Overview of Shoulder Arthrocentesis Technique
Draining fluid from the shoulder, known as shoulder arthrocentesis or aspiration, is a very useful procedure. Not only can it help to diagnose certain conditions, it can also be used as a treatment in itself. A range of healthcare providers, including emergency doctors, surgeons, and general practitioners, often carry out the procedure.
In terms of diagnosis, the aspiration method allows doctors to get a sample of the joint fluid in the shoulder. This can be very helpful when trying to figure out if a patient’s joint inflammation or arthritis is caused by an infection or a condition such as gout, pseudogout, or a traumatic joint bleed (hemarthrosis).
As a treatment, shoulder aspiration can relieve pain and swelling by removing excess fluid from the joint. The procedure can also involve injecting a steroid or a local anesthetic into the joint for added pain relief. This can make it easier for a doctor to move a patient’s shoulder back into its normal position while the patient is awake, reducing the risks associated with sedatives and pain medications given through an IV. Injecting medication into the shoulder joint is also used to manage pain in degenerative joint diseases.
In cases where a patient has had shoulder surgery (such as a total shoulder replacement, reverse total shoulder replacement, or shoulder hemiarthroplasty), this aspiration procedure can be used to check for post-surgery infections around the new joint. Doctors can send the fluid sample for extended culture incubation to detect any bacteria or other microorganisms, guiding them in deciding the best treatment for the patient.
Anatomy and Physiology of Shoulder Arthrocentesis Technique
Doctors need to understand the parts of the shoulder, known as the glenohumeral (GH) joint and shoulder girdle, to avoid any complications during treatment.
The shoulder girdle is made up of the scapula (shoulder blade) and clavicle (collarbone), which connect to the chest wall. It also includes the top part of the humerus (the upper arm bone), which connects to the scapula at a spot called the glenoid. The glenoid and the ball-shaped top of the humerus create part of the shoulder joint.
Other bone structures around the shoulder, including the main part of the scapula, its spine-like projection, and the outermost part known as the acromion, could be affected by certain related health conditions. For instance, the acromion can influence conditions related to shoulder impingement and rotator cuff syndrome, conditions that affect the movement and stability of the shoulder.
Another important part of the shoulder is a small, fluid-filled sac called the bursa. This is situated in the subacromial space of the shoulder, which is a cavity between the rotator cuff (a group of muscles and tendons that secure the shoulder joint) at the bottom and the acromion process at the top. This cavity opens into another space, called the subdeltoid bursa, on its most lateral (outer) side.
Understanding the nerves and blood vessels around the shoulder is also highly important when dealing with procedures involving shoulder joint aspiration or injection, where fluid is removed or medicine is injected into the joint.
The shoulder joint receives its nerve supply from three offshoots of the brachial plexus (a network of nerves running from the neck to the arm) identified as C5/C6:
- Suprascapular nerve
- Axillary nerve
- Lateral pectoral nerve
The axillary nerve and a blood vessel called the posterior circumflex humeral artery pass through the quadrilateral space, located at the back and bottom part relative to the GH joint. This space is bordered by different muscles and parts of the humerus, the bone in the upper arm.
Why do People Need Shoulder Arthrocentesis Technique
There are a few reasons why a doctor might look into a condition called infectious or septic arthritis. They might also check for conditions referred to as inflammatory arthritides or crystalline arthropathy. In simpler terms, these are different types of inflammation and swelling in the joints. Each of these conditions require a diagnosis to decide the right treatment. Checking for these conditions might also be necessary if a person has suffered a traumatic injury, like a bone break or a ligament tear, or if the doctor needs to see if a penetrating injury happened. These injuries could be a deep cut or a gunshot wound.
