Innovative Management of Brodie’s Abscess: Continuous Local Antibiotic Perfusion in a 14-Year-Old Patient

Introduction

Brodie’s abscess is a rare form of subacute osteomyelitis that commonly occurs in the metaphyseal regions of long bones and predominantly affects adolescents during their growth period [1]. Clinically, the diagnosis is often delayed because acute symptoms are unremarkable, and pain and local swelling develop gradually. Imaging studies such as radiography and magnetic resonance imaging (MRI) are useful for diagnosis, and bone biopsies may be performed for a definitive diagnosis [1,2]. The standard recommended treatment for Brodie’s abscess includes surgical drainage and curettage of the lesion, followed by at least 6 weeks of systemic antibiotic therapy [1,3]. Additionally, autogenous bone grafting is recommended when the lesion size is >3 cm [4]. However, conventional treatments have issues such as high recurrence rates, adverse effects of long-term antibiotic therapy, and bone grafting-associated invasiveness and complications [1,3].

Continuous local antibiotic perfusion (CLAP) has attracted attention as a novel approach for local antibiotic delivery, utilizing a combination of intramedullary antibiotic perfusion (iMAP) pins and intra-soft tissue antibiotic perfusion (iSAP) tubes [5,6]. In this method, a high concentration of antibiotics is continuously administered at the infection site, thereby minimizing systemic adverse effects and achieving high therapeutic efficacy. Treatment with CLAP does not require extensive curettage of the lesion and results in relatively little bone loss and may avoid bone grafting. Moreover, the local administration of high concentrations of antibiotics may shorten the duration of systemic antimicrobial therapy. To the best of our knowledge, there are no reports on the treatment of Brodie’s abscess with CLAP.

In this report, we present a case of Brodie’s abscess treated with CLAP, in which infection control was achieved with short systemic antimicrobial therapy and without the need for bone grafting. Here, we aimed to highlight the advantages and challenges of CLAP and demonstrate its potential as a new treatment modality for Brodie’s abscess. We emphasize the importance of a comprehensive evaluation of the infection site, precise construction of the CLAP circuit, and effective management of antibiotic blood levels to deliver antibiotics directly to the infection site while minimizing systemic toxicity.

Case Report

The patient was a 14-year-old boy with no significant medical history or history of smoking, alcohol use, or regular medication. He had been playing tennis regularly. However, he developed pain near the tibial tuberosity of the left knee joint without any obvious cause, including trauma, and visited an orthopaedic clinic. MRI of the knee joint revealed mild inflammation of the patellar tendon, and the patient was prescribed painkillers. Although the pain was temporarily reduced, 2 months later, he experienced pain in his distal thigh, especially at night, and visited a general hospital. Medical examination revealed no swelling, warmth, or tenderness in the left thigh. Radiography (Figure 1A) and computed tomography (CT) (Figure 1B) revealed a periosteal bone formation extending approximately 15 cm into the medial cortex of the left femur, and localized thinning of the cortical bone. MRI revealed a large lesion centered in the medial cortex of the left femur, characterized by low-to-isointense signals on T1-weighted images, high signal intensity on T2-weighted images, and high signal intensity on short tau inversion recovery (STIR) images (Figure 1C). These findings indicated a high probability of tumor development; subsequent positron emission tomography (PET)-CT demonstrated increased metabolic activity in both the medial cortex and intramedullary space, with the pseudocavity in the cortex exhibiting higher metabolic activity than the medullary space (Figure 1D). Blood examination revealed white blood cell counts and C-reactive protein (CRP) levels of 10 800/μL and 6.04 mg/dL, respectively. An incisional biopsy allowed drainage of the bone cortex, punctured using a Kirschner wire (K-wire). A 1×1 cm2 cortical window was used for a medullary tissue biopsy. Unexpectedly, pus flowed out of the medullary canal, and a Penrose drain was placed prior to wound closure. Gram staining of the abscess revealed gram-positive cocci, and the patient was referred to our hospital for further management.

At our institution, it was determined that the Brodie’s abscess extended from the bone marrow to the periosteal space of the femoral cortex. Based on the PET-CT findings, the primary infection site was within the intracortical pseudocavity. Therefore, we planned to treat the patient with CLAP by connecting the pseudocavity to the medullary cavity using a K-wire, placing iMAP pins in the pseudo cavity, and constructing a circuit to collect antibiotics infused into the infected area via an iSAP tube placed in the soft tissue. Furthermore, the PET-CT findings showed biological activity in the bone tissue surrounding the abscess, and we determined that curettage around the abscess and subsequent bone grafting were not necessary.

