Introduction

Cruciate retaining knee replacements are only implanted into patients with “healthy” ligaments. However, partial anterior cruciate ligament (ACL) tears are difficult to diagnose with conventional MRI. Variations of signal intensity within the ligament are suggestive of injury but it is not possible to confirm damage or assess the collagen alignment within the ligaments. The potential use of Magic Angle Directional Imaging (MADI) as a collagen contrast mechanism is not new, but has remained a challenge. In theory, ligament tearing or joint degeneration would decrease tissue anisotropy and reduce the magic angle effect. Spontaneous cruciate ligament rupture is relatively common in dogs. This study presents results from ten canine knees.

Interventional MRI provides a novel non-invasive method of in-vivo weight-bearing analysis of the talo-calcaneal joint. Six healthy males (mean 28.8 years) underwent static right foot weight bearing MRI imaging at 0o, 15o inversion, and eversion. Using known radiological markers the motion of the talus and calcaneum were analysed.

The calcaneum externally rotates, plantar-flexes and angulates into varus. The talus shows greater plantarflexion with similar varus angulation, with variable axial rotation. Relative talo-calcaneal motion thus involves, 6o relative talar internal rotation, 3.2o flexion and no motion in the frontal plane. Concurrently the talus moves laterally on the calcaneum, by 6.5mm, with variable translations in other planes.

The calcaneum plantar-flexes, undergoes valgus angulation, and shows variable rotation in the axial plane. The talus plantar-flexes less, externally rotates, and shifts into varus. Relative motion in the axial and saggital plane reverses rotations seen during inversion. The 8o of relative valgus talo-calcaneal angulation is achieved through considerable varus angulation of the talus, in a direction opposite to the input motion. This phenomenon has not been previously reported. From coronal MRI data, comparative talo-calcaneal motion in inversion is prevented by high bony congruity, whereas during eversion, the taut posterior tibio-talar ligament appears to prevent talar valgus angulation.

We have demonstrated that Interventional MRI scanning is a valuable tool in analysing the weight-bearing motion of the talo-calcaneal joint, whilst approaching the diagnostic accuracy of stereophotogammetry. We have also demonstrated consistent unexpected talar motion in the frontal plane. Talo-calcaneal motion is highly complex involving simultaneous rotation and translation, and hence calculations of instantaneous axes of rotation cannot effectively describe talo-calca-neal motion. We would suggest that relating individual and relative motion of the talus / calcaneum better describes subtalar kinematics.

Introduction and Aims: To assess the tibiofemoral kinematics of the PCL deficient knee using vertical open-access ‘dynamic’ MRI.

Method: Tibiofemoral motion was assessed using open-access MRI, weight-bearing in a squat, through the arc of flexion from zero to 90 degrees in six patients with isolated rupture of the PCL in one knee [diagnosed from conventional MRI scanning and clinical assessment] and a normal contralateral knee. Mid-medial and mid-lateral sagittal images were analysed in all chosen positions of flexion in both knees to assess the relative tibiofemoral relationships. Passive sagittal laxity was assessed by performing the posterior and anterior drawer tests, while the knees were scanned, again using the same MRI scanner. The tibiofemoral positions during this stress MRI examination was measured from mid-medial and mid-lateral sagittal images of the knees.

Results: Rupture of the PCL leads to an increase in passive sagittal laxity in the medial compartment of the knee [P< 0.006]. In the weight-bearing scans, PCL rupture alters the kinematics of the knee with persistent posterior subluxation of the medial tibia so that the femoral condyle rides up the anterior upslope of the medial tibial plateau. This ‘fixed’ subluxation was observed throughout the extension-flexion arc being statistically significant at all flexion angles (P< 0.018 at 0°, P< 0.013 at 20°, P< 0.014 at 45°, P< 0.004 at 90°). The kinematics of the lateral compartment were not altered by PCL rupture to a statistically significant degree. The posterior drawer test showed increased laxity in the medial compartment.

Conclusion: PCL rupture alters the kinematics of the medial compartment of the knee resulting in ‘fixed’ anterior subluxation of the medial femoral condyle [posterior subluxation of the medial tibial condyle]. This study helps to explain the observation of increased incidence of osteoarthritis in the medial compartment and specifically femoral condyle, in PCL deficient knees.

