56 Conversion of Failed Hemiarthroplasty to Reverse Shoulder Arthroplasty

10.1055/b-0039-167705

56 Conversion of Failed Hemiarthroplasty to Reverse Shoulder Arthroplasty

Brandon Horn and Jonathan C. Levy

Abstract

Revision of failed hemiarthroplasty to reverse shoulder arthroplasty most commonly occurs when hemiarthroplasty has been used to treat proximal humerus fractures, cuff tear arthropathy, and end stage arthritis. Each of these common indications presents unique challenges in managing the presenting pathology. Failed hemairthroplasty for proximal humerus fractures often have significant proximal humeral bone loss. Failed hemiarthroplasty for cuff tear arthropathy and osteoarthritis often have significant glenoid bone loss. While many currently available implants offer the opportunity to convert the hemiarthroplasty to a reverse humeral component, removal of the humeral stem is often necessary to create proper soft-tissue balancing.

56.1 Introduction

The clinical success of total shoulder arthroplasty (TSA) for patients with osteoarthritis together with the recent success of reverse shoulder arthroplasty (RSA) in managing rotator cuff-tear arthropathy (CTA) and fractures not amenable to osteosynthesis has resulted in a decline in the utilization of hemiarthroplasty. Nonetheless, shoulder surgeons are often faced with the need to revise a patient previously treated with a shoulder hemiarthroplasty. There are three common clinical scenarios where a shoulder hemiarthroplasty may have failed and a reverse shoulder replacement is selected as a revision. These include hemiarthroplasties used in treating proximal humerus fractures, those used to treat CTA, and those used to treat various forms of end-stage arthritis. While RSA has demonstrated versatility in managing the complex pathology associated with various hemiarthroplasty cases, each clinical scenario presents its own challenges. Over the course of this chapter, we will outline these three common clinical scenarios in which we employ a reverse shoulder prosthesis (RSP) in a revision setting and present algorithms that can be utilized to address challenging problems that can be encountered.

Common to all clinical scenarios is the need to remove the humeral stem. While many of the more modern humeral components have the ability to be converted to a reverse shoulder replacement, previous generations of implants do not. We will address convertibility of stems in the final section of this chapter. In the setting of uncemented humeral stems, standard stem extraction techniques are utilized. Stem extraction begins by disrupting the prosthetic–bone or prosthetic–cement interface of the proximal body and fins of the stem. This is typically performed using flexible osteotomes and/or a high-speed pencil-tip burr. It is important to obtain clear visualization of all fins to avoid fracture of the tuberosities during stem extraction. A first attempt at stem removal is then performed by either backslapping (using company-specific instrumentation) or utilizing a retrograde impaction at the medial neck junction of the stem with a carbide tip punch ( Fig. 56.1 ). In the setting of a cemented humeral stem, the stem is removed with similar extraction techniques. After the stem is removed, the cement mantle is addressed to determine if it is well fixed or loose. In a well-fixed cement mantle, new stems can be cemented into the prior mantle. If the new stem is too long to fit into the previous cement mantle, it can be modified and shortened using a carbide wheel burr. Additionally, smaller diameter stems are often utilized to fit within the previous cement mantle, especially if the previous hemiarthroplasty had flutes that make the minimum diameter of the cement mantle smaller. In a loose cement mantle, the old cement can be removed via osteotome, episiotomy, cortical window, or intramedullary cement extraction technique ( Box Text 1 ).

**Fig. 56.1** Intraoperative photograph of carbide tip punch (Innomed, Savannah, GA) placed at the medial neck of the humeral stem for retrograde extraction.

Technical Tip I: Cement Extraction

Acquire appropriate equipment:
1. A 2.8-mm threaded guide wire (cannulated screw set).
2. A 5.0-mm threaded cannulated drill bit (cannulated screw set).
3. A 6.5-mm cannulated tap (cannulated screw set).
4. Vice grip pliers.
5. A mallet.
Under fluoroscopic guidance, advance a 2.8-mm threaded guide wire into the cement mantle, ensuring pin placement is center-center to allow appropriate drilling and tap placement to avoid humerus breakthrough.
Advance a 5.0-mm threaded cannulated drill bit over guide wire; confirm on fluoroscopy that placement is center-center.
Advance a 6.5-mm cannulated tap 2 to 3 cm over the guide wire. Advance to ensure snug fit in the cement mantle.
Place the vice grip pliers on cannulated tap as far from humerus as possible to allow strong decisive blows with the mallet to disimpact cement from the cement–bone interface:
1. Strikes with the mallet should be in line with the cannulated tap to maximize force and prevent iatrogenic damage to the proximal humerus.
Repeat steps, confirming center-center placement of the 2.8-mm threaded guide wire, 5.0-mm threaded cannulated drill bit, and snug fit in the cement mantle with 6.5-mm cannulated tap.
Loose pieces can be removed with pituitary rongeurs and extended pickups.

56.2 Failed Hemiarthroplasty for Fracture

Primary hemiarthroplasty for comminuted proximal humerus fracture remains one of the most challenging surgical procedures for a busy shoulder surgeon. The procedure is not only technically demanding, but also quite unforgiving. The procedure requires that several technical steps be performed accurately to ensure optimal functional outcomes. Accurate stem height, humeral retroversion, and anatomic reduction and secure fixation of the greater and lesser tuberosities are critical to achieve restoration of shoulder function. Tuberosity failure can result from resorption, nonunion, or malunion of the tuberosities following the index procedure, and can be quite common in older patients. Tuberosity failure mimics rotator cuff deficiency, and many of these patients not only lose function, but also often complain of pain. In this setting, revision shoulder arthroplasty is often considered.

When planning a conversion of a failed hemiarthroplasty for fracture to a reverse shoulder replacement, the challenging pathology relates to the humerus. These cases are commonly associated with various forms of proximal humeral bone loss from tuberosity resorption, nonunion, or malunion, and are approached using the algorithm detailed in Fig. 56.2 . Appreciation of proximal humeral bone deficiency is critical, as restoring appropriate soft-tissue tension can be challenging in the setting of proximal humeral bone loss. Levy et al ¹ first reported higher rates of humeral-sided complications of RSA performed in the setting of proximal humeral bone loss. The additional stress placed across reverse shoulder humeral stem modular junctions in the setting of proximal humeral bone loss can result in modular segment failure. This was confirmed in a mechanical testing model of proximal humeral bone loss by Cuff et al. ² In an effort to avoid humeral-sided complications and to restore the pulley effect of the deltoid, ³ a bulk proximal humeral allograft is often utilized ( Box Text 2 ). When the proximal humeral bone was restored using a bulk proximal humeral allograft, humeral-sided complications such as dissociations or dislocations were found to be significantly lower. ⁴ The decision of when to use a proximal humeral allograft relates to the amount of proximal humeral bone loss as well as the overall flexibility of the shoulder joint.

**Fig. 56.2** Algorithm for management of humeral stem in failed nonconvertible shoulder hemiarthroplasty.

Technical Tip II: Proximal Humeral Allograft Technical Tip

A fresh-frozen proximal humeral allograft with tendon attachments is selected matching the side of the operative shoulder.
All soft tissue is removed, with the exception of the subscapularis tendon.
The allograft’s humeral head is resected at the anatomic neck.
All of the cancellous allograft bone is removed from the intramedullary canal.
An oscillating saw is then used to create a step cut of the metaphyseal bone such that 5 cm of bone remained laterally and 1 to 2 cm of bone remained medially, resulting in a lateral plate ( Fig. 56.6 ).
The allograft tendon attachment is later used for repair of the subscapularis. ⁴