Abstract
Background:
Knee extensor strength deficits occur after ACL reconstruction (ACLR). Prior studies have reported that age affects quadriceps strength after ACLR, however strength deficits in relation to age have not been assessed among adolescents. Isokinetic dynamometric strength testing is a tool frequently used to assess strength post-operatively in order to identify these deficits.
Purposes:
1) To examine the effect of age on isokinetic extensor and flexor deficits among adolescents who were 5-10 months post-ACLR. We hypothesized that age would be inversely related to extensor strength deficit. 2) To determine if extensor or flexor strength deficits exist between adolescents post-ACLR with and without concomitant meniscus surgery. We hypothesized that those with concomitant meniscus surgery would demonstrate greater deficits in flexor and extensor strength.
Methods:
Study participants completed isokinetic testing within 5-10 months after primary quadriceps tendon ACLR, but before return to sport. The protocol consisted of assessing peak torque at 60, 180, and 300 degrees/s, through a limited range of knee extension and flexion. Our primary outcome variables were peak torque percent deficit of involved leg compared to uninvolved leg for flexion and extension. To address purpose 1, we constructed a series of multivariable regression models, where age was the independent variable, peak torque flexor/extensor deficits at each testing speed was the dependent variable, and sex and weight were covariates. To address purpose 2, we compared peak torque extensor and flexor deficits between those with and without concomitant meniscus surgery using independent samples t-tests.
Results:
A total of 44 completed the study protocol. There were no significant demographic differences between those with and without concomitant meniscus surgery (Table 1). The relationship between age at surgery and peak torque extensor deficits at 300d/s demonstrated a linear but non-significant association (Table 2; Figure 1). For every year increase in age, the expected deficit at 300d/s increased by approximately 3%. Patients who underwent isolated ACLR demonstrated significantly greater flexor deficits than those who underwent ACLR with concomitant meniscus surgery when tested at 180d/s and 300d/s (Table 3).
Conclusion:
Contrary to our first hypothesis, extensor deficits at 300d/s demonstrated an apparent association with older age. We observed a steady increase in strength deficit at 300d/s associated with increasing age. Contrary to our second hypothesis, no significant differences were found in extensor strength between those with and without meniscus surgery. Additionally, those with concomitant meniscus surgery demonstrated significantly less flexor deficit than those without meniscus surgery.
Demographics characteristics of patients who did and did not undergo concomitant meniscus surgery during ACL reconstruction. Data are presented as mean (sd) or n (%).
|
|
|
|
|
|---|---|---|---|
| Age (years) | 16.0 (1.4) | 15.7 (1.5) | 0.51 |
| Sex (female) | 15 (60%) | 14 (74%) | 0.52 |
| Sport type played during injury (contact/collision sport) |
22 (88%) | 15 (79%) | 0.44 |
| Height (cm) | 166.3 (9.5) | 164.6 (10.8) | 0.58 |
| Mass (kg) | 70.1 (19.4) | 60.2 (11.6) | 0.06 |
| Dominant leg (right) | 24 (96%) | 18 (95%) | 0.99 |
Regression models assessing the association between age at the time of surgery and peak flexor and extensor deficits at the three testing speeds, while adjusting for sex and weight.
| Testing Speed | β coefficient | Standard Error | 95 % confidence interval | P value |
|---|---|---|---|---|
| Extensor Deficits | ||||
| 60 degrees / s | 0.68 | 1.60 | -2.56, 3.92 | 0.67 |
| 180 degrees / s | 2.61 | 1.55 | -0.53, 5.74 | 0.10 |
| 300 degrees / s | 2.98 | 1.57 | -0.21, 6.16 | 0.06 |
| Flexor Deficits | ||||
| 60 degrees / s | 0.38 | 1.27 | -2.18, 2.93 | 0.77 |
| 180 degrees / s | -0.22 | 1.54 | -3.34, 2.91 | 0.89 |
| 300 degrees / s | -1.07 | 1.91 | -4.94, 2.80 | 0.58 |
Scatterplot describing the relationship between age at surgery and peak torque extensor deficits when tested at 300 degrees/s (r = 0.24).
Comparison of isokinetic outcomes between patients who underwent concomitant meniscus surgery during ACL reconstruction compared to those who underwent isolated ACL reconstruction. Data are presented as means (sd).
| Variable | ACL reconstruction + meniscus surgery |
Isolated ACL reconstruction |
P value |
|---|---|---|---|
| Extensor Deficits | |||
| 60 degrees / s | 28.2 (14.9) | 27.5 (11.8) | 0.87 |
| 180 degrees / s | 21.4 (14.2) | 22.8 (12.6) | 0.73 |
| 300 degrees / s | 17.8 (14.8) | 20.2 (13.0) | 0.58 |
| Flexor Deficits | |||
| 60 degrees / s | 6.9 (12.3) | 8.7 (9.2) | 0.59 |
| 180 degrees / s* | -3.7 (14.1) | 5.2 (9.9) | 0.02 |
| 300 degrees / s* | -6.4 (15.1) | 6.8 (17.5) | 0.01 |
*Patients who underwent isolated ACLR demonstrated significantly greater flexor deficits than those who underwent ACLR with concomitant meniscus surgery when tested at 180 degrees/s and 300 degrees/s.