Cadaveric Tibiae Research Articles

Paper 274: Tibial Fixation in Posterior Cruciate Ligament Reconstruction: A Biomechanical Comparison Study between Biodegradable Interference Screw and Biodegradable Cross Pin

The purpose of this study was to compare ultimate tensile load, stiffness and slippage after cyclic loading of biodegradable interference screw and biodegradable cross pin for tibial fixation in posterior cruciate ligament reconstruction. Biomechanical testing of 2 different fixation techniques was performed by use of human cadaver tibia and Achilles tendon. Two independent testing sessions were examined. The A session compared biodegradable interference screw and cross pin for Achilles bone block (10 x 30 mm). The B session compared hybrid fixation of soft tissue with the use of cancellous screw-washer in each group. The tibia-graft fixation compex was cyclically loaded between 50 N and 250 N at 1 Hz for 1000 cycles. After cycling, the amount of graft slippage was determined by measuring the change in grip to grip distance. The complex was then loaded to failure at 1mm/s, and ultimate tensile strength, stiffness, and mode of failure were determined. In session A, cross pin fixation group resulted in a significantly higher ultimate tensile strength (917.80 ± 102.4 vs 514.58 ± 148.4, p<0.01), significantly higher stiffness (302.3 ± 52.9 vs 193.5 ± 12.1, p < 0.05), and significantly less slippage (3.75 ± 1.0 mm vs 5.66 ± 0.6, p<0.001) than interference screw fixation group. In session B, cross pin fixation with additional screw group resulted in a significantly higher ultimate tensile strength (1023.75 ± 94.4 vs 816.81 ± 115.3, p<0.01), significantly higher stiffness (341.5 ± 64.9 vs 223.5 ± 38.1, p < 0.05), and less slippage (13.70 ± 1.3 mm vs 12.75 ± 1.0, p>0.05) than interference screw fixation with additional screw group. The failure mode of cross pin fixation group was pin breakage in all specimens. The failure mode of interference screw fixation group was pullout of the graft in all specimens. Our study showed that cross pin tibial fixation both bone block and soft tissue in posterior cruciate ligament reconstruction is stronger than interference screw with respect to ultimate tensile strength, stiffness, and slippage.

Preoperative estimation of tibial nail length—Because size does matter

IntroductionSelecting the correct tibial nail length is essential for satisfactory outcomes. Nails that are inserted and are found to be of inappropriate length should be removed. Accurate preoperative nail estimation has the potential to reduce intra-operative errors, operative time and radiation exposure. MethodsWe compared the most commonly used radiological, anthropometric and intra-operative techniques to determine ideal nail lengths for 16 paired cadaveric tibiae. Five different anthropometric measurements were taken from each intact cadaver including: knee joint line to ankle joint line distance (JJD), medial knee joint line to medial malleolus distance (MMD), tibial tuberosity to medial malleolus distance (TMD), olecranon to 5th metacarpal head distance (OMD) and body height (BHR). Each tibia also underwent antero–posterior (AP) and lateral scanograms. Computerised tomography was used to determine the ideal nail length for each tibia. Each anthropometric and radiological measurement was recorded by two orthopaedic surgeons independently. An expert tibial nail was then inserted after nail length estimation was performed using a guidewire technique and an intra-operative radiographic ruler. ResultsThe AP scanogram was found to be 100% accurate in selecting ideal nail length. The lateral scanogram was also found to be reasonably accurate but in 19% (3/16) of cases it led to a nail being too long. The intra-operative radiographic ruler was found to give a good indication of the ideal nail size, as did the guidewire technique, with only 6% (1/16) of cases producing an incorrect nail size. In general, the anatomical measurements gave a poor indication of ideal nail size compared with the other techniques. The following accuracies were noted: JJD 56%, MMD 50%, TMD 38%, BHR 13% and OMD 56%. ConclusionsWe found that radiological methods such as using an AP radiograph with known magnification and intra-operative radiographic ruler were able to predict nail length very accurately and we suggest that these measurements should be performed routinely. The guidewire technique was also effective but we recommend that it not be used in isolation as errors can occur. We found that anatomical measurements are not accurate for predicting tibial nail length.

