Acetabular fractures with medial displacement of the femoral head (protrusio) are often insufficiency fractures of the anterior column (AC) that are characterized by displacement of the quadrilateral surface and impaction of the superior articular surface of the acetabulum (Figs. 1A, 2A). In these injuries, the comminuted quadrilateral surface dissociates from the posterior column, and the femoral head medializes through the gap between the quadrilateral surface fragments and the displaced AC. As the femoral head displaces medially, the remaining portion of the superior articular surface attached to the intact ilium can become impacted. Anglen et al1 described the “gull sign” as a pathognomonic representation of impaction of the superior articular surface in their series (Fig. 2A, inset). Notably, these authors encountered difficulty in treating the impacted dome segment through a standard ilioinguinal approach reporting failure in 100% of their 10 patients.
These poor outcomes may be explained by the difficulty in exposure using the traditional ilioinguinal approach. The articular impaction in these injuries typically occurs along the medial aspect of the dome. Although the middle or “vascular” window may allow limited access to this area, placing an instrument through this window to disimpact the fragments is typically not possible. In many cases, the surgeon must rely on a cortical window created by osteotomizing the ilium cephalad to the impacted segment. In the authors' opinion, disimpaction in this manner is unpredictable, and reduction and stabilization of the often very thin osteochondral fragments can be difficult. The disimpacted segment is subject to malreduction or postoperative “settling,” either of which can lead to a poor outcome. The modified Stoppa (anterior intrapelvic approach or AIP) was introduced by Cole and Bolhofner in 19942 and has been used by surgeons who desire improved access to the medial aspect of the acetabulum and quadrilateral surface.3–9 This approach provides enhanced exposure for reduction of the impacted articular surface, the quadrilateral surface, and even the posterior column if necessary when compared with the standard ilioinguinal approach (Figs. 1B, 2B).3–5
Studies of acetabular fracture repair in general have discussed results in terms of quality of acetabular reduction; however, few have specifically analyzed the effect of dome impaction or quadrilateral surface injury.5,7,9 Although the presence of dome impaction and quadrilateral surface injury likely plays a pivotal role in outcomes, several clinical questions remain: How frequently does dome impaction occur? If present, how is dome impaction best treated? How do dome impaction and its repair affect functional results? What is the impact of restoration of displaced and comminuted quadrilateral surface fractures? The goal of this article is to illustrate 2 clinical cases to discuss reduction of articular dome impaction and the reduction of the quadrilateral surface in the context of acetabular fracture repair using the AIP approach.
IMPACTED ARTICULAR DOME: REDUCTION THROUGH THE MEDIAL FRACTURE
In contrast to the ilioinguinal approach,10 the AIP approach allows direct accessibility and visualization of the superior acetabular articular surface, the quadrilateral surface, and any superior medial dome-impacted fragments.4,5,8
As previously discussed, the medial aspect of the AC (iliac fossa) typically displaces cranially, whereas the quadrilateral surface displaces medially (Figs. 1B, 2B). In many cases, access for reduction of the central medial or medial dome impaction can be gained through the displaced fracture before quadrilateral surface repair. The displaced articular dome segment may be marginally impacted, in other words, hinged on a lateral pedicle (“gull sign,” Fig. 2A), made up of a “free-floating” osteochondral fragment(s), and/or impacted into the cortical bone cranially (Fig. 1A). The impacted segment may involve a small portion of the joint or may consist of the majority of the weight-bearing dome. It may be made up of multiple separate fragments (Fig. 2A) and can extend far posteriorly. Two “technical trick” articles have been dedicated specifically to reduction of the impacted dome fracture using the AIP approach. Both use a well-positioned femoral head as a guide for disimpaction and restoration of a congruent articular relationship between the acetabulum and the femur. Casstevens et al5 describes approaching the articular impaction through the AC fracture both with and without an osteotomy of the adjacent ilium along the fracture line. Their reduction is stabilized with a buttress screw superior and adjacent to the joint. Laflamme and Hebert-Davies7 visualize the dome fragment through the AIP window after repair of the AC by “accentuating displacement of the medialized (hinged) quadrilateral fragment.”
