Middle and ring fingers are more exposed to pulley rupture than index and little during sport-climbing: a biomechanical explanation

An investigation of tendon strains in jersey finger injury load cases using a finite element neuromuscular human body model

Introduction: A common hand injury in American football, rugby and basketball is the so-called jersey finger injury (JFI), in which an eccentric overextension of the distal interphalangeal joint leads to an avulsion of the connected musculus flexor digitorum profundus (FDP) tendon. In the field of automotive safety assessment, finite element (FE) neuromuscular human body models (NHBMs) have been validated and are employed to evaluate different injury types related to car crash scenarios. The goal of this study is to show, how such a model can be modified to assess JFIs by adapting the hand of an FE-NHBM for the computational analysis of tendon strains during a generalized JFI load case. Methods: A jersey finger injury criterion (JFIC) covering the injury mechanisms of tendon straining and avulsion was defined based on biomechanical experiments found in the literature. The hand of the Total Human Model for Safety (THUMS) version 3.0 was combined with the musculature of THUMS version 5.03 to create a model with appropriate finger mobility. Muscle routing paths of FDP and musculus flexor digitorum superficialis (FDS) as well as tendon material parameters were optimized using literature data. A simplified JFI load case was simulated as the gripping of a cylindrical rod with finger flexor activation levels between 0% and 100%, which was then retracted with the velocity of a sprinting college football player to forcefully open the closed hand. Results: The optimization of the muscle routing node positions and tendon material parameters yielded good results with minimum normalized mean absolute error values of 0.79% and 7.16% respectively. Tendon avulsion injuries were detected in the middle and little finger for muscle activation levels of 80% and above, while no tendon or muscle strain injuries of any kind occurred. Discussion: The presented work outlines the steps necessary to adapt the hand model of a FE-NHBM for the assessment of JFIs using a newly defined injury criterion called the JFIC. The injury assessment results are in good agreement with documented JFI symptoms. At the same time, the need to rethink commonly asserted paradigms concerning the choice of muscle material parameters is highlighted.

A Biomechanical Analysis of the H-Taping Method Used by Rock Climbers as Prophylactic or Stabilizing Fixation of Partial A2 Pulley Tears

PURPOSE

Rock climbing can lead to upper-extremity injuries, such as A2 pulley ruptures, leading to the bowstringing of the flexor tendons. Climbing finger positions are specific and can put undue stress on the pulley systems. This causes severe hand dysfunction and is a difficult problem to treat, and prevention is important. Using a cadaveric, experimental model, we evaluated the effectiveness of the H-taping method, commonly used by rock climbers, to prevent and treat A2 pulley tears.

METHODS

Using fourteen matched pairs of fresh-frozen cadaveric hands with forearms, four experiments were conducted with 56 paired comparisons evaluating the failure force, fingertip force, and mode of failure (112 total tests). Comparisons were as follows: index fingers- intact versus 50% distal A2 pulley tears without H-taping (control); ring fingers- intact versus H-taping as a prophylactic for A2 pulley tears; little fingers- 50% distal A2 pulley tears with H-tape versus without tape; and middle fingers- H-taping as a prophylactic versus H-taping as a stabilizing treatment of torn pulleys.

RESULTS

The mean index finger failure force was significantly higher in intact vs torn A2 pulleys (control). Failure force for intact H-taped fingers was significantly higher than torn H-taped fingers, but no other finger comparisons for failure force were significant. There were no significant findings in comparison of mean fingertip force values in any of the experiments.

CONCLUSIONS

We found that H-taping is not effective as prophylaxis against A2 pulley ruptures or as a stabilizing treatment method for partially ruptured pulleys.

CLINICAL RELEVANCE

While H-taping has not been recommended as prophylaxis for preventing A2 pulley ruptures, the climbing community has embraced this technique as a preventative measure. The present study provides biomechanical evidence against H-taping for this purpose. Furthermore, it does not appear to aid in increasing fingertip force after injury.

