Flexor Digitorum Superficialis Research Articles

Camptodactyly.

Camptodactyly is a congenital difference with flexion contracture of the proximal interphalangeal (PIP) joint. Camptodactyly limited to one finger is believed to be due to an anomaly of the lumbrical muscle that inserts into the flexor digitorum superficialis (FDS) tendon instead of the extensor expansion, whereas multiple finger camptodactyly is believed to be a result of shortage of soft tissues on the flexor surface of the fingers. It is important to differentiate camptodactyly from other causes of extension lag at the PIP joint. It is difficult to obtain good results after the release of flexion contractures in camptodactyly. The main goal of surgery is to prevent progressive contracture with appropriate postoperative therapy using night splinting and stretching. We should strive for a considered approach based on a thorough understanding of the pathophysiology of camptodactyly. Level of Evidence: Level V (Therapeutic).

Management Options and Clinical Outcomes After Flexor Tendon Ruptures Following Volar Plating of Distal Radius Fractures.

The transition to volar locking plates for the treatment of distal radius fractures has improved patients' range of motion, reduced extensor tendon issues, and hastened return to activity compared to older fixation methods or nonoperative treatment. One drawback to volar plating is the potential for flexor tendon ruptures due to aberrant plate or screw placement. This study aims to describe the reconstruction options and patient outcomes after flexor tendon rupture due to volar plating. This is a single-institution, retrospective review of patients who presented with flexor tendon rupture from 2014 to 2023 after a distal radius fracture previously managed with a volar plate. Patient demographics, operative details, range of motion, complications, and patient-reported outcomes were collected. Ten patients presented with flexor tendon ruptures after volar plating for distal radius fractures from 2014 to 2023. The most common rupture was flexor pollicis longus (FPL) in 7 patients, followed by index finger flexor digitorum profundus (FDP) in 2 patients, and small and ring finger FDP rupture in 1 patient. Flexor pollicis longus (FPL) was reconstructed with a palmaris longus (PL) graft in 4 patients, ring finger flexor digitorum superficialis transfer in 2 patients, and repaired primarily in 1 patient. All patients with FPL ruptures regained functional thumb interphalangeal flexion except for 1 patient who reruptured 4 weeks after surgery. Flexor tendon ruptures can occur following volar plating of distal radius fractures, even years after fixation of the fracture. These are attritional ruptures and generally reconstructed with tendon grafting of transfer, providing functional flexion of the affected digit.

Nerve compression after opponensplasty: a cadaveric study

Background: We describe the differences in thumb opposition between different opponensplasty tendon transfers and determine the immediate pressure on the median and ulnar nerves incurred by each transfer. Methods: Using fresh frozen cadavers (8 specimens), opponensplasties were performed using extensor indicis proprius (EIP), flexor digitorum superficialis (FDS) with flexor carpi ulnaris (FCU) pulley, palmaris longus (PL, Camitz procedure), and PL utilizing the thenar fascia as a pulley (PLwP). Each tendon transfer was tensioned, and the thumb flexion, abduction and pronation were measured. The pressure on the median and ulnar nerves were measured for each tendon transfer at varying tensions. Results: There were no differences seen in flexion or pronation between any of the four tendon transfers. FDS, PL and PLwP demonstrated more abduction than the EIP transfer, however differences were less than 10°. EIP and FDS transfers caused significantly more pressure on the median nerve than PL or PLwP at high tendon tensions. Both EIP and FDS tendon transfers caused significantly more pressure on the ulnar nerve than PL or PLwP, and the pressure increased as tension on the transfer increased. No pressure differences were seen between PL and PLwP. Conclusions: No significant differences were seen in thumb flexion or pronation between the four tendon transfers. Differences were seen for abduction with EIP showing the least amount of abduction. EIP and FDS caused more median nerve compression than PL transfers at high tension. Both EIP and FDS tendon transfers cause more ulnar nerve compression than PL transfers at all tensions. Level of Evidence Level: V

Efficacy of Dry Needling in Enhancing Hand Function and Reducing Spasticity in MCA Stroke Patients: A Prospective Case Report