A linear-actuated torsional device to replicate clinically relevant spiral fractures in long bones

To better understand the mechanisms underlying spiral fracture we would like to carry out biomechanical tests of long bones loaded in torsion to failure. A device was fabricated to perform torsional tests of long bones using a single-axis linear actuator. The principal operation of the device was to transform the vertical displacement of a material testing machine's linear actuator into rotational movement using a spur gear and rack system. Accuracy and precision of the device were quantified using cast-acrylic rods with known torque-rotation behavior. Cadaveric experimentation was used to replicate a clinically relevant spiral fracture in eleven human proximal tibiae; strain-gage data were recorded for a single specimen. The device had an experimental error of less than 0.2 Nm and was repeatable to within 0.3%. Strain gage data were in line with those expected from pure torsion and the cadaveric tibiae illustrated spiral fractures at ultimate torque and rotation values of 130.6 +/- 53.2 Nm and 8.3 +/- 1.5 degrees, respectively. Ultimate torque was highly correlated with DXA assessed bone mineral density (r = 0.87; p < 0.00 1). The device presented is applicable to any torsional testing of long bone when only a single-axis linear actuator is available.

Partial resection of the PCL insertion site during tibial preparation in cruciate-retaining TKA

Based on the anatomy of the tibial PCL insertion site, we hypothesized that at least part of it is damaged while performing a standard tibial cut in a PCL-retaining total knee replacement. The purpose of this study was to determine and quantify the amount of resection of the tibial PCL attachment with a 9 mm tibial cut with 3 degrees of posterior slope. Twenty cadaver tibias were used. The borders of the PCL footprint were demarcated, and calibrated digital pictures were taken in order to determine the surface area. A standard tibial intramedullary guide was used to prepare and perform a tibial cut at a depth of 9 mm with 3 degrees posterior slope. After the tibial cut was made, a second digital picture was taken using the same methodology to measure the surface area of the remaining PCL insertion. The mean surface area of the intact tibial PCL footprint before the cut was 148.9 ± 25.8 mm(2) and after the tibial cut 47.1 ± 28.0 mm(2). On average, 68.8 ± 15.3 % of the surface area of the PCL insertion was removed. The results of this study, therefore, indicate that the conventional technique for tibial preparation in cruciate-retaining total knee arthroplasty can result in damage or removal of a significant part of the tibial PCL insertion.

Development of an interlocked nail for segmental defects in the rabbit tibia

Previous animal models have been developed to study intramedullary nailing for challenging segmental defects in the tibia. In large animals, interlocked nail fixation created a stable environment suitable to study new bone growth technologies placed in the defect. To our knowledge, there are no comparable interlocked tibial defect models for the rabbit in which new technologies could be evaluated. Such a model would be helpful since the rabbit is a popular initial model for orthopedic research studies owing to its wide availability and low cost. While numerous studies have nailed the rabbit tibia, all were non-locked implants that allowed some degree of instability between the fracture fragments. In addition, the non-locked nails were constructed of stainless steel, whereas human nails are increasingly made from titanium alloy. In the current study, an interlocked titanium nail was developed for the rabbit tibia. It was implanted in cadaver tibiae and subjected to fatigue cycling in combined compression and bending at physiologic levels to 21,061 cycles. This duration is estimated to represent 12 weeks of gait by the animal. Before and after fatigue cycling, monotonic testing was performed in compression and bending at physiologic levels. The intact contralateral limbs served as controls. All limbs completed the cycling; the instrumented limbs exhibited interfragmentary cyclic strain amplitudes during fatigue (616 +/- 139 micro-strain), which was significantly greater than the control limbs (136 +/- 35 microstrain). Monotonic strain amplitudes for the test limbs in bending and compression were 4839 +/- 1028 and 542 +/- 122 microstrain, respectively; corresponding values for the control bones were 407 +/- 118 and 95 +/- 38 microstrain, respectively. These data are similar to those presented in prior studies in larger bone models. The current study presents one method for interlocked nail fixation for this complex tibial shaft fracture in a small animal.

