Multicoil Dixon chemical species separation with an iterative least-squares estimation method

This work describes a new approach to multipoint Dixon fat-water separation that is amenable to pulse sequences that require short echo time (TE) increments, such as steady-state free precession (SSFP) and fast spin-echo (FSE) imaging. Using an iterative linear least-squares method that decomposes water and fat images from source images acquired at short TE increments, images with a high signal-to-noise ratio (SNR) and uniform separation of water and fat are obtained. This algorithm extends to multicoil reconstruction with minimal additional complexity. Examples of single- and multicoil fat-water decompositions are shown from source images acquired at both 1.5T and 3.0T. Examples in the knee, ankle, pelvis, abdomen, and heart are shown, using FSE, SSFP, and spoiled gradient-echo (SPGR) pulse sequences. The algorithm was applied to systems with multiple chemical species, and an example of water-fat-silicone separation is shown. An analysis of the noise performance of this method is described, and methods to improve noise performance through multicoil acquisition and field map smoothing are discussed.

In vivo human gastrocnemius architecture with changing joint angle at rest and during graded isometric contraction

1. Human gastrocnemius medialis architecture was analysed in vivo, by ultrasonography, as a function of joint angle at rest and during voluntary isometric contractions up to the maximum force (MCV). maximum force (MVC). 2. At rest, as ankle joint angle increased from 90 to 150 deg, pennation increased from 15.8 to 27.7 deg, fibre length decreased from 57.0 to 34.0 mm and the physiological cross-sectional area (PCSA) increased from 42.1 to 63.5 cm2. 3. From rest to MVC, at a fixed ankle joint angle of 110 deg, pennation angle increased from 15.5 to 33.6 deg and fibre length decreased from 50.8 to 32.9 mm, with no significant change in the distance between the aponeuroses. As a result of these changes the PCSA increased by 34.8%. 4. Measurements of pennation angle, fibre length and distance between the aponeuroses of the gastrocnemius medialis were also performed by ultrasound on a cadaver leg and found to be in good agreement with direct anatomical measurements. 5. It is concluded that human gastrocnemius medialis architecture is significantly affected both by changes of joint angle at rest and by isometric contraction intensity. The remarkable shortening observed during isometric contraction suggests that, at rest, the gastrocnemius muscle and tendon are considerably slack. The extrapolation of muscle architectural data obtained from cadavers to in vivo conditions should be made only for matching muscle lengths.

Thickness of human articular cartilage in joints of the lower limb

OBJECTIVES

(a) To determine the topographical variations in cartilage thickness over the entire surfaces of cadaveric lower limb joints, and (b) to examine the correlations between: cartilage thickness and its site specific modulus; cartilage thickness and donor age, weight, height, and body mass index.

METHODS

The cartilage thickness of 11 sets of cadaveric human joints each comprising an ankle, knee, and hip was measured using a needle probe technique. Statistical analysis was used to compare the cartilage thickness of the different lower limb joints and the differences in cartilage thickness over the surface of individual joints. It was further examined whether cartilage had a correlation with its stiffness, and any of the details of the specimen donors such as age, weight, height, and body mass index.

RESULTS

The mean cartilage thickness of the knee was significantly greater than that of the ankle and hip (p < 0.001) in all 11 sets of joints, while the cartilage thickness of the hip was significantly greater than that of the ankle in 10 sets of joints (p < 0.001). The mass of specimen donors was found to correlate with the mean cartilage thickness of all three lower limb joints. A correlation was also found between the height of donors and the mean cartilage thickness of the knee and hip joints, while only in the ankle joint was a correlation found between the mean cartilage thickness and the body mass index of the specimen donors. A further correlation was found between cartilage thickness and its modulus; the thinner the cartilage, the higher the modulus.

CONCLUSIONS

The thickness of articular cartilage seems to be related to the congruance of a joint; thin cartilage is found in congruent joints such as the ankle, whereas thick cartilage is found in incongruent joints such as the knee. The correlations in this study imply that the larger and heavier was a donor the thicker was the cartilage in the lower limb joints. The data further suggest the presence of an inverse relation between the mean cartilage thickness and mean compressive modulus in each of the joints examined.

