Imaging in shoulder arthroplasty: Current applications and future perspectives

Abstract

Shoulder arthroplasty has become a standard surgical procedure for treating a variety of complex shoulder disorders, including those with degenerative and traumatic aetiologies. The ever-improving success rates of shoulder arthroplasty could be attributed to advancements in endoprosthesis design, improvements in the biomechanics of endoprosthetic components, and improvements in surgical techniques. It improves patient outcomes and helps restore shoulder joint function and mobility.

Imaging plays a vital role by enabling surgeons to plan arthroplasty procedures, help guide endoprosthesis placement, and monitor postoperative outcomes. In addition, imaging plays a role in assessing the residual bone stock and status of rotator cuff integrity and in correcting the placement of prosthetic components to restore shoulder mobility.

CT-guided navigation aids surgeons by helping them choose appropriate components for implants and ensuring that implants are placed optimally during surgery. It can lead to better surgical results with reduced patient morbidity and a longer duration of prosthetic stability. After surgery, it is crucial to use imaging techniques to detect issues such as periprosthetic loosening, infections, or fractures to start effective management strategies to enhance patient recovery.

This article aims to provide orthopaedic surgeons and radiologists with knowledge on the imaging methods used in shoulder arthroplasty and their role in presurgical planning, intraoperative guidance and postoperative assessment. In this study, we aimed to investigate the rationale behind utilising various types of shoulder replacements: total shoulder replacement (TSA), reverse total shoulder arthroplasty (RTSA), and hemiarthroplasty; methods, their respective advantages and limitations; and outcomes. Our objective is to comprehensively analyse the procedures mentioned above and highlight their unique features and benefits to facilitate a better understanding of these approaches. Additionally, we will discuss how these imaging techniques help identify issues such as loose components, fractures around the implant site, joint instability and infections.

1. Introduction

When conservative treatments such as medical therapy, lifestyle modifications and minimally invasive interventional procedures fail to address patients' complaints, surgeons consider shoulder arthroplasty surgeries.¹ There are three different varieties of shoulder replacements that can be performed: (1) hemiarthroplasty/resurfacing procedures, (2) total shoulder arthroplasty (TSA), and (3) reverse shoulder arthroplasty (RTSA). Each of these procedures has specific indications, prerequisites and complications.^2,3

The shoulder joint is a complex, ball-and-socket type of joint that connects the humeral head (ball) and the glenoid (socket). Its unique design provides greater flexibility and mobility but at the cost of stability. Due to its focus on mobility rather than stability, the shoulder joint is prone to injuries, wear and tear, and instability. In addition to clinical assessments, radiological imaging is crucial for managing patients with shoulder issues.⁴

Although third only to hip and knee replacement surgeries, shoulder arthroplasty has evolved over the last few decades to effectively manage patients with shoulder pain, irreparable rotator cuff function, end-stage arthritis, or severe loss of bone stock to restore patient function.^5,6 Radiological imaging is integral to the diagnostic assessment and management of patients evaluated for shoulder arthroplasty.⁷

Plain radiographs tend to be the initial tool for assessing such patients. However, modern imaging modalities, including ultrasound (USG), magnetic resonance imaging (MRI), computed tomography (CT) and various nuclear medicine techniques, allow global evaluation of the different components of the anatomy and the replaced joint.8, 9, 10, 11 The radiological evaluation of shoulder arthroplasty, especially a failed surgery, requires careful evaluation.¹²

This article provides an overview of various modalities for evaluating and postoperative imaging of shoulder arthroplasty and offers insights into the future.

2. Applied radiological anatomy and biomechanics of shoulder joints

Due to the differences in size and form between the larger, shallower glenoid surface and the convex humeral head, which covers 25 %–30 % of the head, the glenohumeral joint is the body's most movable joint.¹³ This joint shape promotes mobility over rigidity, relying heavily on surrounding soft tissues for joint stabilisation. The deltoid muscle aids in arm abduction and elevation, while the rotator cuff muscles help to centre and lower the humeral head.¹⁴ Shoulder arthroplasty requires awareness of these biomechanics to mimic the native joint's function as closely as possible.