Heat Generation by Two Different Saw Blades Used for Tibial Plateau Leveling Osteotomies

During tibial plateau leveling osteotomy (TPLO) the saw blade produces frictional heat. The purpose of this study was to evaluate and compare heat generated by two TPLO blade designs (Slocum Enterprises [SE] and New Generation Devices [NDG]), with or without irrigation, on cadaveric canine tibias. Thirty-six paired tibias were used to continuously measure bone temperatures during osteotomy through both cortices (i.e., the cis and trans cortices). Each pair was assigned to either an irrigation or nonirrigation group during osteotomy, and each tibia within a pair was osteotomized using a different saw blade design. Saw blade temperatures were recorded and temperatures were compared for all combinations of blade type, cortex, and irrigation. In the cis cortex group, the SE blade generated more bone heat than the NGD blade (P=0.0258). Significant differences in temperature generation between saw blade types were seen only when the osteotomy site was not irrigated (P=0.0156). For all variables measured, bone and saw blade temperature generation was lower with irrigation (P<0.05). None of the osteotomies performed with either saw blade produced a critical duration of damaging temperature ranges in this study. Although saw blade design and irrigation influence heat generation during the TPLO, the potential for bone thermal damage during TPLO is low. The use of the NGD blade with irrigation is recommended.

Evaluation of the Biofidelity of the HIII and MIL-Lx Lower Leg Surrogates Under Axial Impact Loading

Objective: Lower leg injury risk is commonly assessed using an anthropomorphic test device (ATD). The current standard leg (the HIII) has been shown to have low biofidelity due to its geometry and material properties. A new surrogate (the MIL-Lx) was developed to address these issues, specifically for anti-vehicular mine blast scenarios but with potential applications to high-force crashes in the automotive industry. Before it is adopted for use, the MIL-Lx must be evaluated under impact loading to ensure that it represents the natural lower leg response. Methods: Axial impact loads were applied to both the HIII and the MIL-Lx at impact velocities of 2 to 7 m/s using a pneumatic impacting device. Testing was also conducted with the foot removed from both surrogates to enable comparison with previous tests of isolated cadaveric tibias at noninjurious and injurious (i.e., fracture) levels. To evaluate the effect of a boot on load attenuation, the HIII was impacted with and without a hiking boot. Results: Forces in the MIL-Lx were between 25 and 100 percent of those in the HIII (depending on impact conditions). The use of a boot reduced the peak force by approximately 65 percent at the highest impact velocities. The MIL-Lx fit the data from noninjurious cadaveric tibia tests with R2 = 0.83. Conclusions: The MIL-Lx is a new surrogate that represents the response of the natural tibia under axial impact loading better than the HIII. The inclusion of a boot has a significant effect on loads in the leg and may influence injury assessment results. The MIL-Lx will be a useful tool for predicting lower leg injury risk over a wide range of impact velocities.

Mechanical Validation of Perfect Tibia 3D Model Using Computed Tomography Scan

In this paper, the Von Mises stresses and stiffnesses measured by experiments on a human cadaveric tibia and composite ones compared to those predicted by a FE model based on the same bone. Modeling of exact geometrical tibia including cortical and spongy bone using human bone CT scan images and mechanical validating of obtained model, is the aim of this study .The model produced by the current study supplies a tool for simulating mechanical test conditions on human tibia.

Cadaveric results of an accelerometer based, extramedullary navigation system for the tibial resection in total knee arthroplasty

IntroductionIn total knee arthroplasty, the accuracy and precision of the tibial resection must be improved. The purpose of this study was to determine the accuracy and time associated with the use of an accelerometer based, extramedullary surgical navigation system for performing the tibial resection. Materials and methodsFour orthopedic surgeons performed a tibial resection utilizing the KneeAlign™ system, each on five separate, cadaveric tibiae. Each surgeon was assigned a preoperative “target” of varus/valgus alignment and posterior slope prior to each resection. The alignment of each resection was measured using both plain radiographs and computed tomography, along with the time required to use the device. ResultsRegarding coronal alignment, the mean absolute difference between the preoperative “target” and tibial resection alignment was 0.77°±0.64° using plain radiograph, and 0.68°±0.46° using CT scan measurements. Regarding the posterior slope, the mean absolute difference between the preoperative “target” and the tibial resection was 1.06°±0.59° using plain radiograph, and 0.70°±0.47° using CT scan measurements. The time to use the KneeAlign™ for the fifth specimen was less than 300s for all four orthopedic surgeons in this study. DiscussionThis cadaveric study demonstrates that the KneeAlign™ system is able to accurately align the tibial resection in both the coronal and sagittal planes. Level of evidenceCadaveric study.

