Comparison of two different screw trajectories in the treatment of oblique scaphoid fractures: A mechanical study on composite bone models.

OBJECTIVES: In this mechanical study, we aimed to compare two different screw trajectories in terms of durability against axial loads on oblique scaphoid fractures using composite bone models. MATERIALS AND METHODS: Oblique osteotomies were made along the dorsal sulcus of 14 composite scaphoid bone models. Following this, all bone models were randomly classified. One group of bones were fixed with a screw placed perpendicular to the osteotomy line and the other group was fixed with a screw placed centrally down the long axis of the scaphoid bone. Each scaphoid bone model was positioned on a mechanical testing machine. Subsequently, axial loading tests were applied on each bone model to measure the amount of loading required to cause 2-mm displacement and failure on the osteotomy side and maximum displacement at the time of failure on scaphoid bone models. RESULTS: There was no statistically significant difference in load to 2-mm displacement and failure between the two groups (p>0.05). Also, there was no statistically significant difference between the two groups in terms of maximum displacement seen on failure (p>0.05). CONCLUSION: In our study, we found that the stability of the screws which laid perpendicular to the fracture line and parallel to the long axis of the scaphoid was the same in fixing oblique scaphoid fractures.

Biomechanical comparison of fracture site stabilities of femur nails after fracture site resorption.

Instability increases after fracture site resorption. This study aimed to compare the fracture site stabilities of different femoral nails after fracture site resorption. Thirty composite femurs were divided into three groups of 10 interlocking nails. Using axial compression-distraction machines and a custom-made torsion device, the fracture site rotational and axial stabilities after 1 mm fracture site resorption were determined. Between 6 Nm external and 6 Nm internal rotation torques, the means of the maximum fracture site rotation arc of motion were 5.94 mm for compression nails, 5.9 mm for interlocking nails and 3.5 mm for CAROT nails. Between 2300 N compression and 150 N distraction forces, the means of the fracture site axial motion were 3.15 mm for interlocking nails, 1.26 mm for compression nails and 1.26 mm for CAROT nails. CAROT nails are superior to compression and interlocking nails in fracture site rotational and axial stabilities after 1 mm fracture site resorption.

A novel anatomical patellar plate for transverse patellar fracture - A biomechanical in-vitro study.

OBJECTIVE: The aim of this study was to assess the safety and stability of our novel anatomical patella plate and to compare its stability with tension band-wire technique. METHODS: A total of 12 cadaveric preserved knees (six right and six left patellae) with close patellar size were chosen to form two groups of six samples. Each group received either plate or tension band-wiring fixation for an experimentally created patella fracture. Cyclic load of an average of 350 N was applied for all specimens and after accomplishing 50 cycles the displacements of all fracture edges were recorded. RESULTS: After completing 50 cycles in each group, the average fracture edges displacement measured in the plate group was 1.98 ± 0.299 mm, whereas the average fracture edges displacement measured in the tension band-wire group was 2.85 ± 0.768 mm (p = 0.016). CONCLUSION: In the operative treatment of displaced transverse patellar fractures, the strength of fixation obtained by titanium curved plates is highly stronger when compared to the fixation with a tension band-wire technique. Fixation with titanium curved plates provides satisfactory stability at the fracture site which allow withstanding the cyclic loads during the postoperative rehabilitation.

Hexagonal grafts in mosaicplasty: Biomechanical comparison of standard cylindrical and novel hexagonal grafts in calf cadaver model.

