Hip Arthrogram

Anatomy and Physiology

Multiple theories exist regarding the cause of developmental dysplasia of the hip, including mechanical factors, hormone-induced joint laxity, genetic inheritance, and primary acetabular dysplasia. The mechanical force of abnormal hip flexion with breech delivery can cause dislocation of the femoral head. There is an increased incidence of dysplasia in cultures that swaddle infants with the mechanically forced in constant extension.

Joint laxity has also been proposed as a contributing factor in developmental dysplasia of the hip. The maternal hormone relaxin may cause ligamentous laxity in utero, allowing for neonatal femoral head dislocation. Genetic inheritance is thought to be a contributing factor in patients with a positive family history of developmental dysplasia of the hip. Primary acetabular dysplasia is also proposed as a risk factor for developmental dysplasia of the hip.[5]

Regardless of the etiology, initial pediatric hip instability leads to developmental dysplasia of the hip. The typical deficiency is in the anterior or anterolateral acetabulum. Pediatric hip dysplasia leads to subluxation and gradual dislocation. A thickened ridge of articular cartilage can develop with repetitive subluxation of the femoral head, called the limbus.

Chronic dislocation of the pediatric hip causes anatomic changes and the development of secondary barriers to hip reduction. Anatomic changes include femoral head flattening, increased acetabular and femoral anteversion, increased obliquity of the acetabular roof, decreased concavity of the acetabular roof, and medial acetabular wall thickening. Barriers to reduction include transverse acetabular ligament hypertrophy, ligamentum teres thickening, pulvinar thickening, and an hourglass configuration of the hip capsule and iliopsoas.[4]

Soft tissue contracture and alterations in the femoral head and acetabular growth cause secondary changes in the hip joint. A shallow acetabulum and femoral anteversion are the most consistent findings in developmental dysplasia of the hip—persistent hip subluxation results in progressive femoral head and acetabular deformation. Secondary soft tissue adaptations develop at the labrum, limbus, ligamentum teres, pulvinar, transverse acetabular ligament, iliopsoas tendon, and hip joint capsule.

The labrum is a fibrocartilaginous structure around the acetabular rim. The labrum contributes to acetabular rim growth and enhances acetabular depth. The labrum can become inverted and mechanically block a concentric hip reduction in developmental dysplasia of the hip.

The labrum is gradually everted with femoral head superior migration, causing capsular tissue to become interposed between the femoral head and outer acetabular wall. Mechanical forces cause fibrous tissue formation, which unites with the acetabular hyaline cartilage at the acetabular rim. This resulting structure, called the limbus, is a pathologic response to abnormal forces at the hip. The limbus may prevent hip concentric reduction. The labrum is best evaluated with hip arthrography.

In persistent hip dislocation, the ligamentum teres lengthens and hypertrophies and can block concentric femoral head reduction. The pulvinar is a fibrous fatty tissue found within the acetabulum. The pulvinar may also block concentric femoral head reduction. Femoral head closed reduction within the acetabulum results in spontaneous pulvinar regression. The femoral head open reduction includes resection of the hypertrophied ligamentum teres and pulvinar for adequate reduction.

The transverse acetabular ligament is located at the caudal perimeter of the acetabulum. The transverse acetabular ligament is a significant block to hip reduction as it contracts in persistent hip dislocations. The transverse acetabular ligament must be incised for adequate hip reduction. The hip capsule is stretched in chronic hip dislocations. The stretched capsule can become constricted by the iliopsoas tendon. These secondary adaptations assume an hourglass configuration on arthrography that prevent hip reduction.

Multiple secondary structures may block a concentric hip reduction in developmental dysplasia of the hip. These secondary adaptions include an inverted labrum, limbus formation, hypertrophied ligamentum teres, pulvinar, contracted capsule, contracted transverse acetabular ligament, and contracted iliopsoas.[4]

Hip arthrography allows for optimal determination of any soft tissue interposition between the acetabulum and displaced femoral head.[6] Arthrography is used to identify secondary soft tissue constrictions, including labral deformity, ligamentum teres hypertrophy, and transverse acetabular ligament obstruction.[7] Arthrography is also used to evaluate hip joint congruency.[8]

Congruency of the hip joint is determined by the width of the medial dye pool and the amount of dye around the femoral head on arthrography. The width of the medial dye pool should be < 6 mm between the acetabulum and femoral head when attempting closed reduction. The chance of a soft tissue block to reduction is high if the medial dye pool is > 6 mm.[7] A medial hip capsule constricted by the iliopsoas tendon is depicted by an hourglass-shaped deformity of the capsule on arthrography.[9] The iliopsoas is a primary hip flexor innervated by direct fibers of L1-L3 of the lumbar plexus. Additional blocks to reduction include the transverse acetabular ligament, ligamentum teres, pulvinar, and an inverted labrum. After reduction, hip joint stability and any possible soft tissue constrictions can be assessed with arthrography.[10]