A novel intramedullary nail for micromotion stimulation of tibial fractures

BackgroundAnimal studies and clinical trials have suggested that early application of controlled axial micromotion can accelerate healing of long bone fractures compared to rigid fixation. However, experimental investigations of micromotion constructs have been limited to external fixators, which have a higher incidence of complications than intramedullary nails. The purpose of this study was to assess whether a novel intramedullary nail design can generate stimulatory micromotion under minimal weight-bearing loads typical of the early healing period. MethodsEight cadaver tibiae were reamed, osteotomised, and implanted with commercially-available IM nails fitted with a custom insert that allowed 1mm of axial micromotion after proximal/distal interlocking. Specimens were mounted in a materials testing machine and subjected to cyclic axial loading while interfragmentary motion was measured using an extensometer. Implants were also tested in standard statically-locked mode. FindingsThe average force required to cause distraction of the fracture gap in micromotion mode was 37.0 (SD 21.7) N. The mean construct stiffness was 1046.8 (SD 193.6) N/mm in static locking mode and 512.4 (SD 99.6) N/mm in micromotion mode (significantly different, P<0.001). InterpretationThese results support the development of a micromotion-enabled IM nail because the forces required to cause interfragmentary movements are very low, less than the weight of the hanging shank and foot. In contrast to rigid-fixation nails, which require significant weight-bearing to induce interfragmentary motion, the micromotion-enabled nail may allow movement in non-weight-bearing patients during the early healing period when the benefits of mechanical stimulation are most critical.

Angular Stability Potentially Permits Fewer Locking Screws Compared With Conventional Locking in Intramedullary Nailed Distal Tibia Fractures: A Biomechanical Study

To compare mechanical stability of angle-stable locking construct with four screws with conventional five screw locking in intramedullary nailed distal tibia fractures under cyclic loading. Ten pairs of fresh-frozen human cadaveric tibiae were intramedullary nailed and assigned to either an angle-stable locking construct consisting of four screws or conventional five-screw locking. After simulating an unstable distal two-fragmental 42-A3.1 fracture, the specimens were mechanically tested under quasistatic and cyclic sinusoidal axial and torsional loading. Bending stiffness of the angle-stable and the conventional fixation was 644.3 N/° and 416.5 N/°, respectively (P = 0.075, power 0.434). Torsional stiffness of the angle-stable locking (1.91 Nm/°) was significantly higher compared with the conventional one (1.13 Nm/°; P = 0.001, power 0.981). Torsional play of the angle-stable fixation (0.08°) was significantly smaller compared with the conventional one (0.46°; P = 0.002, power 0.965). The angle-stable locking revealed significantly less torsional deformation in the fracture gap after one cycle (0.74°) than the conventional one (1.75°; P = 0.005, power 0.915) and also after 1000 cycles (angle-stable: 1.56°; conventional: 2.51°; P = 0.042, power 0.562). Modes of failure were fracture of the distal fragment, loosening of distal locking screws, nail breakage, and their combination, equally distributed between the groups (P = 0.325). Both the angle-stable locking technique using four screws and conventional locking consisting of five screws showed high biomechanical properties. Hence, angle-stable locking reflects a potential to maintain fixation stability while reducing the number of locking screws compared with conventional locking in intramedullary nailed unstable distal tibia fractures.

