SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Humerus

170

Influential theories of imitation have proposed that humans inherit a neural mechanism - an “active intermodal matching ” (AIM) mechanism or a mirror neuron system - that functions from birth to automatically match sensory input from others' actions to motor programs for performing those same actions, and thus produces imitation. To test these proposals, 160 1- to 2½-year-old toddlers were asked to imitate two simple movements- bending the arm to make an elbow, and moving the bent elbow laterally. Both behaviors were almost certain to be in each child’s repertoire, and the lateral movement was goal-directed (used to hit a plastic cup). Thus, one or both behaviors should have been imitable by toddlers with a functioning AIM or mirror neuron system. Each child saw the two behaviors repeated 18 times, and was encouraged to imitate. Children were also asked to locate their own elbows. Almost no children below age 2 imitated either behavior. Instead, younger children gave clear evidence of a developmental progression, from reproducing only the outcome of the models' movements (hitting the object), through trying (but failing) to reproduce the model’s arm posture and/or the arm-cup relations they had seen, to accurate imitation of arm bending by age 2 and of both movements by age 2½. Across age levels, almost all children who knew the word ‘elbow’ imitated both behaviors: very few who did not know the word imitated either behavior. The evidence is most consistent with a view of early imitation as the product of a complex system of language, cognitive, social, and motor competencies that develop in infancy. The findings do not rule out a role for an inherited neural mechanism, but they suggest that such a system would not by itself be sufficient to explain imitation at any age.

Concepts: Psychology, Human, Reproduction, Humerus, Motor control, Child, Childhood, Mirror neuron

170

A 46-year old male patient was admitted with a history of an extremely painful right upper arm, associated with unilateral clubbing. Duplex scanning and magnetic resonance imaging were suggestive of a pseudo-aneurysm of the brachial artery. Digital angiography showed an irregular brachial artery, associated with a small pseudo-aneurysm. The brachial artery was partially resected and reconstructed with a venous interposition graft. Pathological examination provided the final diagnosis of fibromuscular dysplasia. Although more encountered in women, this case report describes the occurrence of fibromuscular dysplasia in an unusual location in a male patient with a long-term follow-up.

Concepts: X-ray, Blood pressure, Medical imaging, Nuclear magnetic resonance, Magnetic resonance imaging, Humerus, Radiology, Brachial plexus

169

Changes in muscle activities are commonly associated with shoulder impingement and theoretically caused by changes in motor program strategies. The purpose of this study was to assess for differences in latencies and deactivation times of scapular muscles between subjects with and without shoulder impingement. Twenty-five healthy subjects and 24 subjects with impingement symptoms were recruited. Glenohumeral kinematic data and myoelectric activities using surface electrodes from upper trapezius (UT), lower trapezius (LT), serratus anterior (SA) and anterior fibers of deltoid were collected as subjects raised and lowered their arm in response to a visual cue. Data were collected during unloaded, loaded and after repetitive arm raising motion conditions. The variables were analyzed using 2 or 3 way mixed model ANOVAs. Subjects with impingement demonstrated significantly earlier contraction of UT while raising in the unloaded condition and an earlier deactivation of SA across all conditions during lowering of the arm. All subjects exhibited an earlier activation and delayed deactivation of LT and SA in conditions with a weight held in hand. The subjects with impingement showed some significant differences to indicate possible differences in motor control strategies. Rehabilitation measures should consider appropriate training measures to improve movement patterns and muscle control.

Concepts: Muscle, Humerus, Shoulder, Deltoid muscle, Clavicle, Glenohumeral joint, Scapula, Serratus anterior muscle

73

Bone abnormalities are common in theropod dinosaur skeletons, but before now no specimen was known with more than four afflicted bones of the pectoral girdle and/or forelimb. Here we describe the pathology of a specimen of the theropod dinosaur Dilophosaurus wetherilli with eight afflicted bones of the pectoral girdle and forelimb. On its left side the animal has a fractured scapula and radius and large fibriscesses in the ulna and the proximal thumb phalanx. On its right side the animal has abnormal torsion of the humeral shaft, bony tumors on the radius, a truncated distal articular surface of metacarpal III, and angular deformities of the first phalanx of the third finger. Healing and remodeling indicates that the animal survived for months and possibly years after its ailments began, but its right third finger was permanently deformed and lacked the capability of flexion. The deformities of the humerus and the right third finger may be due to developmental osteodysplasia, a condition known in extant birds but unreported in non-avian dinosaurs before now.

