Minna Kääriäinen

Muscle Injuries Biology and Treatment

Muscle injuries are one of the most common traumas occurring in sports. Despite their clinical importance, few clinical studies exist on the treatment of these traumas. Thus, the current treatment principles of muscle injuries have either been derived from experimental studies or been tested only empirically. Although nonoperative treatment results in good functional outcomes in the majority of athletes with muscle injuries, the consequences of failed treatment can be very dramatic, possibly postponing an athletes return to sports for weeks or even months. Moreover, the recognition of some basic principles of skeletal muscle regeneration and healing processes can considerably help in both avoiding the imminent dangers and accelerating the return to competition. Accordingly, in this review, the authors have summarized the prevailing understanding on the biology of muscle regeneration. Furthermore, they have reviewed the existing data on the different treatment modalities (such as medication, therapeutic ultrasound, physical therapy) thought to influence the healing of injured skeletal muscle. In the end, they extend these findings to clinical practice in an attempt to propose an evidence-based approach for the diagnosis and optimal treatment of skeletal muscle injuries.

Muscle strain injuries

Muscle injuries--lacerations, contusions or strains--are by far the most common injuries in sports. After first aid following the RICE principle (Rest, Ice, Compression and Elevation), therapy must be tailored according to the severity of the injury and based on the knowledge gained from experimental studies on regeneration of injured muscle. Most muscle injuries can be treated conservatively with excellent recovery, but complete ruptures with complete loss of function should be managed surgically. Immediately after the injury, a short period of immobilization is needed to accelerate formation of the scar between the stumps of the ruptured myofibers, to which the stumps adhere. The optimal length of immobilization depends on the grade of the injury, and should not be longer than needed for the scar to bear the pulling forces without rerupture. Early mobilization is required to invigorate adhesion, orientation of the regenerating muscle fibers, revascularization and resorption of the connective tissue scar. Another important aim of early mobilization, especially in clinical sports medicine, is to minimize inactivity-induced atrophy as well as loss of strength and extensibility, which are rapidly appearing adverse sequelae of prolonged immobilization.

Relation between myofibers and connective tissue during muscle injury repair.

The connective tissue framework in skeletal muscle combines the contractile myofibers into a functional unit, in which the contraction of myofibers is transformed into movement via myotendinous junctions (MTJs) at their ends, where myofibers attach to tendons/fascia. The cytoskeletal contractile myofilament apparatus adheres through subsarcolemmal and transmembrane molecules to the surrounding extracellular matrix, with integrin and dystrophin associated chains of molecules being the two main adhesion complexes. In shearing type of muscle injury both myofibers and the connective tissue framework are ruptured and thereby the functional tendon–muscle–tendon units are disrupted. The stumps of the ruptured myofibers are separated and at the same time joined by a connective tissue scar, through which the ends of regenerating myofibers try to pierce, but as the scar becomes more compact the ends attach to the scar by new mini‐MTJs. During the early phase ruptured myofibers try to compensate for the lost MTJ attachment by reinforcing their integrin mediated lateral adhesion, which returns to normal low level after formation of the mini‐MTJs and at which time complementary increase of dystrophin and associated molecules on lateral sarcolemma takes place. The stumps appear to remain separated by and attached to the interposed scar for many months, possibly for ever, i.e. the original tendon–muscle–tendon units may have become permanently divided into two consecutive units. Remarkably, axon sprouts are able to penetrate through the interposed scar to form new neuromuscular junctions on those abjunctional stumps which were denervated by the rupture.

Integrin and dystrophin associated adhesion protein complexes during regeneration of shearing-type muscle injury

In shearing injury both the myofibres and connective tissue framework are breached and the muscle tendon continuity is disrupted. During regeneration the firm myofibre to extracellular matrix (ECM) adhesion must be re-established. We have analysed the expression of selected molecules implementing this adhesion in regenerating myofibres 2-56 days after transection of rat soleus muscle using quantitative immunohistochemistry and Northern blotting. Beta1 integrin mRNA level and alpha7 integrin and vinculin immunoreactivities were transiently increased in both the intact and regenerating parts of the transected myofibres by day 5-7 with normalization by day 10-14. After day 14, alpha7 integrin and vinculin accumulated at the tips of the regenerating myofibres, indicating formation of new mini-myotendinous junctions (mMTJ). Immunoreactivities for dystrophin and associated proteins as well as merosin appeared in regenerating myotubes by day 3-4 reaching control levels by day 56. Our results suggest that integrin and dystrophin associated molecules are complementary in myofibre-ECM adhesion. During regeneration, ruptured myofibres temporarily reinforce their integrin mediated lateral adhesion until mMTJs are formed. Thereby the load on the newly formed scar and the risk of rerupture are reduced. Dystrophin associated molecules appear later and replace integrin on the lateral aspects, while both complexes are abundant at the mMTJs. These molecular events correspond to our previous results on tensile strength.

