The Foot and Ankle Kinematics of a Simulated Progressive Collapsing Foot Deformity During Stance Phase: A Cadaveric Study.

BACKGROUND: Progressive collapsing foot deformity (PCFD) is a complex pathology associated with tendon insufficiency, ligamentous failure, joint malalignment, and aberrant plantar force distribution. Existing knowledge of PCFD consists of static measurements, which provide information about structure but little about foot and ankle kinematics during gait. A model of PCFD was simulated in cadavers (sPCFD) to quantify the difference in joint kinematics and plantar pressure between the intact and sPCFD conditions during simulated stance phase of gait. METHODS: In 12 cadaveric foot and ankle specimens, the sPCFD condition was created via sectioning of the spring ligament and the medial talonavicular joint capsule followed by cyclic axial compression. Specimens were then analyzed in intact and sPCFD conditions via a robotic gait simulator, using actuators to control the extrinsic tendons and a rotating force plate underneath the specimen to mimic the stance phase of walking. Force plate position and muscle forces were optimized using a fuzzy logic iterative process to converge and simulate in vivo ground reaction forces. An 8-camera motion capture system recorded the positions of markers fixed to bones, which were then used to calculate joint kinematics, and a plantar pressure mat collected pressure distribution data. Joint kinematics and plantar pressures were compared between intact and sPCFD conditions. RESULTS: The sPCFD condition increased subtalar eversion in early, mid-, and late stance (P < .05), increased talonavicular abduction in mid- and late stance (P < .05), and increased ankle plantarflexion (P < .05), adduction (P < .05), and inversion (P < .05). The center of plantar pressure was significantly (P < .01) medialized in this model of sPCFD and simulated stance phase of gait. DISCUSSION: Subtalar and talonavicular joint kinematics and plantar pressure distribution significantly changed with the sPCFD and in the directions expected from a PCFD foot. We also found that ankle joint kinematics changed with medial and plantar drift of the talar head, indicating abnormal talar rotation. Although comparison to an in vivo PCFD foot was not performed, this sPCFD model produced changes in foot kinematics and indicates that concomitant abnormal changes may occur at the ankle joint with PCFD. CLINICAL RELEVANCE: This study describes the dynamic kinematic and plantar pressure changes in a cadaveric model of simulated progressive collapsing foot deformity during simulated stance phase.

Cadaveric Gait Simulation of the Effect of Subtalar Arthrodesis on Total Ankle Replacement Kinematics.

BACKGROUND: Patients undergoing total ankle replacement (TAR) often have symptomatic adjacent joint arthritis and deformity. Subtalar arthrodesis can effectively address a degenerative and/or malaligned hindfoot, but there is concern that it places abnormal stresses on the TAR and adjacent joints of the foot, potentially leading to early TAR failure. This study hypothesized that ankle and talonavicular joint kinematics would be altered after subtalar arthrodesis in the setting of TAR. METHODS: Thirteen mid-tibia cadaveric specimens with neutral alignment were tested in a robotic gait simulator. To simulate gait, each specimen was secured to a static mounting fixture about a 6-degree of freedom robotic platform, and a force plate moves relative to the stationary specimen based on standardized gait parameters. Specimens were tested sequentially in TAR and TAR with subtalar arthrodesis (TAR-STfuse). Kinematics and range of motion of the ankle and talonavicular joint were compared between TAR and TAR-STfuse. RESULTS: There were significant differences in kinematics and range of motion between TAR and TAR-STfuse groups. At the ankle joint, TAR-STfuse had less internal rotation in early-mid stance (P < .05), with decreased range of motion in the sagittal (-2.7 degrees, P = .008) and axial (-1.8 degrees, P = .002) planes in early stance, and increased range of motion in the coronal plane in middle (+1.2 degrees, P < .001) and late (+2.5 degrees, P = .012) stance. At the talonavicular joint, there were significant differences in axial and coronal kinematics in early and late stance (P < .05). Subtalar arthrodesis resulted in significantly decreased talonavicular range of motion in all planes in early and late stance (P < .003). CONCLUSION: In ankles implanted with the TAR design used in this study, kinematics of the ankle and talonavicular joint were found to be altered after subtalar arthrodesis. Aberrant motion may reflect altered contact mechanics at the prosthesis and increased stress at the bone-implant interface, and affect the progression of adjacent joint arthritis in the talonavicular joint. CLINICAL RELEVANCE: These findings may provide a correlate to clinical studies that have cited hindfoot arthrodesis as a risk factor for TAR failure.

