Use of intrinsic thumb muscles may help to improve lateral pinch function restored by tendon transfer

BACKGROUND

For surgical reconstruction of lateral pinch following tetraplegia, the function of the paralyzed flexor pollicis longus is commonly restored. The purpose of this study was to investigate if one of the intrinsic muscles could generate a more suitably directed thumb-tip force during lateral pinch than that of flexor pollicis longus.

METHODS

Endpoint force resulting from 10 N applied to each thumb muscle was measured in eleven upper extremity cadaveric specimens. We utilized the Kruskal-Wallis test (alpha=0.05) to determine whether thumb-tip forces of intrinsic muscles were less directed toward the base of the thumb, i.e., proximally directed, than the thumb-tip force produced by flexor pollicis longus. Additionally, a biomechanical model was used to assess the effect of an increase in tendon force on intrinsic muscle endpoint forces.

FINDINGS

All of the intrinsic muscles produced thumb-tip force vectors, ranging from 127 degrees to 156 degrees , that were significantly (P<0.009) less proximally directed than that of flexor pollicis longus (66 degrees (46 degrees )). A biomechanical model predicted that intrinsic muscle thumb-tip forces would vary non-linearly with tendon force. A 2-fold increase in tendon force produced, on average, a 2.3-fold increase in force magnitude and an 8 degrees shift in force direction across all intrinsic muscles.

INTERPRETATION

This study suggests the possibility of using an intrinsic muscle, e.g., the flexor pollicis brevis (ulnar head), instead of flexor pollicis longus, to produce a more advantageously directed thumb-tip force during lateral pinch in the surgically-reconstructed tetraplegic thumb and thus potentially enhance function.

Dupuytren's disease: history, diagnosis, and treatment

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Describe the clinical features of the disease. 2. Describe the pathoanatomical structures in Dupuytren's disease. 3. Outline the various factors associated with Dupuytren's disease. 4. Describe the modalities for surgical and nonsurgical treatment of the condition. 5. Outline recent biomolecular knowledge about the basis of Dupuytren's disease.

SUMMARY

Dupuytren's disease is characterized by nodule formation and contracture of the palmar fascia, resulting in flexion deformity of the fingers and loss of hand function. The authors review the historical background, clinical features, and current therapy of Dupuytren's disease; preview treatment innovations; and present molecular data related to Dupuytren's disease. These new findings may improve screening for Dupuytren's disease and provide a better understanding of the disease's pathogenesis.

Late reconstruction for ulnar nerve palsy

Long term paralysis of the ulnar nerve is associated with an array of specific deficits and deformities. The numerous options for reconstruction are reviewed, as well as the specific patient considerations in selecting a strategy. An approach to late reconstruction for late ulnar nerve palsy is presented based upon the authors' experience and the available literature.

Tumours of the hand

Hand tumours of soft-tissue and bony origin are frequently encountered, and clinicians must be able to distinguish typical benign entities from life-threatening or limb-threatening malignant diseases. In this Review, we present a diagnostic approach to hand tumours and describe selected cancers and their treatments. Soft-tissue tumours include ganglion cysts, giant-cell cancers and fibromas of the tendon sheath, epidermal inclusion cysts, lipomas, vascular lesions, peripheral-nerve tumours, skin cancers, and soft-tissue sarcomas. Bony tumours encompass enchondromas, aneurysmal bone cysts, osteoid osteomas, giant-cell lesions of bone, bone sarcomas, and metastases. We look at rates of recurrence and 5-year survival, and recommendations for adjunct chemotherapy and radiotherapy for malignant lesions.

Is microsurgical treatment of brachial plexus palsy better than conventional treatment?

There are some plexus injuries for which microneural plexus reconstruction provides the only good possibility of achieving useful limb function. These injuries include complete plexus palsies in the adult and baby, and incomplete upper plexus lesions in the adult. There are plexus injuries for which there is little to no role for microneurosurgery, such as the isolated C8, T1 injury in the adult (this is an extremely rare injury in babies). This article explores conventional versus microneurosurgical reconstruction for adult traumatic and birth-related brachial plexus palsies.

Variability in surgical technique for brachioradialis tendon transfer. Evidence and implications

BACKGROUND

Transfer of the tendon of the brachioradialis muscle to the tendon of the flexor pollicis longus restores lateral pinch function after cervical spinal cord injury. However, the outcomes of the procedure are unpredictable, and the reasons for this are not understood. The purpose of this study was to document the degree of variability observed in the performance of this tendon transfer.