Neuromechanics of finger hangs with arm lock-offs: analyzing joint moments and muscle activations to improve practice guidelines for climbing

Introduction

Climbing imposes substantial demands on the upper limbs and understanding the mechanical loads experienced by the joints during climbing movements is crucial for injury prevention and optimizing training protocols. This study aimed to quantify and compare upper limb joint loads and muscle activations during isometric finger hanging exercises with different arm lock-off positions.

Methods

Seventeen recreational climbers performed six finger dead hangs with arm lock-offs at 90° and 135° of elbow flexion, as well as arms fully extended. Upper limb joint moments were calculated using personalized models in OpenSim, based on three-dimensional motion capture data and forces measured on an instrumented hang board. Muscle activations of upper limb muscles were recorded with surface electromyography electrodes.

Results

Results revealed that the shoulder exhibited higher flexion moments during arm lock-offs at 90° compared to full extension (p = 0.006). The adduction moment was higher at 135° and 90° compared to full extension (p < 0.001), as well as the rotation moments (p < 0.001). The elbows exhibited increasing flexion moments with the increase in the arm lock-off angle (p < 0.001). Muscle activations varied across conditions for biceps brachii (p < 0.001), trapezius (p < 0.001), and latissimus dorsi, except for the finger flexors (p = 0.15).

Discussion

Our findings indicate that isometric finger dead hangs with arms fully extended are effective for training forearm force capacities while minimizing stress on the elbow and shoulder joints. These findings have important implications for injury prevention and optimizing training strategies in climbing.

Closed flexor pulley injuries: A literature review and current practice

Background

Closed flexor pulley injuries are a clinical entity of great interest in hand surgery, and these lesions could be observed mainly in rock-climbing athletes.

Objective

An extensive literature search of PubMed, SCOPUS, Cochrane Library, and Web of Sciences databases on closed finger pulley rupture, related treatments, and outcomes were performed. All relevant information was used in this literature review.

Conclusions

Many athletes are potentially exposed to these uncommon injuries. Therefore, these lesions require careful examination and a high index of suspicion to confirm the diagnosis and identify the degree of soft tissue injury, particularly in patients not involved in sporting activities. The data summarized in this literature review demonstrated that according to Schöffl's classification, conservative treatment should be indicated for low-grade injuries (grade 1 or 2), whereas surgical treatment should be performed in patients with more severe acute injuries (grade 4). Grade 3 flexor pulley injuries lie in a grey area where conservative and surgical treatment may give good clinical and return-to-sport patient results.

Cortical Bone Thickness, Base Osteophyte Occurrence and Radiological Signs of Osteoarthritis in the Fingers of Male Elite Sport Climbers: A Cross-Sectional 10-Year Follow-Up Study

Background: Sport climbing places high mechanical loads on fingers. In 2012, our research group demonstrated adaptations of climbers’ cortical bones with the presence of osteophytes compared to non-climbing controls.

Objectives: 1) To investigate 10-year changes in cortical bone thickness, base osteophyte occurrence and radiological signs of osteoarthritis in the fingers of elite male sport climbers with more than 25 years of climbing history and 2) to compare cortical bone thickness, base osteophyte occurrence and radiological signs of osteoarthritis between male sport climbers and age-matched controls at the 10-year follow-up.

Methods: All 31 elite sport climbers who participated in both the baseline and 10-year follow-up assessments (follow-up rate 100%) were examined by means of X-rays. Cortical bone thickness, presence of osteophytes and signs of osteoarthritis according to Kellgren-Lawrence were obtained and compared to the baseline values 10 years earlier and to age-matched controls at the follow-up (n = 15).

