2.2.1 Access

The Kocher-Langenbeck is the standard posterior surgical approach for open reduction and internal fixation of a posterior wall acetabular fracture (see Chapter 2.7). This approach provides direct visualization of the entire lateral aspect of the posterior column of the acetabulum ( Fig 2.10.2-6 ). The most inferior portion of the ilium is accessible but the superior gluteal neurovascular bundle limits proximal exposure. Visualization may be extended anterosuperiorly by releasing a portion of the gluteus medius insertion or performing a transtrochanteric osteotomy. However, proximal access is still largely limited ( Fig 2.10.2-6 ). An alternative, such as the modified Gibson posterolateral approach, can be used to allow better access to a superior (weight-bearing dome) fracture fragment or to avoid an incision through an area of injured posterior soft tissue [7, 8]. The modified Gibson approach differs from the Kocher-Langenbeck approach in that the interval between the gluteus maximus and tensor fasciae lata muscles is developed, rather than splitting the gluteus maximus muscle. In this way, the neurovascular supply to the anterior portion of the gluteus maximus muscle is not at risk. In addition, anterosuperior visualization and access are extended ( Fig 2.10.2-7 ). Having a straight, rather than angled, skin incision may make the modified Gibson more cosmetically appealing, especially in obese female patients. The modified Gibson approach can be combined with a trochanteric flip osteotomy to further improve access to superior fracture fragments. In addition, posterior dislocation of the femoral head is facilitated with this procedure, allowing direct inspection of the articular surface. However, the Kocher-Langenbeck approach remains the mainstay for open reduction and internal fixation of posterior wall acetabular fractures.

Although definitive study is lacking, patient positioning has generally been believed to affect surgical access with the full extent of the surgical approach only being realized by using the prone patient position. However, the surgical approach can be performed with the patient either lateral or prone. The benefits of the prone position are realized by maintaining the femoral head in a reduced position. Gravity becomes a help rather than a hindrance in fracture exposure and reduction. In addition, the knee is held in a flexed position with the hip slightly extended, keeping tension off the sciatic nerve.

2.2.2 Instruments and implants

Special instrumentation is not usually required for open reduction and internal fixation of a posterior wall fracture. However, a straight ball spike ( Fig 2.10.2-2 ) is useful for holding small fragments in position during the reduction and fixation sequence. This surgery requires conventional 3.5 mm hardware, including malleable reconstruction-type plates, one-third tubular plates, and 3.5 mm cortex screws. Cortex fully threaded mini-screws (1.5 mm and 2.0 mm) and 1.5 mm bioabsorbable pegs are helpful in securing small osteochondral fragments often associated with these fractures. In addition, small wall fragments often require 2.7 mm screws for fixation. The most common mini-screw and bioabsorbable peg length is 40 mm; therefore, screws 40–50 mm in length (which may not be part of conventional mini-screw fracture fixation sets) should be on hand. In addition, mini-screws having a smaller, flatter cruciate head are much easier to countersink below the cancellous bone surface. A modified one-third tubular plate (spring plate) can be helpful in stabilizing small posterior wall fragments ( Fig 2.10.2-8 ). By allowing controlled distraction of the hip joint, and thereby unloading the fracture fragments, intraoperative traction is often important in obtaining fracture reduction. In this regard, the fracture table serves as an intraoperative reduction tool. Traction is applied through use of a distal femoral pin with the knee flexed to approximately 90°. This angle of knee flexion places the sciatic nerve in a relaxed position, minimizing the risk of intraoperative sciatic nerve injury. An unscrubbed assistant is required for intraoperative adjustment of the table. Alternatively, traction can be applied manually through a Schanz screw inserted into the greater trochanter or by a femoral distractor using supraacetabular and proximal femoral Schanz screws ( Fig 2.10.2-9 ). No matter what type operating room table is used, it should be radiolucent. Intraoperative C-arm image intensifier imaging can then be used to assess fracture reduction and hardware location.

2.2.3 Reduction

Posterior wall fractures are often comminuted with intraarticular free fragments. All fracture fragments must be delineated and cleared of debris while maintaining (if at all possible) soft-tissue attachments to preserve blood supply to the bone. The posterior wall fragments must be reflected on their soft-tissue hinge, like the cover of a book, exposing the underlying femoral head. The capsule invariably is torn with the tear usually extending outward from the margins of the fractured posterior wall segment. Some surgical extension of the capsular tear may be performed to afford better visualization of the hip. This capsulorrhaphy should be made at the acetabular side of the hip, just distal to the acetabular labrum (3–5 mm). Great care should be used so as not to detach the posterior wall, thereby creating a free—and devitalized—wall fragment. If a fragment of the posterior wall is incarcerated within the joint with its capsular attachments intact, the capsular attachments should not be sacrificed to retrieve the fragment. Often it can be teased out of the joint, using a right-angle clamp hooked to its anterosuperior edge or a trochanteric flip osteotomy may allow the improved access and visualization required to retrieve the fragment with its blood supply intact. This situation should be anticipated from the preoperative planning, as lateral positioning of the patient is required.

