Nicolas Holzer

Membrane Hyperpolarization Triggers Myogenin and Myocyte Enhancer Factor-2 Expression during Human Myoblast Differentiation

It is widely thought that myogenin is one of the earliest detectable markers of skeletal muscle differentiation. Here we show that, during human myoblast differentiation, an inward rectifier K+ channel (Kir2.1) and its associated hyperpolarization trigger expression and activity of the myogenic transcription factors, myogenin and myocyte enhancer factor-2 (MEF2). Furthermore, Kir2.1 current precedes and is required for the developmental increase in expression/activity of myogenin and MEF2. Drugs or antisense reducing Kir2.1 current diminished or suppressed fusion as well as expression/activity of myogenin and MEF2. In contrast, LY294002, an inhibitor of phosphatidylinositol 3-kinase (a pathway controlling initiation of the myogenic program) that inhibited both myogenin/MEF2 expression and fusion, did not affect Kir2.1 current. This non-blockade by LY294002 indicates that Kir2.1 acts upstream of myogenin and MEF2. We propose that Kir2.1 channel activation is a required key early event that initiates myogenesis by turning on myogenin and MEF2 transcription factors via a hyperpolarization-activated Ca2+-dependent pathway.

Autologous transplantation of porcine myogenic precursor cells in skeletal muscle

Myoblast transplantation is a potential therapy for severe muscle trauma, myopathies and heart infarct. Success with this therapy relies on the ability to obtain cell preparations enriched in myogenic precursor cells and on their survival after transplantation. To define myoblast transplantation strategies applicable to patients, we used a large animal model, the pig. Muscle dissociation procedures adapted to porcine tissue gave high yields of cells containing at least 80% myogenic precursor cells. Autologous transplantation of 3[H]-thymidine labeled porcine myogenic precursor cells indicated 60% survival at day 1 followed by a decay to 10% at day 5 post-injection. Nuclei of myogenic precursor cells transduced with a lentivirus encoding the nls-lacZ reporter gene were present in host myotubes 8 days post-transplantation, indicating that injected myogenic precursor cells contribute to muscle regeneration. This work suggests that pig is an adequate large animal model for exploring myogenic precursor cells transplantation strategies applicable in patients.

Calcium sources used by post-natal human myoblasts during initial differentiation.

Increases in cytoplasmic Ca2+ are crucial for inducing the initial steps of myoblast differentiation that ultimately lead to fusion; yet the mechanisms that produce this elevated Ca2+ have not been fully resolved. For example, it is still unclear whether the increase comes exclusively from membrane Ca2+ influx or also from Ca2+ release from internal stores. To address this, we investigated early differentiation of myoblast clones each derived from single post‐natal human satellite cells. Initial differentiation was assayed by immunostaining myonuclei for the transcription factor MEF2. When Ca2+ influx was eliminated by using low external Ca2+ media, we found that approximately half the clones could still differentiate. Of the clones that required influx of external Ca2+, most clones used T‐type Ca2+ channels, but others used store‐operated channels as influx‐generating mechanisms. On the other hand, clones that differentiated in low external Ca2+ relied on Ca2+ release from internal stores through IP3 receptors. Interestingly, by following clones over time, we observed that some switched their preferred Ca2+ source: clones that initially used calcium release from internal stores to differentiate later required Ca2+ influx and inversely. In conclusion, we show that human myoblasts can use three alternative mechanisms to increase cytoplasmic Ca2+ at the onset of the differentiation process: influx through T‐types Ca2+ channels, influx through store operated channels and release from internal stores through IP3 receptors. In addition, we suggest that, probably because Ca2+ elevation is essential during initial differentiation, myoblasts may be able to select between these alternate Ca2+ pathways. J. Cell. Physiol. 208: 435–445, 2006.

