Septic Arthritis of the Pediatric Hip

                                Dr. KS Dhillon

Introduction

Septic arthritis of the hip in children is an emergent surgical condition. If not treated rapidly, can lead to hip destruction, sepsis, and even death. Septic arthritis of the pediatric hip has to be differentiated from transient synovitis of the hip. Transient synovitis is a non-emergent and non-surgical condition. It can resolve with symptomatic pain management. Significant morbidity may result from the improper diagnosis of either of these conditions. To make a proper diagnosis the infecting organism has to be identified. The organism will vary depending on the comorbidities of the patient and the age of the patient (1-3).

Etiology

The most common mechanism for the development of pediatric septic arthritis is by hematogenous spread of bacteria into the hip joint. In about 80% of the cases the septic arthritis is preceded by an upper respiratory tract infection. The bacteria involved in about 70% of the cases is Kingella kingae a gram-negative coccobacillus. Staphylococcus organisms account for 10% of the cases. Haemophilus species have been the most common organisms causing septic arthritis of the hip in children younger than two years of age (4-6).

Blood pooling in the metaphyseal vessels of long bones permits bacterial seeding into this area. Bacteria then spread through the blood vessels of the bone into the bony epiphysis and result in an intracapsular infection of the hip joint hip.

Epidemiology

About 50% of children presenting with septic arthritis of the hip are younger than 2 years of age. It occurs twice as often in males as compared to females. Children who are immunocompromised, have sickle cell disease, or hemophilia are more likely to develop septic arthritis of the hip. In areas where Lyme disease is endemic, this condition should be considered as a possible diagnosis. This is especially true if other signs of Lyme disease such as transient polyarthralgia, typical erythema migrans (bull's eye rash), heart palpitations, and irregular heartbeat are present. Serological testing (Lyme titer /western blot) can be ordered to confirm the diagnosis of Lyme disease.

Pathophysiology

The release of cytokines in the pus within a septic joint leads to hydrolysis of collagen and proteoglycans in the hyaline cartilage covering the end of the bones within the joint. This leads to the destruction of the hyaline cartilage and articular bone which results in deformity, chronic loss of function, and pain. If the infection is left untreated, septicemia and death can occur.

History and Physical

Children with septic arthritis of the hip usually present with acute onset of pain in the hip joint. If they walk, they may be a limp. They will resist weight bearing on the affected leg. Children who do not walk will usually lie in bed holding their hip in the most comfortable position i.e. flexed and abducted. This is a position that allows the hip capsule to be lax, and it decreases pressure from intraarticular effusion that may be causing pain. They usually do not have fever. The children may have a history of a recent oropharyngeal infection.

When the children are in bed, log rolling of the child will produce severe hip pain. Passive movements of the hip joint are very painful.

Evaluation

It is difficult to differentiate acute hip pain caused by septic arthritis from that caused by transient synovitis of the hip. The best way to differentiate the two is by hip aspiration. The Kocher Criteria for diagnosing septic arthritis of the hip can be used to determine if an aggressive approach to the management of the patient is needed. The four criteria used in order of sensitivity in the Kocher criteria are:

• Fever higher than 38.5 C

• ESR more than 40

• Weight-bearing status (non-weight bearing)

• White blood cell count of more than 12,000

Children who meet 1 out of 4 of these criteria have a 3% incidence of septic arthritis, 2 out of 4 have a 40% incidence, 3 out of 4 have a 93% incidence, and 4 out of 4 have a 99% incidence (7-9).

X-rays of the hip should be done in older children to rule out the possibility of Perthes disease or a slipped femoral capital epiphysis (10).

Treatment

Children who have pain in the hip but only meet one out of the four Kocher criteria should be observed. They should be watched for further progression of the condition. Children with two or more of the criteria should have hip aspiration with a gram stain and cell count. If bacteria are identified or if the cell count reveals a WBC count of over 50,000 WBC/mm3 with greater than 75% PMN cells and a glucose level of more than 50 mg/dl less than that of the serum level, than the hip joint should be explored and irrigated with saline and an antibacterial agent (11,12).

The synovial fluid WBC count is considered more sensitive than the blood WBC count when diagnosing septic arthritis. A finding of 85% PMNs has an 88% sensitivity.

The duration of intravenous (IV) antibiotic use varies.  Usually, 2 days of IV antibiotics followed by a 3-week course of oral antibiotics is adequate. Some authors recommend one week of IV antibiotic therapy followed by 2  weeks of oral antibiotics. Kingella kingae is known to be resistant to clindamycin and vancomycin. These infections are treated with IV beta-lactamase antibiotics and then their oral forms. The sooner the treatment is started, the better the results. 

Surgical approaches to the hip for treatment of these patients are either anterior or anterior lateral.  Recent literature shows that the results are similar when comparing open drainage of the hip to arthroscopic drainage.

Long-term follow-up is necessary to detect complications of septic arthritis of the hip.  These complications can include growth disturbances of the hip, avascular necrosis of the femoral head, and the development of post-infection arthritis of the hip.

Differential Diagnosis

• Crystalline Arthritides

• Drug-Induced Arthritis

• Arthritis of Intrinsic Bowel Disease

• Postinfectious Diarrhea

• Postmeningococcal

• Postmeningococcal Arthritis

• Vasculitis

Conclusion

Swift diagnosis and treatment significantly impacts outcome in children with septic arthritis of the hip. Staphylococcus aureus, especially methicillin sensitive strains prevail. Resistant strains are however increasing. Early treatment is crucial. Delays, high CRP/ESR levels, and younger age correlate with worse outcome. Accurate diagnosis can be made by clinical examination and ultrasound. Treatment can include surgery and less invasive methods, often combined with tailored antibiotics. Antibiotic resistance can pose a challenge, requiring ongoing vigilance. Further research is needed to address the evolving landscape of antibiotic resistance and explore potential interventions to improve outcomes in septic arthritis of hip patients.

References

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10. Cruz AI, Anari JB, Ramirez JM, Sankar WN, Baldwin KD. Distinguishing Pediatric Lyme Arthritis of the Hip from Transient Synovitis and Acute Bacterial Septic Arthritis: A Systematic Review and Meta-analysis. Cureus. 2018 Jan 25;10(1):e2112.

11. Higuera CA, Zmistowski B, Malcom T, Barsoum WK, Sporer SM, Mommsen P, Kendoff D, Della Valle CJ, Parvizi J. Synovial Fluid Cell Count for Diagnosis of Chronic Periprosthetic Hip Infection. J Bone Joint Surg Am. 2017 May 03;99(9):753-759.

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