More Effective Joint

A Better Wrist

Abstract

I choose to modify the wrist as the joint for my project. I first researched the most common injuries that occur in a wrist which was spraining a wrist. Then I followed the layout of the write up provided to fill in the information needed for the bones, ligaments, tendons, nerves, and blood vessels in the joint. Afterward, I started thinking up different ways to prevent wrist sprains from occurring and the best solution seemed to be adding cartilage behind the wrist to add protection and still allowing flexibility and taking up little room. Then I added in all the necessary extra material needed to support the new cartilage such as nerves and blood vessels.

Overview

The joint that is being redesigned is the wrist. The wrist connects the hand to the forearm and is responsible for a multitude of human activities such as grabbing, pulling, pushing, and lifting ourselves and objects.

Bones

The wrist is made up of bones including the distal ends of the radius and ulna and the 8 carpal bones along with the proximal ends of the 5 metacarpal bones.

Ligaments

The wrist has a very complex arrangement of ligaments that are classified as extrinsic ligaments, intrinsic ligaments, and interosseous ligaments. The most important ligaments in the wrist are the collateral ligaments. There are two collateral ligaments, one on each side of the wrist. They connect the wrist to the forearm. These ligaments help stabilize the wrist and keep it from bending too far to the side.

Tendons

There is a multitude of tendons that run across the wrist that first start as muscles in the forearm. The tendons that cross the palm side of the wrist are called flexor tendons. These tendons curl the fingers and thumb and bend the wrist. The tendons that run along the back of the wrist are called extensor tendons run through multiple tunnels called compartments. The compartments are lined with fluid to prevent friction between the tendon and the compartment.

Nerves

The main nerves in the wrist come from the radial, median, and ulnar nerves. The radial nerve runs along the thumb side of the forearm, and it gives sensation to the back of the hand. The median nerve travels through the carpal tunnel. It gives nerve supply to the thenar muscles of the thumb and also sends sensory fibers to the palm and first three fingers. The ulnar nerve runs through a separate tunnel called the Guyon’s Canal. The ulnar nerve branches out to supply sensation to the pinky and ring finger along with smaller muscles in the hand.

Blood Vessels

Large blood vessels run through the wrist to supply the hand and keep up with its mass number of activities it completes every day. One of these blood vessels is the radial artery that runs across the front of the wrist near the thumb. The ulnar artery runs alongside the ulnar nerve. The ulnar and radial artery arch together in the palm of the hand to supply the hand and its fingers with blood.

Wrist Sprain

By far, the most common injury in the wrist is a sprained wrist. Wrist sprains are common in athletes, motorcyclists, gymnasts, and others. A sprained wrist occurs in many athletes and in a lot of daily movement. All it takes to sprain a wrist is a second of loss of balance that causes someone to fall. A common reaction to a fall is to stick a hand out and break the fall. Doing so applies a lot of force to the wrist bending it a little too far backward towards the forearm. This force can tear the ligament that connects the wrist to the carpal bones, or in worse cases, break the ligament. Minor to moderate wrist sprains can heal on their own, but require some time to rest the wrist, icing it, or compressing it. In severe wrist sprains, the ligament can snap, requiring surgery to repair.

Design

One design feature I could add to the wrist to prevent injury from wrist sprains is by adding a layer of cartilage on top of the carpal bones to the distal ends of the radius and ulna bone covering the wrist. Adding a layer of cartilage here will make the wrist more firm by making it harder to bend the wrist too far backward. Cartilage is firm and flexible so it will be able to protect the wrist from injury while also allowing the wrist to continue its multitude of motions. Since the cartilage is connective tissue itself, it won’t require any extra or new tendons or ligaments. The radial nerve already runs through the back of the wrist to provide sensation for the back of the hand. However, the cartilage will require an additional blood vessel to run through the wrist since the existing blood vessels only run through the palm side of the wrist. This new blood vessel can run alongside the radial nerve and borrow the tunnel that the nerve travels through. Now the new cartilage can be formed to protect the wrist from future wrist sprains while being supplied with new blood vessels that take up as little room as possible.

Diagram

Discussion

Most wrist sprains are caused by a fall that bends the wrist too far backward and tears the ligaments. I thought about adding more bones around the ligaments to give it more structure and prevent damage. However, adding bones will require additional ligaments since ligaments are required to connect bone to bone. I then thought about adding muscle behind the wrist to soak up the impact when a person falls. But muscles are useful in protecting the body from their function is strictly movement. I wanted to add a strong material to could defend the wrist from being pushed too far back, but was also flexible enough to allow the wrist its flexible range of motion. I thought about adding cartilage to the wrist since it's a bendy firm structure used the ear and nose. Cartilage could prevent damage when a person falls since it can restrict the hand from bending too far back.

Prevention

Wrist sprains are generally hard to prevent since they normally occur in unpredicted accidents. However, tools such as wrist guards and tape can be used to prevent the wrist from bending too far backward causing a wrist sprain.

Works Cited

Phillips, Benjamin Z., Md. "Wrist Joint Anatomy." Overview, Gross Anatomy, Natural Variants. Medscape, 28 Oct. 2016. Web. 09 May 2017. <http://emedicine.medscape.com/article/1899456-overview>.

"Wrist Sprain." WebMD. WebMD, n.d. Web. 09 May 2017. <http://www.webmd.com/fitness-exercise/wrist-sprain#1>.

Wrist Anatomy." Wrist Parts & Anatomy | Houston Methodist. Houston Methodist, n.d. Web. 09 May 2017. <http://www.houstonmethodist.org/orthopedics/where-does-it-hurt/wrist/wrist-anatomy/>.

Code, Keith. A Twist of the Wrist. Glendale Calif.: Code Break, 2002. Print.

Wrist X-ray picture

"Scapholunate Advanced Collapse Wrist." Wikimedia Commons, 27 Oct. 2012. Web. 9 May 2017.<https://commons.wikimedia.org/wiki/File:Scapholunate_advanced_collapse_wrist.jpg>.

Wrist guard picture

Liew, Cheon Fong. "3M Futuro Reversible Splint Wrist Brace." Flickr. Yahoo!, 24 Nov. 2011. Web. 09 May 2017. <https://www.flickr.com/photos/liewcf/6393617505>.