METHODS

The surgical technique used for the brachioradialis tendon transfer was assessed in two ways. First, the surgical attachment length of the brachioradialis was quantified, after transfer to the flexor pollicis longus, with use of intraoperative laser diffraction to measure muscle sarcomere length in eleven individuals (twelve limbs) with tetraplegia. Second, ten surgeons who regularly performed this procedure were surveyed regarding their tensioning preferences. Using a biomechanical model of the upper extremity, we investigated theoretically the effect of different surgical approaches on the active muscle-force-generating capacity of the transferred brachioradialis in functionally relevant elbow, wrist, and hand postures.

RESULTS

The average sarcomere length (and standard deviation) of the transferred brachioradialis was 3.5 +/- 0.3 mum. That length was significantly correlated to the in situ sarcomere length (r(2) = 0.53, p < 0.05). Surgical tensioning preferences varied considerably; however, six of the ten surgeons positioned the patient's elbow between full extension (0 degrees of elbow flexion) and 50 degrees of flexion when selecting the attachment length, and six of the ten stated that their goal was to tension the transfer slightly tighter than its resting tension. The computer simulations suggested that a "tighter" brachioradialis transfer would produce its peak active force in an elbow position that is more flexed than the elbow position in which a "looser" transfer would produce its peak active force.

CONCLUSIONS

This study provides evidence that experienced surgeons perform this tendon transfer differently from one another. Biomechanical simulations suggested that these differences could result in substantial variability in the active force that the transferred brachioradialis can produce in functionally relevant postures.

CLINICAL RELEVANCE

The surgical attachment length and the position of the patient's limb at the time of tendon transfer are both controllable and measurable parameters. Understanding the relationship between surgical technique and postoperative muscle function may provide surgeons with more control of clinical outcomes.

Congenital brachial plexus exploration

Stanford's experience in the management of obstetrical brachial plexus palsy dates from 1983. A formal clinic service began in 1992. The tenets of management include early evaluations, a dependency on sequential evolution for decision-making, and very early neural surgery for babies with abnormal hands. We watch babies with normal hands for a longer time before advising surgery. At exploration, common patterns of injury are observed. Intraoperative evoked potentials are used to make surgical decisions. Reconstructive goals for upper plexus injuries include shoulder and elbow control. The paramount goal for babies with global palsies is hand function. Therapy throughout the child's growth years is vital. Sequelae, particularly shoulder contractures, require early surgical intervention. Secondary reconstructive procedures are typically beneficial in improving function. Since 1992, over 400 children have been examined, 62 have had neural reconstruction, and 102 have undergone secondary procedures. Surgery has been remarkably complication free. All children having neural reconstruction except 2 have been benefited.

Activation of brachioradialis muscles transferred to restore lateral pinch in tetraplegia

PURPOSE

Surgical transfers of muscles are used to restore lateral pinch in tetraplegia; however, outcomes are variable. The purpose of this study was to compare activation of the brachioradialis (Br) after transfer to the flexor pollicis longus during maximum effort in its primary function (elbow flexion) with maximum effort in its postoperative function (lateral pinch) and to record Br activation during functional tasks.

METHODS

Fine-wire electrodes recorded activation of the Br in 11 arms with tetraplegia. Subjects produced maximum lateral pinch force with and without elbow stabilization and were classified according to elbow strength. The elbow was stabilized by supporting the arm and limiting elbow motion. A force sensor mounted on a custom grip recorded the pinch force. Electromyographic (EMG) signals recorded during lateral pinch were expressed as a percentage of the maximum voluntary contraction recorded during maximum-effort elbow flexion.

RESULTS

The EMG activation was significantly lower during lateral pinch compared with resisted elbow flexion. The mean EMG during lateral pinch in the self-supported elbow condition was 34% of the maximum voluntary contraction; with the elbow stabilized the EMG increased to 55% of the maximum voluntary contraction. Postoperative pinch-force magnitude was 14 N with self-support and 20 N with the elbow stabilized. Subjects with weak elbow extension strength produced significantly lower pinch forces compared with subjects with strong elbow extension but had similar ability to activate the Br. The Br activation was higher when the pinch tasks were performed successfully.

CONCLUSIONS

These findings suggest a reduced ability to activate the transferred muscle fully in lateral pinch function after surgery, even with the addition of elbow support. The Br activation is linked to successful performance of lateral pinch tasks. The subjects' inability to activate the transferred muscle fully may be affected by postoperative muscle re-education and contribute to postoperative weakness.

