Design and Implementation of a Novel Morselized Bone Interbody Cage in Posterior Lumbar Spinal Fusion: A Biomechanical Study

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Ahmadi Pirshahid_Ali_msc_2024_thesis.pdf (2.78 MB)

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2024-12-04

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Abstract

Posterior lumbar instrumented fusion (PLIF) is commonly used to correct a variety of spine pathologies. Poly-ether-ether-ketone (PEEK) cages are standard of practice in many centers. These cages are associated with high cost, end-plate subsidence, and pseudarthrosis. The purpose of this study is to provide an in-depth systematic review and meta-analysis of existing clinical literature comparing impacted local morselized bone and synthetic cages, describe the creation of a novel autograft morselized bone interbody fusion (MBIF) cage, and perform biomechanical testing of this cage.

A novel MBIF cage was designed and compared to the PEEK cage initially under axial-load testing with polyurethane blocks simulating healthy and osteoporotic bone. A cadaveric study design was then used to assess displacement in axial rotation, flexion-extension, and lateral bending at the L3/4 segment in 8 cadaveric spine segments. Intact segments were initially tested. They then underwent preparation and were tested in 3 states in random order: MBIF cage, PEEK cage, or posterior instrumentation only.

The systematic review and meta-analysis of 7 studies comparing synthetic cages to impacted local morselized bone showed no difference in fusion rates, functional outcomes, complication profile, and height change between the two groups. Upon comparing the PEEK cage with the MBIF cage in polyurethane blocks, we found comparable results under healthy bone conditions, while the MBIF cage outperformed the PEEK cage in osteoporotic conditions. Cadaveric testing showed comparable performance between the two cages. In conclusion, the MBIF showed promising preliminary testing. A continued focus needs to be placed on the evaluation and development of this cage prior to clinical implementation.

Summary for Lay Audience

Various lower (lumbar) spinal problems that can cause back pain, leg pain, numbness/tingling, and weakness in the legs are addressed by a procedure known as posterior lumbar interbody fusion (PLIF) surgery. This procedure involves removing the non-bony disc between two bony vertebrae and placing either real bone or synthetic material acting like bone in-between, so that over time these vertebrae fuse together, thereby eliminating motion between them that can cause pain and dysfunction. The synthetic material used is called a “cage”, often being made of a special plastic polymer or various metal alloys. This cage can help restore the space between the vertebrae and to correct spinal alignment. Previously, bone taken from the patient’s pelvis was used for this purpose instead of a synthetic cage. This has the disadvantage of persistent pain in the pelvis and because of this, synthetic cages made of plastic polymer or metal alloys have been more commonly used. The main disadvantage of these cages is their tendency to sink into bone with time, especially in patients with low bone mineral density. This can result in residual leg and back pain and discomfort for the patient. Furthermore, these synthetic cages can be quite expensive, ranging from 1000 to 7000 dollars, which can be prohibitive, especially in countries with limited healthcare resources. In this thesis, we performed a preliminary analysis of studies published to date that compare using the patients’ own back bone to using synthetic cages in the clinical setting, to see if there are known limitations of this method. Results from this review suggest that there is no difference between the two groups in the rate of healing or improvement from symptoms. For the second part of this thesis, we aimed to create a new cage design mainly composed of patients own bone taken from their back during the PLIF procedure and reinforced by a thin stainless steel mesh layer around it for added strength. Using this bone from the patient’s own vertebra can theoretically have a lower capacity to sink into the patient’s vertebrae over time, have a larger surface area to promote faster fusion of vertebrae together, and not have the donor site pain that a cage taken from the patient’s pelvis would typically cause. We used cadaveric spines (from people who donated their body to research), to compare the strength of cage with a synthetically made plastic polymer cage. Testing involved moving the spine in a way to simulate normal human movements and comparing how the different cages performed. We showed that our cage has a performance comparable to the synthetic cage under healthy bone conditions. When bone mineral density is lower, our cage can outperform the PEEK cage as it causes less sinking into bone. These results are promising and suggest that our cage can be a suitable alternative to synthetic cages. More research is needed in the future to translate these initial results into using this in real-life surgeries.

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Orthopedic surgery, spine surgery, biomechanics, posterior lumbar instrumented fusion, PEEK cage, lumbar spine, local autograft

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https://hdl.handle.net/20.500.14721/39361

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