The patient underwent surgery on the day of admission. The incision made by the previous surgeon was extended 10 cm along the long axis of the femur. The fascia of the vastus medialis was also extended from the previous incision, and blunt dissection was performed along the muscle fibers to reach the femur, where a purulent exudate was encountered. Extensive periosteal thickening and pseudocavity formation were observed, and a 3 mm fistula was found at the center of the pseudocavity, along with the proliferation of inflammatory granulation tissue in the surrounding area. We planned to construct a flow pathway from the inlets at the proximal and distal ends of the cavity to the outlet of the fistula at the center of the cavity. Two bone marrow needles (Senko Medical, Tokyo, Japan), hereafter referred to as iMAP pins, were inserted into the pseudocavity in the cortical bone: the first at the most proximal (φ5 mm) and the second at the most distal (φ3 mm) location. Necessary and minimal curettage of non-bioactive tissue was performed through the widening of the fistula. To establish the water stream into the infection area, multiple drill holes were created from the cortical surface of the bone through the pseudocavity and into the medullary cavity, and a 0.8 mm K-wire was used to connect them. Additional drilling was performed to connect some of the separate pseudocavities that were not communicating due to septa using a 1.0 mm K-wire (Figure 2). These steps were repeated until a positive “flow test” was observed by saline injection through the iMAP pin and confirmation that the fluid irrigated throughout the infected area had drained through the window opening (Figure 3). A 22 Fr double tube (Salem sump tube; Covidien, Japan), hereafter referred to as an iSAP tube, was placed along the cortical window to aspirate the injected antibiotic solution and infectious exudate and to deliver the antibiotic solution from the sub-lumen of the tip of the tube (Figure 4). The fluid injected through the iMAP pins and iSAP tube was aspirated through the iSAP tube connected to a negative-pressure maintenance device used in negative-pressure wound therapy. Finally, the wound was closed.

Immediately after surgery, gentamicin (1200 µg/mL) was continuously infused at a rate of 2.0 mL/h through 2 iMAP pins and an iSAP tube. Inflammatory markers improved, and white blood cell counts and CRP levels were within normal limits by 10 days postoperatively (Figure 5). The serum gentamicin concentration was maintained below 1.0 µg/mL, and administration was continued for 18 days, after which the pins and tubes were removed. Gentamicin concentrations in the drainage fluid ranged from 1160 to 1600 µg/mL. Pathological examination of the biopsy tissue revealed no evidence of malignancy, and cultures showed methicillin-sensitive Staphylococcus aureus that was sensitive to gentamicin. The patient received intravenous ampicillin/sulbactam (6.0 g/day) for 18 days postoperatively, followed by oral cefaclor (1.5 g/day), and the total period of systemic antibiotic administration was 1 month. During the period when the iMAP pins and iSAP tube were in place, range of motion exercises of the hip and knee joints were restricted to prevent accidental dislodgement; however, range of motion exercises were initiated immediately after the removal of the pins and tube. The patient began unrestricted weight-bearing exercises on postoperative day 25, was able to walk independently by day 33, and was discharged on day 34. During follow-up in the outpatient clinic, the patient experienced no pain recurrence, and bone remodeling in the periosteal area had progressed gradually (Figure 6). At the final follow-up at 5 years postoperatively, no recurrence, treatment-related adverse effects, or growth disturbances were noted, and no additional surgery was required.

Discussion

This is the first report of a Brodie’s abscess treated with CLAP, offering a new therapeutic option compared with conventional therapy. CLAP delivers high concentrations of antibiotics directly to the infection site, reducing the need for extensive curettage while effectively eradicating the infection. Despite the large periosteal bone growth associated with widespread infection, infection control was achieved without the need for extensive curettage, bone grafting, or major adverse effects.

The conventional treatment for Brodie’s abscess is thorough curettage [7] and systemic antibiotic therapy for at least 6 weeks. Long-term antibiotic therapy is recommended for extensive abscesses; however, for abscesses >3 cm, curettage alone is inadequate, and bone grafting is strongly recommended [3,4]. These treatments pose several challenges. Long-term systemic antibiotic therapy is associated with systemic adverse effects, while autologous iliac bone grafting – the most commonly used bone grafting method – is linked to various complications, including persistent donor site pain, sensory disturbances, infection, hematoma formation, and fractures [8,9].

Furthermore, recurrence rates with conventional treatments remain high, reported at 15.6% in a systematic review [1]. One key factor contributing to this high recurrence rate is the limited penetration of orally or intravenously administered antibiotics into bone tissue. In particular, cortical bone exhibits even lower antibiotic penetration compared with cancellous bone [10], which may contribute to a higher recurrence rate in cases where the infection is primarily localized within the cortical bone.