OBJECTIVE: Cylindrical grafts are currently used to cover defected area in mosaicplasty. However, there are some difficulties with cylindrical grafts, such as potential dead space between grafts and insufficient coverage. Hexagonal graft (honeycomb model) was created and evaluated in this biomechanical study. Hypothesis was that harvesting grafts with hexagonal shape, which has the best volume geometry characteristics in nature, would be biomechanically advantageous and provide superior pull-out strength. METHODS: Total of 24 fresh calf femurs were divided into 3 equal groups. In the first group, 1 cylindrical and 1 hexagonal graft were compared. Second group consisted of 3 cylindrical and 3 hexagonal grafts. Third group was designed to evaluate effect of graft depth; hexagonal graft implanted at 5 mm depth was compared with 20-mm-deep hexagonal graft. All specimens were subjected to pull-out test. Friction field and graft surface area were also evaluated. RESULTS: Pull-out strength comparison of 15-mm-deep triple cylindrical grafts and 15-mm-deep triple hexagonal grafts in second group revealed statistically significant difference in favor of hexagonal grafts (p < 0.05). Surface area of cylindrical graft with 9-mm diameter was calculated to be 50.27 mm2, while hexagonal graft surface area was 55.425 mm2. Volume ratio of cylindrical and hexagonal grafts was 753.98 mm3 and 831.375 mm3, respectively. CONCLUSION: This biomechanical study demonstrated that graft geometry, especially in multiple graft applications, is a factor that influences stability. Hexagonal grafts appear to be more stable than cylindrical grafts in multiple applications, and they may be used to cover a larger defected area.

Biomechanical comparison of pullout strengths of five cortical screw types: An innovative measurement method.

OBJECTIVES: This study aims to assess five different cortical screw types using artificial femurs, under equated testing conditions. MATERIALS AND METHODS: We investigated the maximum force needed to cause deformation at screw-bone interface using fourth generation composite femurs by conducting separate pullout tests for each screw type. We normalized obtained results with traditional methods and cross-comparison. To conduct pullout tests dependent on screw dimensions, we eliminated the effect of bicortical bone thickness by equalizing the conditions of screw insertion. RESULTS: Non-locking screws with larger diameter and pitch depth required larger pullout forces to be extracted, showing statistically superior performance compared to locking screws with smaller dimensions. However, the statistical differences between the absolute pullout forces decreased after the traditional normalization of the results. We proposed a new normalization method based on solid geometric reasoning. CONCLUSION: This novel approach showed that a screw type that appeared to show average performance, in fact, did not have statistically significantly different results than the top performers. Surgeons are not required to prefer larger dimension screws in small dimension host bones.

The Mechanical Effect of Rod Contouring on Rod-Screw System Strength in Spine Fixation.

OBJECTIVE: Rod-screw fixation systems are widely used for spinal instrumentation. Although many biomechanical studies on rod-screw systems have been carried out, but the effects of rod contouring on the construct strength is still not very well defined in the literature. This work examines the mechanical impact of straight, 20° kyphotic, and 20° lordotic rod contouring on rod-screw fixation systems, by forming a corpectomy model. METHODS: The corpectomy groups were prepared using ultra-high molecular weight polyethylene samples. Non-destructive loads were applied during flexion/extension and torsion testing. Spine-loading conditions were simulated by load subjections of 100 N with a velocity of 5 mm min(-1), to ensure 8.4-Nm moment. For torsional loading, the corpectomy models were subjected to rotational displacement of 0.5° s(-1) to an end point of 5.0°, in a torsion testing machine. RESULTS: Under both flexion and extension loading conditions the stiffness values for the lordotic rod-screw system were the highest. Under torsional loading conditions, the lordotic rod-screw system exhibited the highest torsional rigidity. CONCLUSION: We concluded that the lordotic rod-screw system was the most rigid among the systems tested and the risk of rod and screw failure is much higher in the kyphotic rod-screw systems. Further biomechanical studies should be attempted to compare between different rod kyphotic angles to minimize the kyphotic rod failure rate and to offer a more stable and rigid rod-screw construct models for surgical application in the kyphotic vertebrae.

Dual plating for fixation of humeral shaft fractures: A mechanical comparison of various combinations of plate lengths.

OBJECTIVE: The role of plate configuration was found inconclusive on the biomechanical effects of the plate size and hole number for dual plate constructions in humeral shaft fractures. The purpose of this study was to test the biomechanical stability of various dual plate constructions. METHODS: Twenty-four left humeri (4th Generation Composite Humerus, Sawbones, Malmö, Sweden) with comminuted midshaft humeral fracture were used. Four groups of plate constructs were tested: laterally fixed 8-hole locking plate and screws were combined with anteriorly locking plates containing 0, 4, 6, or 8 holes in groups I, II, III, and IV, respectively. The alterations in axial, bending, and torsional angles were recorded. RESULTS: There were no fixation failures during axial, bending, or torsional stiffness testing within the elastic behavior limits. Axial stiffness was highest in Group IV. Torsional stiffness, posterior-to-anterior bending stiffness, lateral-to-medial bending stiffness, and medial-to-lateral bending stiffness were lowest in Group I. CONCLUSION: The similar stiffness values for the 8-to-4 hole and 8-to-6 hole plate constructions indicate that the 8-to-4 hole construction is an option in young adults, while the stiffest 8-to-8 hole combination may be an option for osteoporotic patients.

