. There is currently insufficient evidence available about the stability of the pelvic binder versus supraacetabular fixation using 1 or 2 Schanz screws. We aimed to analyze the stability of the pelvic binder and supraacetabular fixateurs using either 1 or 2 Schanz screws in a cadaver model of an induced pelvic B-type fracture.

MATERIALS AND METHODS

The study was undertaken in 7 human fresh-frozen cadaveric pelvises with induced AO-type B fractures. Three stabilization techniques were compared: T-POD (pelvic bandage), supraacetabular external fixator with 1 pin on each side and external fixator with 2 pins on each side. Stability and stiffness were analyzed in a biomechanical testing machine using a 5-step protocol with static and dynamic loading, dislocation data were retrieved by ultrasound sensors at the fracture sites.

RESULTS

No significant differences in fracture fragment displacement were detected when using either the T-POD, a 1-pin external fixator or a 2-pin external fixator (P > 0.05). The average difference in displacement between the three methods was < 1 mm.

CONCLUSIONS

Pelvic binders are suitable for reduction of pelvic B-type fractures. They provide stability comparable to that of supraacetabular fixators, independently of whether 1 or 2 Schanz screws per side are used. Pelvic binders provide sufficient biomechanical stability for transferring patients without the need to first replace them with surgically applied external fixators. However, soft tissue irritation has to be taken into consideration and prolonged wear should be avoided.

LEVEL OF EVIDENCE

Level III.

Comparison of various tendon repair techniques in extansor zone 3 injuries: an experimental biomechanical cadaver study

PURPOSE

To compare five different repair techniques for extensor tendon zone III modified Kessler (MK), double-modified Kessler (DMK), modified Kessler epitendinous (MKE), double-modified Kessler epitendinous (DMKE), and running-interlocking horizontal mattress (RIHM) in terms of shortening, stiffness, gap formation, and ultimate load to failure.

METHODS

A total of 35 human cadaver fingers were randomly assigned to five suture techniques with 7 fingers each and were tested under dynamic and static loading conditions.

RESULTS

DMK was found to be superior over MK in terms of ultimate load to failure (36 N vs. 24 N, respectively), shortening (1.75 vs. 2.20 mm, respectively) and gap formation. However, these two methods had similar characteristics in terms of stiffness. The addition of epitendinous sutures to the repair methods resulted in approximately 40% increase in ultimate load to failure, whereas epitendinous sutures had no effect on shortening. DMKE was found to be superior over MKE in terms of shortening (1.77 vs. 2.22 mm, respectively). However, these two methods had similar characteristics in terms of mean ultimate load to failure and stiffness. RIHM was found to be superior over the other four methods in terms of ultimate load to failure (89 N), stiffness, and shortening (0.75 mm).

CONCLUSION

RIHM was found to be stronger and more durable for extensor tendon zone III than the other techniques in terms of ultimate load to failure and stiffness.

[Anatomy of the metacarpophalangeal and proximal interphalangeal finger joint with respect to arthroplasty]

BACKGROUND

Precise knowledge of the anatomy and biomechanics of the metacarpophalangeal and proximal interphalangeal joint is the basis for both indication and implantation of a finger joint prosthesis. Currently available finger joint prostheses inadequately take into account individual, ethnological, gender, age, and side differences. They can remain compromised despite the possible combination of their components.

OBJECTIVES

To elucidate which problems of finger joint arthroplasty exist due to the anatomy and biomechanics of the metacarpophalangeal and proximal interphalangeal joints.

METHODS

The anatomy and biomechanics of the metacarpophalangeal and proximal interphalangeal joint are described, and the problems and solutions of finger joint arthroplasty are presented.

RESULTS

Despite precise knowledge of the anatomy and biomechanics of the metacarpophalangeal and proximal interphalangeal joint, not all problems of finger joint arthroplasty have been solved. However, a modular surface replacement appears promising for the proximal interphalangeal joint.

CONCLUSIONS

Artificial joint replacement of the metacarpophalangeal and proximal interphalangeal joint is difficult with regard to morphology, small bone dimensions, complex biomechanics, and the strain of the hand. Further improvements, especially in design, should be achieved by exact anatomical imitation.