Results: Significantly increased cortical bone thickness over the past 10 years was observed in climbers (mean absolute difference with 95% CI:0.98 mm (0.77 mm, 1.19 mm); p <0.001). Moreover, compared to age-matched controls, climbers had significantly thicker cortical bone at the 10-year follow-up (mean absolute difference with 95% CI:0.86 mm (0.61 mm, 1.12 mm); p <0.001). In climbers, osteophytes and clear signs of osteoarthritis were mainly seen in DIP joints. Signs of osteoarthritis according to Kellgren-Lawrence were more prevalent than 10 years before in most joints. In lateral radiographs, base osteophytes were not significantly more prevalent than 10 years before in most of the joints. The percentage of climbers who had osteophytes in any DIP (PIP) joint increased from 93.5% (67.7%) at baseline to 100% (74.2%) at the 10-year follow-up. The percentage of climbers who had clear signs of osteoarthritis according to Kellgren-Lawrence in any DIP (PIP) joint increased from 12.9% (9.7%) at baseline to 74.2% (64.5%) at 10-year follow-up. Only a few such degenerative changes were found in age-matched controls.

Conclusion: An accumulation of repetitive climbing-related stress to the fingers of elite sport climbers over the career may induce lifelong mechano-adaptation of the cortical bone thickness of all phalanges. At the 10-year follow-up, a further significant increase in radiographic signs of osteoarthritic changes was observed.

Coaches' Attitudes Toward Campus Board Training in Adolescent Climbers in the United States

INTRODUCTION

Campus board training in adolescent climbers is controversial. Evidence, albeit limited, suggests this type of training may lead to the development of finger epiphyseal stress fractures. The purpose of the present study was to investigate coaches' attitudes toward campus board training in the United States.

METHODS

Surveys were sent to 116 coaches at gyms across the United States with affiliated adolescent climbing teams. Outcomes collected included demographic information, training time, campus board use prevalence, coaches' attitudes toward campus board use, and willingness to participate in future research.

RESULTS

Seventy-three coaches representing 3090 adolescent climbers completed the survey. Forty-six coaches (63%) reported using full weight (no foot contact) campus board training in some or all of their climbers. A variety of factors were cited by coaches when deciding which climbers should or should not use the campus board, including physical maturity, climbing ability, and age, among others.

CONCLUSIONS

Climbing coaches in the United States disagree on the use of campus board training in adolescent climbers. Some coaches avoid using this training modality entirely, whereas others believe certain climbers can use it safely. There is lack of consensus in determining who those certain climbers are.

Unusual rupture of the middle finger flexor digitorum superficialis tendon in a climber: Biomechanical analysis

Sport climbing is increasingly popular and consultations by climbers in hand surgery departments are on the increase. The pathologies related to this sport concern essentially the pulley system, tendons being rarely affected. We report the case of a male climber who presented an atypical rupture of the flexor superficialis tendon in his left middle finger sustained when using an atypical climbing grip technique: the "hook grip". This consists in extension of the metacarpophalangeal joints and maximal flexion of the proximal interphalangeal joints with force exerted only on middle phalanx of the middle finger. A biomechanical analysis using finger musculoskeletal modeling was performed to compare the hook grip to other grips, and the patient's recovery performance was assessed. Adapted functional treatment with physiotherapy seems to have been a good option for the treatment of this atypical lesion since the patient recovered normal use of his finger in daily life. He recovered maximal force in climbing holds. The biomechanical analysis confirmed that the atypical "hook grip" was likely at the origin of the rupture, since flexor digitorum superficialis tendon force for this grip is greater than in other climbing grip techniques. The "hook grip" seems to be dangerous and should be used cautiously by climbers to prevent similar pathology. Additionally, the patient should henceforth be careful when climbing, since the biomechanical model showed that the remaining flexor digitorum profundus tendon was overused.

