OPTIONS

Avascular necrosis is a devastating complication that results in death of the osteocytes in the femoral head, subsequent chondral collapse, and secondary degenerative osteoarthritis of the hip joint. Death of these osteocytes is thought to occur because of ischemia from damage to the blood supply to the femoral head.¹ Blood is supplied to the femoral head through both extraosseous and intraosseous vessels. Extraosseous vessels include the medial femoral circumflex, the ligamentum teres, and the retinacular vessels.^2,3 Several basic science studies have shown that traumatic dislocation of the hip places tension on the medial femoral circumflex artery and more proximally at the junction of the common femoral artery with the external iliac artery.^4–6 This leads to disruption of both the intraosseous and extraosseous vasculature. Does this disruption improve with early reduction of the hip?

Reduction of a dislocated hip is often delayed for several reasons. Significant trauma is required to produce a hip dislocation; thus, patients with a dislocated hip tend to have multiple severe injuries. Head or abdominal injuries may require treatment before the dislocated hip. In the setting of the patient with multiple injuries, the hip dislocation may be missed. The patient may be transferred a significant distance from a referring hospital. What is the prognosis for the patient with a hip dislocation whose reduction has been delayed?

A subset of hip dislocations (3–13% in the literature) are irreducible closed and require open reduction.^7–11 These irreducible hip dislocations are frequently associated with fracture of the femoral head or acetabulum with incarceration of a bony fragment in the hip joint. Alternatively, the head may have “buttonholed” through the hip capsule, the piriformis muscle may block relocation of the head, or the labrum may have torn and flipped into the joint.¹² Given this scenario, when should surgical relocation of the hip be preformed? Most general orthopedic surgeons can perform an open reduction of a hip dislocation; however, those associated with femoral head or acetabular fracture often necessitate referral to a trauma specialist for definitive fixation. Should the referring surgeon perform an open reduction and relocate the hip before transferring to the specialist for a second procedure to fix the fracture? Should relocation of the hip be deferred and managed definitively by the trauma specialist?

EVIDENCE

Animal studies suggest that the disruption of the vascular supply to the femoral head may improve with reduction within 12 hours. Duncan and Shim⁴ found that early reduction of the dislocated hip improved early and complete recovery of blood supply to the femoral head in a rabbit model. Reduction of the dislocated hip delayed beyond 12 hours did not benefit the rate and extent of the circulatory recovery of the femoral head. Histologic avascular necrosis was observed in hips reduced early and late; however, it was less frequently observed and less severe in those reduced early. In a subsequent study using rabbits and canines, Shim⁵ found that vascular damage was largely due to compression, traction, and spasm of the extraosseous vessels (only a minority of these was ruptured). This is reinforced by a human cadaveric study demonstrating that dislocation caused compression of the medial femoral circumflex and common femoral vessels.⁶ These basic science studies suggest that the vascular disruption is reversible with reduction of the hip. Furthermore, early reduction may reverse ischemic changes that occur in the femoral head at a cellular level.

Clinical studies that explore the effect of timing of hip reduction on the rates of avascular necrosis are largely retrospective cohort studies. No study was identified that focused solely on the rate of avascular necrosis as a function of time to reduction. Rather, these studies explored several different outcome measures (e.g., avascular necrosis, patient satisfaction, degenerative osteoarthritis) and several different variables (e.g., type of dislocation, time to weight bearing). We have identified six Level II and three Level IV studies with regard to effect of reduction on rate of avascular necrosis (Table 57-1).

Brav⁸ reviewed traumatic hip dislocations that presented to U.S. Army hospitals during a 12-year period from 1947 to 1958.⁸ He found that the rate of avascular necrosis was 17.6% when reduction occurred before 12 hours and 56.9% when reduction was delayed over 12 hours. Although no statistical analysis was done to prove significance (no P value was reported), there is a definite trend to reduced avascular necrosis in the group treated early.

Subsequent Level II studies have presented similar results with respect to timing of reduction and rates of avascular necrosis. Şahin and colleagues¹³ examined 62 cases of traumatic hip dislocation (5 anterior and 57 posterior with associated acetabular fracture) and found a trend for decreased avascular necrosis when the hip was reduced within 12 hours (2.9%) as compared with after 12 hours (14.8%). In addition, they found that there was no significant difference between hips reduced less than 6 hours and those reduced between 6 to 12 hours after injury. Moed and coworkers¹⁴ also note a significant reduction in rates of avascular necrosis in hips reduced within 12 hours (P < 0.001) but did not comment on the absolute rates. Yang and coauthors¹⁵