Incidence of distal femoral periprosthetic fractures after total knee arthroplasty.
One advance in TKA implants includes the addition of femoral lugs, which are designed to increase femoral fixation, especially if zone four bone loss compromises femoral fixation. The femoral lug would resist flexion-extension, toggling, or micro-motion, which could lead to loosening. Lugged femoral implants were introduced at our institution in 2000. The impact of lugged femoral implants on the incidence of distal femoral periprosthetic fractures has not been reported.
In 2002, intramedullary bone grafting was introduced at our institution to fill the distal femoral intramedullary canal following use of an intramedullary alignment guide. Theoretically, this intramedullary bone graft may improve the quantity and quality of distal femoral bone and possibly enhance femoral fixation. Periprosthetic bone loss is a risk factor for distal femoral periprosthetic fractures. The impact of a distal femoral intramedullary bone graft on the incidence of distal femoral periprosthetic fractures has not been reported.
The purpose of this study was to identify the incidence of distal femoral periprosthetic fractures following TKA at one institution using one knee implant over a 16-year interval. We hypothesized that the incidence of these fractures may be lowered after the introduction of lugged femoral implants and insertion of a distal femoral intramedullary bone graft.
Materials and Methods
We retrospectively reviewed 4,943 primary TKAs at our institution between 1994 and 2010. Distal femoral periprosthetic fractures were identified by ICD-9 code in the medical record, Total Joint Arthroplasty Data Base review, and Morbidity and Mortality log review. Fractures were characterized using the Lewis and Rorabeck classification system (Fig. 1). We favor the Lewis and Rorabeck classification system because it includes prosthesis stability and emphasizes the need for revision arthroplasty if the implant is loose. (10) Exclusion criteria included revision TKA and previous periprosthetic fracture in the ipsilateral knee.
The DePuy Synthes PFC[R] knee system (Johnson & Johnson) was used for all patients. The original PFC[R] system was used from 1994 to 1998. The PFC[R] Sigma[R] system was used from 1998 to 2010. The femoral implants were changed in 2000 when distal femoral lugs were added to the femoral implants. In this series, 1,236 TKA operations were performed with femoral implants without lugs, and 3,707 TKA operations were performed with femoral implants with lugs.
The surgical technique for the TKA operation was changed in 2002 when a distal femoral bone graft was implemented. Cancellous autograft, composed of the distal femoral anterior chamfer bone fragment, was packed tightly into the distal femoral intramedullary canal. The anterior chamfer bone fragment was folded over itself in the middle to create a four-sided bone peg. A rongeur was used to nibble the corners and create a rounded bone peg that was tapped into the distal intramedullary bone (Fig. 2). Among the 4,943 TKA operations, 1,653 knees did not have a distal femoral bone graft, and 3,290 knees did have a distal femoral bone graft.
Four groups were evaluated and compared: all 4,943 knees; 1,236 knees without femoral lugs and no femoral bone graft; 417 knees with femoral lugs and no femoral bone graft; and 3,290 knees with femoral lugs and with femoral bone graft (Table 1).
The four groups were comparable. There was no significant difference among the groups in age, weight, gender, or primary knee diagnosis. There was no difference among the groups in the incidence of osteopenia, inflammatory diseases, and corticosteroid use.
All patients were followed by the operating surgeon, and patient data was recorded in the Hospital Joint Replacement Database. Patients were evaluated at 14 days, 6 weeks, 1 year, and biannually. To the best of our knowledge, no distal femoral periprosthetic fracture was missed. In this series, chi-squared statistical tests were performed to identify if there was a significant difference in fracture rate between knees without lugged femoral implants and bone graft compared to knees with lugged femoral implants and bone graft.
Distal femoral periprosthetic fractures occurred in 21 knees following 4,943 primary TKA operations for an incidence of 0.42%. The majority of patients who sustained a periprosthetic fracture were women over the age of 65 (Table 1).
There was no significant difference in the incidence of distal femoral periprosthetic fracture between knees treated with femoral implants without lugs and knees treated with femoral implants with lugs (p = 0.705). Six fractures occurred in 1,236 knees with femoral implants without femoral fixation lugs (0.49%). Fifteen fractures occurred in 3,707 knees with femoral implants with femoral lugs (0.40%).
There was no significant difference in the incidence of distal femoral periprosthetic fracture between knees treated without distal femoral bone graft and knees treated with distal femoral bone graft (p = 0.65). Eight fractures occurred in 1,653 knees that did not have intramedullary bone graft (0.48%). Thirteen fractures occurred in 3,290 knees that had intramedullary bone graft (0.40%).
The impact of femoral lugs and distal femoral bone graft on distal femoral periprosthetic fracture was evaluated by analyzing four treatment groups (Table 1). There was no significant difference among the following: all knees, knees with no femoral lugs and no bone graft, knees with femoral lugs and no bone graft, and knees with femoral lugs and bone graft (p = 0.90).
