Bora Uzun

Subtrochanteric shortening in total hip arthroplasty: biomechanical comparison of four techniques.

Safe reduction of the femoral head into the true acetabulum requires a certain amount of femoral shortening in patients with high dislocation of the hip. In subtrochanteric shortening applications, to reduce complications it is necessary to maintain a stable fixation at the osteotomy line. The purpose of this study is to investigate frequently used methods from a biomechanical point of view. Four osteotomy groups were created with composite femurs to investigate subtrochanteric osteotomies; transverse, oblique, z-subtrochanteric and double Chevron. All loading tests were carried out with two implant types both with and without strut graft and cable fixation. No single inherent feature increasing the stability of the investigated osteotomy types was found. Additionally graft application did not have a significant contribution to stability.

Which is the best fixation method for lateral cortex disruption in the medial open wedge high tibial osteotomy? A biomechanical study.

When performing a medial opening wedge upper tibial osteotomy, a fracture into the lateral cortex can lead to loss of stability of the construct. The aim of this study was to assess different intra-operative techniques to overcome this problem, and test the stability under axial compression. Twenty eight calf tibias had a medial opening wedge osteotomy and lateral cortical fracture created and then were tested in four groups depending on how this fracture was fixed; none, a plate and screws, two staples, and a circular external fixator. Loss of medial height of the osteotomy line and lateral cortex micromotion was evaluated under maximal axial loading of 2,500 N. No fixation had significantly inferior results compared with the other three types. The plate and screws and staples showed better results than circular external fixation in terms of preserving the medial height, whereas the plate and screws and circular external fixator showed better results compared with staples in terms of lateral cortex stability. This study suggests that plate and screw fixation for lateral cortex disruption during the medial opening wedge upper tibial osteotomy has better stability under axial compression than staples or a circular external fixator.

Biomechanical evaluation of different internal fixation methods for humerus shaft fractures with medial butterfly fragment

OBJECTIVE The aim of this study was to compare the biomechanical strength of three fixation methods in humerus shaft fractures with medial butterfly fragment. METHODS An AO 12B2 fracture with butterfly fragment was created in 21 synthetic cortical shell humeri. Humeri were divided into 3 groups which underwent bridge plating, antegrade intramedullary nailing or retrograde intramedullary nailing. Rotational and four-point bending test displacement curves were obtained. RESULTS Mean displacement values in the torsion tests were 37.38 (range: 25.75 to 55.69) mm in the bridge plating group, 26.55 (range: 21.25 to 41.81) mm in the antegrade nailing group, and 33.23 (range: 27.50 to 46.45) mm in the retrograde nailing group. Mean displacement values in the four-point bending test were 3.27 (range: 2.54 to 3.73) mm in the bridge plating group, 3.17 (range: 2.69 to 3.55) mm in the antegrade nailing group, and 3.15 (range: 2.10 to 4.03) mm in the retrograde nailing group. No significant difference was found among the groups (p>0.05). CONCLUSION The biomechanical stability of bridge plating, antegrade intramedullary nailing and retrograde intramedullary nailing appears to be similar in the fixation of humerus shaft fractures with medial butterfly fragment.

Straight-Forward versus Bicortical Fixation Penetrating Endplate in Lumbosacral Fixation-A Biomechanical Study

Objective Many lumbosacral fixation techniques have been described to offer a more screw-bone purchase. The forward anatomical fixation parallel to the endplate is still the most preferred method. Literature revealed little knowledge regarding the mechanical stability of lumbosacral trans-endplate fixation compared to the traditional trans-pedicular screw fixation method. The aim of this study is to assess the pull-out strength of lumbosacral screws penetrating the end plate and comparing it to the conventional trans-pedicular screw insertion method. Methods Eight lumbar and eight sacral vertebrae, with average age 69.4 years, Left pedicles of the 5th lumbar vertebrae were used for trans-endplate screw fixation, group 1A, right pedicles were used for anatomical trans-pedicular screw fixation, group 1B. In the sacral vertebrae, the right side S1 pedicles were used for trans-endplate fixation, group 2A, left side pedicles were used for anatomical trans-pedicular screw fixation, group 2B. The biomechanical tests were performed using the axial compression testing machine. All tests were applied using 2 mm/min traction speed. Results The average pull-out strength values of groups 1A and 1B were 403.78±11.71 N and 306.26±17.55 N, respectively. A statistical significance was detected with p=0.012. The average pull-out strength values of groups 2A and 2B were 388.73±17.03 N and 299.84±17.52 N, respectively. A statistical significance was detected with p=0.012. Conclusion The trans-endplate lumbosacral fixation method is a trustable fixation method with a stronger screw-bone purchase and offer a good alternative for surgeons specially in patients with osteoporosis.

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.

Central defect type partial ACL injury model on goat knees: the effect of infrapatellar fat pad excision

BackgroundThe mid-substance central defect injury has been used to investigate the primary healing capacity of the anterior cruciate ligament (ACL) in a goat model. The sagittal plane stability on this model has not been confirmed, and possible effects of fat pad excision on healing have not been evaluated. We hypothesize that excising the fat pad tissue results in poorer ligament healing as assessed histologically and decreased tensile strength of the healing ligament. We further hypothesize that the creation of a central defect does not affect sagittal plane knee stability.MethodsA mid-substance central defect was created with a 4-mm arthroscopic punch in the ACLs of right knees of all the subjects through a medial mini-arthrotomy. Goats were assigned to groups based on whether the fat pad was preserved (group 1, n = 5) or excised completely (group 2, n = 5). The left knees served as controls in each goat. Histopathology of the defect area along with measurement of type I collagen in one goat from each group were performed at 10th week postoperatively. The remaining knees were evaluated biomechanically at the 12th week, by measuring anterior tibial translation (ATT) of the knee joints at 90° of flexion and testing tensile properties (ultimate tensile load (UTL), ultimate elongation (UE), stiffness (S), failure mode (FM)) of the femur-ACL-tibia complex.Results and discussionHistopathology analysis revealed that the central defect area was fully filled macroscopically and microscopically. However, myxoid degeneration and fibrosis were observed in group 2 and increased collagen type I content was noted in group 2. There were no significant differences within and between groups in terms of ATT values (p = 0.715 and p = 0.149, respectively). There were no significance between or within groups in terms of ultimate tensile load and ultimate elongation; however, group 2 demonstrated greater stiffness than group 1 that was correlated with the fibrotic changes detected microscopically (p = 0.043).ConclusionsThe central defect type injury model was confirmed to be biomechanically stable in a goat model. Resection of the fat pad was noted to negatively affect defect healing and increase ligament stiffness in the central defect injury model.

Extendable intramedullary nail with mechanical loading

There are various extremity lengthening methods in the literature. Lentghening with intramedullary nails is also important method which is emphasized recent years. In this study, in the light of previous studies, it is aimed to develop a new expandable intramedullary system providing lengthening in order to remove previous problems and complications and to annihilate leg length discrepancies at present and future without second surgical intervention as far as possibble by lenghtening the intramedullary nail.