Orthosis and Foot Structure Affect the Fifth Metatarsal Principal Strains During Simulated Level Walking.

BACKGROUND: Fractures of the proximal fifth metatarsal bone are common injuries in elite athletes and are associated with high rates of delayed union and nonunion. Structural features of the foot may increase fracture risk in some individuals, emphasizing the need for intervention strategies to prevent fracture. Although orthotic devices have shown promise in reducing fractures of the fifth metatarsal bone, the effect of orthosis on fifth metatarsal strains is not well understood. PURPOSE: To quantify the effects of different foot orthotic constructs on principal tensile strains in the proximal fifth metatarsal bone during cadaveric simulations of level walking. An additional purpose was to investigate the relationships between structural features of the foot and corresponding strains on the fifth metatarsal bone during level walking. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 10 midtibial cadaveric specimens were attached to a 6 degrees of freedom robotic gait simulator. Strain gauges were placed at the metaphyseal-diaphyseal junction (zone II) and the proximal diaphysis (zone III) during level walking simulations using 11 different foot orthotic configurations. Images of each specimen were used to measure structural features of the foot in an axially loaded position. The peak tensile strains were measured and reported relative to the sneaker-only condition for each orthotic condition and orthotic-specific association between structural features and principal strains of both zones. RESULTS: In total, 2 of the 11 orthotic conditions significantly reduced strain relative to the sneaker-only condition in zone II. Further, 6 orthotic conditions significantly reduced strain relative to the sneaker-only condition in zone III. Increased zone II principal strain incurred during level walking in the sneaker-only condition showed a significant association with increases in the Meary's angle. Changes in zone III principal strain relative to the sneaker-only condition were significantly associated with increases in the Meary's angle and fourth-fifth intermetatarsal angle. CONCLUSION: The use of orthotic devices reduced principal strain relative to the condition of a sneaker without any orthosis in zone II and zone III. The ability to reduce strain relative to the sneaker-only condition in zone III was indicated by increasing values of the Meary's angle and levels of the fourth-fifth intermetatarsal angle. CLINICAL RELEVANCE: Clinicians can use characteristics of foot structure to determine the proper foot orthosis to potentially reduce stress fracture risk in high-risk individuals.

Finite Element Modeling of Planus and Rectus Foot Types for the Study of First Metatarsophalangeal and First Metatarsocuneiform Joint Contact Mechanics.

The foot is a highly complex biomechanical system for which finite element (FE) modeling has been used to evaluate its loading environment. However, there is limited knowledge of first metatarsophalangeal (MTP) and first metatarsocuneiform (MTC) joint contact mechanics. Our goal was to develop a framework for FE modeling of the medial forefoot which could accurately predict experimental measurements of first MTP and first MTC joint loading. Simulations of planus and rectus foot types were conducted for midstance of gait. A custom-built force-controlled cadaveric test-rig was used to derive intracapsular pressure sensor measurements of contact pressure, force, and area during quasi-static loading. The FE model was driven under the same boundary and loading conditions as the cadaver. Mesh sensitivity analyses and best-fit calibrations of moduli for first MTP and first MTC joint cartilage were performed. Consistent with previous experimental research, a lower compressive modulus was best-fit to the first MTP compared to first MTC joint at 10 MPa and 20 MPa, respectively. Mean errors in contact pressures, forces, and areas were 24%, 4%, and 40% at the first MTP joint and 23%, 12%, and 19% at the first MTC joint, respectively. The present developmental framework may provide a basis for future modeling of first MTP and first MTC joint contact mechanics. This study acts as a precursor to validation of realistic physiological loading across gait to investigate joint loading, foot type biomechanics, and surgical interventions of the medial forefoot.

