Background

Injuries to the anterior cruciate ligament (ACL) are frequent among athletes who play violent sports like American football, basketball, and soccer. Over 60% of knee injuries in sports involving rapid movements are ACL tears. To regain knee joint stabilization following the majority of ACL injuries, anterior cruciate ligament reconstruction (ACLR) is necessary [1].

One of the significant changes following ACLR is the persistence of rectus femoris (RF) and vastus intermedius (VI) weakness after rehabilitation is completed [2]. If this weakness continues, it could be dangerous for the patients since it might change their movement patterns, reduce their functional activity, and raise their risk of re-injury. Additionally, it might reduce patients’ quality of life by delaying their return to regular activities. The full functionality of the RF and VI muscles must be restored in order to best prepare the patient for recovery, but this is frequently not accomplished despite targeted rehabilitation [3, 4].

Further understanding of quadriceps atrophy and strength limits may be possible by recognizing the effects of ACLR on the size and volume of these muscles. In addition, systematic rehabilitation plans can be made based on the size of the quadriceps. Therefore, if muscle loss is detected early after surgery, we can develop structured rehabilitation programs to aid the patient’s recovery [3, 5].

Magnetic resonance imaging (MRI) and computed tomography (CT) scans are the best methods currently available for measuring muscle volume and RF and VI thickness, but because of the limited resources, they are neither widely available nor cost-effective for the majority of the population. These techniques are expensive and require specific tools and safety precautions [3, 6].

The aim of this study is to measure the (RF) thickness, (VI) thickness and the total (RF + VI) thickness on (ACL) reconstructed limb and the non-reconstructed limb of athletes using ultrasound and to compare the results pre-operatively and 6–8 months post-operative.

Methods

This prospective study was approved by our Research and Ethics committee (approval code: N-225-2023).

Sixty athletic male patients who were candidates for ACLR surgery were referred to the diagnostic radiology department from the outpatient clinic of the orthopaedic department in the time period from November 2022 to June 2023. All patients presented with ACL tears during playing football were included in our study. Their age ranged from 18 years to 35 years, the mean ± standard deviation age was 26.28 ± 18.2 years and the median was 27 years. Nonathletic patients, patients with bilateral ACL tears, and patients with a history of related operations or internal fixations were excluded from this study.

All cases (n = 60/60) were subjected to B-mode ultrasound (US) pre-operative and 6–8 months post-operative on both reconstructed (RL) and non-reconstructed limbs (NRL) to measure the thickness of rectus femoris, vastus intermedius and the total thickness.

Technique and analysis of the ultrasonographic examination

The Toshiba Ultrasound Aplio 500; Toshiba Medical, Japan machine with the 18 MHz linear probe was used to assess the patients.

With the patient supine and hip external rotation avoided, the thickness of the rectus femoris, vastus intermedius, and total thickness was measured. At the halfway point (50%) between the superior pole of the patella and the anterior superior iliac spine (ASIS), the RF and VI thickness were measured. The depth of the image was assessed when the femur was in the centre of the screen after the image had been modified till the muscle boundary was visible on the screen. A single examiner with more than 15 years’ experience in musculoskeletal ultrasound, recorded the ultrasound measurements three times per muscle. The distance between the muscle's superficial and deep borders was used to define the RF thickness. The distance between the superficial border of the muscle and the superficial border of the femur was used to define the VI thickness. The distance between the superficial borders of the RF muscle and the femur was used to define the total thickness.

Statistical analysis

Data were fed to the computer and analyzed using IBM SPSS software package version 25.0 (IBM Corp. Released 2017. IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp). Qualitative data were described using numbers and percentages. The Kolmogorve–Smirnov test was used to verify the normality of distribution. Quantitative data were described using range (minimum and maximum), mean, standard deviation, median and interquartile range (IQR). The significance of the obtained results was judged at the 5% level.

The used tests were

  1. 1.

    Wilcoxon Rank test was used to compare two related samples, matched samples, or to conduct a paired difference test of repeated measurements on a single sample to assess whether their population mean ranks differ.

  2. 2.

    Mann–Whitney test For abnormally distributed quantitative variables, to compare between two studied groups

Sample size calculation

Sample size calculation was carried out using G*Power 3 software [7]. A calculated sample of 52 respondents (26 athletes with ACLR during the rehabilitation period and 26 controls) will be needed to detect an effect size of 0.2 [8] in the mean difference of RF and VI muscles thickness on two repeated measures, with an error probability of 0.05 and 80% power on a two-tailed test.