Delta screw versus RetroScrew tibial fixation for ACL reconstruction

The purpose of this study is to determine whether the RetroScrew tibial fixation system offers a biomechanical advantage over the Delta screw for anterior cruciate ligament (ACL) reconstruction in cadaveric tibias with low bone mineral density (BMD). Ten matched pairs of osteoporotic cadaveric tibiae underwent simulated ACL reconstruction using quadrupled hamstring grafts with one of the two tibial fixation constructs. Group 1 was fixed with the Delta screw (DS; 35-mm antegrade biointerference screw), and group 2 was fixed with the RetroScrew system (RSS; 20-mm retrograde and 17-mm antegrade biointerference screws). Each construct was cyclically loaded (50-200 N, 1 Hz, 500 cycles) and subsequently loaded to failure (20 mm/s). All specimens were osteoporotic without significant segmental (proximal, middle, and distal) BMD differences between groups by quantitative computed tomography (P = n.s.). A trend was noted for more construct failures due to graft slippage in the DS group (n = 3) over the RSS group (n = 1). There were no significant differences in cyclic displacement (P = n.s.), maximum cyclic stiffness (P = n.s.), maximum load at failure (P = n.s.), or pullout stiffness (P = n.s.) between groups. In an osteoporotic cadaveric model, there was no significant biomechanical advantage of the RetroScrew system versus the Delta screw for tibial fixation in soft tissue graft ACL reconstruction. However, a trend toward lower graft fixation failure to cyclic loading was noted with the RetroScrew system.

A Robotic Cadaveric Flatfoot Analysis of Stance Phase

The symptomatic flatfoot deformity (pes planus with peri-talar subluxation) can be a debilitating condition. Cadaveric flatfoot models have been employed to study the etiology of the deformity, as well as invasive and noninvasive surgical treatment strategies, by evaluating bone positions. Prior cadaveric flatfoot simulators, however, have not leveraged industrial robotic technologies, which provide several advantages as compared with the previously developed custom fabricated devices. Utilizing a robotic device allows the researcher to experimentally evaluate the flatfoot model at many static instants in the gait cycle, compared with most studies, which model only one to a maximum of three instances. Furthermore, the cadaveric tibia can be statically positioned with more degrees of freedom and with a greater accuracy, and then a custom device typically allows. We created a six degree of freedom robotic cadaveric simulator and used it with a flatfoot model to quantify static bone positions at ten discrete instants over the stance phase of gait. In vivo tibial gait kinematics and ground reaction forces were averaged from ten flatfoot subjects. A fresh frozen cadaveric lower limb was dissected and mounted in the robotic gait simulator (RGS). Biomechanically realistic extrinsic tendon forces, tibial kinematics, and vertical ground reaction forces were applied to the limb. In vitro bone angular position of the tibia, calcaneus, talus, navicular, medial cuneiform, and first metatarsal were recorded between 0% and 90% of stance phase at discrete 10% increments using a retroreflective six-camera motion analysis system. The foot was conditioned flat through ligament attenuation and axial cyclic loading. Post-flat testing was repeated to study the pes planus deformity. Comparison was then made between the pre-flat and post-flat conditions. The RGS was able to recreate ten gait positions of the in vivo pes planus subjects in static increments. The in vitro vertical ground reaction force was within ± 1 standard deviation (SD) of the in vivo data. The in vitro sagittal, coronal, and transverse plane tibial kinematics were almost entirely within ± 1 SD of the in vivo data. The model showed changes consistent with the flexible flatfoot pathology including the collapse of the medial arch and abduction of the forefoot, despite unexpected hindfoot inversion. Unlike previous static flatfoot models that use simplified tibial degrees of freedom to characterize only the midpoint of the stance phase or at most three gait positions, our simulator represented the stance phase of gait with ten discrete positions and with six tibial degrees of freedom. This system has the potential to replicate foot function to permit both noninvasive and surgical treatment evaluations throughout the stance phase of gait, perhaps eliciting unknown advantages or disadvantages of these treatments at other points in the gait cycle.

Effects of Ti2448 half-pin with low elastic modulus on pin loosening in unilateral external fixation

The objective of this study was to compare the benefits of titanium 2448 (Ti2448) half-pin and titanium-6 aluminium-4 vanadium (TAV) half-pin on reducing pin loosening during external fracture fixation. Although having similar strength, Ti2448 half-pin had even lower elastic modules (33 GPa) when compared with TAV half-pin (110 GPa), which was similar to that of cortical bone (20 GPa). In the external fixation of tibial model fractures and canine cadaveric tibia fractures, Ti2448 half-pin had greater recoverable deformation and less stress concentration at the pin-bone interface in compression, torsion, and four-points bending test. Then, tibial fractures were created in 24 dogs and stabilized with four half-pins of either Ti2448 or TAV in each animal. At 4 and 8 weeks postoperatively, fracture healing and pin loosening was assessed by radiographic grading scale. The scores of Ti2448 group were significantly higher than those of TAV group. Micro-CT analysis also indicated larger quantity and higher quality of newly formed bone at pin-bone interface in Ti2448 group. Histology observation showed the newly formed bone integrated well into the threads of Ti2448 half-pins. In contrast, there was a layer of necrotic tissue between the bone tissue and TAV half-pin at pin-bone interface in TAV group. The extraction torque values of Ti2448 half-pins near the fracture line were significantly higher than those TAV pins. In conclusion, the Ti2448 half-pin with low elastic modulus could enhance osseointegration and reduce pin loosening when compared with TAV half-pin. It is a promising biomaterial for constructing external fixation system in clinical application.