In vivo human tendon mechanical properties

1. The aim of the present study was to measure the mechanical properties of human tibialis anterior (TA) tendon in vivo. 2. Measurements were taken in five males at the neutral ankle position and involved: (a) isometric dynamometry upon increasing the voltage of percutaneous electrical stimulation of the TA muscle, (b) real-time ultrasonography for measurements of the TA tendon origin displacement during contraction and tendon cross-sectional area, and (c) magnetic resonance imaging for estimation of the TA tendon length and moment arm. 3. From the measured joint moments and estimated moment arms, the values of tendon force were calculated and divided by cross-sectional area to obtain stress values. The displacements of the TA tendon origin from rest to all contraction intensities were normalized to tendon length to obtain strain values. From the data obtained, the tendon force-displacement and stress-strain relationships were determined and the tendon stiffness and Young's modulus were calculated. 4. Tendon force and stress increased curvilinearly as a function of displacement and strain, respectively. The tendon force and displacement at maximum isometric load were 530 N and 4.1 mm, and the corresponding stress and strain values were 25 MPa and 2.5 %, respectively. The tendon stiffness and Young's modulus at maximum isometric load were 161 N mm-1 and 1.2 GPa, respectively. These results are in agreement with previous reports on in vitro testing of isolated tendons and suggest that under physiological loading the TA tendon operates within the elastic 'toe' region.

A musculoskeletal model of the human lower extremity: the effect of muscle, tendon, and moment arm on the moment-angle relationship of musculotendon actuators at the hip, knee, and ankle

We have developed a musculoskeletal model of the human lower extremity for computer simulation studies of musculotendon function and muscle coordination during movement. This model incorporates the salient features of muscle and tendon, specifies the musculoskeletal geometry and musculotendon parameters of 18 musculotendon actuators, and defines the active isometric moment of these actuators about the hip, knee, and ankle joints in the sagittal plane. We found that tendon slack length, optimal muscle-fiber length, and moment arm are different for each actuator, thus each actuator develops peak isometric moment at a different joint angle. The joint angle where an actuator produces peak moment does not necessarily coincide with the joint angle where: (1) muscle force peaks, (2) moment arm peaks, or (3) the in vivo moment developed by maximum voluntary contractions peaks. We conclude that when tendon is neglected in analyses of musculotendon force or moment about joints, erroneous predictions of human musculotendon function may be stated, not only in static situations as studied here, but during movement as well.

Water-fat separation with IDEAL gradient-echo imaging

PURPOSE

To combine gradient-echo (GRE) imaging with a multipoint water-fat separation method known as "iterative decomposition of water and fat with echo asymmetry and least squares estimation" (IDEAL) for uniform water-fat separation. Robust fat suppression is necessary for many GRE imaging applications; unfortunately, uniform fat suppression is challenging in the presence of B(0) inhomogeneities. These challenges are addressed with the IDEAL technique.

MATERIALS AND METHODS

Echo shifts for three-point IDEAL were chosen to optimize noise performance of the water-fat estimation, which is dependent on the relative proportion of water and fat within a voxel. Phantom experiments were performed to validate theoretical SNR predictions. Theoretical echo combinations that maximize noise performance are discussed, and examples of clinical applications at 1.5T and 3.0T are shown.

RESULTS

The measured SNR performance validated theoretical predictions and demonstrated improved image quality compared to unoptimized echo combinations. Clinical examples of the liver, breast, heart, knee, and ankle are shown, including the combination of IDEAL with parallel imaging. Excellent water-fat separation was achieved in all cases. The utility of recombining water and fat images into "in-phase," "out-of-phase," and "fat signal fraction" images is also discussed.

CONCLUSION

IDEAL-SPGR provides robust water-fat separation with optimized SNR performance at both 1.5T and 3.0T with multicoil acquisitions and parallel imaging in multiple regions of the body.

