Anterior Drainage of the Septic Hip in Children
DEFINITION
Septic arthritis of the hip affects children of all ages, from the newborn to adolescents. The principles of treatment include early and accurate diagnosis, prompt surgical drainage, appropriate antibiotic coverage, and judicial management of late sequelae. The worse outcomes occur when there has been a marked delay in the diagnosis.
ANATOMY
Synovial membrane with its rich blood supply lines the joint capsule.
Blood supply to the hip is from the medial and lateral femoral circumflex vessels (FIG 1).
Intra-articular retinacular vessels travel up the femoral neck and enter the femoral head. These vessels do not cross the proximal femoral physis.
Because the proximal femur is an intra-articular metaphysis, primary femoral osteomyelitis in this location can decompress into the hip joint.
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FIG 1 • A. Anterior hip vascularity. The medial and somewhat the lateral femoral circumflex vessels from the deep femoral artery supply the vascularity to the femoral head. B. Posterior hip vascularity. Intracapsular retinacular vessels from the medial circumflex vessel pierce through the capsule and travel up the posterior femoral neck.
Many muscles that are in close proximity to the hip joint, including iliopsoas, piriformis, and obturator internus and externus, may develop pyomyositis or an abscess; this can mimic septic hip arthritis.
PATHOGENESIS
Bacteria can enter the hip joint cavity directly via the hematogenous route to the subsynovial layer of the capsule or indirectly from the proximal femoral metaphysis and occasionally from adjacent acetabular infection.
Polymorphonuclear cells enter the joint cavity with plasma proteins and inflammatory fluid. The resulting tense effusion can increase intracapsular pressure.
Articular cartilage destruction occurs from proteolytic enzyme degradation from cells of the synovial membrane and from interleukin-1 from monocytes, which releases proteases by chondrocytes and synoviocytes.
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Animal studies show that proteoglycan matrix can be lost by 5 days and collagen by 9 days after an infection starts.4 Antibiotics do not completely prevent this degradation if treatment is delayed.
NATURAL HISTORY
Although most patients have excellent outcomes, the hip joint accounts for about 75% of published reports of poor outcome from septic arthritis.
Poor results occur more frequently in infants younger than 6 months of age, if there is a delay in treatment of greater than 4 days, and with associated proximal femoral osteomyelitis and infection with Staphylococcus
aureus.6
Over the past several decades, there has been an increase in the incidence and the severity of musculoskeletal infections. Commonly, there is a spectrum of infections in which septic arthritis may occur with osteomyelitis, pyomyositis, and deep and superficial abscesses.
During this time, there has been an increase in the incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections, leading to severe complications such as deep venous thrombosis, septic emboli, and
life-threatening multisystem organ failure.11
The most severe sequelae are more often seen in newborns and infants.
A frequent scenario when there is a poor outcome is the failure to make the diagnosis of septic hip arthritis, either from not recognizing the serious nature of the condition or failure to promptly perform adequate surgical drainage and administer appropriate intravenous antibiotics.
PATIENT HISTORY AND PHYSICAL FINDINGS
The history should include a detailed timeline of events leading up to presentation.
In the most recent prospective studies evaluating clinical predictors for septic hip arthritis, a fever above 38.5° C was the strongest predictor.1, 8, 9
The severity of pain, particularly pain at rest and night pain, indicates inflammation.
Associated illnesses and infections, history of trauma to the hip, recent dental procedures, and underlying medical conditions or steroid use may lead to infection in a susceptible host.
Always ask about recent antibiotic treatment because this may mask many of the findings of septic hip arthritis
and change the threshold for obtaining imaging studies and for performing hip aspiration.
Conduct a visual inspection with the child lying supine on the table, noting whether the hip is in abduction, flexion, and external rotation (FIG 2).
A septic hip joint assumes this position of least intracapsular pressure.