The 21 fractures were evaluated and compared (Table 2). There was no significant difference in age, sex, weight, or primary diagnosis between the four groups. The majority of patients in each group, 4/6 (67%) in Group B, 2/2 (100%) in Group C, and 11/13 (85%) in Group D, sustained Type II fractures as classified by Lewis and Rorabeck. [down arrow]
In this series of 4,943 TKA operations, the incidence of distal femoral periprosthetic fractures was 0.42%, which is within the range of the previously reported incidence of this type of fracture. In fact, it is on the low side of previous reports.
Two changes were implemented to the TKA operation during the study interval. There was no significant change in the incidence of distal femoral periprosthetic fracture associated with adding fixation lugs to the femoral implant or inserting a bone graft into the distal femoral intramedullary alignment hole.
The pathogenesis of distal femoral periprosthetic fractures is multifactorial. These fractures have been associated with a difference in the elastic modulus between the implant and the distal femoral cortex, (13) femoral notching, (14) generalized osteoporosis in elderly patients, and osteolysis due to polyethylene wear. (15) Other risk factors for distal femoral periprosthetic fracture following TKA include osteoporosis, rheumatoid arthritis, chronic steroid use, and revision total knee arthroplasty. (8,11,15)
Distal femoral lugs increase femoral implant fixation and theoretically reduce motion at the distal femoral bone-implant interface. Although improved femoral component fixation may lead to better clinical outcomes and longer prosthesis survivorship, our data suggests that femoral lugs do not decrease the incidence of distal femoral periprosthetic fracture.
Insertion of a bone graft into the distal femoral intramedullary hole may increase bone density around the femoral implant, but our results do not support the conclusion that improved distal femoral cancellous bone quality decreases distal femoral periprosthetic fracture risk. A biomechanical study evaluating the effect of femoral notching demonstrated that intact cortical bone helps protect the distal femur from fracture. (14) However, distal femoral cancellous bone loss equal to the diameter of our intramedullary drill (8 mm) does not appear to compromise the integrity of bone sufficiently to increase the incidence of periprosthetic fracture. A biomechanical study might help elucidate how much intramedullary bone loss is needed to decrease the strength of the distal femur enough for a fracture to occur under physiologic stress.
There were several limitations to this study. First, it was a retrospective review. We may not have accounted for all periprosthetic fractures as some patients may have sought care at an outside hospital in the setting of a periprosthetic fracture. However, our database and record keeping is excellent; we looked for patients with fractures at several sites, and it is unlikely that we missed any of these fractures among our TKA patients. Second, the number of periprosthetic fractures in each cohort was low, which increases the chance that we mistakenly confirmed the null hypothesis (beta error). Third, there was shorter follow-up for Group D knees that had both lugged femoral implants and intramedullary bone graft compared to Group B. Given that the fracture incidence was similar in the shorter follow-up period for the patients with intramedullary bone graft and lugged femoral components compared to the group who had surgery without either modification, it is possible that the fracture rate may actually be higher for the cohort who had surgery after modifications were implemented. Fourth, we do not have a valid evaluation of the number of osteopenic patients in the four groups. A disproportionate number of osteopenic patients in a group, high or low, could affect the comparative results.
In conclusion, our incidence of distal femoral periprosthetic fracture of 0.42% was consistent with prior reports, and a change in the femoral implant design and a change in TKA surgical technique did not reduce the incidence of these fractures. Further study to elucidate how improvements in implant design or distal femoral bone quality may help decrease the incidence of distal femoral periprosthetic fractures would be helpful.
None of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.
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Tyler Welch, M.D., Department of Orthopaedic Surgery, Boston University Medical Center, Boston; and Department of Orthopaedic Surgery, Lahey Clinic Medical Center, Burlington, Massachusetts. Richard Iorio, M.D., Department of Orthopaedic Surgery, New York University Langone Medical Center, Hospital for Joint Diseases, New York, New York. Andrew J. Marcantonio, M.D., Michael S. H. Kain, M.D., John F. Tilzey, M.D., Lawrence M. Specht, M.D., and William L. Healy, M.D., Department of Orthopaedic Surgery, Lahey Clinic Medical Center, Burlington, Massachusetts.
Correspondence: Tyler Welch, M.D., Atlantic Orthopaedics & Sports Medicine, 150 US-1 BYP, Portsmouth, New Hampshire 03801; firstname.lastname@example.org.
Caption: Figure 1 Lewis and Rorabeck classification of supracondylar periprosthetic fractures proximal to total knee arthroplasty. A, Type I: nondisplaced fracture-prosthesis intact. B, Type II: displaced fracture-prosthesis intact. C, Type III: displaced or nondisplaced fracture-prosthesis loose or failing (i.e., significant instability or polyethylene wear).
Caption: Figure 2 Intramedullary bone graft utilizing anterior chamfer bone cut. To view this figure in color, see www.hjdbulletin.org.
