Shoulder Arthroplasty Complications

Shoulder arthroplasty has the highest revision rate of all joint replacements, approximately 10% at 10 years for anatomic TSA and 15% for reverse shoulder arthroplasty (RSA). Registry data show complication rates increasing with time, so surveillance has to be long term.

What a complication costs. Outcome scores drop by 20-30 points after a complication, and patient satisfaction falls from 90% to under 60% when the complication is major. A revision procedure costs 2-3 times as much as the primary arthroplasty.

Complications arise from three mechanisms, and naming the mechanism guides both prevention and treatment.

Biological. Bacteria form a biofilm on the implant surface; Staphylococcus epidermidis and Cutibacterium acnes are the typical organisms. Polyethylene wear debris triggers macrophage activation and osteolysis. Bone is also lost to stress shielding from the humeral stem and to glenoid bone loss, and the soft tissues fail when a subscapularis repair gives way or rotator cuff disease progresses.

Mechanical. Instability follows insufficient soft-tissue tension or component malposition. Glenoid loosening follows eccentric loading and poor fixation. Impingement takes the form of scapular notching in RSA and subacromial impingement in TSA, and the metal-on-polyethylene articulation wears over time.

Technical. Malposition, sizing errors and nerve injury are the technical complications.

Complications are classified three ways: by when they appear, by which component fails, and by how severe they are. Timing is the key to the differential diagnosis, although instability can occur early or late.

Each complication has its own pain pattern, functional loss and signs, and the time since surgery narrows the list before the examination begins.

The first two weeks. A nerve injury shows immediately after surgery as deltoid weakness or sensory loss. Acute infection declares itself with wound drainage persisting beyond 5 days, fever and a raised WBC, and early instability as failure to reach range-of-motion milestones or a feeling of subluxation.

Two weeks to three months. Wounds may heal slowly, keep draining or develop a superficial infection. Instability now presents as dislocation during therapy or after minor trauma, or as recurrent subluxation, and a fall during recovery brings the new pain and deformity of a periprosthetic fracture.

Three months to two years. Chronic infection shows as persistent pain despite an appropriate recovery, with a raised CRP. Component loosening gives progressive pain with loading and mechanical clicking, and subscapularis failure costs internal rotation and brings symptoms of anterior instability.

After two years. Glenoid loosening brings progressive pain and crepitus, with loss of previously good function. Polyethylene wear causes clicking, catching, reduced range of motion and metallosis symptoms, and a late cuff tear presents as pseudoparalysis after a period of good function.

Differential Diagnosis of the Painful Shoulder Arthroplasty

The painful or poorly functioning replaced shoulder is a common exam scenario. The key discriminator is to exclude infection first in every case, then separate mechanical, neurological and extrinsic causes using timing, examination and targeted imaging.

First line. Radiographs in three views, AP, scapular Y and axillary lateral, show component position, lucent lines and fracture. Serial films compared with previous ones are essential for detecting progression. CRP and ESR are more useful as a trend than as absolute values, and the white cell count and differential are raised in acute infection.

Advanced imaging. Each modality answers a different question:

• CT: component version, bone defects and fracture characterisation
• MRI: rotator cuff integrity and soft-tissue assessment, within the limits of metal artefact
• Ultrasound: aspiration guidance, fluid collections and subscapularis integrity
• Nuclear medicine: Tc-99 bone scan or WBC scan if infection is suspected

The Infection Workup

The diagnostic criteria divide into major and minor. The major criterion is two positive cultures of the same organism; the minor criteria are a raised ESR or CRP, positive histology and purulence. The workup runs in order:

1. Clinical suspicion (day 0). Persistent pain, fever, wound problems or raised inflammatory markers. Take a full blood count, ESR and CRP before antibiotics if possible, and radiographs for component position and lucent lines.
2. Aspiration (days 1-2). Under ultrasound or fluoroscopic guidance, by an anterior approach. Send fluid for cell count with differential, aerobic and anaerobic cultures on a 14-day hold, and Gram stain. Over 3000 WBC with over 80% PMNs suggests infection.
3. Culture results (days 5-14). Standard cultures report common organisms at 5 days; the extended hold is for slow-growing C. acnes. If cultures are negative, consider alpha-defensin, extended culture or surgical biopsy.
4. Surgical confirmation. Take a minimum of 5-6 tissue samples from different sites and send removed components for sonication, which increases culture yield by 15-25%. On frozen section, more than 5 PMNs per high-power field suggests infection.