The authors' preferred technique is as follows. The patient is positioned supine with a small lumbar roll on the side of the injured acetabulum. A Foley catheter is placed, and pharmacologic paralysis is induced. Initially, the femoral head is reduced from its superior and medialized position to a more anatomic position beneath the lateral dome, which is intact in AC variant acetabular fractures. Repositioning the femoral head in this manner allows an unobstructed reduction of the acetabular articular surface and gives the surgeon a template for reduction of the impacted dome fragments. Lateralization of the femoral head can be accomplished with static traction using a 5.0-mm Schanz pin placed in the proximal femur and 5–10 pounds of weight in line with the femoral neck (Fig. 2C). Occasionally, use of static inline traction on the femur may help as well, especially if the intact lateral dome is very small (Fig. 1C) or if the injury involves the entire joint, as is the case in an associated both column acetabular fracture. In these situations, the position of the head must be very carefully assessed before reduction and repair. Successful reduction of the femoral head to the intact acetabulum is confirmed on standard C-arm views (anteroposterior and Judet) and through direct visualization through the medial fracture planes if possible.
The AIP surgical approach is performed as previously described.2,3,8 Briefly, a “Pfannenstiel” skin incision is made and may be extended as necessary. The rectus muscle is split at the midline, and the soft tissues are elevated medially to laterally along the pelvic brim until the fracture lines along the AC are exposed. The quadrilateral surface is exposed by elevation of the obturator internus muscle. The obturator neurovascular bundle is identified in the true pelvis running posterior to anteriorly from near the ischial spine toward the lateral aspect of the obturator foramen. A lighted retractor or headlight facilitates visualization of the deeper extents of the approach and into the joint.
The quadrilateral surface can usually be hinged open to allow improved access to the joint for acetabular reconstruction. Assessment of the position of the femoral head, the reduction of the dome fragments, and position of the implant are possible through this interval. Technical efforts such as the fracture reduction (disimpaction), provisional pinning and screw preparation, and void filling can be directly performed through this interval as well. A small lamina spreader or osteotome “pry bar” placed between the AC brim and the quadrilateral surface may be helpful in opening the fracture gap. Once exposure is achieved, the joint and accessible fracture lines are debrided of clot and irreparable debris. Occasionally, osteotomy of the intact pelvic brim adjacent to the joint can be helpful to improve visualization. The bone in this region is robust and is readily mobilized and repaired if additional access to the joint is required. The pelvic brim osteotomy is accomplished with a drill and osteotome and can be prepared for repair with predrilling and tapping. Accomplishing surgical goals sometimes requires exposure of the lateral window to aid in the reduction of high AC fractures, application of a pelvic brim plate, or placement of posterior column lag screws. In our hands, use of the middle or vascular window with the AIP is rarely employed because many of the benefits of the former can be achieved through the AIP exposure.
Fracture reduction deserves further discussion. A combination of C-arm fluoroscopy and direct visualization through the medial fracture play important roles in assessing the reduction. Restoration of the impacted dome should be carefully planned. Relatively flat instruments with blunt sides, such as large bent angle elevator or a curved 1/2 inch osteotome, are most useful in disimpacting dome fragments. In osteoporotic bone (most cases with this injury pattern), reduction should be achieved on the first or second attempt. Repeated manipulation of the fragments may rapidly result in thin osteochondral wafers not amenable to screw fixation. In severely osteoporotic patients, the impacted dome segment may be compressed into the bone of the AC's medial margin. Separation of the 2 must be performed with care to maintain as much cancellous bone with the osteochondral fragments as possible to facilitate fracture fixation. The reduction tool is placed above the displaced joint segment (Figs. 1C, 2C), and the fragment is either levered or otherwise moved caudally (Fig. 2C) to reduce it to the femoral head and intact lateral articular surface. If there are additional posterior impaction fragments, the surgeon must decide if these are reducible and repairable. If reduction is deemed necessary, similar techniques may be used, although in our experience, working far posteriorly can be difficult.
Once the fragments are reduced, stabilization is required. Similar to the treatment of other impacted articular fractures, a stable raft of 2 or more screws along with backfilling of the disimpaction cavity with some sort of structural material seems to be optimal. Ideally, multiple screws will capture both the subchondral bone of the reduced dome fragments and the dense uninjured bone in the near and far cortex to create a stable “rafter.” We have found that long 2-mm Kirschner wires can initially be inserted by the AIP window through the gapped AC fracture to capture the reduced impaction segment (Fig. 1C.c). The wire(s) then is passed laterally through the relatively undamaged supraacetabular bone and out through the gluteal muscle and skin. If desired, these pins can later be carefully passed back medially after the quadrilateral plate has been reduced and ultimately can be exchanged for 2.7 mm screws (Fig. 1C.d). Alternatively, they may be used as radiographic “guides” to apply other position screws (eg, 3.5-mm “rafter” screws) once all of the important fracture lines are reduced. These screws can be placed at the surgeon's discretion either medial to lateral through the intrapelvic wound (white arrow) or lateral to medial through a percutaneous stab wound.
