Posterior Tibial Slope Is Not Correlated With Meniscal Tears in Anterior Cruciate Ligament Reconstruction

Abstract

Purpose

To evaluate the impact of the tibial slope on the severity and location of meniscal tears in patients presenting with anterior cruciate ligament (ACL) rupture.

Methods

We conducted a single-center retrospective observational study. We analyzed charts and records of patients who underwent ACL tear surgery between 2018 and 2021, excluding those with multiligamentous knee injuries or osteoarthritis. Posterior tibial slope was measured from lateral radiographs, and data on meniscal tears characteristics were collected, including laterality, anatomical location, blood supply zone, tear type, and treatment modality.

Results

We included 749 patients (127 female, 622 male) who underwent ACL reconstruction (hamstring tendons, n = 59; bone−patellar tendon−bone, n = 659; quadriceps tendon, n = 31). Concomitant meniscal tears occurred in 361 patients (medial meniscus, 50.7%; lateral meniscus, 31.9%; both menisci, 17.4%). No correlation was found between posterior tibial slope and meniscal injury overall (P = .8). However, a significant correlation was noted between tibial slope and lateral meniscal body tear (P = .023).

Conclusions

Our findings suggest that an increased tibial slope, as measured on lateral radiographs, is not indicative of concomitant meniscal tears. However, in cases in which meniscal tears did occur in patients with a high posterior tibial slope, they predominantly affected the lateral meniscal body.

Level of Evidence

Level IV, prognostic, case series.

Meniscal tears are one of the most common sports-related orthopaedic injuries, as they often carry substantial long-term morbidity as the result of articular cartilage degeneration leading to early-onset osteoarthritis.¹ Surgical management for pain or mechanical symptoms has been the standard treatment strategy,^2,3 with a recent trend of increased meniscal repairs observed as opposed to meniscectomy.⁴

Multiple studies have long evaluated risk factors for meniscal tears, which can be classified as modifiable and nonmodifiable. Within the nonmodifiable risk factors, the most important included male sex, age older than 60 years, and ligamentous laxity, whereas modifiable risk factors include participation in sports, particularly soccer and rugby, as well as high body mass index.^2,5 In addition, medial meniscus tears are consistently more common than lateral tears in sports-related injuries.⁶ Recently, studies have aimed to evaluate the association between meniscal tears and posterior tibial slope, with some showing an association between increased posterior tibial slope (PTS) and posterior medial meniscus root tears as the result of increased compression and posterior shear force^7,8 and increased PTS and lateral meniscal posterior root tears in the setting of anterior cruciate ligament injuries.^9,10 Despite the growing interest in the relationship between meniscal tears and tibial slope, there is a paucity of comprehensive research investigating this association. Therefore, a well-designed study examining the correlation between meniscal tears and tibial slope could provide valuable insights into the pathogenesis and prevention of these injuries.

The purpose of our study was to evaluate the impact of the tibial slope on the severity and location of meniscal tears in patients presenting with anterior cruciate ligament (ACL) rupture. We hypothesized that increased PTS would be positively associated with the severity and location of meniscal tears in patients presenting with ACL rupture.

Methods

Study Design

This is a retrospective case series study. All charts and records of patients operated between 2018 and 2021 for an ACL tear were retrieved and analyzed. Approval from the ethical committee of our institution was granted before the conduction of the study. Approval to undergo the present work was waived by our institutional review board, Clinical, arthroscopic and radiologic evaluations were performed by an independent observer.

Selection Criteria

The inclusion criteria were set as follows: (1) ACL tear treated with a reconstruction, (2) a recorded arthroscopic procedure, and (3) available preoperative radiographs. Exclusion factors were set to be (1) absence of a videorecorded surgical procedure; (2) patients with multiligamentous knee injuries, and (3) patients with osteoarthritis.

Study Variables

Demographic data, presence or absence of an associated meniscal tear, laterality, and location, type, and treatment of the meniscal tear were recorded and analyzed. All arthroscopic procedures were revisited by our senior author to record the association of meniscal tear and its characteristics. Tibial slope was measured, and the status of growth plate was analyzed (open-closed) by 2 different radiologists. Patients were divided into 2 subgroups according to the presence or absence of meniscal tear.