3. Overview of current shoulder arthroplasty techniques

3.1. Anatomic total shoulder arthroplasty (TSA)

The primary reasons for performing TSA include osteoarthritis, inflammatory arthritis, partial joint replacement failure, and advanced stages of avascular necrosis.¹⁴ The procedure requires an undamaged rotator cuff and adequate glenoid bone stock.

The TSA comprises the humeral and glenoid components. The humeral component can be with or without a stem or involve surface replacement (resurfacing). There are two types of glenoid components: cemented polyethene and metal-backed components..¹⁰ Currently, glenoid implants consist of radiolucent ultrahigh molecular weight polyethene. These may have a polyethene keel or pegs that are secured to the cancellous bone using polymethylmethacrylate cement.¹⁵

A visible linear radiopaque marker is typically added to the central keel or peg to ensure that the glenoid component stays in place correctly and for radiographic positioning. Both the glenoid and humeral components can be cemented or uncemented..¹⁰Postoperative radiographs help to demonstrate that the glenoid component is aligned perpendicularly to the scapular axis on an axillary view. Similarly, no inferior tilt should be observed in the placement of the glenoid component on a Grashey view.

The humeral head should be centred with the glenoid, forming a smooth arc between the inferior glenoid, scapular neck and medial humeral cortex on the anteroposterior (AP) radiograph..¹⁵ The humeral stem should be well centred within and aligned with the humeral shaft. Additionally, the cranial margin of the humeral head is ideally situated 2–5 mm superior to the top of the greater tuberosity when measured perpendicular to the shaft of the humerus. For uncemented components, a lucency of less than 0.6 mm can be observed at the interface between the prosthesis and bone.15, 16, 17 Conversely, the cement should exhibit a uniform distribution around the prosthesis for cemented stemmed components without any radiolucency between the prosthesis and cement. Radiolucency at the interface between the bone and prosthesis should ideally measure less than 2 mm and remain stable in follow-up studies..¹⁵

3.2. Partial shoulder arthroplasty (PSA)

A broken proximal humerus, humeral head avascular necrosis without glenoid involvement, osteoarthritis predominantly affecting the humeral head, poor glenoid bone stock, large Hill-Sachs lesions, and large focal osteochondral defects are the main reasons for partial shoulder arthroplasty (PSA). Before intervention, the integrity of the rotator cuff and sufficient glenoid bone stock must be checked.

In some isolated cases, it may be possible to address these issues by resurfacing or replacing the humeral head without inserting a glenoid component. Surgeons may consider other options for humeral implants, including resurfacing the humeral head, performing stemless humeral arthroplasty, and using either cemented or press-fit stemmed humeral components..^15,18,19

3.3. Reverse total shoulder arthroplasty(RTSA)

The RTSA is used to treat conditions that include complex proximal humerus fractures, massive rotator cuff tears, post-tumour resection, failed TSA from an irreparable rotator cuff tear, and subsequent unsuccessful reconstruction. An intact deltoid muscle is a prerequisite for this procedure, but a rotator cuff is not.

In reverse total shoulder arthroplasty (RTSA), the traditional ball and socket configuration of the shoulder joint is reversed with a convex glenoid hemisphere and a concave humerus articulating cup. In this technique, the rotation centre is shifted downwards and inwards. The RSA alters the shear forces around the shoulder into compressive forces, leading to arm abduction by activating the rotational movements of the deltoid muscle. The increased glenohumeral surface area in the RSA contributes to increased shoulder stability and expands the potential range of movement.²⁰

