The effect of implant placement on sacroiliac joint range of motion: posterior versus transarticular

STUDY DESIGN

A human cadaveric biomechanical study of 2 sacroiliac (SI) joint fusion implant placement techniques.

OBJECTIVE

To evaluate and compare the biomechanical properties of 2 implant placement techniques for SI joint fusion.

SUMMARY OF BACKGROUND DATA

Minimally invasive placement of SI joint fusion implants is a potential treatment of SI joint disruptions and degenerative sacroiliitis. Biomechanical studies of screw fixation within the sacrum have shown that placement and trajectory are important in the overall stability of the implant. Although clinical results have been promising, there is the possibility that a more optimal arrangement of implants may exist.

METHODS

Bilateral SI joints in 7 cadaveric lumbopelvic (L4-pelvis) specimens were tested using a single leg stance model. All joints were tested intact, pubic symphysis sectioned, and treated (3 SI joint fusion implants). The implants were laterally placed using either a posterior or transarticular placement technique. The posterior technique places the implants inline in the inlet view, parallel in the outlet view, and parallel to the posterior sacral body in the lateral view. The transarticular technique places all implants across the articular portion of the SI joint. For all conditions, the range of motion was tested in flexion-extension, lateral bending, and axial rotation.

RESULTS

The posterior technique significantly reduced the range of motion in flexion-extension, lateral bending, and axial rotation by 27% ± 24% (P = 0.024), 28% ± 26% (P = 0.028), and 32% ± 21% (P = 0.008), respectively. The transarticular technique significantly reduced the range of motion in flexion-extension, lateral bending, and axial rotation by 41% ± 31% (P = 0.013), 36% ± 38% (P = 0.049), and 36% ± 28% (P = 0.015), respectively. No significant differences were detected between the posterior and transarticular placement techniques (P > 0.25).

CONCLUSION

Posterior and transarticular placement of SI joint fusion implants stabilized the SI joint in flexion-extension, lateral bending, and axial rotation.

LEVEL OF EVIDENCE

N/A.

The current testing protocols for biomechanical evaluation of lumbar spinal implants in laboratory setting: a review of the literature

In vitro biomechanical investigations have become a routinely employed technique to explore new lumbar instrumentation. One of the most important advantages of such investigations is the low risk present when compared to clinical trials. However, the best use of any experimental data can be made when standard testing protocols are adopted by investigators, thus allowing comparisons among studies. Experimental variables, such as the length of the specimen, operative level, type of loading (e.g., dynamic versus quasistatic), magnitude, and rate of load applied, are among the most common variables controlled during spinal biomechanical testing. Although important efforts have been made to standardize these protocols, high variability can be found in the current literature. The aim of this investigation was to conduct a systematic review of the literature to identify the current trends in the protocols reported for the evaluation of new lumbar spinal implants under laboratory setting.