Fracture of the femur after a hip or knee arthroplasty presents a difficult challenge that seems to be increasing in prevalence.32,34 The rate of postoperative fractures after total hip arthroplasties (THA) is 0.1% to 2.1%.3,20,25,34,40 Postoperative fractures after revision arthroplasties are more common with a rate of 4%.3 Femur fractures after hemiarthroplasties also may be more common for primary cemented hemiarthroplasties (3.7%) and revision hemiarthroplasties (10.7%).44 The rate of femur fractures above total knee arthroplasties (TKA) is 0.3% to 2.5%.9,10,46,52 These periprosthetic fractures may become even more common because of the increasing number of patients having hip and knee arthroplasties, and an increasing number of older patients with a propensity to fall.32,34
Although general algorithms for treatment of femur fractures associated with hip12,20,25,34,49,56 and knee9,10,46,52 prostheses are being established, these fractures still have substantial complication rates. Su et al reported an overall complication rate of 19% for 221 femur fractures above TKAs that were treated surgically.52 Complication rates as much as 53% have been reported for fractures treated below a stable hip prosthesis.2,25,55
The best treatment for fractures that involve a stable prosthesis is still uncertain. Numerous authors agree that fractures in patients with stable prostheses are best treated with some method of internal fixation and without stem revision. 9,10,20,25,34,46,49,52,56 However, there is no consensus regarding the type of implant for fractures about either the hip or knee prostheses.
Locking plates are becoming increasingly popular for the treatment of fractures.17,24 There are two main theoretical advantages of locking plates: improved biomechanics of fixation and less disruption to the blood supply at the fracture site.17,24 The Less Invasive Stabilization System (LISS, Synthes Inc, Paoli, PA) is a locking plate system designed specifically for treatment of distal femur fractures.16 The theoretical advantages of the LISS may be particularly important in elderly patients with osteoporotic bone.
Given the system's success in treating patients with acute femur fractures resulting from high-energy trauma,28,48,50 and the high complication rate of treating peri- prosthetic femur fractures with other devices,2,25,52,55 we wished to evaluate the clinical effectiveness of the LISS for treatment of periprosthetic femur fractures. Our hypothesis was that the LISS would provide a complication rate that would be lower than rates of other devices historically used to treat femur fractures ipsilateral to a hip or knee prosthesis. Specifically, we wished to evaluate the rate of nonunion, infection, malunion, collapse, or other complications.
MATERIALS AND METHODS
To investigate if complication rates after treatment of a femur fracture ipsilateral to a hip or knee prosethesis with a LISS were less than rates of historical controls, we performed a retrospective review of patients prospectively collected in our orthopaedic trauma database. We compared our study population to historical controls. The study was approved by the investigational review board. All patients with femur fractures treated with a LISS at two Level I trauma centers from July 1, 2001 to July 1, 2003 were prospectively followed up. The study group consisted of all patients with acute femur fractures treated with the LISS who also had previous ipsilateral TKAs and/or ipsilateral THAs. Patients with either THAs or hemiarthroplasties were included in the hip arthroplasty group. Patients with sliding hip screws and other fixation devices were not included in the hip arthroplasty group. The patients with fractures were followed up until healing and for a minimum of at least 3 months.
The indications for use of the LISS were patients with femur fractures associated with TKAs and/or hip arthroplasties, with stable prostheses that were amenable to open reduction and internal fixation without revision of the arthroplasty. The surgeries were performed with the patient supine, under fluoroscopic guidance, using the general techniques for insertion of the LISS that have been described.28 A percutaneous or open approach was used at the discretion of the attending surgeon. The use of cerclage wire and/or unicortical screws abutting a hip prosthesis when the LISS plate overlapped a hip prosthesis also was left to the descretion of the attending surgeon. The 24 primary surgeries were performed by eight attending surgeons. Seventeen procedures were performed by three of the authors (MS, DE, and MV).
Twenty-four fractures in 24 patients met the inclusion criteria including nine fractures above TKAs (Fig 1), 10 fractures below hip arthroplasties, and five fractures with ipsilateral TKAs and hip arthroplasties (Fig 2). Of the 15 patients with hip arthroplas- ties, nine had hemiarthroplasties and six had THAs. Six of the nine hemiarthroplasties were done using cemented fixation, and four of the six THAs were done using cemented fixation. Thirteen TKAs were done using cemented fixation. The average age of the patients was 79.5 years (range, 64-93 years) at the time of injury (Table 1). The injury mechanism was a low-energy fall for all 24 patients, and all fractures were closed. All of the patients were women. One patient had a contralateral olecranon fracture, but all other patients sustained isolated injuries. Comorbidities that placed the patients at risk for periprosthetic fractures included rheumatoid arthritis (one patient), corticosteroid treatment for pulmonary disease (two patients), and a history of cerebrovascular accident leading to falls (one patient).
