The relationship between ankle, hindfoot, and forefoot position and posterior tibial muscle excursion

BACKGROUND: The purpose of this study was to examine the relationship of forefoot position in the transverse plane (abduction/adduction), hindfoot position in the frontal plane (eversion/inversion), and ankle position in the sagittal plane (plantarflexion/dorsiflexion) with posterior tibialis (PT) muscle excursion using an in vitro cadaver model. METHODS: Seven fresh-frozen cadaver specimens were potted and mounted on a frame. The PT tendon was dissected 15 cm proximal to the medial malleolus, and a 5-kg weight was sutured to the tendon. A six-camera motion analysis system (Optotrak, Northern Digital, Inc.) was used to track three-dimensional (3-D) motion of the tibia, calcaneus (hindfoot) and first metatarsal (forefoot) using bone pins. The ankle, hindfoot, and forefoot were manually placed in 24 different ankle and foot positions. A stepwise regression analysis was used to examine the relationship among ankle, hindfoot, and forefoot kinematics and PT muscle excursion. RESULTS: Hindfoot eversion/inversion and forefoot abduction/adduction accounted for 77% of the variance in PT muscle excursion, with small contributions from ankle plantarflexion/dorsiflexion (5.7%) and forefoot plantarflexion/dorsiflexion (1.9%). A combined regression equation applied to individual specimens resulted in average errors of less than 2.5 mm. CONCLUSIONS: This study supports the hypothesis that PT muscle excursion can be estimated using specific foot and ankle kinematic variables. Further, these data suggest that hindfoot eversion and forefoot abduction account for most of the variance in PT muscle excursion and are theorized to be important to control clinically altering the length of the posterior tibial muscle.     

The range of joint motions of the extremities in healthy Japanese people--the difference according to the age (author's transl)]

The passive range of motion was measured in the shoulder, elbow, forearm, wrist, hip, knee and ankle joints in 624 healthy Japanese persons ranging from the neonatal to 80 years of age, by the method formally decided by the Japanese Orthopaedic Association and the Japanese Association of Rehabilitation Medicine in 1974, followed by a statistical analysis. 1. The joint motions, the range of motion value of which being remarkably different by age, were found among the movements in external rotation and horizontal abduction of the shoulder, extension, abduction, adduction, external rotation, internal rotation of the hip and dorsiflexion of the ankle. 2. Elbow flexion, forearm pronation and supination, wrist dorsiflexion and knee flexion showed little change by age. 3. Extension, external rotation and horizontal abduction of the shoulder, dorsiflexion of the wrist, flexion of the hip, flexion of the knee and dorsiflexion and plantar flexion of the ankle gave values exceeding the normal range indicated by the associations. 4. The fluctuation in the range of joint motion was especially wide in the infant and the aged person.     

Analysis of ankle-hindfoot stability in multiple planes: an in vitro study

BACKGROUND: It is necessary to have an understanding of ankle and hindfoot motion and stability to accurately diagnosis and treat ankle-hindfoot disorders. METHODS: We devised an ankle ligament testing apparatus to more critically determine ankle stability in all planes with a constant rotational force applied (inversion, eversion, internal rotation, external rotation) throughout the range of sagittal plane motion in 13 cadaver specimens. Three-dimensional kinematics were determined with a magnetic tracking device. RESULTS: With inversion force applied, calcaneal-tibial inversion was greatest in maximal plantarflexion (mean 22.1 +/- 6.0 degrees) and gradually decreased with dorsiflexion, which indicated that the ankle had the most inversion instability in plantarflexion. With eversion force applied, calcaneal-tibial eversion gradually increased with increasing dorsiflexion to 12.7 +/- 7.4 degrees indicating that the most eversion instability was in dorsiflexion. With internal rotation force applied, calcaneal-tibial internal rotation from plantarflexion to neutral ankle position increased. With external rotation force application, external rotation from neutral to maximal dorsiflexion increased. CONCLUSIONS: Ankle laxity was not constant but varied depending on the plantarflexion-dorsiflexion position and the direction of the applied force. The degree of ankle laxity was greater with inversion and internal rotation torque. Variation in laxity between specimens was observed, consistent with previous reports. These data indicate that the ankle is less stable in plantarflexion when inversion and internal rotation forces are applied. This may explain why the lateral ankle ligaments are most prone to injury in this position. The ankle was less stable in dorsiflexion when eversion and external rotation forces were applied. This is consistent with the observation that deltoid ligament injuries occur in the neutral to dorsiflexion position. The study demonstrates the importance of examining patients with suspected ankle ligament injuries in several ankle positions. The ankle testing device has potential application for in vivo testing of patients with suspected ankle ligament instability.     

