Abstract
Introduction
Periprosthetic fractures around the knee (PPF) are a devastating complication of total knee arthroplasty (TKA). Anterior femoral notching during TKA is considered a risk factor for PPF. The aim of this paper is to determine if an anterior femoral notch after total knee arthroplasty may affect the fracture pattern when a PPF appears postoperatively.
Material and methods
50 patients diagnosed in our centre of a PPF from January 2010 to December 2013 were retrospectively enrolled. 100 patients who underwent a total knee arthroplasty without fracture were randomly obtained as a control group. Evidence of the notch was searched in both groups in postoperative X-rays. In the PPF group, distance from the shield of the femoral component to the most distal (d) and proximal (D) point of the fracture were measured.
Results
Two different groups were obtained: 1) d = 0 (33 out of 50 patients); the fracture is supposed to be related with the notch as it's a theoretically weaker area. 2) d > 0 (17 out of 50 patients); the fracture pattern has no relationship with the notch. Prevalence of patients suffering a fracture in the shield of the prosthesis (d = 0), was similar in both patients with notch (66,7%) and without it (68%).
Conclusions
In conclusion, fracture pattern is not related with the existence of a femoral notch in the clinical setting.
Keywords: Periprosthetic fractures, Knee, Fracture pattern, Femoral notch
1. Introduction
Periprosthetic fracture around the knee (PPF) is a rare complication after a primary total knee arthroplasty (0,3–2,5% depending on the series). They usually appear in females over 70 years related to falls from their own height.1, 2, 3, 4
Many risk factors have been historically associated with the production of a PPF.1, 2, 3, 4 Among them, notching of the anterior femoral cortex during surgery, is perhaps the most controversial to date.5, 6, 7, 8, 9
Biomechanical studies demonstrate that a femoral notch creates a weaker area in the distal part of the femur favoring the production of the fracture through the notch.5, 6, 7 However, there is no clinical evidence to date that support these theories.8,9
The objective of this study is to determine if the existence of a femoral notch is associated with the fracture pattern of PPF in the clinical setting.
2. Material and methods
A retrospective database was used to find patients diagnosed in our centre of a Periprosthetic Fracture (PPF) from 1 st of January 2010 to 31th of December 2013. The inclusion criteria for were: a) Total knee arthroplasty (TKA) performed for primary degenerative osteoarthritis, and b) to have proper x-ray records available of their follow-up. Exclusion criteria were: a) No records available or inadequate lateral x-ray records.
Among those patients who underwent a TKA and who did not sustain a PPF in their follow-up, a control group matched in aged and sex with the PPF group was also randomly selected.
Evidence of the anterior femoral notch and its depth was documented in both groups in the postoperative true lateral radiographs. If this was not a true lateral x-ray, those taken within the first year were used. The Tayside classification was used to identify the grade of femoral notching depending on its depth.9
In the PPF group, distance from the shield of the femoral component to the most distal (d) and proximal (D) point of the fracture (Fig. 1) were measured, as previously described by Hoffmann et al. in 2012.10 According to the measures taken in the fracture patterns of the PPF group (d and D), two different groups were obtained: 1) d = 0: the fracture is supposed to be related to the notch as it's a theoretically weaker area. 2) d > 0: the fracture pattern has no relationship with the notch. For all the previous measures a calibrated x-ray software was used (IMPAX Web1000 ver. 3.1, AGFA healthcare, Belgium).
Fig. 1.
An anteroposterior view of a periprosthetic fracture around the knee. (d) Shorter distance between the fracture line and the anterior shield of the prosthesis. (D) Longer distance between the fracture line and the anterior shield of the prosthesis. Both measurements were obtained on the AP X-ray view. The fracture pattern is considered to be related with the notch when d = 0.
Statistical analysis was performed using SPSS statistic package v15.0 (SPSS Institute Inc. Headquarters, Chicago, IL, USA). The significance level was considered p < 0.05. Kolmogorov-Smirnov Test was used to determine normal distribution of data in both groups. Student’s t-test and Wilcoxon’s signed rank test were used to determine if there was any difference between groups regarding sex and age. A Chi-square analysis was used to determine whether the existence of Notch was associated with the appearance of a PFK through the most distal point of the fracture (d).
3. Results
50 patients (48 women and 2 men) were finally enrolled in the periprosthetic fracture (PPF) group. Mean age was 78,02 years (range: 58–94). Mean follow-up time since the TKA was implanted to the date of fracture was 5,85 years (range: 0,3–13,6).