Biomechanical Performance of Hip Labral Repair Techniques.

PURPOSE: To determine the strength of various suture techniques and the impact of suture passer size on cyclically loaded hip labra. METHODS: We assigned 63 bovine hip labra to 9 simple knotless suture technique groups using OrthoCord suture: (1) penetrating grasper (2.6 mm)-placed horizontal mattress, (2) penetrating grasper-placed vertical mattress, (3) SutureLasso (1.8 mm)-placed vertical mattress, (4) penetrating grasper-placed oblique repair, (5) penetrating grasper-placed vertical mattress plus radiofrequency, (6) SutureLasso-placed horizontal mattress, (7) SutureLasso-placed oblique mattress, (8) SutureLasso-placed horizontal mattress plus radiofrequency, and (9) SutureLasso-placed oblique mattress plus radiofrequency. After 20 cycles of uniaxial tensile loading (5 to 80 N), destructive testing was performed. RESULTS: Penetrating grasper-placed horizontal mattress sutures showed lower ultimate failure loads than vertical and oblique mattress sutures (P < .05). Penetrating grasper-placed vertical mattress sutures had higher peak-to-peak displacement than SutureLasso-placed vertical mattress sutures (P = .04). SutureLasso-placed oblique mattress sutures had a higher ultimate load (P < .01) and stiffness (P = .04) than SutureLasso-placed horizontal mattress sutures. SutureLasso-placed horizontal mattress sutures had lower cyclic elongation than penetrating grasper-placed horizontal mattress sutures (P = .01) and lower ultimate load (P < .01) and stiffness than SutureLasso-placed vertical mattress sutures (P < .01). Horizontal mattress sutures with radiofrequency had a higher ultimate load (P = .02), stiffness, and cyclic elongation (P < .01) than without radiofrequency. CONCLUSIONS: A horizontal mattress hip labrum stitch shows a lower ultimate failure load than vertical or oblique mattress stitches. Smaller-diameter suture-passing devices show less cyclic displacement and elongation than larger-diameter devices. Radiofrequency labral treatment does not alter vertical stitch strength but does alter horizontal mattress stitch strength. CLINICAL RELEVANCE: Vertical and oblique stitches are stronger than horizontal stitches. A 1.8-mm passing device shows a better cyclic loading performance than a 2.6-mm device.

A new femoral nail with single distal locking screw for maximum interfragment rotational stability.

OBJECTIVE: One of the problems for interlocking nailing of the femur is interfragment rotation motion, affecting fracture healing. The nails with single distal locking screw are advantageous for decreasing operation time and radiation exposure. We investigated which single distal screw nail is the best for interfragment rotational stability. METHODS: We used a total of 30 composite femurs, ten for each group. We determined interfragment rotational displacement of composite femurs with three types of single distal screw nails (10 interlocking nails, 10 compression nails and 10 Mehmet anti-rotation nails compressed by tube) at 6-Nm external- 6 Nm internal and 10 Nm extern- 6 Nm internal torques, which imitating respectively the level walking and descending stairs, using an axial distraction testing machine and a custom designed rotation apparatus. RESULTS: Between 10 Nm external and 6 Nm internal torques with single distal locking screw, the interfragment rotational displacement in the Mehmet nail compressed by the 8 Nm torque wrench was mean 1.14 mm and 540% less than mean 7.31 mm in interlocking nails and 400% less than 5.72 mm in compression nails compressed by the 2.5 Nm torque wrench. CONCLUSION: The single distal screw Mehmet nail is superior than other single (or even some double) distal screw nails for maximum rotational stability, with no interfragment distraction gap, no superior nail migration, decreased operation time, and less radiation exposure in axially stable transverse and short oblique femur fractures in daily activities like stair descending or level walking.

