Increased distal femoral torsion is a predictor of non-contact anterior cruciate ligament injury: a case control study

doi:10.21203/rs.3.rs-2099257/v1

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Increased distal femoral torsion is a predictor of non-contact anterior cruciate ligament injury: a case control study

https://doi.org/10.21203/rs.3.rs-2099257/v1

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Background

The Anterior cruciate ligament (ACL) is one of the most easily injured ligaments in the knee. Abnormal femur and knee rotation may lead to ACL injury, while an increased proportion of the lateral femoral condyle is also a potential factor in ACL injury. Therefore, distal femoral torsion (DFT) may be closely related to ACL injury. Thus, this study aims to investigate the associations of DFT with the risk of ACL injury and the severity of the injury.

Methods

582 patients who received ACL reconstruction surgery between 2014 and 2019 were examined retrospectively, and 114 patients were selected for analysis. Among them, 32 experienced ACL and anterolateral ligament (ALL) injury (ACL + ALL-injury group), and 32 experienced only ACL injury (only ACL injury group). In addition, 50 patients with similar age and BMI, but without ACL or ALL injury, were selected as the control group. DFT was assessed via the surgical posterior condylar angle (sPCA) on MRI by a blinded researcher. Inter-group differences were assessed via ANOVA. An ROC (Receiver Operating Characteristic) curve was generated to elucidate the ACL injury risk, and to establish the appropriate threshold value.

Result

The average sPCA was 3.68 ± 1.26° among the ACL + ALL-injury and ACL-injury only patients. Notably, the 3.77 ± 1.15° sPCA among the ACL + ALL-injury patients, and the 3.58 ± 1.37° sPCA among the ACL-injury patients were markedly enhanced, compared to the 2.41 ± 1.48° value in control patients. The ACL + ALL patients displayed an augmented sPCA trend over ACL-alone patients, however, it did not reach significance. Moreover, based on the ROC curve, sPCA > 2.37° was indicative of an enhanced ACL injury risk among the ACL-intact individuals.

Conclusion

Based on our analysis, augmented sPCA values were intricately linked to enhanced ACL injury risk in non-contact ACL ruptured patients. Nevertheless, its usage as a predictor of ACL injury severity is scarce. The conclusions of this study will likely assist orthopedic surgeons in identifying patients who may benefit from targeted ACL injury prevention.

ACL injury

Distal femoral torsion

Surgical posterior condylar angle

Anterolateral ligament

Among the commonly disrupted knee ligaments is the anterior cruciate ligament (ACL). ACL injuries are common across nearly all age ranges, and they result in profound effects on quality of life[1–5]. Thus far, intensive research efforts have been devoted to the identification of ACL injury etiology over the past 2 decades[6]. A multitude of risk factors were proposed, namely, body mass index (BMI), neuromuscular defects, hormone levels, joint laxity, and gender[7–10]. In addition to these, several bony morphological characteristics, namely, enhanced posterior tibial slope (PTS) and reduced femoral notch width, were reported to enhance ACL injury risk[11–17].

Certain recent laboratory studies indicated a link between femoral rotational aberrations and ACL rupture susceptibility[18]. Likewise, enhanced hip anteversion and hip internal rotation were also shown to associate with non-contact ACL injury[19–21]. Furthermore, Saper et al.[22] reported that the Tibial Tuberosity-Trochlear Groove (TT-TG) distance was considerably elevated in knees with noncontact ACL injury versus non-injury in adolescents and young adults, indicating that knee rotational aberrations may be a strong indicator of non-contact ACL injuries.

More recently, Pfeiffer et al.[23] suggested that a higher lateral femoral condyle ratio is a predictor of ACL injury. Likewise, our investigation also revealed that an augmented lateral femoral condyle ratio is strongly linked to higher incidences of ACL injury in non-contact ACL ruptured patients[24]. The aforementioned studies indicate that the altered posterior femoral condylar depth likely changes the strain on the lateral collateral ligament, anterolateral capsule, and anterolateral ligament in flexion. The knee joint thus laxity in the vicinity of complete flexion, which is where most ACL injury occurs. However, the strain of the medial and lateral collateral ligaments and anterolateral ligament are not just maintained by lateral femoral condyle. Instead, the inner mechanism might be due to the rotational abnormality or the imbalance of medial and lateral femoral condyle.

