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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Dislocation, loosening and infection after arthroplasty

Musculoskeletal medicine and orthopaedics · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Dislocation, sepsis, fracture and neurovascular change need immediate action

A replaced joint can fail through dislocation, peri-prosthetic fracture, acute infection or implant migration; delay risks nerve or vessel injury, tissue damage, bacteraemia and loss of reconstructive options.

Action: Assess ABCDE and distal neurovascular status, obtain urgent radiographs, keep a dislocated or fractured limb protected and nil by mouth, reduce dislocation promptly under appropriate analgesia and imaging, and take blood cultures then start intravenous antibiotics and arrange emergency drainage when acute prosthetic-joint infection causes sepsis.

Overview

Triage a painful hip or knee replacement into immediate mechanical emergency, infection and gradual failure pathways; use comparison imaging and disciplined sampling, and avoid revision without a specific diagnosis.

Start with timing. Immediate postoperative pain, acute pain after a previously well interval and gradual progressive pain carry different probabilities. Ask about original indication and implant, wound healing, drainage, later infections or bacteraemia, antibiotic exposure, falls, clicks, instability, start-up pain, night pain and systemic symptoms. Establish whether the hip or knee ever functioned well. Obtain operative and implant records and compare serial radiographs; revision planning without knowing components and previous exposures is unsafe.

For acute suspected dislocation or fracture, assess limb length, rotation, swelling, wounds and distal pulses, capillary refill, motor and sensory function. Obtain orthogonal radiographs including the whole relevant implant and adjacent bone. Keep nil by mouth, provide analgesia and avoid unsupported weight bearing. Closed reduction needs adequate relaxation, appropriate personnel and readiness for fracture or irreducibility. Repeat neurovascular examination and radiographs afterwards. CT is indicated when fracture, component failure or uncertain concentric reduction persists.

Practice

Two practice questions

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Musculoskeletal medicine and orthopaedicsOriginal SBA

First problematic-knee tests

A patient has increasing pain and perceived instability two years after knee replacement without acute sepsis. Which initial investigation set is most appropriate?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • BOASt - Investigation and Management of Patients with Problematic Knee Replacements
  • BOASt - Acute Management of Peri-Prosthetic Joint Infection
  • BOA Best Practice Hip Arthroplasty
  • NICE NG125 Surgical site infections: prevention and treatment

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom

A problematic replacement needs structured consultant-led assessment. BOASt for knee replacement recommends clinical examination, radiographs and infection serology as initial tests. Full weight-bearing AP and lateral, long-leg alignment and patellar skyline views are standard for knee; partial replacements need appropriate flexion views. For hips obtain AP pelvis and lateral views and assess migration, lucency, osteolysis, wear, fracture, leg length and component orientation. Serial change is more convincing than a single subtle line.

Always exclude infection before labelling loosening aseptic or revising for another reason. Examine the wound and any sinus without probing, take FBC and CRP or ESR, and obtain blood cultures in systemic illness. A communicating sinus or visible prosthesis is confirmatory. A stable patient should not receive antibiotics before image-guided aspiration or planned deep sampling. Send synovial count, differential, cultures and crystals and apply validated infection criteria. At surgery use five deep microbiology specimens and appropriate histology with separate instruments.

Aseptic loosening typically causes load or start-up pain with progressive radiolucency, migration, subsidence or osteolysis. CT maps bone loss, component rotation and occult fracture. SPECT-CT may help selected uncertain cases but complex testing belongs in the revision MDT. Bone scanning and minor exploratory operations have no routine role in a problematic knee under BOASt. Investigate metal-related adverse tissue reaction only for relevant bearing and clinical context using the current implant-safety pathway.

After first hip dislocation, identify precipitating movement, component orientation, impingement, abductor function, neurological disease and spinopelvic stiffness. A brace is selective rather than automatic. Recurrent dislocation, irreducibility, component malposition, fracture, liner failure or major soft-tissue deficiency may require revision. Educate on safe movement according to surgical approach and individual cause without imposing indefinite generic restrictions that delay mobility.

