Hearing as substitution for sensation: a new principle for artificial sensibility

We describe a new principle for artificial sensibility of the hand based on sense substitution, using hearing as substitution for loss of sensation. The experiments were performed on 3 patients who had recently undergone isolated median nerve repair, 1 patient with replantation of an amputated forearm, 1 patient using a myoelectric prosthesis, and 4 patients using cosmetic prostheses. Small condenser microphones were mounted dorsally on the distal phalanges of multiple fingers of the nonsensate hands or prostheses. The friction sound, reflecting the vibrotactile stimuli generated by the moving touch of the objects, was picked up by the microphones and processed in a stereo amplifier that separated signals from individual fingers into different channels. The signals were transmitted to earphones, making possible a spatial resolution that enabled identification of each finger by the generated acoustic stimuli. Since the friction sound is characteristic of specific surfaces and textures, the corresponding acoustic stimuli made possible identification of different textures, such as glass, metal, wood, and paper, without using vision. We conclude that sense substitution using specifically processed acoustic stimuli as a substitute for sensation may represent a useful principle for generation of artificial sensibility in prostheses or hands lacking sensibility due to lesions in the peripheral or central nervous system or because of neurologic disease.     

Early use of artificial sensibility in hand transplantation.

Hands were transplanted from brain-dead donors for the treatment of two male unilateral amputees, aged 35 years and 32 years, involved in the Italian Hand Transplantation Programme. Each had lost his right dominant hand, in a farming accident and an explosion, respectively. In one case artificial sensibility was applied postoperatively using a Sensor Glove that transformed vibrotactile stimuli induced by touch, to stereophonic vibroacoustic stimuli perceived through earphones. The principle is based on the brain's capacity for multimodal plasticity, implying that deprivation of one sense (somatosensory) can be compensated for by another sense (auditory). Functional magnetic resonance images (fMRI) taken at regular intervals showed that cortical remodelling of the transplanted hand within the sensory-motor maps occurred early in the patient who used the artificial sensibility regimen compared with the one who did not. We conclude that postoperative use of a device using hearing as a substitution for sensation in hand transplantation may have considerable potential value for speeding up cortical integration of a transplanted hand.     

Kombinierte Beugesehnen- und Nervenverletzungen der Hand

Any restoration of hand function following tendon and nerve injury has to include the repair or replacement of the hand’s ability to perform a great many tasks. It is hard at first to appreciate fully the loss that occurs with flexor tendon injury. Also sensibility can be compromised from tendon injury without direct injury to the nerve, as object recognition in the absence of vision requires finger movement. When peripheral nerve injury is combined with flexor tendon injury, sensibility is directly impaired. There is a loss in the sense of finger or thumb position, pain temperature and touch or pressure recognition, in addition to the tendon injury. However, the outcome after operative treatment of these“minor” injuries of the hand is horrible. Therefore, we try to summarize practical consequences for the repair of combined flexor tendon and nerve injuries which will improve operative outcome. These guidelines are based on current scientific knowledge and our own experience.     

Precision grip function after hand replantation and digital nerve injury.

Understanding how the loss of digital sensibility affects manual dexterity could have important implications for rehabilitation after hand injury. We investigated precision grip function during lifting tasks in seven patients after hand replantation, in five after single digital nerve injury and in four volunteers subjected to digital anaesthesia. Using their affected hand, all participants could successfully lift test objects with parallel and vertical grip surfaces and they all reliably increased the grip force with increasing object weight (0.11-0.55 kg). However, the grip forces used were frequently significantly higher than those applied by the unaffected hand. This was partly due to participants compensating for loss of sensibility with high grip force safety margins against slips, and partly related to misalignments of the fingertips on the grasp surfaces. The latter was most prominent after hand replantation. In a second series of lifting experiments we changed the shape of the grip surfaces in order to investigate the participants' ability to adapt grip forces based on tactile recognition of object shape. An important finding from this series was that in patients with poor clinical outcomes, the contralateral unaffected hand tended to mirror the abnormal grasp patterns of the injured hand. This suggests that control strategies developed for the impaired hand can influence the control of the contralateral uninjured hand.     