The RTSA has four components: a glenosphere, a humeral prosthesis, polyethylene insert, a metaglene,.¹⁰ The humeral prosthesis consists of a modular or monoblock stem, either uncemented or cemented, with a proximal cup-shaped portion on which a polyethene insert is located..¹⁰ The modular glenoid components also have a base, i.e., metaglene, over which the glenosphere is fixed..¹⁰ Metaglene is securely attached to the glenoid using screws, which can be locked or unlocked. Additionally, a central screw is used to affix the glenosphere to the metaglene.²¹

Early complications include instability (subluxation or dislocation), superficial or deep infection, hematoma, ulnar nerve dysfunction, and scapular spine fracture..¹⁵ The delayed complications included fractures (humeral and glenoid), loosening of the metaglene, and notching of the scapula.¹⁵

4. Imaging modalities used for shoulder arthroplasty assessment

4.1. Radiographs

Radiographs are commonly used to evaluate shoulder arthroplasty because they are widely available and can be used to diagnose complications. [Fig. 1]. Different views, such as the anteroposterior (AP) or Grashey views (taken at a 30–45° angle from a lateral position), as well as axillary and scapular Y-rays, are used for this purpose.^22,23 [Fig. 2].

Fig. 1.

Anteroposterior radiograph of a normal left shoulder resurfacing hemiarthroplasty showing congruent humeral prosthesis and native glenoid. There is no glenoid wear or prosthetic loosening.

Fig. 2.

Anteroposterior (a) and axillary (b) radiographs of a normal right shoulder hemiarthroplasty with congruency of the humeral prosthetic head and native glenoid.

Follow-up imaging typically involves obtaining two to four radiographs at 3–6 weeks post-surgery to establish a baseline study for comparison with future assessments. This approach applies to both total and hemi shoulder arthroplasties.²⁴

Radiographs should be the initial imaging modality utilised in cases of suspected complications. Standard radiographs can effectively demonstrate prosthesis loosening, cranial humeral migration indicating failure of the rotator cuff, periprosthetic fractures (acute or stress-related), and progressive glenoid wear in hemiarthroplasty patients.^10,23

4.2. Computed tomography (CT)

Hardware-related artefacts pose a significant challenge in CT imaging following shoulder arthroplasty. However, with the availability of advanced scanners, these artefacts can be minimised, making CT a preferred modality for assessing periprosthetic soft tissue. It is crucial to employ a soft tissue reconstruction algorithm and increased tube voltage and current to optimise image quality. Dual-energy CT can further reduce beam-hardening artefacts by creating virtually monochromatic spectral images. Despite these advancements, metal artefact reduction software remains an effective tool for mitigating photon starvation effects.²⁵

To enhance the assessment of glenoid loosening, a specific patient position, such as lateral decubitus to three-quarters decubitus, can be adopted to reduce hardening artefacts. CT excels over radiographs in detecting and characterising radiolucent lines and osteolysis around a prosthesis.²⁶ It is also superior for identifying scapular spine and acromion fractures after reverse shoulder arthroplasty (RSA). CT imaging is recommended for a more accurate assessment in cases where the radiographic findings are inconclusive but where particle disease is suspected. Additionally, CT is crucial in preoperative planning for revision surgery.²⁵

4.3. Ultrasound (USG)

The widespread availability and absence of hardware-related artefacts have led to an increased preference for ultrasound as an effective imaging modality for analysing periarticular soft tissue disorders.²⁷ Ultrasound has proven particularly useful in detecting soft tissue issues such as cuff tears, pathology of the long head of the bicep tendon, and any soft tissue or intra-articular infections. Additionally, ultrasound enables dynamic evaluation of the shoulder joint.

Rotator cuff integrity is commonly assessed using ultrasound, which has demonstrated high accuracy in postoperative shoulder evaluations, detecting tears in more than 50 % of symptomatic post-arthroplasty shoulders.

