Management of Humeral and Glenoid Bone Defects in Reverse Shoulder Arthroplasty

Lisa G. M. Friedman, MD, MA; Grant E. Garrigues, MD

Disclosures

J Am Acad Orthop Surg. 2021;29(17):e846-e859. 

In This Article

Abstract and Introduction

Abstract

Bone loss of either the glenoid or the humerus is a challenging problem in reverse total shoulder arthroplasty. When left unaddressed, it can lead to early failure of the implant and poor outcomes. Humeral bone loss can be addressed with the use of an endoprosthesis or allograft prosthetic implant. Glenoid bone loss can be treated with a variety of grafting options, such as augmented implants, patient-specific navigation, and implantation systems.

Introduction

Shoulder pain is a common problem for which reverse total shoulder arthroplasty (RTSA) is a reliable and durable treatment with an expanding number of indications. However, in the setting of glenoid or humeral bone loss, shoulder arthroplasty becomes more challenging, with a higher risk of complications.

Bone loss on either the humeral or glenoid side can lead to an increased rate of loosening. Poor initial fixation leads to increased micromotion. Beyond approximately 150 micrometers of motion, bone ingrowth is unlikely and the implant will eventually fail through gross loosening.[1,2] RTSA is commonly used in the revision setting because its design accommodates for soft-tissue deficiencies of the rotator cuff and stabilizing capsule. However, the semiconstrained nature of this implant transmits increased forces to the bone-implant interface. Thus, sufficient bone stock is necessary for the stability and longevity of the implant because these forces are transmitted to a smaller amount of bone in the setting of notable bone loss.[3] As a result, there is a higher rate of revision surgery, in general, and baseplate loosening, in particular, in the setting of notable bone loss.[4]

In addition to concerns about loosening, loss of bone stock also has notable implications for the stability of the glenohumeral joint after RTSA. Implant micromotion not only leads to loosening but can also lead to rotational instability, leading to dislocation and dissociation of the implant. Modular implants are theoretically at higher risk for these complications than are monoblock implants because failure to osseointegrate at the bone-implant interface transmits force to the implant itself. In this setting, modular junctions may become the weak link, and thus, the load to failure for these implants is lower.[1] Not surprisingly, revision RTSA, a setting in which bone loss may be prevalent and soft-tissue injury present, has a much higher rate of instability of 8% to 10% as compared with primary RTSA of 0% to 4%, in which bone loss is uncommon.[5–8] Bone loss in the revision setting leads to increased instability rates because there is often the loss of attachment sites for muscles, critical for stabilizing structures across the joint. In addition, in the setting of bone loss, there is a decreased deltoid wrapping effect, which has been shown to help stabilize the prosthetic articulation.[9,10] Furthermore, when there is not enough humeral bone for adequate implantation, this can lead to humeral shortening and disruption of length-tension relationships of the musculature, particularly the deltoid, leading to instability.[11]

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