Superficial Flexor Research Articles

Sensitization of high mechanothreshold superficial dorsal horn and flexor motor neurones following chemosensitive primary afferent activation

Nociceptive primary afferents have the capacity to induce a state of increased excitability or central sensitization in dorsal horn neurones. This contributes to the mechanical hypersensitivity (allodynia) which occurs after peripheral tissue injury where low-mechanothreshold primary afferent activation begins to elicit pain. The relative susceptibility of dorsal horn cells with an apparent exclusive nociceptive input (nociceptive-specific (NS) or high-threshold (HT) cells) and those with a convergent input from low- and high-threshold mechanoreceptors (wide-dynamic-range (WDR) or multireceptive neurones) to sensitivity changes has been disputed. We have examined whether high-mechanothreshold neurones in the superficial dorsal and the ventral horn can modify their sensitivity following cutaneous application of the chemical irritant mustard oil. This produced both a prolonged reduction in the mechanical threshold of the cutaneous flexion withdrawal reflex, recorded from semitendinosus α-motor neurones, and an increase in the activity evoked in these neurones by low-intensity touch stimuli to the glabrous skin. Eight NS or HT only cells, defined in terms of their cutaneous mechanoreceptive field properties, were recorded in the superficial dorsal horn before and after cutaneous application of mustard oil. Mustard oil was applied outside of the mechanical receptive field of the cells and produced a transient increase in action potential discharge in 4 cells but increased the mechanoreceptive field size in all cells for 30–60 min. Mechanical thresholds declined in 6 cells to levels associated with low-threshold (LT) and WDR cells, and this was accompanied by recruitment of a novel brush/ touch response in 5 cells. The responses evoked by graded electrical stimulation of the sural nerve were tested in 5 cells. Only 1 cell failed to show any change after mustard oil. In 3 cells, an increase in the response to A-fibre afferents occurred, a novel A-fibre response was recruited in 2 cells and the C-fibre response increased in 2 cells. Cells in the superficial dorsal horn of the rat spinal cord that are normally NS can begin, therefore, to respond to LT primary afferent mechanoreceptors after an increase in central excitability produced by activation of peripheral chemoreceptors. Sensitization of these, as well as of WDR cells, may contribute to the generation of post-injury mechanical pain and reflex hypersensitivity.

Muscle recruitment variations during wrist flexion exercise: MR evaluation.

Many exercise protocols used in physiological studies assume homogeneous and diffuse muscle recruitment. To test this assumption during a "standard" wrist flexion protocol, variations in muscle recruitment were assessed using MRI in eight healthy subjects. Variations were assessed by comparing the right to the left forearms and the effect of slight (15 degrees) pronation or supination at the wrist. Postexercise imaging showed focal regions of increased signal intensity (SI), indicating relatively strong recruitment, most often in entire muscles, although occasionally only in subvolumes of muscles. In 15 of 26 studies, flexor carpi radialis (FCR) showed more SI than flexor carpi ulnaris, while in 11 studies SI in these muscles increased equivalently. Relatively greater FCR recruitment was seen during pronation and/or use of the nondominant side. Palmaris longus, a wrist flexor, did not appear recruited in 4 of 11 forearms in which it was present. A portion of the superficial finger flexor became hyperintense in 89% of studies, while recruitment of the deep finger flexor was seen only in 43%. Inter- and intraindividual variations in forearm muscle recruitment should be anticipated in physiological studies of standard wrist flexion exercise protocols.

Simultaneous rupture of both flexor tendons in a finger

Simultaneous rupture of the flexor superficialis and profundus tendons is an exceedingly rare injury, particularly if the tendons have not been previously damaged, either by disease or attrition. This case report involves ruptures of both tendons at their respective insertions, and injury that to our knowledge has not been previously reported.