Restoration of myofiber continuity after transection injury in the rat soleus.

In a shearing type of muscle injury, scar formation prevents restoration of myofiber continuity and the transected myofibers may become permanently divided into two separate myofibers. We have analysed whether the injured myofiber stumps can fuse and continuity of the transected fibers be re-established, if the stumps are surgically closely apposed immediately after injury. 55 rat soleus muscles were transected, after which the epimysium was carefully sutured and the leg was immobilised for seven days. The animals were sacrificed at 2, 5, 7, 10, 14 and 25 days after surgery. All muscles were analysed by light and electron microscopy as well as by immunohistochemistry. Mechanical strength was also measured at day 10 and 25. We observed that suturing reduced the extent of the intervening scar and accelerated healing. More importantly our results indicate that fusion of the stumps and thus restoration of myofiber continuity, is possible after myofiber transection injury.

Expression of α7β1 Integrin Splicing Variants during Skeletal Muscle Regeneration

Integrin α7β1 is a laminin receptor, both subunits of which have alternatively spliced, developmentally regulated variants. In skeletal muscle β1 has two major splice variants of the intracellular domain (β1A and β1D). α7×1 and α7×2 represent variants of the α7 ectodomain, whereas α7A and α7B are variants of the intracellular domain. Previously we showed that during early regeneration after transection injury of muscle α7 integrin mediates dynamic adhesion of myofibers along their lateral aspects to the extracellular matrix. Stable attachment of myofibers to the extracellular matrix occurs during the third week after injury, when new myotendinous junctions develop at the ends of the regenerating myofibers. Now we have analyzed the relative expression of β1A/β1D and α7A/α7B and α7×1/α7×2 isoforms during regeneration for 2 to 56 days after transection of rat soleus muscle using reverse transcriptase-polymerase chain reaction and immunohistochemistry. During early regeneration β1A was the predominant isoform in both the muscle and scar tissue. Expression of muscle-specific β1D was detected in regenerating myofibers from day 4 onwards, ie, when myogenic mitotic activity began to decrease, and it became more abundant with the progression of regeneration. α7B isoform predominated on day 2. Thereafter, the relative expression of α7A transcripts increased until day 7 with the concomitant appearance of α7A immunoreactivity on regenerating myofibers. Finally, α7B again became the predominant variant in highly regenerated myofibers. Similarly as in the controls, α7×1 and α7×2 isoforms were both expressed throughout the regeneration with a peak in α7×1 expression on day 4 coinciding with the dynamic adhesion stage. The results suggest that during regeneration of skeletal muscle the splicing of β1 and α7 integrin subunits is regulated according to functional requirements. α7A and α7×1 appear to have a specific role during the dynamic phase of adhesion, whereas α7B, α7×2, and β1D predominate during stable adhesion.

Regulation of α7 integrin by mechanical stress during skeletal muscle regeneration

Abstract The continuity of the tendon–myofibre–tendon units disrupted by shearing injury must be re-established during regeneration. We have previously demonstrated in freely moving rats that transected myofibres reinforce their lateral integrin-mediated adhesion, with the maximum around days 5–7. After day 14, most integrin molecules are redistributed to the newly formed myotendinous junctions, by which the ends of regenerating myofibres attach to the scar between the stumps. Here, we analyzed the effects of mechanical stress (free and forced mobilization vs. immobilization and denervation separately and in combination) on the expression of α7 integrin and merosin in regenerating myofibres using quantitative in situ hybridization and immunohistochemistry. In all groups, α7 integrin expression was upregulated at mRNA level, whereas increased protein accumulation in lateral sarcolemma occurred only in the mobilized groups. The accumulation of merosin was not affected by the stress level. The results demonstrate that active mechanical stress reinforces early lateral integrin-mediated adhesion; molecules may at the same time mediate signals from matrix to cells for adaptation to the altered biomechanical status.

Skeletal muscle injury and repair: the effect of disuse and denervation on muscle and clinical relevance in pedicled and free muscle flaps.

