Introduction
Tibial plateau fractures come in many forms from the senile nursing home patient falling on the way to the bathroom to the young motorcyclist driving into a tractor-trailer. Similarly, external fixators range from simple uniplanar large pin frames to complex ring fixators that take hours to construct and “fine tune.” This chapter is a guide to fitting the frame to the problem.
The treatment of bicondylar tibial plateau fractures can be a daunting undertaking. The orthopedic trauma surgeon must keep in mind that the amount of energy transferred to the bone also takes its toll on the soft tissues. Not only can the injury to the cartilage and the subchondral plate lead to arthrosis but the injury to the soft-tissue envelope can also cause many complications involved with open reduction and plate fixation of these fractures. Oftentimes, treatment requires dual plating, which in itself involves extensive mobilization of the already severely injured soft tissues from the comminuted bone with impaired blood supply, walking the fine line of being able to heal as well as not becoming infected.
Ringed external fixators have previously been utilized in the treatment of these high-energy injuries but have the potential for the added complication of a septic knee joint from intraarticular pins. Recent modifications to pin placement based on anatomic studies. have led to a resurgence in the use of ringed fixators for the treatment of these devastating injuries. This chapter will guide you through pin placement and configuration for a ringed fixator as well as simple large pin external fixators.
Biomechanics
The construction of the ring external fixator allows the surgeon to adjust the stiffness of the construct as well as to customize the fixation based on the injury pattern. With adjustments to the transfixion wire spread, the crossing angle, ring diameter, half-pin diameter, number of rings, and the ring symmetry the surgeon can adjust the stiffness of the construct. All of these variables can be used to increase or decrease the stiffness and, therefore, the overall stability of the construct.
A crossing angle of the tensioned wires in the proximal tibia increased from 30 to 90 degrees will increase the axial, torsional, and bending stiffness by 75%. , Transfixion pin angles between 60 and 90 degrees allow appropriate stiffness and resistance to shear forces in the sagittal plane with knee range of motion , , but can lead to the placement of pins outside of the soft-tissue safe corridors. An additional half-pin placed in the anterior position in the proximal tibia will augment sagittal stability. Gellar et al. changed the pin configuration so that the pins did not all cross the tibia in the center, allowing for crossing angles of 80 degrees, while placing them more within the sagittal plane. However, this places the pins outside the soft-tissue safe corridors , and can lead to impingement on the patellar tendon. Antoci et al. experimented with varying wire-crossing configurations while maintaining 60-degree crossing angles. Wire placement with two pins crossing 1 cm posterior to the center of the plateau and the horizontal wire in the coronal plane passing 1 cm anteriorly and inferiorly from the center of the tibia increased the sagittal plane stiffness without decreasing coronal or torsional stiffness ( Fig. 4.1 ). Three wires are sufficient for weight bearing and stiffness of the construct, but more wires may be used if desired to further increase stability. Wires 1.8 mm in diameter are small enough to capture smaller fragments of comminution as well as stiff enough once tensioned to resist loads ; however, the larger the diameter, the greater the stability imparted. Tensioning olive wires on both sides of the fracture and placing them on the side of bending will also increase the bending stiffness of the external fixator. Tensioned wires cannot be placed in the anterior-posterior direction as this would place the posterior tibial artery, nerve, and muscles at risk of injury. The greatest deforming force is in the sagittal (anteroposterior [AP]) plane when walking, and half-pins apply greater frame stiffness in this plane and are therefore used to add to the stability in the sagittal plane. , A second ring added to the proximal segment as well as wires in two levels will also increase the stability of the construct. , Hybrid fixators follow similar principles with the addition of half-pins in the diaphysis where the half-pins have greater purchase. Using pins mounted on rings will also increase the overall stiffness. ,
The stability of traditional knee-spanning constructs with half-pins and bars is less critical as they are, in general, temporary in nature. Half-pin diameter, the number of half-pins, multiplanar half-pins, bar height relative to the bone, pin to fracture distance, and the working length of the fixator are all variables that can be adjusted to manage the stiffness of the montage. ,
Indications
The general indication for external fixation of a proximal tibia fracture is a complex fracture with soft-tissue injury, which would make open plating unsafe due to increased risk of infection and/or further soft-tissue injury. Fracture patterns can be used as an indication for external fixation; more specifically, Schatzker type V and VI fractures, proximal tibia fractures with metaphyseal and subchondral comminution not amendable to routine plating, soft-tissue compromise (i.e., compartment syndrome), mangled limbs, fractures with soft-tissue defects, and fractures in the multiply injured patient. , , , , Schatzker type IV fracture may also be considered for external fixation. These can be deceptively high-energy fractures with compromise of the soft tissue, knee dislocation, or neurovascular injury. ,
X-ray clues that staged management may reduce complications include the following:
- 1.