Concepts: Bone, Skeletal system, Humerus, Bird, Dinosaur, Theropoda, Ceratosauria, Dilophosauridae

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PURPOSE: It is commonly stated that supraspinatus initiates abduction; however, there is no direct evidence to support this claim. Therefore, the aims of the present study were to determine whether supraspinatus initiates shoulder abduction by activating prior to movement and significantly earlier than other shoulder muscles and to determine if load or plane of movement influenced the recruitment timing of supraspinatus. METHODS: Electromyographic recordings were taken from seven shoulder muscles of fourteen volunteers during shoulder abduction in the coronal and scapular planes and a plane 30° anterior to the scapular plane, at 25%, 50% and 75% of maximum load. Initial activation timing of a muscle was determined as the time at which the average activation (over a 25ms moving window) was greater than three standard deviations above baseline measures. RESULTS: All muscles tested were activated prior to movement onset. Subscapularis was activated significantly later than supraspinatus, infraspinatus, deltoid and upper trapezius, while supraspinatus, infraspinatus, upper trapezius, lower trapezius, serratus anterior and deltoid all had similar initial activation times. The effects of load or plane of movement were not significant. CONCLUSIONS: Supraspinatus is recruited prior to movement of the humerus into abduction but not earlier than many other shoulder muscles, including infraspinatus, deltoid and axioscapular muscles. The common statement that supraspinatus initiates abduction is therefore, misleading.

Concepts: Humerus, Shoulder, Rotator cuff, Supraspinatus muscle, Deltoid muscle, Muscles of the upper limb, Scapula, Serratus anterior muscle

33

We describe and analyze a Neandertal postcranial skeleton and dentition, which together show unambiguous signs of right-handedness. Asymmetries between the left and right upper arm in Regourdou 1 were identified nearly 20 years ago, then confirmed by more detailed analyses of the inner bone structure for the clavicle, humerus, radius and ulna. The total pattern of all bones in the shoulder and arm reveals that Regourdou 1 was a right-hander. Confirmatory evidence comes from the mandibular incisors, which display a distinct pattern of right oblique scratches, typical of right-handed manipulations performed at the front of the mouth. Regourdou’s right handedness is consistent with the strong pattern of manual lateralization in Neandertals and further confirms a modern pattern of left brain dominance, presumably signally linguistic competence. These observations along with cultural, genetic and morphological evidence indicate language competence in Neandertals and their European precursors.

Concepts: Bone, Humerus, Ulna, Left-handedness, Upper limb anatomy, Upper limb, Handedness, Right-handedness

28

The deltoid is a fascinating muscle with a significant role in shoulder function. It is comprised of three distinct portions (anterior or clavicular, middle or acromial, and posterior or spinal) and acts mainly as an abductor of the shoulder and stabilizer of the humeral head. Deltoid tears are not infrequently associated with large or massive rotator cuff tears and may further jeopardize shoulder function. A variety of other pathologies may affect the deltoid muscle including enthesitis, calcific tendinitis, myositis, infection, tumors, and chronic avulsion injury. Contracture of the deltoid following repeated intramuscular injections could present with progressive abduction deformity and winging of the scapula. The deltoid muscle and its innervating axillary nerve may be injured during shoulder surgery, which may have disastrous functional consequences. Axillary neuropathies leading to deltoid muscle dysfunction include traumatic injuries, quadrilateral space and Parsonage-Turner syndromes, and cause denervation of the deltoid muscle. Finally, abnormalities of the deltoid may originate from nearby pathologies of subdeltoid bursa, acromion, and distal clavicle.

Concepts: Humerus, Shoulder, Rotator cuff, Deltoid muscle, Axillary nerve, Clavicle, Scapula, Acromion

28

Purpose: Snapping ulnar nerve syndrome (dislocation of the ulnar nerve over the medial epicondyle) is one of many causes of ulnar neuropathy at the elbow. This preliminary study was performed to search for sonographic signs suggesting the presence of this condition.Methods and Materials: We retrospectively investigated 11 patients with snapping ulnar nerve syndrome (SNAP) in comparison with an age-matched group of 20 patients with idiopathic cubital tunnel syndrome (SNU). Patients were grouped according to the presence of paretic or merely sensory deficits. Nerve cross section area (CSA) and thickness of outer epineurium (ET) was measured and correlated with neurological findings. Statistical differences were evaluated with the Mann-Whitney U-Test.Results: 5 SNAP (10 SNU) patients had sensory symptoms only, 6 SNAP (10 SNU) patients had paretic deficits. CSA in sensory SNU was 0.14 cm2, in paretic SNU 0.19 cm2, in sensory SNAP 0.15 cm2 and in paretic SNAP 0.14 cm2. ET in sensory SNU was 0.85 mm, 0.8 mm in paretic SNU, 1.05 mm in sensory SNAP and 1.1 in paretic SNAP. Differences in CSA were not significant depending on symptoms or group, differences in ET were not significant depending on symptoms but on group (SNAP versus SNU) at α = 0.05.Conclusion: A thickened, hyperechoic outer epineurium in a patient with ulnar neuropathy at the elbow might be a statistically significant differential feature of snapping ulnar nerve syndrome and should be involved in a further functional sonographic evaluation during flexion/extension of the elbow.

