1. Introduction
eriprosthetic fracture is a challenging complication after Total Knee Arthroplasty (TKA). Also, the incidence of this fracture has continually increased since the last few years owing to the increased number of TKA procedures [1, 2, 3]. The majority of these fractures occur in the distal femur, with an incidence of 0.3% to 5.5% after primary TKA. Periprosthetic fractures of the tibia and patella are uncommon, with an incidence of 0.3% to 0.5% and 0.1% to 2.5%, respectively [4]. 
Treatment of these fractures is a significant challenge, mainly because of the insufficient bone stock and old age of the patients [5]. Non-operative treatment is generally associated with a high rate of complications. However, there is no consensus regarding the best choice of surgical treatment. Although various fixation methods, including dynamic compression plate [6], blade plate [7], locking condylar plate [8], and retrograde intramedullary nail [9], have been used for the treatment of these fractures, none has yielded acceptable results [10], and a complication rate of 25% to 75% has been reported following the fracture treatment [11]. Therefore, further studies are required to achieve a consensus regarding the optimal treatment of such fractures.
Anatomic distal femur Locking Compression Plate (LCP) is generally used to fix distal femur fractures [12, 13, 14]. However, in the TKA setting, these plates impinge with the prosthesis. To avoid this adverse effect, the surgeon had no choice but to shift the plate posteriorly, which leads to the protrusion of the proximal part of the plate from the proximal part of the femur, irritating adjacent soft tissue (Figure 1). We hypothesized that low-profile proximal tibial LCP would be a suitable alternative for short anatomic distal femur LCP for periprosthetic femoral fractures. Actually, its thinner and narrower design prevents impingement with the prosthesis, and therefore, does not need a posterior shift with its consequences.
Objectives
 In this study, we reviewed the outcome of periprosthetic femoral fracture following TKA in a series of patients mainly fixed with a long low-profile proximal tibial LCP.
2. Methods
This study was approved by the Review Board of our institute. Medical profiles of patients who underwent TKA for end-stage primary knee osteoarthritis were reviewed at our center between 2012 and 2018. Patients with a periprosthetic femoral fracture above prosthesis and follow-up of at least one year were included in the study. Patients with an inadequate data set, those who were managed conservatively, patients who lost to follow-up, and patients with pathologic fractures were excluded from the study. Finally, 12 patients were included in the study. According to the Su et al. classification, all fractures were type II, originating from the femoral component with proximal extension [15]. 
Surgical procedure
The patients were placed supine on a radiolucent table, and the fracture was reduced with open reduction. Then, through a lateral approach and under fluoroscopic guidance, the plate was slipped into the submuscular, extraperiosteal position. The plate choice was either a long low-profile proximal tibial LCP (Kanchi, China) or a short plate (8-hole dynamic compression plate or anatomic distal femur LCP). When using a long plate, the fracture fixation was bridged so that only proximal and distal locking screws were implemented. After intraoperative assessment of fixation, the wound was closed. 
The patients were instructed to remain non-weight-bearing for four weeks after the surgery. After that, partial weight-bearing was started until three months after the surgery. Full weight-bearing was initiated afterward. The first follow-up of the patients was 3 weeks after the surgery. The subsequent follow-ups were at 6 weeks, 12 weeks, 3 months, and 6 months after surgery. The functional outcome of the patients was assessed 6 months after the surgery using the Knee Society Score (KSS), in which a higher score indicates lower disability [16].
3. Results
The study population included 11 (91.7%) women and one man (8.3%) with a Mean±SD age of 74.5±9.3 years (range: 66-94 years). All fractures were located above the proximal edge of the prosthesis. Surgical fixation was done with a short plate in 3 patients and long locking in 9 patients. The mechanism of injury was low-energy trauma (falling during walking) in all patients. The Mean±SD time interval from the primary TKA to fracture was 4.3±3.2 years (range: 3-6.5 years). Table 1 presents the characteristics of the patients. 


The Mean±SD follow-up of the patients after fracture treatment was 2.8±1.3 years (range: 2-4 years). The follow-up of nine patients in whom a long plate was used for fracture fixation was event-free, as well (Figures 2 and 3). In these patients, the :union: of fracture was observed during a Mean±SD period of 3.1±2.1 months (range: 2-5). Fixation failed in all three patients who were managed with a short plate (Figure 4). In these patients, the fracture site started a curve about 3 months after the surgery, which progressed during the following months. The increased angulation of the knee led to the revision surgery at a Mean±SD period of 6.1±1.2 weeks (range: 5-7) after the surgery. These patients underwent revision surgery in which the fracture was fixed with a long proximal tibial plate. In two of these patients, the fracture was united without complication. In the remaining patient, the plate was fractured and complicated with infection. This patient was finally managed with a tumor prosthesis. 
