Periprosthetic Fractures 

Fractures around implants pose unique fixation challenges. The original placement of the implant may predispose to later fracture, the long-term presence of the device may change the structure of the bone and increase susceptibility to fracture, and the implant itself may interfere with healing or the placement of other fixation devices. The number of implants in the femur is increasing as the population ages, and the indications for joint replacement and fixation increase.

Fractures around joint replacement prostheses are commonly called periprosthetic fractures, while fractures around plates, rods, or prostheses can be more generally termed peri-implant fractures. As more peri-implant fractures occur, the orthopedic surgeon needs to learn methods to manage the specific problems involved.

An image depicting a fracture around an implant can be seen below.

The number of orthopedic implants placed in the femur is increasing.^[1] More than 123,000 total hip and 150,000 total knee arthroplasties are completed each year in the United States, with the numbers expected to increase as the population ages).^[2] The major complications of total joint arthroplasty are loosening and osteolysis. The rate of osteolysis increases with time, and osteolytic bone defects are stress risers, which predispose the patient to fractures.^[3]

More than 300,000 hip fractures occur yearly, and almost all are treated operatively with internal fixation or prosthetic replacement. Furthermore, the number of implants placed in other bones is increasing, with expanding indications for shoulder, elbow, and ankle replacement, and internal fixation continues to be used in all the long bones, especially the tibia and humerus.

Improvements in cancer treatment also have resulted in longer life spans with increased likelihood of metastatic bone lesions and impending or actual pathologic fractures that require internal fixation. The ability of tumor to "outgrow" a fixation device and the decreased ability of irradiated or tumor-replaced bone to heal fractures also results in an increasing frequency of peri-implant fractures.

As the number of implants placed increases, it is inevitable that associated fractures also become more common. Once a fracture occurs, treatment is complicated by osteoporosis,^[4] defects in the bone, and the presence of the implant.^{[4, 5]} Common problems include malalignment, stiffness, and nonunion.^[5] If malalignment occurs after a periprosthetic fracture, the abnormal joint biomechanics may cause a high rate of revision secondary to loosening.^[4]

The implant may impair fracture healing because of endosteal ischemia.^[6] Rates of nonunion for supracondylar fractures proximal to total knee prostheses are higher than for supracondylar fractures without the implant.^[6] Stems, rods, screws, and methylmethacrylate may block the medullary canal, preventing intramedullary fixation of fractures. Stems and rods also block screw fixation through the medullary canal to hold plates on bone. The techniques for treating peri-implant fractures may be more difficult, with more limited options and more frequent complications than the techniques used in treating fractures without the presence of an implant.

Frequency

The incidence of supracondylar fracture after total knee replacement is 0.6-2.5%.^{[6, 4]} Fracture can occur more than 10 years after joint replacement^[7] ; thus, as the number of patients with replacements accumulates, more fractures occur. The exact incidence and frequency of other peri-implant fractures has not been established.

Peri-implant fractures can be caused by technical problems during their placement. Many studies have implicated notching of the anterior cortex of the femur during knee arthroplasty as the cause of supracondylar fracture,^[6] with a 40% fracture rate even 8 years after surgery.^[4] However, other studies have questioned the association.^[8] The calcar may fracture during hip arthroplasty^{[9, 10]} , the stem may penetrate the femoral shaft, or distal femoral fracture can occur with manipulation and preparation of the femur (see image below).^{[11, 10]}

Fractures can occur during internal fixation when screws are placed too close or bone holding devices crack the bone, especially in osteoporotic bone. Any drill hole up to 20% of the diameter of the bone weakens the bone by 40% of its original strength. Ninety percent of fractures around fracture fixation implants occur through a drill hole (see image below).^[12]

Displacement of unrecognized femoral neck fracture or new fracture occurs in 3% of intramedullary nailings of femoral shaft fractures.^{[13, 14]} With any implant, the end of the device becomes a stress riser in which the weaker osteoporotic bone tends to fracture first when excessive load is applied.^[12]

Removal of devices is also associated with refracture. After plate removal, the cortical bone has been stress shielded and needs to be protected. Zickel intramedullary hip nails have been associated with subtrochanteric fracture when removed,^[12] and the more modern intramedullary hip screw systems may do the same. During prosthetic revisions, the rate of fracture is 17.6%, compared to 3.5% for primary procedures because osteoporotic bone or bone with osteolytic defects may fail while the prosthesis or its cement is being removed.^[10]

Treatment of periprosthetic fractures requires strict adherence to the basic principles of treating any fracture. The surgeon must restore the biomechanical integrity of the bone. This requires restoration of a biologic environment in which the bone can heal and a mechanically stable construct to give the bone a chance to heal.

Biology is maintained by strict soft tissue and indirect reduction techniques, when possible, to preserve periosteal and/or endosteal blood supply. The surgeon should minimize periosteal stripping, avoid dead space, and consider bone grafting if the biological environment is compromised. The patient's medical condition should be optimized. The patient should be encouraged to stop smoking when applicable.

Mechanical stability is obtained by restoring the anatomic integrity of the bone and following Association for the Study of Internal Fixation (AO/ASIF) principles with adequate fixation distal and proximal to the fracture.

Patients present with the usual signs of fracture with a history of previous prosthesis or implant. They have pain, deformity, swelling, possible limb length inequality, and inability to use the limb. The fracture can occur with minimal trauma (especially with a previously loose prosthesis or osteoporotic bone) or an obvious traumatic incident.

Essentially all periprosthetic fractures require some treatment. Stable nondisplaced fractures may only require protected weightbearing or cast/brace immobilization (and pain medication), but most unstable peri-implant fractures require surgical stabilization and/or implant replacement to restore function. Surgical intervention for peri-implant fractures follows the same guidelines as for other fractures. The goals of treatment include early ambulation, which helps avoid pulmonary complications, decubiti, disuse osteoporosis, and other complications of prolonged bedrest; restoration of axial alignment, which helps prevent eccentric stress on the prosthesis that leads to early loosening; and stabilization of the limb, which allows joint motion and helps prevent stiffness and muscle atrophy.

Treatment is rarely contraindicated after periprosthetic fracture. Observation of a fracture in a paralyzed limb may be indicated, but, even then, surgery is often useful to help with nursing care. Cancer patients with widespread resistant metastases also may be treated better with hospice or pain control alone. Patients with unstable medical conditions should be in optimal condition before surgery. If an associated infection exists, its treatment should be part of the surgical plan. Peri-implant fractures usually occur in elderly patients, and a team approach is often required for treatment.