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Previous studies have shown that reconstructive surgery alone following injury to the anterior cruciate ligament (ACL) does not prevent the development of post-traumatic osteoarthritis (PTOA). Poloxamer 188 (P188) has been shown to prevent cell death following trauma in both articular cartilage and meniscal tissue. This study aims to test the efficacy of single or multiple administrations of P188 in conjunction with reconstructive surgery to help prevent or delay the onset of the disease. Thirty skeletally mature rabbits underwent closed-joint trauma that resulted in ACL rupture and meniscal damage and were randomly assigned to one of four treatment groups with varying doses of P188. ACL reconstruction was then performed using an autograft from the semitendinosus tendon. Animals were euthanized 1-month following trauma, meniscal tissue was assessed for changes in morphology, mechanical properties, and proteoglycan content. Femurs and tibias were scanned using microcomputed tomography to determine changes in bone quality, architecture, and osteophyte formation. The medial meniscus experienced more damage and a decrease in the instantaneous modulus regardless of treatment group, while P188 treatment tended to limit degenerative changes in the lateral meniscus. Both lateral and medial menisci had documented decreases in the equilibrium modulus and inconsistent changes in proteoglycan content. Minimal changes were documented in the tibias and femurs, with the only significant change being the formation of osteophytes in both bones regardless of treatment group. The data suggest that P188 was able to limit some degenerative changes in the meniscus associated with PTOA and may warrant future studies.

Post-traumatic osteoarthritis (PTOA) of the knee is often attributed to anterior cruciate ligament (ACL) and meniscus injury. The development of PTOA, however, does not seem to depend on whether or not the damaged ACL is reconstructed. There has been a need to develop animal models to study the mechanisms of PTOA following reconstruction of a traumatized knee. Eighteen rabbits underwent closed-joint trauma to produce ACL rupture and meniscus damage. Then, for the first time, the traumatized knee was surgically repaired in this animal model. Upon euthanasia at 1-, 3- or 6-month post-trauma, joint stability, cartilage morphology and mechanical properties, as well as histology of the cartilage and subchondral bone were evaluated. Trauma-induced knee injury involved 72% mid-substance ACL rupture, 28% partial ACL tear and 56% concurrent medial meniscal damage. ACL reconstruction effectively restored joint stability by reducing joint laxity to a level similar to that in the contralateral intact knee. Compared to their contralateral controls, reconstructed limbs showed osteoarthritic changes to the cartilage and subchondral bone as early as 1-month post-trauma. The degeneration progressed over time up to 6-month. Overall, the medial compartments had more tissue damage than their corresponding lateral counterparts. Damage patterns to the ACL, the frequency of observed concurrent meniscal injury, and reductions in cartilage integrity and health were consistent with clinical observations of human patients who undergo ACL injury and reconstruction. Thus, we believe the combined closed-joint injury and surgical repair lapine model of PTOA, being first-ever and clinically relevant, shows promise to evaluate well-targeted therapeutics and other interventions for this chronic disease.

Knowing the ground reaction forces (GRFs) during walking has various biomechanical applications in injury prevention, gait analysis, as well as prosthetic and footwear design. The current study presents a method for predicting the GRFs in level and incline/decline walking that may be used in various outdoor biomechanics studies geared towards the above applications. The method was developed to predict the complete set of GRFs at walking inclinations of 0°, ±5°, ±10°, ±15°, and ±20°. Plantar pressure insoles were used to obtain inclination-specific, linear regression models based on three periods of gait stance phase, and the model-determined GRFs were compared with those measured from a forceplate. The three periods were determined based on the observed shifting of load-bearing insole sensors from heel to forefoot during walking, i.e., heel-strike, midstance, and toe-off. Six subjects wearing minimalist shoes fitted with plantar pressure insoles containing 99 pressure sensors performed ten walking trials at each of the aforementioned inclinations on an adjustable ramp with an embedded forceplate. Data from contact of the instrumented shoes with the forceplate were used to create linear regressions to transform insole pressure data into a complete set of GRFs. The root mean square error (RMSE) over peak recorded values were on average 10%, 3%, 21% for level walking and 11%, 4%, 23% for ramp walking in the respective anteroposterior, vertical, and mediolateral directions. The multistage linear regression model developed in the current study may be an acceptable option for estimating GRFs during walking in various environments without the restraint of a forceplate.

Despite reconstruction surgery to repair a torn anterior cruciate ligament (ACL), patients often still show signs of post-traumatic osteoarthritis (PTOA) years following the procedure. The goal of this study was to document changes in the meniscus and subchondral bone due to closed-joint impact and surgical reconstruction in a lapine model. Animals received insult to the joint followed by surgical reconstruction of the ACL and partial meniscectomy. Following euthanasia of the animals at 1, 3, and 6-months post-impact, meniscal tissue was assessed for changes in morphology, mechanical properties and proteoglycan content. Femurs and tibias were scanned via micro-computed tomography to determine changes in bone quality, morphometry, and formation of osteophytes. Both the lateral and medial menisci showed severe degradation and tearing at all-time points, with higher degree of degeneration being observed at 6-months. Decreases in both the instantaneous and equilibrium modulus were documented in both menisci. Minimal changes were found in bone quality and morphometry, with most change documented in the tibia. Bones from the reconstructed limbs showed large volumes of osteophyte formations, with an increase in volume over time. The initial changes that were representative of PTOA may have been limited to the meniscus, but at later time points consistent changes due to the disease were seen in both tissues. This study, which builds on a previous study by this laboratory, suggests that the addition of surgical reconstruction of the ACL to our model was not sufficient to prevent the development of PTOA.

This study was aimed at analyzing bone properties of Lohmann White hens in different commercial housing systems at various points throughout production. Pullets reared in conventional cages (CC) were either continued in CC or moved to enriched colony cages (EN) at 19 weeks. Pullets reared in cage-free aviaries (AV) were moved to AV hen houses. Bone samples were collected from 60 hens at each of 18 and 72 wk and 30 hens at 26 and 56 wk from each housing system. Left tibiae and humeri were broken under uniform bending to analyze mechanical properties. Cortical geometry was analyzed using digital calipers at the fracture site. Contralateral tibiae and humeri were used for measurement of ash percentage. AV pullets' humeri had 41% greater cortical areas, and tibiae had 19% greater cortical areas than the CC pullets (P < 0.05). Average humeri diameter was greater in AV pullets than in CC pullets (P < 0.05), whereas the tibiae outer dimensions were similar. Aviary pullet bones had greater stiffness (31 and 7% greater for tibiae and humeri, respectively) and second moment of inertia (43 and 13% greater for tibiae and humeri, respectively) than CC pullets (P < 0.05). The differences between bones of AV and CC hens persisted throughout the laying cycle. Moving CC pullets to EN resulted in decreased endosteal resorption in humeri, evident by a 7.5% greater cortical area in the EN hens (P < 0.05). Whole-bone breaking strength did not change with age. Stiffness increased with age, while energy to failure decreased in both the tibiae and humeri. These results indicated that tibiae and humeri of laying hens become stiffer but lose toughness and become brittle with age. Furthermore, AV and EN systems can bring positive changes in mechanical and structural properties that are more pronounced in the humerus than the tibia.