Foot Deformity Correction with Hexapod External Fixator,the Ortho-SUV Frame™

External fixators enable distraction osteogenesis and gradual foot deformity corrections. Hexapod fixators have become more popular than the Ilizarov apparatus. The Ortho-SUV Frame? (OSF; Ortho-SUV Ltd, St. Petersburg, Russia), a hexapod that was developed in 2006, allows flexible joint attachment such that multiple assemblies are available. We assessed the reduction capability of several assemblies. An artificial bone model with a 270-mm-long longitudinal foot was used. A 130-mm tibial full ring was attached 60 mm proximal to the ankle joint. A 140-mm, two-third ring forefoot was attached perpendicular to the metatarsal bone axis. A 130-mm, two-third ring hindfoot was attached parallel to the tibial ring. A V-osteotomy, which was combined with 2 oblique osteotomies at the navicular–cuboid bone and the calcaneus, was performed. The middle part of the foot, including the talus, was connected to the tibial ring. We assessed 5 types of forefoot applications and 4 types of hindfoot applications. The range of correction included flexion/extension in the sagittal plane, adduction/abduction in the horizontal plane, and pronation/supination in the coronal plane. Additionally, we reported the short-term results in 9 clinical cases. The forefoot applications in which the axis of the hexapod was parallel to the axis of the metatarsal bones had good results, with 52°/76° for flexion/extension, 48°/53° for adduction/abduction, and 43°/51° for pronation/supination. The hindfoot applications in which the hexapod encircled the ankle joint also had good results, with corresponding values of 47°/58°, 20°/35°, and 28°/31°. Clinically, all deformities were corrected as planned. Thus, multiple assemblies and a wide range of corrections are available with the OSF.     

Biomechanical evaluation of the ability of casts and braces to immobilize the ankle and hindfoot

We evaluated the ability of seven devices to immobilize a prosthetic ankle-foot complex against plantarflexion, dorsiflexion, inversion, and eversion forces: two casts (plaster of Paris and Fiberglas) and five removable braces (molded ankle/foot orthosis, composite boot brace, pneumatic boot walker, nonarticulating fracture boot, and ankle stirrup). Each device was applied to a prosthetic ankle-foot complex and evaluated on a test frame for resistance to sagittal motion and coronal torque. Results showed that casts offered significantly (P < or = 0.05) more resistance to motion in all directions tested than did the braces. The resistance offered by the devices tested depends on the conformity of the device to the shape of the foot in that plane and the material properties of the device. Braces offer the advantage of being easily removed and reapplied. Different braces offer specific advantages and disadvantages in different planes tested, and immobilization selection should be individualized based on this information.     

Kinematic changes after fusion and total replacement of the ankle: part 2: Movement transfer