Background: Interventional MRI provides a novel non-invasive method of in-vivo weight-bearing analysis of the subtalar joint. Preceding in-vivo experimentation with stereophotogammetry of volunteers embedded with tantalum beads has produced valuable data on relative talo-calcaneal motion (Lundberg et al. 1989). However the independent motion of each bone remains unanswered.

Materials and Methods: Six healthy males (mean 28.8 years), with no previous foot pathology, underwent static right foot weight bearing MRI imaging at 0°, 15° inversion, and 15° eversion. Using identifiable radiological markers the absolute and relative rotational and translational motion of the talus and calcaneum were analysed.

Results and Discussion: Inversion: The calcaneum externally rotates, plantar-flexes and angulates into varus. The talus shows greater plantar-flexion with similar varus angulation, with variable axial rotation. Relative talo-calcaneal motion thus involves, 6° relative talar internal rotation, 3.2° flexion and no motion in the frontal plane. Concurrently the talus moves laterally on the calcaneum, by 6.5mm, with variable translations in other planes. This results in posterior facet gapping and riding up of the talus at its posterolateral prominence. Eversion: The calcaneum plantar-flexes, undergoes valgus angulation, and shows variable rotation in the axial plane. The talus plantar-flexes less, externally rotates, and shifts into varus. Relative motion in the axial plane reverses rotations seen during inversion (2.5° talar external rotation). The 8° of relative valgus talo-calcaneal angulation is achieved consistently through considerable varus angulation of the talus, in a direction opposite to the input motion. This phenomenon has not been previously reported. From coronal MRI data, comparative talo-calcaneal motion in inversion is prevented by high bony congruity, whereas during eversion, the taut posterior tibio-talar ligament prevents talar valgus angulation.

Conclusion: We have demonstrated that Interventional MRI scanning is a valuable tool to analysing the weight bearing motion of the talo-calcaneal joint, whilst approaching the diagnostic accuracy of stereophoto-gammetry. We have also demonstrated consistent unexpected talar motion in the frontal plane. Talo-calcaneal motion is highly complex involving simultaneous rotation and translation, and hence calculations of instantaneous axes of rotation cannot effectively describe talo-calcaneal motion. We would suggest that relating individual and relative motion of the talus / calcaneum better describes subtalar kinematics.

Purpose: To assess if ACL reconstruction restores normal knee kinematics.

Methods: Tibiofemoral motion was assessed weight-bearing through the arc of flexion from 0 to 90° in ten patients who were at least 6 months following successful hamstring graft ACL reconstruction. Lachman’s test was also performed using dynamic MRI. Mid-medial and mid-lateral images were analysed in all positions to assess the tibiofemoral relationship.

Results: The laxity of the reconstructed knees was reduced to within normal limits. However the normal tibiofemoral relationship was not restored after ACL reconstruction with persistent anterior subluxation of the lateral tibial plateau throughout the arc of flexion 0–90°(p< 0.001).

Conclusion: Successful ACL reconstruction reduces joint laxity and improves stability but it does not restore normal knee kinematics.

The vertical configuration open MRI Scanner (Signa SPIO, General Electric) has been used to assess the place of interventional MR in the management of developmental dysplasia of the hip over the last four years. Twenty-six patients have been studied. In static mode, coronal and axial T1 – weighted spin echo images are initially obtained to assess the anatomy of the hip, followed by dynamic imaging in near-real time.

In all cases, dynamic imaging was very good for assessing and demonstrating stability. The best position for containment can be assessed and a hip spica applied. Scanning in two planes gives more information and allows more accurate positioning than an arthrogram. Confirmation of location of the hip after application of the spica can be easily demonstrated. Adductor tenotomies have been performed within the imaging volume, and in two cases, this enabled planning of femoral osteotomies. All patients have had a satisfactory outcome, but five have required open reduction and a Salter innominate osteotomy.

In ten cases, the opportunity has also arisen to alternative perform an arthrogram, either because of the complexity of the cases, or at a later date as an alternative to a repeat MRI, or because of difficulty with access to the machine.

The place of interventional MRI in DDH is not yet defined. As machines get better and the definition improves, the amount of information about the nature of dislocation, the relative size of the acetabulum to the femoral head, the state of the limbus, the best position for containment and stability, and the potential for growth of the acetabulum, particularly posteriorly will be increased.

It follows that the potential for more accurate definition of each hip and the outcome is better – and safer – than by arthrography, which remains the ‘gold standard’ but involves radiation and is only one-dimensional.