Strength of the Joshi External Stabilising System

To conduct an in vitro strength test for the Joshi External Stabilising System (JESS) for stabilisation of tibial fractures using a cadaveric tibia and steel rods. The configuration of the JESS specimens was based on a 62-year-old man with a metaphyseal tibial fracture. Two types of JESS specimens were prepared, using either the tibia of an average male adult cadaver (n=1) or stainless steel cylindrical rods (n=3). The strength of the JESS rather than that of the rods was measured using a universal testing machine. The axial compressive load was gradually increased at 1 mm/min to 35 N. Axial deformation of the fracture fragment was recorded. Each experiment was repeated 3 times in identical manner. A finite element analysis of the JESS was developed. The axial compressive loads and corresponding interfragmentary displacement in the experimental specimens and in the finite element analysis were compared. The mean strength of the JESS was 32.5 N/mm in experiments and 35.3 N/mm in finite element analysis; the difference was 8.4%. The interfragmentary displacement was directly proportional to the axial compressive load. The strength of the JESS is one fourth of that of the Ilizarov fixator, and therefore not suitable for full load bearing activities.

Development of a finite element model of the tibia for short-duration high-force axial impact loading

Finite element (FE) models can allow computer simulations of impact loading, providing a useful companion to cadaveric testing. These models allow injury evaluations to be conducted under a variety of conditions, but must be validated against experimental data. An FE model of a cadaveric tibia was developed using geometry from CT scans, and the quality of the mesh was evaluated. Loading and boundary conditions from experimental tests were simulated, and the model was optimised to best represent the response of natural bone to impacts. The model was shown to have good agreement for impact force, duration, impulse and strain during simulation of three non-injurious and one injurious axial impact when compared with experimental test data for the specimen. Failure criteria were evaluated for their ability to predict fracture. This model of the tibia can be used for future injury prediction assessment studies.

Effect on Dynamic Mechanical Stability and Interfragmentary Movement of Angle-Stable Locking of Intramedullary Nails in Unstable Distal Tibia Fractures: A Biomechanical Study

Unstable distal tibia fractures are challenging injuries that require surgery. Increasingly, intramedullary nails are being used. However, fracture site anatomy may cause distal-fragment stabilization and fixation problems and lead to malunion/nonunion. We studied the influence of angle-stable nail locking on fracture gap movement and other biomechanical parameters. Eight pairs of fresh human cadaver tibiae were used. The bone mineral density (BMD) was determined. All tibiae were nailed with a Synthes Expert tibial nail. Within each pair, one tibia was randomized to receive conventional locking screws; the other, angle-stable screws with sleeves. A 7-mm osteotomy was created 10 mm above the upper distal locking screw, to simulate an AO 42-A3 fracture. Biomechanical testing involved nondestructive mediolateral and anteroposterior pure bending, followed by cyclic combined axial and torsional loading to catastrophic failure. The neutral zone was determined. Fracture gap movement was monitored with 3-D motion tracking. The angle-stable locked constructs had a significantly smaller mediolateral neutral zone (mean: 0.04 degree; p=0.039) and significantly smaller fracture gap angulation (p=0.043). The number of cycles to failure did not differ significantly between the locking configurations. BMD was a significant covariate affecting the number of cycles to failure (p=0.008). However, over the first 20,000 cycles, there was no significant correlation in the angle-stable construct. Angle-stable locking of the Expert tibial nail was associated with a significant reduction in the mediolateral neutral zone and in fracture gap movement. Angle-stable fixation also reduced the influence of BMD over the first 20,000 cycles.