INTRODUCTION: The purpose of this in vitro study was to determine the biomechanical characteristics of the ankle based on the movement transfer between foot and leg before and after ankle arthrodesis, and after implantation of three currently used total ankle prostheses. METHODS: A 6-df device with an axial load of 200 N and a four-camera high-speed video system were used for the measurement of the range of motion in six fresh-frozen cadaveric leg specimens. While the foot was moved through the range of dorsiflexion/plantarflexion, the resulting foot eversion/inversion and tibial rotation were recorded. Analogously, the resulting foot eversion/inversion from tibial rotation and, vice versa, the resulting tibial rotation from foot eversion/inversion were determined. The same measurements were performed for the normal ankle, the fused ankle, and after total ankle replacement by the AGILITY, HINTEGRA, and S.T.A.R. prostheses. RESULTS: While in dorsiflexion/plantarflexion of the foot, ankle joint fusion increased the movement transfer to tibial rotation by a 2.4 factor and to eversion/inversion by a 18.5 factor, whereas, this movement transfer did not change for all prostheses conditions. The movement transfer between foot eversion and tibial rotation was found to decrease for all ankle prostheses, but more in the AGILITY and S.T.A.R. prosthesis than in the HINTEGRA. CONCLUSIONS: The three tested ankle joint prostheses changed the movement transferred within the ankle joint complex less than ankle fusion did, especially for dorsiflexion/plantarflexion movement of the foot. The closer the design was to the normal anatomy of the ankle, the closer the transfer of movement was shown to be replicated with respect to normal joint. It is suggested that success of total ankle arthroplasty depends on how successfully designs can mimic the movement transfer of the normal ankle, while dissipating the rotational forces and maintaining the stability of the joint.     

Kinematic changes after fusion and total replacement of the ankle: part 1: Range of motion

BACKGROUND: The purpose of this study was to determine how closely the present designs of ankle prostheses mimic the unique requirements of the foot and ankle. The three-dimensional range of motion (ROM) of the ankle joint complex, before and after ankle arthrodesis and after implantation of three currently used total ankle prostheses, was investigated. METHODS: The three-dimensional ROM was determined in six fresh-frozen cadaver leg specimens using a 6-df device with an axial load of 200 N and a four-camera high-speed video system. A moment of 100 Nm was applied to the footplate to determine the ROM in the sagittal (dorsiflexion and plantarflexion) and frontal (inversion and eversion) planes. The same moment was applied to the tibia to determine the ROM for the internal and external tibial rotation. The measurements were performed for the normal ankle, the fused ankle, and the AGILITY, HINTEGRA, and S.T.A.R. prostheses. RESULTS: Compared to the normal condition, the ROM for dorsiflexion and plantarflexion was changed for all surgical interventions. The changes were highest for the ankle arthrodesis. The changes due to the prostheses were significantly less than the changes due to ankle arthrodesis. Compared to the normal condition, the total ROM for inversion/eversion was slightly decreased by the fused ankle and not changed by the three-component prostheses (HINTEGRA, S.T.A.R.). However, the ROM for inversion/eversion was significantly higher for the two-component prosthesis, AGILITY. The ROM for internal and external tibial rotation was not altered by the AGILITY and HINTEGRA ankle, but it was significantly reduced by the ankle arthrodesis. S.T.A.R. showed a significant shift of the total ROM toward internal tibial rotation. CONCLUSIONS: The three tested ankle joint prostheses changed the ROM of the ankle joint complex less than ankle fusion did. Total ankle prostheses were shown to replicate normal joint ROM closely. However, ankle arthrodesis was found to reduce the ROM substantially in all three planes: the sagittal, frontal, and horizontal planes. CLINICAL IMPLICATIONS: With respect to the ROM, total ankle replacement changes the natural ankle joint condition less than ankle arthrodesis, which reduces the ROM in all three planes and might increase stress in adjacent structures. The prosthesis that replicated the normal ankle joint ROM best was the one with the most anatomical design.     

Kinematic changes after fusion and total replacement of the ankle: part 3: Talar movement

