Sage Journals: Discover world-class research

Abstract

Purpose

Many factors in the etiology of anterior cruciate ligament (ACL) tears, predisposing factors related to knee morphology have also been reported. This study aimed to determine whether the Insall–Salvati (IS) index, which measures patella height, is a predisposing risk factor for ACL tears.

Methods

The IS index, patellar length (PL), and patellar tendon length (PTL) values of patients (study group) that underwent arthroscopic reconstruction for ACL tears obtained by preoperative magnetic resonance imaging (MRI) were compared with the index values in the preoperative MRIs of patients that underwent knee arthroscopy for reasons besides ACL tears. In addition, the anterior tibial translation (ATT) of both groups was also measured and compared on MRI images. The MRI findings of the subjects included in both study groups were arthroscopically confirmed.

Results

The mean ages of the study group (n = 120) and control group (n = 90) were 29.1 ± 8.2 years and 31.8 ± 9.8 years, respectively. There was a statistically significant difference between the study and control groups in terms of the PL and PTL values (p = 0.016 and p = 0.001, respectively). The IS index was statistically significantly higher in the study group with ACL tears (p = 0.009). The ATT was 8.61 ± 4.68 mm in the study group and 3.80 ± 1.92 mm in the control group. The ATT results of both groups were evaluated, and it was found that the study group was significantly higher than the control group (p = 0.001)

Conclusions

As a result of our current study, we observed higher IS index values in patients with ACL tears than in patients without ACL tears. It should be kept in mind that patella alta, which is associated with a high IS index as one of the factors of knee morphology associated with ACL tears, may play a role in the etiology of ACL tears.

Keywords

Anterior cruciate ligament Insall–Salvati index knee injuries patella

Introduction

Anterior cruciate ligament (ACL) tears are one of the most common knee injuries.¹ They are particularly observed more frequently in sport activities that involve jumping, rotation, and direction changes, such as football and basketball.^2,3 There are many studies in the literature that have evaluated in whom ACL tears occur more frequently and have investigated which factors are associated with ACL tears. These studies have focused on several factors, such as reduced width of the intercondylar notch,⁴ Q angle,⁵ volume of the ACL,⁶ height of the lateral meniscus,⁷ width of the femoral diaphysis,⁸ muscle tone,⁹ and sex differences.¹⁰

Although some studies in the literature have reported that patella position (for both patella alta and baja) in the knee joint is also a risk factor for ACL tears,^9,11no consensus could be suggested on the IS index in these studies. Singerman et al.¹² reported that patella baja further reduced contact stress compared to patella alta. They showed that, in some situations, such as torsion, valgus or varus, as well as flexion and extension of the knee joint, translation is increased to prevent further stress on the patella and femur, which causes strain and tear in the ACL. When the patellar tendon lengthens (high IS index), it places a load on the quadriceps tendon and reduces its strength, leading to ACL injury as a result of increased anterior tibial translation (ATT).¹³

The Insall–Salvati (IS) index is an easily applied method in clinical practice. The IS index can also be measured by MRI and computed tomography (CT), as well as radiographic measurement. MRI, as one of these radiological imaging methods, has been reported to be more reliable than other techniques, since it can display patellar length (PL), patellar tendon length (PTL), and patellotrochlear cartilage more clearly.^14,15 In addition, the IS index was found to be the most reliable method for measuring patella height.¹⁶

In the present study, we aimed to evaluate whether the patellar height is a predictive risk factor in ACL tears by measuring the IS index in the preoperative knee MRIs of patients in the study group that underwent arthroscopic-guided ACL reconstruction and patients in the control group without ACL tears. To the best of our knowledge, this is the first study in the literature to examine the relationship between ACL tears and the IS index by evaluating MRIs only in men.

Methods

A total of 120 patients in the study group who underwent arthroscopic-guided ACL reconstruction using a hamstring graft and a total of 90 patients in the control group without ACL tears who were operated on for pathologies besides ACL tears between January 2014 and January 2020 were comparatively analyzed. Preoperative knee MRIs were examined, and PL, PTL, and IS index were comparatively measured by a radiologist experienced in reading images of the musculoskeletal system in both study groups. The ATT of the study and control groups was also measured on MRI.