Rotational alignment, which refers to the implant positioning in the axial plane, was first described in total knee arthroplasty (TKA). It is typically measured via the surgical posterior condylar angle (sPCA), and it is a good indicator of distal femoral torsion (DFT)[25]. Hence, the goal of this investigation was to (1) elucidate the sPCA differences between patients with a history of non-contact ACL injury and no injury, and to (2) assess the correlation between DFT and ACL injury severity. We hypothesized that ACL-deficient knees will have augmented sPCA, compared to non-injured knees, and sPCA can be used as a reliable predictive of ACL injury severity.

This work received ethical approval from the participating institution. Prospectively-collected patient information between the years 2014–2019 was retrieved and analyzed retrospectively. In total, 582 arthroscopic ACL reconstruction patients were reviewed for study eligibility, based on a computer-based recording program.

Patient selection

Patient eligibility was assessed via review of medical and surgical records. In particular, special attention was given to patients who underwent primary ACL reconstruction to correct noncontact ACL tear. Patients eliminated from analysis met one or more of the following criteria: 1. Partial ACL injury; 2. Prior knee surgery on the affected side; 3. Co- or multi-ligament injuries, such as, PCL, MCL, and PLC injuries; 4. Cartilage degeneration > 2 based on the Kellgren-Lawrence grade; 5. Extreme lower limb misalignment; 6. General joint laxity. Upon patient selection, they were separated into 3 cohorts: (1) Control, patients with no ACL or anterolateral ligament (ALL) injury, (2) Patients with ACL injury only, and (3) Patients with ACL + ALL injury. All 3 patient cohorts had comparable age and BMI. The patient selection process is detailed in Fig. 1.

Data collection

Patient demographics, such as, age and sex, as well as medical history and examination reports were retrieved from corresponding medical reports. The preoperative MRI was independently evaluated by a sport medicine-specializing orthopedic surgeon and a musculoskeletal imaging-specializing radiologist. The sagittal, coronal, and axial sequences with T1 and T2 MRI phases were examined. The ALL status was based on the T2 weighted coronal plane assessment (Fig. 2).

The DFT was assessed based on the sPCA (described as a line passing through the medial sulcus/apex of the lateral epicondyle, and a line passing through the posterior condylar axis on the same slice) (Fig. 3), as it is regarded as a stable reference for the femoral rotation in the axial plane[26].

Statistical analysis

The age, BMI, and sPCA of the study subjects are presented as mean ± standard deviation. Gender is provided as frequency. Intraclass correlation coefficients (ICCs) were utilized to assess the interobserver reproducibility of sPCA. ICC value > 0.9 represented excellent, and values of 0.8–0.9 represented good reliability.

Continuous data analysis was done via the Student t test, whereas, categorical data employed the chi-square test. Inter-variable associations were assessed via the Pearson’s correlation coefficient. ICC was employed for measurement performance evaluation. A receiver operating characteristic (ROC) curve analysis was employed to establish an appropriate threshold for ACL injury detection using the sPCA of all patient cohorts. The appropriate threshold with the maximum sensitivity and specificity were identified using the Youden index. Subsequently, the odds ratio (OR) was computed to assess whether an enhanced sPCA was an indicator of ACL injury. The levels of significance were set at 0.05. SPSS 21.0 was used for data analysis.

Finally, 114 patients were enrolled. The respective groups were: Group A. ACL + ALL-injury (32 cases); Group B. ACL injury alone (32 cases); and Group C. Control (ACL intact) (50 cases). The patient demographics are presented in Table 1. There were no differences in patient age and BMI among the cohorts. Additionally, the study group had more males than females. The ALL status (ICC = 0.90) exhibited excellent interobserver reproducibility, and the interobserver ICC was 0.83 for the sPCA measurement, indicating good reliability.