Biomechanical properties of the brachioradialis muscle: Implications for surgical tendon transfer

PURPOSE

To understand the mechanical properties of the brachioradialis (BR) muscle and to use this information to simulate a BR-to-flexor pollicis longus (FPL) tendon transfer for restoration of lateral pinch.

METHODS

The BR mechanical properties were measured intraoperatively. Passive elastic properties were measured by elongating BR muscles at constant velocity while they were attached directly to a dual-mode servomotor. Sarcomere length was measured intraoperatively and in situ by laser diffraction with the elbow fully extended. Then both the mechanical and structural properties were programmed into a surgical simulator to test the hand surgeon's decision making when tensioning muscles in a simulated BR-to-FPL tendon transfer.

RESULTS

Passive mechanical BR properties were highly nonlinear. Under slack conditions sarcomere length (mean +/- standard deviation) was 2.81 +/- 0.10 microm (n = 4), corresponding to an active force of 93% maximum. Sarcomere length of the BR measured in situ with the elbow fully extended and the forearm in neutral rotation was 3.90 +/- 0.27 microm (n = 8), corresponding to an active force of only 23% maximum. Surgeons, who tensioned the BR for transfer into the FPL using only tactile feedback from the surgical simulator, attached the muscle at a passive tension of 5.87 +/- 0.97 N, which corresponded to a sarcomere length of 3.84 microm and an active muscle force of 27% maximum. Passive BR tension when both tactile and visual information were provided to the surgeon was significantly lower (2.42 +/- 0.72 N), corresponding to a sarcomere length of 3.56 mum and a much higher active muscle force of 45% maximum.

CONCLUSIONS

When these data were used to model pretransfer and posttransfer function dramatic differences in predicted function were obtained depending on the tensioning protocol chosen. This emphasizes the point that the decision-making process used during muscle tensioning has a profound effect on the functional outcome of the transfer.

The effect of percutaneous pin fixation of the interphalangeal joint on the thumb-tip force produced by the flexor pollicis longus: a cadaver study

PURPOSE

Interphalangeal joint stabilization often is performed concomitantly with tendon transfers that restore key pinch (lateral pinch) to the paralyzed thumb. The goal of this study was to measure the effect of interphalangeal joint stabilization via percutaneous pin fixation on the thumb-tip force produced by the flexor pollicis longus (FPL).

METHODS

We applied 10 N of force to the tendon of the FPL in 7 cadaveric specimens and measured the resulting thumb-tip force in the intact thumb and after stabilization of the interphalangeal joint.

RESULTS

The nominal thumb-tip force was approximately 6 times less than the applied force and was directed primarily in the thumb's plane of flexion-extension at an oblique angle of 44 degrees relative to the palmar direction (the direction that is perpendicular to the thumb tip in the plane). Joint stabilization increased significantly the nominal force and oriented the force more toward the palmar direction (ie, decreased the obliqueness of the force).

CONCLUSIONS

After paralysis and a tendon transfer to the paralyzed FPL the FPL is often the only muscle actuating the thumb. We conclude that the oblique nominal force direction is prone to cause the thumb to slip during pinch. Joint stabilization, however, has the capacity to reduce the tendency for slippage because it rotates the force toward the palmar direction.

Biomechanics of the Steindler flexorplasty surgery: a computer simulation study

PURPOSE

Our goal was to investigate the capacity of a Steindler flexorplasty to restore elbow flexion to persons with C5-C6 brachial plexus palsy. In this procedure the origin of the flexor-pronator mass is moved proximally onto the humeral shaft. We examined how the choice of the proximal attachment site for the flexor-pronator mass affects elbow flexion restoration, especially considering possible side effects including limited wrist and forearm motion owing to passive restraint from stretched muscles.

METHODS

A computer model of the upper extremity was used to simulate the biomechanical consequences of various surgical alterations. Unimpaired, preoperative, and postoperative conditions were simulated. Seven possible transfer locations were used to investigate the effects of choice of transfer location.

RESULTS

Each transfer site produced a large increase in elbow flexion strength. Transfer to more proximal attachment sites also produced large increases in passive resistance to wrist extension and forearm supination.

CONCLUSIONS

To reduce detrimental side effects while achieving clinical goals our theoretical analysis suggests a transfer to the distal limit of the traditional transfer region.

