The University of Southampton

Author: Emma Deverill

Spinal Motion in Post-Surgical Scoliosis

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Scoliosis is an abnormal lateral curvature of the spine, causing misalignment. In order to be considered true scoliosis, the curvature, measured by the Cobb angle, must be more than 10 degrees. Spine specialists recommend different treatment options depending on this angle, with more severe and progressive cases resulting in surgery.

Examples of a mild, moderate, and severe case of scoliosis

Spinal Fusion

Spinal fusion, which has been the standard surgery for scoliosis for the past century, involves realigning and fusing the curved vertebrae with screws and rods. Although this procedure has good outcomes, with low complication and re-operation rates, it can diminish spinal mobility and flexibility. This means that those taking an interest in sports who undergo spinal fusion, for example, can lose their ability to perform. As someone with scoliosis myself (although mild), and having previously competed in tennis tournaments, this got me thinking about alternative spinal surgeries that do not have a negative impact on mobility.

An example of a patient before and after spinal fusion

“The desire to maintain spine motion has fuelled the development of various growth modulation procedures. The goals of these procedures are to correct the spinal deformity and maintain motion.”

Scott. J. Luhmann, M.D.

Vertebral Body Tethering

As of recent, non-fusion spinal surgery has been used on those with scoliosis to correct curvature, while preserving flexibility and mobility. One method is through vertebral body tethering (VBT). This is where anchors (coated in hydroxyapatite, the substance that bones are composed of) are anteriorly attached to the vertebrae on the convex side of the scoliotic curve, with a flexible tether (made from polyethylene-terephthalate) connecting these anchors. The foundation of the procedure is that the tension from the tether slows the growth on the convex side of the spine, giving time for the concave side to catch up and driving the spine into the correct alignment. Due to the flexibility of the tether, and the absence of bone fusion, this allows for better spinal mobility post-surgery. Because VBT works via growth modulation, the most suitable candidates are those who have yet to reach skeletal maturity or are experiencing progressive scoliosis. This therefore means that VBT is less generalised than spinal fusion, and due to it being a new approach, there is some uncertainty with its long-term outcomes. Possible complications surround the fact that the tether may break through prolonged stress, though this does not pose much of an issue once spinal correction has completed. Early reports into the post-operative results of VBT do however demonstrate a high success rate and low revision rate.

Image showing what a scoliotic spine would look like before and after VBT
Video of the VBT procedure

Posterior Dynamic Correction and The ApiFix

Another non-fusion surgery for scoliosis is posterior dynamic correction, which occurs with the use of the ApiFix. The ApiFix is a self-adjusting rod, implanted on the concave side of the spine using a posterior approach, serving as an internal brace, and helping straighten the spine. The device can expand and so accommodates skeletal growth and additional correction. It is fastened to the spine with a single-level fusion (meaning only two vertebrae are being fused), with a total of only three screws needed. The rod features two polyaxial joints in which the vertebrae are fused, providing a greater degree of motion than spinal fusion. The ApiFix is most suitable for those with single spine curves and a Cobb angle between 35 and 60 degrees. Because this device and the procedure is novel, questions have arisen about its success rates. For example, possible complications include rod breakage and osteolysis (destruction of bone tissue). Early reports into the post-operative results of posterior dynamic correction with the ApiFix do however display its success and provides preventative measures to decrease failure and re-operation rates.

Image showing a scoliotic spine before and after posterior dynamic correction with the ApiFix
Video of the ApiFix procedure

Final Thoughts

As I researched into the topic of surgical treatments for scoliosis, I was pleased to find other options as well as spinal fusion that can help preserve the individuals spinal mobility and flexibility. I believe that it is important to offer various treatments, while considering patient suitability, in order to improve the patient’s condition while not having a negative impact on their lifestyle. With the nature of these procedures, it has given me insight into how individuals requiring scoliosis corrective surgery have to negotiate between greater spinal motion with some uncertainty in long-term outcomes, or a long-lasting solution with diminished spinal motion. Personally, I would decide to go with the former option, with spinal fusion becoming a last resort if long-term outcomes are not successful. Nevertheless, I am excited to observe the follow-up results of these newer procedures and the advances technology will have on scoliosis corrective surgery.

