Stiffness of the healing human Achilles tendon

Abstract: Achilles tendon ruptures in humans are followed by a long period of immobilisation, rehabilitation and limitations of physical activity and sometimes work also. This prolonged period probably leaves a marginal for improvement in the management of this injury. Animal studies have shown that there are several possibilities to influence and improve tendon healing.The aim of this thesis was to find a way to examine the mechanical properties of the healing human Achilles tendon and, by using that method, to gain a better understanding of the tissue properties and healing process in these tendons. It was also our aim to use our knowledge from animal studies in an attempt to improve tendon healing in humans.We developed a radiological method using radiostereophotogrammetric analysis (RSA) and computed tomography (CT), which enabled us to measure the stiffness of the healing Achilles tendon. The results of these measurements, as early as 7 weeks after injury correlated with the late clinical results in all studies. Clinical results were measured using a heel-raise test comparing the injured with the non-injured tendon. We could not find a significant difference in stiffness between patients treated surgically or non-surgically. Neither could we demonstrate that platelet-rich plasma improved the mechanical properties of the healing tendon or the clinical outcome, within the limits of the statistical power. In contrast, patients following a specific training programme with early tension loading of the tendon twice a day developed stiffer tendon tissue later in the healing process.Since RSA is unsuitable for routine clinical use, we evaluated the possibility to use radiodensity findings from CT as a proxy for healing and its correlation to mechanical and clinical results. Density and mechanical properties correlated strongly when analysing all time points together, but only weakly at each particular point in time. Density may still be useful in describing mechanical properties at a later stage of repair, but this remains to be seen.In conclusion, these studies show that early mechanical properties correlate to late clinical outcome and that the early use of daily tension loading sessions leads to an improvement in the mechanical properties of the tendon tissue.