Articular cartilage thickness changes differ between males and females 4 years following anterior cruciate ligament reconstruction.

Anterior cruciate ligament injury and reconstruction (ACLR) affects articular cartilage thickness profiles about the tibial, femoral, and patellar surfaces; however, it's unclear whether the magnitudes of change in cartilage thickness, as well as the locations and areas over which these changes occur, differ between males and females. This is important to consider as differences exist between the sexes with regard to knee biomechanics, patellofemoral pain, and anatomic alignment, which influence risk of an index and repeated injury. Subjects underwent ACLR with a bone-patella tendon-bone autograft. At 4-year follow-up, they had asymptomatic knees; however, significant ACL injured-to-contralateral normal knee differences in articular cartilage thickness values were observed. Both thickening and thinning of cartilage occurred about the tibiofemoral and patellofemoral joints, relative to matched control subjects with normal knees. Further, the location of the areas and magnitudes of thickening and thinning were different between females and males. Thickening (swelling) of articular cartilage is an early finding associated with the onset of posttraumatic osteoarthritis (PTOA). Therefore, the increases in cartilage thickness that were observed in this cohort may represent early signs of the onset of PTOA that occur prior to the patient developing symptoms and radiographic evidence of this disease. The different locations of areas that underwent a change in cartilage thicknesses between males and females suggest that each sex responds differently to knee ligament trauma, reconstruction, rehabilitation, and return to activity, and indicates that sex-specific analysis should be utilized in studies of PTOA.

The Lateral Femoral Condyle Index Is Not a Risk Factor for Primary Noncontact Anterior Cruciate Ligament Injury.

BACKGROUND: The lateral femoral condyle index (LFCI)-a recently developed measure of the sphericity of the lateral femoral condyle-was reported to be a risk factor for anterior cruciate ligament (ACL) injury. However, issues have been raised regarding how the index was measured and regarding the patient group and the knee in which it was measured. PURPOSE: To investigate the association between the LFCI and the risk of sustaining a primary, noncontact ACL injury, and to examine whether this association was moderated by the posterior-inferior-directed slope of the lateral tibial plateau. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A secondary analysis was conducted of deidentified magnetic resonance images of the uninjured knees of 86 athletes with ACL injury and the corresponding knees of 86 control athletes, matched for sports team, sex, and age. From those images, we measured the LFCI and the posterior-inferior-directed slope of the middle region articular cartilage surface of the tibial plateau's lateral compartment. Conditional logistic regressions were performed to determine whether the LFCI was significantly associated with ACL injury risk and whether the lateral tibial compartment middle cartilage slope moderated this association. Data were analyzed for female and male participants separately as well as for both groups combined. RESULTS: The LFCI was not found to be significantly associated with experiencing a primary, noncontact ACL injury for all analyses. The lateral tibial slope measure was not found to moderate the association between the LFCI and ACL injury. A conditional logistic regression analysis using the LFCI data of the injured knees, instead of the uninjured knees, of the participants with ACL injury revealed that the LFCI was significantly associated with ACL injury. CONCLUSION: In this population of athletically active female and male participants, the LFCI was not found to be a risk factor for noncontact ACL injury, regardless of the geometric features of the lateral tibial slope.

Clinical-Grade MRI-Based Methods to Identify Combined Anatomic Factors That Predict ACL Injury Risk in Male and Female Athletes.

