Junichiro Hamada

Analysis of the scapulohumeral rhythm and electromyography of the shoulder muscles during elevation and lowering: comparison of dominant and nondominant shoulders.

HYPOTHESIS Assessment of whether elevation and lowering of the dominant and nondominant arms occur in a similar manner in healthy individuals is clinically important in terms of shoulder disorders. MATERIALS AND METHODS We examined the scapulohumeral rhythm (SHR) and performed electromyography (EMG) for the middle deltoid, upper trapezius, lower trapezius, and lower part of the serratus anterior muscles of both shoulders in 18 healthy volunteers (14 men, 4 women) with a mean age of 24 years (range, 19-30 years). The participants randomly elevated and lowered either the right or left arm in the scapular plane, and the motion was measured using a 3-dimensional motion analyzer. RESULTS The average angles of maximum arm elevation and scapular upward rotation were 130.3 degrees +/- 7.9 degrees and 32.2 degrees +/- 5.6 degrees, respectively, for dominant arms, and 130.8 degrees +/- 6.4 degrees and 31.8 degrees +/- 5.8 degrees, respectively, for nondominant arms. The SHR in each 10 degrees increment did not differ significantly between the dominant and nondominant arms in each participant during elevation (P = .337) and lowering (P = .1). A significant difference was found in the percentage integrated EMG (%IEMG) of the lower trapezius between the 2 shoulders (P < .049). DISCUSSION If the kinematic difference is identified between both shoulders, we can predict the dysfunction or disorder in shoulder complex. Moreover, we should evaluate how shoulder muscles are used and whether the muscle becomes weak. CONCLUSIONS Healthy individuals elevate and lower the dominant and nondominant shoulders in a similar kinematical pattern despite 3 of 4 muscles indicating different EMG activities between both shoulders.

Different scapular kinematics in healthy subjects during arm elevation and lowering: Glenohumeral and scapulothoracic patterns

HYPOTHESIS The scapulothoracic (ST) joint affects glenohumeral (GH) joint function. We observed 3-dimensional scapular motions during arm elevation and lowering to identify the scapulohumeral rhythm in healthy subjects and to compare it between the dominant and nondominant arms. MATERIALS AND METHODS Twenty-one healthy subjects participated in this study. Participants randomly elevated and lowered the arms in the scapular plane, and data were recorded by a computerized 3-dimensional motion analyzer at each 10 degrees increment. RESULTS Of the 42 shoulders, 21 showed a greater ratio of GH motion relative to ST motion whereas the other 21 showed a smaller ratio of GH motion relative to ST motion. The angle of upward rotation of the scapula showed a statistically significant difference between both types. The mean maximum angles of upward rotation, posterior tilting, and internal rotation were 36.2 degrees +/- 7.0 degrees , 38.7 degrees +/- 5.7 degrees , and 36.8 degrees +/- 12.2 degrees , respectively. No significant difference was found in angles of 3 scapular rotations between the dominant and nondominant arms. DISCUSSION These results indicate that there are 2 distinctly different scapulohumeral rhythms in healthy subjects but without a significant difference between dominant and nondominant arms. These findings should be referred to when one is interpreting kinematics in a variety of shoulder disorders.

Recurrences after the open Bankart repair: A potential risk with use of suture anchors

Eighty-seven consecutive patients were treated with an open Bankart repair for traumatic, recurrent anterior instability of the shoulder. Forty-six of these patients underwent a transosseous suture technique. Forty-one patients were operated on with suture anchors. After follow-ups that ranged from 18 to 85 months, 7 of the 87 patients showed signs of recurrence and another 14 patients reported apprehension. Compared with the 66 patients without residual instability, these 21 patients were more likely to have been operated on with suture anchors (P < .05), had a greater incidence of hypermobility in joints other than the shoulder (P < .05), and had had a greater number of preoperative episodes (P < .05). In light of this data we recommend the transosseous suture technique for open Bankart repairs. In addition, a cautious and extensive capsular repair may be required when a patient reports frequent subluxations preoperatively or has hypermobility in some joints, if not in the shoulder per se.

A cadaveric study of the serratus anterior muscle and the long thoracic nerve.

The anatomy and function of the serratus anterior muscle and the long thoracic nerve have not been fully elucidated. The purposes of this investigation were (1) to clarify which nerve roots of the cervical spine supply each part of the muscle and contribute to the long thoracic nerve and (2) to investigate the anatomy of the 3 parts of the muscle to understand the function of each part. We collected specimens from 70 dissections of 35 cadavers (11 men and 24 women). The serratus anterior muscle consisted of the upper, middle, and lower parts. The upper part was supplied mainly by the C5 nerve root, and the C4, C6, or C7 nerve roots also had multiple branches in 64 of 70 dissections. The long thoracic nerve, consisting of the C6 and C7 nerve roots, innervated the middle and lower parts. The upper part traversed in a posterior direction compared with the middle or lower part. The upper part of the muscle, which is supplied from multiple nerve roots and runs in a posterior direction, may stabilize the rotational motion of the scapula on the thorax in shoulder elevation. The middle part provides the scapular abduction, and the lower part contributes to upward rotation, abduction, and posterior tilting.