Prosthetic-joint infection management depends on sepsis, symptom duration, implant stability, soft tissue and organism. A septic patient receives urgent cultures, immediate parenteral treatment and drainage. Carefully selected early postoperative or short-duration haematogenous infection may undergo open debridement, modular-component exchange and implant retention. Chronic biofilm, loosening, sinus or unsuitable organisms usually requires component exchange. Antimicrobial choice and duration are tied to surgery through the infection MDT.

Revision should correct a defined mechanism. BOASt warns that surgery without a firm diagnosis is less likely to benefit; unexplained cases need MDT discussion and may need pain, physiotherapy or other specialist pathways. Explain that further surgery can worsen pain, stiffness, bone loss and infection. After intervention, follow wound, cultures, radiographs, stability and personal functional goals. Urgent return signs include fever, drainage, recurrent deformity, inability to bear weight, new neurological symptoms and calf or chest symptoms.

Key points

  • For sudden deformity or loss of function, record neurovascular status and obtain AP and orthogonal radiographs before and after reduction; do not repeatedly manipulate a possible fracture.
  • A first hip dislocation is reduced promptly with adequate sedation or anaesthesia, then assessed for fracture, component position, cause and stability; recurrent episodes need revision expertise.
  • A painful replacement is not automatically loose or infected. Build a timeline of surgery, wound, pain-free interval, trauma, bacteraemia, antibiotics, mechanical symptoms and systemic features.
  • Initial problematic-knee assessment includes consultant review, examination, infection screening and full weight-bearing AP and lateral, long-leg alignment and skyline radiographs.
  • A sinus communicating with the prosthesis confirms infection. Stable suspected infection stays off antibiotics until aspiration or deep samples; septic infection receives blood cultures, immediate intravenous therapy and drainage.
  • Loosening is assessed first on comparison radiographs; CT clarifies rotation, bone loss or occult fracture, while more complex tests should be targeted through the revision arthroplasty MDT.
  • Do not perform revision for unexplained pain. Identify a specific correctable cause such as infection, loosening, instability, malposition, stiffness, fracture, wear or extensor failure.
  • After reduction, DAIR or revision, monitor wound, infection markers, component stability, thrombosis, neurovascular status and rehabilitation and provide explicit recurrence and emergency instructions.

Aetiology

01

Dislocation mechanics

Component position, soft-tissue tension, impingement, abductor failure, spinal stiffness and high-risk movement can overcome hip stability, especially early after surgery.

02

Aseptic loosening

Wear particles, interface micromotion and biological osteolysis progressively weaken implant fixation without necessarily producing systemic inflammation.

03

Prosthetic-joint infection

Organisms enter perioperatively, through wound breakdown or later bacteraemia and form implant biofilm that resists host clearance and standard short courses.

04

Trauma and tissue failure

Falls, periprosthetic bone loss, extensor or abductor rupture and component breakage create abrupt mechanical symptoms and may coexist with infection.

Pathophysiology

  1. 1
    Instability and impingement

    Contact between neck, liner, bone or soft tissue levers a prosthetic hip out of articulation when orientation and dynamic control are inadequate.

  2. 2
    Particle-mediated osteolysis

    Macrophage response to wear debris activates bone resorption around the interface, causing progressive migration, pain and fracture risk.

  3. 3
    Biofilm maturation

    Adherent bacteria enter protected communities on the implant, making surgical strategy and symptom duration central to eradication.

  4. 4
    Stress redistribution

    Implants alter load transfer; local bone loss or stress concentration predisposes to peri-prosthetic fracture and further loosening.

  5. 5
    Soft-tissue dysfunction

    Abductor, extensor mechanism or ligament failure produces limp, instability, weakness and recurrent mechanical overload despite fixed components.

Clinical features and red flags

Hip dislocation

Sudden pain, shortened rotated limb and loss of movement after replacement requires radiographic confirmation and prompt reduction.

Aseptic loosening

Progressive start-up or load pain with serial migration, lucency or osteolysis supports interface failure after infection exclusion.

Acute prosthetic infection

Renewed severe pain, effusion, wound drainage, fever or bacteraemia in a previously functioning implant requires urgent sampling and source control.

Chronic prosthetic infection

Progressive pain, stiffness, loosening or a communicating sinus may occur without fever or markedly raised serum markers.

Periprosthetic fracture

Acute pain and inability to load after trauma or sudden implant migration demands protected imaging of the whole construct.