Musculoskeletal models of a human and bonobo finger: parameter identification and comparison to in vitro experiments

Introduction

Knowledge of internal finger loading during human and non-human primate activities such as tool use or knuckle-walking has become increasingly important to reconstruct the behaviour of fossil hominins based on bone morphology. Musculoskeletal models have proven useful for predicting these internal loads during human activities, but load predictions for non-human primate activities are missing due to a lack of suitable finger models. The main goal of this study was to implement both a human and a representative non-human primate finger model to facilitate comparative studies on metacarpal bone loading. To ensure that the model predictions are sufficiently accurate, the specific goals were: (1) to identify species-specific model parameters based on in vitro measured fingertip forces resulting from single tendon loading and (2) to evaluate the model accuracy of predicted fingertip forces and net metacarpal bone loading in a different loading scenario.

Materials & Methods

Three human and one bonobo (Pan paniscus) fingers were tested in vitro using a previously developed experimental setup. The cadaveric fingers were positioned in four static postures and load was applied by attaching weights to the tendons of the finger muscles. For parameter identification, fingertip forces were measured by loading each tendon individually in each posture. For the evaluation of model accuracy, the extrinsic flexor muscles were loaded simultaneously and both the fingertip force and net metacarpal bone force were measured. The finger models were implemented using custom Python scripts. Initial parameters were taken from literature for the human model and own dissection data for the bonobo model. Optimized model parameters were identified by minimizing the error between predicted and experimentally measured fingertip forces. Fingertip forces and net metacarpal bone loading in the combined loading scenario were predicted using the optimized models and the remaining error with respect to the experimental data was evaluated.

Results

The parameter identification procedure led to minor model adjustments but considerably reduced the error in the predicted fingertip forces (root mean square error reduced from 0.53/0.69 N to 0.11/0.20 N for the human/bonobo model). Both models remained physiologically plausible after the parameter identification. In the combined loading scenario, fingertip and net metacarpal forces were predicted with average directional errors below 6° and magnitude errors below 12%.

Conclusions

This study presents the first attempt to implement both a human and non-human primate finger model for comparative palaeoanthropological studies. The good agreement between predicted and experimental forces involving the action of extrinsic flexors—which are most relevant for forceful grasping—shows that the models are likely sufficiently accurate for comparisons of internal loads occurring during human and non-human primate manual activities.

Effects of finger taping on forearm muscle activation in rock climbers

Flexor tendon pulley injury is associated with a change in relative activation of the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) muscles. The purpose of this study was to determine the effect of taping of the fingers on relative muscle activation of the FDS and FDP muscles in uninjured rock climbers. Muscle activation in 10 healthy volunteers were recorded using intramuscular electromyography (EMG) during a static hang with subjects utilizing the crimp grip without tape, with a circumferential tape and with an H-tape in random order. EMG data were normalized to a static hang with a non-crimp grip (RVC). Average EMG activity of the FDS as a percentage of RVC was 102.4 ± 59.1 without tape, 116.9 ± 35.3 with H-tape and 99.3 ± 35.3 with circumferential tape. Average EMG activity of the FDP as a percentage of RVC was 96.6 ± 40.0 without tape, 98.9 ± 30.3 with H-tape and 90.6 ± 28.7 with circumferential tape. Taping did not have a significant effect on average relative muscle activation of the FDS or FDP muscles (p = 0.069). This study showed that finger taping may not significantly affect the activity of the FDS and FDP during static holds while rock climbing.

Long-Term Radiographic Adaptations to Stress of High-Level and Recreational Rock Climbing in Former Adolescent Athletes: An 11-Year Prospective Longitudinal Study

BACKGROUND

In the past few years, competition climbing has grown in popularity, and younger people are being drawn to the sport.

