Safe treatment of trigger finger with longitudinal and transverse landmarks: an anatomic study of the border fingers for percutaneous release

Transverse landmarks have recently been determined to predict the proximal and distal edges of the A1 pulley for trigger finger release. Percutaneous A1 pulley release has been discouraged for the border digits because of the risk of injury to the neurovascular structures of the index and small fingers. The purpose of the study was to identify longitudinal surface landmarks to prevent injury to the neurovascular bundles during percutaneous A1 pulley release of the ulnar and radial border digits. Longitudinal surface landmarks were identified and marked on 29 cadaver hands. Proximal and distal landmarks for the longitudinal vector through which the A1 pulley of the small finger was released include the midline of the proximal digital crease and the scaphoid tubercle. Proximal and distal landmarks for the longitudinal line through which the index finger A1 pulley was released include the midline of proximal digital crease and radial edge of the pisiform. Longitudinal incisions were performed between these landmarks, straight through the skin and deep enough to score the A1 pulley. The distance of the medial edge of the neurovascular structures from the longitudinal incision in the A1 pulley was measured for each small finger and index finger. Using these longitudinal landmarks for the index and small fingers, none of the neurovascular structures was injured while performing these longitudinal incisions through the skin, scoring the A1 pulley. In fact, the average distance for the neurovascular structures from the longitudinal vector of the small finger was 5.4 +/- 1.4 mm radially and 6.7 +/- 1.9 mm ulnarly. The average distance for the neurovascular structures from the longitudinal line of the index finger was 8.5 +/- 1.8 mm radially and 6.2 +/- 1.7 mm ulnarly. Based on the findings of this anatomical study, these longitudinal landmarks can be used to avoid injury to neurovascular structures in the management of trigger finger involving the border digits with steroid-injection, open, or percutaneous A1 pulley release.     

Biomechanical model for the determination of the forces acting on the finger pulley system

A mathematical model proposed by Hume et al., 1991. Journal of Hand Surgery-American Volume 16, 722-730 for the determination of the forces acting on the A2 and A4 pulley was used. The parameters necessary for this determination include the angle of flexion, the positioning of the pulley with respect to the centre of rotation in the proximal interphalangeal joint (PIP), the relative mismatch between bone and tendon width at the location of the respective pulleys as well as the tendon height at this position. This model was further developed to include the stiffness of the respective pulley, as well as the fact, that there are two flexor tendons of which only one passes through both pulleys. Each parameter was then evaluated using a sensitivity analysis proposed by Fasham et al., 1990. Journal of Marine Research 48, 591-639 in order to determine their relative importance for the outcome of the model. The most important parameter proofed to be the positioning of the pulley with respect to the centre of rotation in the PIP joint. This observation enabled us to give the best possible placement for a pulley graft after pulley rupture.     

Estimation of finger muscle tendon tensions and pulley forces during specific sport-climbing grip techniques

The present work displayed the first quantitative data of forces acting on tendons and pulleys during specific sport-climbing grip techniques. A three-dimensional static biomechanical model was used to estimate finger muscle tendon and pulley forces during the "slope" and the "crimp" grip. In the slope grip the finger joints are flexed, and in the crimp grip the distal interphalangeal (DIP) joint is hyperextended while the other joints are flexed. The tendons of the flexor digitorum profundus and superficialis (FDP and FDS), the extensor digitorum communis (EDC), the ulnar and radial interosseus (UI and RI), the lumbrical muscle (LU) and two annular pulleys (A2 and A4) were considered in the model. For the crimp grip in equilibrium conditions, a passive moment for the DIP joint was taken into account in the biomechanical model. This moment was quantified by relating the FDP intramuscular electromyogram (EMG) to the DIP joint external moment. Its intensity was estimated at a quarter of the external moment. The involvement of this parameter in the moment equilibrium equation for the DIP joint is thus essential. The FDP-to-FDS tendon-force ratio was 1.75:1 in the crimp grip and 0.88:1 in the slope grip. This result showed that the FDP was the prime finger flexor in the crimp grip, whereas the tendon tensions were equally distributed between the FDP and FDS tendons in the slope grip. The forces acting on the pulleys were 36 times lower for A2 in the slope grip than in the crimp grip, while the forces acting on A4 were 4 times lower. This current work provides both an experimental procedure and a biomechanical model that allows estimation of tendon tensions and pulley forces crucial for the knowledge about finger injuries in sport climbing.     