Inspect for skin rash, erythema, warmth, swelling, and tenderness over overlying muscles and the hip joint. The clinician should palpate the pelvis and lower extremities for local swelling and tenderness.
Examine the child walking. Antalgic limp indicates that the patient is unable to spend much time weight bearing on the hip joint. The child may have mild pain early or the pain may be so severe that the patient is unable to walk.
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FIG 2 • Right hip is held in flexion, abduction, and external rotation.
Observe the hip range of motion. Gradually, there is limited ability to move the hip joint as inflammation and pressure of the hip joint increase. Pain with hip extension and internal rotation suggests involvement of the psoas muscle.
Inspect and palpate the spine. Septic discitis in a young child can present as refusal to walk and can resemble septic hip arthritis.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Imaging and laboratory studies are determined by the clinical evaluation, probability of the findings being septic hip arthritis, and need to exclude other conditions.
Plain radiographs (FIG 3A)
Key features include hip abduction, increased soft tissue density, widened medial joint space, osteopenia if the infection is long-standing, and femoral or acetabular osteolytic lesions.
A particularly worrisome finding in the neonate is a painful dislocated hip (FIG 3B). Bone lesions and destruction are typically delayed 1 to 2 weeks.
Ultrasound imaging (FIG 3C) is performed bilaterally, with images obtained along the axis of the anterior femoral neck. This is very specific for detecting intra-articular fluid in the hip.
Because the pelvis is deep and difficult to examine, magnetic resonance imaging (MRI) is an extremely useful imaging modality to examine the tissues surrounding the hip joint or within the pelvis (FIG 3D-F).
It is the preferred imaging technique if the hip joint moves better than would be expected for septic hip arthritis but the patient has symptoms within or near the pelvis suggesting myositis or an abscess.7, 13
MRI is useful if by 48 hours there is an inadequate response to treatment of septic hip arthritis, suggesting persistent hip joint infection, pelvic osteomyelitis, or infection in the muscles near the hip joint.
With the changing clinical spectrum of musculoskeletal infections, the severity of infections is increasing. MRI is becoming the preferred imaging modality to provide detailed anatomy, clinical classification, and
clarify early surgical decision making.5
A bone scan is not generally recommended. If the patient has a septic hip arthritis, he or she should be in the operating room, not the nuclear medicine department.
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FIG 3 • Diagnostic imaging. A,B. Anteroposterior (AP) radiographs. A. The right hip is held in abduction with increased soft tissue density and slight lateral displacement of the femoral head. B. Left hip of an infant showing acute displacement from septic hip arthritis. The left proximal femur is laterally displaced compared with the right. C. Ultrasound imaging of hip along axis of the femoral neck. The distance between the femoral neck and head is shown by the red line. There is increased intracapsular fluid. D-F. MRIs in an 11-year-old boy with fever and pain with internal rotation of the hip. He was limping but able to walk. ESR was 50 mm per hour and CRP level was 5.8 mg/L. The radiograph was normal. D. T1-weighted coronal image of pelvis. There is an abscess (asterisk) within the obturator internus muscle. E. T2-weighted coronal image of pelvis. The abscess (asterisk) is more apparent, as is the involvement of the acetabulum (solid dot) and small hip joint effusion (dashed outline). (continued)
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FIG 3 • (continued) F. T1-weighted coronal image with gadolinium for enhancement. Cavitary nature of the abscess (asterisk) is even more apparent. Patient underwent percutaneous interventional radiology catheter drainage on two occasions and received intravenous antibiotics for treatment of this methicillin-sensitive Staphylococcus aureus infection. G,H. Hip aspiration. G. Aspiration of right hip through adductor approach. The large-bore needle is inserted just posterior to the adductor longus and is directed toward the femoral head. H. Fluoroscopy image of needle tip at the junction of the femoral head and proximal femoral metaphysis. (A: From Sucato DJ, Schwend RM, Gillespie R. Septic arthritis of the hip in children. J Am Acad Orthop Surg 1997;5:249-260; D-F: Courtesy of Mark Sinclair, MD, Children's Mercy Hospital, Kansas City, MO.)
