Artificial disc and vertebra system: a novel motion preservation device for cervical spinal disease after vertebral corpectomy

Does the novel artificial cervical joint complex resolve the conflict between stability and mobility after anterior cervical surgery? a finite element study

Background and objective

Our group has developed a novel artificial cervical joint complex (ACJC) as a motion preservation instrument for cervical corpectomy procedures. Through finite element analysis (FEA), this study aims to assess this prosthesis's mobility and stability in the context of physiological reconstruction of the cervical spine.

Materials and methods

A finite element (FE)model of the subaxial cervical spine (C3-C7) was established and validated. ACJC arthroplasty, anterior cervical corpectomy and fusion (ACCF), and two-level cervical disc arthroplasty (CDA) were performed at C4-C6. Range of motion (ROM), intervertebral disc pressure (IDP), facet joint stress (FJS), and maximum von Mises stress on the prosthesis and vertebrae during loading were compared.

Results

Compared to the intact model, the ROM in all three surgical groups demonstrated a decline, with the ACCF group exhibiting the most significant mobility loss, and the highest compensatory motion in adjacent segments. ACJC and artificial cervical disc prosthesis (ACDP) well-preserved cervical mobility. In the ACCF model, IDP and FJS in adjacent segments increased notably, whereas the index segments experienced the most significant FJS elevation in the CDA model. The ROM, IDP, and FJS in both index and adjacent segments of the ACJC model were intermediate between the other two. Stress distribution of ACCF instruments and ACJC prosthesis during the loading process was more dispersed, resulting in less impact on the adjacent vertebrae than in the CDA model.

Conclusion

The biomechanical properties of the novel ACJC were comparable to the ACCF in constructing postoperative stability and equally preserved physiological mobility of the cervical spine as CDA without much impact on adjacent segments and facet joints. Thus, the novel ACJC effectively balanced postoperative stability with cervical motion preservation.

Intrafacet Spacer Placement as a Mobility-Sparing Bailout Option in Atlantoaxial Fusion Construct Salvage

Background: Salvage revisions of atlantoaxial (AA) joint complex posterior segmental instrumented fusion constructs require careful individualized planning to prevent occipital extension. In this case report, we describe the use of bilateral intrafacet spacer placement as a mobility-sparing bailout option for the revision surgery. Case Report: A 64-year-old male with a history of diffuse idiopathic skeletal hyperostosis, extremely limited baseline cervical mobility, and prior AA posterior segmental instrumented fusion presented with increasing pain at his 6-month follow-up. Imaging showed fusion and hardware failures and dynamic instability. To prevent occipitocervical fixation, AA intra-articular fusion via a DTRAX spinal system (Providence Medical Technology, Inc) was used as an adjunct to a navigated C1 lateral mass and C2 pars screw posterior segmental instrumented fusion construct. The patient had an uneventful postoperative course and was discharged with resolution of symptoms. Three-month postoperative follow-up confirmed persistent resolution of symptoms and absence of complaints, along with successful arthrodesis on imaging. Conclusion: AA posterior segmental instrumented fusion revision is technically challenging, particularly when partial preservation of craniovertebral junction mobility is required. Bilateral intra-articular cages may be used as an adjunct to hardware revision in construct salvage when sturdy arthrodesis is desired without occipital extension and may represent a major potential strength of intra-articular cages.

Range of motion of the mid-cervical spine: human versus goat

BACKGROUND

The goat cervical spine represents a promising alternative for human specimen in spinal implant testing, but the range of motion (ROM) of the spine is lacking. We aimed to evaluate and compare the ROMs of fresh goat and human mid-cervical spine specimens.

METHODS

Ten fresh adult healthy male goat cervical spine specimens (G group) and ten fresh frozen adult healthy human cervical spine specimens (average age: 49.5 ± 12.1 years; 6 males, 4 females) (H group) were included. The ROMs of each specimen were biomechanically tested at the C_2-3, C_3-4, C_4-5 and C_2-5 levels at 1.5 Nm and 2.5 Nm torque and recorded. The ROMs of different levels of goat cervical samples were compared to those of human cervical samples using an independent sample t test. Significance was defined as a P value of less than 0.05.