Objective To determine the efficacy of single and multiple administrations of Poloxamer 188 (P188) in saving meniscal cells following an injurious impact. Methods Meniscal explants were harvested from both the lateral and medial menisci of Flemish Giant rabbits. After a 24-h incubation period, explants were subjected to 50% impact strain to simulate traumatic joint injury, and the explants were then placed in media with or without supplemented P188. Temporal administrations of P188 over a 14-day period were given based on one of 6 different treatments regimes. Over the 14-day period, explants were cyclically loaded to 10% strain at 1 Hz for 1 h per day, five days a week. Cell viability was assessed on day 14, with the remainder of the tissue being fixed to determine cell apoptosis levels and proteoglycan changes via histology. Results The injurious impact proved to produce significant levels of cell death in meniscal explants. The ability of P188 to prevent cell death was not affected by the number of P188 doses (single versus multiple). P188 treatment proved to maintain cell viability levels comparable to those from unimpacted explants. There were no significant changes in cell apoptosis or proteoglycan coverage in the tissues over a 14-day period for any group, all treatment groups were statistically similar to the unimpacted explants. Conclusion A single dose of P188 following impact is all that is necessary to inhibit cell death in the meniscus following a traumatic impact. Thus, orthopaedic surgeons may choose to administer P188 in addition to treating any other acute damage due to a traumatic load to the knee, such as anterior cruciate ligament rupture, although more in depth in vivo studies are necessary.

The rotational stiffness of footwear has been previously shown to have an effect on ankle kinematics and injury risk, but this relationship has not yet been modeled. The aim of this study was to derive equations from experimental data that were able to predict ankle kinematics under various torsional stiffness constraints and use these equations to estimate ligament strains. Three athletic tapes were tested for their ability to constrain the ankle during external rotation. Six subjects then performed a voluntary external foot rotation using the selected tape designs to constrain the ankle, as well as with no constraints. The motion of the calcaneus with respect to the tibia (tibiocalcaneal motion) from 0° to 15° of tibia rotation and predictive equations were determined to establish tibiocalcaneal rotation, eversion, and flexion as a function of gross tibia motion and tape stiffness. These predictive equations were then used to drive a computational model in which ankle ligament strains were determined at 15° of tibia rotation and for ankle constraint stiffness ranging from 0 to 30 N m/deg. The three tapes provided significantly different constraint stiffnesses during external foot rotation. There was no statistical effect of ankle constraint on the dorsiflexion response of the ankle (p = 0.461). In contrast, there was an effect of constraint stiffness on tibiocalcaneal external rotation (p

The objective of this study was to compare longitudinal results from two models of combined anterior cruciate ligament (ACL) and meniscal injury. A modified ACL transection (mACLT) model and a traumatic impact (ACLF) model were used to create an ACL rupture and acute meniscal damage in a Flemish Giant animal model. The animals were euthanized at time points of 4, 8, or 12 weeks. The menisci were assessed for equilibrium and instantaneous compressive modulus, as well as glycosaminoglycan (GAG) coverage. The articular cartilage was mechanically assessed for thickness, matrix modulus, fiber modulus, and permeability. Articular cartilage GAG coverage, fissuring, tidemark integrity, and subchondral bone thickness were measured. Both models resulted in damage indicative of osteoarthritis, including decreased meniscal mechanics and GAG coverage, increased permeability and fissuring of articular cartilage, and decreased GAG coverage. The mACLT model had an early and lasting effect on the menisci mechanics and GAG coverage, while cartilage damage was not significantly affected until 12 weeks. The ACLF model resulted in an earlier change of articular cartilage GAG coverage and fissuring in both the 8 and 12 week groups. The menisci were only significantly affected at the 12 week time point in the ACLF model. We concluded the progression of post traumatic osteoarthritis was dependent on injury modality: a point to be considered in future investigations. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:486-495, 2017.

Osteoporosis in caged hens is one driving factor for the United States egg industry to explore options regarding alternative housing systems for laying hens. The aim of our research was to study the influence of housing systems on tibiae and humeri of 77-week-old Lohmann White hens. Pullets raised in an aviary system were either continued in aviary hen systems (AV) or conventional cages (AC) whereas pullets reared in conventional cages continued in conventional hen cages (CC) or enriched colony cages (EN) at 19 weeks. From each group, 120 hens were randomly euthanized and right and left tibae and humeri were excised for structural and mechanical analysis. Volumetric density of the cortical bone was measured using quantitative computed tomography (QCT). Aviary (AV) hens had greater cortical thickness and density but similar outer dimensions to AC hens (P < 0.05). Hens in EN system had humeri with similar cortical thickness and density but wider outer dimensions than the humeri of CC hens (P < 0.05). Cortical geometry of the tibiae was the same for the EN and CC hens, whereas EN hens had denser tibial cortex than CC hens (P < 0.05). Geometrical changes in the humeri suggest that hens in the AV system were better able to protect their structure from endosteal resorption during the laying phase. Humeri of AV and EN hens had increased second moment of area compared to the AC and CC hens; however, the changes were not observed in tibiae. Mechanical property differences were observed, with bones of AV hens having greater failure moment and stiffness than AC hens and the same difference was observed between the EN and CC hens, (P < 0.05). These findings indicate that movement limitation causes loss of bone mass and density whereas provision of moderate movement increases certain bone quality parameters during adulthood in laying hens.

Objective Long bone fractures are a common injury in the pediatric population. Differentiation between abusive, or non-accidental trauma, and accidental trauma in children remains challenging for forensic practitioners. A recent clinical-based study was able to separate pediatric abusive from accidental trauma based on femoral fracture pattern using the ratio of fracture length over bone diameter (fracture ratio), as determined from radiographic analysis of this fractured bone. The forensic literature indicates more cases of abuse in younger pediatric victims than accidental cases. While this was the case in the clinical study, the effect was not shown to be statistically significant. Furthermore, while speed of trauma was not considered in the clinical study, a laboratory study with an immature bovine model indicates rotational speed influences fracture pattern, but specimen age was not varied in that study. Therefore, the objective of the current study was to use immature porcine femora to investigate the effects of age and rate of twist on a modified version of this fracture ratio parameter. Methods Fifteen pairs of porcine femora with various ages were twisted until observable failure using a custom-built torsional fixture. The left femur of each pair was twisted to failure at a rate of 3 deg/s, while the right femur was twisted at a rate of 90 deg/s. The torque and angle of rotation were recorded at a sampling rate of 10,000 Hz. Fracture ratio was defined as total fracture length divided by bone diameter. Results Fracture ratio increased with specimen age, with specimens under the low rate of twist yielding a consistently lower fracture ratio than those from specimens under the high rate of twist. The results showed that both specimen age and rate of twist were significant factors influencing fracture ratio. Conclusion The determination of abusive from accidental trauma in criminal cases, based on the pattern of long bone fracture alone, may need to include additional data on the specific age of the pediatric victim and the potential speed of the traumatic event.