White blood cell (WBC) count is always done but may not always be elevated in septic hip arthritis. Blood culture is positive in 40% to 50% of cases.
Erythrocyte sedimentation rate (ESR) is slow to respond to inflammation.
In septic hip arthritis, C-reactive protein (CRP) increases and returns to normal earlier with treatment than does the ESR.
CRP is a very useful indicator of disease progression and response to therapy.
A CRP level above 20 mg/L is an important independent risk factor for the presence of septic hip arthritis.1 Hip aspiration, either under ultrasound guidance in the younger child or with fluoroscopic guidance, is useful if
the diagnosis is not clear and there is a reasonable possibility of a septic hip arthritis (FIG 3G,H).9, 12
If it is performed under fluoroscopy, the clinicians must always confirm a negative aspiration (dry tap) with an arthrogram to document that the needle was intra-articular.
Any fluid obtained is sent to the laboratory for cell count, gram stain, and cultures. WBC above 50,000
cells/mm3 is highly suggestive of septic arthritis; a level below 25,000 is suggestive of reactive arthritis. Gram stain and cultures may be positive in more than 50% of cases.
Several recent studies have related clinical and laboratory findings to the child's chance of having septic hip arthritis.
An oral temperature above 38.5° C has been found to be the best predictor of septic arthritis; an elevated CRP, elevated ESR, non-weight-bearing status, and elevated serum WBC are considered to be other
predictive factors.1
Another prospective study of clinical predictors of septic arthritis has shown that with a combination of fever, non-weight-bearing status, ESR above 40 mm per hour, and serum WBC of more than 12,000 cells/mm3, the probability of hip sepsis was 86%.8
However, this algorithm has shown lower predictive value when tested at other centers.7
DIFFERENTIAL DIAGNOSIS
Transient synovitis Trauma
Pelvic or proximal femur osteomyelitis
Pyomyositis of the adductors, hamstrings, obturator muscles, or piriformis muscles Pericapsular pyomyositis, which can mimic septic hip arthritis, may be more common.10
Langerhans cell histiocytosis
Leukemia, Ewing sarcoma, metastatic neuroblastoma
Other forms of arthritis, including Lyme disease, tuberculosis, fungal or chronic childhood arthritis Iliopsoas or iliacus abscess
Appendicitis or ovarian cyst Child abuse
Osteonecrosis of the femoral head and sickle cell disease
NONOPERATIVE MANAGEMENT
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There is growing interest to apply evidence-based treatment guidelines by multidisciplinary teams to triage and treat children with musculoskeletal infections. This can expedite evaluation, increase the yield of cultured
organisms, and improve efficiency of antibiotic treatment.3
Surgical treatment is indicated when septic hip arthritis has been confirmed.
Nonoperative management is an adjuvant to surgery and includes making an early and specific bacterial
diagnosis, administering the correct intravenous antibiotic and dose, and adjusting the antibiotic coverage based on culture and sensitivity results.
Intravenous antibiotics are converted to oral when the child is clearly recovering (feels well, afebrile, able to walk, minimal pain with hip range of motion, and improving laboratory studies). The duration of antibiotic treatment is generally shorter than for osteomyelitis and depends on the severity of infection and the virulence of the organism.
A peripherally inserted central catheter (PICC) is used if intravenous antibiotics will be given for several weeks. An infectious disease consultation is helpful for cases with an unusual organism, unusual host, or unusual site of infection.
SURGICAL MANAGEMENT
Confirmed septic hip arthritis is a surgical emergency and the hip should be drained without excessive delay. If the joint aspiration is performed in the operating room, the arthrotomy can be performed in the same setting.
The principles of surgical intervention include open arthrotomy, irrigation of purulence, and débridement of dead tissue.
