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Knee Instability

Causes, Symptoms, Treatment, AND Other Resources

What is Knee Instability?

Knee instability is a condition that results when the knee joint is unstable and does not move or function normally. This can cause the knee to feel like it is going to give out or buckle. It can be caused by a variety of factors, including:

  • Trauma or injury to the knee
  • Ligament injury
  • Arthritis or other degenerative diseases of the knee
  • Weakness or instability of the muscles around the knee
  • Muscle atrophy 
  • Injury to another joint in the body that creates imbalance 

Knee stability, and stability in general, is very important. Lack of knee stability can lead to more problems over time, such as pain and arthritis. What would cause you to suspect you have instability in your knees? You may notice your knee joint cracking or popping, or you might experience a sudden shift in the joint with a particular movement. Or you could already have some pain or swelling in the knee joint.

Causes of Instability in the Knees

There are a few common causes of instability of the knees. One is an injury to the ligaments that support the knee joint. Another is damage to the meniscus, the cartilage that cushions the knee. Obesity can also lead to unstable knees, as can diseases such as arthritis.

4 At-Home Tests for Checking Your Knee for Signs of Instability

There are also four simple tests you may do at home to check your knee for instability. If you believe you have unstable knees after executing these checks, you should schedule an appointment with one of our doctors for further evaluation.

  1. Single-Leg Deep Knee Bend   
  2. Single-Leg Balance
  3. Lower Back Test 1: 90-Degree Sit-Up
  4. Lower Back Test 2: Back Extension

Learn more about how those tests are done, what they mean, and what it means to pass or fail one of these knee tests here.

What are the symptoms?

Fibular Head Pain

The proximal fibula is the part of the bone that lives just below the knee joint on the outside. It’s attached to the leg bone (tibia) via strong ligaments and there is a small joint here. There are many things that attach here, so it’s a critical point where pain can occur. There is a small joint between the fibula and the tibia known as the proximal tibiofibular joint. This is a plane-type joint which allows some sliding of the fibula on the tibia. It has cartilage just like the knee joint, so it can get arthritis which means worn down cartilage and bone spurs.

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Knee Buckling

Knees can buckle, causing a sensation of one or both knees giving out that affects nearly 17% of adults. The knees are regarded to be one of the most essential (and biggest) joints in the human body because they play significant roles in basic activities such as walking and sitting. When our knees begin to feel unstable, weak, or begin giving out, it is easy to become stressed since we rely so heavily on them for movement. The knee can become stable from numerous types of injuries. The knee is kept stable by the following structures: Tendons attach the leg muscles…

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Knee Clicking

Clicking in the knee can occur for a number of reasons. The 5 major causes include: ligament injuries, meniscus tears, knee arthritis, patellofemoral syndrome, and soft/scar tissue. Let us start with ligament tears. A ligament is a thick piece of connective tissue that connects one bone to another. The knee has 4 principal ligaments: ACL, PCL, MCL, and LCL. Ligaments provide important stability for the knee (1). If injured or torn, ligaments can create instability. This instability can cause clicking in the knee. As ligaments travel across boney surfaces they can also catch make the knee click. The meniscus is a C-shaped cushion situated between the thigh bone and shin bone.

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Knee Hyperextension

The knee is a hinge joint between the femur and the tibia along with an accessory bone, the fibula. These bones are held together via ligaments that keep the bones aligned while the joint goes through its natural range of motion. These ligaments are: Medial Collateral Ligament (MCL), Lateral Collateral Ligament (LCL), Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL). from zero degrees fully extended to 140 degrees fully flexed. BUT when a force from the front to the back overcomes the strength of the ligaments the knee is forced into an unnatural position called “Hyperextension” which, in turn, can…

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Knee Making Crackling Sound

Crepitus is the medical term for this cracking or catching sensation. It can affect various regions of the body, but it is most common in the knee. It can happen due to air bubbles forming in bodily tissues (this is what happens most of the time), but it can also happen as a result of patellofemoral syndrome, damaged cartilage, osteoarthritis, or other conditions. Patients describe the sound of the popping with the following terms: popping, snapping, catching, clicking, crunching, cracking, crackling, creaking, grinding, grating, and Clunking. When Should You Be Concerned? When the crackling is accompanied by pain and/or the feeling of instability in the knee, that’s a good time to consult a physician. If the cracking is also associated….