Correctable knee problem

Instability, stiffness, malrotation, patellar dysfunction, wear, fracture and extensor failure should be specifically sought before revision.

Red flags requiring action

  • A shortened deformed limb, sudden inability to move after hip replacement or an abnormal radiograph indicates dislocation or fracture and requires urgent orthopaedic management.
  • Fever, wound drainage, sinus, acute severe implant pain or systemic illness requires prosthetic-joint infection assessment; sepsis treatment must not wait for elective aspiration.
  • New foot weakness, numbness, absent pulses or severe swelling before or after reduction requires immediate neurovascular reassessment and escalation.
  • Rapidly increasing pain with trauma, deformity or inability to bear weight raises peri-prosthetic fracture or component migration and requires protected transfer and full-length imaging.

Investigations

  1. 01
    Immediate orthogonal radiographsFirst step
    Why
    Confirm dislocation, fracture and component position.
    Interpretation and limitations
    Image before and after reduction where safe and include enough bone to avoid missing a peri-prosthetic fracture.
  2. 02
    Standing implant-series radiographs
    Why
    Assess alignment, migration, loosening, wear and bone loss.
    Interpretation and limitations
    Compare with earlier films; full weight-bearing knee and appropriate hip views are the initial mechanical standard.
  3. 03
    FBC, CRP and ESR
    Why
    Screen for infection and provide a response baseline.
    Interpretation and limitations
    Normal markers do not exclude low-grade infection and abnormal values are not specific after surgery or inflammatory disease.
  4. 04
    Joint aspiration before antibiotics when stable
    Why
    Obtain synovial microbiology and inflammatory evidence.
    Interpretation and limitations
    Send differential, Gram stain, aerobic and anaerobic cultures and crystals and interpret with validated prosthetic-infection criteria.
  5. 05
    CT
    Why
    Define component rotation, bone loss, occult fracture and reduction congruity.
    Interpretation and limitations
    Use for a specific mechanical question; artefact-reduction technique and revision-team interpretation improve value.
  6. 06
    Five deep samples at surgery
    Why
    Identify independent organisms from the prosthetic interface.
    Interpretation and limitations
    Use separate instruments before antibiotics and irrigation when physiology permits and add histology for chronic or uncertain infection.
  7. 07
    Targeted advanced tests
    Why
    Resolve a defined uncertainty through the revision MDT.
    Interpretation and limitations
    SPECT-CT or metal-reaction tests are selective; avoid routine bone scan and exploratory minor surgery without a diagnosis.

Differential diagnosis

01

Referred spinal or hip pain

Lumbar radiculopathy, trochanteric pain and vascular claudication can mimic implant pain and should be examined before revision decisions.

02

Expected postoperative recovery

Early pain and swelling should improve directionally; renewed deterioration, drainage or loss of function is not routine recovery.

03

Crystal arthritis

A prosthetic knee can develop crystal synovitis with high inflammatory markers, but crystals do not exclude simultaneous infection.

04

Tendon or bursal disorder

Psoas impingement, abductor pathology, pes anserine pain and patellar problems can cause local symptoms with stable components.

05

Occult periprosthetic fracture

Acute load pain after a fall may require CT when initial radiographs do not explain inability to bear weight.

Management

01Acute mechanicalProtect, image and restore anatomyFirst stepDislocation, fracture or abrupt component failure produces deformity or inability to load.+
  1. 1Document distal neurovascular status, provide analgesia, protect the limb and obtain urgent full implant radiographs.
  2. 2Reduce a confirmed dislocation promptly with adequate relaxation and orthopaedic support; avoid force when fracture is possible.
  3. 3Repeat examination and imaging and use CT for fracture, component or non-concentric reduction uncertainty.
  4. 4EscalationEscalate irreducible, recurrent, malpositioned or fractured constructs to revision expertise.
02InfectionSeparate stable sampling from septic treatmentPain, drainage, sinus, effusion or systemic illness makes prosthetic infection plausible.+
  1. 1If septic, take blood cultures, start intravenous treatment and drain urgently; if stable, withhold antibiotics before aspiration.
  2. 2Apply validated criteria and obtain five deep cultures and histology at surgery.
  3. 3Select DAIR, exchange or salvage from timing, fixation, tissue, organism and host.
  4. 4Link organism-directed therapy, interaction monitoring and recurrence surveillance to the exact operation.
03Chronic mechanicalName the failure before revisionProgressive pain, stiffness or dysfunction occurs without immediate instability.+
  1. 1Complete consultant examination, standing radiographs and infection screen and compare all prior imaging.
  2. 2Use CT or other advanced study only to answer a defined revision-MDT question.
  3. 3Identify loosening, malposition, instability, wear, fracture, stiffness or soft-tissue dysfunction before offering surgery.
  4. 4If no cause is found, use MDT-led rehabilitation and pain support rather than diagnostic revision.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Provides sufficient relaxation and pain control for a safer atraumatic reduction and reliable post-reduction examination.