Alternatively, Kirschner wires can be passed lateral to medial cranial (or cranial and posterior) to the dome on the anteroposterior view (Fig. 2D.a and b). When the medial dome is disimpacted, these wires can be passed into that fragment. A lateral fluoroscopy view may be helpful with this technique. Finally, if the vascular window has been exposed, a drill or Kirschner wire can be used from anterior–superior to posterior–inferior to create a pilot hole that will capture the same disimpacted fragment at an almost a 90-degree direction to other available “rafter” screws. Sometimes this drill or pin can be directly visualized through the displaced quadrilateral plate fracture. Placing 2 or more of screws that capture the reduced dome fragment (especially if 1 or more can be placed through a plate) probably optimizes the stability of the repair.
With regard to the quadrilateral surface, reduction can be readily achieved through the AIP window with a ball-spike pusher or an angled Matta reduction clamp applied directly to the quadrilateral surface with a laterally directed vector (Fig. 2D.c). The fracture is then stabilized with provisional Kirschner wires or definitively with a lag screw(s) (Fig. 2D.d). Alternatively, the “King Tong” clamp can be applied through the lateral window over the brim onto the quadrilateral surface to affect a reduction.
Plate fixation is then applied, usually with a slightly overcontoured buttress plate placed through the AIP window. Hardware placement in this fashion is a powerful tool to neutralize the medially directed forces of the femoral head on the quadrilateral surface (Figs. 1, 2; see Figure, Supplemental Digital Content 1, http://links.lww.com/BOT/A252). Infrapectineal plates placed through the AIP are applied directly along the quadrilateral surface. The buttress screws are placed through the plate capturing the dense bone inferior to the pelvic brim just anterior to the sacroiliac joint. Optimal contouring of the plate will provide a lateralizing force both for reduction and stabilization of the quadrilateral surface. A short (eg, 4- or 5-hole 3.5-mm reconstruction) plate secured posteriorly can be used in relatively dense bone and achieve a good buttress effect, but a longer plate (eg, 8–10 holes) secured at both ends is more appropriate in osteoporotic patients. When a longer medial buttress plate is used, the anterior extension of the plate is contoured to curve up onto the superior or posterior–superior aspect of the pubic ramus. Certainly, other plate options are available for this purpose, including 3.5-mm reconstruction or pelvic plates, radial “T” plates, and others. There are also now anatomically contoured plates specifically manufactured for this area (Fig. 2; see Figure, Supplemental Digital Content 1, http://links.lww.com/BOT/A252). Guy et al11 describe a safe zone for placing screws in these buttress plates to avoid acetabular penetration.
After reduction and fixation of the fracture, the authors prefer to backfill the disimpaction cavity in osteoporotic patients with calcium phosphate void filler (Fig. 1C.f), as opposed to autograft or allograft, to provide optimal mechanical stability to the construct.12 Settling of the disimpacted articular fragment(s) is common without stable fixation and may allow medialization of the femoral head and presumably a sacrificed outcome. Some surgeons prefer to place the graft or void filler through the displaced quadrilateral plate fracture before reduction, but we have found that this technique may cause underfilling or overfilling of the defect. We place calcium cement through a drill hole into the contained defect after definitive reduction and fixation of the fractures. The hole is drilled just posterior to the acetabulum along the pelvic brim so that it communicates with the void, and the void filler is injected using a low-pressure backfilling technique under fluoroscopy to minimize the risk for intraarticular extravasation.
In summary, acetabular fractures of the AC commonly involve displacement and/or impaction of the medial weight-bearing dome along with medial displacement of the quadrilateral surface. Failure to optimally restore and stabilize these components of acetabular fractures may contribute to poor outcomes. Using the techniques described, reduction and fixation of these injuries may be better addressed from the medial direction using the AIP exposure as opposed to the traditional ilioinguinal approach.
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