The mechanical axis of the tibia is not in line with the femur—there is significant varus, valgus, or displacement anteriorly or posteriorly.
- 2.
The spread of the tibial condyles is wider than the spread of the distal femoral condyles.
- 3.
The fibular head is disassociated from the tibia.
- 4.
The tibial tuberosity is pulled anteriorly by the patella ligament.
- 5.
There is air in the proximal tibia or the interosseous space.
- 6.
A part of the plateau is displaced posteriorly.
Technique
Ring Fixators
The patient is positioned supine on a radiolucent fracture table with fluoroscopic control. The operative thigh and leg is elevated on a bolster to allow 360 degree viewing and access to the operative limb. A tourniquet is in place and can be inflated when needed. Manual traction or a femoral distractor may be used to obtain length and use ligamentotaxis to reduce the fracture fragments. If there are areas of comminution blocking reduction, limited incisions over the major fracture line may be made and an elevator or a forceps used to manipulate the fragments into place. Next, small and large bone clamps may be applied to assemble the fracture site. If the articular surface is depressed, a bone tamp can be introduced through an incision over the major fracture line and under fluoroscopy used to elevate depressed bone into place where it can be held temporarily with a bone clamp or kept in position with k-wires ( Fig. 4.2 ). Once an appropriate reduction is obtained and confirmed by good biplanar fluoroscopic views, one or more cancellous screws can be placed across the proximal tibia to compress the fracture and stabilize the joint ( Fig. 4.3 ). It is important to ensure that the screw will not interfere with future wire placement in the proximal tibia. Any voids in the metaphyseal bone can be filled with autogenous bone graft or bone graft substitute.
The ring fixator construct begins with choosing appropriate size rings for the patient, ensuring two- to three-fingerbreadth clearance around the ring when in place. Generally, the tibia is in the anterior portion of the ring. An incomplete ring may be used to allow for better knee range of motion as it is open in the back ( Fig. 4.4 ) or a full ring may be utilized for better fracture stabilization. If a full ring is chosen, a stack of surgical towels should be placed under the calf so that the tibia does not sag within the ring ( Fig. 4.5 ). This will maintain the two- to three-fingerbreadth distance between the ring and the limb, preventing impingement on the soft tissues.
Due to the capsular extension of the knee ( Fig. 4.6 ), the reference wire should be placed 14 mm distal to the joint line on the fluoroscopic AP and lateral views; this will ensure extra-articular placement of the wires. , The key is to ensure a true lateral of the joint with the femoral condyles superimposed to avoid inaccurate wire placement. Once the location for a wire is identified, we recommend utilizing a small stab incision and sweeping the soft tissue with a hemostat to clear away any neurovascular structures. The wire should also be placed approximately 1 cm anterior to the midportion of the proximal tibia ( Fig. 4.7 ). The ring can then be attached to the reference wire to aid in positioning the two olive wires, one from posterolateral through the fibular head if necessary, angled 60 degrees so that the wire will cross with the following posteromedial wire 1 cm posterior to the midproximal tibia. , , Although the ideal angle is 90 degrees, and a technique has been described by Geller et al. that obtains a crossing angle of 80 degrees, the surgeon must keep in mind that this will bring the wires more anterior and they may then impinge on the patellar tendon, which needs 2 cm of clearance from the pins. , Again, the wires should be at least 14 mm distal to the joint line. It is important to not pass the lateral wire distal to the fibular neck as this may injure the common peroneal nerve. The knee can also be flexed to help protect the nerve by moving it posteriorly. The olive wires are then tensioned sequentially at 90 lbs. from the side opposite the olive. The olives are used to compress the fracture and should be checked with fluoroscopy after tensioning. Be certain that during tensioning, the olive is not pulled into the tibia. This can be avoided by tensioning partway, then fixing the wire to the ring on the olive side, and then completing the tensioning. A second ring placed 2 cm below the proximal ring may be needed to increase stability. This can be done with fine wires with or without olives. Again, ensuring that the safe corridors are maintained, the wires are passed in the same posterolateral and posteromedial fashion but may need to be slightly more anterior than the previous wires. A 5-mm half-pin can also be placed 10 to 15 degrees off the medial aspect of the tibia to add more sagittal stability, especially if an oblique fracture is present.