PURPOSE

While radiographic changes in long-term climbers are known, there are little data available on adolescent climbers. The question arises as to whether climbing at high levels at a young age leads to radiographic changes and possibly an early onset of osteoarthritis of the finger joints.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

A total of 19 members of the German Junior National Team (GJNT group) and 18 recreational climbers (RC group) were examined clinically and radiographically in 1999. In 2011, these climbers were re-examined (mean follow-up, 11.3 ± 1.2 years). Radiographs were evaluated using a standard protocol, searching for physiological adaptations such as cortical thickness of the middle phalanx and an increased adopted Barnett-Nordin index, as well as for early-onset osteoarthritic changes of the hand. In contrast to the Kellgren-Lawrence scale, subchondral sclerosis was added to the group of physiological, adaptive stress reactions and was not defined as osteoarthritis. Osteoarthritis was defined by a Kellgren-Lawrence grade ≥2.

RESULTS

Overall, 15 of 19 (follow-up rate, 78.9%) climbers in the GJNT group and 13 of 18 in the RC group (follow-up rate, 72.2%), with a mean age of 26.8 years, were examined at the 11-year follow-up. Five climbers (33%) in the GJNT group presented with a decreased range of motion for the finger joints, in contrast to only 1 climber (8%) in the RC group. Radiographic stress reactions of the hand were found in 80% of the GJNT group and 46% of the RC group, including cortical hypertrophy (GJNT: 73%; RC: 23%), subchondral sclerosis (GJNT: 80%; RC: 31%), a broadened proximal interphalangeal joint base (GJNT: 67%; RC: 38%), and a broadened distal interphalangeal joint base (GJNT: 53%; RC: 31%). Training intensity in 1999 and body weight in 1999 were significant for the development of radiographic stress reactions in 2011 (P < .05 for both). Signs of early-stage osteoarthritis were seen in 6 climbers: 4 (27%) in the GJNT group and 2 (15%) in the RC group. Significant statistical influences for the development of early-onset osteoarthritis were found for overall total training years (P = .024), use of campus board training in 1999 (P = .033), and climbing level (P = .030).

CONCLUSION

One-quarter of climbers who performed at a high level in their youth showed a "mild" form of osteoarthritis (Kellgren-Lawrence grade 2). In analyzing the training regimens of our climbers for longer than 10 years, we conclude that intensive finger training (eg, campus board training) can lead to early-onset osteoarthritis of the hand. We also demonstrate that a high Union Internationale des Associations d'Alpinisme (UIAA) climbing level correlates with the risk for early-onset osteoarthritis of the hand and therefore must be seen as a risk factor for developing early-onset osteoarthritis of the finger joints.

Sagittal band, boutonniere, and pulley injuries in the athlete

PURPOSE OF REVIEW

While hand injuries occur frequently in the athletic population, sagittal band ruptures, boutonniere deformities, and pulley ruptures are infrequently encountered. These injuries represent diagnostic challenges and can result in significant impairment. Early recognition with appropriate treatment is necessary to maximize recovery and minimize return to athletic competition. This review will focus on the underlying mechanism, pathophysiology of injury, diagnosis, and treatment of each of these injuries.

RECENT FINDINGS

With respect to sagittal band ruptures, boutonniere deformities, and pulley ruptures, the recent literature has been limited in scope. For sagittal band injuries, current efforts have focused on alternative techniques for sagittal band reconstruction. Little progress has been made in recent years with respect to boutonniere injuries in the athletic population; prevention of fixed deformities remains the backbone of treatment. The exact contribution from individual and combined pulley injuries in the creation of bowstringing remains controversial. Recent anatomical studies have failed to definitively answer the question of what degree of rupture is necessary to create symptomatic bowstringing. Favorable outcomes, with respect to both preventing bowstringing and returning to full athletic participation, have been newly reported following pulley reconstruction in rock climbers. Due to the infrequent nature of sagittal band ruptures, boutonniere deformities, and pulley ruptures, current treatment is mostly guided by historically established methods, limited case series, and case reports. Nonsurgical treatment remains the mainstay for most injuries and, if employed early, often precludes the need for surgery. Further anatomical and clinical research, including outcome studies, is necessary in guiding treatment algorithms.

