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Current Data Regarding Subsequent ACL injury after ACL Reconstruction

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Factors Affecting Subsequent ACL Injury After ACL Reconstruction

Current Data Regarding Subsequent ACL injury after ACL Reconstruction

1 Introduction >
2 Introduction to ACL injury and Intercondylar Notch Width >
3 Intercondylar Notch Width and Ligament Size >
4 Intercondylar Notch Width and Height, Weight and Sex >
5 Current Data Regarding Subsequent ACL injury after ACL Reconstruction
6 Conclusions >
7 References >

When looking at subsequent ACL injuries after ACL reconstruction, it is important to consider not only ACL graft tears but also ACL tears to the opposite (normal) knee. I have heard many physicians boast an extremely low ACL graft rate by saying, "My ACL reconstruction was so strong that the patient tore the ACL in the other knee instead."

We have found that, when the ACL reconstructed leg is not rehabilitated to achieve strength and range of motion equal to the opposite normal knee, the risk of injury to the normal knee is increased. Therefore, it is important to consider injury to the normal knee after ACL reconstruction as part of the outcome from ACL surgery.

This current data analysis reflects the results of ipsilateral (using a patella tendon graft from the same knee as ACL injury) ACL reconstructions performed between 1992 and 2003. The mean intercondylar notch width by sex and notch width group is shown in Table 1. Women have statistically significant narrower notches than men.

Table 1 - Intercondylar Notch Width (Mean ± Standard Deviation (range))

Group Women Men
All patients 13.3 mm ± 1.4 mm (7-15) 15.2 mm ± 1.5 mm (8-24)
Small notch group ( < 15 mm) 13.1 mm ± 1.5 mm (7-15) 13.6 mm ± 1.4 mm (8-15)
Large notch group ( > 16 mm) 17.0 mm ± 1.0 mm (16-20) 17.9 mm ± 1.7 mm (16-24)

Table 2 shows the ACL graft tear rate and the rate of ACL injury to the normal contralateral (other side) knee based on intercondylar notch width and sex. These numbers reflect the results of ACL reconstruction between 1992 and 2003. The data show that ACL graft tear rates after ACL reconstruction are similar for men and women. The ACL graft is 10 mm wide and approximately 5 mm thick for all patients. The factors present in women that would make them have a higher incidence of ACL still would be present after ACL reconstruction. One would assume that the ACL graft tear rate would be higher for women than men, but these data do not confirm this theory.

Similar to our findings in 1998, men and women who have small intercondylar notches tend to have a subsequent injury to the contralateral normal knee. Patients who have a notch width of < 15 mm have a native ACL in the contralateral normal knee that is most likely smaller than the ACL graft (approximately 6 mm wide versus 10 mm wide for the ACL graft). Patients who have narrow intercondylar notch widths ( < 15 mm) had a 9.2% rate of injuring the contralateral (normal) ACL compared with a 2.5% ACL graft tear rate.

This phenomenon appears to be more prominent in women, but within the small and large notch groups, women still have a much smaller intercondylar notch than men. Overall, only 17% of the men had a notch that was less than 14 mm; whereas, 46% of women did. Conversely, only 6.7% of the women had a notch wider than 17mm, where as 48% of men had a notch wider than 17 mm. Women in the large notch group have a contralateral ACL tear rate of 8.8% versus an ACL graft tear rate of 1.5%. This is probably due to the fact that the ACL graft, which measures 10 mm wide is still much larger than the ligament in a knee with an intercondylar notch of 16 or 17 mm wide.

Men with narrow notches, like women with narrow notches, have a low incidence of ACL graft tears after ACL reconstruction and are more likely to tear the ACL in the normal contralateral knee that has the smaller ligament. Men in the large notch category have similar incident rates of tearing the ACL graft or the ACL in the normal contralateral knee. We suspect that this is because the ligament size is similar between knees, and once the patient returns to normal athletic activities, his knees are at equal risk for re-injury.

Table 2 - Incident rate of injury to either knee after ACL reconstruction based on notch width and sex

  Females
n (%)
Males
n (%)
Total injuries/patients
ACL-graft tears      
< 15 mm notch 3/194 (1.5) 7/210 (3.3) 10/404 (2.5)
> 16 mm notch 1/68 (1.5) 19/274 (6.9) 20/342 (5.8)
       
Opposite knee ACL tears      
< 15 mm notch 21/194 (10.8) 16/210 (7.6) 37/404 (9.2)
> 16 mm notch

6/68 (8.8)

16/274 (5.8)

22/342 (6.4)

       
Total injuries/patients 31/262 (11.9) 48/484 (9.9) 79/746 (10.6)

6 Conclusions >