INTRODUCTION: The purpose of this study was to determine talar movement (e.g., talar rotation and talar shift during (dorsiflexion/plantarflexion) with respect to the tibia in the normal ankle, in the fused ankle, and in the replaced ankle by currently used prosthetic designs. METHODS: A 6-df device with an axial load of 200 N and a four-camera high-speed video system were used for the measurement of the range of motion in six fresh-frozen cadaveri leg specimens. While moving the foot through the whole range of motion for plantarflexion/dorsiflexion, segmental motion of the marked bones of the foot and shank were measured dynamically. Rotation and medial-lateral shift of the talus were then calculated with regard to flexion position of the foot. RESULTS: In the normal ankle, plantarflexion movement was coupled with talar inversion of 3.5 degrees, and dorsiflexion movement with talar eversion of 1.0 degree, in totally accounting for 4.5 degrees of talar rotation. While both the HINTEGRA and the S.T.A.R. prostheses did not show changes to the normal condition during the dorsiflexion/plantarflexion cycle (p < .05), talar rotation had a 60% decrease (p < .05) for the AGILITY prosthesis. In the normal ankle joint, a lateral talar shift of 1.4 mm was found to occur during dorsiflexion, and a lateral talar shift of 5.2 mm during plantarflexion. In both, the HINTEGRA and S.T.A.R. ankles, talar shift was converted into medial direction during dorsiflexion of the foot (difference to normal: p < .05), whereas talar shift in the lateral direction was found to occur during plantarflexion of the foot which was comparable to the normal ankle. The AGILITY ankle evidenced an 80% decrease of talar shift (p < .05) during the whole dorsiflexion/plantarflexion cycle. DISCUSSION: The two-component ankle (AGILITY) obviously tends to restrict tremendously talar motion within the ankle mortise, whereas the three-component ankles (HINTEGRA, S.T.A.R.) seem to allow talar range of motion comparable to that in the normal ankle. It is suggested that such a restriction of talar motion results in an increase of stress forces within and around the prosthesis, leading to polyethylene wear and potential loosening at the bone-implant interfaces. Therefore, a successful prosthetic design for the ankle should consist of three components that are shaped as anatomically as possible to provide a normal range of motion and to allow the full transmission of movement transfer between foot and shank and unconstrained movement of the talus within the ankle mortise.     

跟骰关节融合对距舟关节三维运动度影响的实验研究

目的探讨跟骰关节融合对距舟关节三维运动度的影响及其临床意义。方法10只新鲜尸体足标本，通过建立非负重位尸体足模型，结合力偶矩、弯矩及平衡加载方法，应用三维坐标仪测量分析跟骰关节融合前、后距舟关节在大体足背屈、跖屈、内收、外展、内翻及外翻运动中的三维运动度变化。结果跟骰关节融合后，距舟关节三维运动度较融合前明显减小（P〈0．01）；其运动范围在矢状面减少31．21％±6．08％，冠状面减少51．46％±7．91％，水平面减少36．98％±4．12％，平均减少41．25％±6．02％。结论跟骰关节融合对距舟关节三维运动度有较大的限制作用，临床应用时不可忽视此负面效应。     

Six DOF in vivo kinematics of the ankle joint complex: Application of a combined dual‐orthogonal fluoroscopic and magnetic resonance imaging technique

Accurate knowledge of in vivo ankle joint complex (AJC) biomechanics is critical for understanding AJC disease states and for improvement of surgical treatments. This study investigated 6 degrees‐of‐freedom (DOF) in vivo kinematics of the human AJC using a combined dual‐orthogonal fluoroscopic and magnetic resonance imaging (MRI) technique. Five healthy ankles of living subjects were studied during three in vivo activities of the foot, including maximum plantarflexion and dorsiflexion, maximum supination and pronation, and three weight‐bearing positions in simulated stance phases of walking. A three‐dimensional (3D) computer model of the AJC (including tibia, fibula, talus, and calcaneus) was constructed using 3D MR images of the foot. The in vivo AJC position at each selected position of the foot was captured using two orthogonally positioned fluoroscopes. In vivo AJC motion could then be reproduced by coupling the orthogonal images with the 3D AJC model in a virtual dual‐orthogonal fluoroscopic system. From maximum dorsiflexion to plantarflexion, the arc of motion of the talocrural joint (47.5 ± 2.2°) was significantly larger than that of the subtalar joint (3.1 ± 6.8°). Both joints showed similar degrees of internal–external and inversion–eversion rotation. From maximum supination to pronation, all rotations and translations of the subtalar joint were significantly larger than those of the talocrural joint. From heel strike to midstance, the plantarflexion contribution from the talocrural joint (9.1 ± 5.3°) was significantly larger than that of the subtalar joint (?0.9 ± 1.2°). From midstance to toe off, internal rotation and inversion of the subtalar joint (12.3 ± 8.3° and ?10.7 ± 3.8°, respectively) were significantly larger than those of the talocrural joint (?1.6 ± 5.9° and ?1.7 ± 2.7°). Strong kinematic coupling between the talocrural and subtalar joints was observed during in vivo AJC activities. The contribution of the talocrural joint to active dorsi‐plantarflexion was higher than that of the subtalar joint, whereas the contribution of the subtalar joint to active supination–pronation was higher than that of the talocrural joint. In addition, the talocrural joint demonstrated larger motion during the early part of stance phase while the subtalar joint contributes more motion during the later part of stance phase. The results add quantitative data to an in vivo database of normals that can be used in clinical diagnosis, treatment, and evaluation of the AJC after injuries. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res     