All radiographs were reviewed on computer workstations by one of the authors (RH) who was blinded to the results of the surgery and was not a member of the surgical team for any of the cases. The 15 fractures that occurred below hip prostheses were classified using the Vancouver classification.6 There were 12 Type C fractures (fracture well below the prosthesis), and three Type B1 fractures (fractures at the level of the implant, with a stable implant). Four of the 15 hip arthroplasties were revisions. The 14 fractures that involved knee prostheses were classified according to the system of Rorabeck and Taylor.45 All of the fractures were Type II displaced fractures with intact prostheses. None of the TKAs had revision stem extensions.
The electronic medical records were reviewed for clinical details at the time of injury. We recorded the patient's age at the time of injury, medical comorbidities, mechanism of injury, details of the prior arthroplasty, and risks for periprosthethetic fractures including steroid use, osteoporosis, and neurologic disorders. Data were recorded and analyzed in Excel spreadsheets (Microsoft Excel version 9.0.3, Microsoft Corporation, Bellevue, WA). The initial operative notes and records were reviewed. The attending surgeon's name, operative time, use of bone graft, use of cerclage wire, size of the implant, time between injury and surgery, and presence of any intraoperative complications were recorded. Discharge summaries, office notes, and all subsequent operative notes were reviewed.
All notes were checked carefully for mentions of any complications. We defined complications as any negative event associated with the fracture or device that required medical treatment. These included deep or superficial infections, nonunions, clinical malunions, hardware failure, vascular injuries, neurologic injuries, wound breakdown, or any events requiring a second surgery. We did not include medical complications such as pneumonia or urinary tract infections in the complication rate. All known postoperative deaths were recorded. Patients typically were followed up at 2 weeks, 6 weeks, 3 months, 6 months, and 1 year postoperatively. The followup schedule was at the discretion of the attending physician, but all patients were followed up for a minimum of 3 months, and then until fracture union.
The postoperative radiographs also were reviewed on computer workstations by one of the authors (RH) who was not involved in the surgery and was unaware of the clinical outcomes. The first postoperative radiographs were measured and compared with the latest followup radiographs. Radiographic malunion was defined as anteroposterior (AP) or mediolateral deviation greater than 5° from anatomic norms. Seven degrees valgus was considered the norm for AP alignment of the distal femur, and 0° was the norm for alignment of the distal femur in the lateral plane. Radiographic collapse was defined as greater than 5° change from the first postoperative radiograph when compared with the most recent radiograph. Radiographic union was defined as bridging cortex at two or more cortices. The presence of any hardware failure was recorded.
Patients were contacted postoperatively by telephone and completed a phone questionnaire once they had given permission. The questionnaire documented postoperative function including: return to work, return to baseline ambulatory status, need for pain medications, presence of any complications, ability to ambulate, and overall satisfaction with the surgical outcome. All phone interviews were done by research assistants.
The statistical analyses were descriptive in nature.
Of the 24 patients in the study group, four died during the followup period (6 days, 21 days, 5 days, 5 months, and 7 months, respectively), and one was lost to followup, leaving 19 patients with full followups. Nineteen of the 20 surviving patients followed up according to study protocol. One patient refused to attend followups, but reported she had no complication 2.5 years postoperatively. The average duration of followup for the 19 patients was 47.7 weeks (range, 17-101 weeks).
Eighteen of the 19 fractures healed without complications (Table 2). The one complication in the series occurred in a 93 year-old woman who was able to ambulate independently. She sustained a Vancouver Type C fracture below a cemented hip hemiarthroplasty. A five-hole LISS plate was used. The hardware lost fixation proximally and was revised 6 weeks after the original surgery. A longer 13-hole LISS plate was placed and the fracture healed uneventfully. There were no infections, symptomatic mal- unions, nonunions, or other known complications in this series of patients.