Results

A total number of 60 patients candidates for ACLR surgery were enrolled in this study. The age of patients ranged from 18 to 35 years, the mean ± standard deviation age was 26.28 ± 18.2 years and the median was 27 years. The left affected limb was reported in more than half of the patients (53.3%).

Post-operative rectus femoris (RF) thickness, vastus intermedius (VI) thickness and the total thickness in the reconstructed limb were significantly smaller compared with their pre-operative thickness in the 1st, 2nd and 3rd measurements (p = 0.001, p = 0.017 and p = 0.001), (p < 0.001, p < 0.001 and p < 0.001), and (p < 0.001, p < 0.001 and p < 0.001) respectively as shown in Tables 1, 2 and 3 and Fig. 1.

Table 1 Comparison between reconstructed and non-reconstructed limbs regarding Rectus Femoris thickness measurement by US before and after surgery
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Table 2 Comparison between reconstructed and non-reconstructed limbs regarding Vastus intermedius measurement by US before and after surgery
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Table 3 Comparison between reconstructed and non-reconstructed limbs regarding total thickness measurement by US before and after surgery
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Fig. 1
figure 1

A 27-year-old male patient candidate for left ACLR surgery. a ultrasonography showing pre-operative RF (10.6 mm) (arrow) and VI (9.1 mm) (dashed arrow) thickness in the reconstructed limb compared to b post-operative RF (10 mm) (arrow) and VI (8.7 mm) (dashed arrow) thickness. c pre-operative total thickness (18.8 mm) compared to d post-operative total thickness (17.8 mm)

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Post-operative rectus femoris (RF) thickness, vastus intermedius (VI) thickness and the total thickness in the non-reconstructed limb were significantly smaller compared with their pre-operative thickness in the 1st, 2nd and 3rd measurements (p = 0.001, p = 0.017 and p = 0.001), (p < 0.001, p < 0.001 and p < 0.001), and (p < 0.001, p < 0.001 and p < 0.001) respectively as shown in Tables 1, 2 and 3 and Fig. 2.

Fig. 2
figure 2

A 29-year-old male patient candidate for left ACLR surgery. a ultrasonography showing pre-operative RF (18 mm) (arrow) and VI (15.2 mm) (dashed arrow) thickness in the non-reconstructed right limb compared to b post-operative RF (14.4 mm) (arrow) and VI (13.7 mm) (dashed arrow) thickness in the non-reconstructed limb. c pre-operative total thickness (33 mm) compared to d post-operative total thickness (27.9 mm) in the non-reconstructed limb

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The reconstructed limb showed a significant decrease in rectus femoris (RF) thickness in the 1st, 2nd and 3rd measurements (p < 0.001, p < 0.001 and p < 0.001 respectively) compared to that of non- reconstructed limb post-operatively as shown in Table 1 and Fig. 3.

Fig. 3
figure 3

A RF muscle thickness in reconstructed & non-reconstructed limbs before and after ACLR

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Vastus intermedius (VI) thickness was significantly decreased in the reconstructed limb in the 1st, 2nd and 3rd measurements (p < 0.001, p < 0.001 and p < 0.001 respectively) compared to that of non- reconstructed limb post-operatively as shown in Table 2 and Figs. 4 and 5.

Fig. 4
figure 4

A VI muscle thickness in reconstructed & non-reconstructed limbs before and after ACLR

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Fig. 5
figure 5

A 20-year-old male patient candidate for right ACLR surgery. a ultrasonography showed decreased VI thickness (11 mm) (dashed arrow) in the reconstructed limb postoperatively compared to b pre-operative VI thickness (15.6 mm) (dashed arrow). c Post-operative decreased VI thickness (13.7 mm) (dashed arrow) compared to d pre-operative VI thickness (15.2 mm) in the non-reconstructed limb

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Post-operatively the total thickness was significantly decreased in the reconstructed limb in the 1st, 2nd and 3rd measurements (p < 0.001, p < 0.001 and p < 0.001 respectively) compared to that of the non-reconstructed limb as shown in Table 3 and Fig. 6.

Fig. 6
figure 6

A Total thickness in reconstructed and non-reconstructed limbs before and after ACLR

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In both limbs, the decrease of vastus intermedius (VI) thickness was significantly higher than rectus femoris in the 1st, 2nd and 3rd measurements (p < 0.001, p < 0.001 and p < 0.001 respectively) post-operatively as shown in Tables 4 and 5.

