What is the significance and management of a positive vascular sign of Narath in hip trauma or disease?

Vascular Sign of Narath

The vascular sign of Narath is a radiographic finding indicating disruption of the retinacular blood vessels supplying the femoral head, typically seen as asymmetry or absence of normal vascular markings on plain radiographs of the hip following intracapsular femoral neck fractures.

Clinical Significance

A positive vascular sign of Narath strongly suggests disruption of the capsular blood supply to the femoral head and indicates high risk for avascular necrosis (AVN), necessitating urgent surgical intervention with arthroplasty rather than internal fixation.

Pathophysiology of Vascular Disruption

• The medial femoral circumflex artery (MFCA) provides the dominant blood supply to the femoral head in the majority of cases, with the inferior gluteal artery (IGA) serving as the main supply in approximately 17% of hips 1
• An anastomosis exists between the MFCA and IGA adjacent to the obturator externus tendon, with terminal vessels passing beneath the posterior hip capsule before ascending to supply the lateral epiphyseal vessels 2
• Intracapsular fractures cause minimal blood loss at injury due to poor vascular supply at the fracture site and capsular tamponade, but this same mechanism disrupts the retinacular vessels 3
• Displaced intracapsular fractures disrupt the capsular blood supply, leading to AVN in 30-50% of cases if left untreated 3

Diagnostic Implications

• Plain radiographs lack diagnostic reliability for AVN until 6 months post-fracture 4
• The vascular sign of Narath on initial radiographs serves as an early warning sign before AVN becomes radiographically apparent 5
• Digital subtraction arteriography demonstrates vascular alterations in 97% of traumatic femoral head necrosis cases, confirming that vascular damage is the major etiological factor 5
• Circulatory embarrassment reaches maximum severity within 24 hours of injury, making early intervention critical 6

Management Algorithm

Immediate Assessment (Within 24 Hours)

• Obtain anteroposterior (AP) pelvis and cross-table lateral hip radiographs to assess fracture displacement and vascular sign 3
• Evaluate for associated pelvic fractures, which occur commonly with proximal femur fractures 3
• Assess patient fitness for surgery, correcting only truly reversible conditions (severe anemia with Hb <8 g/dL, plasma sodium <120 or >150 mmol/L, potassium <2.8 or >6.0 mmol/L) 3

Surgical Decision-Making

For displaced intracapsular fractures with positive vascular sign of Narath:

• Proceed directly to arthroplasty (hemiarthroplasty or total hip arthroplasty) rather than internal fixation 3
• Cemented arthroplasty is preferred over uncemented, as it improves hip function and reduces residual postoperative pain 3
• Total hip arthroplasty is increasingly preferred for younger patients due to lower rates of long-term arthritis 3
• Internal fixation with multiple screws or sliding hip screw should be reserved only for truly undisplaced fractures without vascular disruption 3

Timing of Surgery

• Delays in diagnosis and treatment increase complication rates, length of hospital stay, and both short- and long-term mortality 3
• Surgery should not be delayed for minor electrolyte abnormalities or awaiting echocardiography 3
• Reduction delayed beyond 12 hours does not benefit circulatory recovery of the femoral head 6

Perioperative Considerations

Anesthetic Management

• Regional anesthesia requires blockade of femoral, obturator, sciatic, and lower subcostal nerves, reliably achieved only with neuraxial blockade 3
• Consider invasive blood pressure monitoring for patients with limited left ventricular function or valvular heart disease 3
• Maintain core temperature monitoring routinely, with active warming strategies to prevent hypothermia 3

Thromboprophylaxis

• Administer fondaparinux or low molecular weight heparin between 18:00-20:00 to minimize bleeding risk with neuraxial anesthesia 3
• Use thromboembolism stockings or intermittent compression devices intraoperatively 3
• Early mobilization provides the most effective DVT prevention 7

Common Pitfalls to Avoid

• Do not attempt internal fixation in displaced intracapsular fractures with vascular disruption, as this leads to high rates of AVN and painful hip with limited function 3
• Avoid distal capsulotomy, which carries significantly higher AVN risk than proximal capsulotomy, particularly posterolaterally and inferomedially where retinacular vessels penetrate 1
• Protect branches of both IGA and MFCA traversing between quadratus femoris and piriformis muscles during surgical approach 1
• Do not delay surgery awaiting "optimization" of minor abnormalities, as delays worsen outcomes 3

Bone Cement Implantation Syndrome Prevention

• Increase inspired oxygen concentration at time of cementation 3
• Ensure adequate intravascular volume before cementation 3
• Use additional hemodynamic monitoring in high-risk patients 3
• Employ good surgical technique including medullary lavage, cement gun use, and femoral venting 3