Background

Mechanical stimulation of joints regulates the biosynthetic activity of chondrocytes. It has been argued that excessive loading might cause chondrocyte death, leading to degeneration of cartilage and cause osteoarthritis. The aims of this study were to apply a high, short-term loading, and a low intensity, long-term loading protocol to intact joints in life animals and determine changes in synovial fluid and the percentage of dead cells in rabbit knee cartilage.

Method

Nine rabbits were subjected to unilateral exercise loading consisting of five sets of 10 maximal eccentric knee contractions. Another 6 rabbits were subjected to submaximal concentric contractions for 30 min at 20% of the maximum isometric knee extensor force. Contralateral joints served as unloaded controls. Cell viability was assessed using confocal microscopy. Synovial fluid was analyzed for total protein concentration and total number of identifiable proteins and was compared to protein content of control rabbits (n = 4).

Findings

Neither the high-intensity, short-term nor the low-intensity, long-term loading protocol caused increased chondrocyte death compared to the unloaded control joints. Total synovial fluid protein concentration was the same before and after exercise. Following the high-intensity exercise protocol, the number of identifiable proteins was decreased, while following the low-intensity exercise protocol, the number of identifiable proteins was increased compared to control.

Interpretation

Chondrocytes are well protected in the intact joint and withstood maximal eccentric muscular loading, and maximal endurance loading. Synovial fluid protein content was changed after exercise, and these changes depended crucially on the type of loading.

中文翻译：

---

最大和次最大循环同心和离心运动对兔膝软骨细胞死亡和滑液蛋白的影响。

背景

关节的机械刺激调节软骨细胞的生物合成活性。有人认为，过度负荷可能导致软骨细胞死亡，导致软骨变性并引起骨关节炎。这项研究的目的是将高，短期负荷和低强度，长期负荷方案应用于活体动物的完整关节，并确定滑液的变化和兔膝软骨中死细胞的百分比。

方法

九只兔子接受了单侧运动负荷，包括五组，每组十次最大的偏心膝盖收缩。另外6只兔子在最大等距膝盖伸肌力的20％下经受最大亚同心收缩30分钟。对侧关节充当卸载控件。使用共聚焦显微镜评估细胞活力。分析滑膜液中的总蛋白浓度和可识别蛋白的总数，并将其与对照兔的蛋白含量进行比较（n  = 4）。

发现

与未加载的对照关节相比，高强度，短期或低强度，长期加载方案均不会导致软骨细胞死亡增加。运动前后滑膜总蛋白浓度相同。遵循高强度锻炼方案，可识别的蛋白质数量减少，而遵循低强度锻炼方案，与对照相比，可识别蛋白数量增加。

解释

软骨细胞在完整的关节中得到很好的保护，可以承受最大的偏心肌肉负荷和最大的耐力负荷。运动后滑液蛋白质含量发生变化，这些变化主要取决于负荷的类型。