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Jan Fridén

Publications and source records attributed to Jan Fridén.

29 records · Page 2Linked to original sources
PubMed2002

Mechanical considerations in the design of surgical reconstructive procedures.

Tendon transfers are used to restore arm and hand function after injury to the peripheral nerves or after spinal cord injury. Traditional guidelines to choose the length at which the transferred muscle should be attached have a poor scientific foundation. We postulate that passive tension only becomes significant at relatively long lengths and that passive tension as the major factor in intra-operative decision making may result in overstretch of the muscle-tendon unit (MTU) and accompanying low-active force generation. It appears unwise to rely on unknown factors, such as slippage or stress relaxation, to correct an overstretched transfer. Instead, we suggest the use of intra-operative sarcomere length measurements to predict and set the optimal MTU length during reconstructive upper limb surgery.

Biomechanical Phenomena↗
PubMed2002

Split distal flexor pollicis longus tenodesis: long-term results.

A thumb lacking intrinsic muscle function but having extrinsic flexion will hyperflex in the interphalangeal joint giving a positive Froment's sign. This can effectively be prevented with split flexor pollicis longus tenodesis. The mean postoperative range of motion in the IP joint of 39 hands was 28 (18) degrees and 23 (20) degrees six and 12 months postoperatively. The procedure makes arthrodesis (temporary or permanent) superfluous. This procedure can be recommended strongly.

Finger Joint↗
PubMed2002

Mechanisms of muscle injury gleaned from animal models.

Eccentric contractions of skeletal muscles produce injury and, ultimately, muscle strengthening. Current data suggest that the earliest events associated with injury are mechanical in nature and may be based primarily on the sarcomere strain experienced by the muscle. In this review, recent experimental data, primarily from rabbit dorsiflexor muscles, are used to provide general information regarding the factors that cause injury and means for preventing injury. Mechanical experiments reveal that excessive sarcomere strain is the primary cause of injury. We hypothesize that excessive strain permits extracellular or intracellular membrane disruption that may permit hydrolysis of structural proteins, leading to the myofibrillar disruption that is commonly observed. Inflammation that occurs after injury further degrades the tissue, but prevention of the inflammation leads to a long-term loss in muscle function. Simple preventative treatments such as increasing muscle oxidative capacity (getting into shape) or cyclic stress-relaxation of tissue (stretching out) have no measurable effect on the magnitude of muscle injury that occurs. Ultimately, an improved understanding of the damage mechanism may improve our ability to provide rehabilitative and strengthening prescriptions that have a rational scientific basis.

Animals↗
PubMed2002

Cytoskeletal disruption after eccentric contraction-induced muscle injury.

Skeletal muscle cytoskeletal proteins are receiving more attention recently based on their importance in maintaining muscle integrity, their role in transmitting force throughout the cell, and their involvement in muscle diseases. In this report, the authors focus on the intermediate filament system of skeletal muscle composed of the protein desmin. Desmin is shown to transmit force from myofibrillar force generators to the muscle surface and to the muscle-tendon junction. This protein is lost rapidly during high-intensity exercise using a rabbit model. Mice were genetically engineered that lack the desmin gene and these muscles were shown to generate lower stress but actually to experience less injury during intense exercise. Finally, direct imaging of muscle cells with fluorescently labeled cytoskeletal proteins shows that lack of the desmin protein results in tremendous disorganization of the myofibrillar lattice which may help to explain desmin myopathies.

Animals↗
PubMed2002

Desmin cytoskeletal modifications after a bout of eccentric exercise in the rat.

Desmin content and immunohistochemical appearance were measured in tibialis anterior muscles of rats subjected to a single bout of 30 eccentric contractions (ECs). Ankle torque was measured before EC and at various recovery times, after which immunohistochemical and immunoblot analyses were performed. Torque decreased by approximately 50% immediately after EC and fully recovered 168 h later (P < 0.001). Loss of desmin staining was maximal 12 h after EC and recovered by 72 h. Immunoblots unexpectedly demonstrated a significant increase in the desmin-to-actin ratio by 72 h after EC (P < 0.01) and was still increasing after 168 h (P < 0.0001). These data demonstrate a relatively rapid qualitative loss of desmin immunostaining immediately after a single EC bout but a tremendous quantitative increase in desmin content 72-168 h later. This dynamic restructuring of the muscle's intermediate filament system may be involved in the mechanism of EC-induced muscle injury and may provide a structural explanation for the protective effects observed in muscle after a single EC bout.

