Intervertebral disc transplantation: a biological approach to motion preservation

Intervertebral disc transplantation was developed in a bipedal animal model through the stages of autograft, fresh allograft and fresh frozen allograft. Results showed that the allografts were able to survive through a deep freezing protocol and maintain cell viability after transplantation without significant immunoreaction. Although degeneration of the allograft appeared to be inevitable, it was able to maintain stability and mobility of the functional spinal unit. These findings were similarly reproduced in the human clinical trial with excellent mid-term clinical results at 5 years. The process of evolution and findings were summarized in this review.

Fresh frozen intervertebral disc allografting in a bipedal animal model

STUDY DESIGN

An in vivo experimental study to examine the possibility of using fresh frozen intervertebral disc allograft in disc transplantation.

OBJECTIVES

To investigate the long-term radiographic, pathologic, biochemical, and biomechanical changes of fresh frozen disc allograft in a bipedal animal model.

SUMMARY OF BACKGROUND DATA

It has been shown that intervertebral disc autograft is able to survive and maintain some degree of tissue metabolism and segmental mobility after transplantation in a bipedal animal model. However, the long-term results of disc allografting and the associated problems of graft rejection are unknown.

METHODS

Seventeen rhesus monkeys (15 male, 2 female) between 5 and 8 years of age and weighing between 6.7 and 11.8 kg were used in this study. Of these 17 subjects, two were used as intervertebral disc donors and three were used as controls for the biomechanical testing. The remaining 12 monkeys were randomly divided into a short-term group (n = 4, followed up for 2, 4, 6, and 8 weeks, respectively), a midterm group (n = 6, 6 months), and a long-term group (n = 2, 24 months). Radiologic, histologic, biochemical, and biomechanical changes were investigated.

RESULTS

Radiography and macro- and microhistologic examination showed severe disc degeneration at 24 months of follow-up. Disc height decreased mainly in the early postoperative stage. Decreased water, proteoglycan, and hydroxyproline contents of the allograft were observed at 6 and 24 months of follow-up. The biomechanical properties of the transplanted allograft were similar to those of control.

CONCLUSION

Fresh frozen disc allografts can survive and maintain some degree of cell metabolism and segmental mobility at 24 months after transplantation. However, severe disc degeneration is also observed at this stage.

Stability of the whole lumbar spine after multilevel fenestration and discectomy

STUDY DESIGN

An investigation of the in vitro biomechanical effects of multilevel fenestrations and discectomies on the behavior of whole lumbar spine motion, using a material testing system (Instron 1341, Instron Limited, High Wycombe, England) and Elite three-dimensional motion analysis system (BTS, Milano, Italy).

OBJECTIVES

To investigate the effects of multilevel fenestrations and discectomies on the stability of the whole lumbar spine, including segmental stiffness and sagittal (horizontal and vertical) translation.

SUMMARY OF BACKGROUND DATA

In the management of lumbar spinal stenosis, wide decompressive laminectomy with partial or total facetectomy has been the standard procedure for multilevel nerve decompression. Main complications with these procedures have been instability and chronic pain syndrome. Multilevel fenestration with undermining enlargement of the spinal canal has been selected for multilevel nerve decompression in recent years. However, the biomechanical effects of multilevel fenestration and discectomy have been controversial and difficult to validate. This study investigated the in vitro biomechanical effects of multilevel fenestrations and discectomies on motion behavior of the whole lumbar spine.

METHODS

Seven fresh human specimens from L1 to sacrum were used in this study. The fenestrations and discectomies consisted of L3-L4 bilateral fenestration, L4-L5 bilateral fenestration, L5-S1 bilateral fenestration, L4-L5 discectomy, and L5-S1 discectomy. Flexion, lateral bending, and axial rotation (torsion) loading were applied. Ranges of motion were determined two-dimensionally by the Elite system with an infrared camera. The postoperation results were compared with the intact conditions.

RESULTS

After multiple fenestrations, the sagittal ranges of motion at L4-L5 increased by 18% anteroposteriorly and 16% vertically under the flexion loads. At L5-S1, the motions increased by 19% and 45%, respectively. After fenestrations and discectomies, the ranges of motion in the sagittal plane increased by 28% horizontally and 71% vertically at L4-L5, and 14% and 166% at L5-S1. Motion increases were statistically significant (P < 0.05) in vertical translations. However, after the multilevel surgeries, no significant motions were found in each of the lumbar segments during lateral bending and axial rotation.