Radiographic Assessment

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Algorithm

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Instability

Incidence and direction. Instability is the most common complication of RSA, occurring in 5-10%, against 1-3% of anatomic TSA. In RSA it is characteristically anterior: the humeral cup escapes anterosuperiorly off the glenosphere. In anatomic TSA the direction follows the cause, anterior with subscapularis failure and posterior with glenoid retroversion and posterior wear (Walch B).

Risk factors. The subscapularis is the primary anterior stabiliser, so its deficiency or a failed repair is a leading risk for RSA instability. The positional and soft-tissue factors are in the table; revision surgery, arthroplasty for fracture sequelae, male sex, high BMI and deltoid or capsular insufficiency add to the risk.

Recognition. The patient has sudden loss of function, pain, a visible deformity and holds the arm protectively. AP and axillary lateral radiographs confirm the direction of dislocation. Document axillary nerve function and the radial pulse before and after reduction.

Closed reduction. Reduce under conscious sedation. For an anterior RSA dislocation, apply traction with gentle adduction and internal rotation to lever the cup back over the glenosphere; muscle relaxation is usually needed because the construct is tensioned. An anterior TSA dislocation reduces with traction, abduction and external rotation. Afterwards the axillary view is essential to confirm a concentric reduction, and the stable arc of motion is assessed.

Component assessment. A CT scan within 1 week measures the component position against its targets:

• Glenoid version: 5-15° retroversion in RSA (target 10°), 5-10° in TSA
• Humeral retroversion: 20-30°
• Glenosphere lateralisation in RSA: minimum 25mm from the glenoid face

The decision. A first dislocation with well-positioned components is treated by immobilisation for 4-6 weeks with physiotherapy; open reduction, soft-tissue repair and a constrained liner if needed are the surgical options at this stage. Any recurrence, or malposition on CT, goes to revision, because once instability recurs non-operative management fails in over 70%. Revision corrects version, tilt or lateralisation and may add a constrained liner, a larger glenosphere, increased tension or soft-tissue reconstruction; soft-tissue deficiency calls for a constrained liner or an augmented glenosphere. In TSA the subscapularis is repaired, with allograft reconstruction if needed, and posterior instability may call for posterior capsular plication. Fusion is the salvage after multiple failed revisions.

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Infection (Periprosthetic Joint Infection)

Incidence and organisms. Infection occurs in 2-6% of shoulder arthroplasties, more often after revision. The organisms, in order of frequency:

• Cutibacterium acnes, 30-40%: indolent, male patients
• Staphylococcus epidermidis, 25-30%: biofilm former; against the indolent C. acnes, it causes more acute presentations
• S. aureus, 15-20%: more acute presentation
• Culture-negative, 10-15%: consider C. acnes with extended culture

Acute or chronic. The dividing line is 4 weeks. Acute infection presents with wound drainage, erythema, fever and a raised WBC. Chronic infection presents with persistent pain, a CRP over 10 mg/L and mechanical symptoms. Positive cultures are part of the criteria for both.

Acute PJI (under 4 weeks). This is a surgical urgency with no conservative option. Debride urgently, within 24-48 hours: remove the polyethylene liner, debride the soft tissues aggressively, take 5-6 tissue cultures and send removed components for sonication. The components are retained only if they are stable, the infection is acute and the organism is known, and the polyethylene liner is exchanged. Antibiotics are culture-directed and continue for at least 6 weeks. If retention fails, the options are two-stage revision or resection arthroplasty.

Chronic PJI (over 4 weeks). Biofilm on the components requires their removal, and the standard is two-stage revision. Stage one removes all components, debrides and places an antibiotic spacer, either static (a cement block) or articulating (PROSTALAC design), made from cement with high-dose vancomycin (3-4g) and tobramycin (2-4g) per 40g. 6-12 weeks of IV antibiotics follow, and stage two reimplants new components once the infection has cleared. Suppressive antibiotics alone are reserved for patients who are not surgical candidates; permanent spacer, resection arthroplasty and fusion are the salvage options.