Radiographic evaluation of posttraumatic osteoarthritis of the ankle: the Kellgren–Lawrence scale is reliable and correlates with clinical symptoms

OBJECTIVE To assess reliability and construct validity of the Kellgren-Lawrence (K&L) scale in posttraumatic ankle osteoarthritis (OA); additionally evaluate the validity of including tibiotalar tilting in the scale. METHOD One-hundred and fifty ankle radiographs (75 patients, unilateral malleolar fractures) evaluated at average of 18 years after surgery. American Orthopaedic Foot & Ankle Society (AOFAS) ankle-hindfoot (HF) score and pain (visual analog scale) were recorded. Grading of OA according to K&L criteria and identification of OA features was performed on standardized radiographs by four physicians. Minimal joint space width, sclerosis, and talar tilt angle were quantified by digital measurements. A modified K&L scale including talar tilting is presented. Validity of original and modified scale was evaluated and expressed as ability to (1) Identify those with clinical symptoms of ankle OA; and (2) Distinguish between different degrees of fracture severity. RESULTS Inter- and intra-observer reliability of OA assessment according to K&L were good (ICC 0.61 and 0.75). Original and modified K&L grades significantly increased with decreasing AOFAS ankle-HF scores and greater pain. A talar-tilt angle > 2° compared with ≤ 2° in grade 3 was associated with significantly higher pain levels (VAS pain 4.2 vs 1.4, respectively; mean difference 2.8, 95% CI 0.5-5.1). More severe fracture patterns at time of surgery were more often in patients with the highest K&L grades. CONCLUSIONS The K&L scale is a valid and reliable radiographic grading system for assessment of ankle OA. Inclusion of the talar tilt angle might allow for better differentiation with respect to clinical outcomes.

Angled BIO-RSA (bony-increased offset-reverse shoulder arthroplasty): a solution for the management of glenoid bone loss and erosion.

BACKGROUND Glenoid deficiency and erosion (excessive retroversion/inclination) must be corrected in reverse shoulder arthroplasty (RSA) to avoid prosthetic notching or instability and to maximize function, range of motion, and prosthesis longevity. This study reports the results of RSA with an angled, autologous glenoid graft harvested from the humerus (angled BIO-RSA). METHODS A trapezoidal bone graft, harvested from the humeral head and fixed with a long-post baseplate and screws, was used to compensate for residual glenoid bone loss/erosion. For simple to moderate (<25°) glenoid defects, standardized instrumentation combined with some eccentric reaming (<15°) was used to reconstruct the glenoid and obtain neutral implant alignment. For severe (>25°) and complex (multiplanar) glenoid bone defects, patient-specific grafts and guides were used after 3-dimensional planning. Patients were reviewed with minimum 2 years of follow-up. Mean follow-up was 36 months (range, 24-81 months). Preoperative and postoperative measurements of inclination and version were performed in the plane of the scapula on computed tomography images. RESULTS The study included 54 patients (41 women, 13 men; mean 73 years old). Fifteen patients had combined vertical and horizontal glenoid bone deficiency. Among E2/E3 glenoids, inclination improved from 37° (range, 14° to 84°) to 10.2° (range -28° to 36°, P < .001). Among B2/C glenoids, retroversion improved from -21° (range, -49° to 0°) to -10.6° (-32° to 4°, P = .06). Complete radiographic incorporation of the graft occurred in 94% (51 of 54). Complications included infection in 1 and clinical aseptic baseplate loosening in 2. Mild notching occurred in 25% (13 of 51) of patients. Constant-Murley and Subjective Shoulder Value assessments increased from 31 to 68 and from 30% to 83%, respectively (P < .001). CONCLUSION Angled BIO-RSA predictably corrects glenoid deficiency, including severe (>25°) multiplanar deformity. Graft incorporation is predictable. Advantages of using an autograftharvested in situ include bone stock augmentation, lateralization, low donor-site morbidity, low relative cost, and flexibility needed to simultaneously correct posterior and superior glenoid defects.

Shoulder strengthening exercises adapted to specific shoulder pathologies can be selected using new simulation techniques: a pilot study

