Septic arthritis is a rather rare but important disease characterized by inflammation of a synovial membrane with purulent effusion into the joint capsule, usually due to bacterial infection. It typically affects monoarticular joints. This disease entity also is referred to in the literature as bacterial, suppurative, purulent, or infectious arthritis. [1, 2, 3, 4, 5] Septic arthritis usually is divided into gonococcal arthritis and nongonococcal arthritis; clinical and treatment regimens for the two types differ. 
The age range of those affected is broad, extending from the neonatal period to advanced age. [7, 8, 9, 10, 11, 12, 13] In adults, septic arthritis most commonly affects the knee; in children, infection into the hip joint predominates. [9, 14, 15, 16, 17] Septic arthritis in neonates and infants can be especially treacherous as a result of blunted inflammatory signals or confounding infection at a distant site (eg, an ear or an umbilical catheter site).
Despite advances in diagnostic studies, powerful antibiotics, and early drainage, significant joint destruction commonly occurs.  Septic arthritis can also cause many complications, including osteomyelitis, bony erosions, fibrous ankylosis, sepsis, and even death.
Treatment consists of a combined medical and surgical approach. [1, 19, 20, 21, 22, 23, 24] On a macroscopic level, controversy still abounds as to which surgical drainage procedure serves the patient best. Barriers to successful management include lack of clinical suspicion in the early phase of presentation, delay in definitive diagnostic needle aspiration, and failure to provide adequate drainage of the joint.
Collins et al found that synovial fluid TREM-1 (triggering receptor expressed on myeloid cells-1) expression is increased in septic arthritis and rheumatoid arthritis.  According to the authors, in patients with acute inflammatory arthritis, elevated synovial fluid TREM-1 levels may help point to a diagnosis of septic arthritis or rheumatoid arthritis. Moreover, in patients with rheumatoid arthritis, targeting TREM-1 may provide therapeutic benefit by reducing local proinflammatory cytokine and chemokine release.
Pessler et al, in an analysis of the synovium in patients with chronic pyogenic arthritis, identified extensive neovascularization and cell proliferation, persistent bacterial colonization, and heterogeneous inflammatory infiltrates rich in CD15+ neutrophils. 
Future research will focus on targeting bacterial factors and immunologic factors that worsen infection.  For example, aside from the excessive amount of pus (and pressure) created by Staphylococcus, the organism also produces staphylokinase, which helps destroy cartilage further. Targeting this enzyme may prove to be beneficial.
In addition, targeting host cell cytokine responses also may prove to be beneficial. For example, interleukin-1 is known to inhibit glycosaminoglycan production, in addition to producing collagenases and metalloproteinases that overwhelmingly destroy cartilage.
If rapid improvement is not achieved with needle aspiration, open drainage and lavage (arthroscopically or via arthrotomy) is strongly recommended. Considerations related to specific joints are outlined below.
Whereas sepsis of the native hip joint is uncommon in adults, it is observed with relative frequency in infants and toddlers. In the evaluation of a young child with acute-onset hip or thigh pain, care must be taken to rule out this diagnosis by means of laboratory tests and aspiration. The diagnosis of purulent arthritis of the hip is an absolute indication for surgical drainage; repeat aspiration is arduous for the surgeon and uncomfortable for the patient.
Standard approaches to the hip joint are appropriate for drainage in cases of septic arthritis. In children, the preferred approach for most surgeons is the anterior Smith-Petersen approach. In adults, additional options include the anterolateral Watson-Jones approach and the posterolateral approach, depending on the surgeon’s comfort level.
Needle aspiration of purulent exudate is the primary method of drainage. Daily joint aspirations are usually required until the joint cultures are negative. The knee joint is probably the joint that is most amenable to repeated aspirations. Most cases of uncomplicated septic arthritis of the knee can be treated satisfactorily by means of repeated closed needle aspirations.
A surgical approach to drainage should be considered in the following situations:
If signs of local sepsis do not abate and synovial fluid analysis does not return to normal within 2 days after treatment
If the purulent fluid becomes too thick to aspirate
If septic arthritis occurs in the setting of rheumatoid arthritis  or another underlying joint disease
In selected patients, tidal irrigation might be beneficial.
Glenohumeral sepsis is often diagnosed at a late stage in this debilitated patient population. When the diagnosis is finally confirmed, treatment can be complicated by advanced joint destruction, including synovitis, purulent loculations, osteomyelitis, erosion of the rotator cuff, and extra-articular extension. Therefore, recurrent aspiration may not be the optimal mode of treatment for this joint, especially considering the technical difficulty of shoulder arthrocentesis (in addition to the patient’s discomfort). 
