Jussi Rantanen

Effects of Therapeutic Ultrasound on the Regeneration of Skeletal Myofibers After Experimental Muscle Injury

Therapeutic ultrasound is used by many in the treatment of muscle injuries, but no previous attempts to objectively assess its effects on regenerating skeletal myofibers have been published. In this descriptive study, we followed the regeneration of contusion injury to the rat gastrocnemius muscle during treatment with pulsed ultrasound. The speed of myoregeneration in ultrasound-treated animals was compared with that in control animals by immunohistochemical, morphometric, and scintigraphic analyses. Although satellite cell proliferation was enhanced significantly (up to 96%) by the ultrasound treatment during the early stages of regeneration, there was no such effect on myotube production. The period of rapid fibroblast proliferation was extended from 3 to 4 days in the control group to 7 to 10 days in the ultrasound therapy groups, whereas recapillarization was virtually unaffected. We conclude that although treatment with pulsed ultrasound can promote the satellite cell proliferation phase of the myoregeneration, it does not seem to have significant effects on the overall morphological manifestations of muscle regeneration.

Rupture of the Pectoralis Major Muscle

Background Total or near-total rupture of the pectoralis major muscle is a rare injury. Fewer than 200 cases have been reported in literature, many of them in single case reports. There is discrepancy regarding whether this kind of injury should be treated operatively. Hypothesis Early surgical treatment is necessary to obtain optimal functional recovery following total or near-total ruptures of the pectoralis major muscle. Study Design A case series of 33 operatively treated pectoralis major ruptures combined with a meta-analysis of the previously published cases in the English literature. Methods The authors have retrospectively analyzed 33 operatively treated cases of total or near-total ruptures of the pectoralis major muscle. They have also analyzed the previously published cases and the final outcomes of their treatment. The difference in outcome between groups of acute operation, delayed operation, and conservative treatment in both their own material and meta-analysis was statistically analyzed. Results Both the case series and the analysis of the cases from the literature showed that early operative treatment is associated with better outcome than delayed treatment. The delayed operation was associated with better outcome than the conservative treatment. Conclusion Early surgical treatment by anatomic repair gives the best results in the treatment of total and near-total ruptures of the pectoralis major muscle.

Tension-Band Wiring for Fractures of the Fifth Metatarsal Located in the Junction of the Proximal Metaphysis and Diaphysis

Background Fractures of the proximal fifth metatarsal, other than those involving the tuberosity, have a tendency to delayed union or even nonunion. Hypothesis Tension-band wire technique is a good alternative in treating fractures of the fifth metatarsal located in the proximal junction of the metaphysis and the diaphysis. Study Design Case series; level of evidence, 4. Methods Between 1996 and 2001, a total of 27 cases of proximal metaphysial/diaphysial fractures of the fifth metatarsal were treated with tension-band wiring. All of the patients had undergone prior unsuccessful nonoperative or operative treatment. The mean delay from the diagnosis of the fracture to the final operative procedure was 19.5 weeks (range, 6-48 weeks). Results The mean length of follow-up was 35 months (range, 12-70 months). All patients were able to return to their prior levels of activity. The mean time for union as shown on radiographs was 12.8 weeks, and the return to full activity took 8 to 20 weeks (mean, 14.7 weeks). There were no delayed unions, nonunions, or refractures during the follow-up. Conclusion The tension-band wire technique seems to give good results in the treatment of proximal metaphysial/diaphysial fractures of the fifth metatarsal in cases of primary unsuccessful nonoperative treatment or primary unsuccessful intramedullary screw fixation.

Lumbar Muscles: Structure and Function

We review new data derived from careful dissection studies on the macroscopic anatomy, innervation and function of the lumbar muscles, as well as information on the fibres in these muscles. The new findings correct previous misconceptions of the functional anatomy of the lumbar muscles. The innervation and function of the erector spinae and multifidus muscles are so different that they cannot be classified as a single unit. The new interpretation of the innervation of multifidus muscle is of importance, for example, for the neurophysiological examination of the lumbar muscles. The relative number of the slow and fast type of muscle fibres in lumbar muscles varies considerably, and selective atrophy of the fast fibres seems to ensue from inactivity, not only in patients with back pain but also in sedentary controls. The atrophy may be corrected by adequate exercise. Both the fibre type composition and degree of atrophy may well influence a persons susceptibility to low back pain arising from the muscles.

Effects of early cryotherapy in experimental skeletal muscle injury

The effects of early cryotherapy on healing of rat gastrocnemius muscle injury were investigated in schedules similar to those in clinical use. After the treatment: (1) hematoma between ruptured myofiber stumps was smaller and (2) extravasation of inflammatory cells to the injury site and (3) activation of satellite cells to myotubes and mature myofibers were delayed. Early proliferation of granulation tissue was not altered. Thus, cryotherapy affected the time‐table of the healing process rather than causing qualitative differences. No negative side effects of cryotherapy were found. Positive effects of cryotherapy in clinical practice most likely depend on factors other than those involved with actual regeneration of the muscle lesion, such as reducing muscle spasms, which can cause reruptures, and analgesia allowing early mobilization. The results support the current clinical practice of treating acute muscle fiber ruptures with initial cold application followed by active early mobilization.

