Research Areas

The Metzger Laboratory is currently investigating several clinically relevant orthopaedic topics, including:

Does Sacral Geometry Affect Biomechanical Behavior
and Facet Forces after Total Disc Replacement
at the Lumbosacral Junction?

Testing a specimen using our custom-designed testing system.


X-ray of a specimen with a TDR device implanted.


μCT of Fused Rat Spine (L4-L5).


Metzger Laboratory test system with spine in place and motion analysis markers on each vertebra. 


This research project, funded by an AOSpine Foundation research grant, investigates how the morphology of the lumbosacral junction influences the kinematics of total disc replacement (TDR) devices, to determine whether there is a limit to the amount of sacral obliquity above which the level of shear force is a counter indication for TDR. Our results provide further support of clinical reports indicating suboptimal interactions between TDRs and the facets at the lumbosacral joint after instrumentation. We were able to demonstrate that the amount of distraction (increased disc height) and shallow ball-and-socket design of TDR devices facilitate greater anterior translation and facet load as observed at lower sacral angles (20-50°). At higher sacral angles (> 50°), we hypothesize the device is forced into an extended posture, transferring shear load from the facets to the polyethylene TDR inlay, resulting in the observed reduced facet pressures and anterior dislocation.


The Relationship between Experimental Serum Vitamin D Levels and Spinal Fusion Strength: A Quantitative Analysis

This study, funded by a grant from the Scoliosis Research Society, analyzes the hypothesis that vitamin D insufficiency reduces the strength, stiffness, volume of new bone, and rate of fusion mass remodeling after an autologous spine fusion procedure, thus increasing the risk for pseudarthrosis (failure to fuse).

Our results suggest vitamin D modulates the consolidation of bone after grafting for spinal fusion and could potentially provide a simple, readily available, cost-effective means to improve fusion outcomes.

Biomechanical Analysis of the Effect of Different Instrumentation Techniques on Adjacent Level Stability after Long Segment Instrumentation of the Thoracic Spine

The purpose of this study is to determine whether using hooks at the top of an all-pedicle screw construct for deformity correction (scoliosis surgery) helps ease the transition to the natural spine and reduce the rate of proximal junctional kyphosis (PJK). PJK is a common phenomenon after scoliosis surgery, defined as a kyphotic deformity immediately above the instrumented portion of the spine. Our initial results indicate hooks help reduce stress at the natural spine segments above the surgical construct, most significantly in extension and torsion and, as hypothesized, may reduce rates of PJK.


Biomechanical Analysis of Direct Lateral Interbody Fusion (DLIF) Strategies for Adjacent Segment Degeneration in the Lumbar Spine

The purpose of this study is to determine the mechanical parameters of several minimally invasive DLIF-based constructs for adjacent segment degeneration after two-level posterior lumbar fusion and compare these to a "standard" construct of a TLIF (Transforaminal Lumbar Interbody Fusion) with pedicle screw-rod fixation, which is the most common clinical strategy currently used. We are in the process of starting this project and hope to show that a less-invasive technique provides adequate/equivalent stability to the more traditional (and invasive) surgical techniques, with the overall goal of reducing surgical time, blood loss and patient morbidity.


The Biomechanics of Sagittal Deformity the Impact of Sacral Slope on Lumbosacral Interbody Fusion 

This research project, funded by a Haid Award through the American Association of Neurological Surgeons, uses a similar testing system to that described in our TDR/sacral slope study (project #1), but is instead focused on determining the stability of newly developed "stand-alone" devices at the lumbosacral junction. The results of this study will eventually help surgeons understand the advantages and limitations of various fusion technologies and will provide useful information to help establish patient selection criteria that optimize clinical outcomes at L5/S1.