Radiologic Analysis

Preoperative plain radiographs, consisting of both anteroposterior and lateral views, were conducted for the patients included in the study. These radiographs were independently assessed by 2 radiologists (T.E.K., S.S.) who were kept blinded to the patients' case statuses. The epiphyseal growth plate was systematically categorized as either open or closed. Subsequently, the measurement of the PTS was carried out on the lateral radiographs (Fig 1) with the use of the tibial proximal anatomic axis (TPAA) as the reference line, because of its high reliability along the tibial axis.

Fig 1.

Measurement of posterior tibial slope on lateral plain radiographs of the knee. Red line: anatomic axis of the tibia. Blue line: perpendicular to anatomic axis of tibia. Green Line: slope of posterior tibial slope. Angle of posterior tibial slope is the angle between the blue and green line.

The TPAA was precisely defined as a line connecting the central points of the tibial cortex located at 5 cm and 15 cm below the tibial tuberosity. Subsequently, the line connecting the most elevated anterior and posterior points of the medial plateau was considered the reference line for determining the tibial slope. The angle formed between the tangent line touching the medial plateau and the perpendicular line to the TPAA was defined as the PTS. This methodology ensured a standardized and accurate assessment of the tibial slope for subsequent analyses.

Arthroscopic Analysis

The recorded arthroscopic procedures underwent meticulous review under the supervision of our senior author. Initially, the presence or absence of meniscal tears was accurately documented. Subsequent to this, several key characteristics of these tears were thoroughly recorded, including their laterality (medial, lateral, or both medial and lateral), anatomical location (posterior horn, body, anterior horn), blood supply zone (red zone, red-white zone, white zone), tear type (bucket handle, meniscocapsular separation, vertical, horizontal, oblique, or complex), and the treatment modality administered (meniscectomy, repair, and rasping). This comprehensive approach allowed for a detailed analysis of each tear's specific features, enhancing the precision of our subsequent assessments and interpretations.

Statistical Analysis

The collected data were analyzed using SPSS (Statistical Package for Social Sciences) software, version 28.0 (IBM Corp.). For descriptive analysis, frequency and percentage were used for categorical variables, mean and standard deviation for quantitative variables. For dependent variables, the median and interquartile region were presented as well; the distribution of these variables were considered normal using visual inspection of the histogram, while the skewness and kurtosis were lower than 1. These conditions are considered compatible with normality with a sample size greater than 300.

For the bivariate analysis of continuous variables, the Student t test was used to compare the means between 2 groups and analysis of variance to compare between 3 groups or more, after checking for homogeneity of variances using the Levene test. In case the variances were not homogenous, the corrected t Test and the Kruskal-Wallis test were used, respectively. After analysis of variance and Kruskal-Wallis significant testing, post hoc analyses were conducted using Bonferroni adjustment. A Pearson correlation coefficient was used to correlate between continuous variables. For categorical variables, the χ² test was used, and the Fisher exact test was used in case of expected values less than 5. In all cases, a P value less than .05 was considered significant. As for the multivariable analysis, a general linear model procedure was applied to implement a multiple linear regression model. Independent variables introduced in the models were those that had a P value less than .1 in the bivariate analysis, taking into account the maximum number allowed of variables to be included given the sample size: sociodemographic, and other independent variables will be added as appropriate.

Results

Seven hundred forty-nine patients (127 female and 622 male) with an average age at the time of surgery of 26.71 ± 8.24 years, who underwent anterior cruciate ligament reconstruction (ACLR) were included in the study. ACLR procedures were performed on both the right (365 cases) and left (384 cases) sides, using various graft types, including hamstrings in 59 cases, bone−patellar tendon−bone in 659 cases, and quadriceps in 31 cases. Concomitant meniscal tears were identified in 361 patients, with 50.7% presenting a medial meniscal tear, 31.9% a lateral meniscal tear, and 17.4% tears in both menisci. Furthermore, 388 patients had an isolated ACL tear (Table 1). A detailed characterization of medial and lateral meniscal tears was conducted (Table 2).

Table 1.

Demographic and Clinical Characteristics and Their Relation to Tibial Slope Measurements

Characteristics	n (%)	Mean Tibial Slope (SD)	P Value
Sex
Female	127 (17)	11.87 (3.10)	.217
Male	622 (83)	12.28 (3.48)
Side
Right	365 (48.7)	12.69 (3.46)	.001
Left	384 (51.3)	11.75 (3.31)
Etiology
Primary	682 (91.1)	12.14 (3.35)	.068
Revision	67 (8.9)	12.94 (4)
Meniscal tear
Yes	361 (48.2)	12.25 (3.29)	.736
No	388 (51.8)	12.17 (3.53)
Tear localization
Medial	183 (24.4)	12.23 (3.28)	.908
Lateral	115 (15.4)	12.39 (3.41)	.580
Both	63 (8.3)	12.08 (3.14)	.645

SD, standard deviation.