Stroke, particularly involving the middle cerebral artery (MCA), often leads to persistent disability, significantly impairing hand function and inducing severe spasticity in the forearm flexors due to complex motor pathway involvement. This case report evaluates the effectiveness of combining dry needling therapy (DNT) with task-oriented training (TOT) in reducing spasticity and improving hand function in a post-MCA stroke patient. A 61-year-old male with right-side hemiplegia following a left MCA stroke, compounded by a history of diabetes, hypertension, and recent kidney stone diagnosis, participated in this study. The patient experienced severe functional limitations due to spasticity (grade 3 on the Modified Ashworth Scale) and scored 31 on the CAHAI-13, indicating significant hand dysfunction. DNT was applied to key forearm muscles (flexor carpi radialis, flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum profundus, and pronator teres), followed by TOT targeting daily tasks. Post-intervention, the patient demonstrated significant improvements: spasticity was reduced (Modified Ashworth Scale score decreased from grade 3 to grade 2), and muscle hypertonicity, as measured by EMG, was reduced in all targeted muscles. Functional hand use improved markedly, with the CAHAI-13 score increasing from 31 to 45. These improvements led to enhanced independence in daily activities. This case report highlights the clinical relevance of integrating DNT with TOT in stroke rehabilitation. The combined intervention not only reduced spasticity and improved neuromuscular function but also led to meaningful gains in hand function, enhancing the patient’s ability to perform daily activities independently. Given the promising results, this combined approach could serve as a practical and effective strategy for improving motor recovery and functional independence in post-stroke patients. Further studies with larger sample sizes are necessary to confirm these findings and explore the broader application of this approach in clinical practice.

Tissue Doppler ultrasound of arm muscles to assess myotonia in myotonic dystrophies: An exploratory study.

Myotonia is a key symptom of myotonic dystrophies (DM), and its quantification is challenging. This exploratory study evaluated the utility of tissue Doppler ultrasound (TDU) to assess myotonia in DM. Twelve DM patients (seven type-1 DM [DM1] and five type-2 DM [DM2]) and 20 age-matched healthy subjects were included in this cross-sectional study. After measuring cross-sectional areas of the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) muscles in a resting state, muscle contraction/relaxation time, time to peak tissue velocity, peak tissue velocity and velocity gradients of these muscles were measured via TDU while performing forced fist unclenching after fist closure. Additionally, grip strength, Medical Research Council Sum score and patient-reported myotonia severity scores were assessed. DM1 and DM2 patients had a lower grip strength than healthy subjects (p = .0001/p = .002). Patient-reported myotonia did not differ between DM1 and DM2 patients. DM1 patients revealed FDS and EDC atrophy compared to DM2 patients and healthy subjects (p = .003/p = .004). TDU revealed prolonged muscle contraction and relaxation times in both DM subtypes, with prolonged time to reach FDS peak relaxation velocity and altered peak FDS relaxation velocity only in DM1 patients (p = .03/p = .003). Peak FDS relaxation velocity correlated inversely with C(C)TG repeat numbers in DM patients. Sensitivity of TDU parameters to detect myotonic dystrophy varied between 50% and 75%, with a specificity of 95%. Our exploratory study suggests that TDU could serve as a novel tool to quantify myotonia in DM patients, but larger follow-up studies are warranted to validate its diagnostic accuracy.

Prevalence of the Absence of the Palmaris Longus and Functional Flexor Digitorum Superficialis of the Little Finger in the Indian Population.

Background The absence of the palmaris longus (PL) varies with race. The presence of a functional flexor digitorum superficialis (FDS) of the little finger also varies widely. The aim of this study is to determine the prevalence of the absence of the PL and functional FDS of the little finger in the Indian population. Materials and Methods This is a prospective observational study conducted as a part of the Indian normative data project of the Indian Society for Surgery of the Hand. The presence of the PL was assessed by Schaeffer's test. The function of the FDS was assessed by the standard test and modified test and its function designated as absent, present independently, or present combinedly with the ring finger FDS. Results A total of 200 volunteers including 84 males and 116 females in the 21- to 60-year age group were examined. Of the 400 hands examined, the PL was absent in 26 upper limbs (6.5%). The PL was absent unilaterally in 12 individuals (6%) and bilaterally in 7 individuals (3.5%). Of the 400 little fingers examined, FDS function was absent in 72 fingers (18%), while 67 fingers (16.75%) had a common function and 261 fingers (65.25%) had an independent function. Only 2% had a bilateral absence of both the PL and functional FDS tendons and 5% had a unilateral absence of both tendons. Conclusion The PL and FDS of the little finger were more absent in the right side than in the left side, but the difference was not statistically significant. There was no significant association between the absence of the PL and the absence of the functional FDS of the little finger.

