Shoulder:Glenohumeral Arthritis/Anatomic Shoulder Arthroplasty

History

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Anecdotes

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Biomechanics

===Introduction===The glenohumeral joint is a complex biomechanical entity. In the physiologic state, the shoulder relies on bony anatomy, as well as on static (labrum and ligaments) and dynamic structures (rotator cuff) to adequately balance the force couples applied to the humeral head (1).

The goal of anatomic total shoulder arthroplasty (ATSA) is, therefore, to restore the premorbid state by recreating normal shoulder kinematics. This simple objective can, however, be challenging to achieve, as anatomy is subject to premorbid variations, in addition to distortion secondary to degenerative or traumatic changes (2).

On the contrary, reverse shoulder arthroplasty (RSA) is a non-anatomic procedure that achieves stability through a semi-constrained design and relies on the deltoid and other remaining muscles to move the humerus around a fixed glenosphere. While originally intended to treat patients with cuff tear arthropathy, its indications are continually expending. Since the initial Grammont design, much innovation has been proposed to optimize active and impingement free range of motion.

This chapter provides an overview of the current biomechanical understanding of ATSA. These principles should help surgeons to plan and perform shoulder replacement surgeries in daily practice.

Indications and Contraindications

Indications

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Contraindications

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Approaches

Surgical technique

The deltopectoral approach consisted of a 10 to 15 cm skin incision being made from the coracoid process toward the deltoid insertion. The infraclavicular fossa (Mohrenheim fossa) is found, the cephalic vein identified and the consistent medial branches, which give the appearance of the Mercedes Benz symbol, are ligated. A self-retaining retractor is used to maintain exposure between the deltoid and pectoralis major. The subacromial bursa was resected to allow the placement of a Hohmann retractor under the deltoid over the top of the coracoid process. The arm was abducted and internally rotated. The subacromial bursa is resected to allow the placement of a Brown-Deltoid retractor.

Subscapularis Tenotomy

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Osteotomy of the Lesser Tuberosity

The osteotomy is initiated at the bicipital groove with a 2-mm saw blade and then completed with a curved osteotome. An approximately 2.5 cm2 in the coronal plane and 5 mm thick fleck of lesser tuberosity is taken such that the osteotomy entered the joint medially without violating the humeral head.

A complete release of the subscapularis tendon is then performed and the tendon is pushed in the subscapularis fossa. A glenoid retractor is placed anteriorly. The humeral head is resected with a guide or a free-handed anatomic cut respecting native humeral head version and inclination.

Subscapularis Repair

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Lesser Osteotomy Repair

Before placement of the humeral stem, two holes are created with a 2-mm drill bit in the bicipital groove at the superior and inferior aspects of the lesser tuberosity osteotomy. One hole was created in the metaphysis just medial to the lesser tuberosity osteotomy. The sutures are then passed from lateral to medial by entering the bicipital groove, passing around the humeral stem, and exiting medially (Figure 16). A racking hitch is positioned to rest in the bicipital groove. The two sutures are passed through the subscapularis just medial to the lesser tuberosity osteotomy. The needle is removed from each construct to leave two superior and two inferior limbs (Figure 17). Then, one of the superior limbs and one of the inferior limbs were shuttled through the superior racking hitch knot (Figure 18). The suture limbs are passed through a tensioner to remove slack and to tension the repair (Figure 19).

Figure 16. Passage of the sutures. A suture with a half racking suture on the end is passed from lateral to medial through the inferior two holes, and (B) a separate suture is passed through the superior hole.	File:Sensitive-content.pngal. The stem is placed so that the sutures pass around the prosthesis. (A) The sutures are passed through the subscapularis tendon, and (B) the wedged ends are cut to provide access to four free limbs.
Figure 18. Passage of the sutures through the knots. (A) One suture limb from each pair is selected and (B) passed through the half racking suture.	Figure 19. Tensioning of the sutures. The suture limbs passed through the half-racking suture are tensioned. Tensioning is done under visual inspection.