In order to evaluate the feasibility of zinc alloys as future biodegradable bone implant materials, the mechanical properties, corrosion resistance, hemocompatibility, cell activity, proliferation and adhesion, in vivo animal implantation experiments have been employed. The experimental results show that the alloying element magnesium, calcium and strontium can significantly improve the mechanical properties of pure zinc, and further deformation processes can further improve the mechanical properties of zinc alloys. Alloying elements can effectively control the corrosion rates of zinc alloys, which are between the rates of magnesium alloys and iron alloys. Zinc and zinc alloys exhibit excellent hemocompatibility and the hemolysis rate is far lower than 5%. After adding alloying elements Mg, Ca and Sr, MG63 and ECV304 cell proliferation rate and activity increased significantly, while for VSMC cell, the influence of alloying elements effect is not obvious. Zinc alloy intramedullary pins can effectively promote the new bone formation, and after 2 months implanted in mice femur, they still maintained a relatively complete structure, indicating that they are able to provide enough mechanical strength and thus more conducive to bone tissue repair and healing.

Fifty-two patients older than sixty years had undergone multilevel lumbar decompression and fusion with instrumentation and reached a minimum two-year follow up. The relationship between abnormal sagittal plane configuration of the proximal segments and the number of lumbar fusion segments was radiographically analyzed. Group A (L1-L5 or S1) patients had two (20%) proximal vertebral compression fractures and four (40%) focal kyphosis. Group B (L2-L5 or S1) patients had one (6%) proximal vertebral compression fractures, five (33%) retrolisthesis and two (13%) focal kyphosis. Group C (L3-S1) had seven (39%) retrolisthesis. Group D had only one retrolisthesis and two disc height loss.

Radiographically analyze the relationship between abnormal sagittal plane configuration of the proximal segments and the number of lumbar fusion segments in patients older than sixty years old.

It appears that lumbar fusion up to L1 causes more kyphotic changes and topping off syndrome in the elderly. Fusion L2-L5 or S1 seems having less severe adjacent level degeneration. Retrolisthesis is a significant problem in fusion from L3-L5 or S1. The least adjacent level degenerative changes were seen in L4-S1 fusion.

Selected limited instrumentation avoiding kyphotic segments or extending the fusion above the thoracolumbar junction may be the needed.

Solid fusion was seen in 46 (88%) patients. There were ten patients in group A, and two (20%) had vertebral compression fractures in the most cranial vertebrae and four (40%) focal kyphosis. Of fifteen patients in group B, one (6%) had compression fracture, five (33%) retrolisthesis, and two (13%) focal kyphosis. Of eighteen patients in group C, retrolisthesis was seen in seven (39%) patients. Group D had nine patients with only one patient having retrolisthesis and two having disc height loss.

Since January 1997, there were fifty-two consecutive patients with an average age of seventy years who have undergone multilevel lumbar decompression and posterolateral fusion with pedicle screw-rod instrumentation, and have reached a minimum two-year follow up. Postoperative radiographs of lumbar fusion were classified into group A (L1-L5 or S1), group B (L2-L5 or S1), group C (L3-L5 or S1) and group D (L4-S1).