Recent advancements in ultrasound technology have further enhanced its utility. Acoustic radiation force impulse (ARFI) can assess deltoid muscle integrity after reverse shoulder arthroplasty (RSA). This technique is utilised to assess the elasticity of the muscle and is particularly useful for determining postoperative outcomes. By measuring the acoustic radiation force exerted on the tissue, ARFI can provide valuable information regarding the overall health and function of the deltoid muscle. This non-invasive method is gaining popularity in clinical practice and is a valuable tool for evaluating the success of RSA procedures. Contrast-enhanced ultrasonography (CEUS) is employed to study perfusion. Postoperatively, the operated deltoid muscle typically exhibits greater stiffness than its non-operated counterpart.²⁸ Reduced perfusion observed on sonography is associated with a limited range of motion and suboptimal outcomes. Ultrasound can also aid in performing image-guided injection of the bursa and aspiration of joints in appropriate clinical scenarios.

4.4. Magnetic resonance imaging (MRI)

Blooming artefacts from metal prostheses used in shoulder arthroplasty have traditionally caused degradation of MR image quality and have remained a sore point for decades. Fortunately, recent advancements in metal artefact reduction techniques (e.g. MAVRIC) have made it possible to reduce these artefacts, leading to increased utilisation of MRI for this purpose. Utilising 1.5-T scanners alongside spin‒echo sequences featuring thin slice thickness, high matrix, and bandwidth is preferred for conventional MRI, as they are less susceptible to local field inhomogeneities than chemical shift-selective fat suppression methods. Short tau inversion recovery (STIR) sequences are recommended over other methods for fat suppression. The incorporation of STIR sequences, ideally in combination with specialised sequences, allows for the use of equivalent T2-weighted and T1-weighted sequences, such as MAVRIC-T1, to produce good shoulder images.²⁹ MRI can be used to evaluate soft tissue structures, including the rotator cuff, deltoid, synovium, joint capsule and neural structures. Advancements in metal suppression imaging techniques have enhanced the ability of MRI to assess osteolysis, loosening, and wear-induced changes in synovitis. Furthermore, hardware-related complications such as metallosis or mechanical failure and secondary neurovascular injuries can now be accurately detected with the help of MR imaging, which can aid in the selection of candidates for revision arthroplasty.

4.5. Single-photon emission computed tomography (SPECT)/CT

Nuclear medicine studies have used SPECT and Technetium 99 m bisphosphonate (BP) bone scans to detect periprosthetic infections. These methods are highly sensitive but lack specificity. By combining the metabolic information of nuclear studies with cross-sectional anatomical CT imaging, SPECT/CT imaging has significantly enhanced our ability to detect infections.

Using [99mTc] BP SPECT/CT, healthcare professionals can accurately diagnose mechanical complications associated with shoulder arthroplasty. These include glenoiditis after hemiarthroplasty, loosening of the glenoid after shoulder arthroplasty and notching of the scapula after reverse shoulder arthroplasty.³⁰

In patients with glenoiditis, increased uptake in the glenoid region and potential chondral erosion can occur..³⁰

The scintigraphic pattern of loosening in TSA typically presents a more focal uptake, particularly in delayed phase images. Increased periprosthetic tracer uptake is observed at the bone-prosthesis interface..^10,30

Clinicians often use [99mTc] BP SPECT/CT in cases of suspected infection because it is easy to use, highly sensitive, and imposes a low radiation burden on patients. The radiotracer is strongly taken up around the endoprosthesis during both the early and delayed phases of imaging and serves as a scintigraphic signature of infection.^31,32

4.6. FDG-PET (Fluoro Deoxy Glucose-Positron Emission tomography) CT

18F-FDG PET-CT is used to identify cases of periprosthetic infections by detecting increased metabolic activity at the interface between the bone and prosthesis. Moreover, elevated FDG activity in the glenoid and humeral components and hypermetabolic axillary lymphadenopathy might indicate potential infection.