The Mean±SD functional score (KSS) of the patients at the final follow-up was 71.6±3.8 (range: 67-74). No patient had substantial limitations in the knee range of motion. 
4. Discussion
There is no consensus regarding the optimal surgical procedure and choice of fixation for the management of periprosthetic fracture after TKA [10, 17, 18]. Before 2016, we used to use the anatomical distal femoral plate for the fixation of these fractures. However, because of the small size of the distal femur in most of our patients, using these plates was associated with impingement and pressure on the lateral tissues of the knee, resulting in a poor fixation. Therefore, we used long low-profile proximal tibial LCP for the fixation of these fractures after 2016.
In this study, we reviewed the outcome of post-TKA periprosthetic fracture in a cohort of 12 patients. According to our results, a long low-profile proximal tibial LCP ‎provides an efficient and secure fixation, while short plates are associated with a high failure rate.
Hou et al. reported the outcome of periprosthetic femoral fractures above TKA in 34 patients fixed with a locking plate. Postoperative complications included three non:union: (9%), three mal:union: (9%), and two (6%) surgical site infections. They concluded that locking plate fixation could provide favorable results in treating patients with periprosthetic femoral fractures [17]. 
Ricci et al. reported the outcome of locking plate fixation combined with minimally invasive insertion technique to treat periprosthetic supracondylar femur fractures above a TKA in 22 patients. The failure rate was 14% (n=3), which included two infected non:union:s and one aseptic non:union:. All patients who developed non:union: were insulin-dependent patients with diabetes. Two patients had postoperative malalignment. Screw fracture in the proximal fragment occurred in four patients [19].
Several other studies have also investigated the role of locking plates in treating periprosthetic fracture after TKA [20, 21, 22, 23]. Wallace et al. performed a review study to find some of the factors that should be considered in the fixation of periprosthetic fractures about a TKA. According to their review, infection and non:union: are the most common postoperative complications after fixation of periprosthetic fracture about a TKA, with a rate of 0%-9% and 0%-19%, respectively [24].
We used long low-profile proximal tibial LCP for the fixation of periprosthetic femoral fracture above the TKA. The fixation was successful in all fractures that were fixed with this plate. Even though the success of treatment in periprosthetic fractures depends on several factors such as type of fracture, bone quality, and site of the fracture [25, 26, 27]. 
Herrera et al. performed a review study to determine the best fixation method for periprosthetic distal femur fractures after TKA. According to their review, locking plates and retrograde intramedullary nailing were successful in the fixation of these fractures. However, retrograde intramedullary nailing was slightly superior to locking plates. They urged the need for continuing research to understand and treat better these types of fractures since the rate of periprosthetic fractures is growing owing to the continuous increase of the TKA performed procedures [28].
Although long low-profile proximal tibial LCP has not been designed for the fixation of periprosthetic fractures, our results reveal that this plate could be a suitable substitute for anatomic distal femoral LCP in this setting because it resolves the problems of anatomic distal femoral LCP, including impingement with prosthesis and anterior protrusion after posterior shifting. Meanwhile, the plate manufacturing companies should focus on designing distal femoral plates with narrower and thinner distal portions, termed anatomic distal femoral plate designed for periprosthetic femoral fractures above the prosthesis.  The present study had several limitations. It was a retrospective study with a small number of patients. The small number of patients did not allow the statistical comparison of failure rate between the short and long plates. Moreover, the characteristics of patients, such as bone quality, should be matched when comparing the efficacy of different plates. The present report is a pilot study using long low-profile proximal tibial LCP to fix displaced periprosthetic femoral fractures. So, future large-scale comparative studies are required to shed more light on the efficacy of these plates for the fixation of such fractures. Finally, it should be noted that the success of treatment in periprosthetic fractures depends on several factors such as type of fracture, bone quality, and site of the fracture. So many confounding factors interfere with the conclusion, and in this survey, the small ‎number of patients is problematic.
5. Conclusion
According to this pilot study, in contrast to short anatomic distal femoral LCP, long low-profile proximal tibial LCP could be an appropriate fixation device for treating displaced periprosthetic femoral fractures as they are not impinged by the prosthesis. However, future large-scale comparative studies are required to provide a consensus regarding the implication of this plate for the fixation of periprosthetic femoral fractures after TKA because they are not designed for the fixation of these fractures.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of the Iran University of Medical Sciences (Code: IR.IUMS.REC.1400.199). 