Effectiveness of posterior structures in the development of proximal junctional kyphosis following posterior instrumentation: A biomechanical study in a sheep spine model

Introduction

Proximal junctional kyphosis – PJK has been defined by a 10 or greater increase in kyphosis at the proximal junction as measured by the Cobb angle from the caudal endplate of the uppermost instrumented vertebrae (UIV) to the cephalad endplate of the vertebrae 1 segments cranial to the UIV. In this biomechanical study, it is aimed to evaluate effects of interspinosus ligament complex distruption and facet joint degeneration on PJK development.

Materials and methods

Posterior instrumentation applied between T2 – T7 vertebrae using pedicle screws to randomly selected 21 sheeps, divided into 3 groups. First group selected as control group (CG), of which posterior soft tissue and facet joints are protected. In second group (spinosus group, SG) interspinosus ligament complex which 1 segment cranial to UIV has been transected, and third group (faset group-FG) was applied facet joint excision. 25 N, 50 N, 100 N, 150 N and 200 N forces applied at frequency of 5 Hertz as 100 cycles axial to the samples. Then, 250 N, 275 N and 300 N forces applied static axially. Interspinosus distance, kyphosis angle and discus heights was measured in radiological evaluation. Abnormal PJK was defined by a proximal junctional angle greater than 10⁰ and at least 10⁰ greater than the corresponding preoperative measurement.

Results

In CG group, average interspinosus distance was 6,6 ± 1.54 mm and kyphosis angle was 2,2 ± 0.46° before biomechanical testing, and they were measured as 9,4 ± 1.21 mm and 3,3 ±0.44° respectively after forces applied to samples. In SG group, average interspinosus distance was 6,2 ± 1.72 mm and kyphosis angle was 2,7 ± 1.01° before experiment, and they were measured as 20,8 ± 5.66 mm and 15,1 ± 2.34° respectively after forces applied to samples. In FG group, average interspinosus distance was 4,8 ± 1.15 mm and kyphosis angle was −1 ± 4.14° before experiment, and they were measured as 11,1 ±1.96mm and 11 ± 2.87° respectively after forces applied to samples. In comparison to group CG, statistically significant junctional kyphosis was seen on both FG and SG group after statistical analysis. (p < 0.05). PJK was seen statistically significant more on SG group than FG group. (p < 0.05). Not any statistically significant difference was seen on measurement of disk distances among three groups. (p > 0.05)

Conclusions

Protecting interspinosus ligament complex and facet joint unity during posterior surgical treatment for spine deformation is vital to prevent PJK development. Based on our literature review, this is the first biomechanical study that reveals interspinosus ligament complex are more effective on preventing PJK development than facet joints.

Laparoscopic pectopexy: a follow-up cyclic biomechanical analysis determining time to functional stability

INTRODUCTION

Pectopexy, a laparoscopic method for prolapse surgery, showed promising results in previous transient testing by this group. It was shown that a single suture, yielding an ultimate load of 35 N, was equivalent to continuous suturing. This was demonstrated in an in vitro cadaver study. This transient data were used to establish an elastic stress-strain envelope. It was now possible to proceed to dynamic in vitro analysis of this surgical method to establish time to functional stability.

METHODS

Cyclic testing of this fixation method was performed on human female embalmed cadaver (cohort 1) and fresh, non-embalmed cadaver (cohort 2) pelvises. The testing envelope was 5-25 N at a speed of 1 mm/s. 100 load regulated cycles were applied.

RESULTS

100 cycles were completed with each model; no overall system failure occurred. Steady state, i.e., functional stability was reached after 14.5 (± 2.9) cycles for the embalmed group and after 19.1 (± 7.2) cycles for the non-embalmed group. This difference was statistically significant p = 0.00025.

CONCLUSION

This trial showed in an in vitro cyclic testing of the pectopexy method that functional stability may be achieved after no more than 19.1 cycles of load exposure. When remaining within the established load envelope of below 25 N, patients do not need to fear global fixation failure. Testing did demonstrate differences in non-embalmed and embalmed cadaver testing. Embalmed cadaver testing tends to underestimate time to steady state by 26.3%.

Isotretinoin induced achilles tendinopathy: Histopathological and biomechanical evaluation on rats

OBJECTIVE

The aim of the present study was to evaluate histopathological and biomechanical effects of isotretinoin on Achilles tendon.