Indications

Most orthopedic literature on hip arthrography focuses on Legg-Calve-Perthes disease and developmental dysplasia of the hip. In Legg-Calve-Perthes disease, hip arthrography is used to analyze the cartilaginous aspects of the femoral head and acetabulum.[11] Arthrography is also used to assess joint congruence and femoral head position relative to the acetabulum in Legg-Calve-Perthes disease.[12]

Hip arthrography is the standard of care for assessing developmental dysplasia of the hip.[13][10] Arthrography aids in evaluating the congruency of the hip joint, joint stability, femoral head sphericity, and reducibility of the femoral head.[14] Arthrography also assists in determining the need for open reduction.[10]

Hip arthrography may also be considered with other conditions affecting the pediatric hip joint. Arthrography can be used to assess fracture reduction of pediatric femoral neck fractures. Additionally, arthrography can be used to visualize the articular surface and assess for hardware breach into the joint during managing femoral neck fractures and slipped capital femoral epiphyses after hardware placement. Arthrography can also be used for treatment planning of any type of pediatric femoral head deformity, specifically regarding proper femoral head placement and required osteotomies.[15]

Contraindications

Contraindications for hip arthrography include active infection of the hip joint, overlying soft tissues, or skin in line with the needle path. Cellulitis overlying the hip joint is a contraindication as infection can seed the joint space when the needle courses from overlying skin into the joint space.[16]

Contraindications for hip joint contrast injection are similar to those for intravenous administration, including contrast allergy and impaired renal function. Adverse reaction risk is lower for intraarticular hip injection compared to intravenous administration of contrast. The decreased risk is secondary to a lower contrast dose and slower systemic absorption. In patients with a contrast allergy, a prophylaxis protocol should be followed.

Steroid prophylaxis is recommended for patients with a history of allergic reactions to contrast. For patients with impaired renal function, the risk of adverse reactions related to intraarticular contrast injection depends on the contrast dose and severity of renal impairment. The lowest contrast dose necessary should be diluted with saline in renal insufficiency patients. The recommendation is to refrain from contrast use in patients eliciting acute renal insufficiency.[15]

Equipment

A hip arthrogram procedure involves the injection of contrast into the hip joint while maintaining a sterile field. Skin cleansers, sterile drapes, sterile gloves, sterile syringes, and sterile needles are needed to maintain a sterile environment.[17]

An 18-gauge spinal needle attached to a 50 mL syringe is utilized as a contrast reservoir. Approximately 18 in of intravenous tubing connects the syringe to the spinal needle. The tubing allows for easier redirection of the needle and proper needle placement during the procedure. Contrast agents can be rather dense and obscure anatomic structures. It is therefore recommended to dilute contrast agents with a 50:50 mixture of sterile saline and contrast agent.[14]

Personnel

The pediatric orthopedic surgeon should know the indications and contraindications for the hip arthrogram procedure. The surgeon should also know of any risks for the patient related to the procedure. The risks should be discussed with the parents in this pediatric scene. A radiology technologist is responsible for ensuring the patient’s safety while obtaining fluoroscopic images for interpretation by the radiologist and orthopedic surgeon.

Preparation

Before the hip arthrogram procedure, informed consent is obtained from the parents in this pediatric scenario. Informed consent includes discussing the risks, benefits, and alternatives to the procedure. The specific joint and laterality should be confirmed before the procedure. The patient’s allergies and reactions should be reviewed.

An injection into the hip joint is performed under ultrasound, fluoroscopic, or CT guidance if a patient is undergoing arthrography. Patients commonly undergo direct arthrography performed under fluoroscopy for developmental dysplasia of the hip. The contrast agent used for arthrography is generally physician-directed. The universal agents of choice are low-osmolar nonionic monomer contrast media.[18] Nonionic agents are better tolerated and have a lower risk of adverse events than high-osmolar ionic monomer contrast media.[19] 

For pediatric patients, a 2 mg/kg dose of contrast is frequently used for contrast-enhanced CT studies.[20] The contrast dose is limited by joint size for arthrography and is less than the dose used for CT. If multiple joints require an injection of contrast for arthrography, it is recommended to administer less than a total dose of 2 mg/kg.[15]

Technique or Treatment

Place the child supine after administration of a general anesthetic. Prep and drape the hip utilizing a sterile technique. Use a sterile gloved fingertip to locate the hip joint. The hip joint is one fingerbreadth lateral to the femoral artery and immediately inferior to the inguinal ligament. Alternatively, the needle can be inserted medially, behind the adductor longus.