While FDG-PET is highly sensitive for detecting infected prostheses, its specificity is limited.³³ A WBC (white blood cell) scan and a BM (bone marrow) scan are typically conducted in cases of suspected prosthesis infection. If the results of these scans do not align with the clinical presentation with blood or joint aspiration tests, subsequent imaging with FDG-PET may be considered to confirm or rule out sepsis.^15,30,34

5. General complications associated with total shoulder arthroplasty surgery

5.1. Peri-prosthetic shoulder infection

Periprosthetic joint infection (PJI) is a complication that can occur after shoulder replacement surgery. Although not common, it can have devastating consequences. Various factors, including prolonged surgery duration, blood transfusions, exposure to temperature and underlying medical conditions such as diabetes, obesity, immune system suppression, cancer, rheumatoid arthritis and chronic infections, can contribute to its development. It is important to note that the risk of infection after RSA is greater in patients with a history of shoulder surgeries such as rotator cuff procedures or unsuccessful arthroplasty. Moreover, there is an increased likelihood of PJI in cases where shoulder hemiarthroplasty is performed due to traumatic causes..35, 36, 37

Radiographically, an infection can manifest as irregular progressive lucency around the prosthesis with periosteal and cortical thickening, indicative of an advanced stage..¹⁰ The suspicion of infection should be increased in the presence of findings suggestive of humeral or glenoid component loosening. However, most imaging modalities lack sensitivity and do not provide conclusive evidence. Aspiration and culture of fluid from the glenohumeral joint are recommended to exclude infection in cases where loosening is encountered, with Propionibacterium acnes being frequently cultured, particularly after Staphylococcus species..¹⁵ Extended culture monitoring of aspirates for 14 days is necessary to improve detection because P. acnes is a slow-growing anaerobe.^15,36,38

The use of labelled white blood cells (WBCs) with [99mTc]-hexamethyl propylene amine oxime paired with [99mTc]-sulfur colloid bone marrow (BM) imaging has shown high specificity and sensitivity and may be the preferred nuclear imaging modality for diagnosing PJI..³⁰ The confirmation of prosthetic sepsis relies on at least one abnormal uptake focus, characterised by a time-dependent uptake increase from early planar to delayed images on shoulder prostheses..³⁰ Additionally, the accumulation of labelled WBCs should not correlate with the photopenic area on the BM scan.³⁰ SPECT/CT helps to identify signs of infection, improving specificity. SPECT/CT helps to decipher the radiological signs of infection that may improve specificity, including 2 mm or more widening of the periprosthetic lucency, subchondral cysts, ill-defined osteolysis, abscess, granuloma, effusion, and florid periosteal reaction.30, 31, 32 Two-stage reimplantation for prosthetic joint infection is reported to have the lowest risk for recurrent infection.³⁹

5.2. Stress shielding

The stress distribution in the humeral stem in the proximal humerus is greater than that in other parts of the bone, which results in resorption of the humeral bone around the proximal prosthesis, termed "stress shielding.".¹⁵ Osteoporosis and the relative size of the stem are predisposing factors for stress shielding. Cortical thinning and a relative increase in central periprosthetic radiolucency are radiographic indicators of stress shielding..^10,40,41

5.3. Periprosthetic fractures

Periprosthetic fractures can occur with all shoulder arthroplasty procedures and can affect humeral and glenoid components. Compared with postoperative fractures, reverse shoulder replacement surgery is relatively more prone to cause periprosthetic fractures, with more frequent intraoperative periprosthetic fractures..⁴² In shoulder replacement surgeries, intraoperative glenoid fractures often result from screw penetration into the glenoid vault and reaming of the glenoid surface..¹⁰ Conversely, postoperative periprosthetic humeral fractures near the implant are more common due to stress shielding effects..^40,41 [Fig. 3, Fig. 4]. Reduced bone density and trauma also play a contributory role. {Fig. 5, Fig. 6, Fig. 7]. Postoperative radiographs were used to identify early periprosthetic fractures to ensure optimal patient recovery..⁴¹

Fig. 3.