Denervated segments of injured skeletal muscle fibers are reinnervated by newly formed neuromuscular junctions

A muscle fiber normally recives its innervation at a single neuromuscular junction (NMJ). Transection of myofiber usually leaves one (abjunctional) stump denervated, while the other (adjunctional) remians innervated. To determine the mechanism of reinnervation of the adjuctional stumps, we transected the rat extensor digitorum muscle (EDL) below the site of the distalmost NMJ> Myofiber regeneration was followed for up to 56 days. Reinnervation began with the appearance of irregular acetylcholinesterase and α-bungarotoxin-positive deposits on abjunctional stumps after 10 to 15 days. These deposits later developed into more regular NMJ. The newly formed NMJ were innervated by sprouting axons which penetrated through the connective tissue scar separating the stumps. While denervated, the myofibers of the abjuctional segments underwent marked atrophy, which was reversed when reinnervation had ensued. In conclusion, we demonstrate for the first time that mature myofiber segments deviod of previous NMJ can induce both sprouting form intact axon terminals and formation of new “ectopic” NMJ on their own surface. This type of reinnervation is likely to occur only when myofibers are asymmetrically transected by a trauma. The signaling molecules possibly involved in this phenomenon are discussed.

Immobilization in neutral versus equinus position after Achilles tendon repair A review of 32 patients

In this retrospective study, we compared Achilles tendon ruptures treated with augmented repair and equinus cast and ruptures treated with end-to-end suture and immobilization of the ankle in neutral position. No differences in the outcome or complication rate were found. We recommend that Achilles tendon rupture should be treated by the simplest method, i.e., end-to-end suture and immobilization of the ankle in neutral position.

Calf muscle atrophy and Achilles tendon healing following experimental tendon division and surgery in rats. Comparison of postoperative immobilization of the muscle-tendon complex in relaxed and tensioned positions.

We used a rat model to study the effects of immobilization of the calf muscle‐tendon complex after an experimental Achilles tendon repair. Immobilizations of the complex in either a relaxed or tensioned position were compared by histochemical and morphometric analyses at the site of the tendon injury as well as in the gastrocnemius and soleus muscle bellies. The type of immobilization did not affect the healing of the tendon injury because no reruptures occurred in either of the treatment groups and the average tendon end‐to‐end distance did not differ between the groups. However, immobilization in a relaxed position led to a significantly more extensive fiber atrophy in the calf muscles. In clinical practice, these results suggest that rehabilitation after Achilles tendon surgery can be early and gradually tension‐ and load‐increasing without a significant increase in the risk of rerupture of the tendon.

Transected myofibres may remain permanently divided in two parts

During regeneration of transected myofibres a scar is formed between their stumps. Myofibres restore their tendon-muscle-tendon continuity and contractile function by attaching to the scar with new myotendinous junctions. The scar contracts with time, and thereby the stumps are pulled close to each other. During early regeneration, myoblasts and myotubes can fuse with the surviving parts of the transected myofibres. However, it is not known whether it is possible that the opposite stumps could eventually fuse to reunite the divided parts of the transected fibres. In this study, we show in rat that even after 12 months the stumps remain attached to the separating scar by myotendinous junctions without showing definite fusion of the stumps. We conclude that transected myofibres probably remain permanently divided in two consecutive tendon-muscle-tendon units.

Mild eccentric stretch injury in skeletal muscle causes transient effects on tensile load and cell proliferation

The biomechanical and regenerative responses in rabbit tibialis anterior muscle following a single eccentric stretch injury were investigated 1, 3 and 7 days after traumatization. The stretch injury produced a transient biomechanical effect. On day 1, the load at failure was decreased in the injured muscles compared with the uninjured controls (P<0.05), but on days 3 and 7 significant biomechanical differences were no longer recorded between the injured and control muscles. In immunohistochemical analyses, no overt myonecrosis or connective tissue disruption was observed in any of the stretch‐injured muscles. Yet satellite cells were activated to incorporate a thymidine analogue, bromodeoxyuridine indicating mitotic activity. They did not, however, produce muscle‐specific proteins, i.e., they did not differentiate further. Furthermore, the intact appearing but mildly injured myofibers of the stretched muscles expressed both neonatal myosin and vimentin near the myotendinous junctions. Collectively, these results suggest that a single mild eccentric stretch of skeletal muscle which does not cause gross structural alterations results in a short‐term decrease in tensile load and induces transient proliferation of satellite cells and fibroblasts together with expression of primitive proteins in myofibers.