Table 2.

Comparison of Medial and Lateral Meniscal Tear Characteristics and Their Association With Tibial Slope Measurements

Meniscal Tear Characteristics	Medial			Lateral
	n (%)	Mean Tibial Slope (SD)	P Value	n (%)	Mean Tibial Slope (SD)	P Value
Anterior	0 (0)	N/A	N/A	2 (0.3)	15.4 (1.97)	.184
Body	117 (15.6)	12.02 (3.43)	.347	175 (23.4)	11.97 (3.54)	.149
Posterior	136 (18.2)	12.32 (3.13)	.775	88 (11.7)	12.33 (3.11)	.927
Red zone	9 (1.2)	11.74 (2.21)	.629	34 (4.5)	12.15 (2.96)	.759
Red-white zone	129 (17.2)	12.10 (3.0)	.310	49 (6.5)	12.13 (3.34)	.657
White zone	47 (6.3)	12.80 (4.08)	.190	92 (12.3)	12.46 (3.41)	.521
Bucket handle	51 (6.8)	12.35 (3.43)	.703	21 (2.8)	11.30 (3.51)	.137
MCS	3 (0.4)	12.5 (0.69)	.871	0 (0)	N/A	N/A
Radial	5 (0.7)	13.44 (3.26)	.388	24 (3.2)	13.25 (4.27)	.135
Vertical	71 (9.5)	11.72 (3.01)	.149	29 (3.9)	12.10 (2.63)	.711
Oblique	31 (4.1)	12.81 (3.39)	.259	63 (8.4)	12.76 (2.98)	.179
Complex	22 (2.9)	12.74 (3.66)	.411	28 (3.7)	11.71 (3.47)	.297
Horizontal	9 (1.2)	11.75 (3.93)	.678	10 (1.3)	11.64 (3.0)	.507

MCS, meniscocapsular separation; N/A, not available; SD, standard deviation.

For medial meniscal tears, the distribution was categorized on the basis of location, revealing that 46% occurred in the body, whereas 54% were in the posterior horn, with no tears noted in the anterior horn. Blood supply zone analysis showed 6% in the red zone, 91% in the red-white zone, and 3% in the white zone. Regarding tear types, the breakdown included 26% bucket-handle tears, 1% meniscocapsular separation, 1% radial tears, 37% vertical tears, 17% oblique tears, 12% complex tears, and 5% horizontal tears.

Concerning lateral meniscal tears, the distribution by location showed 50% in the body, 49% in the posterior horn, and 1% in the anterior horn. Blood supply zone analysis indicated 20% in the red zone, 28% in the red-white zone, and 52% in the white zone. Tear types were classified as 15% bucket-handle tears, 19% radial tears, 22% vertical tears, 48% oblique tears, 22% complex tears, and 8% horizontal tears, with no instances of meniscocapsular separation noted. A multivariate analysis was conducted, its results are illustrated in Table 3.

Table 3.

Multivariate Regression Analysis of Factors Affecting Tibial Slope Measurements

Parameter	Beta	Significance	95% Confidence Interval		Partial Eta Square
			Lower Bound	Upper Bound
Left side	−0.603	.265	−1.667	0.462	0.013
Primary	0.72	.599	−1.976	3.415	0.003
Lateral meniscal tear: body	3.418	.023	0.481	6.355	0.054
Lateral meniscal tear: posterior	2.796	.064	−0.159	5.751	0.043
Lateral meniscal tear: white zone	−1.948	.152	−4.619	0.724	0.002
Lateral meniscal tear: bucket handle	−1.27	.297	−3.668	1.128	0.010
Closed growth plate	−0.036	.359	−0.113	0.041	0.000

Left knee, lateral view.

The mean tibial slope was 12.21 ± 3.42°. There was no significant difference in PTS between male and female patients (P = .249), as well as no significant difference in PTS between patients with isolated ACL tear and patients with ACL tear associated with a meniscal tear (P = .8). Particularly, a significant correlation was observed between tibial slope and lateral meniscal body tear (P = .023).

Discussion

Our findings indicate that an increased PTS, as measured on lateral radiographs, does not reliably predict the presence of concomitant meniscal tears in patients undergoing ACLR. However, in patients who did present a meniscal tear, a correlation with the PTS was found and lateral meniscal body tears. This gives valuable insights concerning the distribution of concomitant meniscal tears in patients presenting for ACL ruptures, depending on the severity of their tibial slope.