Post-traumatic osteoarthritis (PTOA) develops as a result of traumatic loading that causes tears of the soft tissues in the knee. A modified transection model, where the anterior cruciate ligament (ACL) and both menisci were transected, was used on skeletally mature Flemish Giant rabbits. Gross morphological assessments, elastic moduli, and glycosaminoglycan (GAG) coverage of the menisci were determined to quantify the amount of tissue damage 12 weeks post injury. This study is one of the first to monitor meniscal changes after inducing combined meniscal and ACL transections. A decrease in elastic moduli as well as a decrease in GAG coverage was seen.

Eversion prior to excessive external foot rotation has been shown to predispose the anterior tibiofibular ligament (ATiFL) to failure, yet protect the anterior deltoid ligament (ADL) from failure despite high levels of foot rotation. The purpose of the current study was to measure the rotations of both the subtalar and talocrural joints during foot external rotation at sub-failure levels in either a neutral or a pre-everted position as a first step towards understanding the mechanisms of injury in previous studies. Fourteen (seven pairs) cadaver lower extremities were externally rotated 20° in either a pre-everted or neutral configuration, without producing injury. Motion capture was performed to track the tibia, talus, and calcaneus motions, and a joint coordinate system was used to analyze motions of the two joints. While talocrural joint rotation was greater in the neutral ankle (13.3±2.0° versus 10.5±2.7°, p=0.006), subtalar joint rotation was greater in the pre-everted ankle (2.4±1.9° versus 1.1±1.0°, p=0.014). Overall, the talocrural joint rotated more than the subtalar joint (11.9±2.8° versus 1.8±1.6°, p

Subchondral bone is thought to play a significant role in the initiation and progression of the post-traumatic osteoarthritis. The goal of this study was to document changes in tibial and femoral subchondral bone that occur as a result of two lapine models of anterior cruciate ligament injury, a modified ACL transection model and a closed-joint traumatic compressive impact model. Twelve weeks post-injury bones were scanned via micro-computed tomography. The subchondral bone of injured limbs from both models showed decreases in bone volume and bone mineral density. Surgical transection animals showed significant bone changes primarily in the medial hemijoint of femurs and tibias, while significant changes were noted in both the medial and lateral hemijoints of both bones for traumatic impact animals. It is believed that subchondral bone changes in the medial hemijoint were likely caused by compromised soft tissue structures seen in both models. Subchondral bone changes in the lateral hemijoint of traumatic impact animals are thought to be due to transmission of the compressive impact force through the joint. The joint-wide bone changes shown in the traumatic impact model were similar to clinical findings from studies investigating the progression of osteoarthritis in humans. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1835–1845, 2015.

Traumatic injury to the knee leads to the development of posttraumatic osteoarthritis. The objective of this study was to characterize the effects of a single intra-articular injection of a non-ionic surfactant, Poloxamer 188 (P188), in preservation of meniscal tissue following trauma through maintenance of meniscal glycosaminoglycan (GAG) content and mechanical properties. Flemish Giant rabbits were subjected to a closed knee joint, traumatic compressive impact with the joint constrained to prevent anterior tibial translation. The contralateral limb served as an un-impacted control. Six animals (treated) received an injection of P188 in phosphate buffered saline (PBS) post trauma, and another six animals (sham) received a single injection of PBS to the impacted limb. Histological analyses for GAG was determined 6 weeks post trauma, and functional outcomes were assessed using stress relaxation micro-indentation. The impacted limbs of the sham group demonstrated a significant decrease in meniscal GAG coverage compared to non-impacted limbs (p < 0.05). GAG coverage of the impacted P188 treated limbs was not significantly different than contralateral non-impacted limbs in all regions except the medial anterior (p < 0.05). No significant changes were documented in mechanics for either the sham or treated groups compared to their respective control limbs. This suggests that a single intra-articular injection of P188 shows promise in prevention of trauma induced GAG loss.

Alternative housing systems for laying hens provide mechanical loading and help reduce bone loss. Moreover, achieving greater peak bone mass during pullet phase can be crucial to prevent fractures in the production period. The aim of this study was to determine the housing system effects on bone quality of pullets. Tibiae and humeri of White Leghorn pullets reared in conventional cages (CCs) and a cage-free aviary (AV) system were studied. At 16 wk, 120 birds at random from each housing system were euthanized. Right and left tibiae and humeri were collected and further analyzed. Cortical bone density and thickness were measured using computed tomography. Periosteal and endosteal dimensions were measured at the fracture site during mechanical testing. At 4, 8, 12, and 16 wk, serum concentrations of osteocalcin and hydroxylysyl pyridinoline were analyzed as markers of bone formation and resorption. Cortical bone density was higher (P

SummaryObjective: To compare the bending properties of String-of-Pearls® (SOP) and Limited Contact Dynamic Compression Plate® (LCDCP) constructs in orthogonal bending directions.Methods: 3.5 mm SOP and LC-DCP plates were fixed to a bone model simulating a comminuted tibial fracture. Specimens were non-destructively tested in both mediolateral and craniocaudal bending for 10 cycles. Bending stiffness and total angular deformation were compared using parametric analyses (p Results: For both constructs, stiffness was significantly less when bending moments were applied against the thickness of the plates (mediolateral bending) than against the width (craniocaudal bending). When compared to the mediolateral plane, bending constructs in the craniocaudal plane resulted in a 49% (SOP group) and 370% (LC-DCP group) increase in stiffness (p Clinical significance: This study found that SOP showed less variability between the orthogonal bending directions than LC-DCP in a comminuted fracture model, and also described the bi-planar bending behaviour of both constructs. Although not exhibiting identical bending properties in both planes, SOP constructs had a more homogenous bending behaviour in orthogonal loading directions. The difference between the SOP with a circular cross sectional shape compared to the rectangular shape of standard plates is probably responsible for this difference.