EVALUATION OF THE EQUINE DIGITAL FLEXOR TENDON SHEATH USING DIAGNOSTIC ULTRASOUND AND CONTRAST RADIOGRAPHY

This study was designed to evaluate the normal anatomy of the digital flexor tendon sheath using contrast radiography and diagnostic ultrasound. Iodinated contrast medium was injected into eight cadaver limbs and the limbs immediately frozen. Lateromedial and dorsopalmar/plantar radiographs were made. These limps were then cut transversely and proximal to distal radiographs of each slab were made. This cross sectional contrast methodology allowed the visualization of the relative size and shape of the superficial and deep digital flexor tendons as well as the potential space taken by effusions of the digital flexor tendon sheath.The second part of the study used twelve live animals with normal digital flexor tendon sheaths. Ultrasonographic measurement of the structures of the digital flexor tendon sheath at each level were compiled. This documented the ability of diagnostic ultrasound to image: 1) the superficial and deep digital flexor tendons, 2) the proximal and distal ring of the manica flexoria, 3) the straight and oblique sesamoidean ligaments, and 4) the mesotendinous attachments to the superficial and deep flexor tendons. Iodinated contrast medium was then injected into the digital flexor tendon sheath and the ultrasonography repeated. These images were compared with those obtained from contrast radiography and prosections of twenty normal limbs. The iodinated contrast medium enhanced sonographic imaging of the structures of the digital tendon sheath, particularly the abaxial borders of the superficial digital flexor tendon branches and the mesotendinous attachments to the superficial and deep digital flexor tendons.

Observations on the in vitro behavior of digital tendons

The force/strain behavior of the common and lateral extensor tendons, the extensor branches of the interosseus muscle, and the superficial flexor tendon have been examined in vitro. The flexor tendon acted as a hard-spring with an initial large strain with small load followed by progressively less strain with increasing load, The distal part of the common extensor tendon and the extensor branches behaved in the same manner during dorsiflexion of the fetlock joint/palmar flexion of the coffin joint. The common extensor tendon behaved in a softening manner during palmar flexion of the fetlock and coffin joints while the lateral extensor and the extensor branches behaved in a nearly linear manner.

Myofibrillar Protein Composition Correlates with Histochemistry in Fibres of the Abdominal Flexor Muscles of the Norway Lobster Nephrops Norvegicus

ABSTRACT The myofibrillar proteins in fibres from the abdominal flexor muscles of the Norway lobster, Nephrops norvegicus, have been identified using SDS–PAGE gel electrophoresis. Several contractile and regulatory proteins are expressed as multiple isoforms in single fibres and, according to these, one fast fibre phenotype (F) can be identified in the deep flexor muscles and two slow fibre phenotypes (S1 and S2) can be distinguished in the superficial flexor muscles. The two slow fibre phenotypes are distributed non-uniformly across the superficial flexor muscle, and in the lateral bundle there is a heterogeneous mixture of both S1 and S2 fibres. Using histochemical procedures applied to intact or freeze-dried fibres in conjunction with measurements of fibre sarcomere length and gel electrophoresis, an exact correspondence can be demonstrated between the morphological properties, enzymatic content and myofibrillar protein composition of individual fibres from the deep and superficial flexor muscles. In the superficial flexor muscle, fibres of the S1 phenotype have a mean sarcomere length of <8 μm, a low oxidative capacity and an acid-labile isoform of myosin ATPase, while fibres of the S2 phenotypes have a longer sarcomere length (mean >9 μm), a higher oxidative capacity and an acid-stable isoform of myosin ATPase. These results are discussed in terms of the relationships between the different muscle fibre properties and the usefulness of procedures applied to single fibres for determining them.

Coactivity Effects upon Carpal Tunnel Contact Forces

Contact force on the carpal tunnel structures due to flexor tendon forces have been identified as an important contributor to the compression of the median nerve. Therefore, a pilot study was conducted to assess the increase in carpal contact force due to the antagonistic coactivity of the finger extensor muscles. Surface EMG activities of the superficial finger flexor and extensor muscles of four subjects were measured during several isometric power grip exertions at seven different wrist angles. The results showed that a linear relation between EMG and muscle force holds under the prescribed isometric conditions. An EMG-assisted model was developed to predict tensile forces in an equivalent flexor tendon. For a given angle, the model predicts increased tensile force in the flexor tendon with increased extensor (antagonist) coactivity in response to isometric grip exertions. It was found that if one accounts for muscle coactivity, predicted force in the flexor tendons would be as much as 33% greater than force predicted by models which neglect coactivity. This increase would also be observed in carpal contact force since this force is linearly related to the flexor tendon force. Models that neglect coactivity severely underestimate flexor tendon forces and consequently contact forces in the carpal tunnel.

