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  • Author or Editor: Cumhur Kılınçer x
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İnceoğlu Serkan, Cumhur Kılınçer, Andrea Tami and Robert F. McLain

Object

Elastic deformation has been proposed as a mechanism by which vertebral pedicles can maintain pullout strength when conical screws are backed out from full insertion. The response to the insertion technique may influence both the extent of deformation and the risk of acute fracture during screw placement. The aim of this study was to determine the deformation characteristics of the lumbar pedicle cortex during screw placement.

Methods

Lumbar pedicles with linear strain gauges attached at the lateral and medial cortices were instrumented using 7.5-mm pedicle screws with or without preconditioning by insertion and removal of 6.5-mm screws. The strains and elastic recoveries of the medial and lateral cortices were determined.

Results

Mean medial wall strains tended to be lower than mean lateral wall strains when the 6.5-mm and 7.5-mm screw data were pooled (p = 0.07). After the screws had been removed, 71 to 79% of the deformation at the lateral cortex and 70 to 96% of the deformation at the medial cortex recovered. When inserted first, the 7.5-mm screw caused more plastic deformation at the cortex than it did when inserted after the 6.5-mm screw. Occasional idiosyncratic strain patterns were observed. No gross fracture was observed during screw placement.

Conclusions

Screw insertion generated plastic deformation at the pedicle cortex even though the screw did not directly contact the cortex. The lateral and medial cortices responded differently to screw insertion. The technique of screw insertion affected the deformation behavior of the lumbar pedicles. With myriad options for screw selection and placement available, further study is needed before optimal placement parameters can be verified.

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Serkan İnceoğlu I, Cumhur Kilinçer, Andrea Tami and Robert F. McLain

Object

Although the gross anatomy of the pedicle in the human spine has been investigated in great detail, knowledge of the microanatomy of trabecular and cortical structures of the pedicle is limited. An understanding of the mechanical properties and structure of the pedicle bone is essential for improving the quality of pedicle screw placement. To enhance this understanding, the authors examined human cadaveric lumbar vertebrae.

Methods

In this study, the authors obtained seven human cadaveric lumbar vertebrae. The lateral and medial cortices of these pedicle specimens were sectioned and embedded in polymethylmethacrylate. Cross-sectional slices of cortex were obtained from each specimen and imaged with the aid of a high-resolution light microscope. Assessments of osteonal orientation, determinations of relative dimensions, and histomorphometric studies were performed.

Results

The cortex of the pedicle in each human lumbar vertebra had an osteonal structure with haversian canals laid down mainly in the anteroposterior (longitudinal) direction. The organization of osteons across the transverse cross-section was not homogeneous. The layer of lamellar bone that typically envelops cortical bone structures (such as in long bones) was not observed, and the lateral cortex was significantly thinner than the medial cortex (p< 0.05).

Conclusions

The cortical bone surrounding the pedicle differed from bone in other anatomical regions such as the anterior vertebral body and femur. The osteonal orientation and lack of a lamellar sheath may account for the unique deformation characteristics of the pedicle cortex seen during pedicle screw placement.

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Cumhur Kilinçer, Michael P. Steinmetz, Moon Jun Sohn, Edward C. Benzel and William Bingaman

Object. Although advances in patient care have enabled surgeons to perform posterior lumbar decompression and fusion (PLDF), increased age remains a major concern when designing a treatment strategy. The authors conducted a study to evaluate if increased age has any effect on lumbar fusion surgery in terms of perioperative events.

Methods. This retrospective study comprised 129 patients (age range 25–91 years) with spondylolisthesis, lumbar stenosis and/or disc degeneration/herniation with instability, or unsuccessful results after a failed previous PLDF. The patients were stratified by age: those younger than 65 years of age (85 patients) and those at least 65 years of age (44 patients). The parameters reviewed included comorbid conditions, American Society of Anesthesiologists score, instrumentation technique (pedicle screws, a combination of pedicle screw fixation [PSF] and posterior lumbar interbody fusion [PLIF], or non-instrumented fusions), number of fused levels, operative time, estimated blood loss (EBL), complications, and hospital length of stay (LOS).

