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The Bone & Joint Journal
Vol. 100-B, Issue 12 | Pages 1600 - 1608
1 Dec 2018
The lever arm ratio of the rotator cuff to deltoid muscle explains and predicts pseudoparalysis of the shoulder
Bouaicha S Ernstbrunner L Jud L Meyer DC Snedeker JG Bachmann E
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Aims

In patients with a rotator cuff tear, tear pattern and tendon involvement are known risk factors for the development of pseudoparalysis of the shoulder. It remains unclear, however, why similar tears often have very different functional consequences. The present study hypothesizes that individual shoulder anatomy, specifically the moment arms (MAs) of the rotator cuff (RC) and the deltoid muscle, as well as their relative recruitment during shoulder abduction, plays a central role in pseudoparalysis.

Materials and Methods

Biomechanical and clinical analyses of the pseudoparalytic shoulder were conducted based on the ratio of the RC/deltoid MAs, which were used to define a novel anatomical descriptor called the Shoulder Abduction Moment (SAM) index. The SAM index is the ratio of the radii of two concentric spheres based on the centre of rotation of the joint. One sphere captures the humeral head (numerator) and the other the deltoid origin of the acromion (denominator). A computational rigid body simulation was used to establish the functional link between the SAM index and a potential predisposition for pseudoparalysis. A retrospective radiological validation study based on these measures was also undertaken using two cohorts with and without pseudoparalysis and massive RC tears.

The Bone & Joint Journal
Vol. 98-B, Issue 11 | Pages 1521 - 1525
1 Nov 2016
Lateral closing isosceles triangular osteotomy for the treatment of a post-traumatic cubitus varus deformity in children
Su Y Nan G
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Aims

Cubitus varus is the most common late complication of a supracondylar fracture of the humerus in children. Correction can be performed using one of a number of techniques of osteotomy but each has disadvantages. We describe a new technique for correcting post-traumatic cubitus varus using a lateral closing wedge isosceles triangular osteotomy.

Patients and Methods

A lateral closing wedge isosceles triangular osteotomy was performed in 25 patients (15 male and ten female with a mean age of 9.5 years (6 to 12)) between May 2010 and April 2013. All patients had cubitus varus secondary to malunion of a supracondylar fracture, with good function of the elbow and a full range of movement. The osteotomy lines were marked on the bone with an isosceles triangular template made before surgery, after which the osteotomy was performed leaving the medial cortex intact. Fixation was performed using two lateral 2 mm Kirschner (K)-wires and patients were immobilised in an above-elbow plaster. By six to eight weeks callus was present and the wires and cast were removed. Patients were reviewed at four and six weeks, three, six and 12 months and then every two years until skeletal maturity. Clinical and radiographic outcomes were categorised as excellent, good or poor.

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