Intraarticular pressure distribution in the talocrural joint is related to lower leg muscle forces.

BACKGROUND: It is of paramount importance to know the magnitude and the distribution of joint contact stress within the most heavily loaded structures of the human foot. In the talocrural joint role of external loading and loading applied by muscles on joint contact stress is not extensively studied. The purpose was to determine the distribution of joint contact stress of the talocrural joint with varying axial tibia loading and extrinsic tendon loading. METHODS: Five cadaveric feet were studied in the intact condition and following transsection of ligaments under seventeen different loading conditions. Joint contact stress was determined from capacitive pressure sensors implanted in the talocrural joint when the specimens were loaded in a specially designed loading simulator. Different axial tibia and extrinsic tendon loads were applied. Motions of the bony structures were assessed by an optical motion analysis system. FINDINGS: The anterior aspect of the joint is predominantly stressed in all loading conditions. The influence of muscle force on the internal joint contact stress distribution is higher than the axial shank loading. The biggest effect on joint contact stress was initiated by the tibialis posterior muscle. The flexor hallucis homogenizes the pressure distribution in intact joint conditions. Joint angles were not substantially changed by muscle force applications. INTERPRETATION: The functions of the muscles of the lower leg are important for maintaining physiologic joint contact stress. Reducing the force potentials of certain muscle tendon units through surgeries, immobilization, fatigue or inappropriate footwear should change the joint contact stress. Such information is helpful to understand the physiological function of the foot. It might also explain the development and manifestation of certain foot pathologies.

[Biomechanical Evaluation of Rehabilitation after Surgical Repair of Achilles Tendon Ruptures]. / Biomechanische Evaluation des Rehabilitationsverlaufs nach operativer Versorgung der Achillessehnenruptur.

Background Muscles and tendons are subjected to a high level of stress in everyday life and sports. This often leads to injuries and is associated with training failure and reduced performance as well as with high costs for treatment and rehabilitation. Fast and successful treatment is therefore very important, both from an athletic and economic point of view. This study aims to demonstrate the relevance of biomechanical procedures for the objective monitoring of rehabilitation. At the same time, the results are to be used to establish progress and evaluation criteria for an efficient and controlled rehabilitation. Patients and methods In a retrospective study, a total of 42 patients were evaluated biomechanically after surgical repair of a complete Achilles tendon rupture 18 (18 W) and 26 weeks (26 W) postoperatively. Ground reaction forces in barefoot walking on a treadmill as well as isokinetic maximum strength for the plantar flexors and dorsal extensors were assessed. Results The push-off force on the injured side increased from 0.88 (18 W) to 0.95 (26 W). The percentage of heel contact time on the injured side was 59 % at 18 W and 55 % at 26 W. Plantar flexion torque increased from 70 Nm (18 W) to 90 Nm (26 W) on average on the injured side. The percentage of the plantar flexion deficit (injured/non-injured side) decreased from 34 % to 21 % on the two postoperative measuring dates. Conclusions The described biomechanical methods allow for a quantitative assessment and an objective control of the rehabilitation process. The results can also be used for the definition of evaluation and progression criteria in order to assess the progress of a patient's therapy and to guide the rehabilitation process in a controlled manner.

Influence of calcaneus angle and muscle forces on strain distribution in the human Achilles tendon.

BACKGROUND: Heterogeneous distribution of tendon strain is considered to contribute to the development of the Achilles tendon overuse injuries. Force distribution between the three portions of the triceps surae muscle and position of the calcaneus might affect the extent of strain differences within the Achilles tendon. Purpose of this study was to determine the effect of changes in force distribution within the triceps muscle and changes in calcaneus position on intratendinous strain distribution of the Achilles tendon. METHODS: Five cadaveric Achilles tendons including complete triceps surae and calcaneus were dissected. Specimens were mounted in a loading simulator allowing independent force application for the three parts of triceps muscle and changes calcaneus eversion and inversion position. Strain was determined in different aspects of the Achilles tendon. FINDINGS: Changes of calcaneus position resulted in intratendinous strain differences up to 15%, changes in force distribution within the triceps muscle resulted in strain differences up to 2.5%. Calcaneal eversion was connected to a higher degree of strain in medial tendon portions, while inversion increased strain in lateral tendon portions. INTERPRETATION: Medio-lateral, proximo-distal and dorsal-ventral distribution of tendon strain is rather influenced by kinematics of the subtalar joint than by muscular imbalances within the triceps muscle. Clinical movement analyses should focus on motion pattern combining rearfoot eversion with high Achilles tendon load. The results indicate that twist of the Achilles tendon fascicles seems of paramount importance in balancing tendon strain. To get more insight into the Achilles tendon injuries pathogenesis future research should focus on methods monitoring heterogeneous distribution of strain in vivo.