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Knee Pain

Knee pain can be caused by many factors. Overuse injuries, direct trauma to the knee and arthritis are the most common causes of knee pain. Damage to the knee structures may cause swelling, scar tissue formation (fibrosis), and loss of function of the joint. Pain is often accompanied by difficulty walking, weakness, and instability. When the knee is overused, the thigh and shin bones (femur and tibia), cartilage, or tendons may experience stress. This leads to pain and discomfort as well as stiffness in the knee. Overuse injuries are common among athletes who participate in sports that involve running, jumping…

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Knee Swelling

Swelling of the knee, also known as water on the knee, is a condition in which fluid collects around the knee joint. Swelling can occur for a variety of reasons and affect patients of any age. Some swelling can be treated with over-the-counter medicines, but persistent and continuous swelling might result in tissue damage, bone softening, and cartilage deterioration. Over-the-counter medicines will assist relieve pain for individuals with a history of osteoarthritis and swelling following physical activity, such as exercise or running. During and after activity, the patient may apply compression sleeves to reduce the inflammation. Ice is another method…

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Pain Behind Knee

First off, this is where the hamstrings and calf muscles attach. They have tendons here that are inserted into the bone. So if there’s a problem in the muscle or the tendon, you’re going to feel it right here. This is also where deep muscles like the popliteus and plantaris live. So, if these have issues, you’re going to feel it in the back of the knee. In addition, the tibial nerve is back here. So if there’s an issue with a nerve in your back or a nerve locally, behind the knee, you’re going to feel it here. And the meniscus or the joint spacer lives back here. And the meniscus or the joint spacer lives back here. So a tear in the meniscus could cause pain…

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Weak in Knees

Weakness in the knee can be a symptom of many different knee conditions. Some of the most common causes of weakness in the knee include ligament tears, meniscus tears, and arthritis. Another important but often overlooked cause of knee weakness is irritation or injury of the nerves in the low back. If you are experiencing any type of weakness in your knee for long durations of time (3 weeks), it is important to see a doctor to determine the cause. Some of the most common symptoms of knee weakness include difficulty standing up from a seated position, difficulty walking, climbing or descending stairs…

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Treatment Options for Instability in the Knees

If you are experiencing symptoms, it is important to see a doctor to determine the cause and to receive treatment. Treatment may include physical therapy, bracing, our image-guided injections of PRP or bone marrow concentrate (containing stem cells), or surgery. 

NSAIDs

The other day I was evaluating a patient and reviewing the treatment options for their spine condition.  After discussing prior treatments, we got to the topic of medications taken for pain relief. She explained that she mainly utilized anti-inflammatory (NSAID) medications and then she told me to hold much she takes and has been for many years…..she takes close to 2 grams (2000 milligrams) on a daily basis which equated to about 9-10 capsules of medication per day.  I was shocked, considering she was pre-diabetic and with high blood pressure plus the kicker of it is that her PCP (primary care physician) is ok with this…

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PRP Knee Injections

PRP stands for Platelet-Rich Plasma. Platelets are blood cells that prevent bleeding. They contain important growth factors that aid in healing. Plasma is the light yellow liquid portion of our blood. So PRP is simply a concentration of a patient’s own platelets that are suspended in plasma and are used to accelerate healing. PRP is NOT stem cell therapy. Regrettably, blood contains few circulating stem cells. Rich sources of stem cells are bone marrow and fat. PRP is rich in growth factors. There are many different types of growth factors with different properties. VEGF is a very important one as it can increase the blood flow to an area.

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Doctors That Assist with Unstable Knees

Christopher J. Centeno, MD

Christopher J. Centeno, M.D. is an international expert and specialist in Interventional Orthopedics and the clinical use of bone marrow concentrate in orthopedics. He is board-certified in physical medicine and rehabilitation with a subspecialty of pain medicine through The American Board of Physical Medicine and Rehabilitation. Dr. Centeno is one of the few physicians in the world with extensive experience in the culture expansion of and clinical use of adult bone marrow concentrate to treat orthopedic injuries. His clinic incorporates a variety of revolutionary pain management techniques to bring its broad patient base relief and results. Dr. Centeno treats patients from all over the US who…

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John Schultz, MD

My passion and specialization are in the evaluation and treatment of cervical disc, facet, ligament and nerve pain, including the non-surgical treatment of Craniocervical instability (CCI). I quit a successful career in anesthesia and traditional pain management to pursue and advance the use of PRP and bone marrow concentrate for common orthopedic conditions. I have been a patient with severe pain and know firsthand the limitations of traditional orthopedic surgery. I am a co-founder of the Centeno-Schultz Clinic which was established in 2005. Being active is a central part of my life as I enjoy time skiing, biking, hiking, sailing with my family and 9 grandchildren.

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John Pitts, M.D.

Dr. Pitts is originally from Chicago, IL but is a medical graduate of Vanderbilt School of Medicine in Nashville, TN. After Vanderbilt, he completed a residency in Physical Medicine and Rehabilitation (PM&R) at Emory University in Atlanta, GA. The focus of PM&R is the restoration of function and quality of life. In residency, he gained much experience in musculoskeletal medicine, rehabilitation, spine, and sports medicine along with some regenerative medicine. He also gained significant experience in fluoroscopically guided spinal procedures and peripheral injections. However, Dr. Pitts wanted to broaden his skills and treatment options beyond the current typical standards of care.

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Jason Markle, D.O.

