In chronic osteomyelitis and fracture-related infection, microbiologically appropriate antibiotics may fail when devitalised tissue remains. Necrotic bone, impaired perfusion and residual dead space can preserve sites of bacterial persistence that antibiotic treatment alone cannot remove.
Summary
Long-term infection control in bone infection remains closely linked to adequate debridement.
Retained devitalised tissue limits effective antimicrobial access and preserves sites of persistence.
Local antibiotic delivery improves exposure but does not remove necrotic bone or eliminate residual dead space.
Current fracture-related infection frameworks place debridement and dead-space management at the centre of treatment.
Why This Matters
Early wound improvement does not necessarily indicate durable infection control. In a cohort of 100 patients treated with gentamicin-PMMA beads and followed for 1 to 12 years, 17 recurrences were recorded and 92 patients were ultimately classified as healed after one or more treatment periods. Within the authors’ protocol, failure of the wound to become dry and improve clinically within 1 to 2 weeks prompted renewed debridement and bead exchange (Walenkamp et al., 1998).
Dead space is not biologically neutral. Fracture-related infection guidance describes it as a poorly perfused environment with low oxygen tension, acidic pH, inflammatory mediators and surfaces that favour bacterial attachment. Debridement reduces the bacterial burden, removes non-viable tissue and changes the local conditions in which systemic and local antibiotics must act (Metsemakers et al., 2020a, 2020b).
What the Evidence Shows
Long-term follow-up separates early wound improvement from durable infection control. In the Walenkamp cohort, recurrence remained possible despite combined surgical treatment and local antibiotics, and unfavourable early wound progress led to further debridement within the treatment protocol. The study does not isolate debridement as a single causal factor, but it shows that local antibiotics were used within a surgical strategy that allowed repeated clearance when the initial response was inadequate (Walenkamp et al., 1998).
Local delivery can produce high antibiotic concentrations at the surgical site while serum concentrations remain low. In a pharmacokinetic study of gentamicin-loaded cement used in total hip replacement, drainage fluid concentrations were approximately 100 µg/ml in the lower-dose group and 308 µg/ml in the higher-dose group. The maximum serum concentration was 2.9 µg/ml and fell below 1 µg/ml after 24 hours. These findings demonstrate local exposure, but do not establish clinical superiority in bone infection or address retained necrotic tissue and residual dead space (Wahlig et al., 1984).
A murine post-traumatic osteomyelitis model supports the biological rationale for combining debridement with antibiotics. Debridement plus antibiotics substantially reduced or eradicated detectable S. aureus across three detection methods, whereas antibiotics alone did not adequately control infection in osteomyelitic bone. Previously infected bone also formed less new bone after debridement than non-infected controls. The model therefore distinguishes bacterial control from subsequent biological recovery, although it does not establish comparative clinical effectiveness in patients (Wagner et al., 2016).
Current fracture-related infection guidance treats local antimicrobials as an adjunct to surgery, not as compensation for incomplete clearance. After debridement, local antimicrobials may help address delivery limitations within residual dead space. Their role is defined by the wider surgical strategy, including debridement, dead-space management, fracture stability and soft-tissue coverage (Metsemakers et al., 2020a, 2020b).
Mechanisms Behind the Pattern
Reduced vascularity can limit antibiotic concentrations within infected tissue. A review of gentamicin-PMMA beads identified compromised vascularity as one reason why systemic administration may not achieve adequate local concentrations. Local delivery can increase exposure at the implantation site, but it does not restore perfusion or remove non-viable tissue (Yu et al., 1990). Current fracture-related infection guidance therefore places local antimicrobials within a wider strategy of debridement and dead-space management (Metsemakers et al., 2020a).