Ankle ligament tensile forces at the end points of passive circumferential rotating motion of the ankle and subtalar joint complex

BACKGROUND: Ankle ligament injuries and instability are commonly observed. Knowledge of the relationship between the foot position and tensile forces of the ankle ligaments could be useful for treatment of ankle ligament disorders. The aim of this study was to measure the tensile forces of the ankle ligaments at the end points of passive circumferential rotating motion of the ankle and subtalar joint complex in various foot positions. METHODS: Ligament tensile forces of the anterior talofibular (ATF), calcaneofibular (CF), posterior talofibular (PTF), and tibiocalcaneal (TC) ligaments were measured simultaneously in eight cadaver specimens, with a force probe in each ligament in a custom-made ankle ligament testing device. Weights of 0.5 kg and 1 kg were applied to the foot through a loading arm to provide axial compression and a bending moment to the foot and ankle. The position of the loading arm was changed circumferentially in 10-degree increments. RESULTS: Maximal tensile force in the ATF ligament was observed in supination with plantarflexion (108 +/- 62.8 N at 0.5 kg and 130 +/- 39.1 N at 1 kg). The maximal tensile force in the CF ligament was observed in pronation with plantarflexion (68 +/- 48.6 N at 0.5 kg and 135 +/- 92.9 N at 1 kg). The maximal tensile force in the PTF ligament was observed in dorsiflexion (131 +/- 80.1 N at 0.5 kg and 109 +/- 36.3 N at 1 kg). The maximal tensile force of the TC ligament was observed in pronation with plantarflexion (49.0 +/- 80.1 N at 0.5 kg and 67.4 +/- 69.6 N at 1 kg). Relatively high magnitudes of tensile force were observed in the ankle ligaments, and the peak forces were related to the anatomic position of individual ligaments. CONCLUSIONS: The ATF ligament has an important role in the supination position in plantarflexion, CF and TC ligaments also are important for pronation in plantarflexion, and the PTF is an important stabilizer in dorsiflexion. This study provides baseline information for further research related to ligament instability and reconstruction operations.     

Kinematic MRI of the normal ankle ligaments using a specially designed passive positioning device

BACKGROUND: Knowledge of the normal MRI appearances of the ankle ligaments and tendons is particularly important in the diagnosis of ankle sprains. In most clinical practices, the ankle is imaged in a neutral position with standard imaging planes and sequences. The purpose of our study was to investigate whether passive positioning influences the MRI appearances of the ligaments of the ankle. METHODS: The axial and coronal T1-weighted MR images obtained from 10 subjects were reviewed by two musculoskeletal radiologists. The following imaging planes were used: dorsiflexion with inversion, dorsiflexion with neutral, dorsiflexion with eversion, neutral with inversion, neutral, neutral with eversion, plantarflexion with inversion, plantarflexion with neutral, and plantarflexion with eversion. A subjective rating system was used to determine the optimal imaging plane and position for individual ligaments in each volunteer. Each ligament was rated on a scale (of 1 to 6). RESULTS: There were significant differences in the appearances of the anterior talofibular (p = 0.0002), calcaneofibular (p < 0.0001), and posterior talofibular (p < 0.0001) ligaments between the optimal and least optimal ankle positions in the axial plane, and in those of the (plantar calcaneonavicular) spring (p < 0.0001), tibiocalcaneal (p < 0.0001), posterior tibiotalar (p = 0.0087) and posterior talofibular (p = 0.0213) ligaments in the coronal plane. CONCLUSIONS: Kinematic MRI of the ankle is feasible and appears to improve visualization of ankle ligaments compared to MRI.     