MATERIALS & METHODS

Sixteen rats were divided into two groups including the control group (n = 8) and isotretinoin group (n = 8). The control group received 1.42 ml/kg soy oil per day whereas the isotretinoin group received 15 mg/kg/day (gavage dose 1.42 ml/kg) isotretinoin dissolved in soy oil through gavage method for 6 weeks. Achilles tendons were excised at the end of week 6. The tendon samples were evaluated by hematoxylin-eosin under a light microscope. Quantitative evaluation was performed via Movin and Bonar scoring. A computer-monitored tensile testing machine was utilised for biomechanical testing. Biomechanical characteristics of the tendon samples (elastic modulus, yield force, ultimate tensile force) were measured.

RESULTS

Histopathological evaluation revealed a significantly higher Movin and Bonar scores in histopathological evaluation. Movin score in isotretinoin group was 4.1 ± 2.5 and it was 2.3 ± 1.0 in control group (p = 0.032). Bonar score in isotretinoin group was 2.9 ± 1.4 and it was 1.6 ± 0.7 in control group (p = 0.022). In line with histopathological evaluation, biomechanical measurements in isotretinoin group (elastic modulus, yield force, ultimate tensile force) were significantly lower than the control group. Elastic modulus in isotretinoin group was 227 ± 27.7 N/mm² and in control group it was 281.7 ± 38.7 N/mm² (p = 0.006). In isotretinoin group; yield force was 33.7 ± 4.3 Pa and in control group it was 40.8 ± 5.9 Pa (p = 0.021). Ultimate tensile force in isotretinoin group was 35.7 ± 4.2 Pa and in control group it was 44 ± 7 Pa (p = 0.009).

CONCLUSION

The present study detected histopathological and biomechanical negative effect of isotretinoin on Achilles tendon. Therefore, isotretinoin should be questioned in medical history of patients with tendinopathy.

Contribution of the xenograft bone plate-screw system in lumbar transpedicular stabilization: An in vivo study in dogs

OBJECTIVES

Xenograft bone plate-screws (XBPSs) can be alternative tools in lumbar transpedicular stabilization (TS). The aim of this study was to show biomechanical and histopathological contribution of the XBPSs system in lumbar TS.

MATERIALS AND METHODS

Fifteen (n = 15) hybrid dog and ten (n = 10) L_2-4 cadaveric specimens were included in the study. The dogs were separated according to surgical techniques: L₃ laminectomy and bilateral facetectomy (LBF) in Group I (experimental group [EG I] (n = 5), L₃ LBF plus TS with metal plate-screws (MPSs) in Group II (EG II) (n = 5), and L₃ LBF plus TS with XBPSs in Group III (EG III) (n = 5). The cadaveric specimens were separated to L_2-4 intact in Group I (CG I), (n = 5), and L₃ LBF in Group II (CG II), (n = 5). The dogs were sacrificed at the end of 3^rd month, and their L_2-4 spinal segments were en bloc removed and prepared as in control groups. Flexion, extension, left-right bending, rotation, and compression tests were applied to all segments. Stiffness values were calculated and analyzed statistically. All dog segments were evaluated histopathologically.

RESULTS

XBPS system showed a higher average stiffness values for left bending, extension, flexion, and compression compared to MPS, but these differences were not statistically meaningful. XBPS system had superiority to the fusion formation, as well.

CONCLUSIONS

XBPSs provide stability and help the fusion formation, but this system does not have a biomechanical advantage over MPS system in TS.

Biomechanical evaluation of the long head of the biceps brachii tendon fixed by three techniques: a sheep model

OBJECTIVE

To evaluate the biomechanical properties of the fixation of the long head of the biceps brachii into the humeral bone with suture anchors, interference screw, and soft tissue suture, comparing strength, highest traction load, and types of fixation failure.

METHODS

Thirty fresh-frozen sheep shoulders were used, separated into three groups of ten for each technique. After fixation, the tendons were subjected to longitudinal continuous loading, obtaining load-to-failure (N) and displacement (mm).