Anteroposterior radiographs of a left shoulder stemmed hemiarthroplasty. There is marked periprosthetic lucency (arrows) of the humeral stem consistent with loosening.

Fig. 4.

Scapular Y-view (a) and anteroposterior (b) radiographs of a left shoulder stemmed hemiarthroplasty. There is marked periprosthetic lucency of the humeral stem consistent with loosening. There is also a periprosthetic fracture (arrows).

Fig. 5.

Anteroposterior radiograph of a cemented left reverse total shoulder arthroplasty demonstrates a spiral periprosthetic fracture of the distal humeral stem (arrow). Note background osteopenia of the humerus.

Fig. 6.

Anteroposterior radiograph of a right shoulder resurfacing hemiarthroplasty with a periprosthetic fracture of the greater tuberosity (arrow) extending into the surgical neck. There is also resorption of lateral clavicle.

Fig. 7.

Anteroposterior radiograph (a) and coronal computed tomography image (b) of a left shoulder resurfacing hemiarthroplasty. There is a subacute periprosthetic fracture (arrows) caudal to the humeral head prosthesis with callus formation.

5.4. Heterotopic ossification

Heterotopic bone formation is a common occurrence following shoulder arthroplasty. It typically develops within a year of surgery, and rotator cuff dysfunction is identified as a significant risk factor for its development. Plain radiographs are often used to detect the presence of heterotopic ossifications.⁴³ Additional information, such as the precise location and extent of ossification, is obtained through CT imaging. This finding becomes clinically relevant when patients exhibit limited active arm elevation.⁴⁴

5.5. Implant failure

Implant failure is an infrequent but consequential occurrence that requires surgical intervention. Such failure can manifest as subluxation or dislocation of humeral or glenoid components, fractures of the prosthesis, and loosening or breakage of screws, pegs, or keel. Additionally, the dissociation of the attachment between the glenosphere and metaglene can lead to implant failure..¹⁰ [Fig. 8, Fig. 9].

Fig. 8.

Anteroposterior radiograph of a right reverse total shoulder arthroplasty with posterosuperior dislocation of the humeral component in relation to the glenoid sphere. Further periprosthetic fracture of the humeral stem distally (arrow).

Fig. 9.

Anteroposterior (a) and axillary (b) radiographs of a cemented right reverse total shoulder arthroplasty with anterosuperior dislocation of the humeral component relative to the glenoid sphere.

5.6. Nerve injury

Nerve injuries following shoulder arthroplasty are infrequent and often resolve spontaneously. The axillary nerve is frequently affected, followed by the brachial plexus. Immediate postoperative imaging may reveal inferior subluxation of the humerus due to deltoid muscle inhibition, which typically resolves on follow-up imaging. Deltoid muscle dysfunction, a significant complication resulting from axillary nerve involvement, can lead to reduced abduction and inferior instability of the shoulder joint.⁴⁵ Ultrasound and elastography are valuable tools for diagnosing deltoid muscle abnormalities, while MRI with metal artefact reduction sequences can also provide helpful diagnostic information.

5.7. Humeral component loosening

Classic risk factors for component loosening include osteoporosis, rheumatoid arthritis, and rotator cuff tear arthropathy. A radiolucency of greater than 0.5 mm at the prosthesis-bone interface in a press-fit component/uncemented prosthesis suggests loosening..^10,15,21 [Fig. 10, Fig. 11].

Fig. 10.

Anteroposterior radiograph of a right total shoulder replacement with endoprosthesis. There is lucency surrounding the distal humeral stem (arrow) with early subsidence consistent with loosening.

Fig. 11.

Anteroposterior radiograph of a cemented right reverse total shoulder arthroplasty with lucency at the bone cement interface of the proximal humeral stem (arrow) measuring > 2 mm indicating loosening.

6. Specific complications of total shoulder arthroplasty

6.1. Glenoid Periprosthetic loosening/failure

Glenoid Periprosthetic loosening is responsible for 35 % of all TSA complications and is more frequent than humeral component loosening [Fig. 13].^10,15,42

Fig. 13.