Table 1

Demographics of the ACL + ALL-injury, ACL-injury and ACL-intact group
		ACL + ALL-injury group	ACL-injury group	ACL-intact group	Total
No.		32	32	50	114
Age* (years)		35.69 ± 10.28	32.56 ± 10.11	36.26 ± 10.74	39.00 ± 14.35
BMI* (kg/m²)		23.71 ± 5.16	23.55 ± 2.81	22.46 ± 4.12
Injury site	Right	13	15	28	56
Injury site	Left	19	17	22	58
Gender	Male	23	28	21	72
	Female	9	4	29	42

* The data are given as the mean and standard deviation.

The radiographic evaluations are provided in Table 2. A significant difference was prominent between the ACL injury patients (including ACL+ALL group and isolated ACL group) (mean, 3.68±1.26°) and controls (mean, 2.41 ± 1.48°) in terms of the sPCA (P <0.001). Furthermore, both ACL+ALL (mean, 3.77±1.15°) and ACL alone (mean, 3.58±1.37°) patients exhibited markedly elevated sPCA, relative to controls (P<0.001). Although the ACL+ALL patients demonstrated an elevated sPCA value, relative to ACL alone, the difference did not reach significance. Lastly, there was a marked difference in sPCA values between males (72 cases, 3.42±1.43°) and females (42 cases, 2.60±1.48°) (Fig. 4).

Based on the ROC curve, a 2.37° threshold for sPCA provided a sensitivity of 83% and specificity of 58% in estimating a markedly enhanced ACL injury risk within the entire cohort (Fig. 5). An sPCA of >2.37° was strongly correlated with an enhanced ACL injury risk (OR = 6.65; 95% CI = 2.8 to 15.7), relative to the uninjured ACL participants.

Table 2

Distal femoral torsion (DFT) for ACL + ALL-injury, ACL-injury and ACL-intact group measured by S-PCA
	ACL + ALL-injury group	ACL-injury group	ACL + ALL-injury group and ACL-injury group	ACL-intact group	Total
No.	32	32	64	50	114
Surgical-PCA(degree)	3.77 ± 1.15	3.58 ± 1.37 *(p = 0.540)	3.68 ± 1.26	2.41 ± 1.48 *(p༜0.001) #(p༜0.001) §(p༜0.001)	3.12 ± 1.50
* significantly different from ACL + ALL-injury group; # significantly different from ACL-injury group; § significantly different from ACL + ALL-injury group and ACL-injury group.

Herein, we demonstrated a strong correlation between enhanced sPCA and augmented ACL injury risk. Specifically, both the ACL + ALL (mean, 3.77 ± 1.15°) and ACL injury only (mean, 3.58 ± 1.37°) patients exhibited markedly elevated sPCA, relative to controls (P < 0.001), thereby indicating that an increasing sPCA is positively related to ACL injury incidence. An sPCA > 2.37° was found to predict a significantly higher risk of ACL injury with a sensitivity and specificity of 83% and 58%, respectively. This finding can assist orthopedic surgeons in identifying patients at risk of ACL injury.

The exact cause of this link is yet to be determined, however, prior research involving knee kinematics and factors that contribute to enhanced ACL injury risk can elucidate the potential roles of enhanced sPCA. Previous investigations suggested a relationship between distal femoral morphology and enhanced ACL injury risk. These include augmented lateral femoral condyle ratio[23], shallow medial tibial plateau, steep medial and lateral tibial slopes[11], large tibial-tubercular groove distance[22], and decreased intercondylar notch width and notch width index[12]. Morphological differences can also contribute to the detrimental effects beyond ACL tear risk, which, in turn, increases the likelihood of further injury to the knee[2, 8, 9, 13, 14].

The link between these morphological factors and ACL injury, particularly non-contact ACL injury, can often be boiled down to altered gait mechanics and rotational abnormalities. Non-contact injuries are by definition caused by internal forces. In terms of ACL injury, they are usually caused by a pivot-shift mechanism[27], whereby, the tibia translates anteriorly and internally rotates while the lateral femoral condyle shifts posteriorly, thus causing anterior subluxation of the lateral tibial plateau over the femoral condyle[28]. This motion not only causes ACL injury and rupture, but also injures the surrounding structures, such as, the ALL, which serves as a secondary ACL stabilizer. sPCA is a measure of knee rotational alignment. This important factor is modulated by the forces that act on the knee joint during rotational movement. As such, sPCA can potentially predict DFT. Therefore, one can conclude that a rise in sPCA can produce enhanced rotational stress on the knee, which, in turn, generates a greater strain on the ACL and other knee structures, thus allowing injuries to occur more easily. Prior investigations revealed that augmented femoral anteversion resulting from enhanced infratrochanteric torsion and reduced internal hip rotation range is associated with ACL injury[18–20]. Future kinematic investigations can further elucidate the impact of these factors on the relationship between sPCA and ACL injury.

