A team of researchers from the Indian Institute of Science, Bangalore, and HOSMAT Hospital, Bangalore, have used an analytical, computer-based model to show how stress on the spine changes after spinal fusion surgery to treat degenerative disc disease.
The spine or the backbone has 33 individual irregular shaped bones, called vertebrae, stacked one over the other. This vertebral column supports about half of a person's bodyweight. According to the curve of the spine, it is divided into five regions. The lumbar region consists of five vertebrae between the rib cage and the pelvis.
An intervertebral disc, a region between every two vertebrae, is made of a gelatinous substance that acts as a shock absorber during movement. Degenerative Disc Disease (DDD) is a medical condition in which one or more of these discs degenerate. The symptoms include short-term to long-term lower back pain while performing daily activities. This pain may increase or spread to other regions as well. In most cases, this is treatable without surgery. However, surgery becomes necessary when there is no relief after two to three months of non-surgical alternatives.
Spinal fusion is one surgical technique, which uses a bone graft to cause fusion of two vertebrae. In this technique, metallic or non-metallic instruments may be used to provide extra support to the spine. "The disadvantage of fusion is that pain relief is achieved at the cost of elimination of existing range of movement in the affected segment", say the authors.
Studies have shown degeneration in segments next to the vertebral fusion site due to stress after such spinal fusion surgeries. This 'adjacent segment degeneration' (ASD) may be asymptomatic for a long time. ASD may show up any time from one year to up to 38 or more years after the first fusion surgery. To understand the mechanism involved, the researchers studied the effects of different types of lumbar surgical interventions on the stresses in the adjacent lumbar discs.
Using CT scan images, the team generated a three-dimensional computer model of the lumbar spine. Keeping the lower end fixed, they applied force from the top and a compressive force to mimic bodyweight and effect of muscles, respectively. To confirm the results of their model, they performed the same experiments on a lumbar spine harvested from a cadaver.
The experiments showed that the adjacent segment disc stresses increased with the length in all types of spinal fusions. Also, instrumentation led to an increase in adjacent level stresses at all levels of fusion. “Fusion with less rigid materials has been attempted and the long term outcomes are not known yet. The best alternative would be a non-fusion (motion preserving) dynamic stabilization of the involved spinal segment. Disc replacement using artificial materials has also been performed but the results are not so overwhelmingly impressive to drive out spinal fusion from the treatment menu. Stabilization of the involved disc segment using elastic materials has also been attempted in clinical trials. A highly effective alternative is yet to be found but attempts are underway,” concludes Dr. M. N. Kumar, an orthopaedic surgeon in HOSMAT Hospital and one of the researchers of the study.
Gunti Srinivas is a research scholar pursuing his PhD in CPDM. Prof. Anindya Deb is a senior professor in the CPDM department and DR. M N Kumar is an orthopaedic surgeon in HOSMAT Hospital, Bangalore.
Prof. Anindya Deb - Professor, CPDM, IISc Bangalore, e-mail - firstname.lastname@example.org; Gunti Ranga Srinivas, Faculty, Sri Siddhartha Institute of Technology, Tumakuru, E mail -email@example.com; Dr. Malhar N Kumar, HOSMAT Hospital, Bangalore, e mail - firstname.lastname@example.org; Goutham Kurnool, Research Scholar, CPDM, IISc, e mail -email@example.com
Gunti Srinivas has completed his tenure as research scholar in IISc and is currently serving as a faculty member in SSIT, Tumakuru. His research interests include computer aided engineering (CAE) and biomedical engineering. Prof. Deb's research interests include CAE and automotive engineering including occupant and pedestrian safety. Dr. Kumar's interests include clinical research and application of CAE for aiding medical research in the field of orthopaedics.