In this case, we employed CLAP treatment as an alternative approach to overcome these challenges. The primary advantage of CLAP is that multiple K-wire punctures in the cortical bone and medullary canal facilitate the establishment of an antibiotic stream, allowing the direct delivery of high-concentration antibiotics to the infected area. This feature is particularly beneficial for lesions in which systemic antibiotics have limited penetration, potentially improving infection control. Furthermore, osteomyelitis-associated bacteria may reside within the bone canaliculi, contributing to recurrence [11]. Since systemically administered antibiotics may not sufficiently penetrate the bone canaliculi, drilling multiple holes using a thin K-wire may enhance the penetration of locally administered antibiotics into these microstructures during CLAP, further improving its therapeutic efficacy. Additionally, this technique may help preserve biologically active bone tissue by inducing localized microtrauma, which could facilitate the recruitment of macrophages and immune cells from the medullary canal to the infection site.

In the present case, even for an abscess with a primary infection site in the cortical bone, where systemically administered antibiotics have limited penetration, infection control was achieved without the need for extensive curettage, suggesting that CLAP may reduce the need for bone grafting in selected cases. Since bone grafting is typically recommended for Brodie’s abscess with bone defects, this approach could help minimize graft-related complications and the overall surgical burden.

While CLAP appears to be a promising therapeutic option, the risk of infection recurrence due to insufficient excision should be carefully considered, necessitating appropriate patient selection and long-term monitoring. If the clinical signs and laboratory data suggest infection recurrence, consecutive curettage or standard radical debridement may be necessary.

Careful management is essential to mitigate the risk of adverse effects associated with the local gentamicin administration during CLAP. In particular, its potential impact on renal function must be considered, and serum trough levels of gentamicin should not exceed 1 µg/mL [12]. In this case, the serum gentamicin level was 0.7 µg/mL at 2 days after CLAP and 0.3, 0.7, and 0.8 µg/mL every 3 days during CLAP, until termination. Thus, appropriate monitoring successfully prevented the adverse effects, and similar management will be necessary in other cases. With proper management, CLAP allows for localized drug delivery directly to the site of infection without systemic toxicity, making it particularly suitable for toxic antibiotics such as aminoglycosides.

Similar to previous reports on PET-CT evaluation of Brodie’s abscesses [13,14], PET-CT played a critical role in both the diagnosis and treatment planning in this case. Specifically, it confirmed that the pseudocavity was the primary infection site, enabling us to design an appropriate CLAP circuit. While PETCT for the evaluation of infections is not covered by Japan’s health insurance system, it remains a useful tool in cases where distinguishing between tumors and infections is challenging. Though not definitive on its own, it provides valuable supplementary information alongside clinical assessments and other diagnostic methods. In addition, PET-CT is valuable for assessing the biological activity of the bone surrounding the abscess. Even in treatment with CLAP, bone tissue that has lost its biological activity due to infection must be removed. The use of PET-CT allowed curettage to be restricted to the necessary areas, demonstrating that PET-CT is a valuable tool for the treatment of infections with CLAP.

CLAP may be widely applied in the future as a potential alternative to conventional treatments such as bone grafting and long-term systemic antibiotic therapy. However, this is only a single case report, and further accumulation of cases is necessary to confirm the efficacy of CLAP in treating Brodie’s abscess. In particular, the potential to reduce the duration of antibiotic therapy and recurrence rates should be clarified in future studies. Sufficient logic and surgical techniques are required to construct CLAP circuits, and their dissemination is another important issue. Another challenge is that during treatment with CLAP in the lower limbs, gait training and range of motion exercises for the major joints of the lower limb are restricted for 2–3 weeks until the pins and tubes are removed. Additionally, the need for inpatient care during this period represents a disadvantage of CLAP treatment. While this may not be a significant issue in younger patients, muscle weakness and joint mobility limitations could become serious concerns in elderly patients. Therefore, when considering the application of CLAP for Brodie’s abscess, the patient’s age and mobility must be considered. Also, when the residual bone quantity is significantly compromised due to the abscess, the risk of pathological fractures may be elevated [15], necessitating consideration of CLAP alongside adjunctive treatments for additional structural support.

Conclusions

This case represents the first reported successful treatment of Brodie’s abscess using CLAP. Even for a cortical bone abscess, where systemically administered antibiotics have limited penetration, CLAP enabled effective infection control. The success of this treatment strategy relies on a comprehensive assessment of the infected area and the appropriate design of the perfusion circuit. The findings of this case suggest that CLAP may serve as a potential treatment option for Brodie’s abscess.