Development of finger movement assistive gloves with pneumatic fabric actuators

We developed flexible, lightweight, and washable gloves with actuators to assist finger movements and improve ease of wearing. Performance and wearability were measured using standardized tests, triangulation of bending angles, electromyography (EMG), and grip strength. User satisfaction was measured using a survey. EMG sensors were attached to the flexor digitorum superficialis and extensor digitorum communis to capture movement data for grasping and releasing, lifting and putting down, and opening and closing an object with (a) gloves and an actuator, (b) gloves and no actuator, and (c) no gloves. The actuator-equipped glove weighed 31.4 g—lighter than in any earlier studies. In situation (a), the average EMG values for the four participants decreased, ranging from −2.06% to −44.1%, confirming the superior performance of the gloves. Survey results revealed high levels of user satisfaction. Our study offers insights into the development of rehabilitation robotic gloves that assist muscle movements and are easy to wear.

The modified Stack procedure for central slip reconstruction: a case series

There are many surgical techniques for reconstruction of the divided or incompetent central slip. Most rely upon postoperative immobilisation to protect the repair. We present our experience using a distally based flexor digitorum superficialis slip to reconstruct the central slip and allow early mobilisation in five patients with intact preoperative intrinsic function. Post-treatment, a mean recovery of 65 degrees of active extension was achieved, albeit at the cost of a mean 22-degree loss of active flexion. We suggest this relatively easy technique provides a useful surgical option in the management of this difficult problem.

Scalp acupuncture guidance for identifying the optimal site for transcranial electrical stimulation of the hand.

Transcranial electrical stimulation (tES) often targets the EEG-guided C3/C4 area that may not accurately represent M1 for hand muscles. This study aimed to determine if the neuroanatomy-based scalp acupuncture-guided site (AC) was a more effective spot than the C3 site for neuromodulation. Fifteen healthy subjects received one 20-minute session of high-definition transcranial alternating current stimulation (HD-tACS) intervention (20Hz at 2mA) at the AC or C3 sites randomly with a 1-week washout period. Subjects performed ball-squeezing exercises with the dominant hand during the HD-tACS intervention. The AC site was indiscernible from the finger flexor hotspot detected by TMS. At the baseline, the MEP amplitude from finger flexors was greater with less variability at the AC site than at the C3 site. HD-tACS intervention at the AC site significantly increased the MEP amplitude. However, no significant changes were observed after tACS was applied to the C3 site. Our results provide evidence that HD-tACS at the AC site produces better neuromodulation effects on the flexor digitorum superficialis (FDS) muscle compared to the C3 site. The AC localization approach can be used for future tES studies.

Relationship between the elasticity of the forearm flexor-pronator muscles and elbow valgus torque in young baseball pitchers: a descriptive laboratory study