Mesovascularized Island Flexor Tendon

Hand surgeons have long sought ways of avoiding adhesions in flexor tendon repair. We report a new concept in tendon surgery—the use of flexor tendons with perfect mesotendon blood supply and an inherent gliding mechanism composed of the paratendon and the common carpal sheath to minimize adhesions during tendon healing. This technique, inspired by reversed ulnar island forearm transfers, makes use of the flexor superficialis of the ring finger, which is supplied by a vascular mesotendon emerging from the ulnar pedicle just before Guyon's canal, and ensures a perfect blood supply, a favorable environment for suturing, and, consequently, impressive digital excursion. (Plast. Reconstr. Surg. 92: 888, 1993.)

Mesovascularized Island Flexor Tendon

Hand surgeons have long sought ways of avoiding adhesions in flexor tendon repair. We report a new concept in tendon surgery--the use of flexor tendons with perfect mesotendon blood supply and an inherent gliding mechanism composed of the paratendon and the common carpal sheath to minimize adhesions during tendon healing. This technique, inspired by reversed ulnar island forearm transfers, makes use of the flexor superficialis of the ring finger, which is supplied by a vascular mesotendon emerging from the ulnar pedicle just before Guyon's canal, and ensures a perfect blood supply, a favorable environment for suturing, and, consequently, impressive digital excursion.

Synaptic repression at crayfish neuromuscular junctions. II. Evidence for calcium involvement.

The inability of synaptic junctions to generate normalisized postsynaptic potentials under normal physiological conditions was studied at crayfish neuromuscular synapses. Synaptic repression in the superficial flexor muscle system of the crayfish was induced by surgery: the nerve was cut in the middle of the target field, and the lateral muscle fibers were removed. After this surgery, the remaining medial synapses were unable to generate normal-sized junction potentials (jp) over the medial muscle population. In an attempt to study the mechanisms underlying this response, we varied the extracellular calcium concentration of the Ringers solution bathing the preparation, in both repressed and control animals, while monitoring the size of the same junction potential. The junction potential generated by the spontaneous activity of the nerve increased in size with increasing calcium concentrations in control animals, but failed to do so in repressed animals, that is, changes in external calcium concentrations did not affect repressed synapses. However, in the presence of the calcium ionophore A23187, control and repressed synapses both show an increase in the junction potential sizes they generate. Our data suggest that calcium is involved in the mechanisms that underlie synaptic repression in this crustacean neuromuscular system.

Synaptic repression at crayfish neuromuscular junctions. I. Generation after partial target area removal.

Synaptic repression, the inability of synaptic junctions to generate normal-sized postsynaptic potentials under normal physiological conditions, is reported here for crayfish neuromuscular synapses. The synapses in the superficial flexor muscle system of the crayfish change their efficiency in generating a postsynaptic response as a result of a specific alteration in their immediate environment. When the superficial flexor nerve is cut halfway into the target muscle field and the lateral muscle fibers are removed, the intact medial synapses do not generate normal-sized junction potentials (JP) at the 17 degrees-19 degrees C temperature of the Ringers solution. JPs cannot be recorded in 83% of the muscle fibers at 2 weeks after the operation and of the few JPs that can be detected, 80% are smaller than 1 mV in size. By 8 weeks after the operation, JPs were detected in 55% of the muscle fibers, and now only 46% of these are smaller than 1 mV. When the lateral muscle fibers are left in place during the original operation, providing a target area for the cut nerve to grow into, JPs were then detected in 60%-80% of all medial fibers at all time periods after the operation; their size profile, with 10%-25% of the muscle fibers having JP's less than 1 mV, was similar to control values. These results suggest that the efficiency of these synaptic contacts become affected as a result of partial axotomy and removal of the target area of the cut branches of the axons.