BACKGROUND: Recently developed multivariate sex-specific statistical models can predict anterior cruciate ligament (ACL) injury risk using various knee anatomic factors. However, screening tools able to identify individuals at an increased injury risk are unlikely to be developed based on these models, given that sophisticated and time-consuming methods were used to measure those factors on research-grade resolution magnetic resonance images (MRIs). PURPOSE: To determine whether simpler methods, amenable to using clinical-grade resolution MRIs, can identify the same knee anatomic factors previously found to contribute to ACL injury risk using sophisticated methods and research-grade resolution images. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: High-resolution 3-dimensional MRIs previously acquired from 87 patients with primary, noncontact, grade III ACL injury and 87 uninjured matched control participants for a series of published studies were downgraded to clinical-grade resolution images. The 4 knee anatomic factors found to contribute to ACL injury risk in women and in men in these published studies-femoral intercondylar notch width at the anterior outlet of the ACL (NW_O), posterior-inferior directed slope of the middle region articular cartilage surface of the tibial plateau's lateral compartment (LatTibMCS), ACL volume, and tibial plateau's lateral compartment posterior meniscus to subchondral bone wedge angle (LatTibMBA)-were measured using clinical-grade resolution MRI-based methods. Stepwise multivariate conditional logistic regressions were used to identify the combinations of factors most highly associated with an ACL injury risk in women and men separately. RESULTS: The multivariate model that best predicted ACL injury risk in the female participants included the LatTibMCS and the NW_O. For the male participants, this model included the ACL volume and the LatTibMBA. These results corroborate the previously published results that reported models with the same knee anatomic factors to best predict injury risk in this group of young women and men. CONCLUSION: Simpler methods using MRIs downgraded to a clinical-grade resolution can identify the same knee anatomic factors previously found to significantly contribute to ACL injury risk using sophisticated methods and research-grade resolution MRIs.

Biomechanical evaluation of total ankle arthroplasty. Part I: Joint loads during simulated level walking.

In total ankle arthroplasty, the interaction at the joint between implant and bone is driven by a complex loading environment. Unfortunately, little is known about the loads at the ankle during daily activities since earlier attempts use two- or three-dimensional models to explore simplified joint mechanics. Our goal was to develop a framework to calculate multi-axial loads at the joint during simulated level walking following total ankle arthroplasty. To accomplish this, we combined robotic simulations of level walking at one-quarter bodyweight in three cadaveric foot and ankle specimens with musculoskeletal modeling to calculate the multi-axial forces and moments at the ankle during the stance phase. The peak compressive forces calculated were between 720 and 873 N occurring around 77%-80% of stance. The peak moment, which was the internal moment for all specimens, was between 6.1 and 11.6 N m and occurred between 72% and 88% of the stance phase. The peak moment did not necessarily occur with the peak force. The ankle joint loads calculated in this study correspond well to previous attempts in the literature; however, our robotic simulator and framework provide an opportunity to resolve the resultant three-dimensional forces and moments as others have not in previous studies. The framework may be useful to calculate ankle joint loads in cadaveric specimens as the first step in evaluating bone-implant interactions in total ankle replacement using specimen specific inputs. This approach also provides a unique opportunity to evaluate changes in joint loads and kinematics following surgical interventions of the foot and ankle.

Biomechanical evaluation of total ankle arthroplasty. Part II: Influence of loading and fixation design on tibial bone-implant interaction.

Finite element (FE) models to evaluate the burden placed on the interaction between total ankle arthroplasty (TAA) implants and the bone often rely on peak axial forces. However, the loading environment of the ankle is complex, and it is unclear whether peak axial forces represent a challenging scenario for the interaction between the implant and the bone. Our goal was to determine how the loads and the design of the fixation of the tibial component of TAA impact the interaction between the implant and the bone. To this end, we developed a framework that integrated robotic cadaveric simulations to determine the ankle kinematics, musculoskeletal models to determine the ankle joint loads, and FE models to evaluate the interaction between TAA and the bone. We compared the bone-implant micromotion and the risk of bone failure of three common fixation designs for the tibial component of TAA: spikes, a stem, and a keel. We found that the most critical conditions for the interaction between the implant and the bone were dependent on the specimen and the fixation design, but always involved submaximal forces and large moments. We also found that while the fixation design influenced the distribution and the peak value of bone-implant micromotion, the amount of bone at risk of failure was specimen dependent. To account for the most critical conditions for the interaction between the implant and the bone, our results support simulating multiple specimens under complex loading profiles that include multiaxial moments and span entire activity cycles.