The relationship between excessive pronation as measured by navicular drop and isokinetic strength of the ankle musculature

EMG research has shown that excessive pronation affects the timing and magnitude of extrinsic muscle activity. This study was designed to investigate the relationship between excessive pronation and isokinetic strength of the ankle. The following measures were performed on 24 subjects (12 pronators, 12 normals) matched for gender and weight: 1) plantarflexion, dorsiflexion, inversion and eversion strength, both eccentrically and concentrically, determined by isokinetic peak torque at 30 degrees/sec; and 2) excessive pronation determined by navicular drop. Subjects with excessive pronation were found to have no difference in invertor strength, but decreased concentric plantarflexion strength when compared to normals. This finding agrees with biomechanical theory suggesting that a pronated foot is less rigid and generates less torque. Differences in strength ratios in excessive pronators were also observed and attributed to the decrease in plantarflexion strength.     

Shank rotation: A measure of rearfoot motion during normal walking

Motion of the shank in the transverse plane is coupled with pronation and supination of the rearfoot, and so its motion relative to the foot can be used as an indicator of the pattern of motion in the rearfoot. Compared to the more commonly used assessment of motion in the frontal plane between the heel and the shank, motion of the shank in the transverse plane relative to the foot provides a more complete measure of the pattern of motion of the rearfoot because it reflects the motion in all three joints of the rearfoot (the ankle, subtalar joint and mid-tarsal joint) not solely the ankle and subtalar components. This work aimed to provide normative data for this alternative measure of rearfoot function. Data on angular displacement, angular velocity and angular acceleration were derived from motion-analysis conducted on 25 subjects. The results suggest a difference between the pattern of angular displacement indicated when motion of the shank relative to the foot is examined and the pattern of angular displacement indicated when motion in the frontal plane between the shank and heel is examined. Specifically, the former suggests that resupination of the rearfoot after rearfoot pronation during the initial period of gait, starts at the beginning of mid-stance, while the latter suggests resupination beginning in late mid-stance. Where comparisons were possible, data on the velocity and acceleration appeared reasonable and provide further parameters with which to investigate the role of motion in the rearfoot in the development of pathologic conditions and the effects of intervention on motion in the rearfoot.     

Clinical biomechanics of the peritalar joint

The peritalar joint includes the articulations between the talus and calcaneus and the talus and navicular. Motion between the talus and calcaneus is described most often as rotation about an axis that points medially, anteriorly, and superiorly. This motion is considered to be triplanar, with inversion, plantar flexion, and adduction occurring together, whereas eversion, dorsiflexion, and abduction are associated. Similar motions have been described between the talus and navicular. Foot deformity, such as a pes planus or a pes cavus foot type, and hindfoot or midfoot joint fusion can alter the biomechanics of the peritalar joint.     

Mobility of the Ankle Joint: Recording of Rotatory Movements in the Talocrural Joint in vitro with and without the Lateral Collateral Ligaments of the Ankle

A method for graphic recording of rotatory movements in osteoligamentous ankle preparations is described. By this method it is possible to record characteristic mobility patterns in two planes at the same time. The ankle is affected by a known torque, so that the individual mobility patterns are reproducible with unchanged condition of the ligaments. Six amputated legs were investigated in the sagittal and horizontal planes and another six in the sagittal and frontal planes. Mobility patterns were recorded with intact ligaments and after successive cutting of the lateral collateral ligaments of the ankle in the anteroposterior direction. In the sagittal plane increased dorsiflexion was observed after total cutting of the lateral ligaments, while plantar flexion remained unchanged. In the horizontal plane the internal rotation of the talus increased in step with increasing injury to the ligament, particularly when the ankle was plantar flexed. When all collateral ligaments had been cut, an increase in external rotation occurred, especially in dorsiflexion. In the frontal plane the talar tilt increased gradually with increasing injury to the ligaments. Talar tilt was at a maximum in the neutral position of the ankle or in plantar flexion. After total severing of the collateral ligaments, however, talar tilt was most marked in dorsiflexion of the ankle.     