Table 1 Incidence of Distal Femoral Periprosthetic Fracture No Femoral Femoral Lugs/No All Knees Lugs/No Bone Grafts (Group A) Bone Graft (Group C) (Group B) N (knees) 4,943 1,236 417 Age (years) 68.6 68.5 69.3 (29 to 95) (31 to 94) (38 to 93) Height (inches) 65.7 65.8 66.1 (50 to 80) (50 to 80) (50 to 76) Weight (pounds) 191.2 187.3 190.0 (80 to 370) (93 to 342) (102 to 300) BMI 31.2 30.5 30.5 (14 to 75) (14 to 58) (17 to 51) Gender Male 2,076 568 179 Female 2,867 668 238 Knee Diagnosis (%) Osteoarthritis 95.3 94.0 96.6 Rheumatoid Arthritis 2.2 3.3 2.0 Traumatic Arthritis 1.1 1.1 1.1 Osteonecrosis 1.4 1.6 0.3 Periprosthetic 21 6 2 Fracture (total number) Periprosthetic 0.43 0.49 0.48 Fracture Incidence (%) Femoral Lugs/Bone Graft (Group D) N (knees) 3,290 Age (years) 68.6 (29 to 95) Height (inches) 65.7 (50 to 78) Weight (pounds) 192.6 (80 to 370) BMI 31.5 (15 to 75) Gender Male 1,316 Female 1,974 Knee Diagnosis (%) Osteoarthritis 95.8 Rheumatoid Arthritis 1.8 Traumatic Arthritis 0.9 Osteonecrosis 1.5 Periprosthetic 13 Fracture (total number) Periprosthetic 0.40 Fracture Incidence (%) Table 2 Distal Femoral Periprosthetic Fractures Age at Fracture Height Weight (years) (inches) (pounds) Group * Gender (56.4 to 90.2) (59 to 66) (114 to 278) B Female 79.9 60 164 B Female 67.9 60 270 B Female 73.6 62 157 B Female 90.2 59 142 B Male 82.5 69 251 B Female 85.0 64 186 C Female 78.7 61 150 C Female 56.4 65 245 D Female 82.1 62 123 D Female 77.2 62 160 D Female 58.0 60 154 D Female 62.2 61 190 D Female 81.3 60 135 D Female 62.7 65 278 D Female 72.6 65 227 D Male 81.3 65 168 D Male 87.2 59 134 D Female 75.1 64 183 D Male 56.6 66 161 D Female 80.2 64 114 D Female 62.6 63 250 BMI Group * (20 to 46) Corticosteroid Diagnosis Use B 32 No Osteoarthritis B 53 No Osteoarthritis B 29 No Osteoarthritis B 29 No Osteoarthritis B 32 No Osteoarthritis B 32 No Osteoarthritis C 28 No Osteoarthritis C 41 No Osteoarthritis D 23 Yes Osteoarthritis D 29 No Osteoarthritis D 30 No Osteoarthritis D 36 No Rheumatoid Arthritis D 26 No Osteoarthritis D 46 No Osteoarthritis D 38 No Osteoarthritis D 28 No Osteoarthritis D 27 No Osteoarthritis D 31 No Osteoarthritis D 26 No Osteoarthritis D 20 No Osteoarthritis D 44 No Osteoarthritis * B = No graft, no lugs, C = Lugs, no graft, D = Lugs and graft. Table 3 Classification and Treatment of Distal Femoral Periprosthetic Fractures Fracture Group * Type Treatment Additional Surgical ([dagger]) Treatment B II ORIF dynamic condylar screw B II ORIF locking plate Ultimately underwent ROH and revision TKA with distal femoral replacement B II ORIF locking plate B III Revision TKA B II ORIF locking plate Incision and drainage, B I Nonoperative (cast) two times for wound C II ORIF locking plate dehiscence C II IM Nail fixation D II ORIF locking plate D II ORIF condylar blade plate D II Closed reduction in OR D II Percutaneous screw ORIF locking plate after fixation fixation failed D II ORIF locking plate D II ORIF locking plate D II ORIF locking plate D I Percutaneous screw fixation D II ORIF locking plate D II ORIF locking plate D I Nonoperative (brace) D II ORIF locking plate D II ORIF locking plate * B = No graft, no lugs, C = Lugs, no graft, D = Lugs and graft. ([dagger]) Type I: nondisplaced, well-fixed prosthesis, Type II: displaced, well-fixed prosthesis, Type III: loose prosthesis. (15)
Please note: Illustration(s) are not available due to copyright restrictions.
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|Author:||Welch, Tyler; Iorio, Richard; Marcantonio, Andrew J.; Kain, Michael S.H.; Tilzey, John F.; Specht, L|
|Publication:||Bulletin of the NYU Hospital for Joint Diseases|
|Date:||Oct 1, 2016|
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