Combined Injury to the ACL and Lateral Meniscus Alters the Geometry of Articular Cartilage and Meniscus Soon After Initial Trauma.

Combined injury to the anterior cruciate ligament (ACL) and meniscus is associated with earlier onset and increased rates of post-traumatic osteoarthritis compared with isolated ACL injury. However, little is known about the initial changes in joint structure associated with these different types of trauma. We hypothesized that trauma to the ACL and lateral meniscus has an immediate effect on morphometry of the articular cartilage and meniscus about the entire tibial plateau that is more pronounced than an ACL tear without meniscus injury. Subjects underwent magnetic resonance imaging scanning soon after injury and prior to surgery. Those that suffered injury to the ACL and lateral meniscus underwent changes in the lateral compartment (increases in the posterior-inferior directed slopes of the articular cartilage surface, and the wedge angle of the posterior horn of the meniscus) and medial compartment (the cartilage-to-bone height decreased in the region located under the posterior horn of the meniscus, and the thickness of cartilage increased and decreased in the mid and posterior regions of the plateau, respectively). Subjects that suffered an isolated ACL tear did not undergo the same magnitude of change to these articular structures. A majority of the changes in morphometry occurred in the lateral compartment of the knee; however, change in the medial compartment of the knee with a normal appearing meniscus also occurred. Statement of clinical significance: Knee injuries that involve combined trauma to the ACL and meniscus directly affect both compartments of the knee, even if the meniscus and articular cartilage appears normal upon arthroscopic examination. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:759-767, 2020.

Influence of Tibial Component Position on Altered Kinematics Following Total Ankle Arthroplasty During Simulated Gait.

BACKGROUND: Ankle and hindfoot kinematics following total ankle arthroplasty (TAA) are poorly understood and it is unclear whether patients can replicate physiologic motion after TAA. Furthermore, the effect of implant position on TAA kinematics is unknown. The objective of this study was to compare ankle and hindfoot kinematics pre- and post-TAA during simulated gait and determine to what degree tibial component position correlated with variations in ankle kinematics. METHODS: Eight midtibia cadaveric specimens were utilized in this institutional review board-approved study. The stance phase of gait was simulated both pre- and post-TAA in each specimen using a 6 degrees of freedom robotic platform. Ankle and hindfoot kinematics were measured from reflective markers attached to bones via surgical pins. The effect of tibial component position on absolute differences in ankle kinematics was assessed using linear regression. RESULTS: No differences were observed in ankle sagittal and coronal plane motion between the intact and TAA conditions. Differences in ankle joint kinematics were identified in the transverse plane, where internal talar rotation was significantly increased following TAA compared with the native condition. The medial-lateral position of the tibial component was found to correlate with the altered transverse plane motion observed after TAA (ß = 1.861 degrees/mm, R2 = 0.72, P = .008). No significant differences in subtalar and talonavicular joint kinematics in any plane were observed comparing the pre- and post-TAA condition. CONCLUSION: This study demonstrated an increased internal rotation of the ankle in the transverse plane following TAA. This increase was correlated with the medial-lateral position of the tibial implant. CLINICAL RELEVANCE: This finding could have clinical implications for how tibial components are positioned during the operative procedure, and how implant design and position may affect ankle kinematics following TAA.

Biomechanical Comparison of Suture-External Button Fixation vs Internal Suspension Fixation for Tendon Transfers of the Feet.

