The gliding characteristics of the flexor pollicis longus tendon in the carpal tunnel: Potential implications for manual pipette users

Abstract

To understand the potential mechanism for hand and wrist complaints in pipette users, whose motion is characterized by repetitive thumb motion in certain wrist positions, the peak (PGR) and mean (MGR) gliding resistance of the flexor pollicis longus (FPL) tendon were measured in nine human cadaver wrists. The PGR with the wrist in 308 ulnar deviation and in the neutral position were significantly lower than the PGR with the wrist in 608 flexion. The MGR with the wrist in 308 ulnar deviation was significantly lower than the MGR with the wrist in 608 flexion, 608 extension, or 208 radial deviation with 408 extension. Based on these data, we believe that a manual pipette designed to be used in neutral to ulnar deviated wrist position could have ergonomic advantages. Hand and wrist complaints, principally affecting the thumb, are common in individuals who use pipettes regularly in their work.1-6 Occurrence of such complaints was reported in up to 90% of individuals who continuously use pipettes for more than 60 min, 2 but little is known about the biomechanics associated with such complaints.One of the characteristics of the pipetting motion is repetitive thumb flexion in various positions of the wrist joint, especially wrist extension with radial deviation.1,3,5 Lee and Jiang 1 showed that the design of the pipette affects not only wrist position during usage, but also both the effectiveness and usability of pipetting. These data suggested to us that wrist position might affect thumb mechanics. To identify the difference of thumb mechanics while pipetting in various wrist positions, we focused on the gliding resistance of the main flexor of the thumb, the flexor pollicis longus (FPL) tendon, as pipetting requires repetitive forced flexion of the thumb with the wrist in various positions depending on the design of the specific pipette. Kutsumi et al.7 measured the gliding resistance of the FPL at the level of A1 to oblique pulley of the thumb, but this location is unaffected by wrist position. As no paper has reported the gliding resistance of the FPL tendon at the wrist level, we decided to measure the gliding resistance of the FPL tendon within the carpal tunnel. Our hypotheses were that the gliding characteristics of the FPL differed according to wrist position and that certain positions might minimize FPL friction during pipetting motions. To test these hypotheses we investigated FPL gliding resistance within the carpal tunnel in a human cadaver model. MATERIALS AND METHODS Specimen PreparationThis study was reviewed and deemed to be exempt by our Institutional Review Board. We used nine fresh frozen human cadaver upper extremities, obtained from five females and three males (mean age: 72.3 AE 13.5 years). Information regarding hand dominance was unavailable. One pair of specimens was bilateral. The specimens were amputated $15 cm proximal to the proximal wrist crease. Review of the medical records was performed on each cadaver donor to obtain demographic data and to be sure the individual did not have...

Thenar and Hypothenar Muscle Coverage on the Transverse Carpal Ligament

“…The finding that the powerful thenar muscles span to over 50% of the TCL on the radial side indicates that in healthy subjects, the muscle-ligament interface predisposes the TCL for tissue remodeling when biomechanical interaction frequently occurs during manual activities of daily life, including those associated with several occupations such as piano playing and pipetting. 2,3 In particular, the radial half of the TCL is connected with the powerful thenar muscles and could undergo thickening and stiffening after prolonged, repetitive thumb activities. The median nerve, closely abutted with the TCL in the radial region, can be particularly vulnerable to compression neuropathy under increased mechanical constraint caused by tissue maladaptation.…”

“…It is shown that the thenar muscles activate to pull the TCL volarly during a pinch movement, 1 and this repeated in vivo tissue mechanics could lead to hypertrophy of the involved muscles and ligament. The TCL is known to remodel to become thicker under repetitive, prolonged use of thumb as associated with pipetting 2 and piano playing. 3 A thickened TCL as a result could compress the median nerve and eventually lead to carpal tunnel syndrome.…”