Surgical management of wrist and finger deformity

The surgical results of upper extremity intervention have been shown to improve hand function from paperweight/passive assist function to active assist function. Although children with cerebral palsy commonly have a sensibility deficiency in conjunction with their motor deficiency, several recent studies have disproved the previous doctrine that hand surgery should not be performed on children with sensibility deficiencies. The author's report of 134 children treated surgically showed that preoperatively 50% had impaired two-point discrimination and 75% had impaired stereognosis: impaired sensibility had no adverse effect on surgical results. Eliasson et al reported on 32 children treated surgically with tendon transfers and muscle releases. Impaired sensibility before the surgery did not influence the outcome. In fact, Dahlin et al reported 36 patients treated operatively and followed for 18 months, finding an improvement in stereognosis function associated with the improvement in their motor function, presumably because of improved functional use. Children with cerebral palsy can improve their motor function and perhaps also their sensibility function with appropriately planned and executed tendon release and transfer surgery. Balance of the wrist and fingers is the key clement in improvement of upper limb function.     

Momentary improvement of hand sensibility by excluding vision

The aim of this study was to investigate the effects of visual input on the results in a sensory testing procedure on hands. Sensory testing was done with the tested hand behind a screen in a counterbalanced setting with open eyes, and blindfolded in 66 healthy persons. Tactile discrimination (2pd) and touch thresholds (Semmes-Weinstein monofilaments) were tested for on the index finger of the dominant hand. Tactile discrimination was significantly better when the test subject was blindfolded than when eyes were open. Our results showed that removal of all visual input during sensibility testing gave improved results compared with testing with visual input (opened eyes but the hand out of sight). The mechanism behind the improvement is probably rapid changes in the brain. Manipulation of visual input during sensibility testing, particularly during tests that include an element of interpretation, influences the test result. These results highlight the importance of standardised procedures in sensibility testing.     

Intralbugineous testicular prosthesis a new technique summary of 30 implants

A study of 16 patients who underwent intralbugineous testicular implants during the practice of orchiectomy is presented. In 14 cases of prostatic carcinoma, after bilateral subcapsular orchiectomy intralbugineous prostheses were implanted and in 2 other cases of testicular torsion unilateral prosthesis was implanted. With this new, easily executed technique the size, mobility and testicular sensibility are maintained.     

Sensory changes with prolonged double-cuff tourniquet time in hand surgery

This study evaluates the sensory changes that occur in the operated hand after the use of the double-cuff tourniquet technique for up to 4 hours. Thirty patients whose hand operations lasted more than 2 hours were evaluated. Tourniquet time ranged between 2 hours and 4 hours, 17 minutes. Light touch, von Frey's aesthesiometry, vibratory sensation, and two-point discrimination were examined. Subjective overall sensation and postoperative edema were also assessed. Patients were evaluated the evening before operation, on the second postoperative day, and at every out-patient follow-up visit, until all examined parameters returned to normal. Of the patients 73% demonstrated clinically normal sensibility test results within 23 days after operation. In 80% of all patients, subjective sensibility of the operated hand was equal to the nonoperated hand within 1 week of operation. Ultimately, all patients (96%) but one, demonstrated normal sensibility test results and normal subjective sensibility. Postoperative edema developed in 53% of the patients; it subsided in less than 4 weeks. The double-cuff technique can prolong tourniquet time safely for up to 4 hours.     

Brain plasticity and hand surgery: an overview

The hand is an extension of the brain, and the hand is projected and represented in large areas of the motor and sensory cortex. The brain is a complicated neural network which continuously remodels itself as a result of changes in sensory input. Such synaptic reorganizational changes may be activity-dependent, based on alterations in hand activity and tactile experience, or a result of deafferentiation such as nerve injury or amputation. Inferior recovery of functional sensibility following nerve repair, as well as phantom experiences in virtual, amputated limbs are phenomena reflecting profound cortical reorganizational changes. Surgical procedures on the hand are always accompanied by synaptic reorganizational changes in the brain cortex, and the outcome from many hand surgical procedures is to a large extent dependent on brain plasticity.     

Sensory mapping.