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
Study concept and design: Mahmoud Jabalameli and Hooman Yahyazadeh; Drafting manuscript: Amirali Karimi; Data collection: Rahmatalah Jokar and Sina Talebi; Reviewing the manuscript critically: Mehdi Mohammadpour. 

Conflict of interest
The authors have no conflict of interest.


References

1. Jabalameli M, Abedi M, Yahyazadeh H, Sobhan MR. Periprosthetic early insufficiency fracture after total knee arthroplasty: A retrospective case series. Curr Orthop Pract. 2021; 32(3):237-41. [DOI:10.1097/BCO.0000000000000980]
2. Rorabeck CH, Taylor JW. Periprosthetic fractures of the femur complicating total knee arthroplasty. Orthop Clin North Am. 1999; 30(2):265-77. [DOI:10.1016/S0030-5898(05)70081-X] [PMID]
3. Kim KI, Egol KA, Hozack WJ, Parvizi J. Periprosthetic fractures after total knee arthroplasties. Clin Orthop Relat Res. 2006; 446:167-75. [DOI:10.1097/01.blo.0000214417.29335.19] [PMID]
4. Platzer P, Schuster R, Aldrian S, Prosquill S, Krumboeck A, Zehetgruber I, et al. Management and outcome of periprosthetic fractures after total knee arthroplasty. J Trauma. 2010; 68(6):1464-70. [DOI:10.1097/TA.0b013e3181d53f81] [PMID]
5. Yoo JD, Kim NK. Periprosthetic fractures following total knee arthroplasty. Knee Surg Relat Res. 2015; 27(1):1-9. [DOI:10.5792/ksrr.2015.27.1.1] [PMID] [PMCID]
6. Sen R, Prasad P, Kumar S, Nagi O. Periprosthetic femoral fractures around well fixed implants: A simple method of fixation using LC-DCP with trochanteric purchase. Acta Orthop Belg. 2007; 73(2):200-6. [PMID]
7. Higgins LD, Figgie MP. Femoral periprosthetic fractures: Blade plates fixation. In: Scuderi GR, Tria AJ, editors. Surgical Techniques in Total Knee Arthroplasty. New York: Springer; 2002. pp. 563-572. https://www.springer.com/gp/book/9780387983899
8. Kanakaris NK, Obakponovwe O, Krkovic M, Costa ML, Shaw D, Mohanty KR, et al. Fixation of periprosthetic or osteoporotic distal femoral fractures with locking plates: A pilot randomised controlled trial. Int Orthop. 2019; 43(5):1193-204. [DOI:10.1007/s00264-018-4061-1] [PMID] [PMCID]
9. Han HS, Oh KW, Kang SB. Retrograde intramedullary nailing for periprosthetic supracondylar fractures of the femur after total knee arthroplasty. Clin Orthop Surg. 2009; 1(4):201-6. [DOI:10.4055/cios.2009.1.4.201] [PMID] [PMCID]
10. Lizaur-Utrilla A, Miralles-Muñoz FA, Sanz-Reig J. Functional outcome of total knee arthroplasty after periprosthetic distal femoral fracture. J Arthroplasty. 2013; 28(9):1585-8. [DOI:10.1016/j.arth.2013.03.007] [PMID]
11. Kassab M, Zalzal P, Azores GMS, Pressman A, Liberman B, Gross AE. Management of periprosthetic femoral fractures after total knee arthroplasty using a distal femoral allograft. J Arthroplasty. 2004; 19(3):361-8. [DOI:10.1016/j.arth.2003.11.003] [PMID]
12. Yeap EJ, Deepak AS. Distal femoral locking compression plate fixation in distal femoral fractures: Early results. Malays Orthop J. 2007; 1(1):12-7. [DOI:10.5704/MOJ.0705.004]
13. Patil K, Patil M, Khadabadi N, Patel C. Distal femoral locking compression plate fixation in distal femoral fractures: One year hospital based study.     J Evol Med Dent Sci. 2014; 3(28):7911-9. [DOI:10.14260/jemds/2014/2990]
14. Bagherifard A, Majdi S, Motaghi P, Heidarikhoo MR, Khayyami K, Sattari SA, et al. Evaluation of the outcome of different surgical techniques in the treatment of distal femur intra-articular fractures: A retrospective study. J Res Orthop Sci. 2021; 8(1):1-8. [DOI:10.32598/JROSJ.8.1.414.1]