The IS index reference interval was accepted as 0.8–1.2, according to the literature. Index values below 0.8 and over 1.2 were evaluated as patella baja and patella alta, respectively.¹⁷ The ATT sign was positive when the ATT distance was more than 5 mm.¹⁸

Patient selection

Study group

Patients who underwent arthroscopic interventions due to full-thickness ACL tears and whose skeletal maturation was completed were included in the study per the eligibility criteria. In addition, patients whose IS index measurements were made on these images with preoperative MRIs were included in the study.

Exclusion criteria were patients who had any additional bone, ligament or cartilage injury; moderate or severe knee arthrosis; and a history of previous surgery. In addition, patients with fractures, bipartite patella, patellar dislocation, multiple ligament injuries, previous ACL surgery, patellar tendon elongation, and preoperative MRI images were excluded from the study.

There were two female patients who underwent ACL reconstruction and were excluded from our study. One of them had multiple ligament injuries, and the other was excluded from the study due to the homogeneity of our study. As a consequence, a total of 120 male patients met the inclusion criteria of the study.

Control group

Our hospital records included the data of the patients operated on for non-ACL tears, for reasons such as meniscopathy, synovial hypertrophy, chondral injury, and plica. The control group was comprised of 90 patients after the exclusion of female patients, patients with osteoarthritis, and patients without available preoperative MRIs from the study. In addition, patients with a history of previous patellar fracture were excluded from the study.

MRI protocol

The images were acquired with a 1.5 T MRI device (MagnetomAmira, Siemens Medical Systems, Forcheim, Germany) using lower extremity coils. The standard knee MRI protocol was implemented in all the patients, and IV contrast agent was not administered.

Protocol: The MRI protocol included axial proton density-weighted, sagittal fat-suppressed T2-weighted, sagittal T1-weighted, and coronal and sagittal proton density-weighted sequences parallel to the ACL plane.

The evaluation of the images

All the acquired images were read by a radiologist experienced in reading images of the musculoskeletal system. The measurements were performed in the midsagittal plane in the sagittal T1-weighted images, since the maximum lengths of the patella and patellar tendon can be acquired in the midsagittal plane and insertions of the patellar tendon into the tibia and patella can be distinguished most optimally in the non–fat-suppressed T1-weighted sequences. The length measurements were obtained using standard measurement calipers in the PACS software of our hospital.

Insall–Salvati index and anterior tibial translation measurement

The PTL was measured from the deep posterior surface of the lower tip of the patella to the tibial tubercle in the MRI. The PL was defined as the greatest diagonal length of the patella. The IS index is the ratio of PTL/PL (Figure 1).

Figure 1.

Insall–Salvati index is calculated by the PTL/PL ratio.

Anterior tibial translationATT distance measurement was performed on a sagittal T1-weighted image in the midsagittal plane of the lateral femoral condyle. The distance between two parallel lines drawn from the posterior cortex of the lateral condyle of the femur and the posterior cortex of the tibia lateral plateau was defined as ATT. The lines were drawn in the cephalocaudal direction, parallel to the long axis of the image to the lateral plateau plane of the tibia (Figure 2).¹⁹

Figure 2.

ATT is measured distance from the posterior border of the medial tibial condyle to the femoral condyle.

Statistical Analysis: Mean, standard deviation, median minimum and maximum, frequency, and percentage values were used in the descriptive analysis of the study data. The distribution normality of the variables was tested by the Kolmogorov–Smirnov test. The quantitative independent data were analyzed using the independent samples t-test and Mann–Whitney U test. The analysis of the qualitative independent data was performed by the chi-square test, while Fisher’s exact test was utilized when the conditions for the chi-square test were not met. The statistical analysis was performed using SPSS software version 26.0. The statistical significance level was accepted as p < 0.05 for all statistical analyses. The sample size was planned to have at least 80 patients in each group, and the power analysis was calculated accordingly. Using the G Power statistics program, according to the results obtained for n = 80 observations for the control (n1) and study (n2) groups, power was calculated as 88%, type-1 error was 5% and effect size was 0.5. However, in order to secure the sample size and keep the power value high, the sample size was increased, and n1 = 90 patients and n2 = 120 patients was used in our study. According to the number of samples, the power (power of the test) increased to 95%.

