Our technique of intramedullary arthrodesis of the knee has been previously described [68]. The original longitudinal incision is used whenever possible. The knee joint is exposed in a manner similar to that used in revision arthroplasty, and all scar tissue is resected. Cancellous bone is completely exposed on the distal femur and proximal tibia. An intramedullary ball-tip guidewire is introduced into the tibial shaft to the plafond of the ankle (Fig. 28.3). The canal is sequentially reamed until the cortex is engaged at the tibial isthmus. This canal width determines the intramedullary rod diameter. The tibial length is measured using the guide rod as a reference .

The ball-tip guidewire is removed from the tibial canal and inserted into the femoral shaft until it contacts the piriformis recess (Fig. 28.4). The femoral canal is reamed until it matches the size of the tibial reamer. The femoral length is measured using the guide rod at the piriformis fossa as a reference. Subtracting 1 cm from the combined length of the femur and tibial measurements determines the appropriate rod length. The guidewire is tapped proximally through the piriformis recess with a mallet (Fig. 28.5). The guidewire is advanced until it can be easily palpated under the skin of the thigh, with the leg in an adducted position. An incision is made over the guidewire, and dissection is carried down through the gluteal musculature to the piriformis recess. The recess is reamed progressively to a size 1 mm larger than the tibial and femoral reamer size (Fig. 28.6). After reaming, an arthrodesis nail of the appropriate length is inserted (Fig. 28.7). Compression is applied to the arthrodesis site by applying a retrograde force to the tibia by striking the heel (Fig. 28.8). The patella may be used to augment the fusion by using two 6.5 mm cancellous screws for fixation at the level of the resection.

In the treatment of traumatic femoral shaft fractures, an intramedullary nail is inserted with its curve following the anterolateral bow of the femur. However, in intramedullary knee arthrodesis, if the rod follows the anterolateral bow of the femur, it creates varus alignment with slight hyperextension. For this reason, the rod is inserted with the curve positioned anteromedially down the femoral shaft. The rod then comes through the tibia in valgus and slight flexion at the knee, which is a preferred position of arthrodesis. An axial load is placed on the proximal tibia against the distal end of the femur during rod insertion. Sometimes the rod forces the anterior tibial flare forward, making closure of the arthrotomy difficult. If this occurs, the surgeon may modify the anterior flare with a reciprocating saw. Resected bone and intramedullary reamings should be used as autograft, although some authors consider this unnecessary [55]. Interlocking screws or wiring of the proximal portion of the rod has been recommended to prevent proximal migration [55, 59].

Alternatively, intramedullary rodding may be accomplished using the Neff femorotibial nail (Zimmer, Inc., Warsaw, IN) or the Wichita nail (Stryker, Allendale, NJ), which is comprised of independent femoral and tibial rods coupled at the knee joint (Fig. 28.9a, b). Advantages of this technique include independent sizing of the femoral and tibial diaphysis, the elimination of proximal or distal rod migration, the elimination of a surgical incision about the hip, and the ability to accommodate a future ipsilateral total hip arthroplasty.

The intramedullary canal is sequentially reamed until the cortex is engaged at the tibial and femoral isthmus. This canal width of the tibia and femur determines the size of the tibial and femoral portions of the nail. The bony surfaces of the tibia and femur are prepared to maximize bony contact. The tibial and femoral lengths are measured using fluoroscopy. The appropriately sized tibial and femoral components are selected. As the components are of a fixed length, any shortening of the components is accomplished with a Midas Rex diamond-tipped cutting wheel. After preparing the femoral and tibial metaphyses to accept the articulated portion of the nail, the actual components are inserted into the tibia and femur, respectively. The male and female portions of the nail are coupled. Several blows to the heel secure compression of the Morse taper, which is then reinforced with two set screws. Autologous bone from the intramedullary reamings is then packed about the fusion site. The patella may be used as an additional source of autologous graft and is secured using two 6.5 mm cancellous screws .

Rigid fixation for arthrodesis can be achieved with internal plate fixation. This technique involves plate osteosynthesis, either in a tension band fashion anteriorly, or dual plating medially and laterally, to compress the distal femur and proximal tibia and achieve rigid fixation. Several studies have evaluated plate fixation for knee arthrodesis with good results [45, 69]. Following arthrodesis with plate fixation, patients may bear partial weight on the operative extremity. While results of plating for knee arthrodesis are promising, one particular downside of this technique is that in the presence of an infection, an internal device may necessitate its removal to eradicate the infection, while compromising the fusion.

Resection arthroplasty is accomplished by excising the opposing articular surfaces of the distal femur and proximal tibia (Fig. 28.10). Complete removal of scar tissue, synovium, and all foreign material, including metallic hardware, knee replacement components, and acrylic cement is mandatory [65, 70]. This option is generally reserved for medically fragile patients who cannot tolerate a two-stage reimplantation protocol . It may also serve as an intermediate step for the patient who has reservations about arthrodesis. Fallahee et al. reported 28 knees that underwent resection arthroplasty for infected total knee arthroplasty [65]. Six patients with prior monarticular osteoarthritis found the resection arthroplasty unacceptable and underwent successful arthrodesis. In three patients, spontaneous bony fusion developed after the resection, with the knee in satisfactory alignment. Patients with more severe disability before the original knee arthroplasty were more likely to be satisfied with the functional results of the resection arthroplasty. Conversely, patients with less disability originally were more likely to find the resection arthroplasty unacceptable. Fifteen patients walked independently. Five of those patients were able to stand and walk without external limb support. The other ten patients used either a knee-ankle-foot orthosis or a universal knee splint. All 15 patients, however, required either a cane or walker and remained either moderately or severely restricted in their overall walking capacity.

Definitive resection arthroplasty is useful for the severely disabled sedentary patient. The procedure is least suitable for patients with relatively minor disability before their original total joint replacement. In the latter group, arthrodesis or reimplantation of a total knee replacement is recommended, if possible, depending on the sensitivity of the organism and adequacy of the antibiotic treatment. The advantage of the resection arthroplasty is that some motion is preserved for sitting and transferring into and out of automobiles. The disadvantages are persistent pain and instability with walking.

A modified resection arthroplasty has been presented for problem cases with sepsis or excessive loss of bone stock, in which exchange arthroplasty or arthrodesis is inadvisable or impossible [71]. The space between the femur and tibia is filled with a bolus of antibiotic-impregnated polymethylmethacrylate after implant removal. The cement spacer improves initial stability and diminishes functional limb length discrepancy. Furthermore, the spacer maintains a potential space for easier reimplantation of a TKA after spacer removal in the future [72–74].

Notable complications of knee arthrodesis include nonunion, fracture, thromboembolism, infection, and neurovascular injury. Patients with insufficient bone stock, infection, or inadequate fixation are prone to nonunion, which can be a source of persistent pain. Regardless of the technique, union may not occur. In our report of 17 intramedullary knee arthrodeses for the treatment of failed septic TKA, complications occurred in ten patients, including recurrent infection, nonunion with subsequent nail breakage, proximal migration of the nail, and perforation of the ankle joint [67]. If the resulting pseudarthrosis is painful, the arthrodesis should be revised to enhance stability at the nonunion site. Failed intramedullary fusion with pseudarthrosis may eventually cause breakage of the rod. Fatigue fracture of the rod occurs at or near the pseudarthrosis site. Arthrodesis may be revised using a larger intramedullary nail supplemented by autologous bone grafting. Other sources of pain can include hip pain from proximal migration of an intramedullary nail, especially if no interlocking screws are used. Femoral or tibial fractures can occur after successful arthrodesis secondary to increased forces generated from a large single bone moment arm.