Objective To compare clinical outcome and callus biomechanical properties of a novel angle stable interlocking nail (AS-ILN) and a 6 mm bolted standard ILN (ILN6b) in a canine tibial fracture model. Study design Experimental in vivo study. Animals Purpose-bred hounds (n = 11). Methods A 5 mm mid-diaphyseal tibial ostectomy was stabilized with an AS-ILN (n = 6) or an ILN6b (n = 5). Orthopedic examinations and radiographs were performed every other week until clinical union (18 weeks). Paired tibiae were tested in torsion until failure. Callus torsional strength and toughness were statistically compared and failure mode described. Total and cortical callus volumes were computed and statistically compared from CT slices of the original ostectomy gap. Statistical significance was set at P

This study presents a method to determine stiffness of the human ankle in internal–external rotation, inversion–eversion,and plantarflexion–dorsiflexion during an in vivo, single-legged, external foot rotation experiment. Five young male sub-jects stood on one foot and performed an internal rotation of the body (external rotation of the foot) on a force plate,while motions were captured with a motion capture system. Hindfoot rotations relative to the tibia and resistivemoments in the above three directions were obtained using a commercial software package. The resistive moments wereplotted against rotation during the loading portions of the curves. Linear approximations of these curves were used todetermine stiffness of the ankle in directions of internal–external, inversion–eversion, and plantarflexion–dorsiflexion.Future data from the above experiment and other athletic motions may be useful for the design of surrogate devices usedto evaluate the potential performance and ankle injury risk characteristics of various shoe–surface interfaces.KeywordsHigh ankle sprain, motion analysis, surrogate testing, shoe–surface interfaces, joint moment

Excessive rotational traction between the foot and the playing surface has been shown to increase the risk of athletic injuries to ligaments in the knee and ankle. It is not currently feasible to accurately determine the free torque generated at the shoe–surface interface utilizing live participants without an embedded force plate. The goal of the current research was to predict the free torques that developed at the shoe–surface interface during voluntary internal and external rotations of the body relative to a planted foot using an insole pressure measurement system. Six participants fitted with a shoe containing an insole pressure measurement device performed trials on an embedded force plate. A pressure sensor mask of specific sensors was determined based on the degree of linear correlation between sensor pressure and the free torque. Linear regression analyses were utilized to develop a General Linear Regression Model and Participant-Specific Linear Regression Models. The results of this study indicated that insole pressure technology, in conjunction with linear regression models, can be utilized to predict free torques generated at the shoe–surface interface during isolated rotational motions of the body with respect to a planted foot. Furthermore, Participant-Specific Linear Regression models may be more accurate in these predictions than a general model, based on a group of participants. When used with computational modeling, this technique might allow the investigation of strains produced in ligaments of the ankle and knee that are generated during internal and external rotations of the body with a planted foot on various turf surfaces outside a laboratory setting.

In many forensic cases, the job of forensic pathologists and anthropologists is to determine whether pediatric death is due to an abusive act or an accidental fall. The goal of this study was to compare the cranial fracture patterns generated on the parietal bone of a developing, infant porcine (pig, Sus scrofa) model by a controlled energy head drop onto a plate versus previous data generated by blunt force impact at the same energy onto the head constrained to a plate. The results showed that blunt force impacts on a head constrained to a rigid plate produces more fracture, but the same general pattern, as that for a head dropped onto the plate with the same level of impact energy. The study suggests that head constraint may be an important factor to consider in the evaluation of death causation for blunt force impacts to the pediatric skull.

Summary Objective The objective of this study was to monitor the progression of joint damage in two animal models of knee joint trauma using two non-invasive, clinically available imaging modalities. Methods A 3-T clinical magnet and micro-computed tomography (μCT) was used to document changes immediately following injury (acute) and post-injury (chronic) at time points of 4, 8, or 12 weeks. Joint damage was recorded at dissection and compared to the chronic magnetic resonance imaging (MRI) record. Fifteen Flemish Giant rabbits were subjected to a single tibiofemoral compressive impact (ACLF), and 18 underwent a combination of anterior cruciate ligament (ACL) and meniscal transection (mACLT). Results All ACLF animals experienced ACL rupture, and 13 also experienced acute meniscal damage. All ACLF and mACLT animals showed meniscal and articular cartilage damages at dissection. Meniscal damage was documented as early as 4 weeks and worsened in 87% of the ACLF animals and 71% of the mACLT animals. Acute cartilage damage also developed further and increased in occurrence with time in both models. A progressive decrease in bone quantity and quality was documented in both models. The MRI data closely aligned with dissection notes suggesting this clinical tool may be a non-invasive method for documenting joint damage in lapine models of knee joint trauma. Conclusions The study investigates the acute to chronic progression of meniscal and cartilage damage at various time points, and chronic changes to the underlying bone in two models of posttraumatic osteoarthritis (PTOA), and highlights the dependency of the model on the location, type, and progression of damage over time.

This review was prepared for the American Society of Mechanical Engineers Lissner Medal. It specifically discusses research performed in the Orthopaedic Biomechanics Laboratories on pediatric cranial bone mechanics and patterns of fracture in collaboration with the Forensic Anthropology Laboratory at Michigan State University. Cranial fractures are often an important element seen by forensic anthropologists during the investigation of pediatric trauma cases litigated in courts. While forensic anthropologists and forensic biomechanists are often called on to testify in these cases, there is little basic science developed in support of their testimony. The following is a review of studies conducted in the above laboratories and supported by the National Institute of Justice to begin an understanding of the mechanics and patterns of pediatric cranial bone fracture. With the lack of human pediatric specimens, the studies utilize an immature porcine model. Because much case evidence involves cranial bone fracture, the studies described below focus on determining input loading based on the resultant bone fracture pattern. The studies involve impact to the parietal bone, the most often fractured cranial bone, and begin with experiments on entrapped heads, progressing to those involving free-falling heads. The studies involve head drops onto different types and shapes of interfaces with variations of impact energy. The studies show linear fractures initiating from sutural boundaries, away from the impact site, for flat surface impacts, in contrast to depressed fractures for more focal impacts. The results have been incorporated into a “Fracture Printing Interface (FPI),” using machine learning and pattern recognition algorithms. The interface has been used to help interpret mechanisms of injury in pediatric death cases collected from medical examiner offices. The ultimate aim of this program of study is to develop a “Human Fracture Printing Interface” that can be used by forensic investigators in determining mechanisms of pediatric cranial bone fracture.

The goal of the current study was to expand on previous work to validate the use of pressure insole technology in conjunction with linear regression models to predict the free torque at the shoe-surface interface that is generated while wearing different athletic shoes. Three distinctly different shoe designs were utilised. The stiffness of each shoe was determined with a material's testing machine. Six participants wore each shoe that was fitted with an insole pressure measurement device and performed rotation trials on an embedded force plate. A pressure sensor mask was constructed from those sensors having a high linear correlation with free torque values. Linear regression models were developed to predict free torques from these pressure sensor data. The models were able to accurately predict their own free torque well (RMS error 3.72 ± 0.74 Nm), but not that of the other shoes (RMS error 10.43 ± 3.79 Nm). Models performing self-prediction were also able to measure differences in shoe stiffness. The results of the current study showed the need for participant-shoe specific linear regression models to insure high prediction accuracy of free torques from pressure sensor data during isolated internal and external rotations of the body with respect to a planted foot.