Results

The mean ages of the 120 patients in the study group and 90 patients in the control group were 29.0 (29.1 ± 8.2) years and 28.0 (31.8 ± 9.8) years, respectively. The study group consisted of 66 right knees and 54 left knees, while the control group consisted of 51 right knees and 39 left knees. There was no statistically significant difference between age and side of involvement in both groups (p = 0.084 and p = 0.810, respectively). The demographic data of the patients are presented in Table 1.

Table 1.

Demographic data of the patients.

		Control group		Study group		p
		Mean±SD/n-%	Median	Mean±SD/n-%	Median	p
Age		31.8 ± 9.8	28.0	29.1 ± 8.2	29	0.084^m
Side	Right	51	56.7%	66	55.0%	0.810^X2
Side	Left	39	43.3%	54	45.0%	0.810^X2
PTL		40.9 ± 4.9	40.9	43.5 ± 5.6	43.4	0.001^t
PL		42.5 ± 3.6	42.4	43.6 ± 3.0	43.5	0.016^t
IS index		0.96 ± 0.14	0.92	1.01 ± 0.15	1.0	0.009^m
ATT		3.80 ± 1.92	3.50	8.61 ± 4.68	8.43	0.001^t

^tt-test/^mMann–Whitney U test/^X2Chi-Square test.

According to Table 1; PL, PTL, and IS index values of the study group were statistically significantly higher than those in the control group (p = 0.016, p = 0.001, and p = 0.009, respectively). These comparisons are shown in Figures 3, 4, and 5.

Figure 3.

The comparison between the group with ACL tear and control group in terms of patellar length.

Figure 4.

The comparison between the group with ACL tear and control group in terms of patellar tendon length.

Figure 5.

The comparison between the group with ACL tear and control group in terms of IS index.

When the ATT results of both groups were evaluated, it was found that the ATT of the study group was significantly higher than that in the control group (p = 0.001) (Table 1).

Discussion

In our study, the IS index values were found to be 1.01 ± 0.15 and 0.96 ± 0.14 in the study group (with ACL tears) and control group (without ACL tears), respectively. Akgün et al.²⁰ detected a mean IS index of 1.11 ± 0.08 vs 1.08 ± 0.06 in similar study and control groups, respectively, and observed that the mean IS index value of the study group was statistically significantly higher than that in the control group. The PTL value was also found to be higher in the study group (with ACL tears), similarly to our study. In that study, sagittal knee MRIs were retrospectively evaluated, and a comparison was performed between the groups with and without ACL tears. A study that compared the findings of ACL tears obtained by MRI with arthroscopic findings determined that the sensitivity and specificity values of MRI for ACL tears were 77.8% and 93–96%, respectively.²¹ The difference in our study compared with the study of Akgün et al.²⁰ was that all the cases were included in our study after arthroscopic confirmation.

Many predisposing factors have been suggested for ACL tears. The well-documented morphological risk factors for the knee include narrowing of the intercondylar notch, sagittal changes in femoral condyles, increased tibial slope, decreased size of tibial eminence, weak tibiofemoral compliance, and decreased volume of the ACL and IS index.^11,22 It has also been reported that increased ATT is associated with ACL tears. We found that ATT was higher in the study group in relation to the IS index.²³

In our study, the ATT was 8.61 ± 4.68 mm in the study group and 3.80 ± 1.92 mm in the control group. Numkarunarunrote et al.²³ found that the length of ATT was 1.5 ± 3.6 mm in individuals with an intact ACL, 5.0 ± 2.8 mm in patients with partial ACL tears and 7.6 ± 3.0 mm in patients with complete ACL tears. In another study, it was reported that quadriceps/hamstring imbalance and the tendency to lengthen the hamstring muscles may cause ACL tears as a result of increased ATT.²⁴ In individuals with high patella, it causes a load on the quadriceps and a decrease in its strength. In addition, ACL tears may occur secondary to decreased tibial support and increased ATT in relation to the PTL.