BACKGROUND: Fixation of tendon transfers in pediatric feet typically involves passing a suture that is secured to a tendon, through an intraosseous tunnel, and tying it over an external button on the plantar foot, with appropriate tension. After adequate time is allowed for bone-tendon healing, the suture and button are removed. This construct can be complicated by suture breakage with loss of fixation, and/or skin ulceration under the button. Internal suspension systems of tendons and ligaments in adults have demonstrated excellent fixation strength and minimal intraosseous tunnel displacement, with no risk of skin ulceration and no need for suture and button removal. This study compared the biomechanical properties of the suture-external button and internal suspension fixation techniques in cadavers. The primary outcome and secondary outcomes were displacement of suture-fixation construct during dynamic loading, and static loading, respectively. METHODS: Nine adult cadaver feet were obtained. Both the external button and internal suspension techniques were tested once in each cadaver, in random order. Relative displacement of the fixation construct within the bone tunnel was recorded with video capture during dynamic and static loading. A custom Matlab script processed video and materials testing data. Static and cyclic displacements were analyzed between fixation groups using a paired t test (alpha value =0.05). RESULTS: Internal suspension fixation had significantly less mean displacement of the tendon within the bone tunnel than the external button technique during dynamic (0.3 mm internal suspension system, 0.7 mm external button, P = .0115) and static loading (0.4 mm internal suspension system, 2.2 mm external button, P = .0019). CONCLUSIONS: Internal suspension systems may provide superior fixation compared to the traditional external button for tendon transfers, with the added benefit of avoiding the risk of skin ulceration and the need for suture and button removal. CLINICAL RELEVANCE: It appears internal suspension method of tendon transfer fixation would be an acceptable alternative to traditional methods of fixation with an external button.

Quantitative Ultrasound Assessment of the Achilles Tendon Under Varied Loads.

This Institutional Review Board-approved pilot study attempted to detect the correlation between ultrasound shear wave elastographic measures and tendon loads. Five male fresh-frozen cadaveric Achilles tendons were loaded in 10-N increments from 0 to 60 N. Shear wave velocity measurements within each Achilles tendon were obtained at each load in longitudinal and transverse orientations. Shear wave velocity measurements were correlated with tendon tension on both longitudinal and transverse plane imaging and showed moderate and strong positive correlation coefficients, respectively. Of note, limitations of the clinically available shear wave elastographic technology for measuring high velocities exist.

Geometric Characteristics of the Knee Are Associated With a Noncontact ACL Injury to the Contralateral Knee After Unilateral ACL Injury in Young Female Athletes.

BACKGROUND: Contralateral anterior cruciate ligament (CACL) injury after recovery from a first-time ACL rupture occurs at a high rate in young females; however, little is known about the risk factors associated with bilateral ACL trauma. HYPOTHESIS: The geometric characteristics of the contralateral knee at the time of the initial ACL injury are associated with risk of suffering a CACL injury in these female athletes. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Sixty-two female athletes who suffered their first noncontact ACL injury while participating in sports at the high school or college level were identified, and geometry of the femoral notch, ACL, tibial spines, tibial subchondral bone, articular cartilage surfaces, and menisci of the contralateral, uninjured, knee was characterized in 3 dimensions. We were unable to contact 7 subjects and followed the remaining 55 until either a CACL injury or an ACL graft injury occurred or, if they were not injured, until the date of last contact (mean, 34 months after their first ACL injury). Cox regression was used to identify risk factors for CACL injury. RESULTS: Ten (18.2%) females suffered a CACL injury. Decreases of 1 SD in femoral intercondylar notch width (measured at its outlet and anterior attachment of the ACL) were associated with increases in the risk of suffering a CACL injury (hazard ratio = 1.88 and 2.05, respectively). Likewise, 1 SD decreases in medial-lateral width of the lateral tibial spine, height of the medial tibial spine, and thickness of the articular cartilage located at the posterior region of the medial tibial compartment were associated with 3.59-, 1.75-, and 2.15-fold increases in the risk of CACL injury, respectively. CONCLUSION: After ACL injury, subsequent injury to the CACL is influenced by geometry of the structures that surround the ACL (the femoral notch and tibial spines). This information can be used to identify individuals at increased risk for CACL trauma, who might benefit from targeted risk-reduction interventions.

Adjacent Joint Kinematics After Ankle Arthrodesis During Cadaveric Gait Simulation.

