- Email: [email protected]
Anterior femoral notching and ipsilateral supracondylar femur fracture in total knee arthroplasty
Anterior Femoral Notching and Ipsilateral Supracondylar Femur Fracture in Total ICanee Arthroplasty
M e r r i l l A.
Ritter, MD,
P h i l i p M . Faris, M D , a n d E. M i c h a e l K e a t i n g , M D
Abstract: The authors reviewed 670 total knee arthroplasties with a 2-10-year
follow-up period. Of these, 180 knees had anterior femoral notching, which was deeper than 3 mm in 138. Two of the 670 knees suffered ipsilateral supracondylar fractures; one of these had a notched femur and one did not. Both fractures occurred at the anterior patellar flange-bon e junction. No correlation was found between anterior femoral notching and ipsilateral supracondylar femur fracture. Key words: total knee anhroplasty, supracondylar femur fracture, anterior femoral notching, fracture, posterior cruciate condylar total knee arthroplasty.
Notching of the anterior femoral cortex during total knee arthroplasty has been implicated as a major factor leading to supracondylar femur fracture after total knee arthroplasty (3, 7). To date, all reports dealing with supracondylar fractures either have been anecdotal ( 4 - 6 ) or have dealt retrospectively with ipsilateral supracondylar fractures after total knee arthroplasty (1, 2). Notching has been variously reported in up to 50% of fractured femurs (3), and as m a n y as 1% of knee arthroplasty patients have suffered an ipsilateral supracondylar fracture (8). To date, however, there are no reports on the incidence of notching in a large series of total knee arthroplasty patients studied to determine whether there is a statistical correlation between anterior femoral notching and ipsilateral supracondylar femoral fractures. Culp et al., in a large series of patients, found an a v e r a g e time from arthroplasty to fracture of 2.9 years (range, 0 - 1 0 years) (3). They determined in a
From the Center for Hip and Knee Surgery, Mooresville, Indiana.
Reprint requests: PhilipM. Faris, MD, 1199 North HadleyRoad, Mooresville, IN 46158.
theoretic study that 3 m m of notching led to a 29.2% reduction in torsional strength. The degree of strength reconstitution with remodeling was not addressed, but it m a y be a significant factor w h e n the length of time from follow-up evaluation to fracture is considered. We undertook this study to evaluate the incidence and extent of anterior femoral notching in a large series of patients and to relate these findings to the incidence of supracondylar fracture.
Materials and Methods We evaluated 670 posterior cruciate condylar total knee arthroplasties performed between 1975 and 1983. The m e a n patient age was 69.7 years (range, 2 2 - 9 1 years). There were 434 w o m e n and 236 men. Postoperative lateral radiographs were evaluated at 2, 6, and 12 months. Depth of notching was measured from the anterior femoral cortex to the base of the notch. The radiograph demonstrating the deepest measured notch was used for this study. All mea-
186
The Journal of Arthroplasty Vol. 3 No. 2 June 1988
surements were made with the use of a standard ruler. Magnification factors were not considered.
Results Some degree of notching occurred in 180 knees (27%). One h u n d r e d thirty-eight knees (20.5%) had notching of 3 m m or more, and 38 knees (6%) had notching greater than 6 ram. Of these 670 knees, only 2 had supracondylar fractures. One of these occurred 22 months after operation through a 5-mm anterior femoral notch; this was in a 50-year-old rheumatoid arthritis patient on chronic steroid therapy (Figs. 1, 2). The other occurred 12 months after operation in an 81-year-old osteoarthritis patient with no notching. This patient fell d o w n three steps and suffered a fracture at the level of the anterior patellar f l a n g e - b o n e junction (Figs. 3, 4). Both fractures were internally fixed with condylar-type Rush ]~ins.
Fig. 2. Fracture after intemal fixation. The fracture line extends to the flange-bone ]unction (arrow).
Fig. 1. Prefracture radiograph, showing 5 mm of anterior femoral notching (arrow).
Fig. 3. Prefracture radiograph, showing no femoral notching.
Notching of the Anterior Femur
* Ritter et al.
187
29% (3). These statistics do not, however, consider the remodeling capability of bone. In dogs, bone remodeling around screw holes returns the torsional strength of the bone to normal in 8 weeks after screw removal (7). This figure is probably too conservative for h u m a n application, but it is clear that bone remodeling and stress redistribution occur. In view of the extremely low incidence of supracondylar fracture despite a very high incidence of significant anterior femoral notching, we believe that this femoral defect is of minimal concern beyond the early postoperative period ( 0 - 6 months). Both of the fractures in this study occurred at the junction of the anterior patellar flange and the anterior femoral cortex and may be related to stress shielding of bone by the patellar flange, inadequate bone remodeling due to postoperative hypovascularity, or a relative difference in elastic modulus between the implant-covered distal femur and the femoral cortex. Ipsilateral s u p r a c o n d y l a r femur fracture after total knee arthroplasty is multifactorial i n origin and may be attributed to osteopenia, inadequate bony remodeling, stress shielding, or increased use of the extremity after the operation. We conclude that femoral notching has been a c o m m o n technical error during total knee arthroplasty and that femoral notching alone does not appear to be an inciting factor in ipsilateral supracondylar femur fracture beyond thdearly postoperative period.