Biomechanical properties of the crimp grip position in rock climbers

Rock climbers are often using the unique crimp grip position to hold small ledges. Thereby the proximal interphalangeal (PIP) joints are flexed about 90 degrees and the distal interphalangeal joints are hyperextended maximally. During this position of the finger joints bowstringing of the flexor tendon is applying very high load to the flexor tendon pulleys and can cause injuries and overuse syndromes. The objective of this study was to investigate bowstringing and forces during crimp grip position. Two devices were built to measure the force and the distance of bowstringing and one device to measure forces at the fingertip. All measurements of 16 fingers of four subjects were made in vivo. The largest amount of bowstringing was caused by the flexor digitorum profundus tendon in the crimp grip position being less using slope grip position (PIP joint extended). During a warm-up, the distance of bowstringing over the distal edge of the A2 pulley increased by 0.6mm (30%) and was loaded about 3 times the force applied at the fingertip during crimp grip position. Load up to 116N was measured over the A2 pulley. Increase of force in one finger holds by the quadriga effect was shown using crimp and slope grip position.     

Update on the anatomy of the pulley system in the chicken foot long digit

The pulley system in the flexor sheath of the long toe of the white leghorn chicken foot was studied. Histologic sections of the pulleys were prepared, and the mechanics of flexion of the long toe was analyzed. An annular flexor pulley that attached to the third phalanx was identified. This pulley, which has not been described previously, was found to be essential for proper flexion of the third interphalangeal joint.     

Moment arms of the human digital flexors

For the extrinsic hand flexors (flexor digitorum profundus, FDP; flexor digitorum superficialis, FDS; flexor pollicis longus, FPL), moment arm corresponds to the tendon's distance from the center of the metacarpalphalangeal (MP), proximal interphalangeal (PIP), or distal interphalangeal (DIP) joint. The clinical value of establishing accurate moment arms has been highlighted for biomechanical modeling, the development of robotic hands, designing rehabilitation protocols, and repairing flexor tendon pulleys (Brand et al., 1975; An et al., 1983; Thompson and Giurintano, 1989; Deshpande et al., 2010; Wu et al., 2010). In this study, we define the moment arms for all of the extrinsic flexor tendons of the hand across all digital joints for all digits in cadaveric hands.     

Impact of taping after finger flexor tendon pulley ruptures in rock climbers

Flexor tendon pulley ruptures are the most common injury in rock climbers. Therapeutic standards usually include a prolonged use of taping applied as a replacement for the lost pulley in a circular fashion at the base of the proximal phalanx. Our biomechanical considerations, however, suggest a new taping method, the H-tape. The purpose of the study is to evaluate whether this new taping method can effectively change the course of the flexor tendon and therefore reduce the tendon-bone distance. In order to compare the effects of different taping methods described in the literature with the newly developed taping method, we performed standardized ultrasound examinations of 8 subjects with singular A2 pulley rupture and multiple pulley ruptures of A2 and A3 pulleys and determined the respective tendon-bone distance for the different taping methods, versus without tape at a preset position on the proximal phalanx. In a second approach, we evaluated the effect of the new taping method on the strength of the injured finger using a force platform on 12 subjects with different pulley ruptures with injuries older than 1 year. The new taping method decreased the tendon-bone distance in the injured finger significantly by 16%, whereas the other taping methods did not. The strength development was significantly better with the new tape for the crimp grip position (+13%), but there was no significant improvement for the hanging position. We recommend taping with the newly presented taping technique after pulley rupture.     

Finger joint force minimization in pianists using optimization techniques

A numerical optimization procedure was used to determine finger positions that minimize and maximize finger tendon and joint force objective functions during piano play. A biomechanical finger model for sagittal plane motion, based on finger anatomy, was used to investigate finger tendon tensions and joint reaction forces for finger positions used in playing the piano. For commonly used piano key strike positions, flexor and intrinsic muscle tendon tensions ranged from 0.7 to 3.2 times the fingertip key strike force, while resultant inter-joint compressive forces ranged from 2 to 7 times the magnitude of the fingertip force. In general, use of a curved finger position, with a large metacarpophalangeal joint flexion angle and a small proximal interphalangeal joint flexion angle, reduces flexor tendon tension and resultant finger joint force.     

The influence of concentric and eccentric loading on the finger pulley system

In this study we investigated the influence of the loading condition (concentric vs. eccentric loading) on the pulley system of the finger. For this purpose 39 cadaver finger (14 hands, 10 donors) were fixed into an isokinetic loading device. The forces in the flexor tendons and at the fingertip were recorded. In the concentric loading condition A2 and A4 ruptures as well as alternative events such as fracture of a phalanx or avulsion of the flexor tendons were almost equally distributed, whereas the A2 pulley rupture was the most common event (59%) in the eccentric loading condition and alternative events were rare (23.5%). The forces in the deep flexor tendon, the fingertip and in the pulleys were significantly lower in the eccentric loading condition. As the ruptures occurred at lower loads in the eccentric than in the concentric loading condition it can be concluded that friction may be an advantage for climbers, supporting the holding force of their flexor muscles but may also increase the susceptibility to injury.     

