[Replacement of the vertebral body with an expansion implant (Synex)].

PURPOSE OF THE STUDY

This paper describes replacement of the vertebral body with the expansion implant Synex. Usually, autologous bone graft is used to replace the vertebral body. In patients with bone cancer or multiple injuries to the spine, cement filling is preferred whereas, in other indicated cases, implants are inserted, of which Harms' titanium cage has been the most common one. However, this needs filling with a large amount of bone tissue and it is often difficult to adjust its size into the space available. Telescopic devices, on the other hand, are easier to implant and their application requires only a minimum amount of autologous bone tissue.

MATERIAL

In the period from January 2000 to June 2001, we used telescopic implants Synex to replace vertebral bodies in 34 patients. Indications for treatment were: vertebral fractures in 14, post-traumatic kyphosis in six, vertebral metastatic tumours in eight and a primary tumour in six patients.

METHODS

In 25 cases, the vertebral body replacement was completed by posterior stabilization using internal fixation and, in nine cases, by anterior stabilization with a Ventrofix fixator. In 32 patients, the implant was inserted from the anterior approach and, in two, from the posterior approach following complete spondylectomy.

RESULTS

The L1 vertebra was replaced most frequently (nine patients), then T 12 (seven patients) and L2 (six patients). For treatment of fresh fractures, the Synex implant was used in 14 cases. Of these one was inserted from the posterior approach in the L1 region where trauma had caused severe injury to the spinal cord. In spinal tumours. Synex was used in 14 patients, i.e., in six with diagnosed plasmacytoma, in two with metastatic dissemination from prostate carcinoma, in four with vertebral metastases from breast cancer and in two patients with non-differentiated metastases. The anterior approach was performed by conventional thoracotomy or combined thoracotomy and lumbotomy in 20 patients and a less invasive retroperitoneal approach was used in 12 patients. One patient died of multiple metastases at 7 months after surgery and one patient had relapse of a local tumour resulting in paraparesis that required a repeat decompression of the spinal canal. The operation took 1 h and 50 min when the anterior approach and anterior stabilization with a Ventrofix fixator were used; the operation lasted from 3 h 20 min to 6 h 10 min when complementary posterior stabilization was involved. The patients were followed up for 2 to 24 months. No failure of the implant in terms of migration, change in position or penetration into adjacent vertebral bodies occurred.

DISCUSSION

The replacement of a vertebral body has conventionally been performed with the use of a massive bone graft. However, collection of an autologous bone graft large enough to suit this purpose is not always possible. Complications at the donor site have been described. A homologous bone graft carries a risk of disease transmission and the reconstruction ability of a massive graft has not been confirmed for certain. Cement filling augmented with Kirschner's wires is usually used in cancer patients. Titanium cages require application of a large amount of spongiose bone tissue into their interior. Consequently, bone in the centre fails to remodel. A sharp edge of the mesh may induce migration of the cage towards the vertebral body and failure of the implant. Mechanical failure and collapse of cages have also been described. Telescopic cylindrical implants, on the other hand, need only a small amount of spongiose bone tissue to fill. They can be adapted directly to the implantation site by means of a special distractor and, therefore, before adjusting its final length, the exact position and orientation of the implant can be achieved in the space prepared. This facilitates close contact with the endplates of adjacent vertebral bodies and the development of osteointegration. The use of telescopic implants enabled us to avoid the force that is often necessary to apply during insertion of Harms' cages in the patients whose spines had already been stabilized with posterior fixation or to avoid the need of a triple surgical procedure in order to achieve better stability of the implant. In two patients, Synex was inserted from a non-standard posterior approach. Indications for Synex implantation should be evaluated in view of disease prognosis in each patient. If only limited survival is expected, cement filling with K-wires should be preferred.

CONCLUSIONS

Synex is a sophisticated implant to replace severely damaged vertebral bodies regardless of the nature of lesion. Its application required additional stabilization by either posterior or anterior fixation (internal transpedicular fixator and Ventrofix or Kaneda, respectively). Its use is indicated in post-traumatic defects of vertebrae in acute or poorly healed scervical.