Fig. 4. The fracture, extending from the flange-bone intersection, has healed.
Discussion In this study, notching of the anterior femoral cortex during total knee arthroplasty occurred more frequently than anticipated (27%). Significant notching occurred in 20.8% of total knee arthroplasties performed in our institution. Notching of the femur with this prosthesis was a technical problem related to a less sophisticated instrumentation system and to the limited n u m b e r of different anterior-posterior sized femoral components. Despite this high incidence of cortical notching, only two ipsilateral supracondylar fractures developed, with a follow-up period ranging from 2 to 12 years. Bone defects of less than 30% of the conical bone diameter create stress concentrations 1.6 times greater than those incurred by the remainder of the b o n e ( 1, 2). An anterior notch of 3 m m theoretically creates a decrease in torsional stress to fracture of
References 1. Bechtol CO: Engineering Principles Applied to Orthopedic Surgery. American Academy of Orthopaedic Surgery, 1952 2. Burstein AH, Currey J, Frankel VH et al: Bone strength: the effect of screw holes. J Bone Joint Surg 54A:1143, 1972 3. Culp RN, Schmidt RG, Hanks G e t al: Supracondylar fracture of the femur following prosthetic knee arthroplasty. Clin Orthop 222:212, 1987 4. Hirsh DW, Bhalla S, Roffman M: Supracondylar fracture of the femur following total knee replacement. J Bone Joint Surg 63A:162, 1981 5. Ritter MA, Stiver P: Supracondylar fracture in a patient with total knee arthroplasty. Clin Orthop 193:168, 1985 6. Short WH, Hootrick DR, Murray DG: Ipsilateral supracondylar fractures following knee arthroplasty. Clin Orthop 158:111, 1987 7. Sisto DJ, Lachiewiez PF. Insall JN: Treatment of supracondylar fractures following prosthetic arthroplasty of the knee. Clin Orihop 196:265, 1985 8. Webster DA, Murray DG: Complications of variable axis total knee arthroplasty. Clin Orthop 193:160, 1985
M e r r i l l A.
Ritter, MD,
P h i l i p M . Faris, M D , a n d E. M i c h a e l K e a t i n g , M D
Abstract: The authors reviewed 670 total knee arthroplasties with a 2-10-year
follow-up period. Of these, 180 knees had anterior femoral notching, which was deeper than 3 mm in 138. Two of the 670 knees suffered ipsilateral supracondylar fractures; one of these had a notched femur and one did not. Both fractures occurred at the anterior patellar flange-bon e junction. No correlation was found between anterior femoral notching and ipsilateral supracondylar femur fracture. Key words: total knee anhroplasty, supracondylar femur fracture, anterior femoral notching, fracture, posterior cruciate condylar total knee arthroplasty.
Notching of the anterior femoral cortex during total knee arthroplasty has been implicated as a major factor leading to supracondylar femur fracture after total knee arthroplasty (3, 7). To date, all reports dealing with supracondylar fractures either have been anecdotal ( 4 - 6 ) or have dealt retrospectively with ipsilateral supracondylar fractures after total knee arthroplasty (1, 2). Notching has been variously reported in up to 50% of fractured femurs (3), and as m a n y as 1% of knee arthroplasty patients have suffered an ipsilateral supracondylar fracture (8). To date, however, there are no reports on the incidence of notching in a large series of total knee arthroplasty patients studied to determine whether there is a statistical correlation between anterior femoral notching and ipsilateral supracondylar femoral fractures. Culp et al., in a large series of patients, found an a v e r a g e time from arthroplasty to fracture of 2.9 years (range, 0 - 1 0 years) (3). They determined in a
From the Center for Hip and Knee Surgery, Mooresville, Indiana.
Reprint requests: PhilipM. Faris, MD, 1199 North HadleyRoad, Mooresville, IN 46158.
theoretic study that 3 m m of notching led to a 29.2% reduction in torsional strength. The degree of strength reconstitution with remodeling was not addressed, but it m a y be a significant factor w h e n the length of time from follow-up evaluation to fracture is considered. We undertook this study to evaluate the incidence and extent of anterior femoral notching in a large series of patients and to relate these findings to the incidence of supracondylar fracture.