Notably, even though there was a strong increase in sPCA in ACL + ALL versus control, no obvious differences were observed in the ACL + ALL and ACL only patient cohorts. A combined injury to the ALL and ACL indicates an injury of higher severity, with damage to more knee structures, and more complicated treatment and recovery. A risk factor that can identify risk of knee injury and risk of severe injury is ideal for usage in clinical assessments. Based on our data, enhanced sPCA can be used to assess ACL injury risk, however, its usage in predicting potential injury severity is currently limited.

Given the enhanced incidence of ACL injury and the profound effects such injuries have on patient quality of life, it is essential to identify factors that may predispose an individual towards ACL injury, and to elucidate the mechanism behind such associations. Using this, physicians can screen for patients at high risk of experiencing ACL injury or re-injury, and work to mitigate these risk factors. This study identified one potential risk factor: enhanced sPCA, which can be easily identified on MRI images. Clinicians must utilize this information while evaluating patients for knee injuries, in order to assess treatment strategies, and evaluate the relative risk of future injury. Extensive knowledge of these risk factors can empower patients and clinicians to make the correct decisions on how best to move forward in the patient treatment plan.

Our work had certain limitations. First, even though the data was collected prospectively, its retrospective analysis may have introduced some unintentional bias. Second, this study matched participants by age and BMI, and not by sex. Our analysis identified a significant difference between male (72 cases, 3.42 ± 1.43°) and female (42 cases, 2.60 ± 1.48°) sPCAs, with female sPCA being significantly smaller. There were also fewer females in the overall study cohort. Given the known differences in ACL injury risk between males and females, as well as the bone morphological differences between the genders[2, 7, 10, 11], it may be pertinent for future investigations to stratify data in order to further define these differences, and examine whether the risk sPCA threshold value can be further refined by gender.

Herein, we demonstrated a strong association between enhanced sPCA and non-contact ACL injury risk. However, its usage as a predictor of potential injury severity is currently limited. It is our belief that our findings can clinically benefit orthopedic surgeons in identifying patients at risk of ACL injury.

ACL: Anterior cruciate ligament; DFT: Distal femoral torsion; ALL: Anterolateral ligament; sPCA: surgical posterior condylar angle; ROC: Receiver Operating Characteristic; BMI: body mass index; PTS: posterior tibial slope; TT-TG: Tibial Tuberosity-Trochlear Groove; TKA: total knee arthroplasty; ICCs: Intraclass correlation coefficients; OR: odds ratio.

Ethical approval and consent to participate: The study was conducted in accordance with the Declaration of Helsinki. This study was approved by the institutional review board of the First Affiliated Hospital of Chongqing Medical University (IRB approval number: 2017-108). This retrospective study was approved by the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University to waive informed consent.

Consent for publication: Not applicable.

Availability of data and materials: All data and materials relating to this article will be available from the corresponding author.

Competing interests: The authors declare that they have no conflict of interest.

Funding: This study was supported by National Natural Science Foundation of China (NO.81902293).

Authors' Contributions:

DHW: Data collection, data analysis and article writing

JC: Data collection, data analysis and article writing

HKF: Data collection, data analysis and article writing

RS: Article writing

XL: Critical revision of the article

WH: Critical revision of the article

XLG: Article review and revision

KL: Study design, article review and revision

Acknowledgements: Not applicable.

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No competing interests reported.

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Increased distal femoral torsion is a predictor of non-contact anterior cruciate ligament injury: a case control study

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Abstract

Background

Methods

Result

Conclusion

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Background

Methods

Patient selection

Data collection

Statistical analysis

Results

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

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