The primary aim in reconstructive surgery of the upper extremity is to provide tactile gnosis to sensory depleted areas. It is essential for restoration of function and successful rehabilitation of the injured hand. Neurovascular free flaps may provide the answer to this catastrophic problem and transform a useless appendage into a functional gripping hand. Sensory mapping techniques can greatly assist the surgeon in precisely defining new donor sites for these transfers. Cutaneous sensibility, cutaneous sensation, and hand function are subjects of great complexity. Much more investigative and clinical work is needed in this challenging field to improve our evaluation of the sensory injury to the hand and to provide new avenues for restoring functional sensibility in the upper extremity.     

Momentary improvement of hand sensibility by excluding vision

Abstract

The aim of this study was to investigate the effects of visual input on the results in a sensory testing procedure on hands. Sensory testing was done with the tested hand behind a screen in a counterbalanced setting with open eyes, and blindfolded in 66 healthy persons. Tactile discrimination (2pd) and touch thresholds (Semmes-Weinstein monofilaments) were tested for on the index finger of the dominant hand. Tactile discrimination was significantly better when the test subject was blindfolded than when eyes were open. Our results showed that removal of all visual input during sensibility testing gave improved results compared with testing with visual input (opened eyes but the hand out of sight). The mechanism behind the improvement is probably rapid changes in the brain. Manipulation of visual input during sensibility testing, particularly during tests that include an element of interpretation, influences the test result. These results highlight the importance of standardised procedures in sensibility testing.     

Long-term sensibility following nonautologous, immediate breast reconstruction

Immediate breast reconstruction after mastectomy, using submuscular expander prostheses, is well established in the treatment of breast cancer. The aim of this study was to survey the postoperative cutaneous somatosensory status and to analyze the patients' subjective opinion about the sensibility in the reconstructed breast. Fourteen patients were included and examined 3-6 years after reconstruction. The untreated contralateral breast served as control. None of the patients had received any locoregional radiotherapy. The perception thresholds to touch, cold, warmth, and heat pain were assessed and a questionnaire about the patients' subjective experience of sensibility was completed. In the quantitative somatosensory testing, statistically significant impairment concerning all the examined modalities was demonstrated. The least affected was the heat pain modality. In the questionnaire, the patients reported weaker nonmodality specific sensibility from the reconstructed breast compared with the control breast. More than half of the patients reported that the reconstructed breast felt like a real breast. In conclusion, the study revealed long-term, overall sensibility impairment following nonautologous, immediate breast reconstruction.     

Hand Surgery and the Development of Hand Prostheses

Hand surgery has shown that afferent impulses to conscious level are essential for control and effective use of any advanced grip. Control of position, motion and load (proprioception) is possible to obtain without joint receptors, by cutaneous receptors alone. Further advances in the construction of hand prostheses must be based on this premise. The value of the key grip is outlined.     

Stellenwert der Endoprothetik im Bereich der Handchirurgie

Alloarthroplasty has largely replaced traditional procedures in arthrosis of hip and knee joints. In contrast the role of alloarthroplasty in comparison to traditional procedures in hand surgery has been uncertain. To evaluate this question every registered hand surgery department (n=307) in Germany received a questionnaire requesting information on number and type of implanted prostheses and traditional procedures concerning the wrist joint, distal radioulnar joint (DRUJ), first carpometacarpal joint (CMC), metacarpal phalangeal joint (MP), interphalangeal joint (PIP), and preferred characteristics of the prostheses. Of the 307 hand surgery departments, 150 (57% of the hospitals and 42% of the visiting surgeons) participated in the inquiry. Per year, only 98 wrist prostheses were implanted (distributed among five different models) but 1534 traditional procedures were performed. The Sauvé-Kapandji procedure was the most popular for the DRUJ and was performed 264 times per year. In comparison 24 hemiarthroplasties were implanted at the DRUJ. Trapezectomy remains the standard procedure for arthrosis of the first CMC joint (n=1399). The future importance of alloarthroplasty of the CMC joint is doubted by the majority of participating hand surgeons (90.3%). In contrast the majority (85.3/71.8%) is convinced that alloarthroplasty will be of importance for the MCP and PIP joints, respectively. Currently, the number of implanted prostheses is close to the number of traditional procedures performed at the MP joint. Irrespective of the joint involved, cementless anchorage is preferred as is the surface replacement anatomical design. The results confirm that alloarthroplasty in hand surgery is of minor importance. Thus, the role of alloarthroplasty differs depending on the joint involved. Traditional procedures except for the MP joint continue to be of major importance in hand surgery.     