15. Su ET, DeWal H, Di Cesare PE. Periprosthetic femoral fractures above total knee replacements. J Am Acad Orthop Surg. 2004; 12(1):12-20. [DOI:10.5435/00124635-200401000-00003] [PMID]
16. Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the knee society clinical rating system. Clin Orthop Relat Res. 1989; 248:13-4. [DOI:10.1097/00003086-198911000-00004] [PMID]
17. Hou Z, Bowen TR, Irgit K, Strohecker K, Matzko ME, Widmaier J, et al. Locked plating of periprosthetic femur fractures above total knee arthroplasty. J Orthop Trauma. 2012; 26(7):427-32. [DOI:10.1097/BOT.0b013e31822c050b] [PMID]
18. Jabalameli M, Khosravi S, Delbari D, Bagheri Fard A, Latifi N. Use of 4.5 non-locking plate as an alternative device in open wedge high tibial osteotomy for treating varus deformity. J Res Orthop Sci. 2020; 7(2):55-60. [DOI:10.32598/JROSJ.7.2.683.1]
19. Ricci WM, Loftus T, Cox C, Borrelli J. Locked plates combined with minimally invasive insertion technique for the treatment of periprosthetic supracondylar femur fractures above a total knee arthroplasty. J Orthop Trauma. 2006; 20(3):190-6. [DOI:10.1097/00005131-200603000-00005] [PMID]
20. Ehlinger M, Adam P, Di Marco A, Arlettaz Y, Moor BK, Bonnomet F. Periprosthetic femoral fractures treated by locked plating: Feasibility assessment of the mini-invasive surgical option. A prospective series of 36 fractures. Orthop Traumatol Surg Res. 2011; 97(6):622-8. [DOI:10.1016/j.otsr.2011.01.017] [PMID]
21. Horneff III JG, Scolaro JA, Jafari SM, Mirza A, Parvizi J, Mehta S. Intramedullary nailing versus locked plate for treating supracondylar periprosthetic femur fractures. Orthopedics. 2013; 36(5):e561-6. [DOI:10.3928/01477447-20130426-16] [PMID]
22. Li B, Gao P, Qiu G, Li T. Locked plate versus retrograde intramedullary nail for periprosthetic femur fractures above total knee arthroplasty: A meta-analysis. Int Orthop. 2016; 40(8):1689-95. [DOI:10.1007/s00264-015-2962-9] [PMID]
23. Song SJ, Kim KI, Song WJ, Kim DK, Bae DK. Treatment of distal femur fractures with locking plates: Comparison of periprosthetic fractures above total knee arthroplasty and non-periprosthetic fractures. Acta Orthop Belg. 2014; 80(3):380-90. [PMID]
24. Wallace SS, Bechtold D, Sassoon A. Periprosthetic fractures of the distal femur after total knee arthroplasty: Plate versus nail fixation. Orthop Traumatol Surg Res. 2017; 103(2):257-62. [DOI:10.1016/j.otsr.2016.11.018] [PMID]
25. Leonidou A, Moazen M, Lepetsos P, Graham SM, Macheras GA, Tsiridis E. The biomechanical effect of bone quality and fracture topography on locking plate fixation in periprosthetic femoral fractures. Injury. 2015; 46(2):213-7. [DOI:10.1016/j.injury.2014.10.060] [PMID]
26. Min BW, Lee KJ, Cho CH, Lee IG, Kim BS. High failure rates of locking compression plate osteosynthesis with transverse fracture around a well-fixed stem tip for periprosthetic femoral fracture. J Clin Med. 2020; 9(11):3758. [DOI:10.3390/jcm9113758] [PMID] [PMCID]
27. Rhee SJ, Cho JY, Choi YY, Sawaguchi T, Suh JT. Femoral periprosthetic fractures after total knee arthroplasty: New surgically oriented classification with a review of current treatments. Knee Surg Relat Res. 2018; 30(4):284-92. [DOI:10.5792/ksrr.17.036] [PMID] [PMCID]
28. Ebraheim NA, Kelley LH, Liu X, Thomas IS, Steiner RB, Liu J. Periprosthetic distal femur fracture after total knee arthroplasty: A systematic review. Orthop Surg. 2015; 7(4):297-305. [DOI:10.1111/os.12199] [PMID] [PMCID]