Three-dimensional hyaluronic acid grafts promote healing and reduce scar formation in skin incision wounds

Hyaluronic acid (HA) has been found to play important roles in tissue regeneration and wound-healing processes. Fetal tissue with a high concentration of HA heals rapidly without scarring. The present study employed HA formed into three-dimensional strands with or without keratinocytes to treat full-thickness skin incision wounds in rats. Wound closure rates of HA strand grafts both with and without keratinocytes were substantially enhanced. The closure times of both HA grafts were less than 1 day (average 16 h), about 1/7 that of the contralateral control incisions (114 h, p <.01). Average wound areas after 10 days were HA-only graft: 0.151 mm2 +/- 0.035; HA + cell grafts: 0.143 mm2 +/- 0.036 and controls: 14.434 mm2 +/- 1.175, experimental areas were 1% of the controls (p < 0.01). Transforming growth factor (TGF) beta1 measured by immunostaining was remarkably reduced in HA-treated wounds compared to the controls. In conclusion, HA grafts appeared to produce a fetal-like environment with reduced TGF-beta1, which is known to be elevated in incipient scars. The HA strands with or without cultured cells may potentially improve clinical wound healing as well as reduce scar formation.

Releasing the A3 pulley and leaving flexor superficialis intact increases pinch force following the Zancolli lasso procedures to prevent claw deformity in the intrinsic palsied finger

Objective estimates of fingertip force magnitude following surgery to prevent digital metacarpophalangeal (MCP) hyperextension (clawing) in cases of paralysis of the hand's intrinsic muscles will assist clinicians in setting realistic expectations for post-operative pinch strength. We used a cadaveric/optimization approach to predict and confirm the maximal biomechanically possible fingertip force in the intrinsic palsied hand before and after two popular tendon transfer methods to the volar plate of the MCP joint. Both surgeries were also evaluated after release of the A3 pulley-a modification predicted by our published computer model of the forefinger to increase fingertip force magnitude. We predicted maximal static fingertip force by mounting eight fresh cadaveric hands on a frame, placing their forefinger in a functional posture (neutral abduction, 45 degrees of flexion at the MCP and proximal interphalangeal joints, and 10 degrees at the distal interphalangeal joint) and pinning the distal phalanx to a 3D dynamometer. We pulled on individual tendons with tensions up to 25% of maximal isometric force of their associated muscle and measured fingertip force and torque output. Using these measurements, we predicted the optimal combination of tendon tensions that maximized palmar force (analogous to pinch force, directed perpendicularly from the midpoint of the distal phalanx, and in the plane of finger flexion-extension) for four cases: (i) the non-paretic case (all muscles available), (ii) intrinsic palsied hand (no intrinsic muscles functioning), (iii) transfer of flexor superficialis tendon to the volar plate of the MCP (Zancolli lasso) in the intrinsic palsied hand, and (iv) leaving flexor superficialis intact and transferring a tendon of comparable strength to the volar plate of the MCP in the intrinsic palsied hand. Lastly, we applied these optimal combinations of tension to the cadaveric tendons and measured fingertip output. With the A3 pulley intact, the maximal palmar force in cases (ii)-(iv) averaged 48 +/- 23% SD (non-paretic = 100%; case (iv) (61 +/- 25%) > cases (ii) and (iii) (43 +/- 23% and 39 +/- 19%, respectively), p < 0.05). Releasing the A3 pulley significantly increased the average palmar force in cases (ii)-(iv) (73 +/- 42%, p < 0.05), with no significant differences among them. Thus, releasing the A3 pulley may improve palmar force magnitude when it is necessary to transfer the digit's own flexor superficialis tendon to the volar plate of the MCP to prevent clawing in the intrinsic palsied hand.

Injury to the dorsal sensory branch of the ulnar nerve in the arthroscopic repair of ulnar-sided triangular fibrocartilage tears using an inside-out technique: a cadaver study

This anatomic study of the commonly described inside-out Tuohy needle technique was performed to better define the course of needle passage relative to the anatomic structures in this region including the dorsal sensory branch of the ulnar nerve (DBUN) and extensor carpi ulnaris (ECU) tendon. Ten fresh-frozen cadaver specimens had arthroscopic-guided passage of a Tuohy needle through the triangular fibrocartilage (TFC). Dissection of the ulnar side of the wrist was performed and various measurements were recorded. The average minimum distance between suture A (the suture closest to the nerve) and the DBUN was 1.9 mm. The average minimum distance between suture B and the DBUN was 2.7 mm. The distance between the 2 sutures at the level of the capsule averaged 6.2 mm. The distance between the DBUN and the ECU averaged 7.2 mm. In 5 of 10 specimens the sutures exited on opposite sides of the DBUN. The DBUN is variable in its course but in every case it passes in close proximity to the sutures that exit the ulnar side of the wrist in arthroscopic repair of ulnar-sided TFC tears.