An anatomic study of the structure and innervation of the pronator quadratus muscle

The pronator quadratus muscle is composed of the superficial and deep heads. However, to date there is no consensus on the variations of each head. To add to this enigma, the innervation patterns of each head have not been thoroughly studied. The present study was conducted to clarify the structure and innervation of the pronator quadratus muscle by minute dissection of 46 forearms from 26 cadavers. The origin, insertion, shape, and direction of the muscle fascicles in each head were observed. The intramuscular distribution and the innervation patterns to each head were investigated. The attachment of the deep head was examined using Masson’s trichrome staining technique. Each head consisted of various muscle fascicles which differed in shape and direction. The most distal muscle fascicle extended toward the head of the ulna. On microscopic study, this most distal fascicle was observed to reach the base of the ulnar styloid process. The nerves innervating the superficial head penetrated through the deep head and ran on the anterior surface of the radius from medial to lateral. This tendency was common to all of the forearms studied. We confirmed that each head of the pronator quadratus muscle consisted of various muscle fascicles. The attachment to the base of the ulnar styloid process is considered to be an important structure that prevents the head of the ulna from impacting against the carpal bones. Knowledge of the innervation pattern to each head is critical for preserving the function of the pronator quadratus muscle during surgery for distal radial fracture.

Subdeltoid approach for removal of large soft-tissue lesions beneath the deltoid muscle: report of two cases.

Lesions that develop beneath the deltoid muscle are rare but may occasionally be large and difficult to excise by a standard surgical approach to the shoulder. Martini 2-4 reported that the subdeltoid approach was useful to obtain wide exposure of the proximal metaphyseal region of the humerus. We describe two patients, one with a subdeltoid lipoma and the other with chronic subdeltoid bursitis, who underwent surgery by the subdeltoid approach and discuss the indications of this surgical exposure. Our operative procedure was based on that described by Martini. 4 In brief, the patient was placed in the lateral decubitus position and the arm was draped free. A V-shaped skin incision was made, starting from the deltoid tuberosity, with the anterior and posterior limb of incision along the anterior and posterior margins of the deltoid muscle (Figure 1). The distal tendon of the deltoid muscle was exposed and incised with the periosteal tissue adjacent to the tendon. The anterior and posterior margins of the deltoid muscle were bluntly dissected to expose the subdeltoid lesion while the distal tendon was lifted and reflected cranially with the overlying skin (Figure 2). Branches of the cephalic vein entering the deltoid muscle were ligated. The axillary nerve was carefully identified and protected from damage while separating the lesion from the deepest layer of the deltoid muscle. The subdeltoid lesion was also dissected from the surface of the humerus and removed en bloc. Finally, the distal tendon of the deltoid muscle was reattached securely with 6 to 8 thick nonabsorbable sutures passed through the holes made in the humeral cortex. Postoperatively, the arm was immobilized for 3 weeks in a sling and swathe with the shoulder at 20° of abduction. Self-assisted range-of-motion exercises of the shoulder were then started. Antigravity motions were encouraged 6 weeks after surgery.

Anatomic study and electromyographic analysis of the teres minor muscle

BACKGROUND The teres minor muscle is a focused topic on the treatment of massive rotator cuff tears and reverse total shoulder arthroplasty. Its precise anatomy and function have not been completely investigated. The purposes of this study were to anatomically investigate the muscle and analyze electromyographic (EMG) activities during shoulder motion. METHODS This anatomic study used 20 shoulders from deceased donors (mean age, 75.0 years). EMG data were recorded from 10 healthy volunteers (mean age, 21.7 years) during flexion, abduction, and external rotations at 0° of abduction, at 90° of abduction, and at 90° of flexion in their dominant arms synchronized with a computerized 3-dimensional motion analysis system. RESULTS The muscle in all specimens consisted of 2 distinct muscular bundles: the upper and lower portions. The upper portion attached to the round area of the greater tuberosity, and the lower portion inserted into the linear shaped area. Both portions were independent in their origins, insertions, and innervation. The muscle engaged force during each shoulder motion. EMG activities of abduction and the 3 forms of external rotation were similar. Maximal voluntary contraction in the 3 forms of external rotation was 32% in maximum external rotation in the neutral position, 25% in flexion, and 40% in abduction. CONCLUSIONS The teres minor consists of independent upper and lower portions. The muscle engages force in all ranges of 5 shoulder motions, and maximum external rotation in abduction is a reliable method to evaluate potential activity of the muscle.

Proximal Humeral Fractures: Classification and Treatment

Proximal humeral fractures account for 4–5 % of all fractures, with the higher incidence in women. The AO/ASIF system and the Neer’s four-segment classification are used to record the fracture anatomy. The Neer’s classification is more appropriate to provide an anatomic basis for guiding treatment regimens.