Sternalis featuring tendomuscular fusion to the contralateral sternocleidomastoid: a cadaveric case report.

PURPOSE: To report the morphologic and spatial relationships of a bilateral sternalis muscle variant. METHODS: Routine cadaveric dissection in an undergraduate anatomy laboratory revealed two sternalis muscles parasternal to the sternal body. Subsequent fine prosection of the anterior thoracic wall and neck was carried out to uncover the soft tissue attachments of both sternalis muscles. Positional relationship to neighboring anterior thoracic and neck structures, and geometric dimensions of the muscle bellies and tendons, were documented. RESULTS: Both sternalis muscles were imbedded in the pectoral fascia, with their muscle fibers running obliquely to the midsternal line. The right sternalis muscle was notably larger in length, width, and thickness compared to the sternalis muscle on the left. The right sternalis muscle featured a distinct superior cord-like intermediate tendon that traversed superolateral and fused directly with the contralateral sternomastoid and sterno-occipital portions of the left sternocleidomastoid muscle. The superior tendon of the left sternalis muscle was aponeurotic and affixed to the cord-tendon of the right sternalis muscle. A distinct tendinous entheses for the sternal head for both sternocleidomastoid muscles were noted at the manubrial body. CONCLUSIONS: This case report describes a unique bilateral sternalis muscle variant with conjoined sternocleidomastoid muscle integration. This anatomical description of a sternalis-sternocleidomastoid muscle morphology may supplement radiographic interpretations and support diagnostic accuracy.

Perception of effort during an isometric contraction is influenced by prior muscle lengthening or shortening.

PURPOSE: Following a shortening or lengthening muscle contraction, torque produced in the isometric steady state is lower (residual torque depression; rTD) or higher (residual torque enhancement; rTE), respectively, compared to a purely isometric contraction at the same final muscle length and level of activation. This is referred to as the history dependence of force. When matching a given torque level, there is greater muscle activation (electromyography; EMG) following shortening and less activation following lengthening. Owing to these differences in neuromuscular activation, it is unclear whether perception of effort is altered by the history dependence of force during plantar-flexion. METHODS: Experiment 1 tested whether perception of effort differed between the rTD and rTE state when torque was matched. Experiment 2 tested whether perception of effort differed between the rTD and rTE state when EMG was matched. Finally, experiment 3 tested whether EMG differed between the rTD and rTE state when perception of effort was matched. RESULTS: When torque was matched, both EMG and perception of effort were higher in the rTD compared to rTE state. When EMG was matched, torque was lower in the rTD compared to rTE state while perception of effort did not differ between the two states. When perception of effort was matched, torque was lower in the rTD compared to rTE state and EMG did not differ between the two states. CONCLUSION: The combined results from these experiments indicate that the history dependence of force alters one's perception of effort, dependent on the level of motor command.

Comparison of the spread pattern of medial-to-lateral and lateral-to-medial rotator interval injections: A cadaveric study.

Objective: Rotator interval (RI) corticosteroid injections are used to alleviate pain associated with adhesive capsulitis, though the pattern of injectate spread remains unclear. The purpose of this anatomical study was to assess the staining patterns of intra-articular, intracapsular/extrasynovial, and pericapsular structures of the glenohumeral joint following medial-to-lateral and lateral-to-medial RI injections. Design: Ten cadaveric specimens were injected with a methylene blue dye injectate: five using a medial-to-lateral RI injection technique and five using a lateral-to-medial RI injection technique. Serial dissection was performed to assess the staining of intra-articular, intracapsular/extrasynovial, and pericapsular structures. The frequency of capture and degree of staining were compared between injection groups. Results: The lateral-to-medial injection resulted in the capture of all intra-articular; intracapsular/extrasynovial; and pericapsular structures, whereas the medial-to-lateral injection did not consistently stain all structures. Intracapsular/extrasynovial structures (superior glenohumeral ligament and the long head of biceps tendon) were more darkly stained in the lateral-to-medial group, and pericapsular structures (supraspinatus tendon and coracohumeral ligament) were more darkly stained in the medial-to-lateral group. Conclusion: The frequency of capture and degree of staining of intra-articular, intracapsular/extrasynovial, and pericapsular structures of the glenohumeral joint differed between medial-to-lateral and lateral-to-medial RI injection techniques, which may influence outcomes in pain management for adhesive capsulitis.

Differential effects of the 1,25D3-MARRS receptor (ERp57/PDIA3) on murine mammary gland development depend on the vitamin D3 dose.