RESULTS

The mean load-to-failure for suture anchors was 95 ± 35.3 N, 152.7 ± 52.7 N for interference screw, and 104.7 ± 23.54 N for soft tissue technique. There was a statistically significant difference (p < 0.05), with interference screw demonstrating higher load-to-failure than suture anchor fixation (p = 0.00307) and soft tissue (p = 0.00473). The strength of interference screw was also superior when compared with the other two methods (p = 0.0000127 and p = 0.00000295, respectively). There were no differences between suture anchors and soft tissue technique regarding load-to-failure (p = 0.9420) and strength (p = 0.141).

CONCLUSION

Tenodesis of the long head of the biceps brachii with interference screw was stronger than the suture anchors and soft tissue techniques. The other two techniques did not differ between themselves.

Biomechanical comparison of orthogonal versus parallel double plating systems in intraarticular distal humerus fractures

OBJECTIVES

In intraarticular distal humerus fractures, internal fixation with double plates is the gold standard treatment. However the optimal plate configuration is not clear in the literature. The aim of this study was to compare the biomechanical stability of the parallel and the orthogonal anatomical locking plating systems in intraarticular distal humerus fractures in artificial humerus models.

METHODS

Intraarticular distal humerus fracture (AO13-C2) with 5 mm metaphyseal defect was created in sixteen artificial humeral models. Models were fixed with either orthogonal or parallel plating systems with locking screws (Acumed elbow plating systems). Both systems were tested for their stiffness with loads in axial compression, varus, valgus, anterior and posterior bending. Then plastic deformation after cyclic loading in posterior bending and load to failure in posterior bending were tested. The failure mechanisms of all the samples were observed.

RESULTS

Stiffness values in every direction were not significantly different among the orthogonal and the parallel plating groups. There was no statistical difference between the two groups in plastic deformation values (0.31 mm-0.29 mm) and load to failure tests in posterior bending (372.4 N-379.7 N). In the orthogonal plating system most of the failures occurred due to the proximal shaft fracture, whereas in the parallel plating system failure occurred due to the shift of the most distal screw in proximal fragment.

CONCLUSION

Our study showed that both plating systems had similar biomechanical stabilities when anatomic plates with distal locking screws were used in intraarticular distal humerus fractures in artificial humerus models.

Rotational stability in screw-fixed scaphoid fractures compared to plate-fixed scaphoid fractures

BACKGROUND

The literature describes the treatment of scaphoid fractures comparing the volar and dorsal approaches, the advantages and disadvantages of percutaneous screw fixation, as well as the treatment of scaphoid nonunions using different types of cancellous or corticocancellous bone grafts. Yet, to date no studies are available comparing the outcome of rotational stability in screw-fixed scaphoid fractures to angular stable systems. The purpose of this study is to provide reliable data about rotational stability in stabilised scaphoid fractures and to gain information about the rigidity and the stability of the different types of fixation.

METHODS

Three groups of different stabilisation methods on standardised scaphoid B2 fractures were tested for rotational stability. Stabilisation was achieved using one or two cannulated compression screws (CCS) or angular stable plating. We performed ten repetitive cycles up to 10°, 20° and 30° rotation, measuring the maximum torque and the average dissipated work at angle level.

RESULTS

Our study showed that rotational stability using a two CCS fixation is significantly (p < 0.05) higher than single CCS fixation. Using the angular stable plate system was also superior to the single CCS (p < 0.05). There was, however, no significant difference between two CCS fixation and angular stable plate fixation.

CONCLUSION

Even though indications of using screws or plate systems might be different and plate osteosynthesis may be preferable in treatment of dislocated or comminuted fractures as well as for nonunions, our study showed a better rotational stability by choosing more than just one screw for osteosynthesis. Angular stable plating of scaphoid fractures also provides more rotational stability than single CCS fixation. The authors therefore hypothesise higher union rates in scaphoid fractures using more stable fixation systems.

Biomechanical investigation of a minimally invasive posterior spine stabilization system in comparison to the Universal Spinal System (USS)

Background

Although minimally invasive posterior spine implant systems have been introduced, clinical studies reported on reduced quality of spinal column realignment due to correction loss. The aim of this study was to compare biomechanically two minimally invasive spine stabilization systems versus the Universal Spine Stabilization system (USS).

Methods

Three groups with 5 specimens each and 2 foam bars per specimen were instrumented with USS (Group 1) or a minimally invasive posterior spine stabilization system with either polyaxial (Group 2) or monoaxial (Group 3) screws.