BackgroundThe forearm flexor-pronator muscles act as a dynamic elbow stabilizer against elbow valgus load during baseball pitching. The elasticity of these muscles increases with pitching. However, it is unclear whether increased muscle elasticity is associated with greater elbow valgus torque during pitching. This study aimed to determine the relationship between the elasticity of the forearm flexor-pronator muscles and elbow valgus torque during pitching in young baseball pitchers. MethodsWe recruited 124 young baseball pitchers aged 9 to 12 years. The exclusion criteria included current pain with pitching, history of surgery on the tested extremity, or injuries on the tested extremity within the past 12 months. Before the examination, participants completed a questionnaire about their age, height, weight, dominant arm and practice time per week. The strain ratios of flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), and pronator teres as the index of muscle elasticity were measured using ultrasound strain elastography. Participants pitched three fastballs at a distance of 52 ft 6 in (16 m) with maximum effort while wearing a sensor sleeve that recorded the elbow valgus torque. A multiple linear regression analysis was conducted to examine the association between muscle elasticity and elbow valgus torque, adjusting for age, height, weight, and practice time. ResultsThe final analysis included 107 pitchers. After adjusting for covariates, increased strain ratio of the FCU was significantly associated with greater elbow valgus torque (coefficients = 0.038, 95% confidence interval [CI], 0.016–0.059, P<.001). Similarly, increased strain ratio of the FDS was significantly associated with greater elbow valgus torque (coefficients = 0.027, 95% CI, 0.013–0.042, P<.001). ConclusionThe high elasticities of the FCU and FDS were associated with greater elbow valgus torque during pitching in young baseball pitchers. The high elasticity of these muscles is a protective response and may be necessary for young baseball pitchers with greater elbow valgus torque during pitching. Among young baseball pitchers with greater elbow valgus torque, those who are unable to produce the higher elasticities of these muscles could have greater elbow valgus load during pitching and be at a higher risk for elbow injuries. The measurement of the elasticities of the FCU and FDS may be useful for identifying young baseball pitchers at risk of sustaining elbow injuries.

Intrathecal Baclofen Infusion-Botulinum Toxin Combined Treatment Efficacy in the Management of Spasticity due to Cerebral Palsy.

Cerebral Palsy (CP) is a group of permanent, but not unchanging, disorders of movement and/or posture and motor function, which are due to a non-progressive interference, lesion, or abnormality of the developing/immature brain. One clinical presentation is muscle spasticity, which leads to a significant impact on the individual's functionality and quality of life. Spasticity treatment is multidisciplinary and includes pharmacological and physical intervention; intrathecal baclofen shows a positive effect in severe spasticity and suboptimal response to oral drugs, while local injection of Botulinum toxin type A (BTXA) improves muscle tone, motion and pain. The aim of this study was to evaluate the efficacy of the combined intrathecal baclofen infusion (ITB) - botulinum toxin treatment in the management of spasticity in CP. 8 patients with spastic tetraparesis were enrolled. All patients were treated with intrathecal Baclofen; in lower limbs, no spastic symptoms appeared, while marked spasticity was noted in upper limbs. We injected the right and left Biceps Brachial (BB) and Flexor Digitorum Superficialis (FDS) muscles with botulinum toxin type A. All patients underwent Myometric measurement, Ashworth Scale, Numerical Rating Scale, and Visual Analogic Scale evaluation before infiltration (T0), 30 days after injection (T1), 60 days after injection (T2), and 90 days after treatment (T3). All data demonstrated an improvement in spasticity, pain, quality of life, and self-care during the study, with p < 0.05. No side effects appeared. This study demonstrated the efficacy and safety of intrathecal baclofen infusion and botulinum toxin combined treatment in the management of spasticity, pain, quality of life, and selfcare in CP patients.

Flexor Digitorum Superficialis to Flexor Digitorum Profundus Tendon Transfer after Wide Excision of Myxoinflammatory Fibroblastic Sarcoma: A Case Report

Myxoinflammatory fibroblastic sarcoma (MIFS) is a rare, low-grade soft tissue neoplasm that typically arises in the extremities. A 72-yearold woman presented with recurrent masses on her left forearm. Four years prior, she underwent an excisional biopsy, diagnosed as MIFS, followed by wide excision and split-thickness skin graft coverage. Preoperative magnetic resonance imaging was conducted for the recurrent mass, revealing multiple tumors invading the flexor digitorum profundus (FDP) muscle and fascia. The tumors including most of the FDP muscle were therefore excised. The third flexor digitorum superficialis (FDS) tendon was harvested, divided in half, and connected to the second and fifth FDP tendons. The same procedure was performed for the third and fourth FDP tendons with fourth FDS tendon. An anterolateral thigh free flap was used to reconstruct the skin and soft tissue defect of the left forearm. Adjuvant radiation therapy was performed. At 12 weeks postoperatively, the patient exhibited no wound complications and achieved spontaneous partial flexion of the metacarpophalangeal and proximal interphalangeal joints.

Daily Eicosapentaenoic Acid Infusion in IUGR Fetal Lambs Reduced Systemic Inflammation, Increased Muscle ADRβ2 Content, and Improved Myoblast Function and Muscle Growth.