Collagen as a clinical target: nonoperative treatment of Dupuytren's disease

The cellular events leading to abnormal synthesis of collagen are important to our understanding of pathologic processes leading to impaired joint function. The contracture of Dupuytren's disease is a notable example. In a series of controlled phase-2 clinical trials, excessive collagen deposition in Dupuytren's disease has been targeted by a unique nonoperative method using enzyme (Clostridial collagenase) injection therapy to lyse and rupture finger cords causing metacarpophalangeal and/or proximal interphalangeal joint contractures. Forty-nine patients were treated in a random, placebo-controlled trial of one dose of collagenase versus placebo at one center. Subsequently 80 patients were treated in a random, placebo-controlled, dose-response study of collagenase at 2 test centers. The results of these studies indicate that nonoperative collagenase injection therapy for Dupuytren's disease is both a safe and effective method of treating this disorder in the majority of patients as an alternative to surgical fasciectomy. Phase-3 efficacy trials are now being planned to further develop and test this method under Food and Drug Administration regulatory guidelines. The findings of our study may lead to simpler and less invasive nonoperative treatments of joint limitation in which collagen plays a major pathologic role.

Surgical strategy: matching the patient with the procedure

The general indications, timing, and choice of procedure can be determined by asking and answering the following questions appropriately: 1. Has the patient achieved neurologic, emotional, and social stability? 2. What is the patient's current level of motor and sensory resources and function? The number and strength of muscles remaining under good voluntary control are the most important variables. 3. Are the patient's expectations realistic? 4. Does the patient possess the necessary intelligence and motivation? Some procedures, such as arthrodesis of a specific joint, require little motivation to succeed; however, a complex set of muscle-tendon transfers requires a great deal of motor reeducation for the patient to achieve an optimal result. 5. Does the patient have the necessary time to invest in achieving a good result? The patient must be able to set aside the time necessary for postoperative immobilization in a cast or splint and for therapy and reeducation. 6. Are the necessary support services and personnel available and committed? 7. Have all preoperative obstacles to success been considered and has a plan developed to overcome any remaining obstacles? 8. Does the patient understand the potential complications and benefits? 9. Can the patient and professional team tolerate a complication, failure, or suboptimal result? Both the medical staff and the patient must be prepared for complications that may lead to a suboptimal outcome or frank failure. 10. Are the patient's current health and well-being ideal? 11. Is the surgical plan consistent with the patient's physical resources, goals, and expectations? 12. Does an alternate plan exist? 13. Does the surgeon understand the scope of the complications and how to salvage an acceptable result should a complication occur?

Reconstruction of the hand in Apert syndrome: a simplified approach

Children born with Apert acrocephalosyndactyly pose great challenges to the pediatric hand surgeon. Reconstructive dilemmas consist of shortened, deviated phalanges and extensive skin deficits following syndactyly release. We present a 10-year review of patients with Apert acrocephalosyndactyly who were treated with a simplified surgical approach. Between 1986 and 1996, 10 patients with Apert syndrome underwent reconstructive surgery of their hands. The overall strategy involved early bilateral separation of syndactylous border digits at 1 year of age, followed by sequential unilateral middle syndactyly mass separation with thumb osteotomy and bone grafting as needed. In these 10 patients, a total of 53 web spaces were released, 49 of which involved osteotomies for complex syndactyly. Only local flaps and full-thickness skin grafts from the groin were used in all cases to achieve soft-tissue coverage. To date, seven of the 53 web spaces have needed revision (revision rate, 13 percent). Eleven thumb osteotomies (nine opening wedge and two closing wedge) were performed. Bone grafts from the proximal ulna or from other digits were used in all cases. To date, none of these thumb osteotomies have needed revision. This early, simplified approach to the complex hand anomalies of Apert acrocephalosyndactyly has been successful in achieving low revision rates and excellent functional outcomes as measured by gross grasp and pinch and by patient and parent satisfaction.