The literature regarding optimal treatment algorithms is confusing at best, with reports in medical journals championing conservative treatment and those in orthopedic journals claiming superior results with early operative drainage. Furthermore, even among those who recommend surgery, debate continues regarding the efficacy of arthroscopic versus open debridement. Some generalizations, however, can be made, including the following.
If diagnosed early (<1 week after the onset of symptoms), a septic shoulder may be treated with serial aspirations and intravenous (IV) antibiotics.  The joint should be tapped dry once or twice daily and fluid sent for cell count each time (the first specimen only for culture). By following the synovial white blood cell (WBC) count, which should steadily decline after the first two or three aspirations, along with the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level, the clinician can monitor the efficacy of treatment (see Periprocedural Care).
Some authors report encouraging results with drainage from an indwelling percutaneous catheter placed under fluoroscopic guidance. The high incidence of local joint pathology, including rotator cuff tears, adhesions, and arthritis, may make any attempts at percutaneous evacuation of the joint space quite difficult.
Arthroscopic irrigation and debridement allow for adequate decompression of the glenohumeral joint and subacromial bursa. However, a limited open exploration of the deltopectoral interval may be necessary to eradicate abscesses surrounding the biceps tendon. Patients requiring these procedures should be identified with preoperative imaging (see Periprocedural Care).
A formal arthrotomy should be strongly considered for patients with extensive osteomyelitis, retained hardware, virulent organisms, or postoperative infections.
No formal guidelines define this timeframe, though several studies suggest that patients diagnosed within 1 month of symptoms have a more favorable prognosis.
Once the diagnosis of a septic elbow has been established and the appropriate antibiotic regimen started, repeated arthrocentesis should be performed as needed to help reduce the bacterial load and intra-articular pus.
Elbow arthroscopy is necessary when arthrocentesis fails to obtain an appropriate amount of joint aspirate for diagnosis.  The clinical results of repeated needle arthrocentesis are similar to those that accompany arthroscopy and arthrotomy in more accessible joints such as the elbow. However, if the infection fails to improve with antibiotics and repeated arthrocentesis within 5-7 days, arthroscopy or arthrotomy should be performed for drainage and debridement.
The threshold for surgical intervention should be lower in patients with comorbid conditions, such as prosthetic elbow implants, diabetes mellitus, rheumatoid arthritis, immunocompromised states, or other systemic illnesses.
Indications for aspiration include the following:
Thick purulent material that cannot be removed by a needle
Infection with loculations
Failure to respond to multiple aspirations and appropriate antibiotics
A retrospective comparison by Sammer and Shin of 36 patients (40 wrists) with septic arthritis of the wrist treated between 1997 and 2007 with either open or arthroscopic irrigation and debridement showed that arthroscopic irrigation and debridement is an effective treatment for patients with isolated septic arthritis of the wrist. 
In this study, patients treated arthroscopically had fewer operations and a shorter hospital stay than patients who received open treatment; however, these benefits were not seen in patients with multiple sites of infection.  The 90-day perioperative mortality was 18% in the open-treatment group and 21% in the arthroscopy group.
Generally, few contraindications to arthrocentesis exist. One caveat to consider is that aspirating from an area that has an established overlying soft-tissue infection should be avoided, because it may introduce bacteria into an otherwise uninfected joint.
Patients with bleeding disorders and those who are on anticoagulant medications pose a difficult challenge, and risks must be weighed against benefits on an individual basis.
Even with proper and quick treatment of septic arthritis, the prognosis remains poor. In general, the prognosis is proportional to the following factors:
Virulence of the offending pathogen - Gonococcal infections have the best treatment outcomes, whereas infections involving Staphylococcus aureus and gram-negative bacilli have the worst
Duration of infection before diagnosis and treatment
General premorbid condition of the patient, including systemic diseases or previous arthritis
Of all the joints, the knee is the most likely to experience complete or nearly complete recovery. Patients with a septic ankle joint are less likely to recover completely without any permanent impairment than individuals without infection.
In a prospective 2-year study of 154 patients (adults and children) by Kaandorp et al, 21% of cases resulted in poor patient outcome (death or severe functional deterioration), and 33% of cases resulted in poor joint outcome (amputation, arthrodesis, prosthetic surgery, or severe functional deterioration). 
In retrospective review assessments of nongonococcal arthritis by Pioro et al, loss of joint function occurred in 34-50% of the general population without comorbidities. Mortality in this same population ranged from 2% to 14%. 
Mortality figures in patients with polyarticular sepsis and rheumatoid arthritis ranged from 23% to 32% and from 16% to 49%, respectively.