Single-stage or two-stage. Single-stage revision, which removes, debrides and reimplants at one sitting, remains controversial. It can be considered for a low-virulence organism such as C. acnes in a healthy patient with good soft tissue and bone stock. Two-stage suits a high-virulence organism such as S. aureus, poor bone stock or an immunocompromised patient. Resection arthroplasty is for insufficient bone stock or a patient who is not a surgical candidate.

Reimplantation. Stage two proceeds only when these conditions are met:

• Clinical: healed wound, no drainage, patient systemically well
• Laboratory: CRP normalised to less than 10 mg/L, with normal ESR and WBC
• Aspiration: negative cultures and synovial WBC less than 1500

Antibiotics. Start empirical vancomycin plus ceftriaxone until cultures are available, then treat the organism:

• C. acnes: penicillin G IV for 4 weeks, then oral amoxicillin for 2-6 months
• S. aureus (MSSA): cefazolin or nafcillin for 6 weeks
• Staphylococcal species: rifampicin is often added for biofilm cover

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Glenoid Component Loosening

The scale of the problem. Glenoid loosening is the leading cause of anatomic TSA failure and accounts for 30-40% of all TSA revisions. Radiolucent lines develop in 20-30% of patients by 10 years, but only 5-10% become symptomatic and need revision. Symptomatic loosening presents late, over 5 years after surgery.

Presentation. Pain is progressive and worse with activity and loading. Mechanical symptoms of clicking, clunking and catching accompany a loss of motion, especially forward elevation and rotation, and weakness follows from pain and the mechanical block. Radiographs show periglenoid radiolucent lines and eccentric glenoid wear.

Reading the lines. Two things are recorded: the zone that locates the line around the component, and its grade on a 0-5 scale. A line under 1mm is often benign and stable, and a line over 2mm is concerning; a progressive line over 2mm, widening on serial films, indicates loosening. The all-polyethylene glenoid is the implant most commonly showing lucent lines, and lucency around the pegs is more predictive. It is progression and migration on serial films, together with symptoms such as pain, clicking and reduced range of motion, that signal failure, not the mere presence of a line.

Management. Asymptomatic loosening is observed with activity modification and serial radiographs. Symptomatic loosening gets activity modification and analgesics only as a temporary measure; the definitive answer is revision, and the rotator cuff decides which. With an intact cuff the option is revision TSA; with a deficient cuff, conversion to RSA. CT defines the bone defects as cavitary or segmental, and bone grafting is needed in 30-50% of revisions. Resection arthroplasty is the salvage when bone stock is poor.

Nerve Injuries

The axillary nerve is the nerve most at risk, injured in 1-4%. Most nerve injuries are neurapraxias that recover in 3-6 months.

Recognition. Examine immediately after surgery and compare with the documented preoperative function. An axillary nerve injury shows as loss of deltoid contraction and numbness over the lateral shoulder; a musculocutaneous injury as a weak biceps and numbness of the lateral forearm; a suprascapular injury as weakness of external rotation (infraspinatus).

Management. The protocol runs by time since injury:

1. Weeks 0-6. Observe, with physiotherapy to maintain range of motion and prevent contractures, a brace for protection, and reassurance about the high recovery rate.
2. EMG/NCS at 3-4 weeks if there is no recovery. The baseline study establishes severity and localisation, and distinguishes axonotmesis from neurapraxia by recruitment and amplitudes.
3. Repeat EMG at 3 months to look for reinnervation.
4. Exploration if there is no recovery by 6 months, meaning complete paralysis with no EMG recovery. Identify the nerve, assess its continuity, and consider neurolysis or grafting. Late exploration, beyond 6 months, has poor outcomes.
5. Permanent deficit. Tendon transfers or functional bracing.

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Periprosthetic Fractures

Risk factors. Patient factors are osteoporosis, age over 70 and rheumatoid arthritis. Surgical factors are excessive reaming, press-fit stems and revision for cuff tear. Uncemented stems carry 3 times the risk of cemented ones, and falls are a risk, especially in RSA with its altered biomechanics.