Skeletal muscle is prone to injury upon trauma or nerve damage. In reconstructive surgery, it is an interesting spare part. Fortunately, skeletal muscle is capable of extensive regeneration. Satellite cells, quiescent myogenic precursor cells, become activated following muscle injury: they divide and form myoblasts, fuse into myotubes, and finally mature to myofibers. Denervation in muscle or muscle flaps leads to myofiber atrophy, fibrosis, and fatty tissue infiltration. Experiments show that muscle flaps that are reinnervated also display a fair amount of atrophy. Muscle mass is better preserved after motor innervation than sensory innervation. Clinical data imply that innervation of the muscle flap does not improve volume preservation significantly compared with denervated flaps. In addition, the softness of the flap remains the same whether the flap is innervated or not. Innervation of the flap seems to be needed only if functional muscle reconstruction is the goal. If reinnervation is successful but the muscle is kept short, disuse atrophy will still proceed. Muscle flaps should therefore be placed into their original length.

Utilization of Three-Dimensional Computer-Aided Preoperative Virtual Planning and Manufacturing in Maxillary and Mandibular Reconstruction with a Microvascular Fibula Flap

BACKGROUND The aim of this study was to analyze the effects of computer-aided three-dimensional virtual planning and the use of customized cutting guides in maxillary and mandibular reconstruction with a microvascular fibula flap. METHODS Patients (n = 17) undergoing free fibula flap (n = 18) reconstruction of the maxilla (n = 2) or mandible (n = 15) from January 2012 through March 2014 were enrolled in the study. Preoperatively, patients underwent high-resolution computed tomography of the maxillofacial and lower leg regions. Three-dimensional virtual planning of the resection and reconstruction was performed. Customized cutting guides for maxillary/mandibular resections and fibular osteotomies, and prebend plates were manufactured. Demographic data, surgical factors, and perioperative and postoperative results were evaluated. RESULTS Sixteen patients had malignant disease and one had benign disease. Sixteen of the flaps were osteomuscular and two were osteomusculocutaneous. Mean ischemia time was 99 minutes and mean operative time was 542 minutes. The flaps fitted into the defects precisely and no bone grafts were needed. Mean length of the fibula flap was 74 mm and the mean number of segments in the flap was 2.1. CONCLUSION Three-dimensional computer-aided preoperative virtual planning allowed for precise planning of the tumor resection and size of the fibula flap, the number and placement of the osteotomies needed, and the manufacture of customized cutting guides. Fibular shaping is easier and faster, which may decrease the ischemia time and total operative time. Exact placement of the flap in the defect may facilitate restoration of the anatomic shape and ossification.

Greater Success of Primary Fascial Closure of the Open Abdomen: A Retrospective Study Analyzing Applied Surgical Techniques, Success of Fascial Closure, and Variables Affecting the Results

Background and Aims: The open abdomen technique is a standard procedure in the treatment of intra-abdominal catastrophe. Achieving primary abdominal closure within the initial hospitalization is a main objective. This study aimed to analyze the success of closure rate and the effect of negative pressure wound therapy, mesh-mediated medial traction, and component separation on the results. We present the treatment algorithm used in our institution in open abdomen situations based on these findings. Material and Methods: Open abdomen patients (n = 61) treated in Tampere University Hospital from May 2005 until October 2013 were included in the study. Patient characteristics, treatment prior to closure, closure technique, and results were retrospectively collected and analyzed. The first group included patients in whom direct or bridged fascial closure was achieved, and the second group included those in whom only the skin was closed or a free skin graft was used. Background variables and variables related to surgery were compared between groups. Results and Conclusion: Most of the open abdomen patients (72.1%) underwent fascial defect repair during the primary hospitalization, and 70.5% of them underwent direct fascial closure. Negative pressure wound therapy was used as a temporary closure method for 86.9% of the patients. Negative pressure wound therapy combined with mesh-mediated medial traction resulted in the shortest open abdomen time (p = 0.039) and the highest fascial repair rate (p = 0.000) compared to negative pressure wound therapy only or no negative pressure wound therapy. The component separation technique was used for 11 patients; direct fascial closure was achieved in 5 and fascial repair by bridging the defect with mesh was achieved in 6. A total of 8 of 37 (21.6%) patients with mesh repair had a mesh infection. The negative pressure wound therapy combined with mesh-mediated medial traction promotes definitive fascial closure with a high closure rate and a shortened open abdomen time. The component separation technique can be used to facilitate fascial repair but it does not guarantee direct fascial closure in open abdomen patients.