Preoperative Planning
Radiolucent table
An aspiration of the hip is performed before an arthrotomy if the diagnosis is not clear. In children, the hip joint is aspirated with a spinal needle inserted just posterior to the adductor longus tendon and directed toward the femoral head (FIG 3G,H).
Positioning
Lateral or semilateral position with hip and lower extremity draped free (FIG 4).
Approach
There are several approaches to draining the pediatric hip, including medial, direct anterior, anterior through a modified Smith-Petersen approach, anterolateral, and posterior.
The posterior approach is not recommended because of the femoral head vascularity and potential for posterior hip instability.
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FIG 4 • Patient is in a semilateral position with the entire hip and lower extremity draped free.
TECHNIQUES
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Modified Smith-Petersen Anterior Approach
The entire hip and lower extremity is draped free so that the hip joint can be moved through a full range of motion.
The incision is a modification of the classic Smith-Petersen approach with a cosmetic and limited incision in the groin, centered just below the anterior superior iliac spine (ASIS) (TECH FIG 1A).
Sharp knife dissection is used to the deep fascia. The incision is continued until no more fat is apparent and the deep fascia is exposed.
A sponge is used to separate the distal flap from the deep fascia.
There is a small interval of fat between the tensor and sartorius muscles several centimeters distal to the ASIS (TECH FIG 1B). The surgeon should incise slightly lateral to the fat on the fascia of the tensor.
Army-Navy retractors are used to separate this internervous interval until the rectus femoris muscle is visualized.
A Kittner sponge is used on the lateral edge of the rectus femoris muscle, and the surgeon dissects along this edge proximally until the reflected head of the rectus femoris muscle is exposed (TECH FIG 1C).
Just lateral to the reflected head is the hip capsule, which is covered with fat.
The fat is reflected to expose the hip capsule. The reflected head of the rectus femoris muscle may be divided for better exposure of the hip capsule.
It is best to visualize a large area of the hip capsule for better orientation before making an incision into it.
The capsule is incised with a no. 15 blade.
A 3-mm, 45-degree Kerrison rongeur is useful to remove several millimeters of the anterior capsule for continued postoperative decompression (TECH FIG 1D).
The joint is irrigated with saline through a large-bore intravenous catheter placed deep within the joint. A suction drain is placed for several days after surgery until there is only minimal drainage.
The skin is closed loosely with interrupted nylon sutures to allow potential drainage.
Closing the deep fascia increases the risk of reaccumulation.
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TECH FIG 1 • Modified Smith-Petersen anterior approach to the right hip. A. The incision is placed in the anterior groin crease for best cosmesis. B. The tensor-sartorius muscle interval is identified distally where the muscles begin to separate. C. The reflected head of the rectus femoris muscle can be released to reveal the underlying hip capsule. D. A 45-degree Kerrison rongeur is used to enlarge the anterior hip capsulorrhaphy.
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Direct Anterior Approach
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The direct anterior approach is especially useful when there is infection in the iliopsoas bursa, which
needs to be opened along with the hip joint.
This is also a direct approach for dividing the psoas tendon over the pelvic brim for a tight tendon, as seen in cerebral palsy, or a snapping hip related to the iliopsoas tendon.
It uses a similar incision as the anterior approach, placed just below the ASIS but centered more medially, between the femoral neurovascular bundle and the ASIS.
Sharp dissection continues to the deep fascia until no further superficial fat is identified. A sponge separates both flaps off the deep fascia.
The medial border of the sartorius muscle is identified. Just medial and slightly deeper is the fascia of the iliacus muscle, which is opened (TECH FIG 2A).
TECH FIG 2 • Direct anterior approach to the right hip. A. The sartorius muscle and the iliacus muscle are covered by deep fascia. B. After opening the fascia of the iliacus muscle, the femoral nerve is identified and protected. C. The femoral nerve is reflected medially, and the deep medial border of the iliacus muscle is exposed until the iliopsoas bursa is located. The iliopsoas bursa is opened to reveal the iliopsoas tendon.