A new friction tester of the flexor tendon.

We have developed a new device to measure the friction force and calculate the friction coefficient between a rabbit flexor tendon, a pulley and a proximal phalanx. The flexor digitorum fibularis tendon of a rabbit was taken intact with the proximal phalanx, and tendon pulleys were attached to both ends of the bone. Both ends of the tendon were clamped to acrylic plates and connected to stainless-steel plates equipped with strain gauges. A pretension of 1.96 N was applied so as not to loosen the tendon. The proximal phalanx was fixed to an acrylic plate on the actuator, which gave 8 mm of transfer to the acrylic plate at a speed of 2 mm/s. The interface between the tendon and the surrounded tissue created the friction force, when the load was applied on the distal pulley. The friction force could be obtained from the difference between the tension of both ends of the tendon, which was measured with strain gauges and sampled with a personal computer. The friction force and the friction coefficient were calculated from the measured force and the applied load. The load and the pre-loading time, which was defined as loading duration before gliding, were varied in order to observe the change of the friction coefficient. The friction coefficient was not affected by the load and increased with the pre-loading time. The value of mu(s) ranged from 0.027 to 0.111 (0.072 +/- 0.023), and that of (mu)d ranged from 0.010 to 0.069 (0.039 +/- 0.014) (pre-loading time was 5 s). Our method will allow for the examination of various surgical treatments and lubricants. Moreover, it can be applied to other tissues of any animals with similar structures to the rabbit's digitorum.     

Macroscopic and microscopic analyses in flexor tendons of the tarsometatarso‐phalangeal joint of ostrich (Struthio camelus) foot with energy storage and shock absorption

Flexor tendons function as energy storage and shock absorption structures in the tarsometatarso‐phalangeal joint (TMTPJ) of ostrich feet during high‐speed and heavy‐load locomotion. In this study, mechanisms underlying the energy storage and shock absorption of three flexor tendons of the third toe were studied using histology and scanning electron microscopy (SEM). Macroscopic and microscopic structures of the flexor tendons in different positions of TMTPJ were analyzed. Histological slices showed collagen fiber bundles of all flexor tendons in the middle TMTPJ were arranged in a linear‐type, but in the proximal and distal TMTPJ, a wavy‐type arrangement was found in the tendon of the M. flexor digitorum longus and tendon of the M. flexor perforans et perforatus digiti III, while no regular‐type was found in the tendon of the M. flexor perforatus digiti III. SEM showed that the collagen fiber bundles of flexor tendons were arranged in a hierarchically staggered way (horizontally linear‐type and vertically linear‐type). Linear‐type and wavy‐type both existed in the proximal TMTPJ for the collagen fiber bundles of the tendon of the M. flexor perforatus digiti III, but only the linear‐type was found in the distal TMTPJ. A number of fibrils were distributed among the collagen fiber bundles, which were likely effective in connection, force transmission and other functions. The morphology and arrangement of collagen fiber bundles were closely related to the tendon functions. We present interpretations of the biological functions in different positions and types of the tendons in the TMTPJ of the ostrich feet.     

Flap irritation phenomenon (FLIP): etiology of chronic tenosynovitis after finger pulley rupture

After a pulley rupture, most climbers regain the full function of their previously uninjured fingers. However, in some cases of pulley rupture, a persistent inflammation of the tendon sheath is observed. In this study, 16 cadaver fingers were loaded until pulley rupture and then studied for the rupturing mechanism. In addition, two patients with this pathology were investigated using ultrasound and MRI, and received surgery. In 13 fingers, a rupture of one or several pulleys occurred and almost always at the medial or lateral insertion. In one finger, a capsizing of the pulley underneath the intact tendon sheath was observed, leading to an avulsion between tendon and tendon sheath. A similar pathology was observed in the ultrasound imaging, in MRI, and during surgery in two patients with prolonged recovery after minor pulley rupture. In cases of prolonged tenosynovitis after minor pulley rupture, a capsizing of the pulley stump is probably the cause for constant friction leading to inflammation. In those cases, a surgical removal of the remaining pulley stump and sometimes a pulley repair may be necessary.     