Classification and management. The Vancouver classification, adapted for the shoulder, is by fracture site, and for Type B by stem stability and bone stock:

• Type A, apophysis (greater or lesser tuberosity): sling immobilisation unless displaced over 5mm
• Type B1, around or just below a stable stem: ORIF with plate and cables preserving the component, or non-operative if undisplaced; revise if fixation fails
• Type B2, around a loose stem: revision to a long-stem prosthesis bypassing the fracture by 2 cortical diameters, with strut allografts
• Type B3, with poor bone stock: long-stem revision with structural or strut allograft
• Type C, well below the stem: treat as a native fracture, ORIF if displaced

Type B is the most common. An intraoperative tuberosity fracture is fixed with cerclage, and rehabilitation is delayed.

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Humeral Stress Shielding and Bone Resorption

Mechanism. A stiff, well-fixed humeral stem carries load down the diaphysis and unloads the proximal humerus (Wolff's law), so the bypassed proximal bone resorbs. The signs are calcar and medial-metaphyseal resorption, greater-tuberosity osteopenia and cortical thinning, often with distal cortical hypertrophy and condensation lines around the stem tip.

Risk factors. Longer, larger-diameter, well-fixed stems carry the risk, especially cemented or extensively coated ones. Stress shielding is less marked with short-stem and stemless designs, which load the metaphysis more physiologically, and this is a major driver of the trend toward shorter humeral fixation.

Distinguishing it from loosening. Stress shielding is adaptive remodelling: proximal resorption with the stem still well fixed. Loosening shows a progressive, circumferential lucent line at the bone-implant interface, with component migration or subsidence. Humeral loosening is less common than glenoid loosening.

Why it matters. Stress shielding is usually asymptomatic and rarely mandates revision in itself. It does erode the bone stock needed at any future revision, and may predispose to periprosthetic fracture.

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Exposure for revision. Use an extended deltopectoral approach for adequate exposure, and identify and protect the neurovascular structures; the axillary nerve is often scarred. Mobilise the subscapularis carefully, as it may need extensive release. Remove the components systematically, the humeral component first and then the glenoid.

Bone defects. Once the components are out, assess the size and location of the defect, cavitary or segmental, and match the reconstruction to it:

• Cavitary defects: impaction bone grafting with morselised cancellous allograft
• Contained or segmental defects under 25% of the surface: eccentric reaming, cement filling or augmented components
• Large segmental defects over 25%: structural allograft wedge grafts or custom implants
• Glenoid vault deficiency: consider a metal augmented baseplate
• Severe bone loss: custom components, tumour prosthesis or salvage procedures

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The first six weeks after revision.

• Sling immobilisation for 6 weeks, against 2-4 weeks after a primary
• DVT prophylaxis, mechanical and chemical (aspirin or LMWH)
• Multimodal analgesia: regional block, paracetamol, NSAIDs, opioids as needed
• Daily wound inspection for drainage, erythema and dehiscence

Slower than a primary. Rehabilitation after revision typically runs 4-6 weeks behind a primary, with strengthening delayed to 16-24 weeks against 12, and bone graft incorporation needs additional protection. The indication adjusts it further. After revision for instability, immobilisation may be prolonged to 8 weeks in the position of stability. After revision for infection, IV antibiotics continue as infectious disease guidance directs, typically for 6-12 weeks. After revision for fracture, activity is restricted until radiographic union.

Monitoring. CRP and ESR are checked weekly during IV antibiotics, then monthly for 3 months after an infection. Radiographs are taken at 6 weeks, 3, 6 and 12 months, then annually, and clinical review is 6-weekly in the first year, more often than after a primary arthroplasty.

Return to activity. Milestones after revision:

• Driving: 8-12 weeks, once an emergency manoeuvre is comfortable
• Sedentary work: 6-8 weeks
• Manual work: 4-6 months or longer, depending on healing
• Golf and swimming: 4-6 months at the earliest

Red flags. Urgent review is needed for new fever or wound drainage, sudden loss of range of motion, mechanical symptoms such as clunking or catching, and new neurological symptoms.

Preoperative planning.

• CT: bone stock, component position and version
• Infection workup: ESR, CRP, and aspiration if there is any concern
• Rotator cuff status by MRI or ultrasound, which determines revision to TSA or RSA
• Implant identification: know the existing system for its extraction tools
• Patient optimisation: nutrition (albumin over 3.5), diabetes (HbA1c under 7%), smoking cessation

The revision construct. On the glenoid side an RSA baseplate may give better fixation than a new TSA glenoid. On the humeral side a long-stem component is used if there is bone loss or fracture risk. Cemented fixation is preferred in the revision setting for immediate stability.