RESULTS

At the C_2-3, C_3-4 and C_4-5 levels, the ROMs of the goat cervical spine were significantly larger than those of the human cervical spine in all directions except extension under 1.5 Nm torque; under 2.5 Nm torque, the ROMs of the goat cervical spine at the C_2-3 and C_3-4 levels were significantly larger than those of humans in the pure movement of flexion, lateral bending and axial rotation, and the ROMs for axial rotation of the goat specimens and human specimens were comparable. Under both 1.5 Nm and 2.5 Nm torque, the goat cervical spine displayed a much greater ROM in all directions at the C_2-5 level.

CONCLUSIONS

Several segmental ROMs of fresh goat and human cervical spine specimens were recorded in this investigation. We recommend using goat cervical specimens as an alternative to fresh human cervical specimens in future studies when focusing only on the ROMs of C_2-3, C_3-4 and C_4-5 in flexion under a torque of 1.5 Nm or the ROMs of C_2-3 and C_3-4 in flexion and rotation under a torque of 2.5 Nm.

Atlantoaxial Non-Fusion Using Biomimetic Artificial Atlanto-Odontoid Joint: Technical Innovation and Initial Biomechanical Study

STUDY DESIGN

A biomechanical in vitro investigation.

OBJECTIVE

To evaluate the function and stability of self-designed biomimetic artificial atlanto-odontoid joint (BAAOJ) replacement on the atlantoaxial joint.

SUMMARY OF BACKGROUND DATA

Upper cervical fusion surgery is a common treatment for various atlantoaxial disorders, and favorable clinical outcome has been achieved. However, the fusion surgery results in loss of atlantoaxial motion as well as adjacent segments degeneration, reducing the quality of life of patients and might produce severe neurological symptoms. Non-fusion technology is expected to solve the above problems, but various designed devices have certain defects and are still in the exploratory phase.

MATERIALS AND METHODS

Biomechanical tests were conducted on 10 fresh human cadaveric craniocervical specimens in the following sequence: 1) intact condition, 2) after the BAAOJ arthroplasty, 3) after BAAOJ fatigue test, 4) after odontoidect-omy, and 5) after anterior rigid plate fixation. Three-dimensional movements of the C1-C2 segment were evaluated to investigate the function and stability of BAAOJ arthroplasty compared with the intact condition after the BAAOJ fatigue test, odontoidect-omy, and rigid plate fixation.

RESULTS

Comparing the BAAOJ implantation to the intact state, the range of motion and neutral zone were slightly reduced in all directions (P > 0.05). Compared with the rigid plate fixation, the BAAOJ implantation significantly increased the range of motion and neutral zone in all directions, especially in the axial rotation (P < 0.05).

CONCLUSION

We designed a BAAOJ for correcting atlantoaxial disorders arising from atlantoaxial instability. As a non-fusion device, the most critical feature of BAAOJ replacement is the retention of flexion-extension, lateral bending, and axial rotation range of motion similar to the normal state. It can also stabilize the atlantoaxial complex, and the BAAOJ itself has a good initial stability.Level of Evidence: 4.

Cervical non-fusion using biomimetic artificial disc and vertebra complex: technical innovation and biomechanics analysis

Background

Changes in spinal mobility after vertebral fusion are important factors contributing to adjacent vertebral disease (ASD). As an implant for spinal non-fusion, the motion-preserving prosthesis is an effective method to reduce the incidence of ASD, but its deficiencies hamper the application in clinical. This study designs a novel motion-preserving artificial cervical disc and vertebra complex with an anti-dislocation mechanism (MACDVC-AM) and verifies its effect on the cervical spine.

Methods

The MACDVC-AM was designed on the data of healthy volunteers. The finite element intact model, fusion model, and MACDVC-AM model were constructed, and the range of motion (ROM) and stress of adjacent discs were compared. The biomechanical tests were performed on fifteen cervical specimens, and the stability index ROM (SI-ROM) were calculated.