Acute flexor superficialis avulsion

Received for publication May 12, 1992; accepted in revised form Sept. 18, 1992. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Robert E. Atkinson, MD, Associate Clinical Professor of Orthopedic Surgery, University of Hawaii, 1380 Lusitana St., Suite 608, Honolulu, HI 96813. 311143849 I solated avulsion of the flexor digitorum superficialis tendon at its insertion is rare. Prior case reports of this entity note the need for late surgical treatment of a contracted, painful proximal interphalangeal (PIP) joint with excision of the superficialis remnant and release of the contracture.‘, ’ We are reporting a case of flexor superficialis tendon avulsion that was associated with an intra-articular fracture of the middle phalanx. To the best of our knowledge, this is the first report of this specific injury.

Avoiding nerve damage during elbow arthroscopy

To define the anatomical relationships of the nerves to the common arthroscopy portals at the elbow an arthroscope was introduced into 20 cadaver elbows and the positions of the nerves were then determined by dissection. In all cases the posterior interosseous nerve lay close to the radiohumeral joint and to the anterolateral portal. Pronation of the forearm displaced the nerve away from the arthroscope. The median nerve passed consistently within 14 mm of the arthroscope when it was introduced through the anteromedial portal. The branches supplying the superficial forearm flexor muscles were at risk.

The Kleinert dynamic splint : where it fails and how it can be modified

After primary tenoraphy of flexor tendons one often finds a hampered function of the DIP-joint. Analysis of the pattern of early mobilization exercised by our patients in the Kleinert splint and analysis of the excursions of the flexor tendons of fresh unembalmed specimens brought us to the conclusion that the Kleinert dynamic splint fails in maintaining a sliding movement of the deep and the superficial flexor tendons along each other because the splint excludes motion at the distal interphalangeal joint. Based on our observations we modified the Kleinert dynamic splint. Our experience with 37 patients shows that this modified splint gives a better function in the DIP-joint.

Local vascular contribution of the superficial palmar arch.

The aim of the present study was to establish a precise topography of the arterial supply of the different layers in the palm of the human hand. Two hundred upper extremities from fresh human cadavers aged 20-80 years were injected either by coloured latex or by India ink and gelatine. Some of our specimens were treated by the Spalteholz technique of transclarification, while some others were treated by acid corrosion. All of the specimens were dissected under the dissecting microscope. The superficial palmar arch (SPA) is the main vascular structure of the palm of the hand. Regardless of its size and of its variation, in addition to the common palmar digital arteries, the SPA supplies the superficial flexor tendons, flexor retinaculum, median and ulnar nerves, tendon of the flexor pollicis longus muscle, lumbrical muscles, palmar aponeurosis and the skin of the palm of the hand. These data may be of interest to those involved in hand surgery.

Histochemical heterogeneity of fibers in the abdominal superficial flexor muscles of the Norway lobster, Nephrops norvegicus (L.).

The superficial flexor muscle in the abdomen of the Norway lobster Nephrops norvegicus (L.), comprises medial and lateral bundles with distinct fiber type composition. Fibers of the medial bundle have long sarcomeres (> 9 microns) and a thick fringe of subsarcolemmal mitochondria. In histochemical tests they have a low total myofibrillar ATPase activity, a pH-stable isoform of myosin ATPase, and a high level of oxidative enzyme activity. A few fibers of the lateral bundle also display these morphological and histochemical properties. However, the majority of lateral fibers have shorter sarcomeres (< 8 microns), no subsarcolemmal mitochondria, but a well-developed tubular system. They also have a higher total myofibrillar ATPase activity, a pH-labile isoform of myosin ATPase, and a low level of oxidative enzyme activity. The heterogeneous pattern of different fiber types in the lateral bundle of this muscle is similar but not identical in the different abdominal segments and in different individuals.