Intrauterine growth-restricted (IUGR) fetuses exhibit systemic inflammation that contributes to programmed deficits in myoblast function and muscle growth. Thus, we sought to determine if targeting fetal inflammation improves muscle growth outcomes. Heat stress-induced IUGR fetal lambs were infused with eicosapentaenoic acid (IUGR+EPA; n = 9) or saline (IUGR; n = 8) for 5 days during late gestation and compared to saline-infused controls (n = 11). Circulating eicosapentaenoic acid was 42% less (p < 0.05) for IUGR fetuses but was recovered in IUGR+EPA fetuses. The infusion did not improve placental function or fetal O2 but resolved the 67% greater (p < 0.05) circulating TNFα observed in IUGR fetuses. This improved myoblast function and muscle growth, as the 23% reduction (p < 0.05) in the ex vivo differentiation of IUGR myoblasts was resolved in IUGR+EPA myoblasts. Semitendinosus, longissimus dorsi, and flexor digitorum superficialis muscles were 24-39% lighter (p < 0.05) for IUGR but not for IUGR+EPA fetuses. Elevated (p < 0.05) IL6R and reduced (p < 0.05) β2 adrenoceptor content in IUGR muscle indicated enhanced inflammatory sensitivity and diminished β2 adrenergic sensitivity. Although IL6R remained elevated, β2 adrenoceptor deficits were resolved in IUGR+EPA muscle, demonstrating a unique underlying mechanism for muscle dysregulation. These findings show that fetal inflammation contributes to IUGR muscle growth deficits and thus may be an effective target for intervention.

The effect of self-identified arm dominance on exercising forearm hemodynamics and skeletal muscle desaturation.

The human forearm model is commonly employed in physiological investigations exploring local vascular function and oxygen delivery; however, the effect of arm dominance on exercising forearm hemodynamics and skeletal muscle oxygen saturation (SmO2) in untrained individuals is poorly understood. Therefore, the purpose of this study was to explore the effect of self-identified arm dominance on forearm hemodynamics and SmO2 in untrained individuals during submaximal, non-ischemic forearm exercise. Twenty healthy individuals (23±4 years, 50% female; 80% right-handed) completed three-minute bouts of supine rhythmic (1 second contraction: 2 second relaxation duty cycle) forearm handgrip exercise at both absolute (10kg; 98N) and relative (30% of maximal voluntary contraction) intensities in each forearm. Beat-by-beat measures of forearm blood flow (FBF; ml/min), mean arterial blood pressure (MAP; mmHg) and flexor digitorum superficialis SmO2 (%) were obtained throughout and averaged during the final 30 seconds of rest, exercise, and recovery while forearm vascular conductance was calculated (FVC; ml/min/100mmHg). Data are Δ from rest (mean±SD). Absolute force production did not differ between non-dominant and dominant arms (97±11 vs. 98±13 N, p = 0.606) whereas relative force production in females did (69±24 vs. 82±25 N, p = 0.001). At both exercise intensities, FBFRELAX, FVCRELAX, MAPRELAX, and the time constant tau for FBF and SmO2 were unaffected by arm dominance (all p>0.05). While arm dominance did not influence SmO2 during absolute intensity exercise (p = 0.506), the non-dominant arm in females experienced an attenuated reduction in SmO2 during relative intensity exercise (-14±10 vs. -19±8%, p = 0.026)-though exercise intensity was also reduced (p = 0.001). The present investigation has demonstrated that arm dominance in untrained individuals does not impact forearm hemodynamics or SmO2 during handgrip exercise.