Fusion strategies in the elderly tended to be more conservative. Repeated operations and PSF/PLIF procedures were less frequent in the older age group. Older age did not result in increased complications, EBL, and operative time. Longer hospital LOS was observed in the older age group (7 ± 3.5 days) compared with the younger age group (5.5 ± 1.9 days) (p = 0.022).

Conclusions. Complications and perioperative events following PLDF in the elderly are comparable with those observed in younger patients. Withholding lumbar spine fusion solely based on advanced age is not warranted.

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Moon-Jun Sohn, Mark M. Kayanja, Cumhur Kilinçer, Lisa A. Ferrara and Edward C. Benzel

Object

The purpose of this study was to measure and compare the ventral and lateral surface strain distributions and stiffness for two types of interbody cage placement: 1) central placement for anterior lumbar interbody fusion (ALIF); and 2) dorsolateral placement for extraforaminal lumbar interbody fusion (ELIF).

Methods

Two functional spine units were obtained for testing in each of 13 cadaveric spines, yielding 26 segments (three of which were not used because of bone abnormalities). Bilateral strain gauges were mounted adjacent to the endplate on the lateral and ventral walls of each vertebral body in the 23 motion segments. Each segment was cyclically tested in compression, flexion, and extension in the following conditions: while intact, postdiscectomy, and instrumented with interbody fusion cages placed using both insertion techniques.

No significant differences were observed between ALIF and ELIF in compressive stiffness, bending stiffness in flexion and extension (p ≥ 0.1), ventral and lateral strain distribution during the intact tests (p ≥ 0.24), and during the flexion tests after fusion (p ≥ 0.22). In compression, higher ventral and lower lateral strain was observed in the ALIF than in the ELIF group (ventral, p = 0.05; lateral, p = 0.04), and in extension, higher ventral (p = 0.01) and higher lateral strain (p = 0.002) was observed in the ELIF than in the ALIF group.

Conclusions

Preservation of the ventral anulus and dorsolateral placement of the interbody cages during ELIF allow alternate load transfer pathways through the dorsolateral vertebral wall and ventral anulus that are not observed following ALIF. These may be associated with a lower incidence of subsidence and a higher rate of fusion due to a more concentrated application of bone healing–enhancing compression forces during the fusion and healing process.

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Cumhur Kılınçer, Talip Asil, Ufuk Utku, Kemal Balcı and Mustafa Kemal Hamacıoglu

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David W. Beck and Darren S. Lovick

Object. Although advances in patient care have enabled surgeons to perform posterior lumbar decompression and fusion (PLDF), increased age remains a major concern when designing a treatment strategy. The authors conducted a study to evaluate if increased age has any effect on lumbar fusion surgery in terms of perioperative events.

Methods. This retrospective study comprised 129 patients (age range 25–91 years) with spondylolisthesis, lumbar stenosis and/or disc degeneration/herniation with instability, or unsuccessful results after a failed previous PLDF. The patients were stratified by age: those younger than 65 years of age (85 patients) and those at least 65 years of age (44 patients). The parameters reviewed included comorbid conditions, American Society of Anesthesiologists score, instrumentation technique (pedicle screws, a combination of pedicle screw fixation [PSF] and posterior lumbar interbody fusion [PLIF], or noninstrumented fusions), number of fused levels, operative time, estimated blood loss (EBL), complications, and hospital length of stay (LOS).

Fusion strategies in the elderly tended to be more conservative. Repeated operations and PSF/PLIF procedures were less frequent in the older age group. Older age did not result in increased complications, EBL, and operative time. Longer hospital LOS was observed in the older age group (7 ± 3.5 days) compared with the younger age group (5.5 ± 1.9 days) (p = 0.022).

Conclusions. Complications and perioperative events following PLDF in the elderly are comparable with those observed in younger patients. Withholding lumbar spine fusion solely based on advanced age is not warranted.