In the literature, there are studies that have been performed with X-rays and MRIs based on the measurement technique of the IS index.²⁵ Verhuslt¹⁶ emphasized that the IS index was better in conventional radiography in a study he conducted with MRI, conventional radiography, and CT. Miller²⁶ stated that MRI was more valuable in measuring the IS index, independent of knee flexion. Additionally, Shabshin et al.²⁷ emphasized that knee MRI gave less erroneous images and was partly more efficient in measuring PTL. The major advantages of MRI include measurement of patellar height (particularly by sagittal MRI), displaying patellofemoral joint cartilage, better visualization of additional soft tissue injuries, and viewing patellotrochlear cartilage overlap, which is clinically more frequently associated with patella alta.²⁸

Female and male gender were usually evaluated together in the studies that addressed the fact whether the IS index may be a predisposing factor for ACL tears in the literature.^9,11,20 It has been noted that the incidence of ACL tears increased due to a partial increase in the laxity of the ACL, resulting from the changes in the estrogen levels caused by the menstrual cycle in women.²⁹ It has been reported that the mean values of the IS index were higher in females than in males,⁹ and the morphology of the intercondylar notch, valgus alignment, shorter flexion range of motion, and increased quadriceps activity also increase the risk for ACL tears.^30,31 All the groups (study and control) included only male patients in our study; thereby, the aspect of gender difference was completely eliminated. Our study may be considered as a different study with this same characteristic.

Degnan et al.¹¹found statistically significantly higher IS index values in the group with ACL tears compared with those in the group without ACL tears in their study carried out in a pediatric patient population (p < 0.001). In the study by Degnan et al., the IS index values were statistically higher in the group with ACL tears, similarly to our study. Degnan et al.¹¹ determined statistically significantly higher PTL values in the group with ACL tears (p < 0.001), whereas the evaluated PL values were statistically insignificant (p = 0.523). Additionally, the diagnostic MRI findings were arthroscopically confirmed in all patients. This study was different from our study, since it was carried out in a pediatric population with a smaller number of patients. It has been noted in the literature review that traction apophysitis (Sinding–Larsen–Johannson disease) located on the inferior pole of the patella in adolescent children may lead to confusion in MRI.^32,33

Lin et al.⁹ conducted an evaluation based on X-rays in 2005 and reported that the IS index was lower in the group with ACL tears. Thus, patella infera is a predisposing risk factor. The patella and patellar tendon can be evaluated more optimally by MRI. More accurate measurements can be obtained, since the patellar tendon is visualized directly.¹¹ In our study, the measurements of all the patients were performed based on MRIs, and it was concluded that patella alta may be a risk factor, in contrast to the study of Lin.

Limitations

The number of patients in the study group may be considered to be relatively small. However, Lin et al.⁹ and Akgün et al.²⁰ carried out their studies on 115 patients and 110 patients with ACL tears, respectively. Another study by Degnan et al.¹¹ was conducted on 34 patients. Therefore, the number of our cases may be considered higher than the other studies mentioned that measured the IS index. On the other hand, arthroscopic confirmation of ACL tears in the patients, as well as MRI findings, was the strong feature of our study. The lack of an evaluation related with the time interval between the occurrence (acute or chronic) and reconstruction of the ACL may be considered another limitation of our study. Some of the patients included in our study were athletes, and some of them were young individuals who did not do active sports. If all individuals included in the study were professional athletes, perhaps more homogeneity could have been achieved. A novel study can be conducted to determine how this time interval affects the IS index to provide a contribution to the literature. Another limitation of our study may be the absence of measurement of the body mass index (BMI). Some studies have reported that an elevated BMI is a risk factor for ACL tears.^2,34 There was no obesity in any of the patients in our study.