Evaluation of hand sensibility: a review.

Many assessment devices and measures have been described to evaluate sensibility, with little consensus on the optimal measurement tool. The purpose of this paper is to review the assessment methods and devices used in the evaluation of hand sensibility. Consideration is given to the characteristics of each measurement tool, the information necessary for complete patient evaluation, and the battery of valid and reliable measurements that provide the most complete and accurate patient assessment.     

On the usefulness of bone scintigraphy for detecting loosening of articular prostheses (author's transl)]

The most important complication of articular substitution is the loosening of the prostheses as a result of permanent overstraining, trauma, chemical or infectious noxae. The value of bone scintigraphy in the diagnosis of loosening of the endoprothesis was examined in 53 articular prostheses (49 hip joints and 4 knee joints). A pathological scan was evident in all cases where the prosthesis had become loose (18 cases), whereas a normal scan was found in 34 firmly positioned prostheses. A false positive scan occurred in one case of periarthritis. Bone scintigraphy can be employed as a means of diagnosing loosening of prostheses after a period of nine months following the operation; up to that time, enhancement can be due to the operation. A positive scan in case of loosening of the prosthesis is manifested earlier than radiological signs. For this reason, scintigraphy can be recommended as a routine examination method in pain after articular substitution surgery.     

The role of endoprostheses in the scope of hand surgery. Endoprostheses vs. traditional surgical procedures

Alloarthroplasty has largely replaced traditional procedures in arthrosis of hip and knee joints. In contrast the role of alloarthroplasty in comparison to traditional procedures in hand surgery has been uncertain. To evaluate this question every registered hand surgery department (n=307) in Germany received a questionnaire requesting information on number and type of implanted prostheses and traditional procedures concerning the wrist joint, distal radioulnar joint (DRUJ), first carpometacarpal joint (CMC), metacarpal phalangeal joint (MP), interphalangeal joint (PIP), and preferred characteristics of the prostheses. Of the 307 hand surgery departments, 150 (57% of the hospitals and 42% of the visiting surgeons) participated in the inquiry. Per year, only 98 wrist prostheses were implanted (distributed among five different models) but 1534 traditional procedures were performed. The Sauve-Kapandji procedure was the most popular for the DRUJ and was performed 264 times per year. In comparison 24 hemiarthroplasties were implanted at the DRUJ. Trapezectomy remains the standard procedure for arthrosis of the first CMC joint (n=1399). The future importance of alloarthroplasty of the CMC joint is doubted by the majority of participating hand surgeons (90.3%). In contrast the majority (85.3/71.8%) is convinced that alloarthroplasty will be of importance for the MCP and PIP joints, respectively. Currently, the number of implanted prostheses is close to the number of traditional procedures performed at the MP joint. Irrespective of the joint involved, cementless anchorage is preferred as is the surface replacement anatomical design. The results confirm that alloarthroplasty in hand surgery is of minor importance. Thus, the role of alloarthroplasty differs depending on the joint involved. Traditional procedures except for the MP joint continue to be of major importance in hand surgery.     

Touch sensibility in the hand

Touch sensibility must be evaluated in most of our patients, and must be re-evaluated in many of them following surgery. Touch sensibility must be tested in our disability evaluations and in order to prognosticate regarding hand function. Touch sensibility evaluation can provide a non-invasive guide to acute compartmental syndrome management. Touch sensibility must be re-educated following nerve repair.     

An objective method for the measurement of skin sensibility

Summary The importance of the return of sensibility in transplanted skin as a functional necessity for the success of a surgical reconstruction, especially in the hand, has led to many studies to develop a technique for the evaluation of postoperative sensibility, in which the application of the sensory stimulus is constant, controlled, and the degree of sensibility recorded without the subjective collaboration of the patient. Since the tactile and pain stimuli are appreciated by nerve fibres which are different from those which register thermal sensation, two different apparatuses have been devised to evaluate these two aspects of sensibility. Experimental studies and clinical application of these two methods are reported.