Anteroposterior (a) and axillary (b) radiographs of a left standard total shoulder arthroplasty. There is lucency surrounding the glenoid component consistent with loosening.

Radiologic assessments are paramount in determining the stability of prosthetic implants. Progressively appearing radiolucent lines exceeding 1.5 mm, as observed in serial radiographs, along with component migration, subsidence, or tilt, may indicate implant loosening. Furthermore, prosthetic components (pegs) containing cement mantles may result in particle disease visible in adjacent soft tissue. Therefore, a thorough radiologic evaluation is essential to ensure the stability and longevity of prosthetic implants..^15,22

6.2. Rotator cuff tear

A rotator cuff tear can cause issues by disrupting shoulder movement and altering biomechanics. A common problem that may occur following shoulder replacement surgery is reduced function of the subscapularis muscle, potentially resulting in anterior shoulder instability. The importance of repairing and reattaching the subscapularis tendon during surgery cannot be overstated, as it significantly impacts adequate tendon healing.²⁷ [Fig. 12].

Fig. 12.

Anteroposterior radiograph (a) and axial CT(b) of a left shoulder total standard shoulder replacement with cystic change (arrow) adjacent to the glenoid cup consistent with loosening.

On standard radiographs, the presence of a supraspinatus tear may be indicated when the distance between the superior aspect of the humeral prosthesis and the acromion measures less than 5 mm.¹⁰ Additionally, anterior translation of the humeral head on anteroposterior and scapular Y view radiographs may suggest insufficiency of subscapularis.^10,42,46 Excessive protrusion of the humeral head superior to the greater tuberosity may lead to increased pressure on the rotator cuff. Furthermore, a humeral-acromial space that measures less than 7 mm or anterior decentring of the humeral head on the axillary view may suggest the presence of a rotator cuff tear.^10,15,46

Ultrasonography aids diagnosis by directly visualising the tear, while MRI is beneficial, provided that the susceptibility artefacts do not impede interpretation. MRI and CT facilitate the detection of fatty degeneration of the rotator cuff.

7. Specific complications of RSA

7.1. Shoulder instability

Instability can occur after RSA. If it is not addressed correctly, instability can result in the loss of function in the upper extremity. The causes of instability are multifactorial and include inadequate restoration of arm length, component malposition, bony impingement, insufficient soft tissue tension, liner wear, infection, and axillary nerve dysfunction.⁴⁷

Instability typically manifests in an anterior-superior direction due to unopposed deltoid contraction. Hence, any factor contributing to suboptimal deltoid tensioning poses a risk.

Common factors contributing to deltoid dysfunction include rupture or incorrect surgical technique, axillary nerve injury, and acromial fracture.¹⁰ The diagnosis of instability is typically straightforward on standard radiographs, where anterior and superior dislocation of the humeral component aligns with the direction of the deltoid muscle.²¹

Surgical management of instability post-RSA is challenging, with reported failure rates of up to 40 %. The recurrence of instability in patients undergoing revision surgery for the same issue is a common concern, highlighting the complexity of addressing this complication effectively.²³

7.2. Scapular notching

Scapular notching is a distinct complication explicitly associated with RSA, with incidence as high as 90 %.^10,48,49 It occurs when the humeral cup impinges on the lateral scapular pillar during adduction..^10,15 On radiographs and CT, bone resorption along the inferior margin of the scapula is typically observed. Furthermore, scapular notching may lead to limited adduction, resulting in particle disease, which manifests as osteolysis.

The Sirveaux classification is used to report the severity of notching. [Table 1]. The significance of Sirveaux's classification is that grade 3 and 4 notching may require revision because of the loosening of components.^15,49

Table 1.

Table 1 showing Sirveaux classification - Severity of scapular notching (Radiographs and CT).

