Leaf spring exercise: A safe quadriceps strengthening exercise after anterior cruciate ligament reconstruction.

BACKGROUND: Leg extensions should be avoided in the early stages after anterior cruciate ligament reconstruction because the force exerted by the quadriceps muscle leads to anterior tibial displacement. To allow for safe quadriceps training in the knee extension range during this period, we devised the leaf spring exercise, which involves placing subjects in the prone position with their knee slightly flexed and instructing them to perform maximum isometric quadriceps contractions while supporting the proximal region of the lower leg's anterior surface and immobilizing the femur's posterior surface to prevent lifting. The current study aimed to examine the safety of Leaf spring exercise by determining the femur-tibia relationship using ultrasound imaging. METHODS: This controlled laboratory study included patients with unilateral anterior cruciate ligament-deficient knees (8 men and 8 women; age, 24.2 ± 8.3 years) who were instructed to perform Leaf spring exercise of both lower limbs. We measured the femur-tibia-step-off, which indicates the distance between the last point of the medial and lateral condyles of the femur and posterior margin of the tibial plateau, as a parameter to evaluate anterior tibial displacement via ultrasound diagnostic device. Further, peak torque of the quadriceps muscle was calculated using force measurement device. FINDINGS: No difference in anterior tibial displacement and peak torque was observed between the uninjured and injured sides during Leaf spring exercise. INTERPRETATION: Leaf spring exercise may add some strain on the reconstructed anterior cruciate ligament; hence, it can be considered a safe quadriceps exercise in the knee extension range.

Quantitative Evaluation of Functional Instability Due to Anterior Cruciate Ligament Deficiency.

BACKGROUND: A safe and simple procedure to evaluate functional instability due to anterior cruciate ligament (ACL) deficiency (ACLD) has not been established. The angle of trunk backward tilting, which is known as a posture at risk for ACL injuries, could be used as a parameter to evaluate functional instability due to ACLD. PURPOSE: To measure the backward tilt angle of the trunk with participants standing upright on 1 leg and to investigate its usefulness to quantitatively evaluate functional instability due to ACLD. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: Our cohort included 50 participants with unilateral ACLD and 40 participants with bilateral healthy knees. The trunk backward tilt (TBT) test was conducted as follows: the participant was asked to maximally tilt the trunk backward in a single-leg standing position, while forward tilt of the index leg was blocked with a custom-made device. The TBT angle was measured using a side-view photograph. Subjective knee instability during the test was recorded using a visual analog scale (VAS). The relative and absolute reliability of the TBT test were verified in a sample of healthy participants and those with ACLD, and comparisons between indicators were performed. Multiple regression analysis was performed with the injured/uninjured side ratio (I/U ratio) of the TBT angle as the dependent variable and the following independent variables: (1) I/U ratio of knee extension muscle strength, (2) I/U ratio of knee flexion muscle strength, (3) side-to-side difference (SSD) of the KT-1000 arthrometer measurement, (4) sex, and (5) SSD of the VAS score. RESULTS: The TBT test had high reliability among healthy participants and those with ACLD. The TBT angle was significantly smaller and the VAS score was significantly higher on the injured side compared with the uninjured side and with healthy knees (P < .001 for all). Among the independent variables, the SSD of the VAS score had a negative influence on the I/U ratio of the TBT angle (R 2 = 0.59; P < .001). CONCLUSION: The TBT test is a simple, safe, and reliable method for quantitatively evaluating functional instability due to ACLD under weightbearing conditions that reflect subjective knee instability. The test will provide an index of treatment outcomes and return to sports through additional objective measurements before and after ACL reconstruction.