Concepts: Statistics, Statistical significance, Humerus, Upper limb anatomy, Ulnar nerve, Median nerve, Cubital tunnel, Ulnar nerve entrapment

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PURPOSE: This study compared the status of suture knots immediately after repair and after shoulder motion to evaluate the possibility of movement-induced knot migration to a location nearer the glenoid. METHODS: We included 10 shoulders from 5 cadavers in the study. After posterior capsulotomy, a Bankart lesion was created. A capsulolabral repair was then performed with 3 knot-tying suture anchors. All knots were positioned on the capsular side, far from the articular surface. After the repair was complete, a photograph was taken with a metal rod placed to reference absolute distance. After passive pendulum motion was applied, another photograph was taken. The length of the suture strand from the knot base to the anchor insertion site was measured during both the initial repair and post-motion periods. RESULTS: Initial distances were 4.83 ± 1.09 mm for the inferior knot, 4.70 ± 0.97 mm for the middle knot, and 3.84 ± 1.25 mm for the superior knot. After motion, the distances were 3.52 ± 1.21 mm (P = .01), 3.07 ± 0.81 mm (P < .001), and 2.69 ± 1.18 mm (P = .016), respectively. Additional observations showed changes in direction and security of the knot. The change in knot direction from an initial orientation facing the capsular side to a new orientation facing the glenoid was observed in 5 of 10 inferior, 7 of 10 middle, and 6 of 10 superior knots. In addition, knot loosening was noted for the last half-hitches in 4 inferior knots and 1 middle knot. CONCLUSIONS: Intentional placement of suture knots away from the joint surface was not maintained after motion at the shoulder. CLINICAL RELEVANCE: Movement-induced knot migration may be detrimental to articular cartilage in the event that a knot becomes interposed between the glenoid and humeral head.

Concepts: Bone, Skeletal system, Humerus, Knee, Shoulder, Distance, Glenoid labrum, Scapula

28

Objective: The purpose of this study was to describe computed tomography (CT) features of the ununited anconeal process and relate them with the following elbow dysplasia signs: medial coronoid disease, medial humeral condyle changes, osteoarthritis (OA), and radioulnar incongruence. Methods: Computed tomographic images of dogs older than six months with an ununited anconeal process were evaluated (n = 13). Ununited anconeal process features were described as being complete or incomplete, and the degree of displacement, volume, and presence of cysts and sclerosis were also evaluated. Medial coronoid disease was defined as an irregular medial coronoid process shape, presence of sclerosis and fragmentation. Medial humeral condyle changes were defined as subchondral bone flattening, lucencies, and sclerosis. Osteoarthritis was graded depending on the osteophytes size. Radioulnar incongruence was measured on a sagittal view at the base of the medial coronoid process. Results: Eleven elbows had a complete and two had an incomplete ununited anconeal process. All ununited anconeal processes had cystic and sclerotic lesions. Seven ununited anconeal processes were displaced and six were non-displaced. Mean ununited anconeal process volume was 1.35 cm3 (0.61 cm³ - 2.08 cm³). Twelve elbows had signs of medial coronoid disease (4 of them with a fragmented medial coronoid process), and one elbow did not show any evidence of medial coronoid disease. Ten elbows had medial humeral condyle changes. One elbow had grade 1 OA, seven elbows had grade 2, and five elbows grade 3. All elbows had radioulnar incongruence: three elbows had a negative and 10 elbows had a positive radioulnar incongruence. Mean radioulnar incongruence was 1.49 mm (0.63 mm - 2.61 mm). Computed tomographic findings were similar in the majority of the elbows studied: complete ununited anconeal processes with signs of medial coronoid disease, positive radioulnar incongruence, high grade of OA, sclerotic medial humeral condyle changes, and large ununited anconeal process volumes. Clinical significance: Incomplete small ununited anconeal process volumes could be associated with a lower incidence of medial coronoid disease or medial humeral condyle changes. We recommend performing preoperative CT of elbows with an ununited anconeal process to evaluate concurrent lesions.

Concepts: Tomographic reconstruction, Humerus, Elbow, Tomography, Second grade, Brachialis muscle, Brachioradialis, Coronoid process of the ulna