Anatomical and physiological study of interneurons in an oligosynaptic cutaneous reflex pathway in the cat hindlimb

Morphological and physiological studies were undertaken in the cat lumbosacral spinal cord in order to examine individual last-order excitatory interneurons in the disynaptic pathway between low threshold superficial peroneal (SP) afferents and flexor digitorum longus (FDL) motoneurons. Last-order interneurons projecting to the FDL motor nucleus were visualized with activity-dependent trans-synaptic transport of lectin-conjugated horseradish peroxidase (WGA-HRP). The location of lumbar interneurons that responded at short latencies (< 3 ms) to electrical stimulation of the SP nerve was further defined using extracellular recording. The projection of individual interneurons to motoneurons in the L 6 segment was defined by spike-triggered averaging of population ventral root potentials (VRPs) using the sucrose gap technique. Measurements of the central latencies from the arrival of the SP afferent volley to interneuron firing, and from interneuron spike to the onset of the VRP EPSPs, confirm the existence of a low threshold, disynaptic SP pathway that excited motoneurons. These data provide useful latency constraints for the interpretation of the synaptic length of cutaneous reflex pathways in the cat hindlimb.

Lateral band translocation for swan-neck deformity

Lateral band translocation involves transfer of the dorsally subluxed radial lateral band to the palmar aspect of the joint where it is maintained by a sling created between the flexor superficialis tendon and the palmar plate. Thirty fingers with swan-neck deformity of differing causes and a preoperative hyperextension deformity averaging 16 degrees were treated. After operation all swan-neck deformities were corrected and the average flexion contracture was 11 degrees. The range of preoperative flexion was either regained or improved. There were no recurrences and no complications. This relatively simple procedure is an effective treatment of swan-neck deformity and an attractive alternative to previously described procedures.

Abdominal postural motor responses initiated by the muscle receptor organ in lobster depend upon centrally generated motor activity.

1. Stretch stimulation of the abdominal muscle receptor organ of the lobster Homarus americanus initiated spike discharge of its tonic sensory neuron (SR1). This sensory response evoked a series of tonic postural reflex responses in the motor neurons that innervate the superficial extensor and flexor muscles of the abdominal postural system. The type of motor response depended on whether a flexion or extension pattern of spontaneous activity was being generated by the postural efferents. Spontaneous shifts between these centrally generated motor activities completely changed the SR1-evoked reflex responses. 2. During spontaneous centrally initiated flexion activity, tonic SR1 neuron discharge elicited an assistance response that included excitation of a medium-sized flexor excitor (f3) and the peripheral extensor inhibitor (e5), and inhibition of at least one extensor excitor. Neither the other flexor excitors nor the peripheral flexor inhibitor (f5) were affected by SR1 excitation. 3. During spontaneous centrally initiated extension activity, SR1 activity elicited a response that included excitation of the extensor excitors and the flexor peripheral inhibitor (f5) only, f3 and e5 spontaneous activities were unchanged. This response was a resistance reflex, since SR1 discharge normally resulted from an imposed abdominal flexion. 4. The SR1-initiated control of postural motor activity in lobster differs from previously published results in the crayfish Procambarus clarkii.

Clinical relevance of radiographic findings in proximal sesamoid bones of two-year-old Standardbreds in their first year of race training

Summary Radiographs of all 4 fetlocks of 71 Standardbred racehorses were obtained at 3-month intervals for 1 year. Radiographic findings in the abaxial surface of the proximal sesamoid bones were classified into 3 types according to the severity of lesions, and correlation was made with clinical findings at time of examination. Type-1 lesions (1 or 2 linear defects ≤ 1 mm wide) were detected in 55% of horses at the start of training; clinical signs of disease were not manifested, and lesions did not become clinically relevant. Type-2 lesions (3 or more linear defects ≤1 mm wide) were detected in horses not manifesting clinical signs of disease, and were more frequently observed after 3 months of training. However, 66% of horses affected with diseases of the suspensory apparatus, including superficial flexor tendinitis and suspensory desmitis, also manifested this type of lesion. When lameness was observed, it was associated with the soft tissue problem, and the sesamoid bone changes were considered secondary. Type-3 lesions (wide, abnormally shaped linear defects) were detected in 7 horses at the start of the study; lesions remained in horses throughout the study and were consistently associated with lameness during training. Type-3 lesions were considered clinically relevant and indicative of primary sesamoiditis.