Biomechanical Aspects of Trigger Finger before and after Pulley Release Surgery

Abstract

Trigger finger is a common problem in hand clinics “Triggering” describes the catching and sudden release phenomenon during finger extension movement The first annular (A1) pulley release surgery has been used to treat trigger finger for over a century The release is required to extend to the second annular (A2) pulley to completely alleviate the symptoms for certain patients The tendon force at triggering is unknown Thus the first aim of this dissertation was to develop a biomechanical model estimating the tendon force at triggering Besides the postoperative finger function was unsatisfying in some patients Therefore the second aim was to propose a practical postoperative rehabilitation protocol with clear treatment goals and programs and provide the quantitative evaluation of finger function The pulley release surgery may lead to hand function change However the effects of the different extent of pulley release have not been well explored Hence the third aim was to investigate the effects of the different extent of pulley release on the tendon excursion efficiency and the changes of tendon moment arms To estimate the tendon forces in trigger fingers a biomechanical model with moment equilibrium equations and method of least squares was developed The “pulling tester” was designed to pull the tested finger from flexion to extension and provide the synchronic measurement of the pulling force and a motion capture system was used to record the finger motion and the direction of the pulling force Ten fingers presented significant triggering effect were tested The tendon tension of flexor digitorum profundus (FDP) was greater than less than or equal to that of flexor digitorum superficialis (FDS) at triggering in the ten subjects Besides the finger joints were locked at different angles These results may imply that varied parts along the flexor tendons were trapped in the annular pulley system A four-week rehabilitation protocol was proposed for trigger finger after percutaneous pulley release surgery Trigger finger patients with joint contracture problems were recruited Nine subjects were in the intervention group which received the postoperative rehabilitation after surgery Twelve subjects were in the control group which received no therapy after surgery A motion capture system was used to measure the finger joint rotation and the fingertip workspace during a sequent movement of five postures The intervention group presented significantly better improvement than the control group in the fingertip workspace the range of motion of distal and proximal interphalangeal joints and the total active range of motion The proposed rehabilitation protocol might be helpful for trigger finger patients with joint contracture problems To understand the effects of the different extent of pulley release four conditions of pulley integrity were investigated including pulley intact A1 pulley release half A2 pulley release and complete A2 pulley release Eight cadaveric hands were used in the experiment and a total of eight middle fingers were tested The joint rotation was measured by a motion capture system and the tendon excursion was measured by linear position sensors The tendon moment arm was determined by the linear fitting result The results present no significant change between A1 and half A2 pulley release in the FDP excursion efficiency and the moment arms of FDP and FDS with respect to the metacarpal phalangeal joint To relieve the discomfort if necessary the pulley release may extend to the half proximal A2 for trigger finger patients This dissertation provides the investigations of trigger finger before and after pulley release surgery from biomechanical perspectives A biomechanical model was developed to estimate the tendon force at triggering in trigger finger and the results of ten subjects were provided Besides a postoperative protocol with clear treatment goals and programs was proposed for trigger finger after the percutaneous pulley release surgery and the benefits of the rehabilitation protocol were quantitatively proved In addition the effects of different extent of pulley release on the tendon excursion efficiency and moment arms were evaluated Hopefully the biomechanical investigations will improve the understanding of trigger finger provide suggestions for clinical practice and further help in developing better assessment and treatment programs

Date of Award	2014 Jan 20
Original language	English
Supervisor	Fong-chin Su (Supervisor)