Table 4 Comparison between Rectus femoris and Vastus intermedius thickness in reconstructed limbs by US before and after surgery
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Table 5 Comparison between Rectus femoris and Vastus intermedius thickness in non-reconstructed limbs by US before and after surgery
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Discussion

The Anterior Cruciate Ligament (ACL) is the most commonly injured.

Quadriceps muscle weakness (including the individual muscles) is a result of cruciate ligament rupture and may persist after reconstruction [7]. Most patients undergo rehabilitation programs, however, they report deficits in knee function that may affect their ability to resume sports. Finding modifiable causes of the decline in self-reported functional levels is crucial for maximizing rehabilitation following ACLR [2].

Imaging‐based measures of quadriceps size (including the individual muscles) help to illustrate the role of quadriceps atrophy as an underlying factor that contributes to quadriceps weakness and functional deficits following ACL injury [5]. Quantifying the quadriceps muscle size (including the individual muscles) in people with ACLR is frequently done using magnetic resonance imaging (MRI) and computed tomography (CT). However, they are not easily accessible and come at a high cost [9, 10].

Therefore, the purpose of this study was to set an affordable and easily available modality for the assessment of RF and VI muscles’ weakness in athletes with ACLR during the rehabilitation period.

Ultrasound was used to examine sixty athletic male patients candidates for ACLR surgery injured during playing football.

Post-operative rectus femoris (RF), vastus intermedius (VI) and total thickness in the reconstructed limb were significantly smaller compared with their pre-operative thickness in the 1st, 2nd and 3rd measurements. This was supported by the study conducted by Yang JH et al. [1] who studied the effects of ACLR on individual quadriceps muscle thickness using ultrasound and found a significant reduction in the total thickness, RF and VI thickness post-operatively.

In the current study, post-operative vastus intermedius (VI) thickness in the reconstructed and non-reconstructed limbs was significantly smaller compared with their pre-operative thickness in the 1st, 2nd and 3rd measurements. The post-reconstruction VI thickness (16.04, 6.13 mm) on RCL was significantly lower than the pre-reconstruction VI thickness (19.89, 6.91 mm, p = 0.001), according to the study by Joo et al. [11], the post-reconstruction VI thickness (20.90, 5.78 mm) on the healthy limb (HL) was also significantly lower than the pre-reconstruction VI thickness (22.88, 6.07 mm, p = 0.019).

Joo et al. [11] aimed to compare the thickness of the rectus femoris muscle in both operated and non-operated limbs, there were significant differences between both lower limbs. This prospective study showed the same results in which the reconstructed limb had a significant decrease in rectus femoris (RF) thickness in the 1st, 2nd and 3rd measurements compared to that of the non-reconstructed limb.

In this study, vastus intermedius (VI) thickness was significantly decreased in the reconstructed limb in the 1st, 2nd and 3rd measurements (p < 0.001, p < 0.001 and p < 0.001 respectively) compared to that of the non-reconstructed limb, this was matching with several previous studies reported that VI thickness in the RCL was smaller than that in the healthy limb (HL) after ACLR, the primary difference was the muscle thickness assessment time period after surgery [11].

There was no effect on the RF muscle thickness (there was only a significant time effect on RF thickness), according to Joo et al. [11], investigating the quadriceps' response to ACLR in a short period of time (48–72 h). This finding was consistent with our long-term study (6–8 months), which found that the decrease in vastus intermedius (VI) thickness was significantly higher than that of the rectus femoris in the 1st, 2nd and 3rd measurements (p < 0.001, p < 0.001 and p < 0.001 respectively).

Limitation of the study

There are some limitations in this study; the specific surgical method and process, such as a selection of graft type and specific surgical techniques, were not controlled. Therefore, there was a possibility of surgical influence on quadriceps atrophy. The sample size is not large enough for a powerful conclusion. Another limiting factor was investigating the patients by a single examiner. Furthermore, the rehabilitation of the subjects after surgery was not controlled. The frequency and intensity of rehabilitation can potentially affect the thickness of each muscle in the quadriceps.

Conclusions

Ultrasound can be used to assess quadriceps atrophy (including the individual muscles) found after ACLR. Ultrasound is an affordable and easily available modality as compared to MRI and CT scans for the assessment of RF and VI muscle weakness in athletes with ACLR during the rehabilitation period and can guide selective rehabilitation protocols if wasting is identified early.