低減肩関節脱臼肩関節内注射
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Q1: Why is intra-articular injection used for shoulder dislocation reduction?
Intra-articular injection with local anesthetic like lidocaine provides significant pain relief during shoulder reduction. Reduction is the best form of analgesia and restores arm function, but the procedure itself is extremely painful. Injecting lidocaine into the joint space decreases pain perception and eliminates the need for complete sedation, reducing complications and emergency department resource requirements.
Q2: What are the main types of shoulder dislocations?
The three major types of shoulder dislocations are anterior, posterior, and inferior. Anterior shoulder dislocation is most common, accounting for approximately 95% of cases. Anterior dislocations are further classified into four subtypes: subcoracoid (75% of anterior cases), subglenoid (20%), subclavicular, and intrathoracic. The shoulder's extensive range of motion and considerable instability make dislocations one of the most common joint disarticulations in emergency settings.
Q3: How do you identify the injection site for intra-articular shoulder injection?
Palpate the posterior acromion and coracoid to locate the lateral sulcus, an abnormal depression in the skin caused by an empty glenoid fossa in anterior shoulder dislocation. Press into the shoulder from the posterolateral or lateral side; the sulcus will be evident by finger intrusion into the space. Mark this site with a skin marker as your insertion point for the injection.
Q4: What confirms successful needle placement in the joint capsule?
When the needle enters the injured joint capsule, serosanguinous fluid will be seen in the syringe upon aspiration. This blood-tinged fluid confirms accurate placement within the joint space. If no fluid is aspirated after full needle insertion, the needle may be too short or in an incorrect position. In such cases, a longer spinal needle or ultrasound guidance may be necessary.
Q5: How does ultrasound guidance improve the intra-articular injection procedure?
Ultrasound guidance allows real-time visualization of the needle tip reaching the appropriate joint space, enhancing procedure success. The linear probe suits thin patients while the curvilinear probe suits larger individuals. Under ultrasound, you can follow the needle in an in-plane approach, direct it toward the blood clot in the empty glenoid fossa, and visualize lidocaine as a swirling motion when injected, confirming correct placement.
Q6: What complications can occur during intra-articular shoulder injection?
Inadequate needle length is a primary complication, especially in obese or muscular patients where regular needles cannot pierce subcutaneous tissue; a longer 22-gauge spinal needle may be required. Inappropriate needle trajectory can cause the needle to abut against bony prominences, creating resistance. Ultrasound guidance helps determine the appropriate pathway and increases procedure success by avoiding these complications.
Q7: How long does intra-articular anesthesia take to become effective?
After injecting 10-20 mL of lidocaine into the joint space, wait 10-15 minutes to assess the anesthetic effect. Ask the patient if their pain has decreased to determine if adequate anesthesia has been achieved. Once sufficient pain relief is confirmed, proceed with shoulder reduction. Ultrasound can then confirm correct humeral head placement in line with the glenoid after reduction.