Effect of tendon orientation on MR imaging signal intensity: a manifestation of the "magic angle" phenomenon

To determine whether orientation in the static field may be responsible for the frequent occurrence of increased signal intensity within normal tendons at magnetic resonance (MR) imaging, seven healthy volunteers were imaged by means of a 1.5-T unit and standard clinical pulse sequences. The wrist, ankle, and shoulder regions were evaluated with local coils. Imaging was performed with tendon orientations ranging from 0 degree to 90 degrees in relation to the constant magnetic induction field (B0). Markedly increased intratendinous signal intensity was observed at the "magic angle" of 55 degrees, intermediate signal intensity was observed at 45 degrees and 65 degrees, and no signal intensity was observed at 0 degree and 90 degrees. Signal intensity was evident only when a short echo time was used. The authors believe that tendon orientation greatly affects tendon signal intensity in vivo. Increased signal intensity due to the magic angle effect may be misdiagnosed as tendinous degeneration, tendinitis, or frank tear.

Osteochondral defects in the ankle: why painful?

Osteochondral defects of the ankle can either heal and remain asymptomatic or progress to deep ankle pain on weight bearing and formation of subchondral bone cysts. The development of a symptomatic OD depends on various factors, including the damage and insufficient repair of the subchondral bone plate. The ankle joint has a high congruency. During loading, compressed cartilage forces its water into the microfractured subchondral bone, leading to a localized high increased flow and pressure of fluid in the subchondral bone. This will result in local osteolysis and can explain the slow development of a subchondral cyst. The pain does not arise from the cartilage lesion, but is most probably caused by repetitive high fluid pressure during walking, which results in stimulation of the highly innervated subchondral bone underneath the cartilage defect. Understanding the natural history of osteochondral defects could lead to the development of strategies for preventing progressive joint damage.

In vivo moment arm calculations at the ankle using magnetic resonance imaging (MRI)

In vivo moment arm lengths for the Achilles tendon and tibialis anterior (TA) were determined in 10 adult male subjects. Moment arms were measured as the perpendicular distance between the joint center of rotation (CR) and the center of the muscle's tendon on a series of sagittal plane magnetic resonance images. The first set of calculations used a fixed CR and the second a moving CR. The position of the CR was determined using a modification of the graphical method of Reuleaux. For both moving and fixed CR conditions, moment arms increased by approximately 20% for the Achilles tendon and decreased by approximately 30% for the TA when the ankle moved from maximum dorsiflexion to maximum plantarflexion. Moment arms averaged 3.1% greater for the Achilles tendon and 2.5% greater for the TA when calculated using a fixed CR. These data suggest that the averaged moment arm lengths for the Achilles tendon and the TA were relatively unaffected by the use of a fixed vs moving CR.

Risk factors for leg injuries in female soccer players: a prospective investigation during one out-door season

The following possible risk factors for leg injuries in female soccer players were studied: age, anatomical alignment, generalized joint laxity, thigh muscle torque, muscle flexibility, ligamentous laxity of the knee and ankle joints, recent injuries, and duration of soccer exposure. A total of 146 players from 13 teams in the second and third Swedish divisions underwent clinical examination, isokinetic measurements of quadriceps and hamstring torques, and testing of postural sway of the legs. All soccer-related leg injuries resulting in absence from at least one scheduled practice session or game were recorded during one outdoor season (April-October). In 50 players there were 61 traumatic injuries, and 17 players sustained 19 overuse injuries. The overall injury incidence rate (traumatic and overuse) was 5.49/1000 h of soccer. Variables significantly increasing the risk of traumatic leg injuries included generalized joint laxity, low postural sway of the legs, hyperextension of the knee joint, and a low hamstring-to-quadriceps ratio during concentric action. Multivariate logistic regression showed hyperextension of the knee joint, a low postural sway, reduced H/Q ratio during concentric action, and a higher exposure to soccer to significantly increase the risk of traumatic leg injury. All five players who suffered an anterior cruciate ligament injury during the study period had a lower hamstring-to-quadriceps ratio during concentric action on the injured side than on their noninjured side.

A radiographic evaluation of the tibiofibular syndesmosis

A radiographic evaluation of the normal as well as the progressively widened tibiofibular interval in the area of the syndesmosis was done using 12 fresh cadaver lower extremities. The width of the tibiofibular "clear space" and the amount of tibiofibular overlap was determined on accurately positioned anterior-posterior and mortise radiographs. Based on a 95% confidence interval, measurements obtained for the intact specimens would support the following criteria as consistent with a normal tibiofibular relationship: (1) a tibiofibular "clear space" on the anterior-posterior and mortise views of less than approximately 6 mm; (2) tibiofibular overlap on the anterior-posterior view of greater than approximately 6 mm or 42% of fibular width; (3) tibiofibular overlap on the mortise view of greater than approximately 1 mm. The width of the tibiofibular "clear space" on both anterior-posterior and mortise views appeared to be the most reliable parameter for detecting early syndesmotic widening.

