An unusual cause of febrile knee pain in children: Septic arthritis of the proximal tibiofibular joint (a case report)

Abstract

Introduction and importance

Septic arthritis (SA), an infection affecting joints, is primarily attributed to bacteria, viruses, or fungi, with the hip, knee, and ankle being common sites of involvement. However, SA of the proximal tibiofibular joint is exceptionally rare. We report a highly uncommon case of lateral knee pain with fever in an 11-year-old boy caused by SA of the proximal tibiofibular joint.

Case presentation

The case involves an 11-year-old male admitted with atraumatic knee pain, fever, and limping. Physical examinations revealed no pain or tenderness of the knee joint, but a painful swelling near the proximal tibiofibular region. The patient had a temperature of 38.6 °C and a petechiae-like rash. Initial bloodwork showed an inflammatory syndrome, and blood cultures were negative. Imaging, including X-rays, ultrasound, and MRI, revealed a fusiform collection near the fibula and a 40*10 mm mass. Surgery, performed through a posterolateral approach, identified purulence in the tibiofibular joint. Bacteriological samples confirmed methicillin-sensitive Staphylococcus aureus, with histopathological results confirming non-specific septic synovial involvement. The patient received a six-week course of dual empirical antibiotics and showed afebrile status postoperatively. At the two-year follow-up, the patient walked independently with no restrictions in joint mobility.

Clinical discussion

SA of the tibiofibular joint is rare but should be considered in febrile knee pain, especially if lateralized.

Conclusions

A favorable outcome require a prompt diagnosis and treatment, involving surgical debridement, appropriate antibiotics, and postoperative immobilization.

Highlights

• •The proximal tibiofibular joint is a very rare localization for septic arthritis.
• •It should be considered in cases of febrile lateralized knee pain.
• •MRI can aid in addressing the diagnosis and eliminating complications.
• •A positive outcome can be achieved through proper and prompt surgical and medical management.

1. Introduction and importance

Septic arthritis (SA) is characterized as a joint infection resulting from bacteria, viruses, or fungi, with bacteria being the most common causative agents [1]. The incidence of SA in the pediatric population is estimated to range from 4 to 37 cases/100,000 individuals [2]. The most frequently affected joints in the body are the large joints of the lower limb, including the hip, knee, and ankle joints [3]. SA of the proximal tibiofibular joint is extremely rare and, to the best of our knowledge, has not been reported in the literature.

We report a highly uncommon case of lateral knee pain with fever in an 11-year-old boy caused by SA of the proximal tibiofibular joint.

2. Case presentation

This work has been reported in line with the SCARE criteria [4].

3. Clinical history

Our patient is an 11-year-old male with no previous medical history, admitted to our department due to atraumatic knee pain accompanied by fever and limping.

4. Physical examination

Physical examinations revealed pain, tenderness, and limited range of motion of the right knee. Palpation identified a painful inflammatory swelling adjacent to the proximal tibiofibular region. No vascular nor nerve complication were noted. Physical examination revealed a temperature of 38,6 °C and a generalized petechiae-like rash.

5. Exploration

Blood cultures were performed and returned negative. X-rays had shown no abnormalities. Subsequently an ultrasound was performed, revealing a 40*10 mm mass near the head of the fibula.

MRI was requested, revealing a 30mmX 4 mm fusiform collection located adjacent to the neck of the fibula, in contact with common peroneal nerve and the proximal tibiofibular joint, with no intraosseous signal abnormalities (Fig. 1).

Fig. 1.

MRI of the patient showing a collection adjacent to the neck of the fibula.

6. Treatment

It was decided to perform surgery on the child using a posterolateral approach (Fig. 2A). After locating and protecting the common peroneal nerve (Fig. 2B), purulence was observed in the tibiofibular joint (Fig. 3). Our intraoperative observations did not reveal the presence of an intramuscular collection nor an abscess around the proximal tibiofibular joint. Bacteriological samples and biopsies were taken.

Fig. 2.

Exposing the tibiofibular joint via a posterolateral approach (A) after locating and protecting the common peroneal nerve (B).

Fig. 3.

Pus release after opening the proximal tibiofibular joint

7. Outcomes

No postoperative nerve complications were noted. The patient was immobilized with a knee brace postoperatively.

The immediate postoperative period saw the initiation of intravenous dual empirical antibiotic therapy, consisting of amoxicillin-clavulanic acid and gentamicin. Bacteriological samples revealed methicillin-sensitive Staphylococcus aureus. The histopathological results confirmed a non-specific septic synovial involvement.