A total of 100 patients (92 women and 8 men) was randomly obtained as a control group between our Total knee arthroplasty (TKA) database of our centre. The mean age was 76,65 (range: 70–86) and the mean follow-up time was 7,5 years (range: 7–7,9).
The main variable analyzed was the existence of anterior femoral notch. The age in both groups (Control and PFK) followed a normal distribution according to Kolmogorov-Smirnov test. There were no differences regarding sex and age between both groups according to Student’s t-test and Wilcoxon’s signed rank.
Main results are shown in Table 1.
Table 1.
This table shows the number of patients in the Periprosthetic fracture group (PPF) with and without notch, related to the fracture pattern. It was assumed that a fracture pattern with d = 0 is related to notch, whereas if d > 0 it is not. The prevalence of PPF that begins in d = 0 is similar in patients with and without notch.
| PPF group | Fracture in d > 0 | Fracture in d = 0 | |
|---|---|---|---|
| Notch | 3 (6%) | 1 (33,3%) | 2 (66,7%) |
| No notch. | 47 (94%) | 16 (32%) | 31 (68%) |
| Total | 50 | 17 | 33 |
Evidence of the notch was found in 3 patients in the PPF group (6%) while in the control group notch was found in 11 patients (11%). All notches in our study are grade I–II from Tayside classification. According to the measures taken in the fracture patterns of the PPF group (d and D) patients were divided into groups: 1) d = 0 (33 out of 50 patients) and 2) d > 0 (17 out of 50 patients).
4. Discussion
When reviewing literature regarding periprosthetic fractures around the knee (PPF), major risk factors for the production of a PPF are osteoporosis and anterior femoral notching.1, 2, 3, 4The femoral notch has been defined as the violation of the anterior cortical of the femur with the saw, just proximal to the shield of the prosthesis, producing a defect of variable depth.8 Many other risk factors, that do not usually appear in a primary arthroplasty have been described in literature such as chronic intake of corticosteroids, rheumatoid arthritis, neurological disorders, and so on.1, 2, 3, 4,11 It is beyond the scope of this paper to discuss them all, so we will focus on the femoral notch.
The incidence of intraoperatory notching during Total Knee Arthroplasty (TKA) has been described between 3,5–26,9% depending on the series.12, 13, 14 A prevalence of notching between this range (11%) was found in the control group of our study (11 notches out of 100 patients). Moreover, the incidence of notch among patients who sustained a PPF has been reported between 7 and 50%.12, 13, 14, 15, 16, 17 A similar prevalence of notching (6%) was found in the PPF group in our study was (3 notches out of 50 patients).
Notching has always been considered as a risk factor for PPF.12,15, 16, 17 However, to date, no study has been able to clinically demonstrate that the notch is a true risk factor.1,8,9
Lesh et al. 5 and Shawen et al. 6 stated that the PPF is inevitably produced in the notch area (d = 0) because of its greater weakness.5,6,15, 16, 17 However, our data show different conclusions. Inside the PPF group a 66% (33 patients) had a fracture pattern that begins in the shield of the prosthesis (d = 0).
If we only take into account the existence of the notch, the prevalence of patients with notch which fracture begins in d = 0 is 66,7% (2 out of 3), similar to the prevalence of patients without notch which fracture begins in d = 0, 68% (31 out of 47). Furthermore, the same fact can be found when we search in the group which fracture pattern begins in d > 0. A 33,3% of patients with notch and a 32% of patients without notch breaks over the shield of the prosthesis (Table 1).
In our study, the prevalence of patients who suffered a fracture through d = 0 was similar in patients with notch (66,7%) than in patients without notch (68%). There is no difference between both percentages, so another risk factor such as osteoporosis or stress shielding may be the cause of the common weakness in d = 0 area.2,7 The main data obtained from our study indicate that there is no relationship between an anterior femoral notch and the place for production of a PPF (p < 0,05).
The limitations of this study are that the number of patients with both PPF associated and notch is small and a larger sample size would have been better for more powerful statistically significant results. The strength of our study is that it represents the only clinical study, to date, that dispels the theory by which the notch is the origin of a weaker area in the bone where PPF might take place.
5. Conclusions
A notch during total knee arthroplasty is not related to a clinically weaker area in the anterior femoral cortex, and thus, is not related to a high prevalence of PPF in the clinical setting. More studies are needed to know the effect of the notch and bone strength in this area.
Conflicts of interest
The authors declare that they have no conflict of interest.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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