The influence of the crimp and slope grip position on the finger pulley system

In this study the influence of the grip position (crimp grip vs. slope grip position) on the pulley system of the finger was investigated. For this purpose 21 cadaver finger (11 hands, 10 donors) were fixed into an isokinetic loading device. Nine fingers were loaded in the slope grip position and 12 fingers in the crimp grip position. The forces in the flexor tendons and at the fingertip were recorded. A rupture of the A4 pulley occurred most often in the crimp grip position (50%) but did not occur in the slope grip position, in which alternative events were the most common (67%). The forces in the deep flexor tendon (FDP) (slope grip: 371 N, crimp grip: 348 N) and at the fingertip (slope grip: 105 N, crimp grip: 161 N) were not significantly different between the 2 finger positions, but the forces acting on the pulleys were higher in the crimp grip position (A2 pulley: 287 N, A4 pulley: 226 N) than in the slope grip position (A2 pulley: 121 N, A4 pulley: 103 N). The crimp grip position may be the main cause for A4 pulley ruptures but the slope grip position may be hazardous for other injuries as the forces recorded in the flexor tendons and at the fingertip were comparable at the occurrence of a terminal event.     

Friction between human finger flexor tendons and pulleys at high loads

A method was developed to indirectly measure friction between the flexor tendons and pulleys of the middle and ring finger in vivo. An isokinetic movement device to determine maximum force of wrist flexion, interphalangeal joint flexion (rolling in and out) and isolated proximal interphalangeal (PIP) joint flexion was built. Eccentric and concentric maximum force of these three different movements where gliding of the flexor tendon sheath was involved differently (least in wrist flexion) was measured and compared. Fifty-one hands in 26 male subjects were evaluated. The greatest difference between eccentric and concentric maximum force (29.9%) was found in flexion of the PIP joint. Differences in the rolling in and out movement (26.8%) and in wrist flexion (14.5%) were significantly smaller. The force of friction between flexor tendons and pulleys can be determined by the greater difference between eccentric and concentric maximum force provided by the same muscles in overcoming an external force during flexion of the interphalangeal joints and suggests the presence of a non-muscular force, such as friction. It constitutes of 9% of the eccentric flexion force in the PIP joint and therefore questions the low friction hypothesis at high loads.     

Connective tissue reinforcing structures of the digital tendon sheaths of the human hand

At a greater number of humid preparated human hands, all the ligamentous supports of the digital tendon sheath were exposed and their dimensions were determined. The osteofibrous channels, which contain the long flexor tendons of the digits, were bounded on the one hand by transversely concave shaft areas of the phalanges and the palmar ligaments and on the other side by the fibrous parts of the tendon sheath. From the second to the 5th finger, it has a regular extension of length, which begins proximal at the heads of the metacarpal bones and runs distal to the base of the nail phalanx. In some cases, there is a continuous communication between the digital tendon sheath of the little finger and the carpal synovial sheath. The tendon sheath of the flexor pollicis longus muscle in comparison with it is always in an open communication with the radial synovial sac of the wrist. At the fibrous supports of the digital tendon sheath, one can find constant and inconstant ligamentous structures. Regular shaped ligaments consist of annular fibers (A1 to A5). The proximal complex of fiber supports is a formation of the A1 and A2 ligaments. The band A1 can be divided into 2 ligaments both of roughly equal length, which lay between the head of the metacarpal bone and the base of the proximal phalanx. The strongest fibrous support of the whole digital tendon sheath represents the band A2. It is attached to the midth of the proximal phalanx and increases in strength from proximal to distal. The middle length varies between 6.7 mm at the thumb and 18.7 mm at the middle finger. The distal margin is strengthened by fibrocartilage tissue to be in accordance with the important function as a pulley. The annular band A4 forms the distal supporting complex height above the shaft of the middle phalanx. At the 2nd to the 5th finger it is, with a middle length of 6 to 7 mm, very much shorter than A2 and restrains first of all the tendon of the flexor digitorum profundus muscle. In the area of the interphalangeal joints, we can find the annular bands A3 and A5, which fiber texture is formed variable. Both ligaments are attached on either both sides with the joint capsule and the palmar plate. The other inconstant supports of the digital sheaths are systematically recorded indeed (C1 to C3), but only in exceptional cases they exist of cruciform fibers (Lig. cruciatum).(ABSTRACT TRUNCATED AT 400 WORDS)     

Hyaluronic acid diminishes the resistance to excursion after flexor tendon repair: an in vitro biomechanical study