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Function after revision. Active forward flexion averages 100-120°, against 140-150° after a primary RSA, and external rotation averages 20-30°. Patient satisfaction is 70-80%, against 85-90% after a primary. The ASES score improves by an average of 30-40 points, less than after a primary.

Prognostic factors. A single prior operation, adequate bone stock, an intact deltoid and a healthy patient predict a better result. Multiple prior revisions, massive bone loss, poor soft tissue and immunocompromise predict a worse one.

Registry signals (AOANJRR, NJR, Nordic).

• Reverse arthroplasty has a higher cumulative revision rate than anatomic TSA at comparable follow-up across the major registries
• Conversion of failed anatomic TSA to RSA generally outperforms revision RSA undertaken for failed RSA
• Instability or dislocation, infection and loosening or lysis are consistently the leading recorded reasons for revision
• Exact percentages vary by registry and report year and should be quoted from the current annual report rather than memorised

Survivorship. In typical reported ranges, primary TSA survives at approximately 90% at 10 years in cohort and registry series. Primary RSA survival is lower, broadly 85-90% depending on indication and design, and revision shoulder arthroplasty survivorship is markedly lower than primary.

Quality of life. Patients after a complication report lower satisfaction than after a primary. Persistent pain remains in 15-25% even after a successful revision, and anxiety about re-revision affects 30-40%.

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Infection.

• Optimise nutrition, control diabetes (HbA1c under 7%) and treat remote infections before surgery
• Cefazolin 2g (3g if over 120kg) within 60 minutes of incision
• Chlorhexidine-alcohol skin preparation, which is superior to povidone-iodine
• A benzoyl peroxide wash protocol for male patients, against C. acnes
• Iodine-impregnated drapes may reduce infection

Instability.

• Verify version and tilt intraoperatively with fluoroscopy, and ensure the minimum lateralisation in RSA
• Repair the subscapularis anatomically in TSA
• Trial-reduce and test stability through the arc before inserting the final components
• Avoid oversizing: the humeral component should not overstuff the joint

Glenoid loosening.

• Ream to cancellous bone and avoid anterior perforation
• Correct excessive retroversion to the target version
• Pressurise the cement with a finger or syringe
• The cemented all-polyethylene pegged glenoid is the standard component
• Consider RSA for young, high-demand patients

Nerve injury.

• Record preoperative nerve function as a baseline, which is also essential for medicolegal protection
• Avoid hyperextension and excessive abduction of the arm under anaesthesia
• Retract gently and avoid pressure on the neurovascular structures
• Release the inferior capsule under direct vision to protect the axillary nerve
• Avoid superior baseplate screws over 30mm long to protect the suprascapular nerve

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Global epidemiology

Shoulder arthroplasty is one of the fastest-growing arthroplasty procedures worldwide, driven overwhelmingly by the expansion of reverse total shoulder arthroplasty (RSA) beyond cuff-tear arthropathy into osteoarthritis with cuff insufficiency, proximal humeral fracture, and revision of failed primaries. Population-based and registry analyses from North America, Europe and Australasia consistently show year-on-year increases in volume and a shift in case-mix toward RSA in older patients. Because indications and implant mix differ between regions, reported complication and revision rates must always be interpreted against the underlying population and implant design.

Major guidelines side by side

Registry evidence (global)

Global practice variation

• Implant choice: RSA now predominates for cuff-deficient and fracture indications in high-resource settings; anatomic TSA is preferred for OA with an intact cuff and good glenoid bone stock. In limited-resource settings, hemiarthroplasty retains a larger role due to cost and implant availability, accepting a higher rate of glenoid erosion.
• Cutibacterium strategy: Routine prolonged culture and benzoyl-peroxide skin preparation are widely adopted in shoulder-specialist centres but inconsistently applied elsewhere.
• Revision pathway: Single-stage versus two-stage revision for low-virulence PJI varies by region and surgeon, reflecting genuine equipoise rather than a settled standard.
• Surveillance: Countries with mandatory or near-complete registries (Australia, Nordic countries, UK) provide the most reliable revision data; elsewhere, complication estimates rely on single-centre series and are more prone to under-reporting.