Distal and lateral subluxation of the femoral head, using one of the described methods, is required to remove intraarticular free fragments, which should be identified preoperatively on the CT scan. The addition of hip flexion can also be helpful; however, care must be taken during this maneuver not to place undue stretch on the sciatic nerve. The ligamentum teres should be removed to improve visualization. These osteochondral free fragments and marginally impacted fragments must be sequentially reduced (assuming there is sufficient attached cancellous bone to allow fragment healing), usually using the femoral head as a template. Otherwise, anatomical reduction of the main posterior wall fragment(s) may be prevented; the residual offset and/or large gaps in the articular surface can adversely affect the contact pressures across the hip joint. After removal of any free fragments, the marginal impaction (if present) is elevated, leaving a void underneath from the impacted cancellous bone. This void must be filled; usually using autogenous cancellous bone or freeze-dried cancellous allograft bone ( Fig 2.10.2-10 ). Once the fragments are reduced, it is difficult to hold them in their positions while reducing the overlying main wall fragment(s). Therefore, it is advisable to fix the fragments with underlying, subchondral mini-screws or bioabsorbable pegs ( Fig 2.10.2-11 ). The accuracy of this reduction should be assessed by applying traction and then inspecting the surface of the distracted joint.

The overlying main posterior wall fragment(s) with the intact capsular attachments are then sequentially reduced and held with a straight ball spike ( Fig 2.10.2-12 ). The reduction is facilitated by gentle longitudinal traction and slight abduction of the leg to relax the hip abductor musculature. The articular surface can no longer be seen. Therefore, the accuracy of the reduction of the articular surface is inferred from the reduction of the acetabular rim and that of the extraarticular cortical fracture lines. Failure to achieve an anatomical reduction of the main posterior wall fragment(s) indicates residual articular incongruity, most likely due to inadequate reduction, or shifting of previously reduced intraarticular fragments.

2.2.4 Fixation

K-wires are unreliable for either temporary or permanent fixation of posterior wall fragments. After reduction, each posterior wall fragment is fixed using at least one screw while maintaining the reduction with the straight ball spike. The standard fixation for this purpose is a 3.5 mm cortex screw inserted using the lag technique; however, actual screw size is dictated by the fragment size. These screws should be placed in a manner to best stabilize the fragment without compromising the joint surface. To eliminate this risk, the hip should be inspected in all planes with the C-arm image intensifier ( Fig 2.10.2-13 ). Screws that appear to compromise the subchondral bone on tangential or axial views should be redirected [9]. The entire construct is then further supported with 3.5 buttress plating, using a reconstruction plate, which is supplemented by a one-third tubular spring plate in selected fractures with extensive comminution of the posterior wall ( Fig 2.10.2-14 ). Application of a buttress plate is important, as it neutralizes the forces directed onto the posterior wall and helps prevent screw fixation failure with consequent fracture displacement. The plate should be well molded to the posterior column, anchored inferiorly at the ischial tuberosity by at least two screws, and superiorly into the dense bone superior to the acetabulum ( Fig 2.10.2-14 , Fig 2.10.2-15 ). It is essential to place this plate accurately over the main portion of the posterior wall fragment and as close to the acetabular rim as possible, but at the same time staying outside the margin of the hip joint. The plate is best placed parallel and close to the rim of the acetabulum where it can provide the best mechanical buttress for the wall fragments. All drill holes should angle away from the joint, especially those in the center of the plate, to avoid penetrating the articular surface ( Fig 2.10.2-15 ). Ideally, each posterior wall fragment also should be held by at least one lag screw placed along the acetabular rim. These rim screws can be inserted before or after buttress-plate application ( Fig 2.10.2-16 ). The hip is again inspected in all planes with the C-arm image intensifier to assess fracture reduction and hardware placement. At any point in the fixation process, screws that appear to compromise the subchondral bone on tangential or axial views should be redirected.

2.2.5 Tips and tricks

As free osteochondral fragments are removed from the joint, their relative position should be recorded to aid in determining where they belong during fracture reduction. In addition, all fragments identified on the preoperative the CT should be accounted for intraoperatively to ensure that none are left behind in the joint. Considering the depth of the wound in some of these patients, insertion of the 2.0 mm mini-screws and 1.5 mm bioabsorbable pegs is facilitated by using a standard 1.6 mm smooth K-wire (rather than a small drill bit) to create the pilot hole. Over drilling to create a gliding hole for the fully threaded screws is not required. Although it is often not possible because of the limited size of the osteochondral fragments, it is desirable to have two points of fixation for each piece to prevent malrotation of the fragment. Usually, there is not enough bone to place more than one screw. In this situation, one mini-screw and one 1.5 mm bioabsorbable peg work well. The fragment should first be fixed with two 1.6 mm smooth K-wires, and then each wire should be sequentially replaced with a 2.0 mm mini-screw and a 1.5 mm peg. Lag screws should always be placed along the rim of posterior wall fragments, and care should be taken to ensure that the plate(s) buttressing the posterior wall are positioned as lateral as possible. Positioning the buttress plate(s) too medially, especially without rim lag screw fixation, may result in loss of stabilization of the posterior wall.