Intermittent Pneumatic Compression Can Enhance Rat Achilles Tendon Repair After Immobilization

Introduction: Achilles tendon ruptures, whether operated or not, are mostly treated with long periods of immobilization. However, accumulating data show that prolonged immobilization is associated with impaired tissue repair including reduced biomechanical properties of the healing tendon. Prolonged immobilization leads to reduced blood flow and hampers the neuro-vascular ingrowth post-rupture [1], which is vital for repair by supplying different growth factors and neuronal mediators to the healing site. Intermittent Pneumatic Compression (IPC) treatment is based on passive increase of local blood flow by use of cyclic external pressure to reduce venous stasis, decrease venous pressure, and enhance arterial blood flow. Previous data have shown that daily IPC enhances neurovascular ingrowth as well as cell proliferation in a tendon rupture model [2]. However, whether IPC treatment could counteract the impairment of the healing process caused by immobilization has not previously been studied. We thus hypothesized that daily treatment with intermittent pneumatic compression may promote the healing of Achilles tendon ruptures under immobilized conditions Materials and Methods: A total of 48 male Sprague Dawley rats (weight 250 g) were divided into three groups of 16 (mobilized, immobilized and immobilized IPC treated). The experiment was approved by the Ethics Committee for Animal Research Stockholm North. Under anesthesia, the right Achilles tendon of the rats was bluntly ruptured. Immobilization was achieved by application of a plastic cast from the toes up to the hip. IPC treatment was applied for one hour daily under anesthesia during the experiment, starting at the first postoperative day. During treatment the casts were temporarily removed. 2 weeks post-rupture, all the rats were euthanized. In 10 rats of each group the Achilles tendons were dissected for biomechanical testing. The remaining 6 rats were perfused with Zambonis fixative and their Achilles tendons sectioned for later morphological assessments. The length of the tendon and the sagittal and transverse diameters of the callus were measured with a slide calliper. The cross-sectional area was estimated assuming elliptical geometry. Biomechanical assessment was a tensile test to measure the peak force, stiffness and energy uptake. Hematoxylin and eosin (H&E) staining was used to quantify the diameter of organized collagen in relation to the total tendon diameter. Sirius Red staining visualized under plain polarized light was applied for semi-quantitative analysis of the density of collagen III-like structures. Results: Compared to mobilization, immobilization caused a significant down-regulation (p<0.05) of peak force (80%), stiffness (77%), energy uptake (75%), tendon length (22%) and cross sectional area (47%), collagen III (83%) and organized collagen (36%). However when immobilization was combined with IPC the values of 5 out of the 7 parameters tested demonstrated a significant increase compared to pure immobilization (Table 1). The values in energy uptake and tendon length even reached the respective levels in the mobilized group. Table 1: Percentage change of the assessed data comparing the immobilized groups; pure immobilization was set as 0%.