The treatments for these conditions vary as well. One common treatment is with injections of steroids or cortisone. These help reduce inflammation. Local anesthetic injections can help to numb the area around the joint, relieving pain. Some conditions may cause a build-up of fluid, known as an effusion, in the joint. If this becomes too much and starts causing discomfort, the doctor may drain the fluid to bring relief. Similarly, if there’s bleeding into a joint space, it can create a condition known as hemarthrosis. This may have to be treated by the doctor to prevent the lining of the joint from thickening and scarring.
When a Person Should Avoid Shoulder Arthrocentesis Technique
The one situation where the procedure should absolutely not be done is if there is an infection of the skin at the point the doctor wants to insert the needle. Still, if there are bacteria in the blood, which is a relative risk, the procedure could introduce these bacteria into the joint, causing an infection there too. However, if your doctor thinks there’s a high chance of bacterial infection in the joint, they may wish to analyze the fluid from the joint even though bacteria is in the blood. This is because not treating a potentially infected joint fully or correctly can do more harm than the slight risk of introducing bacteria into the joint through the procedure.
Other circumstances that might make the procedure risky, include if you have a bleeding disorder or are on anti-clotting drugs, as this might cause bleeding into the joints during or after the procedure. However, this risk is considered quite low when compared to the risks of not treating an infected joint.
If you have an artificial joint, some believe it’s not a good idea to perform this procedure outside of a very clean, surgical surrounding. Although, if such an environment is not available and there’s an urgent need to drain and analyze fluid from the joint, your doctor may still decide to go ahead with it. In a situation like this, they will explain to you the risks and benefits before proceeding.
Equipment used for Shoulder Arthrocentesis Technique
Materials
Aseptic Skin Preparation
* Sterile gloves are needed to protect both the doctor and the patient from any possible sources of infection.
* A solution of iodine or chlorhexidine is used to clean the skin and remove any harmful microbes or germs.
* Sterile gauze pads are used to absorb and clean any fluids that might come out during the procedure.
* Sterile, fenestrated drapes, which are cloths with a hole in the center, are used to keep everything but the specific area of operation clean and free of germs.
Needles
* 25G or 27G needles are used for injecting the anesthetic and steroid medicines. These are relatively thin needles, which reduces the discomfort for the patient.
* 20-22G needles are used if fluid needs to be taken out or aspirated. The specific size used can depend on how thick the fluid is.
Luer-Lok Syringes
* 3-5 mL syringes are used for injections.
* 5-20 mL syringes are used when fluid needs to be aspirated or removed.
Medications
* Anesthetic: Lidocaine 1% or Bupivacaine 0.5%. These are both numbing medications which will make sure the patient doesn’t feel the procedure. The shoulder will take about 3-5 mL of these.
* Steroid: Methylprednisolone acetate (Depo Medrol) 40 mg or Triamcinolone acetonide (Kenalog) 40 mg. These are anti-inflammatory medications that help to reduce swelling and pain.
Testing Equipment
Specimen collection tubes
* Hematology tube is used for cell count and differential. This means it’s used to count the number of different types of blood cells, which is important for diagnosis and treatment.
* Sterile tube for Gram stain, culture, and smear. This is a tube used to collect a sample which can then be studied under microscope for diagnosis.
* Heparinized tube is used for crystal analysis. This means it’s designed to prevent the blood from clotting so that the presence of any crystals can be detected, which is helpful for certain diagnoses.
Preparing for Shoulder Arthrocentesis Technique
Success in any medical procedure often depends on careful preparation. Arthrocentesis, or the process of extracting fluid from a joint in the shoulder, is no exception. Since this procedure doesn’t need to be done in urgent or emergency situations, it’s important to always take the time to prepare thoroughly. This helps to make the procedure as successful as possible and reduces the risk of any potential complications.
How is Shoulder Arthrocentesis Technique performed
Anesthesia is a crucial part of the procedure and the skin over the injection area can be numbed with a local anesthetic like lidocaine. This is given using a thin needle. Alternatively, a substance that cools rapidly such as ethyl chloride can be used to provide temporary numbness of the skin at the injection point. These methods can also be combined so that both the skin and the tissue underneath are numbed, which can make the procedure more comfortable.