Animals↗
PubMed2002

Evidence for increased myofibrillar mobility in desmin-null mouse skeletal muscle.

Quantitative electron microscopy was used to characterize the longitudinal mobility of myofibrils during muscle extension to investigate the functional roles of skeletal muscle intermediate filaments. Extensor digitorum longus fifth toe muscles from wild-type (+/+) and desmin-null (des -/-) animals were passively stretched to varying lengths, and the horizontal displacement of adjacent Z-disks in neighboring myofibrils (Deltax(myo)) and average sarcomere length (SL) were calculated. At short SL (<2.20 microm), wild-type and desmin-null Deltax(myo) were not significantly different, although there was a trend towards greater Z-disk misalignment in muscles from knockout animals (Deltax(myo) 0.34+/-0.04 microm versus 0.22+/-0.09 microm; P>0.2; means +/- S.E.M.). However, at higher SL (>2.90 microm), muscles from knockout animals displayed a dramatically increased Deltax(myo) relative to wild-type muscles (0.49+/-0.10 microm versus 0.25+/-0.07 microm; P<0.05). The results, which establish a maximum extension of the desmin network surrounding the Z-disk, provide what we believe to be the first quantitative estimation of the functional limits of the desmin intermediate filament system in the presence of an intact myofibrillar lattice. The existence of a limit on the extension of desmin suggests a mechanism for the recruitment of desmin into a network of force transmission, whether as a longitudinal load bearer or as a component in a radial force-transmission system.

Animals↗
PubMed2002

Tendon transfer surgery: clinical implications of experimental studies.

Tendon transfers commonly are used to restore arm and hand function after injury to the main motor nerves or after spinal cord injury. Surgeons traditionally use passive tension to determine the length at which a muscle should be attached during tendon transfer. The principles used to choose the length at which the transferred muscle should be attached still are relatively vague and have not been examined thoroughly. Misunderstanding of the sarcomere length-passive tension relationship can result in severe overstretch of the muscle and poor function. Upper extremity muscles have operating ranges that vary between synergists and antagonists, and recent architectural and biochemical data suggest that upper extremity muscles are designed to provide optimal control of joint position and stability. It is hypothesized that a significant functional improvement will be realized when muscles are reattached during tendon transfer procedures at the appropriate length and tension.

Adaptation, Physiological↗
PubMedDate not supplied

Dorsal transfer of the brachioradialis to the flexor pollicis longus enables simultaneous powering of key pinch and forearm pronation.

PURPOSE: To show biomechanically that the brachioradialis (BR) muscle can be transferred to restore key pinch and forearm pronation simultaneously. METHODS: Nine fresh-frozen forearms were thawed and instrumented with a custom muscle-tendon excursion jig. Maximum BR muscle-tendon excursion was measured with the wrist and thumb mobile. Muscle-tendon excursion then was measured from 60 degrees of supination to 60 degrees of pronation in 15 degrees increments with the wrist and thumb fixed. Measurements were performed in 3 configurations: the native BR, the BR transferred volarly to the flexor pollicis longus (FPL) tendon, and the BR transferred dorsally (posterior to the radius) through the interosseous membrane to the FPL tendon. Muscle excursion-joint angle data were differentiated to compute pronation/supination moment arms. Two-way analyses of variance and post hoc Tukey tests were used to compare transfer conditions. RESULTS: Maximum muscle excursion was nearly identical when volar and dorsal transfer conditions were compared. When pronation/supination motions were isolated, however, the volar transfer was associated with muscle shortening and small pronation moment arms through 30 degrees +/- 9 degrees of supination. Importantly, the dorsal transfer was associated with muscle shortening and larger pronation moment arms through 28 degrees +/- 10 degrees of pronation, a significant difference of 58.0 degrees +/- 16.0 degrees compared to the traditional volar transfer. CONCLUSIONS: These data suggest that dorsal BR-to-FPL transfers can power key pinch and forearm pronation simultaneously even in the absence of other functional pronators. This transfer can be accomplished without changes to total muscle excursion compared with the traditional volar BR-to-FPL transfer. This result may enable the use of the BR-to-FPL transfer in patients who need key pinch but who lack functional pronation muscle groups (eg, ocular cutaneous 3). As result a larger patient population may benefit from the BR-to-FPL reconstructive procedure.

Aged↗