A direct method to express the center of pressure (CoP) measured by an insole pressure sensor system (IPSS) into a known coordinate system measured by motion tracking equipment is presented. A custom probe was constructed with reflective markers to allow its tip to be precisely tracked with motion tracking equipment. This probe was utilized to activate individual sensors on an IPSS that was placed in a shoe fitted with reflective markers used to establish a local shoe coordinate system. When pressed onto the IPSS the location of the probe's tip was coincident with the CoP measured by the IPSS (IPSS-CoP). Two separate pushes (i.e., data points) were used to develop vectors in each respective coordinate system. Simple vector mathematics determined the rotational and translational components of the transformation matrix needed to express the IPSS-CoP into the local shoe coordinate system. Validation was performed by comparing IPSS-CoP with an embedded force plate measured CoP (FP-CoP) from data gathered during kinematic trials. Six male subjects stood on an embedded FP and performed anterior/posterior (AP) sway, internal rotation, and external rotation of the body relative to a firmly planted foot. The IPSS-CoP was highly correlated with the FP-CoP for all motions, root mean square errors (RMSRRs) were comparable to other research, and there were no statistical differences between the displacement of the IPSS-CoP and FP-CoP for both the AP and medial/lateral (ML) axes, respectively. The results demonstrated that this methodology could be utilized to determine the transformation variables need to express IPSS-CoP into a known coordinate system measured by motion tracking equipment and that these variables can be determined outside the laboratory anywhere motion tracking equipment is available.

The objective of this study was to compare longitudinal results from two models of combined anterior cruciate ligament (ACL) and meniscal injury. A modified ACL transection (mACLT) model and a traumatic impact (ACLF) model were used to create an ACL rupture and acute meniscal damage in a Flemish Giant animal model. The animals were euthanized at time points of 4, 8, or 12 weeks. The menisci were assessed for equilibrium and instantaneous compressive modulus, as well as glycosaminoglycan (GAG) coverage. The articular cartilage was mechanically assessed for thickness, matrix modulus, fiber modulus, and permeability. Articular cartilage GAG coverage, fissuring, tidemark integrity, and subchondral bone thickness were measured. Both models resulted in damage indicative of osteoarthritis, including decreased meniscal mechanics and GAG coverage, increased permeability and fissuring of articular cartilage, and decreased GAG coverage. The mACLT model had an early and lasting effect on the menisci mechanics and GAG coverage, while cartilage damage was not significantly affected until 12 weeks. The ACLF model resulted in an earlier change of articular cartilage GAG coverage and fissuring in both the 8 and 12 week groups. The menisci were only significantly affected at the 12 week time point in the ACLF model. We concluded the progression of post traumatic osteoarthritis was dependent on injury modality: a point to be considered in future investigations. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:486-495, 2017.

While conventional mechanical testing has been regarded as a gold standard for the evaluation of bone heath in numerous studies, with recent advances in medical imaging, virtual methods of biomechanics are rapidly evolving in the human literature. The objective of the current study was to evaluate the feasibility of determining the elastic and failure properties of poultry long bones using established methods of analysis from the human literature. In order to incorporate a large range of bone sizes and densities, a small number of specimens were utilized from an ongoing study of Regmi et al. (2016) that involved humeri and tibiae from 3 groups of animals (10 from each) including aviary, enriched, and conventional housing systems. Half the animals from each group were used for 'training' that involved the development of a regression equation relating bone density and geometry to bending properties from conventional mechanical tests. The remaining specimens from each group were used for 'testing' in which the mechanical properties from conventional tests were compared to those predicted by the regression equations. Based on the regression equations, the coefficients of determination for the 'test' set of data were 0.798 for bending bone stiffness and 0.901 for the yield (or failure) moment of the bones. All regression slopes and intercepts values for the tests versus predicted plots were not significantly different from 1 and 0, respectively. The study showed the feasibility of developing future methods of virtual biomechanics for the evaluation of poultry long bones. With further development, virtual biomechanics may have utility in future in vivo studies to assess laying hen bone health over time without the need to sacrifice large groups of animals at each time point.

While high ankle sprains are often clinically ascribed to excessive external foot rotation, no experimental study documents isolated anterior tibiofibular ligament (ATiFL) injury under this loading. We hypothesized that external rotation of a highly everted foot would generate ATiFL injury, in contrast to deltoid ligament injury from external rotation of a neutral foot. Twelve (six pairs) male cadaveric lower extremity limbs underwent external foot rotation until gross failure. All limbs were positioned in 20° of dorsiflexion and restrained with elastic athletic tape. Right limbs were in neutral while left limbs were everted 20°. Talus motion relative to the tibia was measured using motion capture. Rotation at failure for everted limbs (46.8 ± 6.1°) was significantly greater than for neutral limbs (37.7 ± 5.4°). Everted limbs showed ATiFL injury only, while neutral limbs mostly demonstrated deltoid ligament failure. This is the first biomechanical study to produce isolated ATiFL injury under external foot rotation. Eversion of the axially loaded foot predisposes the ATiFL to injury, forming a basis for high ankle sprain. The study helps clarify a mechanism of high ankle sprain and may heighten clinical awareness of isolated ATiFL injury in cases of foot eversion prior to external rotation. It may also provide guidance to investigate the effect of prophylactic measures for this injury. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1423–1429, 2012

SummaryObjective: To compare the mechanical properties of pancarpal arthrodesis (PCA) constructs stabilized at 20° of extension using either a 3.5 mm limited contact dynamic compression plate (LC-DCP) or a 3.5/2.7 mm hybrid plate (HP).Methods: Seven forelimb pairs were used from dogs of similar size. All soft tissues were removed except for supporting structures of the carpus and proximal metacarpal region. All plates were accurately bent to 20°, and then instrumented with two, 350Ω strain gauges applied at the level of the bend. Constructs were embedded in epoxy moulds then mounted onto a servo-hydraulic testing machine. Specimens were loaded for 10 cycles at 100N, 200N and 300N. Tenth cycle construct compliance (CC), maximum angular deformation (MAD), and peak plate strain (PPS) were compared using two-factor analysis of variance (ANOVA) and Student-Newman- Keuls post-hoc tests (p Results: Regardless of load, CC was 29% to 33% smaller in the HP than the LC-DCP group (p Clinical significance: The mechanical advantages of the HP over the LC-DCP make it a viable alternative for PCA. Smaller CC, MAD and PSS of the HP may reduce the risk of implant failure and postoperative morbidity following PCA.

The objective of this study was to document patterns of fracture on infant porcine skulls aged 2-28 days ( = 57) because of a sin- gle, high energy blunt impact to the parietal bone with rigid (nondeformable) and compliant (deformable) interfaces. Fracture patterns were mapped using Geographic Information System software. For the same generated impact force, the rigid interface produced more fractures than the compliant interface for all ages. This study also showed that this increased level of impact energy versus an earlier study using a lower energy resulted in new sites of fracture initiation and also caused previously defined fractures that propagate into an adjacent bone. Several unique characteristics of bone and diastatic fracture were documented as a function of specimen age, impact energy, and interface. These data describe some baseline characteristics of skull fracture using an animal model that may help guide future studies from forensic case files.

