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An Unusual Complication after Infected Total Knee Arthroplasty

One-stage or two-stage revision total knee arthroplasty (TKA) in periprosthetic joint infections has been at the center of scientific debate for many years. As regards two-stage revision TKA, cement spacers have a good infection control rate with successful results reportable up to 96%, though some studies describe related spacer complications such as stiffness and loss of bone stock. We report a case of a fracture close to the antibiotic-loaded cement spacer in a 74-year-old female patient. Due to the blood tests and high risk of infection, we performed a hybrid external fixator. Six months after the surgery, X-rays did not show signs of fracture consolidation and nonunion was considered as an impending complication; therefore, the decision was made to perform tumor-like total knee arthroplasty. The postoperative evolution was satisfactory and return to daily activity without pain. At the 5-year follow-up, the patient showed a good score of 36-Item Short Form Health Survey and a range of motion from 0 to 90° without pain. The X-rays did not show signs of mobilization, dislocation, recurrence of infection, or other complications.


Introduction
Infection is a severe complication after primary total knee arthroplasty (TKA), with an incidence rate of 1 to 4.4%. 1,2 One-stage revision TKA involves one surgical procedure to remove the old prosthesis and to implant a new one. However, it also involves aggressive and complete tissue debridement. Although one-stage revision TKA can be performed in some cases, the current standard of care is considered to be two-stage revision TKA, including removal of the prosthesis and cement, thorough debridement, placement of an antibiotic-impregnated cement spacer, a course of intravenous antibiotics, and a delayed two-stage revision TKA.
Nowadays, two types of antibiotic-loaded cement spacers exist: static and dynamic. Static spacers basically create a "temporary arthrodesis" with antibiotic-loaded cement, while dynamic spacers can be created intraoperatively by using different tools or may be prepackaged by the manufacturer. 3 Cement spacers have a good infection control rate with successful results reportable up to 96%, though some studies describe related spacer complications such as stiffness, loss of bone stock, and extensor mechanism contracture. [4][5][6][7] We report a case of a fracture close to the antibioticloaded cement spacer.

Case Presentation
A 74-year-old female was admitted to the outpatient department of our clinic with a 1-year history of right knee pain, inability to bear weight on the right side, and the presence of a secreting fistula localized on popliteal region.
Clinical examination revealed positive thermo tactile sensation. Passive and active movement of the right knee was painful and limited (lack of full extension due to fixed flexion deformity of -5°, flexion up to 100°). Initial blood tests revealed raised serum erythrocyte sedimentation rate (ESR) Keywords ► fracture ► spacer ► tumor-type prosthesis

Abstract
One-stage or two-stage revision total knee arthroplasty (TKA) in periprosthetic joint infections has been at the center of scientific debate for many years. As regards twostage revision TKA, cement spacers have a good infection control rate with successful results reportable up to 96%, though some studies describe related spacer complications such as stiffness and loss of bone stock. We report a case of a fracture close to the antibiotic-loaded cement spacer in a 74-year-old female patient. Due to the blood tests and high risk of infection, we performed a hybrid external fixator. Six months after the surgery, X-rays did not show signs of fracture consolidation and nonunion was considered as an impending complication; therefore, the decision was made to perform tumor-like total knee arthroplasty. The postoperative evolution was satisfactory and return to daily activity without pain. At the 5-year follow-up, the patient showed a good score of 36-Item Short Form Health Survey and a range of motion from 0 to 90°without pain. The X-rays did not show signs of mobilization, dislocation, recurrence of infection, or other complications.
at 54 and C-reactive protein (CRP) at 16. Three different swabs from fistula were positive to Staphylococcus lugdunensis. X-rays revealed a cemented "rotational Knee Joint Prosthesis" (Endo-model, Waldemar Link, Hamburg, Germany) (►Fig. 1); this implant is characterized by two cementing stems that increase the security of the prosthetic alignment. The bone scan was positive for septic mobilization of the implant; the decision was to perform a two-stage revision TKA.
At the first stage, the femoral and tibial prosthetic components were removed to allow complete removal of the cement; on both the femoral and tibial sides, bony windows were created; they were fixed with multiple metallic wires (►Fig. 2).
The tibial and femoral intramedullary shafts were rinsed with 5 L of saline solution, while the antibiotic handmade cement spacer was created.
The intraoperative cultural examinations confirmed the bacterial infection by Staphylococcus lugdunensis. Postoperatively, the patient was treated with specific antibiotic therapy and immobilized in an above-the-knee brace fixed in full extension; weight bearing was denied.
One month postoperatively, after a fall, the patient was readmitted to the hospital due to pain in the operated limb. X-rays showed a diaphyseal fracture above the spacer and close to the proximal cerclage (►Fig. 3).   Blood tests revealed that there had been no reduction in levels of ESR (36) and CRP (72) since the first operation.
The decision was, therefore, made to perform a closed reduction and fixation of the fracture with a hybrid external fixator (HEF) (Orthofix SRL, Verona, Italy) (►Fig. 4).
Due to the fact that the fracture did not show signs of consolidation, at X-ray, 6 months after HEF, nonunion was an impending complication. Furthermore, the laboratory results revealed a normal ESR at 20 and CRP at 2 (►Fig. 5).
We therefore decided to perform a tumor-like total knee arthroplasty (►Fig. 6).
Intraoperative cultural and histological examinations were negative for infection.
At the 5-year follow-up, the patient showed a range of motion between 0 and 90°without pain.
The X-rays did not show signs of mobilization, dislocation, recurrence of infection, or other complications (►Fig. 7).

Discussion
Antibiotic-loaded cement spacers are used routinely in twostage revision TKA. The goal of two-stage revision TKA is to radically eliminate the infection and to create the healthiest tissue possible for the new implant. 8 Wan et al and Choi et al evaluated the use of different spacers in two-stage treatment for infected TKA. 9,10 Their analyses demonstrated that articulating spacers can provide good results in terms of infection control and functional outcome. However, their studies lack a thorough evaluation of spacer-related problems.  Only 43% of all spacers were considered optimal, while a total of 12% showed major spacer issues such as fracture of the spacer, spacer dislocation, or knee subluxation. 6 Fracture close to the spacer is the object of discussion in this case report.
Although the literature has widely discussed the management of periprosthetic fractures, there is a lack of information regarding the treatment of the fracture close to the spacer.
The early recovery of function and ambulation is critical in patients with these injuries, and effective surgical strategies to achieve these goals are essential. 8,11 The optimum treatment of periprosthetic fractures in the region of the distal femur is undefined. When there is no presence of infection and the implant is well-fixed, the option to retain the implant should be taken. Operative strategies in this context include the use of retrograde intramedullary nail, plates, or external fixator.
When there is a poor bone stock, comminuted fracture, or loose components, the use of a tumor-type prosthesis shows favorable results with low complication rates and rapid mobilization. 12,13 Therefore, in our view, these guidelines can be applied also for the treatment of the fractures close to the spacer.

Conclusion
In our case report, we applied similar guidelines to those for total knee periprosthetic distal femur fractures: the use of megaprosthesis was associated with good functional and satisfactory levels.
We can conclude that the use of megaprosthesis is a reliable option in such cases

Conflict of Interest
None declared.