A procedure for ultrasound-guided injection into the lower joint space of the temporomandibular joint is presented.
Ultrasonography is one of the modalities used for imaging of the temporomandibular joint (TMJ); it is most often used for the diagnosis of degenerative changes of the condyle, effusion, or disc displacement. The main disadvantage of ultrasonography is the limited imaging capacity in the superior and medial part of the condyle and disc. These structures are hidden by acoustic shadow (i.e. signal reduction under the zygomatic arch) caused by rebound and absorption of ultrasound waves in the zygomatic bone.
Ultrasonography may also be used for the directed application of medications into the TMJ (e.g. hyaluronic acid, corticosteroids, platelet-rich plasma (PRP), or autologous blood). Application into the superior joint space is performed routinely without the need for image-guidance. Ultrasound control enables accurate application into the lower joint space, which is difficult without image-guidance.
A linear probe (frequency 7.5–14 MHz, the same as used for imaging of the TMJ structures) is used for targeted injection into the lower joint space under ultrasonographic control. The probe is positioned vertically in the pre-auricular region (in front of the tragus), i.e. in the TMJ region, with extension over the zygomatic arch. The structures are imaged in the coronal plane. The orientation of the resulting image depends on the probe position; the cranial pole of the area under investigation is on the left side of the resulting Image.
The procedure is performed in the closed-mouth position. The point of needle insertion is pre-auricular, 15 mm under the zygomatic arch. The needle is inserted at an angulation of 60° to the expected top of the condyle, in an anterior direction ( Fig. 1 ). Depending on the mutual probe and needle positions, two imaging options are possible. The first is exact imaging of the entire needle and joint structures simultaneously, which is difficult to perform (as a result of single-plane imaging). The second option comprises clear visualization of the joint structures and only parts of the needle ( Fig. 2 ); control of the correct needle position is by extension and narrowing of the lower joint space during the procedure (i.e. application and aspiration of the fluid). The authors prefer the second option.