Pronation and supination of the foot: confused terminology

Many health professionals with interests in the foot are uncertain about the use of the terms inversion/eversion and pronation/supination. Inversion and eversion originate from 19th century anatomy texts and pronation and supination derive from works on comparative anatomy and evolution. In the 20th century, similar numbers of authorities use inversion/eversion and supination/pronation for movements of the whole foot about the antero-posterior axis or the oblique axis at the subtalar joint complex. Recently, it has become standard practice to use pronation/supination for movements of the whole foot when it is on the ground (closed-chain kinetics). Papers describing movements at individual foot joints generally use pronation/supination or define their own system. MacConaill’s useful concept of an osseofibrous plate has led to the concept of the forefoot being pronated or supinated with respect to the hindfoot. Clinicians describing inversion or eversion of the heel when assessing movement at the subtalar joint are referring to movement of the calcaneus about its anteroposterior axis rather than its triplane motion.     

Anterior plate supplementation increases ankle arthrodesis construct rigidity

BACKGROUND: The success of ankle arthrodesis for the treatment of post-traumatic ankle arthritis depends on achieving and maintaining rigid fixation of the prepared tibiotalar interface. The purpose of this study was to examine the biomechanical effect of anterior plate supplementation of a popular three-screw fusion construct. METHODS: Six fresh-frozen cadaver ankles were prepared and instrumented with three partially threaded screws compressing the tibiotalar interface. Testing was done with and without supplementary anterior plate fixation under three different decoupled loading conditions: plantarflexion/dorsiflexion, inversion/eversion, and rotation. Motion at the tibiotalar interface was recorded. RESULTS: Anterior plating increased construct stiffness by a factor of 3.5, 1.9, and 1.4 for the sagittal, coronal, and torsion modes, respectively. Less motion occurred at the tibiotalar interface in all to the three different loading conditions (p = 0.031) with plate supplementation. CONCLUSIONS: Compared to screws alone, anterior plate supplementation increases construct rigidity and decreases micromotion at the ankle fusion interface.     

Influence of foot position on the measurement of first metatarsal axial rotation using the first metatarsal axial radiographs

BackgroundThe purpose of this study was to clarify 1) the measurement error of the pronation angle using the first metatarsal axial radiograph with the pronation angle along the longitudinal axis of the first metatarsal as the reference standard, 2) the influence of variability in the foot position on the measurement error, and 3) the intra- and interrater reliability of pronation angle measurement using digitally reconstructed radiographs.MethodsDigitally reconstructed radiographs of the first metatarsal were generated from the computed tomography images of 10 feet without hallux valgus (non-HV group) and 10 feet with hallux valgus (HV group). In total, 135 images were created at different degrees of supination, plantarflexion, and adduction from each foot to simulate the first metatarsal axial view. Then, the pronation angle of the first metatarsal was measured. The measurement error was determined using the mean error and 95% limits of agreement. Simple linear regression analysis was used to test the correlations of the measurement error with pronation, plantarflexion and adduction angles. The intra- and interrater reliability of measurement was assessed using the intraclass correlation coefficient and minimum detectable change values.ResultsThe mean measurement errors were 0.1° for both the non-HV and HV groups. There was no significant correlation of the measurement error with pronation, plantarflexion or adduction angles for both groups. Additionally, the intraclass correlation coefficients for the intra- and interrater reliability were more than 0.9 in both the non-HV and HV groups with the minimum detectable change values ranging from 0.7° to 1.4°.ConclusionThe measurement error of first metatarsal pronation using the axial view was clinically acceptable. The measurements were not influenced by the variability in foot position while obtaining the radiograph. The first metatarsal axial view could be used to quantify the first metatarsal coronal rotation.