How does the consecutive use of intraoral scanners affect musculoskeletal health? A preliminary clinical study

BackgroundMinimizing muscle strain and reducing the risk of musculoskeletal disorders associated with intraoral scanner (IOS) usage require ergonomic awareness, device selection, and workplace adjustments in dental practice. This preliminary clinical study aimed to simulate intraoral scanning tasks using wired and wireless IOSs and assess muscle activation and fatigue for both types.Materials and methodsFourteen participants performed intraoral scanning tasks using wired and wireless IOSs (i700; MEDIT), with weights of 280 g and 328 g, respectively. The same computer system and software conditions were maintained for both groups (N = 14 per IOS group). Electrodes were placed on arm, neck, and shoulder muscles, and maximal voluntary contraction (MVC) was measured. Surface electromyography (EMG) was performed during the simulation, and EMG values were normalized using MVC. The root mean square EMG (%MVC) and muscle fatigue (%) values were calculated. Statistical comparisons were performed using the Mann–Whitney U and Friedman tests, with the Bonferroni adjustment for multiple comparisons (α = 0.05).ResultsArm (flexor digitorum superficialis) and neck muscles (left sternocleidomastoid and left splenius capitis) showed significantly higher EMG values with wireless IOS (P < 0.05). The neck (left sternocleidomastoid and right levator scapulae) and shoulder muscles (right trapezius descendens) demonstrated significantly higher muscle fatigue with wireless IOS (P < 0.05).ConclusionsThe consecutive use of heavier wireless IOS may increase the risk of muscle activation and fatigue in certain muscles, which may have clinical implications for dentists in terms of ergonomics and musculoskeletal health.

Muscular branches from the ulnar artery are the basis for a pedicled partial flexor digitorum superficialis muscle flap.

The feasibility of a pedicled flexor digitorum superficialis muscle flap was studied in 10 fresh cadavers. The number, length and distance from the flexion wrist crease of muscular branches from the ulnar artery in the distal 10 cm of the forearm were recorded. The mean number of muscular branches was 2.7 (range 1-4). The mean distance of the most distal branch was 35 mm (range 26-40) from the proximal wrist flexion crease. Its mean length was 20 mm (range 16-26). A partial muscle flap was raised on the most distal branch and transposed over the median nerve in the distal forearm. Dissection and transposition of this flap were feasible in all specimens. The reliable pattern of muscular branches to the flexor digitorum superficialis allows the elevation of a pedicled partial muscle flap that can cover the median nerve in the distal forearm.Level of evidence: V.

Three Levels of Neural Control Contributing to Performance-stabilizing Synergies in Multi-finger Tasks

We tested a hypothesis on force-stabilizing synergies during four-finger accurate force production at three levels: (1) The level of the reciprocal and coactivation commands, estimated as the referent coordinate and apparent stiffness of all four fingers combined; (2) The level of individual finger forces; and (3) The level of firing of individual motor units (MU). Young, healthy participants performed accurate four-finger force production at a comfortable, non-fatiguing level under visual feedback on the total force magnitude. Mechanical reflections of the reciprocal and coactivation commands were estimated using small, smooth finger perturbations applied by the “inverse piano” device. Firing frequencies of motor units in the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) were estimated using surface recording. Principal component analysis was used to identify robust MU groups (MU-modes) with parallel changes in the firing frequency. The framework of the uncontrolled manifold hypothesis was used to compute synergy indices in the spaces of referent coordinate and apparent stiffness, finger forces, and MU-mode magnitudes. Force-stabilizing synergies were seen at all three levels. They were present in the MU-mode spaces defined for MUs in FDS, in EDC, and pooled over both muscles. No effects of hand dominance were seen. The synergy indices defined at different levels of analysis showed no correlations across the participants. The findings are interpreted within the theory of control with spatial referent coordinates for the effectors. We conclude that force stabilization gets contributions from three levels of neural control, likely associated with cortical, subcortical, and spinal circuitry.

The effect of baseball grips on the hardness of the flexor digitorum superficialis.

In baseball pitches, the forkball requires a special grip, pinching the ball between the second and third fingers to achieve the resulting breaking ball trajectory. We hypothesized that the forkball grip would have a substantial impact on the hardness of the flexor digitorum superficialis. The aim was to quantify and clarify the change in the hardness of the flexor digitorum superficialis due to the forkball grip. Twenty-one adult male subjects were recruited and instructed to perform two baseball grips with the ball: fast and forkball, and the rest without the ball. The shear wave speeds of the pronator teres, flexor carpi radialis, flexor digitorum superficialis, and flexor carpi ulnaris were measured using shear wave elastography. In the forkball grip, compared with the fastball grip and the rest without the ball, the shear wave speed of the flexor digitorum superficialis was significantly higher than those of the pronator teres, flexor carpi radialis, and flexor carpi ulnaris (P<0.001), indicating that muscle hardness increased due to the forkball grip. In contrast, no significant differences were found between the conditions for the other forearm flexor-pronator muscles. Quantification of muscle hardness using shear wave elastography showed that gripping a forked ball increased muscle hardness in the flexor digitorum superficialis.