BACKGROUND: Arthrodesis is an effective and reliable treatment for end-stage ankle arthritis; however, many patients develop ipsilateral adjacent joint arthritis following surgery. The mechanism that drives adjacent joint arthritis remains uncertain. Cadaveric simulation permits direct investigation of the effects of both arthrodesis and movement strategy on adjacent joints during simulated walking. The objective of this study was to identify the isolated effect of ankle arthrodesis on adjacent joint kinematics during simulated walking. METHODS: Effects of ankle arthrodesis on adjacent joint kinematics were assessed in 8 cadaveric foot and ankle specimens using a robotic gait simulator. Gait parameters acquired from healthy adults and patients with ankle arthrodesis were used as inputs for simulations. Three-dimensional subtalar and talonavicular joint kinematics were directly measured before and after ankle arthrodesis, and healthy- and arthrodesis-gait parameters were applied to identify the isolated effect of the ankle arthrodesis on adjacent joint kinematics. RESULTS: Ankle arthrodesis increased subtalar and talonavicular joint motion during early and midstance independent of which gait parameters were used as inputs to the gait simulator. However, adjacent joint motions did not differ between the control and arthrodesis condition during late stance, when the healthy gait parameters were used as inputs. Conversely, adjacent joint motion decreased during late stance following arthrodesis when simulating gait using parameters typical in arthrodesis patients. CONCLUSIONS: Regardless of the gait parameter inputs, subtalar and talonavicular joint motions increased from normal kinematics, which likely increase the biomechanical burden placed on these adjacent joints and may lead to joint degeneration. CLINICAL RELEVANCE: Increased motion of the adjacent joints caused by ankle arthrodesis may explain the articular degeneration observed clinically.

Relationship between geometry of the extensor mechanism of the knee and risk of anterior cruciate ligament injury.

The complex inter-segmental forces that are developed across an extended knee by body weight and contraction of the quadriceps muscle group transmits an anteriorly directed force on the tibia that strain the anterior cruciate ligament (ACL). We hypothesized that a relationship exists between geometry of the knees extensor mechanism and the risk of sustaining a non-contact ACL injury. Geometry of the extensor mechanism was characterized using MRI scans of the knees of 88 subjects that suffered their first non-contact ACL injury and 88 matched control subjects with normal knees that were on the same team. The orientation of the patellar tendon axis was measured relative to the femoral flexion-extension axis to determine the extensor moment arm (EMA), and relative to tibial long axis to measure coronal patellar tendon angle (CPTA) and sagittal patellar tendon angle (SPTA). Associations between these parameters and ACL injury risk were tested with and without adjustment for flexion and internal rotation position of the tibia relative to the femur during MRI data acquisition. After adjustment for internal rotation position of the tibia relative to the femur there were no associations between EMA, CPTA, and SPTA and risk of suffering an ACL injury. However, increased internal rotation position of the tibia relative to the femur was significantly associated with increased risk of ACL injury in female athletes both in univariate analysis (Odds Ratio = 1.16 per degree of internal rotation of the tibia, p = 0.002), as well as after adjustment for EMA, CPTA, and SPTA.: © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:965-973, 2017.

Geometric Risk Factors Associated With Noncontact Anterior Cruciate Ligament Graft Rupture.

BACKGROUND: Anterior cruciate ligament (ACL) graft rupture occurs at a high rate, especially in young athletes. The geometries of the tibial plateau and femoral intercondylar notch are risk factors for first-time ACL injury; however, little is known about the relationship between these geometries and risk of ACL graft rupture. HYPOTHESIS: The geometric risk factors for noncontact graft rupture are similar to those previously identified for first-time noncontact ACL injury, and sex-specific differences exist. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Eleven subjects who suffered a noncontact ACL graft rupture and 44 subjects who underwent ACL reconstruction but did not experience graft rupture were included in the study. Using magnetic resonance imaging, the geometries of the tibial plateau subchondral bone, articular cartilage, meniscus, tibial spines, and femoral notch were measured. Risk factors associated with ACL graft rupture were identified using Cox regression. RESULTS: The following were associated with increased risk of ACL graft injury in males: increased posterior-inferior-directed slope of the articular cartilage in the lateral tibial plateau measured at 2 locations (hazard ratio [HR] = 1.50, P = .029; HR = 1.39, P = .006), increased volume (HR = 1.45, P = .01) and anteroposterior length (HR = 1.34, P = .0023) of the medial tibial spine, and increased length (HR = 1.18, P = .0005) and mediolateral width (HR = 2.19, P = .0004) of the lateral tibial spine. In females, the following were associated with increased risk of injury: decreased volume (HR = 0.45, P = .02) and height (HR = 0.46, P = .02) of the medial tibial spine, decreased slope of the lateral tibial subchondral bone (HR = 0.72, P = .01), decreased height of the posterior horn of the medial meniscus (HR = 0.09, P = .001), and decreased intercondylar notch width at the anterior attachment of the ACL (HR = 0.72, P = .02). CONCLUSION: The geometric risk factors for ACL graft rupture are different for males and females. For females, a decreased femoral intercondylar notch width and a decreased height of the posterior medial meniscus were risk factors for ACL graft rupture that have also been found to be risk factors for first-time injury. There were no risk factors in common between ACL graft injury and first-time ACL injury for males.