Previous research has established that a steep PTS increases loading stress on the ACL, thereby elevating the risk of isolated ACL (or ACL graft) tear.^11,12 Similarly, an increased PTS has been associated with an increased incidence of isolated meniscal injuries.^8,13,14

However, the impact of a steep PTS on meniscal tears in the context of acute ACL rupture remains debated. A recent study by Shu et al.¹⁵ using a finite element knee model showed that even a slight increase in PTS in an ACL-deficient knee resulted in significantly larger loading on the medial meniscus, when compared to an ACL intact knee.

In clinical settings of ACL ruptures, some studies have observed greater rates of Lateral meniscal lesions rates in patients with a steeper lateral tibial slope measured on magnetic resonance imaging (MRI).^16,17 In the same way, an increase in the medial tibial slope on MRI has been linked to a higher rate of Medial meniscal tear and Ramp lesions in other studies.18, 19, 20

Bernholt et al.⁹ even found that more lateral meniscal posterior root tears were noted with increased lateral and medial PTS. Conversely, El Mansori et al.²¹ reported that an increase in lateral PTS led to an increased rate of both meniscus injuries. Some studies, such as those conducted by Markl et al.²² and Beel et al.,²³ did not even find any statistically difference between PTS and meniscal tears. This can partially be explained by the relatively small sample size in both studies, which may have limited the statistical power to detect a significant difference, or by the grouping of the PTS into only 2 categories (>10° and ≤10°) in the study of Beel et al., which might have missed nuances in the relationship between specific degrees of slope and meniscal tears. In our study, we chose to analyze the PTS as a continuous value.

Even when using the lateral radiographic views for measurement of the PTS (such as in our study), previous studies have reached different conclusions. Lee et al.²⁴ showed that a PTS≥13° is a risk factor for secondary medial meniscal tears in ACL-deficient knees, whereas Okoroha et al.²⁵ showed that increased tibial slopes was found to increase the risk of lateral meniscal posterior root tear. In addition, authors like Yoshihara et al.²⁶ and Kolbe et al.²⁷ introduced the concept of slope asymmetry between medial and lateral tibial plateau as a risk factor for posterolateral meniscal tear, rather than the PTS itself.

This brief review of the current literature brings out a large spectrum of conclusions regarding the effect of the PTS on meniscal tears pattern in ACL injured knees. These discrepancies can be explained by the varying imaging modalities used to measure PTS (MRI vs radiographs), the heterogeneity of the populations across the studies, the variations in sample sizes, and the different statistical methods that were used. Other confounding factors, such as pre-existing asymptomatic meniscal injuries or the chronicity of ACL ruptures, might also have led to discrepancies in the reported results. Given the discordance in existing literature, larger studies were warranted to settle the debate, leading to the present study.

Previous systematic reviews, such as that by Jiang et al.²⁸ in 2022, have discussed several studies investigating the effect of tibial slope on the menisci in the context of ACL tears, but all had a smaller number of patients than the present study.

On the basis of our findings, we observed that an increased tibial slope is not a good predictor of concomitant meniscal tear. However, when meniscal tears occurred in patients with high PTS, they predominantly tended to occur within the lateral meniscal body. PTS did not seem to be correlated to the type of meniscal tear (radial, vertical, oblique, complex tears, or horizontal) nor the location within the red or white areas. Further multi-center studies are needed to confirm these findings across diverse populations.

Limitations

This study is not without limitations. One limitation of the present study is the potential for residual confounding, particularly regarding the lack of consideration for laxity and chronicity of meniscal injuries. Patients may have sustained asymptomatic or undocumented meniscal injuries before ACL rupture, which could influence outcomes but are difficult to account for fully in this type of study. In addition, the findings may not be fully generalizable due to the study being conducted within a single institution, and variations in patient demographics may affect the broader applicability of the results. Also The high number of classifications with a small number of subjects in each subgroup analysis creates a high risk for a type II error.

Conclusions

Our findings suggest that an increased tibial slope, as measured on lateral radiographs, is not indicative of concomitant meniscal tears. However, in cases where meniscal tears did occur in patients with a high posterior tibial slope, they predominantly affected the lateral meniscal body.

Disclosures

All authors (A.E.A., T.E.K., J.G., J.O., S.S., P.S., A.K.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.