Mechanical Interaction Between the Tendons of the Extrinsic Finger Flexors

ABSTRACTHumans possess an incredible capacity for dexterity, but independent finger control is limited. One factor constraining finger independence is the connections between the tendons of the extrinsic finger muscles. The aim of this study was to assess to what extent the linkages between the distal tendons of flexor digitorum profundus (FDP) and those of the flexor digitorum superficialis (FDS) constrain finger independence. Experiments on human fresh frozen cadaveric upper extremities (n = 6) were performed. First, one finger (target) was flexed whereas the other (nontarget) fingers were held in a nearly extended position. The change (Δ) in total flexion angle (∑Θ; i.e., the sum of angles of the different finger joints) of the target finger from the ∑Θ corresponding to the extended position at the start of the movement until the ∑Θ corresponding to the onset of force exertion at the nontarget fingers was assessed. Second, the distribution of force across the four fingers upon loading the tendon of the target finger was assessed for two finger positions (extended, 90° flexion of metacarpal phalangeal joint). For both muscles and for all fingers, the range of independent movement was small (&lt;7°). Δ∑Θ at force onset was lowest for fingers immediately adjacent to the target finger and highest for more distant fingers. For both muscles and for all fingers, some of the target finger force (&lt;14% for FDP, &lt;2% for FDS) was distributed to the nontarget fingers, which increased (up to 58%) only for FDP in response to target finger flexion. We conclude that mechanical connections between the FDP and FDS tendons constrain finger independence. Such constraints become apparent when moving one finger relative to the other fingers.

Characteristics of the Gantzer muscle and implications for its use as a tendon-graft source in upper extremity reconstruction

BackgroundThe Gantzer muscle is an anatomical variant muscle that functions in flexion of the volar forearm. The prevalence and laterality of this muscle has been studied more recently in the literature. This study aimed to determine the prevalence and size of this muscle and tendon. MethodsThis was an observational study done from September 2021 to January 2022 at the University of North Texas Health Science Center in Fort Worth, Texas. Cadaveric dissection was conducted in the Department of Physiology and Anatomy. 50 pairs for a total of 100 forearms were dissected bilaterally in cadavers comprising 17 females (34 %) and 33 males (66 %) to identify the Gantzer muscle. The mean age at death was 68.8 years of age (range 40–91 years). When present, the dimensions of each Gantzer tendon were measured in millimeters using digital calipers. As a study of cadaveric specimens, this study was exempt from Institutional Review Board (IRB) approval. ResultsThe Gantzer muscle was present in 62 of the 100 forearms (62 %). All 62 Gantzer muscles originated from flexor digitorum superficialis (FDS) (100 %). Of the 62 Gantzer muscles, 42 inserted distally into flexor pollicus longus (FPL) (72.5 %), while the remaining 17 muscles inserted distally into flexor digitorum profundus (FDP) (27.5 %). The tendons inserting into FDP had an average length of 65.495 mm, while those inserting into FPL had an average length of 16.353 mm (p = 0.002). The Gantzer muscle was present in 24 of the 33 male specimens (72.7 %) and 13 of the 17 female specimens (76.4 %). Of the 62 Gantzer muscles, 50 were present bilaterally (80.6 %), and there was no significant difference in bilateral occurrence between sexes (p = 0.189). ConclusionsOur results suggest that the Gantzer muscle may be of sufficient size and present commonly enough in the general population to be considered as an alternative graft source for certain upper extremity reconstruction procedures in place of, or in addition to, palmaris longus, extensor toe tendons, and other commonly used tendon grafts. In this study, when palmaris longus was absent in a specimen, a Gantzer muscle was likely present, and may provide surgeons an alternative tendon graft source in the upper extremity without requiring additional incisions in the lower extremity for alternative tendon graft sources. Further biomechanical testing of the Gantzer tendon with comparisons to other common tendon graft sources is warranted.