The antibiotic treatment was maintained for a duration of six weeks, administered both intravenously and orally. Afebrile status was achieved on the first day postoperatively, and the C-reactive protein was negative on day 15 postoperatively. At the latest two-year follow-up, the patient regained the ability to walk independently, and there were no restrictions in the range of motion (Fig. 4). The examination revealed a painless proximal tibiofibular joint without signs of instability. No recurrence was noted.

Fig. 4.

Patient at last follow-up.

8. Clinical discussion

The proximal tibiofibular joint is a compact synovial joint featuring a synovial membrane and cartilage. It gains stability from a capsule, along with anterior and posterior ligaments. This joint serves primarily to disperse torsional loads exerted at the ankle joint and absorb lateral tibial bending moments [5].

It forms after the twelfth week of fetal life and communicates with the knee in 10–15 % of adults [6,7]. In individuals where there is a communication between the two joint spaces, arthritis affecting one joint may lead to arthritis in the other through the transfer of inflammatory cells, mediators or bacteria [8].In our case, operative finding has not showed any communication between the two joints. An infection spreading from an adjacent intramuscular mass to the proximal tibiofibular joint could explain the contamination process, especially since the knee joint remained unaffected [1]. However, despite thorough examination during surgery, no such mass or infection was found. For this, the hematogenous route of infection was considered due to the patient's generalized petechiae-like rash that preceded this episode.

SA affecting the proximal tibiofibular joint should be considered as a potential cause of knee pain with fever. The differential diagnosis for pain in this region should encompass several conditions such as proximal fibular or tibial osteomyelitis, chronic arthritis, tumoral etiologies, pigmented villonodular synovitis, and ganglion cysts [9]. Hence Wakabayashi et al. reported an isolated and chronic proximal tibiofibular joint arthritis in a 14-year-old girl diagnosed with juvenile idiopathic arthritis [10]. Several cases of inflammatory arthritis affecting the proximal tibiofibular joint caused by ankylosing spondylitis have been reported in the literature [11,12]. However, a septic arthritis of this joint, to the best of our knowledge, has never been reported in the literature.

Like in our case, gram-positive cocci such as Staphylococcus aureus are the most frequently identified causative organisms for SA in children [13].

For the diagnosis of SA, imaging assessments, including ultrasound and MRI, are essential to evaluate joint involvement and detect complications. Ultrasound is valuable for effusion detection and treatment guidance, while MRI provides detailed information on soft tissue involvement and helps rule out potential complications such as osteomyelitis [14].

Diagnosis of SA is confirmed by the positivity of joint fluid analyses and the presence of microorganisms, whether associated with altered neutrophil polymorphonuclear cells or not [1,14].

A synovial biopsy is systematically undertaken in cases of septic arthritis (SA). This aids in guiding treatment in cases of resistance, aiming to identify atypical pathogens and exclude autoimmune conditions [14,15]. In our case, a histopathological exam of the synovial cells was performed due to the rarity of septic localization and the intriguing onset of the disease.

It is imperative to administer prompt and suitable treatment for children with septic arthritis to avert permanent joint damage and disability. The main treatment goals include eradicating the infection, reducing joint inflammation and swelling in order to maintain joint function and promoting healing [16]. These goals are accomplished through a blend of antibiotic therapy, surgical drainage, and immobilization of the joint [17].

Like any other joint, SA of the proximal tibiofibular joint can lead to complications osteomyelitis, and pathologic fractures and instability [18]. These complications can be prevented with timely and proper treatment [17,19]. In the last follow-up, our patient did not exhibit any signs of these complications. However, close follow-up is necessary to detect complications such as recurrence of the disease [3,17].

9. Conclusion

SA of the tibiofibular joint is a highly uncommon localization and could be overlooked due to its rarity. All orthopedic surgeons should consider this diagnosis in cases of febrile knee pain, particularly when the pain is lateralized. Radiological assessments using MRI and bacteriological examination of the joint fluid can aid in addressing this diagnosis. A favorable outcome can be expected with prompt and proper treatment, including surgical debridement, appropriate antibiotics, and postoperative immobilization.

Ethical approval

The ethical committee approval was not required given the article type (case report).

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contribution

Ben Brahim Safouen

Jlidi Mohamed

Ben Ammar Ahmed

Bouaicha Walid

Daas Selim

Khorbi Adel

Guarantor

Jlidi Mohamed

Ben Brahim Safouen

Registration of research studies

Not applicable.

Consent statement

Written informed consent was obtained from the patient guardian for publication and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Declaration of competing interest

The author(s) declared no potential conflicts of interest.