The distal portion of the frame can be attached by fine wires and rings, half-pins and rings, or a combination of wires and half-pins. The diaphyseal bone with its thicker cortices is able to maintain half-pins better than the metaphyseal bone; therefore, they can be used in the distal portion of the construct. Half-pins with rings , distally increase the stability of the overall construct compared to half-pins and bars or fine wires. Once overall mechanical alignment is confirmed with fluoroscopy, a smooth wire is passed 90 degrees to the distal tibia and tensioned. This is followed by additional smooth wires or a 5-mm half-pin 90 degrees to the distal reference wire. Another alternative is two half-pins per ring placed in the tibial shaft from the medial face in multiple planes. Once the alignment is confirmed by C-arm, three threaded rods are used to attach the distal and proximal rings ( Fig. 4.8 ). Mechanical alignments can be confirmed using an electrocautery cord from the Anterior superior iliac spine (ASIS) passing through the femoral head, the center of the knee, and the ankle center down to the second ray.
Hybrid Construct
A hybrid construct is one that utilizes proximal periarticular tensioned wires and ring(s) connected to the tibial shaft by half-pins and bars. These constructs are often used for the treatment of proximal tibial metaphyseal fractures.
The proximal portion is completed in the same manner as that previously described for the ringed fixator. The distal portion is attached to the diaphysis with multiple pin holding clamps with two parallel 5-mm half-pins and a third pin in another plane. Bars are then connected from the ring to the distal pin groups ( Fig. 4.9 ).
Knee Spanning External Fixator
A simple, stable, and quickly applied uniplanar external fixator connects a pin group in the lateral distal femur with a pin group in the proximal medial tibia. The distal femoral pins are aimed a bit posteromedial and the medial tibia face pins start on the broad medial face of the proximal tibia and angle somewhat posterolateral. This usually allows a single bar to pass from the proximal to the distal group to complete the frame. This uniplanar frame works well unless there is appreciable instability about the knee ( Fig. 4.10 ). For unstable patterns, a multiplanar frame with two lateral and one medial distal femoral pins works better. Knee spanning external fixators are generally temporary in nature; however, they can be used definitively if needed, and this should be kept in mind when constructing the fixator. With proximal tibia and tibial plateau fractures, the knee is spanned utilizing a standard pin and bar external fixator to avoid placing pins in the zones of injury.
The multiplanar frame is constructed as follows. Starting at the distal femur, a 5-mm half-pin is placed in the supracondylar femur laterally. A pin to bar clamp is attached followed by a “stop sign” style bar around the distal femur. Utilizing this bar, another pin to bar clamp is attached and used to guide an anterolateral pin into place. Again, utilizing the bar and pin clamp as a guide, an anteromedial pin is placed in the femur and secured with a pin to bar clamp.
Ensuring that the tibial pins will be outside the zone of injury and future fixation, a 5-mm half-pin is placed on the medial face of the tibia angled 10 to 15 degrees lateral. A pin clamp is attached to guide the next pin. Side rails are placed on the clamp with bar-to-bar clamps, with a pin-to-bar clamp attached to one of the tibial pins. Three spanning bars are attached to the bar-to-bar clamps. Utilizing bump and traction, the fracture is reduced under fluoroscopy and the clamps tightened. The knee should be slightly flexed when the construct is tightened to help prevent compartment syndrome. If the fracture pattern is such that there is a portion of the tibial condyle that is not reducing with traction and gentle manipulation, a half-pin can be placed into the fracture to maneuver the fragment into place and attach it to the construct to maintain the reduction. This overall construct allows multiple planes of reduction, which if necessary can be utilized as definitive treatment ( Fig. 4.11 ).
