Where is the tendon sheath landmark for injection?

Tendon Sheath Landmark for Injection

The tendon sheath landmark for injection is located at the level of the metacarpophalangeal (MCP) joint crease for finger flexor tendons, with the needle inserted directly into the tendon sheath space between the tendon and its surrounding synovial covering. 1, 2

Anatomical Landmarks by Location

Hand/Finger Flexor Tendons

• Entry point: Make the injection at the palmar crease overlying the MCP joint, which corresponds to the A1 pulley location 3
• Needle positioning: Insert perpendicular to the skin surface, advancing until the needle enters the space between the flexor tendon and its sheath 1, 2
• Confirmation: Successful injection is confirmed by observing distention of the tendon sheath during real-time visualization with ultrasound, or by feeling minimal resistance to injection 4, 2

Flexor Hallucis Longus (Ankle)

• Patient positioning: Prone position with the transducer placed along the posteromedial ankle 4
• Entry point: Lateral to the Achilles tendon at the level of the posterior sulcus 4
• Target depth: Inject at the level of the posterior sulcus for the FHL, with distention of the tendon sheath as the desired endpoint 4

Alternative Mid-Axial Technique (Fingers)

• Entry point: Mid-axial approach at the level of the MCP joint, which causes significantly less pain than the conventional palmar approach (VAS 40.19 vs 48.39, p<0.05) 5
• Advantage: This technique avoids direct needle insertion into the tendon substance, reducing risk of tendon rupture 5

Critical Technical Points

Needle Selection

• Use 25-gauge, 1.5-inch needle or 22-gauge spinal needle for most tendon sheath injections 4
• Smaller gauge needles (25G) minimize tissue trauma and patient discomfort 4

Injection Technique

• Strict aseptic technique is mandatory 1
• Inject into the tendon sheath rather than the tendon substance to avoid tendon rupture 1, 5
• For tenosynovitis, ensure the corticosteroid enters the sheath space, not the tendon proper 1
• Inject without delay after drawing up medication to prevent settling in the syringe 1

Ultrasound-Guided vs Blind Injection

Ultrasound guidance dramatically improves accuracy and safety compared to blind injection. 2

Accuracy Data

• Ultrasound-guided: 70% optimal placement (dye only in tendon sheath) 2
• Blind injection: Only 15% optimal placement (p=0.001) 2
• Safety advantage: 0% tendon penetration with ultrasound vs 30% with blind technique (p=0.02) 2

Ultrasound Advantages

• Real-time visualization allows needle adjustment to ensure proper medication delivery 4, 6
• Can confirm successful injection by observing tendon sheath distention during injection 4
• Provides excellent accuracy and improved clinical effectiveness compared to unguided procedures 6
• Allows visualization of neurovascular structures to avoid injury 7

Common Pitfalls and How to Avoid Them

Avoid Tendon Substance Injection

• Risk: Direct injection into the tendon can cause tendon rupture 1, 5
• Prevention: Use ultrasound guidance to visualize the needle tip entering the sheath space, not the tendon 2
• Confirmation: Minimal resistance to injection and visible sheath distention indicate proper placement 4

Avoid Subcutaneous Fat Injection

• Risk: Injection into surrounding tissues causes tissue atrophy 1
• Prevention: Ensure adequate needle depth to reach the tendon sheath, particularly in the deltoid region 1

Protect Neurovascular Structures

• For thumb injections, identify and protect the radial digital nerve, which courses directly over the A1 pulley 3
• Ultrasound allows direct visualization of these structures 7

Injection Volume and Medication

• Standard therapeutic mixture includes anesthetic and long-acting corticosteroid 4
• For intra-articular/tendon sheath injections: 2.5-5 mg triamcinolone for smaller areas, 5-15 mg for larger areas 1
• Observe for sheath distention to confirm adequate volume delivery 4