Multivariate Analysis of the Risk Factors for First-Time Noncontact ACL Injury in High School and College Athletes: A Prospective Cohort Study With a Nested, Matched Case-Control Analysis.

BACKGROUND: Multivariate analysis that identifies the combination of risk factors associated with anterior cruciate ligament (ACL) trauma is important because it provides insight into whether a variable has a direct causal effect on risk or an indirect effect that is mediated by other variables. It can also reveal risk factors that might not be evident in univariate analyses; if a variable's effect is moderated by other variables, its association with risk may be apparent only after adjustment for the other variables. Most important, multivariate analyses can identify combinations of risk factors that are more predictive of risk than individual risk factors. HYPOTHESIS: A diverse combination of risk factors predispose athletes to first-time noncontact ACL injury, and these relationships are different for male and female athletes. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Athletes competing in organized sports at the high school and college levels participated in this study. Data from injured subjects (109 suffering an ACL injury) and matched controls (227 subjects) from the same athletic team were analyzed with multivariate conditional logistic regression to examine the effects of combinations of variables (demographic characteristics, joint laxity, lower extremity alignment, strength, and personality traits) on the risk of suffering their first ACL injury and to construct risk models. RESULTS: For male athletes, increases in anterior-posterior displacement of the tibia relative to the femur (knee laxity), posterior knee stiffness, navicular drop, and a decrease in standing quadriceps angle were jointly predictive of suffering an ACL injury. For female athletes the combined effects of having a parent who had suffered an ACL injury and increases in anterior-posterior knee laxity and body mass index were predictive of ACL injury. CONCLUSION: Multivariate models provided more information about ACL injury risk than individual risk factors. Both male and female risk models included increased anterior-posterior knee laxity as a predictor of ACL injury but were otherwise dissimilar.

Cadaveric gait simulation reproduces foot and ankle kinematics from population-specific inputs.

Cadaveric gait simulation allows researchers to directly investigate biomechanical consequences of surgeries using invasive measurement techniques. However, it is unclear if foot and ankle kinematics that are population-specific are reproduced using these devices. Therefore, we assessed foot and ankle kinematics produced in a cadaveric gait simulator during the stance phase of gait in a set of five cadaveric feet. Tibial motions and ground reaction forces previously collected in vivo in a group of healthy adults were applied as inputs parameters. In vitro foot and ankle kinematics were acquired and directly compared to population-specific in vivo kinematics of the same healthy adults from which input parameters were acquired. Analyses were completed using cross correlation to determine the similarities in kinematic profiles and joint ranges of motion were calculated to determine absolute differences in kinematics. Ankle, subtalar, and talonavicular in vitro joint kinematics were positively correlated to in vivo joint kinematics (rxy = 0.57-0.87). Further, in vivo and in vitro foot and ankle kinematics demonstrated similar amounts of within-group variability (rxy = 0.50-0.85 and rxy = 0.72-0.76, respectively). Our findings demonstrate that cadaveric gait simulation techniques reproduce population-specific foot and ankle kinematics, providing a valuable research tool for testing surgical treatments of foot and ankle maladies. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1663-1668, 2016.