External rotation of the foot has been implicated in high ankle sprains. Recent studies by this laboratory, and others, have suggested that torsional traction characteristics of the shoe-surface interface may play a role in ankle injury. While ankle injuries most often involve damage to ligaments due to excessive strains, the studies conducted by this laboratory and others have largely used surrogate models of the lower extremity to determine shoe-surface interface characteristics based on torque measures alone. The objective of this study was to develop a methodology that would integrate a motion analysis-based kinematic foot model with a computational model of the ankle to determine dynamic ankle ligament strains during external foot rotation. Six subjects performed single-legged, internal rotation of the body with a planted foot while a marker-based motion analysis was conducted to track the hindfoot motion relative to the tibia. These kinematic data were used to drive an established computational ankle model. Ankle ligament strains, as a function of time, were determined. The anterior tibiofibular ligament (ATiFL) experienced the highest strain at 9.2±1.1%, followed by the anterior deltoid ligament (ADL) at 7.8±0.7%, averaged over the six subjects. The peak ATiFL strain occurred prior to peak strain in the ADL in all subjects. This novel methodology may provide new insights into mechanisms of high ankle sprains and offer a basis for future evaluations of shoe-surface interface characteristics using human subjects rather than mechanical surrogate devices.

Recent studies, using two different manners of foot constraint, potted and taped, document altered failure characteristics in the human cadaver ankle under controlled external rotation of the foot. The posterior talofibular ligament (PTaFL) was commonly injured when the foot was constrained in potting material, while the frequency of deltoid ligament injury was higher for the taped foot. In this study an existing multibody computational modeling approach was validated to include the influence of foot constraint, determine the kinematics of the joint under external foot rotation, and consequently obtain strains in various ligaments. It was hypothesized that the location of ankle injury due to excessive levels of external foot rotation is a function of foot constraint. The results from this model simulation supported this hypothesis and helped to explain the mechanisms of injury in the cadaver experiments. An excessive external foot rotation might generate a PTaFL injury for a rigid foot constraint, and an anterior deltoid ligament injury for a pliant foot constraint. The computational models may be further developed and modified to simulate the human response for different shoe designs, as well as on various athletic shoe-surface interfaces, so as to provide a computational basis for optimizing athletic performance with minimal injury risk.

The menisci have crucial weight-bearing roles in the knee. Regional variations in structure and cellularity of the meniscus have only been minimally investigated. Therefore, the goal of this study was to illustrate the regional cell density, tissue area, and structure of healthy lapine menisci. Skeletally mature Flemish Giant rabbits were used for this study. Upon sacrifice, menisci were removed, fixed in formalin, and cryosectioned. Histological analysis was performed for the detection of sulfated glycosaminoglycans (GAG), collagen Types I and II, cellular density, and tissue area. ANOVA and paired t tests were used for testing of statistical significance. Glycosaminoglycan coverage of the medial meniscus significantly varied between regions, with the anterior region demonstrating significantly more GAG coverage than the posterior region. Inter- and intra-meniscal comparisons revealed variations between zones, with trends that outer zones of the medial menisci had less GAG coverage. Collagen Types I and II had marked characteristics and varying degrees of coverage across regions. Tissue area varied between regions for both medial and lateral menisci. Cellular density was dependent on region in the lateral meniscus. This is the first study to illustrate regional and zonal variation in glycosaminoglycan coverage, size, and cellular density for healthy lapine meniscal tissue. This data provides baseline information for future investigations in meniscal injury models in rabbits.

This study documents four clinical cases of fatal crush injuries to children between 1.5 and 6 years of age with correlations between modeled stress and clinically observed fracture patterns. The clinical case fractures were concentrated in the basicranium, bridged the impact sites, and traversed the middle cranial fossa in the area of the spheno-occipital synchondrosis. The crushing forces from these cases were recreated on a simplified finite element model of a cranium by applying bilateral pressures to corresponding regions. Numerous trials were run to develop a representative pattern of principal stress directions. In all cases, the highest tensile stresses were located on the basicranium and corresponded to the observed fracture path(s). These results suggest that prefailure stress field diagrams may predict fracture propagation paths, although these will not be exact. Also, these analyses indicate that quasi-static bilateral loading of the cranium may lead to predictable fracture of the basicranium.

This study documents skull fracture characteristics on infant porcine specimens under known impact conditions with respect to age and interface. A single impact causing fracture was conducted on the skull of porcine specimens aged 2–28 days (n = 76). Paired rigid and compliant impacts at the same energy were conducted at each specimen age. Impact force, impact duration, and fracture length were recorded. Energy required to initiate skull fracture increased with specimen age. For a given energy, impact of the skull with a compliant interface caused more fracture damage than with a rigid interface for specimens aged under 17 days, but less damage for specimens aged 24–28 days. The documentation of energy required to cause fracture and resulting fracture propagation with respect to impact interface and age may be of critical importance in forensic investigations of infant skull trauma.

Recent studies have indicated that there may be a correlation between acute chondrocyte damage and joint degeneration reminiscent of early-stage osteoarthritis (OA). P188 surfactant has been shown to acutely restore the integrity of damaged chondrocytes; however, its long-term efficacy is unknown. The hypothesis of this study was that a single injection of P188 into a traumatized joint would acutely repair damaged cell membranes and maintain their viability in the long term. Twelve rabbits were divided into two groups, with and without P188, and sacrificed 4 days after tibiofemoral (TF) impact. Another six rabbits were sacrificed after 6 weeks and divided into two groups, with and without P188 treatment immediately posttrauma. Treatment with P188 increased the viable cell density 4 days posttrauma. A higher density of viable cells was also documented 6 weeks posttrauma in the treated versus untreated limb. The results of the current study confirm the acute efficacy of P188 treatment, and may suggest long-term efficacy of treatment, but additional studies are still needed to investigate the chronic implications of the acute repair of cells in the traumatized joint.

Biofidelic devices are used in the automobile industry to assess injury risk during a vehicular accident. Similar biofidelic devices may have broad applicability in the field of sports injury prevention and could be used to enhance player safety. Ankle sprains constitute one of the most common sports injuries. Past studies have suggested that high rotational traction at the shoe—surface interface may increase the likelihood of lower-extremity injury. Researchers have assessed this risk by measuring the peak torque during an applied rotation. On the other hand, ankle sprains may be dependent upon the amount of strain developed in the ankle ligaments during rotation of the foot—ankle complex and not the magnitude of torque. The current study quantifies the torsional stiffness of the human foot—ankle complex based on cadaver experiments. The development of a surrogate foot—ankle complex is then detailed and compared with the human response. Finally, the results of a rotational traction study on a couple of football shoe—surface interfaces are presented using the surrogate ankle. The testing resulted in a new outcome variable, namely the peak twist of the ankle, that may allow assessment of the risk of injury to the ankle due to excessive rotational traction at the shoe—surface interface.

