Bone & Joint Infections in HIV

HIV infection produces a spectrum of musculoskeletal manifestations — both directly related to the virus itself and secondary to the opportunistic infections and medications that accompany immunodeficiency. As antiretroviral therapy (ART) has transformed HIV from a fatal disease into a chronic manageable condition, the MSK complications of long-term HIV and ART have become increasingly clinically important. The orthopaedic surgeon must be familiar with the common presentations, their investigation, and the principles of management in this immunocompromised population.

• Global burden: approximately 39 million people worldwide are living with HIV; sub-Saharan Africa bears the highest burden; in high-income countries, HIV-positive individuals now have near-normal life expectancy on ART; MSK complications affect up to 60–70% of HIV-positive patients at some point in their illness
• CD4 count and infection risk: CD4 >500/mm³ = normal immune function; most HIV-related infections occur at CD4 <200/mm³ (AIDS-defining threshold); septic arthritis and haematogenous osteomyelitis can occur at any CD4 count; opportunistic organisms (atypical mycobacteria, fungi — Cryptococcus, Candida) predominate at CD4 <50–100/mm³; Staphylococcus aureus and Salmonella species are disproportionately common MSK pathogens in HIV regardless of CD4 count (due to impaired opsonisation)
• The spectrum of MSK disease in HIV: septic arthritis; osteomyelitis; septic bursitis; HIV-associated arthropathy (non-infective); reactive arthritis (formerly Reiter`s syndrome — dramatically more common and severe in HIV); psoriatic arthritis; avascular necrosis (AVN — particularly of the femoral head, associated with ART and corticosteroid use); osteoporosis and fragility fractures; pyomyositis (tropical myositis — more common in HIV); soft tissue infections

• Causative organisms: Staphylococcus aureus remains the most common cause of septic arthritis in HIV, as in the general population; however, several organisms are disproportionately common in HIV — Salmonella species (haematogenous joint infection from Salmonella bacteraemia; particularly in Africa; associated with CD4 <200); atypical mycobacteria (Mycobacterium avium complex — MAC; M. kansasii; M. marinum; typically CD4 <50; subacute indolent presentation; requires prolonged specific antimycobacterial therapy); fungal arthritis (Cryptococcus neoformans; Candida; Histoplasma); and bacterial arthritis from IV drug use (Pseudomonas, Staphylococcus epidermidis)
• Clinical presentation: similar to the general population (hot swollen joint, fever) but may be attenuated due to immunosuppression; the inflammatory response is blunted, resulting in less fever and less marked synovitis than in immunocompetent patients; a low threshold for joint aspiration is required
• Joint fluid analysis in HIV: WBC >50,000/mm³ with >90% neutrophils remains the standard threshold for septic arthritis; however, in HIV patients the WBC may be lower (immunosuppression blunts the inflammatory response) and still represent true infection; all joint aspirates in HIV patients must be sent for: standard culture and sensitivity; mycobacterial culture (AFB smear + Ziehl-Neelsen stain + Lowenstein-Jensen culture — takes 4–8 weeks); fungal culture; cytology (to exclude HIV-associated lymphoma presenting as joint effusion)
• Management: urgent joint aspiration and washout (as for septic arthritis in any patient); empirical antibiotics covering Staphylococcus aureus + Gram-negatives (consider Salmonella coverage with a fluoroquinolone in endemic areas); adjust based on culture results; if mycobacterial or fungal infection is suspected or confirmed, specific targeted therapy is required (rifampicin + isoniazid + ethambutol for mycobacteria; fluconazole or amphotericin B for fungal)

• Organisms: Staphylococcus aureus (most common); Salmonella (particularly in sub-Saharan Africa — Salmonella osteomyelitis is a classic HIV-associated infection; long bones are affected; associated with Salmonella bacteraemia); Bartonella henselae (cat scratch disease — causes bacillary angiomatosis and osteolytic bone lesions in AIDS; CD4 <50); atypical mycobacteria (multifocal bone involvement); Mycobacterium tuberculosis (spinal osteomyelitis — Pott`s disease — is significantly more common in HIV)
• Pott`s disease (TB spinal osteomyelitis) and HIV: the risk of active tuberculosis is 20–30 times higher in HIV-positive individuals; spinal TB (Pott`s disease) presents with back pain, fever, weight loss, and neurological deficit (if paravertebral abscess or gibbus deformity compresses the spinal cord); MRI shows vertebral body destruction, disc involvement, and paravertebral/psoas abscess (`cold abscess` — without the warmth of pyogenic infection); CT-guided biopsy confirms the diagnosis (ZN stain + mycobacterial culture ± PCR); treatment — standard anti-TB therapy (2HRZE/4HR — 6 months total for uncomplicated spinal TB; 9–12 months for HIV-positive); surgical decompression + stabilisation for neurological deficit, instability, or failure to respond to antibiotics
• Investigations: MRI for extent; blood cultures; bone biopsy for culture (AFB + standard + fungal); HIV viral load and CD4 count to assess immunosuppression; chest X-ray (TB screening); IGRA/Mantoux test