Providing better options for prosthetic hand users

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A prosthetic hand acts as a substitute limb for those that may be missing one from birth or lost one later in life. There are several types of prosthetic hands, all functioning in their own way and prioritising different aspects for the user. Electrically-powered prosthetic hands offer a range of functions, however are costly. Alternatively, cosmetic prostheses are more affordable but do not provide active function. Because of this, many users ultimately settle with a prosthetic that does not perform to their expectations.

Recently, I watched a documentary that looked into resolving this issue. It showed Masahiro Yoshikawa, a professor from the Faculty of Robotics and Design at the Osaka Institute of Technology, focusing on creating highly functional protheses, while keeping costs low. This is an aspect of prosthetic research that I view as important, as it is essential that prosthetic users are not denied choice because of affordability. Prior to his research, a myoelectric prosthetic was the superior option. This consists of a prosthetic with sensors that detect electrical signals created by muscle movement from the residual limb, triggering a motor. The motor then converts the signal into finger movements, allowing the user to grasp objects. However, this technology is expensive and the prosthetic is heavy, which is not ideal for most individuals.

Offering a low-cost, lightweight, and highly functional prosthetic

Yoshikawa reviewed the manufacturing process for myoelectric prostheses, and figured out that one reason they are so expensive to make is due to the plaster moulds that have to be created prior to making the socket. He concluded that using a 3D printer to create the socket would eliminate the need to produce a mould beforehand, both decreasing manufacturing time and manufacturing cost.

“At the core of Yoshikawa’s research is the desire to create prosthetic hands that people want to wear, rather than something people wear because they have no other choice.”

NHK World – Japan: Helping Prosthetic Hand Users Become Choosers

Another improvement Yoshikawa set to develop was the issue of the myoelectric prosthetics malfunctioning after prolonged use. This was because, when users perspirate inside the device, it resulted in a short circuit between electrodes and disrupted the detection of the myoelectric signals. He proposed that, by measuring the height of the muscle as a change in distance, this signal instead could be used to generate motion. More specifically, through using a photoelectric sensor inside the socket, the muscle bulge created by movement of the residual limb will produce a change in distance from the sensor, detected via infrared rays, activating the motor. Consequently, with the sensor not directly resting on the skin and being surrounded by the urethane foam, the issue with perspiration is resolved alongside the benefit of the photoelectric sensor being significantly cheaper than the myoelectric one.

Mechanics of the photoelectric sensor

Since the filming of this documentary, this foundation has been used to create a three-fingered device and a five-fingered device, with realistic options available through the use of a silicone glove.

Different prosthetics created by Yoshikawa

This video shows the three-fingered device in action.

Through researching this topic, it has enabled me to understand the components that need to be considered when developing new prostheses, along with providing equal options for everyone. By developing a lightweight, cost effective, highly functional prosthetic, this has opened up options for individuals who would have previously been limited to a purely cosmetic prosthetic. Hopefully, with the advancement of technology, like what Yoshikawa has demonstrated, a wider range of prosthetic options will be available which users can choose from dependent on their lifestyle.

Check out the link below for the documentary:

https://www3.nhk.or.jp/nhkworld/en/ondemand/video/2015286/

Engineering Replacement Body Parts

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As a second year psychology student, I was provided many choices for my semester 2 optional module. However, I became torn between cognitive neuroscience and engineering replacement body parts. I ended up choosing this module as I wanted to learn more about prothesis and stem cells. Recently, I have been watching many episodes on NHK wherein prothesis was being discussed and I found these very interesting, ultimately influencing my decision to choose this module. One of the episodes focused on a guitarist who was born with congenital limb deficiency yet she is able to play guitar with a device that her dad developed. As someone who is also interested in guitar myself, I found myself engaged in the episode and wanted to learn more about prothesis and other aspects that compromise engineering replacement body parts.