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Video Transcript – Hip and Knee Biomechanics


Before we start explaining what biomechanics is let’s first see a few examples. Musculoskeletal injuries
such as muscles sprains, strains, and bone breaks, and dislocations can occur throughout many activities, but are especially common in athletics. These injuries can be very painful and many require rehabilitation or surgery to fix the issues. To treat any injury properly we need to make informed decisions and have evidence to support what we do. This is where our biomechanics research comes into play. We provide that evidence that supports the treatments for injury.

What do you think biomechanics is? Biomechanics is the study of the mechanical principles that control our biological systems. Basically it’s the math and physics that controls our cells and body. We want to study movement so we can better understand disease and injury and design targeted treatments and surgical interventions. We work in labs at Washington University in St. Louis and Boise State University in Boise Idaho.

What information do you think is relevant to treat an injury? To understand an injury in the musculoskeletal system we have to understand the anatomy and mechanics of the joints in which they occur. This requires an understanding of what goes on below the surface of the skin. This is possible through experimental data, medical imaging, and computer modeling. Biomechanics experiments involve collecting data relevant to motion such as how your joints move when your muscles are turned on and how much force there is between you and the floor. From analyzing experimental data and model outputs we can better understand what is happening at the joint. This can help us decide on the best treatment whether that is surgical intervention or even exercises to help prevent injury from happening in the first place. For every patient, information about their anatomy and motion at the joint must be collected. To understand a person’s anatomy at the joint level we use medical imaging such as MRI or x-ray to see the underlying structures. To study movement we use a system called motion capture. This involves putting reflective markers on the patient at specific bony anatomical points around the joints of interest. Cameras then track the motion at each of their joints in three-dimensional space as they move. Motion capture is even used in movies and video games to create realistic animations.

What do we do next with his anatomy and movement information? We use it to study the person’s kinematics and build subject-specific models to understand what is happening at the joint. For example take two specific projects looking at the hip and knee joints. The hip joint consists of the femur and pelvis bones and is important for weight bearing and stability around the hip joint. Changing the angle between the femur and the pelvis can change how weight is distributed over the joint. Let’s think about this in a simple motion, the squat.

How do you think a wide versus a narrow squat would affect the loading in the hip joint? Something as simple as widening or narrowing your stance in a squat can dramatically change how much weight your body can handle due to the different muscles used. A wider squat will activate more of your butt or hip muscles while a narrower squat uses more muscles around the knee such as your quads. If you’re a professional weight lifter the wider stance allows you to lift larger weights because of the stronger muscles. In addition changing squatting form can change where in the hip joint loads are being directed. This is especially important in hip diseases such as hip dysplasia which is something we study at Washington University. Patients with hip dysplasia have much shallower hip sockets than healthy patients so there is less coverage of the femoral head. This can cause the loads on the hip to be further on the edge of the hip socket which can lead to damage. A patient with hip dysplasia performing a narrow squat might experience more damaging loads than a healthy person performing the same squat. While we now know some of the importance of the hip in human movement we must consider other joints, such as the knee and the work being done by our friends at Boise. Dislocation of the kneecap or the patella is a common injury in young athletes. Most of the time the patella sits within a groove on the thigh bone, the femur. But some people have anatomy that make them more vulnerable to the kneecap slipping out of this groove.

How do you think the depth of the groove would affect the likelihood of dislocation? One risk factor is how high the kneecap sits on the femur. A higher kneecap puts people at higher risk for this injury. Another risk factor is the depth of the groove that the kneecap sits in. People with a flatter or shallower femoral groove are more prone to this type of injury. Some people develop a recurrent dislocation which means a dislocation that occurs again and again. For these people surgery can be a good treatment option to prevent recurrent injury. We can use medical imaging to build models of patients knees to help us understand why this injury occurs and how surgery may improve the stability of a person’s joint. These models simulate the changes to the joint as a result of the surgery. We can use these types of models to evaluate different surgery types to see which would be most optimal for a patient.

What else do you think might be involved injury or treatment? Think about other anatomical factors and external factors that might play a role. Hip dysplasia and patellar dislocation both relate to stability in the joint but what happens to the rest of the body if we have an injury in one of these joints? The joints are interconnected so injury or degeneration in one joint may lead to issues in other joints as well. This is because neighboring joints share a lot of the same anatomical features such as the femur bone for the hip and the knee. Treatment must target the joint with the specific injury without causing negative effects in the rest of the musculoskeletal system.

What are some other injuries that biomechanics can be used to study? So where do we see biomechanics happening? Biomechanics isn’t limited to just the laboratory setting. For example in various types of clinics and even hospitals physical therapists and physical therapist assistants use biomechanics to help people move around more easily. They can work with athletes, people with neurological conditions, and people with musculoskeletal injuries. Certain types of medical doctors such as physiatrists and sports medicine physicians also utilize biomechanics in their practice.

There are also a variety of biomechanics careers at universities or even in the business world. For example universities hire scientists with different perspectives to help understand how people move. Also companies often hire kinesiologists, biomedical engineers, and many other specialties to help with product design and testing. Due to the range of interests of people in biomechanics many of the classes you are taking right now can be useful. For example classes such as physics, math, biology, health sciences, and even sports and performance can be helpful for getting into biomechanics related careers.

Where do you see biomechanics happening in your life?