Uterine Dilators

Developmental dysplasia of the hip (DDH) is one of the most common lower extremity anomalies in newborns. Initial management of DDH traditionally involves one of several bracing options, such as a Pavlik harness. For patients who fail orthotic treatment or who present later in life, surgical management in the form of closed or open hip reduction with hip spica casting is usually recommended. Closed reduction is generally performed in younger patients, while open reduction is reserved for cases of failed closed reduction, older patients, and irreducible dislocations.1–4 For patients that do require open reduction, typical blocks to reduction that must be addressed at the time of surgery include an hourglass-shaped capsule from a tight psoas tendon, a thickened ligamentum teres, a tight transverse acetabular ligament, and/or an inverted labrum (limbus). Even after technically proficient surgery that adequately addresses each of these issues, a concentric reduction can be challenging to obtain due to growth-related alterations in the shape of the acetabulum and/or the femoral head. In particular, a hypoplastic acetabulum that is much smaller than the size of the femoral head can create significant intraoperative challenges.5,6 Some surgeons have excised cartilaginous portions of the acetabulum or made radial cuts in the limbus in order to expand the acetabular opening to allow the femoral head to reduce; however, this approach runs the risk of damaging important growth centers of the acetabulum.6–8 In this article, we present an alternative approach to this challenge of a hypoplastic acetabulum, using sequential uterine dilators to expand the acetabular mouth and allow the femoral head to reduce. We have anecdotally found this technique to be very helpful in cases of a size mismatch between the femoral head and the acetabulum without causing damage to acetabular growth centers. TECHNIQUE When performing an open reduction, the patient is positioned supine on the operating table with a slight bump placed under the ipsilateral sacrum. After prepping and draping the hip in the usual sterile fashion, a surgical incision is made obliquely for a bikini-type approach. Subcutaneous tissues are dissected and the obliques are elevated over the iliac crest. Distally, the Smith-Peterson interval is entered. Blunt dissection is performed down to the level of the rectus tendon, which is then skeletonized and released off its origin. The anterior hip capsule is exposed, and the plane overlying the femoral head underneath the abductor musculature is developed. The apophysis is split and the inner and outer tables are elevated. The intervening tissue is released from anterior to posterior to expose the outer table, as well as fully expose the femoral head with the capsule overlying it. Working medially, the psoas tendon is identified and isolated with a right-angle clamp. We confirm that muscle fibers going into it and that the structure tightens with internal rotation, to be sure that we have not isolated the femoral nerve. After confirming that it does not excite with light-touch of Bovie cautery, the psoas tendon is transected. The medial capsule all the way down to the base of the acetabulum is exposed by working underneath the lengthened psoas tendon. An arthrotomy is then performed along the acetabular margin, and the ligamentum teres is then isolated and released off the femoral head. The medial capsule is then fully released to the base of the joint following the line of the ligamentum teres, which is then excised. The transverse acetabular ligament is released and the pulvinar is removed with a pituitary rongeur. A trial reduction is now attempted and an adductor tenotomy and/or femoral shortening osteotomy is performed if necessary to balance soft tissue tension. At this point, it will be evident whether the acetabulum is too small to accommodate the femoral head if the hip cannot medialize even after the tension has been balanced. To dilate the acetabular mouth, a uterine dilator (Fig. 1) is inserted into the base of the acetabulum in an upward angle similar to the angle used to implant an acetabular component during a total hip replacement (Fig. 2). The image intensifier can be used to confirm the appropriate trajectory (Fig. 3). The dilators are twisted in place to widen the acetabular opening and then exchanged sequentially for the next size. Typically, we start at 16mm and dilate up to the maximum of 24mm. With the acetabulum expanded, the hip can usually be relocated with improved medialization of the epiphysis (Fig. 4). At this point, capsular sutures are placed from the supero-medial capsule along the medial rim to the infero-lateral capsule to create a capsular shift. If a pelvic osteotomy is warranted based on preoperative planning, it is performed at this time. The capsule sutures are then tied snugly, and the reduction and position of the hip are confirmed with the image intensifier. The direct head of the rectus femoris is repaired, the apophysis closed, and the superficial tissues closed in a layered fashion. A one-and-a-half-leg spica cast is applied and kept in place for 6 weeks.FIGURE 1: Intraoperative photograph of Hegar uterine dilators starting from 19 (bottom of the image) to 26 mm (top of the image).FIGURE 2: Intraoperative photograph of the left hip of a 3-year-old patient demonstrating the use of a Hegar uterine dilator to dilate the acetabulum at an upward angle.FIGURE 3: (A) Intraoperative fluoroscopy image of the left hip of the same 3-year-old patient confirming the trajectory of the uterine dilator into the base of the acetabulum. (B) Dilators are sequentially upsized.FIGURE 4: (A) Preoperative AP pelvis of a 19-month-old patient demonstrating dislocation of the right hip. Intraoperatively, the hypoplastic acetabulum was dilated with uterine dilators, which facilitated reduction. (B) 1-year postoperative AP pelvis of the same patient following open reduction and Salter innominate osteotomy (and subsequent implant removal) showing a well-located right hip with favorable acetabular remodeling.EXPECTED OUTCOMES Open reduction of the hip in DDH can be a challenging procedure, especially in the setting of a hypoplastic acetabulum. Our technique is easy to execute and utilizes readily available surgical equipment to facilitate reduction of the femoral head into a small acetabulum. Although the safety of this technique and its effect on subsequent growth of the acetabulum cannot be proven by this report, we have observed that it aids in the reduction of the hip without visible damage to the acetabular growth centers or surrounding soft tissues intraoperatively. The primary benefit of the dilator technique is to help achieve reduction, particularly in cases of a hypoplastic acetabulum. We have used this technique ∼30 times thus far in our collective clinical practices. As this is just one component of a larger operation, it is difficult to deduce outcomes specific to the use of a uterine dilator. Anecdotally we have found this to be quite useful in several cases of severely hypoplastic acetabuli, and further research is needed to confirm these observations. COMPLICATIONS Potential complications of improper execution are primarily related to excessive application of mechanical forces—bruising, bleeding, and soft tissue damage. Gentle and sequential insertion of the dilators with a twisting motion help expand the acetabular mouth without creating excessive damage to the articular surface or the rim structures. CONCLUSIONS We have found the use of uterine dilators to facilitate reduction of the femoral head in settings of a hypoplastic acetabulum to be extremely helpful. Slow and sequential dilation of the acetabular ring harnesses the viscoelastic properties of cartilaginous tissues to achieve structural dilation. The technique does not create visible damage to the acetabulum nor the surrounding soft tissues, and employs surgical instruments that are widely available in most operating rooms. The true origin of this technical tip remains obscure. The senior author adopted this technique following a conversation with Norris Carroll, who, in turn, we believe, learned it from Robert Salter, but this cannot be entirely confirmed. Regardless of its origin, this intraoperative tip has been very useful in our hands and we hope it will benefit other surgeons who are faced with challenging intraoperative reductions when managing DDH, particularly those with a hypoplastic acetabulum.