Diagnosis, Treatment, and Return to Play for Four Common Sports Injuries of the Hand and Wrist

Hand and wrist injuries in the high-level athlete are challenging because they may be underestimated by the patient, family, and team, and return to play may be longer than desired. The needs of the player and the team must be balanced with the long-term functional ramifications of the injury. Four common soft-tissue sports injuries are flexor digitorum profundus avulsion, flexor pulley rupture, extensor carpi ulnaris dislocation, and thumb metacarpophalangeal joint ulnar collateral ligament injury. For each of these injuries, the assessment, treatment, and considerations for return to play should be individualized on the basis of the patient, the sport, and the timing of the injury.

Evaluation of finger A3 pulley rupture in the crimp grip position-a magnetic resonance imaging cadaver study

PURPOSE

The correct diagnosis of an A3 pulley rupture is challenging for musculoskeletal radiologists. An A3 pulley rupture should in theory influence the shape of the proximal interphalangeal joint volar plate (VP) and the amount of bowstringing at level of the VP during finger flexion. The purpose of this study was to perform MRI with metric analysis of the VP configuration and VP bowstringing in cadaver fingers in the crimp grip position and to determine cut points for A3 pulley rupture.

MATERIALS AND METHODS

MRI in the crimp grip position was performed in 21 cadaver fingers with artificially created flexor tendon pulley tears (fingers with A3 pulley rupture n = 16, fingers without A3 pulley rupture n = 5). The distances of the translation of the VP relative to the middle phalanx base, the distances between the flexor tendons and the VP body, and the distances between the flexor tendon and bone (TB) were measured.

RESULTS

Statistical analysis showed significantly lower VP translation distances and significantly higher VP tendon distances if the A3 pulley was ruptured. A2 TB and A4 TB distances did not differ significantly in specimens with and without A3 pulley rupture. The optimal cut points for A3 pulley rupture were a VP translation distance <2.8 mm and a VP tendon distance >1.4 mm.

CONCLUSION

Reduction of the VP translation distance and augmentation of the VP tendon distance are suitable indirect signs of A3 pulley rupture.

Estimation of hand and wrist muscle capacities in rock climbers

PURPOSE

This study investigated the hand and wrist muscle capacities among expert rock climbers and compared them with those of non-climbers. The objective was to identify the adaptations resulting from several years of climbing practice.

METHODS

Twelve climbers (nine males and three females) and 13 non-climber males participated in this study. Each subject performed a set of maximal voluntary contractions about the wrist and the metacarpo-phalengeal joints during which net joint moments and electromyographic activities were recorded. From this data set, the muscle capacities of the five main muscle groups of the hand (wrist flexors, wrist extensors, finger flexors, finger extensors and intrinsic muscles) were estimated using a biomechanical model. This process consisted in adjusting the physiological cross-sectional area (PCSA) and the maximal muscle stress value from an initial generic model.

RESULTS

Results obtained from the model provided several new pieces of information compared to the analysis of only the net joint moments. Particularly, the capacities of the climbers were 37.1 % higher for finger flexors compared to non-climbers and were similar for finger extensor and for the other muscle groups. Climbers thus presented a greater imbalance between flexor and extensor capacities which suggests a potential risk of pathologies.

CONCLUSIONS

The practice of climbing not only increased the strength of climbers but also resulted in specific adaptations among hand muscles. The proposed method and the obtained data could be re-used to optimize the training programs as well as the rehabilitation processes following hand pathologies.

The role of proximal pulleys in preventing tendon bowstringing: pulley rupture and tendon bowstringing

PURPOSE

The aim of this study was to investigate factors that contribute to tendon bowstringing at the proximal phalanx. We hypothesised that: (1) a partial rupture of the A2 pulley leads to significant bowstringing, (2) the location of the A2 rupture, starting proximally or distally, influences bowstringing, (3) an additional A3 pulley rupture causes a significant increase in bowstringing following a complete A2 pulley rupture and (4) the skin and tendon sheath may prevent bowstringing in A2 and A3 pulley ruptures.