Analgesia and procedural sedation for dislocation

Give titrated intravenous analgesia and procedural sedation or general anaesthesia under the emergency department and anaesthetic protocol, with continuous monitoring and personnel able to manage airway and fracture complications; no fixed drug combination replaces patient-specific assessment.

Older adults are vulnerable to hypotension, respiratory depression and delirium; account for fasting, frailty, cardiopulmonary disease and opioids already given, and never attempt forceful repeated reduction without adequate conditions.

Treats bacteraemia and peri-prosthetic burden while emergency drainage achieves source control.

Empirical parenteral therapy for septic prosthetic-joint infection

After urgent blood cultures, give the full adult sepsis and prosthetic-joint-infection protocol regimen immediately; obtain deep samples at emergency drainage and narrow to organism, renal function and the selected implant operation.

Stable patients should remain off empirical therapy until aspiration or deep samples; document allergy, renal injury, prior resistance and all interactions, and do not use antibiotics alone for a loose infected implant or mature biofilm.

Complications

01

Recurrent dislocation

Each episode damages soft tissue and may reveal component or spinopelvic problems requiring revision rather than repeated closed reduction.

02

Bone loss and fracture

Progressive particle-mediated osteolysis weakens implant fixation and host bone, complicates revision reconstruction and can culminate in peri-prosthetic fracture.

03

Chronic infection

Delayed diagnosis permits mature biofilm, sinus, bone loss and the need for staged exchange, fusion, resection or amputation.

04

Neurovascular injury

Dislocation, fracture, excessive traction during reduction or postoperative haematoma can damage sciatic, common peroneal or major vascular structures.

05

Persistent pain after revision

Revision without a specific correctable diagnosis has a lower chance of benefit and can create infection, stiffness and further bone loss.

Monitoring and follow-up

  • Repeat distal neurovascular examination before and after reduction and after any increase in pain or swelling.
  • Review reduction stability, fracture and component position on post-procedure imaging before mobilisation advice.
  • Track wound, effusion, CRP, blood cultures and deep culture results through suspected infection care.
  • Compare serial radiographs for migration, osteolysis, wear and fracture rather than interpreting one film in isolation.
  • Monitor antimicrobial renal, hepatic and marrow toxicity and interaction-sensitive anticoagulants or other medicines.
  • Measure pain, stability, range, gait and patient goals after conservative care, DAIR or revision.

Special situations

Reduction is not the diagnosis

Restoring a dislocated hip treats the immediate anatomy but recurrent-risk assessment still requires component, soft-tissue and spinal reasoning.

Loosening can be infected

Every apparently aseptic loose implant needs a deliberate infection exclusion strategy before revision.

A sinus settles the category

A tract communicating with the prosthesis confirms infection even when CRP is normal or a superficial swab is negative.

Serial films tell the story

Migration and expanding lucency are more persuasive than a stable isolated radiolucent line.

Unexplained revision performs poorly

Operating without a specific correctable cause exposes the person to additional harm with a lower chance of benefit.

Crystals do not clear a prosthesis

Crystal synovitis can coexist with infection, so cultures and validated criteria remain necessary.

Common pitfalls

  1. 01

    Reducing a painful deformed limb repeatedly without first excluding periprosthetic fracture.

  2. 02

    Failing to document neurovascular status before and after reduction.

  3. 03

    Calling loosening aseptic without infection screening and planned samples.

  4. 04

    Giving empirical antibiotics to a stable painful implant before aspiration.

  5. 05

    Using complex imaging before basic standing radiographs and examination.

  6. 06

    Offering revision for unexplained pain without a specific diagnosis and MDT review.