Results

Compared with the intervertebral ROMs of the intact model, the MACDVC-AM model reduced by 28–70% in adjacent segments and increased by 26–54% in operated segments, but the fusion model showed the opposite result. In contrast to the fusion model, the MACDVC-AM model diminished the stress of adjacent intervertebral discs. In biomechanical tests, the MACDVC-AM group showed no significant difference with the ROMs of the intact group (p > 0.05). The SI-ROM of the MACDVC-AM group is negative but close to zero and showed no significant difference with the intact group (p > 0.05).

Conclusions

The MACDVC-AM was successfully designed. The results indicate that the MACDVC-AM can provide physiological mobility and stability, reduce adjacent intervertebral compensatory motion, and alleviate the stress change of adjacent discs, which contributes to protect adjacent discs and reduce the occurrence of ASD.

Design and preliminary biomechanical analysis of a novel motion preservation device for lumbar spinal disease after vertebral corpectomy

OBJECTIVE

To design a novel prosthesis, a movable artificial lumbar complex (MALC), for non-fusion reconstruction after lumbar subtotal corpectomy and to evaluate the stability, range of motion and load-bearing strength in the human cadaveric lumbar spine.

METHODS

Biomechanical tests were performed on lumbar spine specimens from 15 healthy cadavers which were divided in three groups: non-fusion, fusion and intact group. The range of motion (ROM), stability and load-bearing strength were measured.

RESULTS

The prosthesis was composed of three parts: the upper and lower artificial lumbar discs and the middle artificial vertebra. Both the MALC and titanium mesh cage re-established vertebral height, and no spinal cord compression or prosthesis dislocation was observed at the operative level. Regarding stability, there was no significant difference in all directions between the intact group and non-fusion group (P > 0.05). Segment movements of the specimens in the non-fusion group revealed significantly decreased T12-L1 ROM and significantly increased L1-2 and L2-3 ROM in flexion/extension and lateral bending compared with those in the fusion group (P < 0.05). Regarding load-bearing strength, when the lumbar vertebra was ruptured, there was no damage to the MALC and titanium mesh cage, but the maximum load in the non-fusion group was larger (P > 0.05).

CONCLUSIONS

Compared with titanium cages, the MALC prosthesis not only restored the vertebral height and effectively preserved segment movements without any abnormal gain of mobility in adjacent inter-vertebral spaces but also bore the lumbar load and reduced the local stress load of adjacent vertebral endplates.

Lumbar subtotal corpectomy non-fusion model produced using a novel prosthesis

OBJECTIVE

In this study, we aimed to design a movable artificial lumbar complex (MALC) prosthesis for non-fusion reconstruction after lumbar subtotal corpectomy and to establish an in vitro anterolateral lumbar corpectomy non-fusion model for evaluating the biomechanical stability, preservation of segment movements and influence on adjacent inter-vertebral movements of this prosthesis.

METHODS

Imaging was performed on a total of 26 fresh goat lumbar spine specimens to determine which of the specimens did not meet the requirements (free of deformity and fractures); the residual specimens were randomly divided into an intact group, a fusion group and a non-fusion group. Bone mineral density (BMD) was tested and compared among the three groups. Biomechanical testing was conducted to obtain the range of motion (ROM) in flexion-extension, lateral bending at L2-3, L3-4 and L4-5 and axial rotation at L2-5 in the three groups.

RESULTS

Two specimens were excluded due to vertebral fractures. BMD showed no statistical significance among three groups (P > 0.05). The stability of the prosthesis did not differ significantly during flexion, extension, and lateral bending at L2-3, L3-4, and L4-5 and axial torsion at L2-5 between the intact group and the non-fusion group (P > 0.05). Segment movements of the specimens in the non-fusion group revealed significantly decreased L2-3 ROM and significantly increased L3-4 and L4-5 ROM in flexion and lateral bending compared with the fusion group (P < 0.05).

CONCLUSIONS

Reconstruction with a MALC prosthesis after lumbar subtotal corpectomy not only produced instant stability but also effectively preserved segment movements, without any abnormal gain of mobility in adjacent inter-vertebral spaces. However, additional studies, including in vivo animal experiments as well as biocompatibility and biomechanical tests of human body specimens are needed.