The patient should be seated upright with the affected arm in a relaxed position. If possible, the patient can be seated in a chair with armrests or on a stretcher with the head elevated and guardrails up. This ensures that not only is the patient comfortable, but also that the clinician has good access to the shoulder joint. Additionally, having the patient seated or lying down can help prevent any falls that might happen if the patient faints.
When it comes to the actual procedure, there’s an Anterior Approach and a Posterior Approach. Both start with cleaning, sterilizing, and draping the skin to prevent any infections. The next step is very important and involves identifying specific landmarks on the shoulder which will tell the clinician where to insert the needle. For the Anterior approach, these landmarks include the rounded part of the upper arm bone, the clavicle, and a small hook-like structure called the coracoid process.
The clinician will then insert the needle into the shoulder joint, making sure it’s perpendicular to the skin. This is done while pulling back on the syringe’s plunger to check for any blood or fluid from the joint. Once the syringe is filled, a small clamp can be put on the hub of the needle, allowing the clinician to easily remove the filled syringe and replace it with a fresh one if needed. This new syringe may be filled with a local anesthetic or steroids as needed. Once this is done, the skin is cleaned again and a bandage is placed over the injection site.
Alternatively, for the Posterior Approach, two fingers are placed below and to the middle of the acromion’s back edge. The needle is then directed forward and inward towards the coracoid process. This process, as before, serves as a guide for the direction in which the needle should be inserted.
Possible Complications of Shoulder Arthrocentesis Technique
As a doctor, it’s my responsibility to talk about all possible risks involved with a surgical procedure. A very small chance exists that you might pick up a germ or bacteria during or after the operation, leading to an infection caused accidentally by medical treatment, this is what we call an “iatrogenic infection”. Even though the chance is tiny, around 1 in 10,000, we need to be aware this could happen.
Other possible issues we should discuss include:
- Pain that can occur after the procedure
- Bleeding, either from the surgical site or into the joint
- Possibility of accidental damage to nearby soft tissues like nerves or tendons
- Potential harm to bones or cartilage
Remember, these risks are generally rare, but awareness and understanding is key to preparing for any procedure.
What Else Should I Know About Shoulder Arthrocentesis Technique?
Synovial fluid analysis is a test that checks the liquid which lubricates your joints, like your knee or elbow. Here’s what the results might tell us:
Normal synovial fluid usually looks clear, has white blood cell (WBC) counts of less than 200 cells per micro-liter, PMNs (a type of white blood cells) representing less than 25% of WBC, synovial lactate (a substance related to energy production in cells) less than 5.6 mmol/L, and glucose levels close to your blood glucose level.
In conditions causing inflammation, such as arthritis or injury, the fluid might be clear or somewhat yellow, with a WBC count of less than 2000 cells per micro-liter, PMNs less than 25%, sticky, and glucose level that also approximates blood glucose level.
If the fluid analysis results show WBC count above 50,000 cells per micro-liter (greater than 1,100 in an artificial joint) and PMNs greater than 90% (over 65% in a prosthetic joint), this could indicate a joint infection. Other signs include synovial lactate over 5.56 mmol/L and an LDH (a type of protein) level higher than 250.
Keep in mind that not having all these indications does not necessarily mean that the joint is free of infection. If there’s suspicion of an infection, a separate “stain” test should be done to verify. This test is very important if there isn’t enough synovial fluid to perform all the necessary tests.
Some key points to remember:
- During the test, there’s a small risk of injuring the protective layers of the joint with the needle. Be careful not to hit the bone.
- The thoracoacromial artery, which supplies blood to some muscles and skin of the chest, is located towards the inner side of an area near the shoulder.
- Pointing the needle slightly upward can avoid injuring blood vessels and nerves.
- Using ultrasound to find the space around the joint can make the test safer and more likely to succeed.