A biomechanical comparison of the Delta screw and RetroScrew tibial fixation on initial intra-articular graft tension

The purpose of this study is to determine the effect of bioabsorbable interference screw (BIS) tibial fixation with the Delta screw (antegrade) and RetroScrew (retrograde) on initial (time zero) intra-articular graft tension in soft tissue anterior cruciate ligament (ACL) reconstruction in a cadaveric model. Ten matched pairs of cadaveric tibias received one of two tibial fixation constructs using quadrupled hamstring grafts, Delta screw (antegrade) or the RetroScrew (retrograde). Each specimen was mounted to the materials testing device with the displacement force vector in line with the tibial tunnel. The construct was pre-tensioned (10-30N, 0.1Hz, 10 cycles), a baseline tension of 25N was introduced, and the change in intra-articular graft tension before and after screw insertion was recorded. Segmental (proximal, middle, distal) BMD was utilized to assess BMD using quantitative computed tomography (qCT). The Delta screw had a higher maximum insertion torque (P=0.03) and exhibited a larger increase in intra-articular graft tension as compared to the RetroScrew (38.3±17.9N, 7.6N±14.4, P=0.004), respectively. There were no significant correlations between intra-articular graft tension increase to maximum insertion torque (P=NS) or corresponding segmental BMD (P=NS). Delta screw tibial fixation (antegrade) in soft tissue ACL reconstruction significantly increases the initial intra-articular graft tension as compared to RetroScrew screw fixation (retrograde) in this cadaveric model. Delta screw (antegrade) tibial fixation may increase initial quadrupled hamstring graft intra-articular tension with currently accepted insertion techniques.

Modification of the cranial closing wedge ostectomy technique for the treatment of canine cruciate disease

To describe a modification of the cranial closing wedge ostectomy (CCWO) technique and to compare its efficacy to the standard technique on cadaveric specimens. The standard and modified CCWO technique were applied to eight pairs of cadaveric tibiae. The following parameters were compared following the ostectomy: degrees of plateau levelling achieved (degrees), tibial long axis shift (degrees), reduction in tibial length (mm), area of bone wedge removed (cm²), and the area of proximal fragment (cm²). The size of the removed wedge of bone and the reduction in tibial length were significantly less with the modified CCWO technique. The modified CCWO has two main advantages. Firstly a smaller wedge is removed, allowing a greater preservation of bone stock in the proximal tibia, which is advantageous for implant placement. Secondly, the tibia is shortened to a lesser degree, which might reduce the risk of recurvatum, fibular fracture and patella desmitis. These factors are particularly propitious for the application of this technique to Terrier breeds with excessive tibial plateau angle, where large angular corrections are required. The modified CCWO is equally effective for plateau levelling and results in an equivalent tibial long-axis shift. A disadvantage with the modified technique is that not all of the cross sectional area of the distal fragment contributes to load sharing at the osteotomy.

Injury Tolerance Criteria for Short-Duration Axial Impulse Loading of the Isolated Tibia

Impulse loading of the lower leg during events such as ejection seat landings or in-vehicle land mine blasts may result in devastating injuries. These impacts achieve higher forces over shorter durations than car crashes, from which experimental results have formed the current basis for protective measures of an axial force limit of 5.4 kN, as registered by an anthropomorphic test device (ATD). The hypotheses of this study were that the injury tolerance of the isolated tibia to short-duration axial loading is higher than that previously reported and that secondary parameters such as momentum or kinetic energy are significant for fracture tolerance, in addition to force. Seven pairs of cadaveric tibias were impacted using a pneumatic testing apparatus, replicating short-duration axial impulse events. One specimen from each pair was impacted with a light mass and the contralateral impacted with a heavy mass, to investigate the effects of momentum and kinetic energy, as well as force, on injury. Impacts were applied incrementally until failure. Force, kinetic energy, age, and height were shown to be significant factors in the probability of fracture. A 10% risk of injury corresponded to an impact force of 7.9 kN, with an average kinetic energy of 240 J. In comparison, this same impact level applied to an ATD would register a force of 16.2 kN because of the higher stiffness of the ATD. These results suggest that the current injury standard may be too conservative for the tibia during high-speed impacts such as in-vehicle land mine blasts and that factors in addition to force should be taken into consideration.