Background Valgus bending of the knee is promoted as an anterior cruciate ligament injury mechanism and is associated with a characteristic “footprint” of bone bruising. The hypothesis of this study was that during ligamentous failure caused by valgus bending of the knee, high tibiofemoral contact pressures induce acute osteochondral microdamage. Methods Four knee pairs were loaded in valgus bending until gross injury with or without a tibiofemoral compression pre-load. The peak valgus moment and resultant motions of the knee joint were recorded. Pressure sensitive film documented the magnitude and location of tibiofemoral contact. Cartilage fissures were documented on the tibial plateau, and microcracks in subchondral bone were documented from micro-computed tomography scans. Findings Injuries were to the anterior cruciate ligament in three knees and the medial collateral ligament in seven knees. The mean (standard deviation) peak bending moment at failure was 107 (64) N m. Valgus bending produced regions of contact on the lateral tibial plateau with average maximum pressures of approximately 30 (8) MPa. Cartilage fissures and subchondral bone microcracks were observed in these regions of high contact pressure. Interpretation Combined valgus bending and tibiofemoral compression produce slightly higher contact pressures, but do not alter the gross injury pattern from isolated valgus bending experiments. Athletes who sustain a severe valgus knee bending moment, may be at risk of acute osteochondral damage especially if the loading mechanism occurs with a significant tibiofemoral compression component.

BackgroundHigh rotational traction between football shoes and the playing surface may be a potential mechanism of injury for the lower extremity.HypothesisRotational traction at the shoe-surface interface depends on shoe design and surface type.Study DesignControlled laboratory study.MethodsA mobile testing apparatus with a compliant ankle was used to apply rotations and measure the torque at the shoe-surface interface. The mechanical surrogate was used to compare 5 football cleat patterns (total of 10 shoe models) and 4 football surfaces (FieldTurf, AstroPlay, and 2 natural grass systems) on site at actual surface installations.ResultsBoth artificial surfaces yielded significantly higher peak torque and rotational stiffness than the natural grass surfaces. The only cleat pattern that produced a peak torque significantly different than all others was the turf-style cleat, and it yielded the lowest torque. The model of shoe had a significant effect on rotational stiffness.ConclusionThe infill artificial surfaces in this study exhibited greater rotational traction characteristics than natural grass. The cleat pattern did not predetermine a shoe's peak torque or rotational stiffness. A potential shoe design factor that may influence rotational stiffness is the material(s) used to construct the shoe's upper.Clinical RelevanceThe study provides data on the rotational traction of shoe-surface interfaces currently employed in football. As football shoe and surface designs continue to be updated, new evaluations of their performance must be assessed under simulated loading conditions to ensure that player performance needs are met while minimizing injury risk.

Summary Objectives: To compare the mechanical properties of various interlocking nail constructs in medio-lateral (ML) and cranio-caudal (CC) bending. Methods: Synthetic bone models simulating a severely comminuted tibial fracture were treated with either screwed or bolted, 6 or 8 mm standard interlocking nails (ILN), or an angle-stable ILN (AS-ILN), after which they were then sequentially tested in ML and CC bending. Construct compliance, maximum angular deformation (MaxDef) and slack were statistically compared (p Results: The compliance of all constructs was significantly greater in CC than in ML bending. However, due to the presence of a greater slack in the ML plane, standard ILN constructs sustained significantly more deformation in that plane. Maximum deformation of the novel AS-ILN constructs was the smallest of all constructs and consistently occurred without slack regardless of bending direction. Clinical significance: This study suggested that standard ILN construct overall deformation and acute instability (slack) may be more critical in ML than in CC bending. Conversely, the small MaxDef and the absence of slack in both bending planes seen in novel angle-stable AS-ILN may provide optimal construct stability and in turn may be more conducive to bone healing.

The knee is one of the most frequently injured joints in the human body. Approximately 91% of ACL injuries occur during sporting activities, usually from a non-contact event. The most common kinetic scenarios related with ACL injuries are internal twisting of the tibia relative to the femur or combined torque and compression during a hard landing. The hypothesis of this study was that the magnitudes and types of motion observed after ACL rupture would significantly change from the relative joint displacements present just before ACL injury. Compression or torsion experiments were conducted on 7 pairs of knee joints with repetitive tests at increasing intensity until catastrophic failure. ACL injury was documented in all cases at 5.4+/-2kN of TF compression or 33+/-13Nm of internal tibial torque. The femur displaced posteriorly relative to the tibia in pre-failure and with a higher magnitude in failure tests under both loading conditions. In compression experiments there was internal rotation of the tibia in pre-failure tests, but external rotation of the tibia after the ACL failed. In torsion experiments, failure occurred at 58+/-19 degrees of internal tibial rotation, and valgus rotation of the femur increased significantly after ACL injury. These new data show that the joint motions can vary in magnitude and direction before and after failure of the ACL. Video-based studies consistently document external rotation of the tibia combined with valgus knee bending as the mechanism of ACL injury although these motions could be occurring after ACL rupture.

The purpose of this study was to investigate the role of infill material and fibre structure on the rotational traction associated with American football shoes on infill-based artificial surfaces. A mobile testing apparatus with a compliant ankle was used to apply rotations and measure the torque produced at the football shoe—surface interface. The mechanical surrogate was used to compare three infill materials in combination with three fibre structures, creating a total of nine unique surfaces. Infill material, fibre structure, and shoe design were all found to significantly affect rotational traction. The cryogenically processed styrene—butadiene rubber (SBR) infill yielded significantly higher peak torques than the ambient ground SBR and extruded thermoplastic elastomer (TPE) infills. An artificial surface with a nylon root zone yielded significantly lower peak torques than similar fibre surfaces without a nylon root zone. The size of infill particles and the presence of a nylon root zone may influence the compactness of the infill layer. These features may act to alter the amount of cleat contact with the infill, thereby influencing rotational traction. The amount of cleat contact with the surface may also be determined by the shoe design.

Objective—To compare the bending properties of pantarsal arthrodesis constructs involving either a commercially available medial arthrodesis plate (MAP1) or a specially designed second-generation plate (MAP2) implanted in cadaveric canine limbs and evaluate the effect of calcaneotibial screw (CTS) augmentation on the structural properties of both constructs. Sample Population—5 pairs of canine hind limbs. Procedures—Within pairs, specimens were stabilized with an MAP1 or MAP2 and loaded to 80% of body weight, with and without CTS augmentation. Compliance, angular deformation (AD), and plate strains were compared. Results—Construct compliance and AD did not differ between plates. Maximum plate strain was lower in the MAP2 than in the MAP1 (difference of approx 30%). Augmentation with a CTS reduced compliance, AD, and strains in MAP1 constructs but had no effect on those variables in MAP2 constructs. Conclusions and Clinical Relevance—Because of lower peak strains, the MAP2 may be less susceptible to failure than the MAP1. Furthermore, CTS augmentation was unnecessary with MAP2s, which could minimize intra- and postoperative morbidity. Compared with what is known for dorsal plates, MAP2 constructs were associated with approximately 35% less AD. As a result of improved local stability, one might anticipate earlier fusion of the talocrural joint with an MAP2. In addition, plate peak strain was approximately 3.5 times lower in MAP2s than in dorsal plate constructs, which should result in greater fatigue resistance. The use of MAP2s may be a better alternative to both MAP1s and dorsal plates and could contribute to lower patient morbidity.