Mechanical testing was performed under quasi-static ramp loading in axial compression and torsion, followed by destructive cyclic loading run under axial compression at constant amplitude and then with progressively increasing amplitude until construct failure.

Bending construct stiffness, torsional stiffness and cycles to failure were investigated.

Results

Initial bending stiffness was highest in Group 3, followed by Group 2 and Group 1, without any significant differences between the groups.

A significant increase in bending stiffness after 20’000 cycles was observed in Group 1 (p = 0.002) and Group 2 (p = 0.001), but not in Group 3, though the secondary bending stiffness showed no significant differences between the groups.

Initial and secondary torsional stiffness was highest in Group 1, followed by Group 3 and Group 2, with significant differences between all groups (p ≤ 0.047). A significant increase in initial torsional stiffness after 20’000 cycles was observed in Group 2 (p = 0.017) and 3 (p = 0.013), but not in Group 1.

The highest number of cycles to failure was detected in Group 1, followed by Group 3 and Group 2. This parameter was significantly different between Group 1 and Group 2 (p = 0.001), between Group 2 and Group 3 (p = 0.002), but not between Group 1 and Group 3.

Conclusions

These findings quantify the correction loss for minimally invasive spine implant systems and imply that unstable spine fractures might benefit from stabilization with conventional implants like the USS.

Comminuted olecranon fracture fixation with pre-contoured plate: Comparison of composite and cadaver bones

AIM: To determine whether use of a precontoured olecranon plate provides adequate fixation to withstand supraphysiologic force in a comminuted olecranon fracture model.

METHODS: Five samples of fourth generation composite bones and five samples of fresh frozen human cadaveric left ulnae were utilized for this study. The cadaveric specimens underwent dual-energy X-ray absorptiometry (DEXA) scanning to quantify the bone quality. The composite and cadaveric bones were prepared by creating a comminuted olecranon fracture and fixed with a pre-contoured olecranon plate with locking screws. Construct stiffness and failure load were measured by subjecting specimens to cantilever bending moments until failure. Fracture site motion was measured with differential variable resistance transducer spanning the fracture. Statistical analysis was performed with two-tailed Mann-Whitney-U test with Monte Carlo Exact test.

RESULTS: There was a significant difference in fixation stiffness and strength between the composite bones and human cadaver bones. Failure modes differed in cadaveric and composite specimens. The load to failure for the composite bones (n = 5) and human cadaver bones (n = 5) specimens were 10.67 nm (range 9.40-11.91 nm) and 13.05 nm (range 12.59-15.38 nm) respectively. This difference was statistically significant (P ˂ 0.007, 97% power). Median stiffness for composite bones and human cadaver bones specimens were 5.69 nm/mm (range 4.69-6.80 nm/mm) and 7.55 nm/mm (range 6.31-7.72 nm/mm). There was a significant difference for stiffness (P ˂ 0.033, 79% power) between composite bones and cadaveric bones. No correlation was found between the DEXA results and stiffness. All cadaveric specimens withstood the physiologic load anticipated postoperatively. Catastrophic failure occurred in all composite specimens. All failures resulted from composite bone failure at the distal screw site and not hardware failure. There were no catastrophic fracture failures in the cadaveric specimens. Failure of 4/5 cadaveric specimens was defined when a fracture gap of 2 mm was observed, but 1/5 cadaveric specimens failed due to a failure of the triceps mechanism. All failures occurred at forces greater than that expected in postoperative period prior to healing.

CONCLUSION: The pre-contoured olecranon plate provides adequate fixation to withstand physiologic force in a composite bone and cadaveric comminuted olecranon fracture model.

Finite element analysis of the stability of transverse acetabular fractures in standing and sitting positions by different fixation options

BACKGROUND

Treatment of a transverse acetabular fracture type is possible from an anterior approach, a posterior approach or both. Different fixation methods have been described but whether one is superior to the other is still under debate. The aim of the current study was to test the different fixation alternatives of stabilization of transverse acetabular fractures under two basic physiological loading conditions: standing and sitting utilizing a finite element model.