METHODS

Index, middle and ring fingers of eight freshly frozen cadaver arms were used. A loading device pulled with 100 N force was attached to the flexor digitorum profundus (FDP). The flexor digitorum superficialis (FDS) was preloaded with 5 N. Bowstringing was measured and quantified by the size of the area between the FDP tendon and the proximal phalanx over a distance of 5 mm with ultrasonography (US).

RESULTS

US images showed that already a 30% excision of the A2 pulley resulted in significant bowstringing. In addition, a partial distal incision of the A2 pulley showed significantly more bowstringing compared to a partial proximal incision. Additional A3 pulley incision and excision of the proximal tendon sheath did not increase bowstringing. Subsequently, removing the skin did increase the bowstringing significantly.

CONCLUSION

A partial A2 pulley rupture causes a significant bowstringing. A partial rupture of the A2 pulley at the distal rim of the A2 pulley resulted in more bowstringing than a partial rupture at the proximal rim.

Quantification of finger joint loadings using musculoskeletal modelling clarifies mechanical risk factors of hand osteoarthritis

Owing to limited quantitative data related to the loadings (forces and pressures) acting upon finger joints, several clinical observations regarding mechanical risk factors of hand osteoarthritis remain misunderstood. To improve the knowledge of this pathology, the present study used musculoskeletal modelling to quantify the forces and pressures acting upon hand joints during two grasping tasks. Kinematic and grip force data were recorded during both a pinch and a power grip tasks. Three-dimensional magnetic resonance imaging measurements were conducted to quantify joint contact areas. Using these datasets as input, a musculoskeletal model of the hand and wrist, including twenty-three degrees of freedom and forty-two muscles, has been developed to estimate joint forces and joint pressures. When compared with the power grip task, the pinch grip task resulted in two to eight times higher joint loadings whereas the grip forces exerted on each finger were twice lower. For both tasks, joint forces and pressures increased along a disto-proximal direction for each finger. The quantitative dataset provided by the present hand model clarified two clinical observations about osteoarthritis development which were not fully understood, i.e., the strong risk associated to pinch grip tasks and the high frequency of thumb-base osteoarthritis.

Changes in the flexor digitorum profundus tendon geometry in the carpal tunnel due to force production and posture of metacarpophalangeal joint of the index finger: an MRI study

BACKGROUND

Carpal tunnel syndrome is a disorder caused by increased pressure in the carpal tunnel associated with repetitive, stereotypical finger actions. Little is known about in vivo geometrical changes in the carpal tunnel caused by motion at the finger joints and exerting a fingertip force.

METHODS

The hands and forearms of five subjects were scanned using a 3.0 T magnetic resonance imaging scanner. The metacarpophalangeal joint of the index finger was placed in: flexion, neutral and extension. For each joint posture subjects either produced no active force (passive condition) or exerted a flexion force to resist a load (~4.0 N) at the fingertip (active condition). Changes in the radii of curvature, position and transverse plane area of the flexor digitorum profundus tendons at the carpal tunnel level were measured.

RESULTS

The radius of curvature of the flexor digitorum profundus tendons, at the carpal tunnel level, was significantly affected by posture of the index finger metacarpophalangeal joint (P<0.05) and the radii was significantly different between fingers (P<0.05). Actively producing force caused a significant shift (P<0.05) in the flexor digitorum profundus tendons in the ventral (palmar) direction. No significant change in the area of an ellipse containing the flexor digitorum profundus tendons was observed between conditions.

INTERPRETATION

The results show that relatively small changes in the posture and force production of a single finger can lead to significant changes in the geometry of all the flexor digitorum profundus tendons in the carpal tunnel. Additionally, voluntary force production at the fingertip increases the moment arm of the FDP tendons about the wrist joint.

