In-vivo ultrasound observations of the surgically repaired flexor digitorum profundus tendon: a case series

Abstract

There are few assessment tools available to objectively measure in-vivo flexor tendon healing in the hand. Ultrasound properties of echogenicity and tendon thickness, which indicate structural properties of the healing tendon, have previously been used to evaluate healing of the surgically repaired Achilles tendon in humans, and various animal tendons. In the past, tendon excursion has been measured invasively by radiographic measurement of implanted metal markers, however a non-invasive alternative is to measure the distance moved by tendon-suture material, which is rendered visible by ultrasound imaging. Gapping of the tendon ends has also been previously measured ultrasonographically, as has margination (definition of tissue borders), which indicates tendon adhesions. In addition, power Doppler ultrasound is a sensitive measure of tendon vascularity and is able to detect change in tendinopathy lesions and inflammatory conditions.

However, it is not known if the ultrasound properties (of echogenicity, thickness, excursion, gap, margination and vascularity) can usefully detect change in the surgically repaired intrasynovial flexor digitorum profundus (FDP) tendon of the hand. Therefore, this study was designed to: 1) document longitudinal change in grey-scale and power Doppler ultrasound measurements of echogenicity, vascularity, thickness and excursion of the surgically repaired intra-synovial FDP tendon during the first eighteen weeks post-operative; 2) document thickness of the corresponding uninjured contra-lateral tendon; 3) record concurrent clinical outcomes at twelve weeks post-operative. Three male participants aged between 33 and 59 years who had undergone surgical repair of the FDP tendon within the digital sheath consented to take part in the study. Repeated estimates of echogenicity and power Doppler signal levels as well as measurements of tendon thickness and excursion were determined using a linear array 13 MHz ultrasound transducer. Measurements were made on five occasions between two weeks and four months post-surgery on each subject. Three sites on the injured digit were assessed: the mid-repair site, 1 cm proximal and 1 cm distal to the surgical repair, along with measurements from the corresponding contra-lateral digit, which served as a control. A radiologist rated the echogenicity, power Doppler signal levels and margination of the transverse area of each site on 0 to 4, 0 to 3, and 1 to 4 scales, respectively, before measuring tendon thickness (mm), defect length (mm), and excursion (mm) using on-screen calipers. Tendon excursion was measured on both passive and active DIP joint motion using suture material as a marker. The standardised protocol of ultrasound evaluations detected a pattern of incremental change in echogenicity scores (4 to between 1 and 3) and power Doppler score (PDS) (no registration to 1 or 2) at the mid-tendon repair site over the sixteen-week period of investigation. Tendon-thickness measurements increased between weeks two and four, then trended downward, averaging 194 to 122 percent of the corresponding uninjured contra-lateral tendon. Excursion of the FDP tendon induced by 30 degrees passive distal interphalangeal (DIP) joint flexion ranged between 1.4 mm and 2.2 mm at 2 weeks, trending upward to between 0.8 mm and 3.6 mm at eighteen weeks post-surgery. Active DIP joint flexion of 30 degrees induced FDP tendon excursions of between 0.8 mm and 1.9 mm at six weeks after surgery, and 1.3 mm to 3.2 mm by eighteen weeks. Dynamic change in the ultrasound variables was most remarkable at the mid-repair site. A greater reduction in echogenicity levels, less variation in tendon thickness and greater tendon excursion were documented in the two participants with good or excellent clinical outcomes (Strickland-Glogovac criteria). For the first time, longitudinal measurement of ultrasound properties of echogenicity, vascularity, thickness, defect length and suture excursion of the surgically repaired intrasynovial FDP tendon has been investigated in-vivo in the human hand. Although the measurement properties of the ultrasound variables are yet to be determined, the ease of measurement and documented change suggest that these variables offer a non-invasive tool for evaluating tendon healing. Future applications include evaluating and validating a range of physical, biological and pharmacological interventions to modulate healing of the intra-synovial digital flexor tendon in the human hand.