• HIV-associated arthropathy: a non-infective oligoarthritis (affecting 1–4 joints) associated with HIV itself; typically affects the large joints (knee, ankle); self-limiting (days to weeks); the joint fluid WBC is <2,000/mm³ (low — distinguishes from septic arthritis); treated with NSAIDs and ART (improving immune function reduces the arthropathy); the diagnosis is one of exclusion — infection must be ruled out first
• Reactive arthritis (ReA / Reiter`s syndrome) in HIV: reactive arthritis is dramatically more frequent and more severe in HIV-positive individuals; triggered by enteric (Salmonella, Shigella, Campylobacter, Yersinia) or genitourinary (Chlamydia) infections; presents with the classic triad of urethritis + conjunctivitis + arthritis (`can`t pee, can`t see, can`t climb a tree`); the arthritis is an asymmetric oligoarthritis predominantly of the lower limbs; additional features — skin lesions (keratoderma blennorrhagica — indistinguishable from pustular psoriasis; circinate balanitis; mouth ulcers; enthesitis; dactylitis); HIV-positive patients with ReA have more florid disease, more skin manifestations, and more rapid joint destruction
• Management of ReA in HIV: NSAIDs; intra-articular corticosteroids; short courses of systemic steroids; sulfasalazine or methotrexate for refractory cases (use with caution in HIV due to immunosuppression); ART improves ReA by restoring immune regulation; biologic DMARDs (TNF inhibitors) are used with caution in HIV given the risk of opportunistic infections

• AVN in HIV: the femoral head is the most common site; incidence of AVN in HIV is approximately 45 times higher than in the general population; causes are multifactorial — antiretroviral drugs (protease inhibitors — indinavir, ritonavir — cause lipodystrophy and hyperlipidaemia which may promote fat embolism to the femoral head); corticosteroid use (common in HIV for various conditions); HIV-associated vasculitis; antiphospholipid antibodies (more common in HIV); hypercoagulability; alcohol and smoking (common comorbidities)
• Clinical presentation: groin pain, restricted hip ROM, limp; bilateral in approximately 50–80% of HIV-related AVN; diagnosis confirmed on MRI (low T1 signal in the femoral head, `double line sign` on T2 — the inner necrotic zone surrounded by reactive interface)
• Management: same principles as AVN in the general population; Ficat Stage I–II (pre-collapse) — core decompression ± vascularised fibular grafting; Ficat Stage III–IV (collapse) — total hip arthroplasty; HIV-positive patients can safely undergo THA with equivalent outcomes to HIV-negative patients on ART; infection rates after THA in HIV are not significantly higher than in the general population if CD4 >200 and viral load is undetectable on ART

• Surgery in HIV — perioperative considerations: HIV-positive patients on ART with CD4 >200/mm³ and undetectable viral load have equivalent surgical outcomes to the general population; those with CD4 <200 or detectable viral load have significantly increased infection risk, impaired wound healing, and higher peri-operative morbidity; elective surgery should be deferred until ART achieves CD4 >200 and undetectable viral load where possible; pre-operative assessment: CD4 count, viral load, ART compliance, concurrent medications (drug interactions with anaesthetic agents — particularly with CYP450-metabolised protease inhibitors), and opportunistic infection screening
• Immune reconstitution inflammatory syndrome (IRIS) and MSK manifestations: when ART is commenced in a severely immunocompromised patient (CD4 <50), the rapid recovery of immune function can cause a paradoxical inflammatory reaction to pre-existing subclinical infections; IRIS may manifest as an acute inflammatory arthritis, worsening mycobacterial osteomyelitis (TB IRIS — the lesion enlarges as immune function is restored), or a reactive-like arthropathy; IRIS is managed by continuing ART and treating the inflammatory component (NSAIDs, short-course corticosteroids); stopping ART due to IRIS is rarely necessary
• Antiretroviral drugs and bone health: tenofovir disoproxil fumarate (TDF — a common ART component) is associated with reduced bone mineral density (osteopenia/osteoporosis) and an increased fracture risk; TDF inhibits renal tubular phosphate reabsorption, leading to phosphate wasting (Fanconi syndrome in severe cases — causing osteomalacia); all HIV-positive patients on TDF should have baseline DEXA scan; switch to tenofovir alafenamide (TAF — lower bone and renal toxicity) is preferred in patients with low bone density; calcium and vitamin D supplementation is recommended for all HIV-positive patients on ART

• HIV MSK infections: Staphylococcus aureus most common at all CD4 counts; Salmonella (haematogenous osteomyelitis and septic arthritis — especially CD4 <200, sub-Saharan Africa); atypical mycobacteria (MAC) at CD4 <50; TB at any stage
• Pott`s disease (TB spinal osteomyelitis): 20–30× higher risk in HIV; back pain + fever + weight loss; `cold abscess` (psoas/paravertebral); MRI diagnosis; 6–12 months anti-TB therapy; surgery for neurological deficit or instability
• Joint fluid in HIV: always send for standard culture + mycobacterial culture (ZN + AFB culture) + fungal culture + cytology; immunosuppression may blunt the WBC response — do not rely on cell count alone to exclude infection
• HIV-associated arthropathy: non-infective oligoarthritis; WBC <2,000/mm³; self-limiting; treat with NSAIDs + ART; diagnosis of exclusion
• Reactive arthritis in HIV: far more frequent and severe; urethritis + conjunctivitis + arthritis (can`t pee, can`t see, can`t climb a tree); keratoderma blennorrhagica; enthesitis; dactylitis; ART improves ReA
• AVN in HIV: femoral head most common; 45× increased risk vs general population; protease inhibitors + steroids + hypercoagulability; bilateral in 50–80%; MRI (`double line sign`); THA safe if CD4 >200 + undetectable VL
• Surgery in HIV: CD4 >200 + undetectable VL = equivalent outcomes to general population; CD4 <200 = significantly increased complications; defer elective surgery until ART optimised
• Tenofovir (TDF): bone mineral density reduction; osteoporosis + fracture risk; Fanconi syndrome (phosphate wasting → osteomalacia); baseline DEXA; switch to TAF; Ca + Vit D supplementation
• IRIS: paradoxical worsening of MSK infection after ART commencement in severely immunocompromised patients; continue ART; treat inflammation; do not stop ART
• Bartonella (bacillary angiomatosis): osteolytic bone lesions in AIDS (CD4 <50); cat scratch disease organism; treat with azithromycin or doxycycline