Changes in Achilles tendon moment arm from rest to maximum isometric plantarflexion: in vivo observations in man

1. The purpose of the present study was to examine the effect of a plantarflexor maximum voluntary contraction (MVC) on Achilles tendon moment arm length. 2. Sagittal magnetic resonance (MR) images of the right ankle were taken in six subjects both at rest and during a plantarflexor MVC in the supine position at a knee angle of 90 deg and at ankle angles of -30 deg (dorsiflexed direction), -15 deg, 0 deg (neutral ankle position), +15 deg (plantarflexed direction), +30 deg and +45 deg. A system of mechanical stops, support triangles and velcro straps was used to secure the subject in the above positions. Location of a moving centre of rotation was calculated for ankle rotations from -30 to 0 deg, -15 to +15 deg, 0 to +30 deg and +15 to +45 deg. All instant centres of rotation were calculated both at rest and during MVC. Achilles tendon moment arms were measured at ankle angles of -15, 0, +15 and +30 deg. 3. At any given ankle angle, Achilles tendon moment arm length during MVC increased by 1-1.5 cm (22-27 %, P < 0.01) compared with rest. This was attributed to a displacement of both Achilles tendon by 0.6-1.1 cm (P < 0.01) and all instant centres of rotation by about 0.3 cm (P < 0.05) away from their corresponding resting positions. 4. The findings of this study have important implications for estimating loads in the musculoskeletal system. Substantially unrealistic Achilles tendon forces and moments generated around the ankle joint during a plantarflexor MVC would be calculated using resting Achilles tendon moment arm measurements.

Anatomy of the lateral ankle ligaments

The anatomy of the lateral ankle ligaments that is frequently described in articles and book chapters often lacks the precision of orientation and attachment points. We believe a knowledge of this precise anatomy is important to better reconstruct or repair lateral ligaments. We dissected cadaveric ankles free of skin and soft tissue and made the following measurements: areas of attachments of the anterior talofibular ligament, length and width of the anterior talofibular ligament, and locations of the attachments on the fibula and talus. The same measurements were made of the calcaneofibular and posterior talofibular ligaments. The distance of the calcaneofibular calcaneal attachments from the subtalar joint as well as the angle in the sagittal plane with the fibula was determined. We then used these anatomic attachments of the ligaments to make comparisons with the Watson-Jones and modified Elmslie reconstructions. Our results enable us to suggest a more anatomic placement for ligaments in a reconstruction.

Effects of arch height of the foot on angular motion of the lower extremities in running

It has been suggested that a relationship exists between the height of the medial longitudinal arch of the foot and athletic injuries to the lower extremities. However, the functional significance of arch height in relation to injury is not well understood. The purpose of this study was to determine the influence of arch height on kinematic variables of the lower extremities that have been associated with the incidence of injury in running in an attempt to gain some insight into a functional relationship between arch height and injury. The three-dimensional kinematics of the lower extremities were measured during running for 30 subjects using high-speed video cameras. A joint coordinate system was used to calculate the three-dimensional orientation of the ankle joint complex for a single stance phase. Simple, linear regression analyses showed that arch height does not influence either maximal eversion movement or maximal internal leg rotation during running stance. However, assuming that knee pain in running can result from the transfer of foot eversion to internal rotation of the tibia, a functional relationship between arch height and injury may exist in that the transfer of foot eversion to internal leg rotation was found to increase significantly with increasing arch height. A substantial (27%), yet incomplete, amount of the variation in the transfer of movement between subjects was explained by arch height, indicating that there must be factors other than arch height that influence the kinematic coupling at the ankle joint complex. Additionally, the transfer of movement is only one factor of many associated with the etiology of knee pain in running.(ABSTRACT TRUNCATED AT 250 WORDS)

Variability of extraarticular tibial rotation references for total knee arthroplasty

