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.

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.

Although the use of split tibialis anterior tendon transfer (combined with the Rose calcaneal osteotomy and reinforcement of the spring ligament) is a recognised procedure in the treatment of stage II tibialis posterior dysfunction, there is a paucity of data regarding its results. Forty-three patients who underwent reconstruction between 1997 and 2003 were evaluated pre- and postoperatively using the AHS scoring system. The average age was 57, and the mean follow-up time was 51 months (range 10–83).

The average AHS score pre-op. was 58 and post-op. was 85. Sixty-six per cent of patients achieved single heel raise. Eighty-four per cent expressed a subjective satisfaction rate, whilst 16% had no improvement. Seventy-eight per cent were able to use normal shoes and 58% did not require the use of any orthotics. The minor complication rate was 16% with no major complications. All osteotomies united uneventfully. Two patients have developed subtalar osteoarthritis, and six calcaneal screws had to be removed for prominence and tenderness.

Our results compare very favourably with other less anatomical reconstructions, but without the donor site morbidity and very low complication rates. A subjective satisfaction rate of 84% has been achieved.