The femoral nerve is identified, reflected medially, and protected (TECH FIG 2B). This provides
assurance that the femoral artery and vein, which lie medial to the femoral nerve, are out of the field.
The dissection is continued along the medial border of the iliacus muscle until the iliopectineus eminence of the pubic bone is identified.
Deep to the iliacus muscle is the large bursa of the iliopsoas (TECH FIG 2C). This is opened and the psoas tendon is isolated proximally and distally.
Deep and lateral to the psoas tendon is the hip capsule.
A small elevator is used to visualize the surface of the capsule before entering it with a no. 15 blade. A 3-mm, 45-degree Kerrison rongeur is used to enlarge the capsulotomy.
The joint is irrigated and a suction drain placed. If this approach is used for infection, the surgeon should not close the deep fascia.
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Anterior Lateral Approach
A straight longitudinal incision centered over the greater trochanter is used. The tensor fascia is divided longitudinally in line with the skin incision.
The interval between the most anterior border of the gluteus medius muscle as it attaches to the greater trochanter and the proximal aspect of the vastus lateralis muscle is identified (TECH FIG 3A).
TECH FIG 3 • A. The most anterior fibers of the gluteus medius muscle are divided (dashed line) as they insert on the vastus lateralis and greater trochanter. B. The gluteus medius muscle is retracted, and the anterior capsule is palpated and visualized.
Several millimeters of the gluteus medius attachment to the greater trochanter is released. This allows the examiner to palpate the anterior aspect of the femoral neck, up to the level of the femoral head.
The gluteus medius muscle is retracted proximally and an incision is made in the anterior capsule (TECH FIG 3B). It can be enlarged with the Kerrison rongeur.
After irrigation and débridement, a drain is left in the hip joint for several days.
The skin is closed with several interrupted nylon sutures, but the deep fascia should not be closed.
PEARLS AND PITFALLS
Newborns and infants
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The child may be systemically ill, with few findings related to the hip.
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In about 70% of cases, there are other sites of infection.
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A painful hip dislocation may be the result of hip joint sepsis.
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Numerous different organisms can be the source of the infection.
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Ultrasound imaging should be obtained and aspiration of both hips should be done if septic hip arthritis is a concern.
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Infants are more likely than older patients to have associated osteomyelitis of the proximal femur.
Be aware of a negative hip aspiration.
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The needle may not be in the hip joint.
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A large-bore needle should be used for joint aspiration.
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A contrast hip arthrogram is done to document intra-articular needle position if there is a question.
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A negative hip aspiration may indicate that the infection is in the acetabulum, proximal femur, or pelvis and has not yet decompressed into the hip joint.
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Pericapsular pyomyositis may have a smaller joint effusion than septic arthritis and be more difficult to obtain fluid on aspiration.10
Bone scan ▪ This test is not necessary to diagnose septic hip arthritis.
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A “cold” bone scan with an area of hypoperfusion indicates poor vascularity and a risk for osteonecrosis; the hip joint should have been drained earlier.
Patient is not responding to treatment.
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The clinician should consider the possibility of coexisting osteomyelitis, seen in 15% of cases.
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Bacteria may be resistant to the selected antibiotic or an inadequate dose is being given.
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Drainage may be inadequate, with reaccumulation of purulence.
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There may be adjacent extension of the infection or abscess.
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There may be unusual host factors such as immune deficiency.
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POSTOPERATIVE CARE
A surgical drain is used for several days. It is removed when it is no longer functioning.
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The family needs to understand that repeat drainage is a possibility should symptoms recur or if improvement is inadequate.
A spica cast is frequently used if the radiograph shows laxity and lateral displacement, especially in the infant.
Another radiograph is obtained when the antibiotics are discontinued to be sure there is no evidence of osteomyelitis.
Another radiograph is obtained at 4 to 6 months to document adequate physeal growth.
