T

he incidence of periprosthetic fractures is increasing with the growing number of total knee arthroplasties (TKAs) being performed. Fractures around the femoral endoprosthesis of a TKA have been reported to occur at a rate of 0.3 to 5.5%. Treatment options for periprosthetic femur fractures include internal fixation with locking compression plate (LCP), intra[1]medullary nailing, cerclage wiring, and revision arthroplasty. The treatment of periprosthetic fractures is challenging and associated with a complication rate as high as 48%. Injection studies of cadaveric femurs comparing open lateral femur plating with percutaneous techniques demonstrated interrup[1]tion of up to 80% of the perforating femoral arteries utilizing the open methods. The resulting compromise of osseous circulationmay increase the risk of delayed union or nonunion. This is of particular concern with knees with cemented stems as no medullary blood supply exists, and all perfusion is derived from extramedullary vasculature. Percutaneous plate fixation for the periprosthetic femoral fractures was first described in theliterature in 2000 by Abhaykumar and Elliott. With the introduction of newer implant designs and surgical techniques, minimally invasive plate osteosynthesis (MIPO) of periprosthetic fractures is proving to be successful. However, in some cases inwhich reduction is impossible (cement or muscle interposition) a mini-open or open approach may be required.

In this review, we discuss indications, preoperative plan[1]ning, technical pearls, implant selection, complications, lim[1]itations, and challenges of the MIPO technique when used for the treatment of periprosthetic fractures about the knee.

Indications and Contraindications for MIPO in Periprosthetic Fractures

Indications

Fractures above awell-fixed total knee prosthesis are generally treated with MIPO. Rorabeck type I and some Rorabeck type II fractures can be treated with MIPO. Long oblique, spiral, and some wedge fractures may be treated with MIPO with the aid of either percutaneous cerclage wire or percutaneous clamp.

Contraindications

Failed, typically loose total knee components represent a gen[1]eral contraindication for MIPO. Failure to identify a loose component commonly leads to implant failure if revision arthroplasty is not performed. Inadequate bone stock in the distal fracture fragment and any cases with loose femoral component are contraindications forMIPO. Highly comminuted periprosthetic fractures of the femur may prove difficult to be reduced by MIPO and routinely require a mini-open technique.

Surgical Techniques

MIPO for Interprosthetic Femur Fractures

Preoperative Planning

Good-quality anteroposterior, lateral, and oblique radio[1]graphs are mandatory. Assessment of the length, alignment, and rotation of the extremity needs to be performed. It is preferable to undertake the procedure within 3 to 5 days after the injury as with delay, technical difficulties are likely to arise during MIPO. These may include troublesome frac[1]ture fragment mobilization due to clot formation and diffi[1]culties with plate instrumentation. Preoperative skin marking guides the procedure and limits the exposure to radiation, and the length of the plate must be considered when marking the skin incisions. Evaluation of the fracture pattern is done to confirm the feasibility of cerclage wire reduction, which can be used for approximating the plate to the bone and reducing spiral or long oblique fractures. Traction helps with the fracture alignment and this can be provided manually or by utilizing a femoral distractor. The rotation of the contralateral extremity is compared fluor[1]oscopically with that of the fractured side by assessing the position of the lesser trochanter at the hip and the head of the fibula at the knee. A cautery cord or a long ball tipped reaming wire can be used to assess mechanical alignment. Similarly, length can be assessed by comparing side-to-side measurements from the proximal and the distal fixed points.

Patient Positioning

The patient is often placed in the lateral position as this provides complete access to the hip joint. This also provides easewhen convertingMIPO tomini-open approachif required.

In addition, in those rare cases where open reduction internal fixation is converted to revision arthroplasty the patient does not need to be repositioned. Some surgeons, however, prefer to operate with the patient in a supine position . One potential advantage is that both legs can be draped into the field in those cases where length and rotation are predicted to be extremely difficult to determine. The limb is draped free from the iliac crest to the foot allowing intraoperative assess[1]ment of length and rotation.

Utilization of Percutaneous Cerclage Wiring for Reduction and Fixation

The cerclage technique aids in reducing a spiral fracture of a long bone as well as in approximating the plate to the bone . Percutaneous cerclage wiring has been found to result in minimal disruption of the femoral blood supply including the associated perforators.5 However, the neuro[1]vascular structures are at great risk in the distal half of the femur and reduction techniques utilizing percutaneous cerc[1]lage should be performed with caution. Typically, one wire loop for an oblique fracture, two separate wire loops for a spiral fracture, and two or three independent loops for a comminuted fracture are required.

Exposure

The proximal and distalincisions for the plate aremarked based on the fluoroscopy images. When an inverted plate is used, the approach is slightly oriented posterior at thelevel of the greater trochanter to keep the procedure minimally invasive.

Placement and Fixation of the Submuscular Plate

The plate is applied in a bridging fashion to bypass the fracture site. A tunneling instrument such as a Cobb elevator or the plate itself may be used to slide over thelateral aspect of the femur to create the tunnel. The appropriate length of the plate should allow atleast four screws proximal to the fracture site and three screws distal to the fracture site. The number of locking and nonlocking screws are usually chosen based on osteoporosis and bone quality. Spreading the screws over a longer distance using a longer plate is preferred. When necessary the plate can be contoured to fit the bone using a plate bender. The bone fragments can be reduced and compressed to the anatomically preshaped plate with the conventional screws.6,7 In the case of an irreducible fracture due to cement or soft tissue interposi[1]tion, a limited approach to reduce the fracture utilizing tem[1]porary bone clamps is advocated.8 When the cerclage wire is used as a reduction aid for the displaced fracture, it is tightened for fracture reduction, and the plate is placed over it.

Periprosthetic screws are occasionally used in the proximal fragment to avoid damage to the cement mantle. These screws are short, designed to be predrilled and to stop short of the prosthesis. Alternatively, nonlocked screws can be placed around the stem proximally to maximize fixation. Often small fragment screws are utilized tominimize the chance of cortical blowout as the screws pass in front and behind the stem.