What Are Knee Joint Injections?
Knee injections are used to treat pain and inflammation involving knee ligaments, tendons, and cartilage.
Because the knee joint supports several types of movement (bending, flexing, and twisting), it is prone to traumatic injury.The knee also functions to bear weight and enable walking, running, and jumping.
Injury to the knee can be very disruptive, impairing the ability to perform activities of daily living.
Knee pain and inflammation may be caused by acute injury or chronic arthritis disease in the joint.
The Centers for Disease Control and Prevention reports 50% of adults over the age of 65 suffer from arthritis.
Osteoarthritis is the most common, causing inflammation and degradation of knee cartilage over a long period of time.
Acute or chronic inflammation of the knee joint may also be diagnosed as tendinitis, injury to the tendons caused by a twisting motion.
The meniscus, a pad of cartilage cushioning the bones of the knee joint, is also susceptible to injury.
The type of injection given depends upon the nature of the knee injury, and may be used to treat inflammation, inhibit the transmission of pain messages, promote healing, or to lubricate the joint.
Types of knee injections include:
- Corticosteroids to reduce pain and inflammation
- Hyaluronic (like Viscosupplementation) to lubricate the joint and control the pain of osteoarthritis
- Platelet rich plasma (PRP) to treat pain and tendon thickening seen in professional athletes and physical laborers, as well as osteoarthritis, bursitis, and ligament injuries (PRP is the injection of a high concentration of the patient’s own platelets to promote healing in areas of the knee with limited blood flow)
- Nerve blocks, most commonly a saphenous block, especially helpful to patients who have been treated with a knee replacement
One of the biggest joints intricately designed to aid in bearing weight and enabling movement, the knee is made up of bones, muscles, and connective tissues. The femur, fibula, tibia, and patella are the four bones of the knee. The quadriceps is the muscle that supports the front of the knee, while hamstrings provide support behind the knee.
The joint is stabilized by ligaments and cartilage including:
- Anterior cruciate ligament (ACL) keeps the femur from putting pressure on the tibia
- Posterior cruciate ligament (PCL) inhibits the femur from sliding forward
- Collateral ligaments (medial and lateral) support the knee joint
- Meniscus (lateral and medial) provides a cushion between the tibia and the femur
- Articular cartilage cushions the patella
Fluid in the knee joint provides lubrication and enables ease of movement. The bursae are fluid-filled sacs that cushion the joint.
Most often, knee injections are a minimally-invasive procedure performed outpatient in a doctor’s office or clinic.
To begin, the patient assumes a comfortable position that gives the physician easy access to the injection site. The skin is cleaned with antiseptic, and the doctor may choose to begin by withdrawing fluid from the joint if swelling is present.
A needle is then inserted to the joint and excess fluid pulled and examined. The removal of fluid often results in immediate relief of pain due to a release of pressure within the joint.
Next, another needle is inserted to the knee joint and medication is injected, along with a local anesthetic to provide immediate pain relief, while the other medication works on long-term pain relief. During the procedure, the physician may opt to use digital imaging to guide the needle to the proper location.
Patients with damage to the musculoskeletal tissues of the knee who have not responded to initial treatments such as physical therapy, over-the-counter pain relievers, hot and cold application, and rest may find relief of pain through knee injections.
Knee injections are minimally-invasive and performed in an outpatient setting, providing an alternative to surgery.
This treatment may decrease pain, promote healing, and improve quality of life in patients whose mobility has been compromised by injury or chronic disease of the joint.
Pain relief from knee injections allows the patient to be more mobile and engage in an active, healthy lifestyle.
As with any injection procedure, there are risks, such as:
- Damage to tissues or nerves
Each type of knee injection carries its own set of specific risks. Some osteoarthritis injections may include processed chicken or rooster combs, and patients with an allergy to eggs or poultry are at risk for an allergic reaction. Sometimes, viscosupplementation injections may cause a pseudo-septic reaction in the knee joint, presenting as pain, swelling and redness.
Corticosteroids are useful in treating pain but carry a serious risk for both local and systemic side effects. Repeated, long-term use of steroid injections pose a risk of cartilage or ligament damage to the patient. There is also the possibility that the corticosteroid will crystallize in the joint and worsen inflammation. Systemic side effects of steroids include:
- Osteoporosis (bone loss)
- Increased blood pressure
- Elevated blood sugar levels
- Degenerative eye disease, such as cataracts and glaucoma
- Weight gain
- Depressed immune function, which increases risk of infection
- Ulcers and bleeding in the gastrointestinal tract
Knee injection treatment depends on the severity of damage. The patient may require only a one-time dose or a series of injections given weekly for three to five weeks. In cases of osteoarthritis, patients usually report decreased pain sensation after four to 12 weeks of treatment. Pain relief may last for months, and repeat treatments may be given as needed.
Corticosteroids effectively reduce pain and swelling, but they do not heal damaged tissues, and pain relief is short-term. The progression of arthritis in the joint is not slowed by corticosteroid treatment.
Viscosupplementation is a new treatment for knee pain demonstrating positive results. The shots are given as part of a series of injections, and 75% of patients who receive this treatment report pain relief.
Documentation on the effectiveness of platelet rich plasma (PRP) injections is limited, but preliminary studies show PRP may be effective in relieving pain and improving movement through the healing of tissues. As an option for patients who have been unable to gain pain relief from other therapies, PRP may provide an alternative to surgical intervention.