MATERIAL AND METHODS

A transtectal transverse fracture model was fixed in five different alternatives: an anterior column plate; a posterior column plate; an anterior column plate combined with a posterior column screw; a posterior column plate combined with an anterior column screw; and a posterior column plate and an anterior column plate. In these models, a load of 400N was applied at standing and sitting positions and the displacements were analyzed by using three-dimensional finite element stress analysis method.

RESULTS

In the model simulating standing human position, overall motion at the posterior column was minimum when two columns were plated (0.071mm). The second best fixation was posterior column plate with an anterior column screw (0.077mm). Overall motion at the anterior column was minimum by posterior column plate with an anterior column screw (0.0326mm). The plating of two columns was associated with motion of (0.0333mm). In the model that simulates sitting position, the motion at the posterior column was minimum when two columns were plated (0.0478mm), and (0.0517mm) when a posterior column plate with an anterior column screw was used. Overall motion in the anterior column was minimum when posterior column plate with an anterior column screw (0.0198mm) was used, whereas the motion was (0.0203mm) when plating of both columns was examined.

CONCLUSION

Posterior column plating combined with an anterior column screw has quite comparable results to a both column plating in transverse fractures, suggesting that two column fixations might be unnecessary. This method is also very superior to anterior column plating combined with a posterior column screw in that type of fractures.

Percutaneous iliosacral fixation in external rotational pelvic fractures. A biomechanical analysis

INTRODUCTION

Although the gold standard in open book pelvic fractures remains the pubic symphysis (PS) plate fixation, the clinical outcomes are not satisfactory, despite the excellent anatomical reduction assessed radiologically. Some authors suggest that residual instability of the posterior pelvic elements may be responsible for the chronic pain and the early osteoarthritic changes in the sacroiliac joint (SIJ).

OBJECTIVE

To evaluate whether the isolated posterior fixation with one or two iliosacral screws (ISSs) is sufficient to provide adequate stability for the treatment of Burgess Young APC-II (YB APC-II) type of pelvic ring injuries.

METHODS

Biomechanical experimental study using 7 fresh human pelvises, where an YB APC-II pelvic injury was previously implemented. The isolated posterior fixation of the pelvic ring with 1 or 2 ISSs directed in the S1 vertebra body was analysed in each specimen following an axial load of 300N. The different displacement of the SIJ and of the PS were analysed in all three spatial axes, using the validated optical measurement system 3D PONTOS 5M. A multivariate version of Friedman test (non-parametric ANOVA for repeated measures) was performed.

RESULTS

The isolated fixation of the SIJ with 1 ISS did not show any differences with respect to the intact pelvis (p=0.851). Regarding the PS, both type of fixations (with 1 or 2 ISSs) confirmed an acceptable correction and adequate control of the PS even though with some differences compared to the intact pelvis (p=0.01). The presence of the second ISS found not to offer any significant additional benefit. The three-dimensional analysis of the behaviour of the pelvic elements, in these two different types of fixation, did not show any statistical significant differences (p=0.645).

CONCLUSION

The posterior fixation with ISS can represent an alternative option for treatment of pelvic injuries associated with rotational instability. Further prospective clinical studies are necessary to determine, the influence of the residual pubic symphysis mobility in the every day life, when the above-mentioned technique is applied.

Reverse polarity shoulder replacement: Current concepts and review of literature

Shoulder replacement in cuff tear arthropathy (CTA) is an unsolved challenge. CTA poses a soft tissue deficiency in an arthritic glenohumeral joint which the anatomical total shoulder replacement and hemiarthroplasty cannot reliably provide stability, range of movement, function or satisfactory long term outcome. In the past two decades since the introduction of the reverse shoulder replacement, the prosthesis has evolved and has shown promising results. It is a partially constraint joint by virtue of its design features. The reversal of the concavity and convexity of the joint to the proximal humerus and the glenoid, respectively, also shifts and improves its center of rotation onto the osseous surface of the glenoid with less exposure to shear stress. It is a successful pain relieving procedure, offering good outcome in patients with irreparable massive rotator cuff tear with or without osteoarthritis. Consequently, this has led to wider use and expansion of its indication to include more complex elective and trauma cases. Whereas originally used in the more elderly patients, there is increasingly more demand in the younger patients. It is important to have good quality long term data to support these increasing indications. Therefore, we review the literature on the concepts of reverse shoulder replacement and the contemporary evidence.