A novel adjustable dynamic plate for treatment of long bone fractures: An in vitro biomechanical study.

INTRODUCTION: Locking compression plate (LCP) system was designed to provide bone stability and to enhance bone healing. However, implant failure, nonunion and instability are still frequently encountered complications. The purpose of this study was to assess and compare the biomechanical characteristics of a novel adjustable dynamic plate (ADP) with the commonly used LCP. MATERIALS AND METHODS: Twelve 4th generation composite artificial femoral bones were used. Transverse fracture was created in all bones, 6 femurs were fixated using the novel ADP, whereas the other 6 femurs were fixated using the traditional LCP. All samples had undergone a non-destructive repetitive different forces (axial compression, bending and torsion), to evaluate the biomechanical differences between the two plating systems. RESULTS: Under axial load the mean stiffness value was 439.0 N/mm for the ADP and 158.9 N/mm for the LCP, ADP showed a statistically significant stiffness value than LCP with a P value of 0.004. There was no significant difference in flexion/extension bending strain values between ADP and LCP. However LCP provided significantly stiffer fixation in medial and lateral bending tests than ADP (P = 0.037) and (P = 0.016) respectively. But no significant difference was detected between the two plating system in the applied torsional stress. CONCLUSION: These results do not show any significant biomechanical difference in the applied torsional and bending stresses between LCP and ADP. However the remarkably increased persistent compression effect of the ADP created a considerable stress on fracture edges which may accelerate bone healing.

Biomechanical comparision of femoral intramedullary nails for interfragmentary rotational stability.

OBJECTIVES: This study aims to investigate which intramedullary nail is biomechanically better for establishing interfragmentary rotational stability. MATERIALS AND METHODS: Thirty composite femurs were utilized in this study. We analyzed interfragmentary rotational arc displacements between 10 Nm external-6 Nm internal torques and 6 Nm external-6 Nm internal torques which imitate rotation torques while walking on a flat surface and descending stairs by administering 10 interlocking nails, 10 compression nails, and 10 Mehmet anti-rotation nails with tube compression. RESULTS: Maximum interfragmentary rotation arc displacement between 10 Nm external rotation and 6 Nm internal rotation torques was mean 1.64 mm in the Mehmet nail compressed by 7 Nm torque wrench. This value was lower by 309% (6.72 mm) from interlocking nail (p=0.000), 201% (5.42 mm) from compression nail compressed by 2.5 Nm torque wrench (p=0.000), and 26% (1.92 mm) from compression nail compressed by 7 Nm torque wrench (p>0.05). CONCLUSION: In axially stable transvers and short oblique femur fractures, Mehmet nail is superior to other intramedullary nails with limited movement between locking screw and hole, more interfragmentary compression without locking screw deformation, and no proximal nail migration.

Biomechanical comparison of three-point bending resistance of titanium and stainless steel locking screws in intramedullary nails.

OBJECTIVES: This study aims to investigate whether there is any significant difference in bending resistance between titanium and stainless steel locking screws of femur nails and to review deformation of locking screws which is a common problem in interlocking nailing. MATERIALS AND METHODS: In this study, a total of 60 pieces of 5 mm major diameter titanium and stainless steel locking screws were used as six groups in three different thread depth structures (high threaded, low threaded, and unthreaded). Three-point bending tests were conducted on steel screws placed inside stainless steel tube with 30 mm inner diameter, which imitated the level of lesser trochanter. We used an axial compression testing machine in order to determine the yield points that permanent deformation occurred in the locking screws. RESULTS: For low threaded locking screws, which are the most frequently used thread type for locking screws, the mean bending yield points were 1413 N on the titanium screws and this level was below 1922 N (2.8 BW) of level walking loading on femur for 70 kg person. On low threaded stainless screws, bending resistance was 2071 N, which was above the value of 1922 N. For high threaded locking screws, the mean bending yield points were 874 N on the titanium screws and 556 N on stainless screws. CONCLUSION: In comminuted femur shaft fractures (in full load bearing conditions), using stainless steel locking screws is better instead of titanium screws to avoid locking screw deformation since low threaded stainless steel screws were 46.5% more resistant to bending deformation than titanium ones. Stainless steel or titanium high threaded locking screws may only be carefully used in non-comminuted fractures.

