Research Areas

The Effect of Hamstring Tendon Autograft Harvest on the Restoration of Knee Stability in the Setting of Anterior Cruciate Ligament Rupture and Concurrent Medial Collateral Ligament Injury

Lab equipment in the Metzger Laboratory.

Anterior cruciate ligament (ACL) and concurrent medial collate ligament (MCL) injuries are quite common. Hamstrings autograft is a common graft used to reconstruct an isolated ACL, however, there is evidence to suggest that the hamstring tendons contribute to medial knee stability.

This research project investigates the hypothesis that the gracilis and semitendinosus tendons significantly contribute to coronal and/or rotational stability of the knee in the setting of an ACL reconstruction with concurrent MCL injury. A biomechanical assessment of internal and external rotation as well as coronal plane stability is analyzed using a cadaveric model of concurrent ACL and MCL injury.

The Effect of Dynamic Bracing on Articular Contact Pressures in Posterior Cruciate Ligament Deficient Knees

Photograph of the testing apparatus for the PCL study.

Proper management and rehabilitation of isolated and combined posterior cruciate ligament (PCL) injuries remains unclear. The natural history of PCL deficiency includes the development of patellofemoral compartment arthrosis, potentially due to elevated articular contact pressure in the patellofemoral compartment. Use of a dynamic brace may help reduce compartmental pressures and ultimately prevent the onset of arthrosis.

The purpose of this biomechanical study is to evaluate whether dynamic bracing reduces patellofemoral compartment pressures in PCL- and combined PCL/PLC-deficient knees at various degrees of knee flexion.

Buried Fixation of Patella Fractures: A Biomechanical Investigation

One of the most common complications following internal fixation of patella fractures is the need for hardware removal. The subcutaneous and exposed nature of the patella predisposes the patient towards prominence and discomfort with retained hardware. While the rate of nonunion is very low, these are accompanied by rates of hardware removal in excess of 30 percent.

Since 2009, a group of orthopaedic surgeons at Cedars-Sinai has used a novel fixation method, which minimizes the amount of exposed hardware in an effort to reduce the need for future removal. This biomechanical study analyzes the hypothesis that our 'buried' method of fixation minimizes the rate of hardware removal while providing adequate stability throughout normal knee motion by comparing it to a more standard technique to validate its mechanical equivalence.

The Impact of Diabetes on Bone Metabolism and Growth after Spinal Fusion

Diabetes mellitus is a chronic metabolic disease with an enormous impact on public health. The incidence of type II diabetes (T2DM) has skyrocketed to epidemic proportions and is expected to rise. As the prevalence of diabetes continues to increase, so does the percentage of diabetics among patients undergoing spinal fusion surgery. Diabetes has previously shown to have detrimental effects on many organs including the renal, circulatory, and nervous systems, and has been increasingly recognized to adversely affect bone health. Some clinical reports suggest diabetes may have a negative effect on spinal fusion outcomes, although no conclusive experimental research has been conducted to investigate the causality, impact, and inherent risks of this growing patient population.

Therefore, the purpose of this study is to analyze the hypothesis that diabetes inhibits the formation of a solid bony union after spinal fusion surgery by altering the local microenvironment at the fusion site through a reduction in growth factors critical for bone formation using a well-validated rat model of diabetes that best mimics the human condition. Data generated in this study will provide further insight into the underlying mechanism of diabetes-induced bone alterations and will eventually help determine whether pharmacological interventions or lifestyle changes can modulate the rate of nonunion in diabetic patients.

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

The purpose of this study is to determine the mechanical parameters of several minimally invasive direct lateral interbody fusion-based constructs for adjacent segment degeneration after two-level posterior lumbar fusion and compare these to a "standard" construct of a transforaminal lumbar interbody fusion with pedicle screw-rod fixation, which is the most common clinical strategy currently used. Our results indicate that a less-invasive technique provides adequate stability to the more traditional (and invasive) surgical techniques, while clinically reducing surgical time, blood loss and patient morbidity.

X‐ray images were taken after each DLIF construct was implanted. Above are representative X‐ray images of: (top left) engage lateral plate at the L2/L3 segments, (top right) spire plate at the L2/L3 spinous processes, (bottom left) bilateral pedicle screws at L2/L3, and (bottom right) bilateral cortical screws at L2/L3.

The Relationship Between Serum Vitamin D Levels, Successful Fusion and Fusion Strength: A Quantitative Analysis

Metabolic risk factors, including vitamin D insufficiency, are often overlooked by spine surgeons. Currently, there are no published data on the causal effect of insufficient or deficient vitamin D levels on the success of establishing solid bony union after a spinal fusion procedure.

The purpose of this study was to determine whether vitamin D can quantifiably improve the formation of a solid bony union after spinal fusion by performing an in vivo dosing study of vitamin D in a rat posterolateral fusion model with autogenous grafting. We hypothesized that a dose-dependent relationship exists between dietary vitamin D3 and fusion success as determined by the rate of fusion, stiffness, and density of the fusion mass formed.

Example high-resolution radiographs (top) with μCT (below) of ex vivo specimens from each of the vitamin D-adjusted chow groups. Robust radiographic fusion is observed in the high vitamin D (40 IU/g) specimen. A radiographic example of “not fused” is included for comparison (left most radiograph).

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

Clinical studies indicate that using less-rigid fixation techniques in place of the standard all-pedicle screw construct when correcting for scoliosis may reduce the incidence of proximal junctional kyphosis and improve patient outcomes. The purpose of this study is to investigate whether there is a biomechanical advantage to using supralaminar hooks in place of pedicle screws at the upper-instrumented vertebrae in a multilevel thoracic construct.

The results of this study demonstrate that use of supralaminar hooks at the top of a multilevel posterior fusion construct reduces the stress at the proximal un-instrumented motion segment. Although further data is needed to provide a definitive link to the clinical occurrence of proximal junctional kyphosis, this in vitro study demonstrates the potential benefit of “easing” the transition between the stiff instrumented spine and the flexible native spine and is the first to demonstrate these results with laminar hooks.

Illustration depicting each of the three upper-instrumented vertebrae anchor type analyzed in this study: (A) bilateral supra-laminar hooks, (B) hybrid with a supra-laminar hook on the left and a unilateral screw on the right and (C) bilateral pedicle screws.

Contact the Metzger Lab

8700 Beverly Blvd.
Davis Building, Room 6006
Los Angeles, CA 90048