Freeze-dried allograft croutons were used in the treatment of one fracture, but all other fractures healed without the addition of bone grafts. Fixation was augmented with cerclage wires in six of the 15 fractures involving hip prostheses. The fixation overlapped the TKAs for all of the fractures above the TKAs and for 12 of the 15 fractures below hip arthroplasties. The Thirteen-hole LISS plates were used for nine fractures, nine-hole LISS plates were used for 12 fractures, and five-hole LISS plates were used for three fractures. The average delay from injury until surgery was 3 days (range, 0-15 days). The average operative time was 110.2 minutes (range, 61-178 minutes). A percutaneous or limited lateral approach was used for 18 of the fractures, and six had more extensive lateral approaches (Table 3).
The result of the patients' self reported functional outcome was good or excellent in 71% of the patients, and 70% reported no or minimal pain associated with the injury and subsequent treatment (Table 4). In contrast, at the time of the followup interview, 70% of the patients had an ambulatory status that was worse than before their injury (Table 4). Of the 20 surviving patients, 17 completed the phone survey. The average time of the survey was 55.1 weeks after the surgery. Sixteen of the patients were retired before their injury and one patient who worked part time returned to work after the surgery.
The LISS has theoretical advantages over other techniques for treatment of femur fractures associated with stable hip or knee prostheses. Locking plates are thought to have biomechanical advantages that are particularly important in osteoporotic bone.17,19,24,26,33,37,54 Locking plates also are thought to be intrinsically less damaging to the bone's blood supply when compared with traditional plate and screw constructs.1,4,5,13-15,17,18,24 Additionally, the potential for percutaneous insertion of the LISS is thought to help preserve blood supply.29-31,35,38,39,42,47,57,59 For these reasons, we theorized that the LISS may be particularly useful for patients with periprosthetic fractures who tend to be older, have osteoporotic bone, and are prone to falls.23 As other surgical techniques historically have been associated with high complication rates for these fractures, we have analyzed our own experience to determine if a locking plate such as the LISS is associated with a lower complication rate for these fractures.
The main limitation of the study is the small sample size with only 24 patients, and 19 surviving with adequate followups. However, our patient population was homogeneous as were the fracture mechanisms and types. A second limitation was that followup was only short-term, with a mean followup less than 1 year. As our main outcome metric was the occurrence of complications, this was less of a limitation because all of the fractures healed well before 1 year. With longer followup, we might see occult infections or other problems. A third limitation was that we did not collect ranges of motion in knees or validated functional outcome scores that would have provided additional information to strengthen our study. Finally, our study design has only historical data to serve as a control group. This limitation will be even more difficult to address in the future as none of the principle investigators is willing to randomize to other treatment options based on our initial positive experience with the LISS in this patient population.
The radiographic analyses in our study should be interpreted with caution. Our radiographic measurements may be unreliable, as the radiographs often are difficult to interpret because the prosthesis and the LISS plate obscure the overall alignment of the fracture. We also did not have full-length views of the extremities to more accurately evaluate alignment. In addition to this inherent difficulty in measuring alignment, it often is difficult to evaluate if malalignment is attributable to the fixation or if it was present with the initial arthroplasty before the injury. Additionally, we have no data regarding intraobserver or interobserver variation for our measures. Several patients had malalignments measured radiographically (Table 5), although no patients were judged to have clinically symptomatic malunions during followup.
Our complication rate of 5.2% using the LISS for peri- prosthetic femur fractures associated with stable hip and knee prostheses is encouraging when compared with rates of historical controls. There were no infections, and there was only one fixation failure. Bone graft was used only once, and no strut allografts were used. The average time for the procedure was less than 2 hours, even though eight of the 24 surgeries were performed by an attending who had never used a LISS for treatment of periprosthetic femur fractures.
The patient-determined functional results show that although there were few complications in our series, this injury is still debilitating at 1 year (Table 4). This is confirmed by the fact that 71% of the patients reported worse ambulatory status after the fractures.
The only complication in our series occurred when a five-hole LISS plate was used for treatment of a Vancouver Type C fracture below a cemented prostheses in a hip hemiarthroplasty. The patient was 93 years old and was a community ambulator. The hardware failed as the plate pulled out of the bone. The plate was revised to a longer LISS plate that overlapped the femoral stem, and the fracture then healed uneventfully. In hindsight, the lateral radio- graph showed that the original five-hole LISS was not well centered on the femur, giving the few screws proximal to the fracture little hold in the bone. This potential problem with use of the LISS was described by Kregor et al.28
The patient population in our study was typical of patients with periprosthetic fractures described in other studies. 3,10,11,23,40,46,51,52 All 24 patients in our series were women. The gender bias is greater than typically seen in other series of patients with periprosthetic fractures, but is similar to the 88% female gender observed in 141 patients with femur fractures after surgery for hip fractures,44 and 11 of 13 females (85%) in another series of patients with femur fractures occurring above knee prostheses.27 Four of our 24 patients died during the postoperative period (16.7%). This is similar to the 3-month, 20% mortality rate reported by McLauchlan et al.36 The mortality rate likely reflects the advanced age and comorbidities of this patient population.