Distal femoral derotational osteotomy with external fixation for correction of excessive femoral anteversion in patients with cerebral palsy.

Patients with cerebral palsy (CP) disorder often develop rotational hip deformity. Increasing deformities impair already diminished walking abilities; femoral osteotomies are often performed to maintain and improve walking abilities. Fixation of osteotomies with condylar plates has been used successfully, but does not often enable immediate postoperative full weight-bearing. To avoid considerable postoperative rehabilitation deficit and additional bone loss because of inactivity, a postoperative treatment with full weight-bearing, is therefore, desirable. Self-tapping Schanz screws with a unilateral external fixator crossing the knee joint providing stronger anchoring in osteopenic bone might fulfill these demands. A retrospective study was carried out on 27 ambulatory CP patients, mean age 17.5 years (range 9-22 years); 11 patients with bilateral severe intoeing deformities underwent a supracondylar femoral osteotomy between September 2008 and April 2012. All patients were allowed to bear their full weight postoperatively. The aim of this study was to describe the technique, the results of this technique, to evaluate the time required for bone healing, and the type of complications associated with a distal derotational femoral osteotomy fixed with a uniaxial external fixator crossing the knee joint. A total of 27 patients were studied [mean weight 48.8 kg (range 29.8-75 kg)]. The mean preoperative rotation included internal rotation of 69° and external rotation of 17°. All patients were evaluated clinically and radiographically for a minimum of 1 year after surgery. There was a significant decrease in the mean medial rotation from 69° to 32° (P=0.00034). The lateral rotation increased significantly from preoperative 17° to postoperative 45° (P=0.0011). The femoral anteversion decreased significantly from a mean of 55° preoperatively to a mean 17° postoperatively (P=0.030). All patients, except one, achieved solid fusion uneventfully. One patient was a 16-year-old female who had sustained a knee flexion contracture of 30° because of a delay in the physiotherapy program. One 13-year-old female patient with a bilateral osteotomy had a nondisplaced fracture in her right femur after a direct trauma 2 weeks after removal of an external fixator, and was treated by a cast. Another 17-year-old male patient developed a nonunion because of loosening of two pins and achieved solid union after revision by dynamic compression plate plating. Besides four cases with superficial pin-tract infection, no other complications were documented. Minimally invasive supracondylar femoral derotational osteotomy fixed with a unilateral external fixators crossing the knee joint is a reliable procedure in CP patients. Most patients can be treated with early postoperative full weight-bearing. However, removal of the knee joint crossing fixator should be performed as early as possible to achieve a full range of motion.

The effect of diclofenac on matrix metalloproteinase levels in the rotator cuff.

INTRODUCTION: Matrix metalloproteinases (MMPs) are involved in physiological events such as restructuring of the tissue, morphogenesis, wound healing and normal developmental process. Use of diclofenac sodium following rotator cuff repair can disrupt healing of tendon through acting on MMPs. MATERIALS AND METHODS: Supraspinatus tendons of rats (n = 84) were detached from their insertion on humerus, and repaired to anatomic footprint. Rats were divided into study group (n = 42) and control group (n = 42). Study group received a dose of 1 mg/kg daily diclofenac sodium subcutaneously. The rats were killed at weeks 1, 3 and 6, and seven rats from each groups were included in biomechanical and immunohistological examinations. Immunohistological staining of MMP-2, MMP-3 and MMP13 were used. RESULTS: Maximum load was reduced in the study group at the end of week 1 (8.76 vs. 5.28 N) (p = 0.01). MMP-3 level was statistically significantly lower in the study group at the end of week 1. MMP-13 level and stiffness decreased towards week 6 in the study group while in the control group the level of MMP-2 decreased towards week 6. CONCLUSION: Diclofenac has an impact on the levels of MMP-2, MMP-3 and MMP-13, which are needed for normal healing process, and it can also lead to disruption of tendon healing.