Introduction of a Novel Injection Technique Focusing on Flexor Tendons for Proximal Interphalangeal Joint Flexion Contracture

There are several relationships between carpal tunnel syndrome (CTS) and trigger finger.
Previous studies have reported that in CTS, collagen protein expression within the fibroblasts of the flexor tendon sheath synovium is significantly suppressed following the administration of triamcinolone.
Trigger finger is often associated with proximal interphalangeal (PIP) joint flexion contracture, which in some cases becomes a problem.We hypothesized that, similar to the antifibrotic effects of triamcinolone in CTS, administering triamcinolone around the flexor tendons in cases of PIP joint flexion contracture would reduce fibrosis and improve PIP joint flexion contracture. 
Here, we introduce a novel technique, the Ultrasound-guided Mid-Axial Injection (UgMAI), which targets the peritendinous area rather than the intrasheath region, with the aim of improving PIP joint flexion contracture in trigger finger. We hypothesized that the primary cause of PIP joint flexion contracture is fibrosis of the vinculum and the membranous portion of the volar plate located outside the tendon sheath. By using ultrasound to precisely inject the antifibrotic agent triamcinolone into these structures, we aimed to demonstrate that this method can improve flexion contracture.

Clinical Study: UgMAI was performed on 10 patients with trigger finger complicated by PIP joint flexion contracture. In these patients, intrasheath injections at the A1 pulley via the palmar approach had proven ineffective. Therefore, under ultrasound guidance, a needle was laterally inserted into the vinculum and the membranous portion of the volar plate on the proximal phalanx, and 4 mg of triamcinolone was injected. The PIP joint extension angle was evaluated and compared before and two weeks after the UgMAI procedure. Additionally, UgMAI was performed on 20 cases where PIP joint flexion contracture persisted even after A1 pulley release surgery, with 4 mg of triamcinolone injected into the vinculum and membranous portion of the volar plate. The PIP joint extension angle was compared before and two weeks after the procedure.


Cadaveric Study: To verify the accuracy of the UgMAI technique, dye was injected into the region between the flexor tendon and the proximal phalanx near the PIP joint in cadavers. Dissection was then performed to evaluate the staining range and confirm accurate targeting of the intended structures.

Clinical Study: Significant improvements in PIP joint extension angles were observed following UgMAI in both non-surgical and post-surgical cases.


Cadaveric Study: Staining of the adipofascial tissue in the vinculum and the membranous portion of the volar plate outside the tendon sheath was confirmed, verifying the accuracy of the UgMAI technique.

UgMAI is a novel and accurate technique that significantly improves PIP joint flexion contracture in both non-surgical and post-surgical cases. This method holds the potential to become a valuable addition to the treatment options for trigger finger.

Keywords: Contracture,Proximal Interphalangeal Joint,Triamcinolone,Flexor tendons,Carpal Tunnel Syndrome,Trigger Finger,Ultrasonography,Ultrasound-Guided Injection,Vinculum,Volar Plate,Cadaver