In our study, there was a higher IS index value in patients with ACL tears compared to those without ACL tears. It should be kept in mind that patella alta may play a role in the etiology of ACL tears as one of the factors of knee morphology associated with ACL tears. The determination of such factors, performing hamstring strengthening exercises and testing adductor and abductor balance may reduce the probability of ACL tears with respect to seasonal competition, particularly in the subjects with sports activities. The regular muscle strengthening exercises in the subjects detected to have high IS index values allows these subjects to keep performing sports activities, as well as prevents the negative psychosocial impacts on these subjects due to ACL tears.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical approval

Our study was approved by the Non-invasive Research Local Ethics Committee (approval dated 10/07/2020 and No: 2020/04–31)

ORCID iD

Necip GÜVEN

References

Griffin

Albohm

Arendt

, et al. Understanding and preventing noncontact anterior cruciate ligament injuries. Am J Sports Med 2006; 34(9): 1512–1532.

Acevedo

Rivera-Vega

Miranda

, et al. Anterior cruciate ligament injury. Curr Sports Med Rep 2014; 13(3): 186–191.

Boden

Dean

Feagin

Jr , et al. Mechanisms of anterior cruciate ligament injury. Orthopedics 2000; 23(6): 573–578.

Zeng

Gao

S-g

Wei

, et al. The influence of the intercondylar notch dimensions on injury of the anterior cruciate ligament: a meta-analysis. Knee Surg Sports Traumatol Arthrosc 2013; 21(4): 804–815.

Kızılgöz

Sivrioğlu

Ulusoy

, et al. Analysis of the risk factors for anterior cruciate ligament injury: an investigation of structural tendencies. Clin Imaging 2018; 50: 20–30.

Everhart

Flanigan

Simon

, et al. Association of noncontact anterior cruciate ligament injury with presence and thickness of a bony ridge on the anteromedial aspect of the femoral intercondylar notch. Am J Sports Med 2010; 38(8): 1667–1673.

Sturnick

Vacek

DeSarno

, et al. Combined anatomic factors predicting risk of anterior cruciate ligament injury for males and females. Am J Sports Med 2015; 43(4): 839–847.

Vasta

Andrade

Pereira

, et al. Bone morphology and morphometry of the lateral femoral condyle is a risk factor for ACL injury. Knee Surg Sports Traumatol Arthrosc 2018; 26(9): 2817–2825.

Lin

C-FJ

J-J

Chen

T-S

, et al. Comparison of the Insall-Salvati ratio of the patella in patients with and without an ACL tear. Knee Surg Sports Traumatol Arthrosc 2005; 13(1): 8–11.

10.

Lin

CY.

Casey

Herman

, et al. Sex differences in common sports injuries. PM&R 2018; 10(10): 1073–1082.

11.

Degnan

Maldjian

Adam

, et al. Comparison of Insall-Salvati ratios in children with an acute anterior cruciate ligament tear and a matched control population. Am J Roentgenology 2015; 204(1): 161–166.

12.

Singerman

Davy

Goldberg

. Effects of patella alta and patella infera on patellofemoral contact forces. J Biomech 1994; 27(8): 1059–1065.

13.

DeMorat

Weinhold

Blackburn

, et al. Aggressive quadriceps loading can induce noncontact anterior cruciate ligament injury. Am J Sports Med 2004; 32(2): 477–483.

14.

Park

Chung

Lee

, et al.

Which is the best method to determine the patellar height in children and adolescents?

Clin Orthopaedics Relat Res 2010; 468(5): 1344–1351.

15.

Diederichs

Issever

Scheffler

. MR imaging of patellar instability: injury patterns and assessment of risk factors. Radiographics 2010; 30(4): 961–981.

16.

Verhulst

van Sambeeck

JDP

Olthuis

, et al. Patellar height measurements: Insall-Salvati ratio is most reliable method. Knee Surg Sports Traumatol Arthrosc 2020; 28(3): 869–875.

17.