Grade	Description
1	Limited to the pillar
2	Contacts the lower metaglene screw
3	Extends over the entire inferior metaglene screw
4	Involvement under the metaglene baseplate

7.3. Acromion and scapular fractures

Fractures of the acromion and spine of scapula represent specific complications associated with RTSA, with a reported incidence of approximately 1 %.^10,15,50 They are more frequently observed in osteopenic patients, particularly those with osteoporosis, and are considered long-term complications.¹⁰ These fractures pose an increased risk for prosthetic revision.^10,50,51 Diagnosing scapular spine and acromion fractures via radiographs can be challenging. Therefore, CT is often employed to detect these fractures accurately.^10,51,52 [Table 2, Table 3].

Table 2.

Table 2 showing different types of Scapular and acromion fractures.

Type of fracture	Description (based on fracture line location relative to the origin of deltoid muscle)
I	Involvement of a portion of the anterior and middle deltoid origin
II	At least the entire middle deltoid origin with a portion but not all the posterior deltoid origin
III	The entire middle and posterior deltoid origin

Table 3.

Table showing complications with imaging features and modality.

Complications	Imaging features
Infection	Irregular progressive lucency around the prosthesis with periosteal and cortical thickening on radiographs and CT SPECT/CT-2 mm or more widening of the periprosthetic lucency, subchondral cysts, ill-defined osteolysis, abscess, granuloma, effusion, and florid periosteal reaction
Stress sheilding	Periprosthetic lucency with cortical thinning on radiographs, CT or MRI
Fractures	Fractures can be seen on radiographs, CT or MRI
Heterotopic ossification	Heterotopic ossification can be seen on radiographs, CT or MRI
Implant failure	Subluxation, dislocation and fracture can be seen on radiographs, CT or MRI
Nerve injury	Nerve injury can be diagnosed on ultrasound, MRI or nerve conduction studies
Rotator cuff tear	These can be diagnosed on ultrasound. MRI and CT can aid using MARS (metal artefact reduction sequence)

8. Specific complications of partial shoulder arthroplasty

• 1.Progressive wear of the glenoid

The main complication of partial shoulder joint replacement is the development of glenoid osteoarthritis..^10,13 [Fig. 14]. Glenoid erosion is the most common long-term complication of hemiarthroplasty.^15,53 This complication is typically identified on imaging as progressive joint space narrowing and decentring of the humeral head..¹⁵ [Fig. 15]. In such cases, prosthetic revision and conversion to TSA are usually performed.⁵⁴

Fig. 14.

Anteroposterior (a) and axillary (b) radiographs of a right shoulder resurfacing hemiarthroplasty. The humeral prosthetic head and the native glenoid are congruent but there is mild sclerosis within the superior glenoid.

Fig. 15.

Anteroposterior (a) and axillary (b) radiographs of a right shoulder resurfacing hemiarthroplasty. The humeral prosthetic head and the native glenoid are congruent but there is marked sclerosis of the glenoid.

9. No funding to declare

No conflicts of interest.

10. Conclusion

Currently, there is an increasing inclination toward performing shoulder arthroplasty. Understanding the expected postoperative imaging findings and complications associated with different types of shoulder arthroplasty is crucial for identifying early complications and ensuring effective management.

Statements and declarations

The authors declare that they have no conflict of interest. No funding to declare.

Consent has been obtained from the patient for publication of anonymized images.

Author statement

(1)conception and design, or acquisition of data, or analysis and interpretation of data, = ²Botchu R.

(2)design, or acquisition of data, or analysis and interpretation of data = ¹Mettu S, ³Iyengar KP, ²Botchu R.

(3)drafting the article or revising it critically for important intellectual content, - ¹Mettu S, ²Shirodkar K, ²Hussein M, ³Iyengar KP, ⁴Chapala S, ²Botchu R.

(4)final approval of the version to be published, ¹Mettu S, ²Shirodkar K, ²Hussein M, ³Iyengar KP, ⁴Chapala S, ²Botchu R.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.