8.1 Introduction

The shoulder is a complex joint affected by a variety of balanced muscular forces. The concept of glenohumeral force-couples emphasizes the presence of both a vertical and horizontal plane. ¹ It is important to understand that, in its natural state, the shoulder is unbalanced in both of these planes (► Fig. 8.1). Vertically, the power of the deltoid exceeds that of the rotator cuff muscles. Likewise, in the horizontal plane, the number of internal rotators exceeds the number of external rotator muscles. ² , ³ In a pathologic shoulder, the delicate balance is disrupted, leading to pain and/or a loss of function. Patients with a nonfunctional shoulder due to massive, irreparable cuff tears can generally be categorized into three groups: (1) those with an isolated loss of active elevation or shoulder pseudoparalysis; (2) those with an isolated loss of active external rotation (ILER); and (3) those with combined loss of elevation and external rotation (CLEER). It is critical for surgeons to be able to appropriately characterize and diagnose patients in order to choose the appropriate surgical therapy.

8.2 Vertical Muscle Balance and Cuff Tear Arthropathy

With aging, the rotator muscles weaken, whereas the deltoid muscle remains relatively strong. The balance between the head-elevating deltoid and head-depressing effect of the rotator cuff becomes disrupted. As the process continues, the rotator cuff tendons are compressed against the undersurface of the acromion, leading to anterosuperior cuff impingement and eventually cuff wear. Proximal retraction of the rotator cuff tear is followed by fatty infiltration and eventually proximal migration of the humeral head under the acromial arch. The shoulder gradually transforms into a constrained joint and becomes more like the hip, with acetabulization of the acromial arch (rounding of the acromion and ossification of the coracoacromial ligament) and femoralization of the humeral head (rounding of the greater tuberosity). This constrained joint may still be balanced and functional (► Fig. 8.2). This process may eventually lead to painful arthritis and/or a pseudoparalyzed shoulder if the shoulder becomes unbalanced. The five stages of cuff tear arthropathy described by Hamada and Fukuda ⁴ are defined as follows:

• 
  

  Stage 1: a balanced cuff tear without proximal migration of the humeral head (acromiohumeral distance more than 6 mm).

  
  
• 
  

  Stage 2: upward migration of the humeral head without any secondary bony changes (acromiohumeral distance 5 mm or less).

  
  
• 
  

  Stage 3: remodeling of the subacromial space with erosion of the undersurface of the acromion and the greater tuberosity (acetabulization and femoralization).

  
  
• 
  

  Stage 4: glenohumeral narrowing in addition to stage 3, with predominantly superior erosion of the glenoid.

  
  
• 
  

  Stage 5: collapse of the humeral head in addition to stage 4.

8.3 Bony-Increased Offset Reverse Shoulder Arthroplasty

Since its introduction in the 1980s by Professor Paul Grammont, the traditional reverse ball-and-socket prosthesis has proven to be a successful surgical treatment for the treatment of cuff tear arthropathy. However, some problems and complications related to the medialized design have been encountered ⁵ , ⁶ , ⁷ : (1) inferior scapular notching, (2) limited shoulder rotation, and (3) prosthetic stability.

Inferior scapular notching of the humeral insert against the pillar of the scapula during adduction and rotation of the arm is responsible for bone erosion and polyethylene wear and has been observed in 50 to 96% of reverse shoulder arthroplasty (RSA) on postoperative radiographs. Likewise, anterior scapular impingement may restrict internal rotation and posterior impingement may restrict external rotation. Humeral medialization may also lead to prosthetic instability, which has been observed in 3 to 6%. ⁸ Finally, humeral medialization may raise a cosmetic concern given that some patients dislike the loss of their normal shoulder contour after an RSA. ²

In an effort to address these issues, changes to the traditional Grammont design have been suggested. A lateralized RSA, with an increase in the offset of the glenosphere or baseplate, has been proposed to reduce the risk of scapular notching, and improve stability and mobility in rotation, while restoring shoulder contour ⁸ , ⁹ and retensioning the remaining rotator cuff. ¹⁰ The net effect of lateralization, however, is increased torque and shear forces on the glenoid component. In a biomechanical study, Harman et al ¹¹ demonstrated a fourfold increase in displacement of the glenoid component when comparing a 7-mm increased-offset baseplate to the traditional medialized Grammont design. In clinical practice, increased-offset RSAs have been associated with higher rates of glenoid component loosening and baseplate screw breakage. In the series of Frankle et al, ⁹ there was no scapular notching observed; however, eight baseplate failures in seven patients required revision (12% rate of glenoid loosening). In contrast, Guery et al ¹² reported a 4% rate of glenoid component loosening between 5 and 10 years of follow-up.

In an effort to neutralize shear forces on the glenoid component, we prefer bony lateralization of the RSA compared to metallic lateralization. This is achieved by bone grafting the reamed glenoid surface with a disk of cancellous bone (usually humeral head autograft) under the glenoid baseplate. Our goal is to obtain bony lateralization of the prosthesis while maintaining the prosthetic center of rotation at the glenoid bone-prosthesis interface. Once the bone graft has healed to the native glenoid, the torque on the glenoid component should be minimal, protecting from glenoid loosening, while the problems related to medialization are prevented. We have named this bony increased-offset reverse shoulder arthroplasty or BIO-RSA.

8.4 Indications for BIO-RSA

The BIO-RSA can be offered as a treatment for patients presenting with a painful and pseudoparalytic or stiff shoulder related to rotator cuff deficiency, that is, disruption of the vertical muscular couple (► Fig. 8.3). Surgeons should be aware that a painful loss of active elevation should not be mistaken with a true pseudoparalyzed shoulder.

8.5 Surgical Technique for BIO-RSA

Related posts:

9 Debate: I Always Repair the Subscapularis Tendon If Possible versus the Subscapularis Tendon: A Vestigial Structure Following Reverse Total Shoulder Arthroplasty? Chapter 10 Reverse Shoulder Arthroplasty for Acute Fracture: Indications and Technique Chapter 11 Reverse Shoulder Arthroplasty for Fracture Sequelae: Indications and Technique 6 Preoperative Work-up and Surgical Approaches for Reverse Shoulder Arthroplasty Chapter 15 Reverse Shoulder Arthroplasty in Revision Shoulder Arthroplasty: What I Look for and How I Do It hapter 13 Reverse Shoulder Arthroplasty for Massive Anterosuperior Rotator Cuff Failure

Stay updated, free articles. Join our Telegram channel

Join