Adhesion between the tendon and tendon sheath after primary flexor tendon repair is seen frequently, and postoperative finger function is occasionally unsatisfactory. A reduction of the friction may facilitate tendon mobilization, which in turn may reduce the risk of the adhesion and restriction of range of motion. We considered the possibility of utilizing the hyaluronic acid (HA) as a lubricant. To evaluate the effect of HA, the gliding resistance between the canine flexor digitorum profundus tendon repaired by a modified Kessler suture technique with running epitendinous suture and the annular pulley located on the proximal phalanx (corresponding to the A2 pulley in humans) was evaluated and compared before and after administration of HA. The HA solution measurement groups were identified as follows; intact tendon as a control; repaired tendon; tendon soaked in 0.1, 1, and 10 mg/ml HA. The resistance increased after repairing, then it decreased after soaking in 10 mg/ml HA solution. The results of this study revealed that HA diminishes the excursion resistance after flexor tendon repair. We believe that some style of administration of the HA might reduce the excursion resistance and prevent adhesion until the synovial surface is fully developed.     

Flexor tendon and synovial gliding during simultaneous and single digit flexion in idiopathic carpal tunnel syndrome

The characteristic pathological finding in carpal tunnel syndrome (CTS) is non-inflammatory fibrosis of the subsynovial connective tissue (SSCT), which lies between the flexor tendons and the visceral synovium (VS). How this fibrosis might affect tendon function is unknown. To better understand the normal function of the SSCT, the relative motion of the middle finger flexor digitorum superficialis (FDS III) tendon and VS was observed during finger flexion in patients with CTS and cadavers with a history of CTS and compared to normal cadavers. A digital camcorder was used to monitor the gliding motion of the FDS III tendon and SSCT in eight patients with idiopathic CTS undergoing carpal tunnel release surgery (CTR), in eight cadavers with an antemortem history of CTS and compared these with eight cadaver controls. There were no significant differences noted in the total movement of the SSCT relative to the FDS III. However, the pattern of SSCT movement relative to the FDS III in the CTS patients and cadavers with an antemortem history of CTS differed from the controls in one of two patterns, reflecting either increased SSCT adherence to FDS III or increased SSCT dissociation from FDS III. In CTS, the gliding characteristics of the SSCT are qualitatively altered. These changes may be the result of increased fibrosis within the SSCT, which in some cases has ruptured, resulting in SSCT-tendon dissociation. Similar changes are also identified postmortem in the CTS patient.     

Structural modifications involved in the fore- and hind limb grip of some flying foxes (Chiroptera: Pteropodidae)

A mechanism which enables flying foxes to lock their hind limb digits and thumbs in flexion is described. The deep digital tendons of the hind limbs have roughened fibrocartilage surfaces. The adjacent flexor tendon sheath supports ridges which interact with the rough tendon surface, temporarily 'locking' the two structures together. This tendon locking mechanism is of importance as it enables bats to reduce the energetic cost of hanging from branches. It does this by reducing, or eliminating, the need for digital flexor muscle activity.     

The harvestman tarsus and tarsal flexor system with notes on appendicular sensory structures in laniatores

The tarsal flexor system, a novel system of retinacular structures, is described for the first time based on morphological and ultrastructural examinations of several Neotropical harvestmen (Opiliones: Laniatores). The tarsal flexor system is made up of many individual pulleys that function to maintain close apposition between the tendon and internal ventral surface of the cuticle in the tarsus. Pulley cells are specialized tendinous cells that form the semi‐circular, retinacular pulley system in the tarsus; these cells contain parallel arrays of microtubules that attach to cuticular fibers extending from deep within the cuticle (i.e., tonofibrillae). The tarsal flexor system is hypothesized to provide mechanical advantage for tarsal flexion and other movements of the tarsus. This system is discussed with regards to other lineages of Opiliones, especially those that exhibit prehensility of the tarsus (i.e., Eupnoi). Comparing tarsal morphology of laniatorid harvestmen to other well‐studied arachnids, we review some literature that may indicate the presence of similar tarsal structures in several arachnid orders. The general internal organization of the tarsus is described, and ultrastructural data are presented for a number of tarsal structures, including sensilla chaetica and the tarsal perforated organ. Sensilla chaetica possess an internal lumen with dendritic processes in the center and exhibit micropores at the distal tip. With respect to the tarsal perforated organ, we found no ultrastructural evidence for a sensory or secretory function, and we argue that this structure is the result of a large pulley attachment site on the internal surface of the cuticle. A small, previously undocumented muscle located in the basitarsus is also reported. J. Morphol. 274:1216–1229, 2013. © 2013 Wiley Periodicals, Inc.