Materials and Methods We evaluated 670 posterior cruciate condylar total knee arthroplasties performed between 1975 and 1983. The m e a n patient age was 69.7 years (range, 2 2 - 9 1 years). There were 434 w o m e n and 236 men. Postoperative lateral radiographs were evaluated at 2, 6, and 12 months. Depth of notching was measured from the anterior femoral cortex to the base of the notch. The radiograph demonstrating the deepest measured notch was used for this study. All mea-
186
The Journal of Arthroplasty Vol. 3 No. 2 June 1988
surements were made with the use of a standard ruler. Magnification factors were not considered.
Results Some degree of notching occurred in 180 knees (27%). One h u n d r e d thirty-eight knees (20.5%) had notching of 3 m m or more, and 38 knees (6%) had notching greater than 6 ram. Of these 670 knees, only 2 had supracondylar fractures. One of these occurred 22 months after operation through a 5-mm anterior femoral notch; this was in a 50-year-old rheumatoid arthritis patient on chronic steroid therapy (Figs. 1, 2). The other occurred 12 months after operation in an 81-year-old osteoarthritis patient with no notching. This patient fell d o w n three steps and suffered a fracture at the level of the anterior patellar f l a n g e - b o n e junction (Figs. 3, 4). Both fractures were internally fixed with condylar-type Rush ]~ins.
Fig. 2. Fracture after intemal fixation. The fracture line extends to the flange-bone ]unction (arrow).
Fig. 1. Prefracture radiograph, showing 5 mm of anterior femoral notching (arrow).
Fig. 3. Prefracture radiograph, showing no femoral notching.
Notching of the Anterior Femur
* Ritter et al.
187
29% (3). These statistics do not, however, consider the remodeling capability of bone. In dogs, bone remodeling around screw holes returns the torsional strength of the bone to normal in 8 weeks after screw removal (7). This figure is probably too conservative for h u m a n application, but it is clear that bone remodeling and stress redistribution occur. In view of the extremely low incidence of supracondylar fracture despite a very high incidence of significant anterior femoral notching, we believe that this femoral defect is of minimal concern beyond the early postoperative period ( 0 - 6 months). Both of the fractures in this study occurred at the junction of the anterior patellar flange and the anterior femoral cortex and may be related to stress shielding of bone by the patellar flange, inadequate bone remodeling due to postoperative hypovascularity, or a relative difference in elastic modulus between the implant-covered distal femur and the femoral cortex. Ipsilateral s u p r a c o n d y l a r femur fracture after total knee arthroplasty is multifactorial i n origin and may be attributed to osteopenia, inadequate bony remodeling, stress shielding, or increased use of the extremity after the operation. We conclude that femoral notching has been a c o m m o n technical error during total knee arthroplasty and that femoral notching alone does not appear to be an inciting factor in ipsilateral supracondylar femur fracture beyond thdearly postoperative period.
Fig. 4. The fracture, extending from the flange-bone intersection, has healed.
Discussion In this study, notching of the anterior femoral cortex during total knee arthroplasty occurred more frequently than anticipated (27%). Significant notching occurred in 20.8% of total knee arthroplasties performed in our institution. Notching of the femur with this prosthesis was a technical problem related to a less sophisticated instrumentation system and to the limited n u m b e r of different anterior-posterior sized femoral components. Despite this high incidence of cortical notching, only two ipsilateral supracondylar fractures developed, with a follow-up period ranging from 2 to 12 years. Bone defects of less than 30% of the conical bone diameter create stress concentrations 1.6 times greater than those incurred by the remainder of the b o n e ( 1, 2). An anterior notch of 3 m m theoretically creates a decrease in torsional stress to fracture of
References 1. Bechtol CO: Engineering Principles Applied to Orthopedic Surgery. American Academy of Orthopaedic Surgery, 1952 2. Burstein AH, Currey J, Frankel VH et al: Bone strength: the effect of screw holes. J Bone Joint Surg 54A:1143, 1972 3. Culp RN, Schmidt RG, Hanks G e t al: Supracondylar fracture of the femur following prosthetic knee arthroplasty. Clin Orthop 222:212, 1987 4. Hirsh DW, Bhalla S, Roffman M: Supracondylar fracture of the femur following total knee replacement. J Bone Joint Surg 63A:162, 1981 5. Ritter MA, Stiver P: Supracondylar fracture in a patient with total knee arthroplasty. Clin Orthop 193:168, 1985 6. Short WH, Hootrick DR, Murray DG: Ipsilateral supracondylar fractures following knee arthroplasty. Clin Orthop 158:111, 1987 7. Sisto DJ, Lachiewiez PF. Insall JN: Treatment of supracondylar fractures following prosthetic arthroplasty of the knee. Clin Orihop 196:265, 1985 8. Webster DA, Murray DG: Complications of variable axis total knee arthroplasty. Clin Orthop 193:160, 1985