Too often workers decide it is easier to jump off equipment than climb down with proper 3-point contact. There are some obvious safety concerns with this behaviour, however, the action itself places joints of your body at risk. In this article we will focus mainly on the impact to your knees.
The Hazards You See
The hazards you can see are obvious risks on the worksite, and hopefully make you think twice about jumping off equipment, knowing a potential for injury exists. But what about those warm, dry days when you are parked on a smooth, flat surface? There are still significant risks for injury that you do not see because they happen within your body.
The Hazards You Do Not See
The impact of landing from a height can have negative effects on the joints and other musculoskeletal parts of your body, regardless of external conditions. When jumping down from a height of approximately 1m, you are increasing the impact force on your knee joint to as high as 7-12 times your body weight (Fathallah, 2000, p 28 & 31). This all depends on your movement patterns while landing, relating to how the body’s energy is absorbed.
Anterior Cruciate Ligament
The Anterior Cruciate Ligament (ACL) is the most important stabilizing ligament of the knee. It is located deep within the knee joint. If the ACL is torn, the knee joint is at a high risk of being unstable, potentially leading to further damage to the joint, pain, and limitations for the individual to perform normal daily activities.
“The ACL rupture is more commonly observed during the deceleration phase of a given action, particularly when the movement also involves a change of direction.”
Depending on how you are landing, the increased compressive force of the knee joint can also put the structures within the knee at risk. Landing in a more upright position with minimal to no knee bend, or potentially in a hyperextended knee position, places the ACL under high stress and risk of injury. Landing with a straight leg also generates higher impact forces compared to landing with a slight knee bend, further increasing the risk for injury (Fathallah, 2000, p. 33).
Hypertension is not the only risk factor for injuring your ACL on landing. If on landing your knee caves inward you are increasing injury risk to your ACL, as well as other soft tissue structures of your knee. The higher the drop, the greater the force through the knee, and the greater the chance of the knee moving inwards. Your risk increases if you are not anticipating the landing, are somewhat fatigued, have a pre-existing knee injury, or have not properly warmed up your body.
Meniscus
Another structure of the knee at risk is the meniscus. There are two menisci located in-between the load-bearing surfaces of the knee. The meniscus provides added surface area for increased stability and shock absorption for the knee joint. Repetitive increased load can cause small micro-tearing of the meniscus, or in other words, increased wear and tear. If landing with even a slight twist to the knee you are at risk of tearing the meniscus. Over time, these tears lead to degeneration and joint space loss, which means less shock absorption properties.
Osteoarthritis
Osteoarthritis (OA) refers to degeneration of the cartilage lining and underlying bone. This process happens naturally over time within our bodies as we age as a result of general wear and tear. The more degenerative changes you have within your knee, the decreased amount of joint space you will have which again means less cushioning in the knee. This often causes pain, however, with proper body mechanics, awareness, and optimal strength, it may go unnoticed unless aggravated. Aggravation can be caused by a number of risk factors, including: overuse/repetition, drastic increase in volume of activity, prolonged static positions, trauma/injury to other structures such as the ACL and meniscus, as well as awkward postures and high force such as pivoting immediately after landing when jumping off equipment.
Proper Mounting/Dismounting
To protect the knee joint when entering and exiting a vehicle or piece of equipment it is important to take 3 point contact seriously.
Occasionally 3 point contact is not achievable due to the lack of handrails, lack of steps, or possibly because the positioning is out of reach or not adequate for your body proportions. This is a perfect example of the importance of the “Prepare the Work Area, Tools, and Equipment” portion of the MoveSafe® Program Main Elements. Plan ahead! Determine if best practises are achievable. And if not, think of potential solutions you have seen, and ask questions to your supervisor or Health and Safety team. Maybe there is a simple solution you are not aware of, or maybe the equipment requires adjustments for optimal healthy performance.
Work Cited
Fathallah, F. A., & Cotnam, J. P. (2000). Maximum forces sustained during various methods of exiting commercial tractors, trailers and trucks. Applied Ergonomics, 31(1), 25–33. https://doi.org/10.1016/s0003-6870(99)00020-4