A 22-gauge spinal needle is inserted until it enters the hip joint with the assistance of fluoroscopy. As the needle passes through the joint capsule, resistance will be met. A 5 mL syringe filled with normal saline solution is then attached to the spinal needle. The saline solution is then injected into the hip joint. As the hip joint capsule becomes distended and the hip gradually flexes, injecting the saline solution will become more difficult with increased resistance felt. If the hip joint has been successfully entered, the saline solution under pressure in the hip joint reverses the plunger, and the fluid escapes into the syringe upon release of the syringe plunger.

The saline solution is aspirated from the hip joint, and the saline solution syringe is removed from the spinal needle. Hold the spinal needle in place within the hip joint capsule while removing the syringe. Fill a syringe with 5 mL of a 25% strength contrast solution and attach intravenous tubing. Confirm that all air has been bled from the contrast syringe and intravenous tubing to avoid air emboli. Hold the spinal needle in place and attach the intravenous tubing and syringe filled with contrast solution.

Using fluoroscopy, inject 1 to 3 mL of the contrast solution into the hip joint. Withdraw the needle and obtain an image of the hip using fluoroscopy while the hip remains unreduced. Gently reduce the hip and obtain a second image. Fluoroscopic images can be utilized to evaluate for adequate hip reduction and safe zone.

When arthrograms of bilateral hips are performed, insert a spinal needle into each hip joint. Confirm that both spinal needles are within each hip joint before either hip is injected with a contrast solution. Once confirmed to be within each hip joint, inject both hips as described here and obtain the necessary images using fluoroscopy.

Complications

Complications with hip arthrography rarely occur, but with any procedure, there are risks. Hip arthrogram risks include septic arthritis, allergic reactions, bleeding, contrast reactions, and damage to surrounding structures. Reports have described complications related to the use of air with a double-contrast technique. One case report noted that a near-fatal air embolus occurred after air was injected into a hip joint during arthrography. The authors discouraged the use of air arthrography to confirm intra-articular needle placement.[21] A review study found a single death related to a double-contrast technique with an air embolus injected during a hip arthrogram.[22] 

Due to these reports, using air with a double-contrast technique is not recommended. It is imperative to properly expulse any air from the intravenous tubing and syringe before contrast injection into the hip joint.

Clinical Significance

Pediatric hip arthrograms provide information integral to proper patient diagnosis and treatment. A previous study found treatment plans were modified based on hip arthrography findings in 12 of 21 patients with developmental dysplasia of the hip.[7] Arthrography has also been beneficial in confirming surgical findings, including an inverted labrum and ligamentum teres hypertrophy.[23] 

In a study of 72 hips with developmental dysplasia of the hip, the shape of the limbus was easily depicted on hip arthrography. Conventional teaching supports that a medial dye pool measuring <6 mm on hip arthrography indicates a deeply reduced hip. Another study supports the medialization ratio to be most helpful in demonstrating hip joint congruency and reducibility. The study revealed prognostic indicators of closed reduction in developmental dysplasia of the hip to be the limbus shape and medialization ratio.[24] 

A separate study evaluated hip osteonecrosis after closed reduction of the hip performed with and without arthrography. Arthrography helped identify soft tissue structures preventing a stable reduction. The incidence of osteonecrosis in patients who underwent closed reduction without arthrography was 29%. While the incidence of osteonecrosis in patients who underwent closed reduction with arthrography was only 7.6%.[7]

Enhancing Healthcare Team Outcomes

The pediatric orthopedic surgeon’s experience level, the technique of making a hip arthrogram, and the ability to interpret a hip arthrogram are all factors to consider for patients with developmental dysplasia of the hip. Diagnosis and treatment aside, a pediatric hip arthrogram involves an entire interprofessional healthcare team in the operating room. The team includes the pediatric orthopedic surgeon, anesthesiologist, nurse anesthetist, surgical technologist, circulating nurse, and radiology technologist.

It is the primary goal of the healthcare team to prioritize the safety of the patient. Patients with developmental dysplasia of the hip commonly undergo frequent radiographic examinations of bilateral hips. During these X-ray examinations, the gonads are exposed to radiation unless a lead shield is used. Although gonad lead shields exist, they often provide inadequate protection secondary to size and improper placement. Gonad lead shields are frequently not used for female patients.

A previous study performed a retrospective analysis using a database in which 766 pediatric female pelvic radiographs were reviewed. A gonad lead shield design was then developed using radiographic measurements based on the distance between the anterior superior iliac spine markers. The researchers made custom lead shields based on these measurements. Standard general-purpose lead shields were then compared to the custom design lead shields regarding shielding rates and shielding accuracy. The gonad shielding rate increased from 14.5 to 72.7% after implementing the custom lead shields. The gonad shield accuracy increased from 8.4 to 32.2% after implementing the custom lead shields.[25]

A gonad lead shield that is available in multiple different sizes and is placed in the anatomically correct position may decrease the likelihood of gonad radiation exposure during radiographic examinations in patients with developmental dysplasia of the hip.