PurposeShoulder strength training exercises represent a major component of rehabilitation protocols designed for conservative or postsurgical management of shoulder pathologies. Numerous methods are described for exercising each shoulder muscle or muscle group. Limited information is available to assess potential deleterious effects of individual methods with respect to specific shoulder pathologies. Thus, the goal of this pilot study was to use a patient-specific 3D measurement technique coupling medical imaging and optical motion capture for evaluation of a set of shoulder strength training exercises regarding glenohumeral, labral and subacromial compression, as well as elongation of the rotator cuff muscles.MethodsOne volunteer underwent magnetic resonance imaging (MRI) and motion capture of the shoulder. Motion data from the volunteer were recorded during three passive rehabilitation exercises and twenty-nine strengthening exercises targeting eleven of the most frequently trained shoulder muscles or muscle groups and using four different techniques when available. For each exercise, glenohumeral and labral compression, subacromial space height and rotator cuff muscles elongation were measured on the entire range of motion.ResultsSignificant differences in glenohumeral, subacromial and labral compressions were observed between sets of exercises targeting individual shoulder muscles. Muscle lengths computed by simulation compared to MRI measurements showed differences of 0–5%.ConclusionsThis study represents the first screening of shoulder strengthening exercises to identify potential deleterious effects on the shoulder joint. Motion capture combined with medical imaging allows for reliable assessment of glenohumeral, labral and subacromial compression, as well as muscle-tendon elongation during shoulder strength training exercises.

Latarjet-Patte Triple-locking Procedure for Recurrent Anterior Instability

Indication to perform an anterior glenoid augmentation by means of a coracoid bone graft in the setting of anterior instability in particular subsets of patients emerges as a new standard of care. Surgical techniques originally described by Latarjet and Helfet were modified by Patte in 1980. The coracoid graft is lying in supine position held in place by a single screw. Systematic capsular retensioning adds a capsular lock to the classical bone block and sling effect of the Latarjet technique. We hypothesized that systematic capsular retensioning could reduce the recurrence rate of instability after surgical stabilization compared with other described techniques. A questionnaire as well as a radiologic workout was obtained from a consecutive series of patients who had undergone this procedure by the same operator between 1986 and 2006. Outcome was determined by the number of redislocations, number of reoperations, the Walch-Duplay score including pain score, and the index of satisfaction. A total of 148 patients responded (42 women and 106 men) with a mean age 28.4±8.7 years (range, 16 to 57 y). The mean follow-up was 14.6 years (range, 2.8 to 22.6 y). Thirty-two patients had hyperlaxity (21%). Three patients (2%) sustained a redislocation or resubluxation. However, none required further operation. Results of the Walch-Duplay score were excellent or good. Fifty-three percent of the patients were pain free, 34% presented occasional pain, 9% moderate pain, and 4% suffered from severe pain. Seventy-nine percent of patients were very satisfied, 18% were satisfied, and 3% were dissatisfied. Mid-term to long-term results of the modification of the Latarjet procedure according to Patte correlate with previous studies with respect to patient satisfaction and functional outcome. The recurrence rate is lower than in previously reported series and may reflect the beneficial effect of systemic capsular retensioning on a flap of coracoacromial ligament. Evidence level IV: Single-surgeon therapeutic case series.

The greater tuberosity angle: a new predictor for rotator cuff tear

BACKGROUND The implication of scapular morphology in rotator cuff tears has been extensively studied. However, the role of the greater tuberosity (GT) should be of equal importance. The aim of this study was to propose a new radiographic marker, the GT angle (GTA), which measures the position of the GT in relation to the center of rotation of the humeral head. The hypothesis was that a higher angle value would be associated with a higher likelihood in detecting a rotator cuff tear. METHODS During 1 year, patients were prospectively recruited from a single institution specialized shoulder clinic in 2 different groups. The patient group consisted of individuals with a degenerative rotator cuff tear involving at least the supraspinatus. The control group consisted of individuals with no rotator cuff pathology. Individuals in both groups with congenital, post-traumatic, or degenerative alterations of the proximal humerus were excluded. The GTA was measured on an anteroposterior shoulder x-ray image with the arm in neutral rotation by 3 observers at 2 different times. RESULTS The study recruited 71 patients (33 patients, 38 controls). Mean GTA value was 72.5° (range, 67.6°-79.2°) in patients and 65.2° (range, 55.8°-70.5°) for controls (P <.001). A value above 70° resulted in 93-fold higher odds of detecting a rotator cuff tear (P <.001). Interobserver and intraobserver reliability were high. CONCLUSIONS GT morphology is implicated in rotator cuff tears. The GTA is a reliable radiographic marker, with more than 70° being highly predictive in detecting such lesions.