Introduction: As Achilles tendon ruptures are healing slowly, many attempts are made trying to improve the healing after injury. Rat experiments have shown that injection of platelets improves tendon healing. A clinical study on patients has also shown a better outcome after injecting platelets into the rupture area. Therefore we wanted to verify the effect of platelets by measuring the mechanical properties of the healing Achilles tendon in a randomised study.

Methods: We included 30 patients with an Achilles tendon rupture. All patients left one blood unit at the hospital blood bank. From this unit of blood approximately 20 ml of platelet concentrate were gained. All patients were operated the next day using an open technique. Just before wound closure, patients were randomised into 2 groups, with one group receiving 10 ml of their own platelet concentrate. In order to measure mechanical properties, we implanted Tantalum beads on either side of the rupture giving us the chance of exactly determining the distance between the beads using RSA and thereby measuring the stiffness of the tendon. CT was used to measure the area of the rupture site. Both groups were postoperatively treated with a cast for 7 weeks. 4 weeks with the ankle in the equines position and 3 weeks in the neutral position. After cast removal, the patients started rehabilitation. The patients in both groups received exactly the same treatment after surgery. Patients were examined with CT and RSA to determine area, stiffness and modulus of elasticity. Measurements were performed at 7 weeks after operation and again at 19 weeks.

Results: 16 patients were randomised to platelet concentrate. One patient got a deep infection and another patient suffered from a rerupture of the Achilles tendon. Both patients had to be excluded after the first CT- and RSA-examination. Both patients had received platelet concentrate. There was no significant difference between both groups after 7 and 19 weeks in area, stiffness or modulus of elasticity.

Discussion: Our results indicate that platelet concentrate does not improve the mechanical properties of the healing Achilles tendon, at least when patients are treated with a cast for 7 weeks.

Studies have shown that the effect of platelet concentrate is depending on a certain loading of the Achilles tendon during the early phase of healing. Unfortunately we do not know much about loading of the Achilles tendon while having the leg in a cast, but the rigid fixation might lead to certain unloading. Further studies are needed to learn more about loading of the Achilles tendon in a cast.

Furthermore we have also done a clinical examination of all patients, as we know from a previous study that there is a correlation between early mechanical properties and clinical outcome but we have not evaluated the clinical results of this study yet.

Local dysregulation of the proteolytic matrix metalloproteinases (MMPs) and their tissue inhibitors of metalloproteinases (TIMPs) is a feature of tendon degeneration and rupture.^1,2 To assess the role of systemic MMPs and TIMPs in tendon rupture we compared serum MMPs and TIMPs between patients who have previously suffered Achilles tendon rupture and healthy controls. We also followed serum MMPs and TIMPs prospectively in patients with acute tendon rupture.

At three years after injury, we measured serum MMP-1, -2, -3, -7, -8, -9 and -13 and TIMP-1 and -2 in eight patients who had suffered Achilles tendon rupture. Serum was also obtained from 12 blood donors with similar age and sex distribution. In another eight patients, MMPs and TIMPs were followed over time, with samples taken at the time of Achilles tendon injury, and after 4, 8 and 24 weeks. MMPs were determined using Fluorokine Multi Analyte Profiling kits while TIMPs were analysed using ELISA (R& D systems). The study was approved by the ethics committee and written informed consent was obtained from all patients.

Patients who had previously suffered tendon rupture had increased levels of MMP-2 (median difference (m.d.) 10 %; p = 0.01), MMP-7 (m.d. 15 %; p = 0.02) and TIMP-2 (m.d. 36%; p = 0.02), as compared to controls. In patients with acute tendon rupture, MMP-2 was the only MMP or TIMP to change significantly over time (p = 0.009). MMP-7 appeared to be higher than control values already at the time of rupture. MMP-13 could not be detected in any sample.

In conclusion, patients with a history of tendon rupture had elevated serum levels of MMP-2, MMP-7 and TIMP-2. Changes in MMP-7 might be present already at the time of rupture. This suggests that disturbances in proteolytic control might render tendons prone to rupture.