Biofilm-associated persistence limits what antibiotic therapy can achieve. Biofilms are structured communities attached to inert or living surfaces within a self-produced matrix, constituting a protected mode of growth. Sessile bacteria are much less susceptible to antibiotics than planktonic organisms, biofilms commonly develop on dead tissue such as sequestra of dead bone, and symptoms often recur after antibiotic cycles until the sessile population is surgically removed (Costerton et al., 1999). This does not reduce bone infection to biofilm alone, but it does clarify why retained necrotic surfaces remain important sites of persistence.
Residual dead space preserves local niches in which infection may persist. Dead space is more than an empty cavity. It is a local environment in which bacterial attachment, impaired clearance, and poor biological recovery can coexist. This is why debridement and dead-space management are addressed together in current fracture-related infection guidance (Metsemakers et al., 2020a, 2020b).
Practical Implications for Clinical Decision-Making
Microbiological susceptibility does not account for retained devitalised tissue or the local biological environment in which treatment must act (Metsemakers et al., 2020a, 2020b).
High local antibiotic concentrations demonstrate exposure, not adequate surgical clearance or clinical superiority (Wahlig et al., 1984).
Local antibiotic studies should be interpreted in relation to debridement, dead-space management, fracture stability and soft-tissue coverage (Metsemakers et al., 2020a, 2020b).
Common Pitfalls
Mistaking high local antibiotic concentrations for adequate infection clearance. Exposure and source control are not the same problem (Wahlig et al., 1984).
Treating recurrence mainly as an antibiotic mismatch. Long-term osteomyelitis data repeatedly point back to retained infected or devitalised tissue (Walenkamp et al., 1998).
Assessing an antibiotic carrier in isolation. Outcomes also depend on debridement, fracture stability, dead-space management and soft-tissue coverage (Metsemakers et al., 2020a, 2020b).
Treating dead space as a geometric defect alone. It is also a poorly perfused biological environment that can support bacterial persistence (Metsemakers et al., 2020a).
Closing Note
Antibiotic treatment cannot remove necrotic bone or eliminate residual dead space. Infection control therefore depends on both antimicrobial activity and the extent to which surgery has removed the tissue and local conditions that support persistence.
References
Walenkamp GHIM, Kleijn LLA, de Leeuw M. Osteomyelitis treated with gentamicin-PMMA beads: 100 patients followed for 1–12 years. Acta Orthop Scand. 1998;69(5):518–522.
Wahlig H, Dingeldein E, Buchholz HW, Buchholz M, Bachmann F. Pharmacokinetic study of gentamicin-loaded cement in total hip replacements: comparative effects of varying dosage. J Bone Joint Surg Br. 1984;66(2):175–179.
Wagner JM, Zöllner H, Wallner C, Ismer B, Schira J, Abraham S, Harati K, Lehnhardt M, Behr B. Surgical debridement is superior to sole antibiotic therapy in a novel murine posttraumatic osteomyelitis model. PLoS One. 2016;11(2):e0149389.
Costerton JW, Stewart PS, Greenberg EP. Bacterial biofilms: a common cause of persistent infections. Science. 1999;284(5418):1318–1322.
Metsemakers WJ, Fragomen AT, Moriarty TF, Morgenstern M, Egol KA, Zalavras C, Obremskey WT, Raschke M, McNally MA; Fracture-Related Infection (FRI) Consensus Group. Evidence-based recommendations for local antimicrobial strategies and dead space management in fracture-related infection. J Orthop Trauma. 2020a;34(1):18–29.
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McKee MD, Li-Bland EA, Wild LM, Schemitsch EH. A prospective, randomized clinical trial comparing an antibiotic-impregnated bioabsorbable bone substitute with standard antibiotic-impregnated cement beads in the treatment of chronic osteomyelitis and infected nonunion. J Orthop Trauma. 2010;24(8):483–490.
Yu GV, Lo Wai-Leng KG, Hughes S. Gentamicin-impregnated polymethylmethacrylate beads: an exposition and explanation of their use. In: Update 1990. The Podiatry Institute; 1990:106–112.