Anatomic reference axes that determine rotational alignment of the tibial component have not been established. To assess variability of three anatomic reference axes (a new tibial anteroposterior axis that we proposed, the transmalleolar axis of the ankle, and the second metatarsus bone axis of the foot), we measured the angles between a defined anteroposterior axis of the tibia (a line perpendicular to the transepicondylar axis) and each of the three axes in 57 knees of healthy subjects using computed tomography scans. The angle between the defined anteroposterior axis and our proposed anteroposterior axis (a line connecting the middle of the posterior cruciate ligament and the medial edge of the patellar tendon attachment) averaged -0.2 degrees +/- 2.8 degrees (range, -5.5 degrees -6.3 degrees). The angle between the defined anteroposterior axis and the transmalleolar axis averaged 25.9 degrees +/- 9 degrees (range, 8 degrees -49.4 degrees), and the angle between the defined anteroposterior axis and the second metatarsus bone axis averaged 5.2 degrees +/- 10 degrees (range, -21.9 degrees -24 degrees). The variability of the anteroposterior axis was less than than the other reference axes. These data indicate that our proposed tibial anteroposterior axis is more reliable for determining rotational alignment of the tibial component in total knee arthroplasty.

Behavior of human muscle fascicles during shortening and lengthening contractions in vivo

The aim of the present study was to investigate the behavior of human muscle fascicles during dynamic contractions. Eight subjects performed maximal isometric dorsiflexion contractions at six ankle joint angles and maximal isokinetic concentric and eccentric contractions at five angular velocities. Tibialis anterior muscle architecture was measured in vivo by use of B-mode ultrasonography. During maximal isometric contraction, fascicle length was shorter and pennation angle larger compared with values at rest (P < 0.01). During isokinetic concentric contractions from 0 to 4.36 rad/s, fascicle length measured at a constant ankle joint angle increased curvilinearly from 49.5 to 69.7 mm (41%; P < 0.01), whereas pennation angle decreased curvilinearly from 14.8 to 9.8 degrees (34%; P < 0.01). During eccentric muscle actions, fascicles contracted quasi-isometrically, independent of angular velocity. The behavior of muscle fascicles during shortening contractions was believed to reflect the degree of stretch applied to the series elastic component, which decreases with increasing contraction velocity. The quasi-isometric behavior of fascicles during eccentric muscle actions suggests that the series elastic component acts as a mechanical buffer during active lengthening.

Anatomy of the tibiofibular syndesmosis and its clinical relevance

The purpose of the present study was to describe the anatomical structure of the tibiofibular syndesmosis. Dissection of the tibiofibular syndesmosis was performed on 30 cadaveric specimens of the ankle in adults. The stability of the tibiofibular mortise is ensured by three ligaments. The interosseous tibiofibular ligament forms a spatial network of fibers of a pyramidal shape filled with fibrofatty tissue. The anterior tibiofibular ligament consists of three parts: the upper one is the shortest, the medial one is the strongest and the lower part is the longest and the thinnest. The posterior tibiofibular ligament is a strong, compact ligament the lower margin of which literally forms the articular labrum for the lateral ridge of the trochlea of the talus. The so-called inferior transverse tibiofibular ligament, as this part of the ligament is sometimes characterized, cannot be considered as a separate ligament. Direct contact between the distal tibia and the fibula was found in 23 cases. Contact facets which were covered with articular cartilage were very small and located in the anterior half of the tibiofibular contact line. In the posterior part of the tibiofibular contact line a vertical V-shaped synovial plica attached by its lateral aspect to the fibula dipped between the two bones. In seven cases where there was no direct contact between the two bones this plica extended anteriorly to the anterior tibiofibular ligament. The findings show that in three quarters of cases the connection of the distal tibia and fibula is not a mere syndesmosis but also a synovial joint. The presented facts change traditional opinions on the structure of the tibiofibular syndesmosis and they should be reflected in the treatment of dislocation-fractures of the ankle as well as in case of so-called anterolateral ankle impingement.