Biedert

Tscholl

. Patella alta: a comprehensive review of current knowledge. Am Journal Orthopedics (Belle Mead, N.J.) 2017; 46(6): 290–300.

18.

Chan

Peterfy

Fritz

, et al. MR diagnosis of complete tears of the anterior cruciate ligament of the knee: importance of anterior subluxation of the tibia. Am J Roentgenology 1994; 162(2): 355–360.

19.

Vahey

Hunt

Shelbourne

. Anterior translocation of the tibia at MR imaging: a secondary sign of anterior cruciate ligament tear. Radiology 1993; 187: 817–819.

20.

Akgün

Agirman

. Associations between Anterior Cruciate Ligament Injuries and Patella Alta and Trochlear Dysplasia in Adults Using Magnetic Resonance Imaging. J Knee Surg 2020; 34: 1220–1226. DOI: 10.1055/s-0040-1702198.

21.

Behairy

Dorgham

Khaled

. Accuracy of routine magnetic resonance imaging in meniscal and ligamentous injuries of the knee: comparison with arthroscopy. Int Orthopaedics 2009; 33(4): 961–967.

22.

Bayer

Meredith

Wilson

, et al. Knee Morphological Risk Factors for Anterior Cruciate Ligament Injury. J Bone Jt Surg 2020; 102(8): 703–718.

23.

Numkarunarunrote

Chaitusaney

. Anterior tibial translation sign: factors affecting interpretation of anterior cruciate ligament tear. J Med Assoc Thailand = Chotmaihet Thangphaet 2015; 98(Suppl 1): S57–S62.

24.

Schneider

Arias

Bankhead

, et al. Greater medial tibial slope is associated with increased anterior tibial translation in females with an ACL-deficient knee. Knee Surg Sports Traumatol Arthrosc 2020; 28(6): 1901–1908.

25.

Lee

Chalian

Carrino

, et al. Multimodality correlations of patellar height measurement on X-ray, CT, and MRI. Skeletal Radiol 2012; 41(10): 1309–1314.

26.

Miller

Staron

Feldman

. Patellar height on sagittal MR imaging of the knee. Am J Roentgenology 1996; 167(2): 339–341.

27.

Shabshin

Schweitzer

Morrison

, et al. MRI criteria for patella alta and baja. Skeletal Radiology 2004; 33(8): 445–450.

28.

Steensen

Bentley

Trinh

, et al. The Prevalence and Combined Prevalences of Anatomic Factors Associated With Recurrent Patellar Dislocation. Am J Sports Med 2015; 43(4): 921–927.

29.

Charlton

WPH

Coslett-Charlton

Ciccotti

. Correlation of estradiol in pregnancy and anterior cruciate ligament laxity. Clin Orthopaedics Relat Res 2001; 387: 165–170.

30.

Fayad

Parellada

Parker

, et al.

MR imaging of anterior cruciate ligament tears: is there a gender gap?

Skeletal Radiol 2003; 32(11): 639–646.

31.

Colby

Francisco

Bing

, et al. Electromyographic and Kinematic Analysis of Cutting Maneuvers. Am J Sports Med 2000; 28(2): 234–240.

32.

Davis

. Imaging pediatric sports injuries: lower extremity. Radiologic Clin North America 2010; 48(6): 1213–1235.

33.

Leschied

Udager

. Imaging of the pediatric knee. Semin Musculoskeletal Radiology 2017; 21(2): 137–146.

34.

LaBella

Hennrikus

Hewett

, et al. Anterior cruciate ligament injuries: diagnosis, treatment, and prevention. Pediatrics 2014; 133(5): e1437–e1450.

Insall–Salvati index is associated with anterior cruciate ligament tears in men: A Case-controlled study

Abstract

Purpose

Methods

Results

Conclusions

Keywords

Introduction

Methods

Patient selection

Study group

Control group

MRI protocol

The evaluation of the images

Insall–Salvati index and anterior tibial translation measurement

Results

Discussion

Limitations

Footnotes

Declaration of conflicting interests

Funding

Ethical approval

ORCID iD

References