1,25 dihydroxyvitamin D3 (1,25D3) is the most potent biologically active form of vitamin D3. Its actions on the mammary gland include cell growth inhibition and anti-cancer effects. This study's purpose was to explore the role of the 1,25D3-membrane associated rapid response steroid (MARRS) receptor in the mammary gland using a tissue-specific knockout mouse model and a vitamin D3 dietary intervention. Three genotype groups were created using the Cre/loxp system to knock-down (+/-) and knockout (-/-) the MARRS receptor in epithelial cells of mammary glands (MG). Abdominal MGs were collected from 6-week old female mice (n = 94) on diets of 10,000 IU/kg (excess), 1,000 IU/kg (sufficient) or 0 IU/kg (deficient) of D3. There was a significant interaction between genotype and diet regarding number of terminal end buds (TEBs) (p = 0.001) and ductal coverage of the fat pad (p = 0.03). MARRS -/- mice on the sufficient diet had significantly fewer TEBs (p = 0.001) compared to MARRS +/+ on the same diet, but the opposite effect was seen in mice on the excess diet. There were no effects of genotype on TEBs when animals were vitamin D3 deficient. These results suggest that there is an effect of MARRS on mammary gland development that is dependent on 25(OH)D status, specifically, altering the number of highly proliferative TEBs. Increased numbers of TEBs have been correlated with increased breast cancer risk later in life. Therefore the results of this study warrant further examination of 25(OH)D status and recommendations in adolescent humans to reduce dietary effects on future breast cancer risk.

The influence of residual force enhancement on spinal and supraspinal excitability.

BACKGROUND: Following active muscle lengthening, there is an increase in steady-state isometric force as compared with a purely isometric contraction at the same muscle length and level of activation. This fundamental property of skeletal muscle is known as residual force enhancement (RFE). While the basic mechanisms contributing to this increase in steady-state isometric force have been well documented, changes in central nervous system (CNS) excitability for submaximal contractions during RFE are unclear. The purpose of this study was to investigate spinal and supraspinal excitability in the RFE isometric steady-state following active lengthening of the ankle dorsiflexor muscles. METHODS: A total of 11 male participants (20-28 years) performed dorsiflexions at a constant level of electromyographic activity (40% of maximum). Half of the contractions were purely isometric (8 s at an ankle angle of 130°), and the other half were during the RFE isometric steady-state following active lengthening (2 s isometric at 90°, a 1 s lengthening phase at 40°/s, and 5 s at 130°). Motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs), and compound muscle action potentials (M-waves) were recorded from the tibialis anterior during the purely isometric contraction and RFE isometric steady-state. RESULTS: Compared to the purely isometric condition, following active lengthening, there was 10% RFE (p < 0.05), with a 17% decrease in normalized CMEP amplitude (CMEP/Mmax) (p < 0.05) and no change in normalized MEP amplitude (MEP/CMEP) (p > 0.05). DISCUSSION: These results indicate that spinal excitability is reduced during submaximal voluntary contractions in the RFE state with no change in supraspinal excitability. These findings may have further implications to everyday life offering insight into how the CNS optimizes control of skeletal muscle following submaximal active muscle lengthening.

Spinal excitability is increased in the torque-depressed isometric steady state following active muscle shortening.

Torque depression (TD) is the reduction in steady-state isometric torque following active muscle shortening when compared with a purely isometric contraction at the same muscle length and level of activation. The purpose of the present study was to assess spinal and supraspinal excitability in the TD state during submaximal contractions of the dorsiflexors. Eleven young (24 ± 2 yrs) males performed 16 contractions at a constant level of electromyographic activity (40% of maximum). Half of the contractions were purely isometric (8 s at an ankle angle of 100°), whereas the other half induced TD (2 s isometric at 140°, a 1 s shortening phase at 40°â€…s-1 and 5 s at 100°). Motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs) and compound muscle action potentials (M-waves) were recorded from tibialis anterior during the TD steady-state and purely isometric contractions. When compared with values in the purely isometric condition, following active shortening, there was a 13% decrease in torque (p < 0.05), with a 10% increase in normalized CMEP amplitude (CMEP/Mmax) (p < 0.05) and no change in normalized MEP amplitude (MEP/CMEP) in the TD state (p > 0.05). These findings indicate that during voluntary contractions in the TD state, the history-dependent properties of muscle can increase spinal excitability and influence voluntary control of submaximal torque production.