In vivo determination of the anatomical axes of the ankle joint complex: an optimization approach

This study investigates the feasibility of a subject-specific three-dimensional model of the ankle joint complex for kinematic and dynamic analysis of movement. The ankle joint complex was modelled as a three-segment system, connected by two ideal hinge joints: the talocrural and the subtalar joint. A mathematical formulation was developed to express the three-dimensional translation and rotation between the foot and shank segments as a function of the two joint angles, and 12 model parameters describing the locations of the joint axes. An optimization method was used to fit the model parameters to three-dimensional kinematic data of foot and shank markers, obtained during test movements throughout the entire physiological range of motion of the ankle joint. The movement of the talus segment, which cannot be measured non-invasively, is not necessary for the analysis. This optimization method was used to determine the position and orientation of the joint axes in 14 normal subjects. After optimization, the discrepancy between the best fitting model and actual marker kinematics was between 1 and 3 mm for all subjects. The predicted inclination of the subtalar joint axis from the horizontal plane was 37.4 +/- 2.7 degrees, and the medial deviation was 18.0 +/- 16.2 degrees. The lateral side of the talucrural axis was directed slightly posteriorly (6.8 +/- 8.1 degrees), and inclined downward by 7.0 +/- 5.4 degrees. These results are similar to previously reported typical results from anatomical, in vitro studies. Reproducibility was evaluated by repeated testing of one subject, which resulted in variations of about one-fifth of the standard deviation within the group, the inclination of the subtalar joint axis was significantly correlated to the arch height and a radiographic 'tarsal index'. It is concluded that this optimization method provides the opportunity to incorporate inter-individual anatomical differences into kinematic and dynamic analysis of the ankle joint complex. This allows a more functional interpretation of kinematic data, and more realistic estimates of internal forces.

Radiographic measurements do not predict syndesmotic injury in ankle fractures: an MRI study

Several radiographic measurements have been described and are used to determine ligamentous injury in ankle fractures, particularly of the deltoid and syndesmosis complex. Because the accuracy of these radiographic measurements has been questioned, we sought to evaluate their accuracy using magnetic resonance imaging as an indicator for injury. Seventy patients with closed ankle fractures were entered prospectively into the study, and all had standard plain radiographic evaluations before reduction (anteroposterior, lateral, and mortise) and magnetic resonance imaging. Four radiographic measurements were made on initial ankle injury films: tibiofibular clear space on the anteroposterior view, tibiofibular overlap on the anteroposterior and mortise views, and medial clear space on the mortise view. These radiographic measurements and their association with magnetic resonance imaging findings then were analyzed. A medial clear space measurement greater than 4 mm correlated with disruption of the deltoid and the tibiofibular ligaments. We found no association between the tibiofibular clear space and overlap measurements on radiographs with syndesmotic injury on magnetic resonance imaging scans.

LEVEL OF EVIDENCE

Prognostic study, Level II-1 (retrospective study). See the Guidelines for Authors for a complete description of levels of evidence.

From the RSNA Refresher Courses. Radiological Society of North America. MR imaging of the ankle and foot

Magnetic resonance (MR) imaging has opened new horizons in the diagnosis and treatment of many musculoskeletal diseases of the ankle and foot. It demonstrates abnormalities in the bones and soft tissues before they become evident at other imaging modalities. The exquisite soft-tissue contrast resolution, noninvasive nature, and multiplanar capabilities of MR imaging make it especially valuable for the detection and assessment of a variety of soft-tissue disorders of the ligaments (eg, sprain), tendons (tendinosis, peritendinosis, tenosynovitis, entrapment, rupture, dislocation), and other soft-tissue structures (eg, anterolateral impingement syndrome, sinus tarsi syndrome, compressive neuropathies [eg, tarsal tunnel syndrome, Morton neuroma], synovial disorders). MR imaging has also been shown to be highly sensitive in the detection and staging of a number of musculoskeletal infections including cellulitis, soft-tissue abscesses, and osteomyelitis. In addition, MR imaging is excellent for the early detection and assessment of a number of osseous abnormalities such as bone contusions, stress and insufficiency fractures, osteochondral fractures, osteonecrosis, and transient bone marrow edema. MR imaging is increasingly being recognized as the modality of choice for assessment of pathologic conditions of the ankle and foot.