Post-residency, Dr. Markle was selected to the Interventional Orthopedic Fellowship program at the Centeno-Schultz Clinic. During his fellowship, he gained significant experience in the new field of Interventional Orthopedics and regenerative medicine, honing his skills in advanced injection techniques into the spine and joints treating patients with autologous, bone marrow concentrate and platelet solutions. Dr. Markle then accepted a full-time attending physician position at the Centeno-Schultz Clinic, where he both treats patients and trains Interventional Orthopedics fellows. Dr. Markle is an active member of the Interventional Orthopedic Foundation and serves as a course instructor, where he trains physicians from around the world.

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Matthew William Hyzy, D.O.

Doctor Hyzy is Board Certified in Physical Medicine and Rehabilitation (Physiatry) and fellowship-trained in Interventional Orthopedics and Spine. Dr. Hyzy is also clinical faculty at the University of Colorado School of Medicine in the Department of Physical Medicine and Rehabilitation; In addition, Dr. Hyzy is an Adjunct Clinical Assistant Professor at The Rocky Vista University College of Osteopathic Medicine. Dr. Hyzy also maintains an active hospital-based practice at Swedish Medical Center and Sky Ridge Medical Center. He is also recognized and qualified as an expert physician witness for medical-legal cases and Life Care Planning. He is published in the use of autologous solutions including…

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Brandon T. Money, D.O., M.S.

Dr. Money is an Indiana native who now proudly calls Colorado home. He attended medical school at Kansas City University and then returned to Indiana to complete a Physical Medicine and Rehabilitation residency program at Indiana University, where he was trained on non-surgical methods to improve health and function as well as rehabilitative care following trauma, stroke, spinal cord injury, brain injury, etc. Dr. Money has been following the ideology behind Centeno-Schultz Clinic and Regenexx since he was in medical school, as he believed there had to be a better way to care for patients than the status quo. The human body has incredible healing capabilities…

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Other Resources

Free Download: The Knee Owner’s Manual

This e-book by Dr. Chris Centeno examines the knee and its role in the human musculoskeletal system and the body as a whole. The Knee Owner’s Manual provides a series of tests and clearly defined exercises that you can perform on your own to assess and monitor your own knee health. It will allow you to look for trouble spots where your own body may be having difficulty with stability, articulation, symmetry, and neuromuscular function. You’ll be able to see how these deficits in other regions of the body relate to the knee.

The Knee Owner’s Manual also discusses how Regenexx is pioneering the development of interventional orthopedics, a new branch of medicine that employs regenerative biologic therapies such as adult bone marrow concentrate and platelet-rich plasma to help repair and strengthen damaged tissues in other areas of the body.

This is contrasted with invasive knee surgeries, which often remove important tissues or replace the entire knee itself when it becomes damaged. With hyperlinks to more detailed information, related studies, and commentary, this book condenses a vast amount of data, images, and resources into an enjoyable and informative read. This is the first edition of The Knee Owner’s Manual, a companion book to Orthopedics 2.0.

  • 6 Meniscus Tear Types And How To Treat Them Properly

    Even a small meniscus tear can make walking difficult for you. If you are experiencing any of these symptoms, you may want to seek medical help as soon as possible, depending on the type of tear you have. Needless to say, a lot depends on understanding the meniscus tear types there are and what each … Continued


  • How To Heal A Torn Meniscus Naturally

    If you have, or suspect you have a torn meniscus, and you’re wondering how to heal a torn meniscus naturally, you’ve landed on the right post. You may be wondering: Do I need surgery? Can you heal a torn meniscus naturally? The short answer is: It depends. What Is a Meniscus? The meniscus is a … Continued


  • How to Avoid Knee Replacement: A Quickstart Guide

    Your knee pain initially was intermittent and mild.  Unfortunately, It is now constant and debilitating.  Your doctor recommends knee replacement surgery. What is the knee composed of?  What are the most common knee injuries?  What is knee replacement surgery? What are the different types of knee replacements?  What is knee replacement surgery success? What are … Continued


  • How to Read a Knee MRI for Meniscal Tear

    Dr. Chris Centeno discusses how to read a knee MRI for meniscal tears and what you need to know about such tears. Transcript Hi, this is Dr. Centeno. And I’d like to go over today How to Read Your Knee MRI: Focus on the Meniscus. I have a whole series of these and reading a … Continued


  • 7 Most Common Symptoms of a Loose Knee Replacement

    Walking became impossible.  Each step was associated with severe pain.  Knee replacement seemed like a good solution.  Unfortunately, months after the surgery problems exist.  Your doctor thinks you have a loose knee replacement.  What is a knee replacement?  What causes a knee replacement to become loose?  What are the 7 most common symptoms of a … Continued


  • How Likely Is a Second ACL Tear On the Same Knee?

    Anterior Cruciate Ligament Injuries and Treatments The ACL (anterior cruciate ligament) is an important knee stabilizing ligament. It prevents the tibia from moving too much frontward (anterior translation) and twisting too much (internal rotation).  It is under most stress with landing from a jump, or a planted foot with twisting, and this is how it … Continued


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