In a growing child with a septic joint, the parents should be informed that growth of the bones in that area can be affected.
OUTCOMES
In reports of poor results from septic arthritis, 75% involve the hip joint.
Severe sequelae with a destroyed femoral head are most commonly seen in newborns and infants and are often related to a delay in diagnosis and treatment (FIG 5).
Infants in particular should be followed for several years to document adequate development of the hip joint.
Simple late reconstruction should focus on maintaining pain-free hip range of motion, realignment procedures if there is a reasonably formed femoral head, and simple procedures to achieve comparable
limb lengths.2
FIG 5 • This 3-year-old child had septic hip arthritis missed as an infant with a week-long delay in treatment, resulting in osteonecrosis of the right femoral head.
Complex late reconstruction should rarely be used unless the functional goal can clearly be stated and the procedure has a reasonable chance of meeting that goal.
COMPLICATIONS
Avascular necrosis of the hips can lead to complete destruction of the femoral head (FIG 6). Septic hip dislocation
Complete separation of the proximal femoral epiphysis
Proximal femur growth arrest and limb length discrepancy12 Closure of the triradiate cartilage
Late arthritis
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FIG 6 • Radiographic classification of the sequelae of septic hip as developed by Hunka et al. (From Hunka L, Said SE, MacKenzie DA, et al. Classification and surgical management of the severe sequelae of septic hips in children. Clin Orthop Relat Res 1982;[171]:30-36.) (continued)
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FIG 6 • (continued)
REFERENCES
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Caird MS, Flynn JM, Leung YL, et al. Factors distinguishing septic arthritis from transient synovitis of the hip in children: a prospective study. J Bone Joint Surg Am 2006;88(6):1251-1257.
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Choi IH, Shin YW, Chung CY, et al. Surgical treatment of the severe sequelae of infantile septic arthritis of
the hip. Clin Orthop Relat Res 2005;(434):102-109.
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Copley LA, Kinsler MA, Gheen T, et al. The impact of evidence-based clinical practice guidelines applied by a multidisciplinary team for the care of children with osteomyelitis. J Bone Joint Surg Am 2013;95(8):686-693.
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Daniel D, Boyer J, Green S, et al. Cartilage destruction in experimentally produced Staphylococcus aureus joint infections: in vivo study. Surg Forum 1973;24:479-481.
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Gafur OA, Copley LA, Hollmig ST, et al. The impact of the current epidemiology of pediatric musculoskeletal infection on evaluation and treatment guidelines. J Pediatr Orthop 2008;28(7):777-785.
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Gillespie R. Septic arthritis of childhood. Clin Orthop Relat Res 1973;(96):152-159.
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Karmazyn B, Kleinman MB, Buckwalter K, et al. Acute pyomyositis of the pelvis: the spectrum of clinical presentations and MR findings. Pediatr Radiol 2006;36:338-343.
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Kocher MS, Mandiga R, Zurakowski D, et al. Validation of a clinical prediction rule for the differentiation between septic arthritis and transient synovitis of the hip in children. J Bone Joint Surg Am 2004; 86-A(8):1629-1635.
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Luhmann SJ, Jones A, Schootman M, et al. Differentiation between septic arthritis and transient synovitis of the hip in children with clinical prediction algorithms. J Bone Joint Surg Am 2004;86-A(5):956-962.
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Mignemi ME, Menge TJ, Cole HA, et al. Epidemiology, diagnosis, and treatment of pericapsular pyomyositis of the hip in children. J Pediatr Orthop 2014;34(3):316-325.
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Morrison MJ, Herman MJ. Hip septic arthritis and other pediatric musculoskeletal infections in the era of methicillin-resistant Staphylococcus aureus. Instr Course Lect 2013;62:405-414.
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Peters W, Irving J, Letts M. Long-term effects of neonatal bone and joint infection on adjacent growth plates. J Pediatr Orthop 1992;12:806-810.
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