Introduction: The foot is a very complex structure acting as the platform for all gait patterns. At present, little is known about the exact biomechanics of the foot due to the difficulties in modeling all of the components of the foot accurately. This has made it virtually impossible to develop a complete understanding of the aetiology of many diseases of the foot including hallux rigidus. We hypothesize that sagittal plane incongruency of the rotation of the 1^st Metatarsophalangeal Joint (MTPJ), or an increase in the tension of the intrinsic plantar flexors is responsible for the development of hallux rigidus.

Materials & Methods: Ground reaction forces and kinematic data from gait analysis together with anthropometric data from MRI scans of a 24 y.o. female were used to create a Mimics model of the articulation of a normal 1st MTPJ during a gait cycle. The centre of rotation was calculated by triangulating the articular surfaces. Finite element analysis was performed on the model and on similar models with the hypothesized;

joint incongruency,

Results: The results demonstrated a significant increase in the peak stresses, contact areas and stress distributions between the incongruent models compared to the congruent models.

Discussion: To the best of our knowledge this is the most accurate FE model of the 1st MTPJ calculated. Hallux Rigidus is a very common forefoot disorder, with multiple etiologies and treatments advocated. This model demonstrates that an increased tension in the plantar flexors results in a reduced ROM with increased contact stresses on the joint surface.

Conclusion: While it is known Hallux Rigidus has a multi-factorial etiology, the authors feel the above study demonstrates an important inherent etiology.

Background: First Metatarsophalangeal joint (MTP) arthrodesis is commonly performed for hallux valgus with an arthritic joint, however previous studies have recommended that this should be combined with another procedure to correct the hallux valgus when the intermetatarsal angle is enlarged. We propose that an arthrodesis of the first MTP joint with a soft tissue release produces a significant correction of the intermetatarsal angle in such a group of patients avoiding the need for a concomitant procedure to change the intermetatatarsal angle.

Patients and Methods: The charts and radiographs of 20 patients who had an arthrodesis of the first MTP joint were retrospectively reviewed. All 20 patients were female with a mean age of 54.2 years (range 42–78 years). The intermetatarsal (IMT) angles were measured by two individuals independently. These were measured on a weight-bearing pre-operative film and a weight-bearing 6-week post-operative film. Fusions were performed using either the Hallu-S® plate or two crossed screws. A Student “t” test was performed on the change of the IMT angle and also on the inter-observer variations for the same.

Results: The mean pre-operative IMT angle was 16.85° (range 12–30°). The mean post-operative IMT angle was 10.6° (range 6–20°). The mean change in the IMT angle was 6.25° (range 2–12°). This change of the IMT angle was statistically significant – p< 0.0001 – Student “t” test. There was no significance in the inter-observer difference (p> 0.5) note in 6 radiographs with a mean of 1.3° (range 1–2°).

Conclusion: This is the first study to show that performing an arthrodesis of the first MTP joint with soft tissue release in patients with hallux valgus and degenerate first MTP joint will significantly correct the IM angle. Therefore, this alleviates the need for performing another procedure on these patients.

It has been well documented that leg length discrepancy can be associated with back, knee and hip problems. Less is known about the effect on the foot. The effect of a simulated leg length discrepancy on foot loading patterns and gait cycle times in normal individuals was investigated.

Thirty feet of normal volunteers were evaluated using a ‘Musgrave Footprint Computerised Pedobarograph System’. Leg length discrepancy was simulated using flexible polyurethane soles of 1 to 5cm thickness, secured to the sole of a sandal worn on the opposite foot. Recordings of foot pressures and load were made barefoot (control) and then recordings were taken with simulated leg length discrepancies of 1 to 5cm. As leg length discrepancy increased, the total loading on the foot increased from 35. 31 to 37. 99 kg/cm²/sec, the forefoot loading increased from 15. 58 to 19 kg/cm²/sec, whereas hindfoot loading remained the same. Further analysis of forefoot loading revealed that all subjects except for female middle loaders demonstrated increased hallux loading as the leg length discrepancy increased (p< 0. 0001). Analysis of gait cycle time with increasing leg length discrepancy showed that the contact phase of gait decreased from a mean of 22% to 13% (p< 0. 0001), the midstance phase remained the same, whereas the propulsion phase increased from 44% to 50% (p< 0. 003).

This study demonstrates for the first time that leg length discrepancy has manifest changes in the foot. When prescribing orthotics to address leg length discrepancy, orthopaedic surgeons should consider attempts to relieve the increased pressure on the 2nd and 3d metatarsal heads, or incorporate a metatarsal bar to decrease the time of metatarsal loading.