Traumatic dislocations of the peroneal tendons

Traumatic dislocation of the peroneal tendons is an often unrecognized injury which has been reported to occur most commonly during snow skiing. The strength of the peroneal retinaculum is exceeded during resistance to violent passive dorsiflexion or to inversion stress. Pain, swelling, and ecchymosis may hinder early diagnosis; however, intense retromalleolar pain on active eversion is a specific, highly suggestive finding. Fracture of a thin shell of the lateral malleolar cortex is diagnostic. In chronic cases, marked dislocation of the tendons is frequently demonstrable, with more than the usual degree of snapping. Surgical repair is advocated, using one of several procedures available. Most acute cases can be treated by simple repair of the torn or fractured structures. In chronic cases, or in acute cases with deficient structures predisposing to dislocation, it is necessary to reconstruct the peroneal retinaculum and/or deepen the peroneal groove. Longitudinal splitting of the peroneus brevis tendon was a new finding in this series.

Talocrural joint in African hominoids: implications for Australopithecus afarensis

Talocrural joints of the African apes, modern humans, and A.L.288-1 are compared in order to investigate ankle function in the Hadar hominids. Comparisons between the hominids and African pongids clearly illustrate the anatomical and mechanical changes that occurred in this joint as a consequence of the evolutionary transition to habitual bipedality. Features which are considered include the obliquity of the distal tibial articular surface, the shape of the talar trochlea, and the location and functional implications of the talocrural axis. In every functionally significant feature examined the A.L.288-1 talocrural joint is fully bipedal. Moreover, the Hadar ankle complex also shows the functional constraints which are necessarily imposed by the adaptation to habitual bipedalism.

The effects of rotation on radiographic evaluation of the tibiofibular syndesmosis

Radiographs of 12 normal cadaveric lower extremities were prepared with each extremity in seven increments of axial rotation, ranging from 5 degrees of external rotation to 25 degrees of internal rotation. The tibiofibular clear space, the tibiofibular overlap, the width of the tibia and fibula, and the medial clear space were measured on each film. The width of the tibiofibular clear space (syndesmosis A) averaged 3.9+/-0.9 mm (range, 2 to 5.5 mm), but did not change significantly with rotation. Its size was independent of the size of tibia and fibula. All other measurements changed dramatically with rotation. In our specimens, a true mortise view of the ankle joint was obtained by internally rotating the extremity an average of 13.6+/-0.7 degrees (range, 12.0 degrees to 17.0 degrees). Based on our results the width of the tibiofibular clear space on the anterior-posterior view is the most reliable parameter for detecting widening of the syndesmosis on plain radiographs. However, due to its variability among different individuals, comparison views of the contralateral extremity are warranted for confirmation of clinical suspicion of syndesmosis disruption.

Ultra-high-field MRI of the musculoskeletal system at 7.0T

High-field (3T) and ultra-high-field (UHF, 7T and above) systems are increasingly being used to explore potential musculoskeletal applications because they provide a high intrinsic signal-to-noise ratio (SNR), potentially higher resolution (spatial and temporal), and improved contrast. However, imaging at 7T and above presents certain challenges, such as homogeneous radiofrequency (RF) coil design, increased chemical shift artifacts, susceptibility artifacts, RF energy deposition, and changes in relaxation times compared to more typical clinical scanners (1.5 and 3T). Despite these issues, MRI at 7T likely will provide some excellent opportunities for high-resolution morphologic imaging and forays into functional imaging of musculoskeletal systems. In this review we address some of these issues and also demonstrate the feasibility of acquiring high-resolution in vivo images of the musculoskeletal system in healthy human volunteers at 7.0T.

Ankle joint biomechanics

A three-dimensional analysis of the human ankle joint is presented to analyse data obtained from gait laboratory tests. The ankle was treated as consisting of two joints, the talocrural (Tc.) and the talocalcaneonavicular (Tcn.), and relevant anatomical dimensions were based upon cadaveric anthropometric data. Seven adult male subjects were studied during the stance phase of normal locomotion. Data was acquired from three orthogonally placed cine cameras and a force platform. Two models were investigated based on force equilibrium; a Mark I model which excluded the posterior tibial and peroneal muscle groups and a Mark II model, which included them. The Mark II model gave the following resultant peak forces expressed as multiples of body weight; Tc. joint force = 3.9; Tcn. joint forces--anterior facet = 2.4, posterior facet = 2.8. The latter model was felt to have good potential in the analytical assessment of ankle pathologies and endoprostheses.