Gene expression of transforming growth factor beta isoforms in interposition nerve grafting

Scar production and neuroma formation at nerve graft coaptation sites may limit axonal regeneration and impair functional outcome. Transforming growth factor beta (TGF-beta) is a family of growth factors that is involved in scar formation, wound healing, and nerve regeneration. Fifteen adult Sprague-Dawley rats underwent autogenous nerve grafting. The nerve grafts were analyzed by in situ hybridization to determine the temporal and spatial expression of TGF-beta1 and TGF-beta3 messenger RNA (mRNA). The grafted nerves showed increased expression of TGF-beta1 and TGF-beta3 mRNA in the nerve and the surrounding connective tissue during the first postoperative week. These data suggest that modulation of TGF-beta levels in the first postoperative week may be effective in helping to control scar formation and improve nerve regeneration.

Efficacy of an implanted neuroprosthesis for restoring hand grasp in tetraplegia: a multicenter study

OBJECTIVE

To evaluate an implanted neuroprosthesis that allows tetraplegic users to control grasp and release in 1 hand.

DESIGN

Multicenter cohort trial with at least 3 years of follow-up. Function for each participant was compared before and after implantation, and with and without the neuroprosthesis activated.

SETTING

Tertiary spinal cord injury (SCI) care centers, 8 in the United States, 1 in the United Kingdom, and 1 in Australia.

PARTICIPANTS

Fifty-one tetraplegic adults with C5 or C6 SCIs.

INTERVENTION

An implanted neuroprosthetic system, in which electric stimulation of the grasping muscles of 1 arm are controlled by using contralateral shoulder movements, and concurrent tendon transfer surgery. Assessed participants' ability to grasp, move, and release standardized objects; degree of assistance required to perform activities of daily living (ADLs), device usage; and user satisfaction.

MAIN OUTCOME MEASURES

Pinch force; grasp and release tests; ADL abilities test and ADL assessment test; and user satisfaction survey.

RESULTS

Pinch force was significantly greater with the neuroprosthesis in all available 50 participants, and grasp-release abilities were improved in 49. All tested participants (49/49) were more independent in performing ADLs with the neuroprosthesis than they were without it. Home use of the device for regular function and exercise was reported by over 90% of the participants, and satisfaction with the neuroprosthesis was high.

CONCLUSIONS

The grasping ability provided by the neuroprosthesis is substantial and lasting. The neuroprosthesis is safe, well accepted by users, and offers improved independence for a population without comparable alternatives.

Surgeon-patient barrier efficiency monitored with an electronic device in three surgical settings

Blood-borne viral pathogens are an occupational threat to health care workers (HCWs), particularly those in the operating room. A major risk is posed by accidental penetrating injury, but skin contamination with body fluids from an infected patient, with prolonged intimate cutaneous contact, is a frequent occurrence during surgery, carrying further risk of transdermal infection. We have monitored barrier failure in three surgical settings (microsurgery, orthopedic surgery, general surgery) by means of an electronic surveillance device. A total of 111 surgical procedures were monitored: 67 microsurgeries, 22 orthopedic surgeries, and 22 general surgeries. Of the 278 electronic alarms signaling barrier failure, 44 (15.8%) were associated with glove perforation, 39 of which (88.6%) were not perceived by the operator. In 16 of those, the skin was visibly stained with the patient's blood. Altogether, 76 of the alarms (27.3%) were consequent to contacts caused by soaked gowns/sleeves, and 121 (43.5%) were attributed to hydration of latex porosities; 37 alarms (13.4%) were unexplained false positives. On only one occasion did a surgeon observe blood stains on his hands without a previous alarm; this event was classified as a device failure due to incorrect wiring. Double-gloving offered satisfactory protection against skin contamination during microsurgery but not during orthopedic surgery. The data presented here indicate that electronic monitoring of the surgical barrier enables prompt detection of barrier failure, especially at the level of the gloves, thereby limiting skin contamination with patients' body fluids during surgery.

Activation patterns of the thumb muscles during stable and unstable pinch tasks

The ability to direct forces between the thumb and fingers is important to secure objects in the hand. We compared the coordination of thumb musculature in key and opposition pinch postures between stable and unstable tasks. The unstable task (producing thumb-tip force wearing a beaded thimble) required well-directed forces; the stable task (producing thumb-tip force against a pinch meter) did not. Fine-wire electromyography of thumb muscles and thumb-tip force magnitudes were recorded. We found no statistical differences in thumb-tip force between postures or stable versus unstable tasks, indicating that the highest magnitudes of force can be accurately directed. Abductor pollicis brevis and extensor pollicis longus were significantly more activated in the unstable tasks, suggesting their importance in directing thumb-tip force. Understanding how pinch forces are directed might influence the choice of muscle-tendon transfers performed to restore function to the severely paralyzed thumb. We introduce a device to quantify the ability to control pinch force magnitude and direction simultaneously.