CONCLUSIONS

The results demonstrate that multilevel fenestrations and discectomies affect lumbar spinal stability in flexion, but have no effect on the stability of the lumbar spine in lateral bending or axial rotation.

Shen instrumentation for the management of unstable thoracolumbar fractures

STUDY DESIGN

A retrospective study was carried out using Shen instrumentation, which is a modified pedicle rod sleeve spinal system, to perform reduction and fusion in patients with unstable thoracolumbar fracture.

OBJECTIVES

To demonstrate that the simple, locally made pedicle rod sleeve instrumentation is as effective as conventional systems in the management of thoracolumbar fractures. The current results are also compared with those reported in the literature.

SUMMARY OF THE BACKGROUND DATA

Many instrumentations, such as Harrington, Luque, and Dick, have been used for the management of thoracolumbar fracture in the past 2 decades. Every device has its advantages and disadvantages based on clinical practice and the biomechanical mechanism of reduction.

METHODS

Between January 1991 and December 1995, 96 consecutive patients who had experienced unstable thoracolumbar fractures were treated surgically with Shen instrumentation, which consists of four components: superior pedicle screws, distraction rods, sleeves, and inferior laminar hooks. Of these 96 patients, 76 were male and 20 were female (age range, 16-68 years; mean, 37 years). Thirty patients had partial paraplegia and 38 patients had complete paraplegia, according to the Frankel classification. Injury categories were as follows: 43 burst fractures, 26 flexion-compression fractures, 22 fracture-dislocation injuries, and 5 flexion-distraction injuries.

RESULTS

The average follow-up was 39 months (range, 24-60 months). Kyphotic deformity was corrected from 27.1 degrees before surgery to 4.2 degrees after surgery, translation was reduced from 30.7% to 0%, height of compressed vertebral bodies was restored from 52.3% to 96.5% of the normal height. Computed tomographic evaluation showed that the cross-canal area was restored from 48.1% before to 70.9% after surgery. Improvement of neurologic function of more than one Frankel grade occurred in 90% of patients.

CONCLUSION

Based on the understanding of biomechanics and the present clinical results, Shen instrumentation is as efficacious as conventional devices available today and may serve as a cost-effective option for thoracolumbar injuries, especially in a developing country.

Intervertebral disc autografting in a bipedal animal model

Fusion of the spine while restoring stability of the spinal segment, fails to preserve spinal mobility. Long term complications of accelerated degeneration in the neighboring segments have been reported. The present study explores the possibility of intervertebral disc autografting in a bipedal animal model by isolating a lumbar disc together with the adjacent end plates and repositioning it with minimal internal fixation. Fourteen Rhesus monkeys were sacrificed at 2, 4, 6, and 12 months after surgery and the grafted discs were examined radiologically, biochemically, pathologically, and biomechanically. Healing of the bony end plate was seen between 2 to 4 months postoperatively. There was early loss of disc height at 2 and 4 months but there was a suggestion of some reconstitution up to 12 months. There was minimal evidence of gross degeneration at all stages. Gradual loss of water content was found in the annulus and the nucleus. The nucleus pulposus seemed to be able to reaccumulate proteoglycan after an initial drop in the first 4 months. There was significant increase in hydroxyproline content in the annulus fibrosus and the nucleus pulposus. Biomechanically, the grafted disc showed hypermobility in the first 4 months but gradually became stabilized with time. Results from this study suggested that a fresh intervertebral disc autograft could survive a period of ischemia. Although the physiology of the disc was deranged, it was able to preserve a certain degree of segmental mobility without sacrificing stability. Further studies are required to validate these results and the field of disc allografting should be explored.

[Studies on in vivo biocompatibility and biodegradation of absorbable material of polylactic acid]

The biocompatibility and biodegradation of polylactic acid (PLA) made in China were investigated in vivo. A total of 20 implants of PLA in 5 rabbits were studied 2 to 16 months after operation to observe the surrounding tissue reaction, degradation and absorption of PLA. The present results demonstrated that the tissue reaction was mild, and there was a capsule around the implant. It was showed there was a degradation of large molecule of PLA firstly, followed by absorption of PLA. The average degradation rate of PLA molecule was 57.02 per cent and the average weight loss of PLA was 8.15 per cent at the end of eight weeks, but no gross change of contour occurred. The biodegradation was gradual and did not cause an accumulation of lactic acid in the body. The present results demonstrate PLA is a promising implant material in surgery.