Boutonnière and pulley rupture in elite athletes

This article discusses injuries to the central slip (boutonnière) and to the annular pulleys in the digit, with an emphasis on the elite athlete. Pertinent anatomy, mechanism of injury, diagnosis, treatment, and a discussion emphasizing the elite athlete and return to play form the basis of the article.

Determination of passive moment-angle relationships at the trapeziometacarpal joint

While modeling the trapeziometacarpal (TMC) joint for determination of tendon forces, the TMC has been considered frictionless and passive moments created by soft tissues neglected. This, however, becomes inaccurate when reaching the joint end range of motion and considering that the TMC is entirely crossed by a complex network of skin, ligaments, soft tissues, and tendons. The objective of this study was to evaluate the passive moments with respect to joint posture in order to further include this relationship in biomechanical modeling. An experimental method was proposed to estimate in vivo a global passive moment including the sum of the actions of each passive anatomical structure. An external force was applied at the level of the metacarpophalangeal joint in various directions ranging from neutral position to full extension and full adduction to full abduction. The passive moment was computed and expressed as a function of the adopted joint angles. An exponential regression was then developed to fit the experimental data and to propose a generic passive moment model. Results showed a good agreement between the proposed exponential regression model and the experimental measures. Moreover, it was shown that joint stiffness could represent more than 60% of the net joint moment during a typical pulp grip task. These results showed the necessity to include the data in biomechanical modeling. The results may help predict more realistic tendons force especially in abduction/adduction muscles.

Comparison of tendon tensions estimated from two biomechanical models of the thumb

Despite the paramount function of the thumb in daily life, thumb biomechanical models have been little developed and studied. Moreover, only two studies provided quantitative anthropometric data of tendon moment arms. To investigate thumb tendon tensions, biomechanicians and clinicians have to know the performances and the limits of these two data sets. The aim of this study was thus to compare the results of these two models and evaluate their performances in regard to prior electromyographic measurements (EMG). Thumb posture was recorded during the classical key pinch and pulp pinch grips. Various fingertip forces applied at the distal segment were simulated in a range including extension, adduction, flexion, abduction. Input data of thumb postures and fingertip forces were used to compute tendon tensions with both models. Tendon tensions obtained using these two models were then compared and correlated to EMG measurements provided in the literature. The results showed that both models predicted relevant muscle coordination for five of the nine muscles modelled. Opponent and abductor longus muscle coordinations were badly estimated by both models. Each model was sensible to kinematic errors but not in the same proportion. This study pointed out the advantages/limits of the two models to use them more appropriately for clinical and/or research purposes.

Friction between finger flexor tendons and the pulley system in the crimp grip position

BACKGROUND

Disruption of the finger flexor tendon pulleys are the most often occurring injury in rock climbers due to bowstringing of tendons during crimp grip position. The aim of this study was to quantify friction between the flexor tendons and pulleys and the influence of high load and speed of movement as a potential factor of pulley disruption.

METHODS

Friction between the flexor tendons and pulleys of eight human cadaver fingers was indirectly determined using an isokinetic movement device. During flexion and extension movement with rotational speed from 30 to 210 deg/s in the proximal interphalangeal joint and with load from 20 to 100 N to the flexor tendons the flexion force at the tip of the finger was measured.

FINDINGS

With 40 N loaded flexor tendons the force at the fingertip was 14.5 N (SD1.5) during extension and 12.6N (SD1.3) during flexion movement. Corresponding force difference of 12.9% and 3.77 N (SD0.6) force of friction can be calculated. Friction peaked at 85.8 degrees (SD2.05) of flexion of the proximal interphalangeal joint. Different speed of motion and load to the flexor tendons did not influence force difference other than linear.

INTERPRETATION

Considerable friction between flexor tendons and pulleys is apparent and therefore may have an influence on pulley injuries. Particularly during the crimp grip position where the proximal interphalangeal joint is flexed about 90 degrees shows the greatest amount of friction. However there was no change of friction during high speed motion and no other than linear increase during high load.