Our complication rate compares with those reported for other treatment techniques for femur fractures below hip prostheses and for femur fractures above knee prostheses. Treatment options for femur fractures associated with stable hip prostheses have been cable plates, traditional plate and screw systems,20,25,34,49,56 or cortical allograft struts.7,8,21,34,49 Complication rates have ranged from 15- 57%.2,25,55 Nonunions, new fractures, fixation failures, varus collapse, implant loosening, and infections led to poor outcomes in greater than 50% in one series of 93 patients.2 These difficulties were not observed in our patients.
Open reduction and internal fixation using traditional plates and screws or special plates modified with cable systems for treatment of fractures occurring below hip prostheses has had mixed results. A larger series had a 33% combined complication rate of nonunions, new fractures, and fixation failure for plate fixation.2 An additional 20% of these patients had loosening of the arthroplasties or infections.2 This resulted in an overall poor outcome in 57% of the patients. Complications from cable plate systems are reported to be 25% (three of 12 fractures),58 and 57% (four of seven fractures).53 In another series, Noorda and Wuisman reported a 28% nonunion rate and recommended against using the Mennen Plate for periprosthetic femur fractures.41
There have been more favorable results reported with use of strut allografts to treat fractures associated with hip prostheses.21,22 One multicenter series, 40 patients were treated with strut allografts, although 21 of the fixations were augmented with plates. There was one infection, one nonunion, and four asymptomatic malunions, yielding a 15% complication rate.21,22
Our results for treatment of fractures occurring above knee prostheses with the LISS plate compares favorably with reported results, as there were no complications in this group of patients. Fractures occurring above knee prostheses historically have been treated with a myriad of devices including retrograde intramedullary nails, fixed angle devices such as a Dynamic Condylar Screw, blade plates, or buttress plates.9,10,46,52 Our results compare favorably with the 19% overall complication rate reported by Su et al, who summarized the literature on operative treatment.52 Nonunions, infections, malunions, and hardware failures are the most common complications.52 In a series similar to ours, Kregor et al27 used a LISS to treat 13 patients with femur fractures that occurred above knee prostheses. One of their patients had a nonunion and one had loosening of the prosthesis during the followup, for an overall complication rate of 15.4%.
Previously published series regarding use of the LISS for femur fractures consist of 236 fractures in a younger patient population with higher-energy injuries.28,48,50 The cumulative complication rate for these patients was 16% (range, 3-21.6%) with a 5.8% overall infection rate, although 26% of the fractures were open. These studies show the usefulness of the LISS for treating distal femur fractures caused by higher-energy trauma in younger patients, whereas our study and the study by Kregor et al27 provide data regarding its use in an older population typical of patients with periprosthetic femur fractures.
Our data show that one advantage of the LISS for treatment of this fracture is the relative ease with which it can be placed, even by surgeons who are first time users of the device. This was evident in our series, as eight of the 24 surgeries were performed by an attending who used the device for the first time for treatment of this fracture. The large number of surgeons may allow us to reflect what the performance of the device might be during the initial learning curve. Most of the surgeries were performed through a percutaneous approach, which has the potential advantage of causing less damage to the bone's blood supply. However, this potential advantage must be weighed against the surgeon's ability to achieve adequate alignment and fixation, and in our series the operating surgeon decided to use a more traditional full approach in 25% of the cases, without any evidence of compromised results.
Some authors have proposed that disadvantages of traditional plates for treating periprosthetic fractures include difficulty in obtaining proximal purchase, promotion of stem failure by violation of the cement mantle, or stress shielding.7,21,43 We have not experienced these difficulties using the LISS to date. Our patients had a low complication rate compared with rates for historical controls. The LISS may be an appropriate treatment alternative for femur fractures associated with stable hip or knee prostheses.
We thank Suzanne Morrison, MPH, for assistance with our database and study logistics, Don Bae, MD, for providing guidance in the initial stages of the project, and Jared Strote, MD, for time and editorial talent.
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