A recent study by our laboratory showed that 14 days of low intensity, intermittent cyclic preloading of chondral explants elevated the concentration of proteoglycans (PGs) to cause a mechanical stiffening of the explants prior to an acute overload and limit the extent of tissue damage. Longer term loading to 21 days resulted in tissue degradation prior to the acute traumatic event and excessive damage from an acute overload. Previous studies by others showed that bathing chondral explants in a supplement of glucosamine–chondroitin sulfate (glcN-CS) upregulated the synthesis of tissue PGs, particularly in stressed tissue, and the supplement served as an anti-inflammatory agent. Our current hypothesis was that the supplementation of culture media with a high concentration of glcN-CS would upregulate the production of tissue PG and limit or mitigate long-term degradation of chondral explants under cyclic preloading and limit tissue damage in an acute overload. We showed that, in the presence of supplement, cyclic preloading significantly increased tissue PG content and matrix modulus by about 65 and 300%, respectively, at 21 days, resulting in a reduction of matrix damage and cell death following an acute overload. These data show a biological action of high concentrations of this supplement and its effect on the mechanical properties in this in vitro model. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:353–359, 2009

Mechanical loading of articular cartilage can influence chondrocyte metabolism and lead to alterations in cartilage matrix composition. Most previous studies have focused on the effect of cyclic loading on cartilage mechanical properties and proteoglycan synthesis. However, the role of proteoglycans synthesized from cyclically loaded cartilage in response to an acute overload has not been elucidated. Therefore, we conducted studies where low intensity, intermittent cyclic loading was applied to chondral explants prior to an acute unconfined compression on the tissue. The chondral explants were randomly assigned to three groups: 7, 14, and 21 days of 10 cycles of 0.2 Hz sinusoidal loading at 0.5 MPa followed by an unloaded interval of 3,600 s. All explants were then taken to 25 MPa of unconfined compression. Biochemical assays were conducted to determine the tissue proteoglycan and hydroxyproline contents. The results showed cyclic preloading increased the proteoglycan content and mechanically stiffened the explants, making them more resistant to matrix damage and cell death under 25 MPa of unconfined compression up to 14 days. After 21 days of cyclic loading, however, the explants lost compressive stiffness and suffered more extensive damage in the unconfined compression test. This study investigated the role of cyclic loading in response of chondral explants to a potentially damaging, acute overload. In the long term, these types of studies may help understand the role of preconditioning of articular cartilage for in vitro or even in vivo studies of blunt force trauma to a joint.

Background The knee is one of the most frequently injured joints, including 80 000 anterior cruciate ligament (ACL) tears in the United States each year. Bone bruises are seen in over 80% of patients with ACL injuries, and have been associated with an overt loss of cartilage overlying those regions within 6 months of injury. Hypothesis The level of contact pressure developed in the human knee joint and the extent of articular cartilage and underlying subchondral bone injuries will depend on the mechanism of applied loads/moments during rupture of the ACL. Study Design Controlled laboratory study. Methods Seven knee pairs, flexed to 30°, were loaded in compression or internal torsion until injury. Pressure-sensitive film recorded the magnitude and location of contact. Histologic analysis and magnetic resonance imaging were used to document microtrauma to the tibial plateau cartilage and subchondral bone. Results All specimens suffered ACL injury, either in the form of a midsubstance rupture or avulsion fracture. The contact area and pressures were higher for compression than torsion experiments. After being loaded, the articular cartilage in the central and posterior regions of the medial tibial plateau showed increased magnetic resonance imaging signal intensity, corresponding to an increased susceptibility to absorb water. Histologically, there were more microcracks in the subchondral bone and more articular cartilage damage in the compression than torsion experiments. Conclusion Significant damage occurs to the articular cartilage and underlying subchondral bone during rupture of the ACL. The types and extent of these tissue injuries are a function of the mechanism of ACL rupture. Clinical Relevance Patients suffering an ACL injury may be at risk of osteochondral damage, especially if the mechanism of injury involves a high compressive loading component, such as during a jump landing.

The importance of fluid-flow-induced shear stress and matrix-induced cell deformation in transmitting the global tendon load into a cellular mechanotransduction response is yet to be determined. A multiscale computational tendon model composed of both matrix and fluid phases was created to examine how global tendon loading may affect fluid-flow-induced shear stresses and membrane strains at the cellular level. The model was then used to develop a quantitative experiment to help understand the roles of membrane strains and fluid-induced shear stresses on the biological response of individual cells. The model was able to predict the global response of tendon to applied strain (stress, fluid exudation), as well as the associated cellular response of increased fluid-flow-induced shear stress with strain rate and matrix-induced cell deformation with strain amplitude. The model analysis, combined with the experimental results, demonstrated that both strain rate and strain amplitude are able to independently alter rat interstitial collagenase gene expression through increases in fluid-flow-induced shear stress and matrix-induced cell deformation, respectively.

Objective— To compare the structural properties of interlocking nails (ILNs) locked with bolts (ILNb) to ILN locked with extended bolts connected with a type-IA external skeletal fixator (ILN–ESF) in a fracture gap model. Study Design— Experimental study. Sample Population— Synthetic tibial bone substitutes. Methods— Custom-made synthetic tibial bone substitutes were implanted with standard ILNs locked with either bolts or extended bolts connected to an external skeletal fixation (ESF). Constructs were tested in torsion, bending, and axial compression (n=4/testing mode). Data, consisting of construct compliance and associated deformation, were compared using t-tests. Results— The ILN–ESF construct compliance and deformation were significantly less than those of the ILNb construct in torsion, bending, and compression (P

Distinguishing between accidental and abusive head trauma in children can be difficult, as there is a lack of baseline data for pediatric cranial fracture patterns. A porcine head model has recently been developed and utilized in a series of studies to investigate the effects of impact energy level, surface type, and constraint condition on cranial fracture patterns. In the current study, an automated pattern recognition method, or a fracture printing interface (FPI), was developed to classify cranial fracture patterns that were associated with different impact scenarios documented in previous experiments. The FPI accurately predicted the energy level when the impact surface type was rigid. Additionally, the FPI was exceedingly successful in determining fractures caused by skulls being dropped with a high-level energy (97% accuracy). The FPI, currently developed on the porcine data, may in the future be transformed to the task of cranial fracture pattern classification for human infant skulls.

The forensic literature suggests that when adolescents fall onto edged and pointed surfaces, depressed fractures can occur at low energy levels. This study documents impact biomechanics and fracture characteristics of infant porcine skulls dropped onto flat, curved, edged, and focal surfaces. Results showed that the energy needed for fracture initiation was nearly four times higher against a flat surface than against the other surfaces. While characteristic measures of fracture such as number and length of fractures did not vary with impact surface shape, the fracture patterns did depend on impact surface shape. While experimental impacts against the flat surface produced linear fractures initiating at sutural boundaries peripheral to the point of impact (POI), more focal impacts produced depressed fractures initiating at the POI. The study supported case-based forensic literature suggesting cranial fracture patterns depend on impact surface shape and that fracture initiation energy is lower for more focal impacts.