Clinical and Biomechanical Study to Develop a Joint-Preserving Therapy for Femoral Head Osteonecrosis

股骨头无菌性骨坏死是一种严重的疾病，如果不治疗会导致髋关节的破坏。一种新的保留股骨头的手术方法已经被开发出来，用于诊断时股骨头仍然完好无损的患者。这项手术的目的是使用一种特殊的工具，通过一个精确定向的钻孔通道，彻底清除所有的坏死组织。然后用以磷酸钙和硫酸钙为基础的骨替代物稳定股骨头。术后，骨替代材料被吸收，并被新形成的松质骨取代。到目前为止，这种治疗的临床随访显示，在不切除坏死组织的情况下，这种治疗方法比传统的髓内减压术和其他保留股骨头的手术效果更好。结果还表明，治疗的成功在很大程度上取决于坏死区的大小和空洞中残留的坏死组织的数量。进一步髓芯减压后塌陷股骨头的组织学研究也证实了完全切除所有坏死组织的必要性，因为骨再生只在健康的松质骨和骨替代材料之间的界面上才能看到。然而，MRI随访检查显示，完全切除所有坏死组织往往是不可能的，因为即使是与最佳钻孔通道位置最小的偏差也会导致明显的下位切除，而目前的器械并不能在所有情况下完全切除。这项研究的目的是优化钻孔程序和去除坏死组织。要做到这一点，有必要更好地了解股骨头的生物力学特性，特别是关于其术后稳定性。因此，将从实验和数值两方面研究钻孔通道的不同入口点和角度，以及随后用两种不同类型的骨替代材料填充的情况。根据结果，将制定一个特殊的规划方案，并与导航系统相结合，在考虑到生物力学条件的情况下，实现最佳的坏死组织切除。这项研究的另一个目的是优化钻井工具。所有修改都将根据接受治疗的患者的后续检查结果进行重新评估。

Aseptic osteonecrosis of the femoral head is a serious disease which results in destruction of the hip if left untreated. A new surgical procedure which preserves the femoral head has been developed for patients with a still intact femoral head at the time of diagnosis. The aim of this procedure is to completely remove all necrotic tissue through an exactly targeted drill channel using a special instrument. The femoral head is then stabilised with a bone substitute based on calcium phosphate and calcium sulphate. Postoperatively, the bone substitute material is resorbed and replaced by newly formed cancellous bone. So far, clinical follow-up of this therapy has revealed better results than the conventional core decompression therapy without removal of the necrotic tissue and other femoral head preserving procedures. The results also showed that the success of the therapy depends significantly on the size of the necrotic area and the amount of necrotic tissue remaining in the void. Histological investigations of collapsed femoral heads after advanced core decompression also confirm the necessity of complete removal of all necrotic tissue, as bone regeneration was seen only at the interface between healthy cancellous bone and the bone substitute material. However, MRI follow-up examinations show that it is often not possible to completely remove all necrotic tissue because even the smallest deviation from the optimal drill channel position leads to markedly inferior resection and current instruments do not enable complete removal in all cases. The aim of this study is to optimise the drilling procedure and removal of necrotic tissue. To achieve this, a better understanding of the biomechanical properties of the femoral head, especially with regard to its postoperative stability, is necessary. Therefore, various entry points and angles of the drilling channel and subsequent filling with two different types of bone substitute material will be investigated, both experimentally and numerically. Based on the results, a special planning programme will be developed and combined with a navigation system which will enable optimal removal of the necrotic tissue taking biomechanical conditions into consideration. A further aim of the study is to optimise the drilling instruments. All modifications will be re-evaluated in the light of findings obtained from follow-up examinations of the patients treated.