Keywords
anterior cruciate ligament - arthroscopy - knee - magnetic resonance imaging - meniscus
Introduction
In contemporary times, injuries to the knee joint resulting from road traffic accidents
and sports activities are ubiquitous.[1] These injuries typically involve the ligaments and meniscus of the knee, disrupting
the stability and normal biomechanics of the joint and hindering routine daily activity.
Hence, prompt and precise diagnosis and management of such injuries are imperative.
Among the common knee injuries are anterior cruciate ligament (ACL) or combined ACL
and posterior cruciate ligament (PCL) injuries. Initially, in the late 1960s and early
1970s, orthopedic surgeons solely relied on clinical examination until numerous reports
suggested the efficacy of arthroscopy in diagnosing and treating various knee disorders.[2] The advent of magnetic resonance imaging (MRI) has revolutionized the diagnosis
and management of ACL and meniscal tears of the knee, making arthroscopy less necessary.
This study aims to evaluate the radiological and arthroscopic findings of the anterior
and posterior cruciate ligaments, correlate the outcomes of both techniques, and determine
which method is superior in accurately diagnosing ACL and PCL injuries.
Methods
The study was approved by the institutional ethics committee number ECR/1092/Inst/KA/2018.
A prospective study was undertaken on a cohort of 200 individuals who were admitted
to a tertiary health care center with knee injuries arising from diverse etiologies
and who satisfied the inclusion criteria. The study was conducted over a period spanning
from November 2019 to November 2022.
Inclusion Criteria
-
Patients aged between 18 and 60 years.
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Patients with positive MRI findings indicating ACL, PCL, or both injuries.
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Patients who subsequently underwent arthroscopy for further evaluation and treatment.
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Patients with confirmed ACL, PCL, or both injuries based on arthroscopic examination,
utilizing the routine method described below.
Routine Arthroscopy Method
The routine arthroscopy method involved the use of anteromedial and lateral portals.
Careful probing of the posterior cruciate ligament (PCL) was conducted to assess for
laxity or lesions. In cases in which PCL issues were suspected based on clinical examination
or preoperative MRI scans, the posteromedial portal was consistently employed during
arthroscopic examination to confirm these findings and ensure a comprehensive evaluation
of the PCL. The utilization of the posteromedial portal allowed for a more thorough
assessment and characterization of PCL injuries identified through clinical examination
or preoperative imaging.
By incorporating the routine arthroscopy method into the inclusion criteria, the paper
provides clarity on the methodology used in the study, ensuring that patients with
positive MRI findings underwent arthroscopy following a specific routine that includes
the use of the anteromedial and lateral portals, as well as the potential use of the
posteromedial portal for comprehensive evaluation of PCL injuries.
Exclusion Criteria
-
Patients with contraindications to MRI, such as having intracerebral aneurysmal clips,
cardiac pacemakers, metallic foreign bodies in the eye, or implants in the middle
ear.
-
Patients who have had a recent knee injury but, upon clinical examination, exhibit
no instability.
-
Patients who are deemed unfit for anesthesia.
Methodology
Following the elicitation of medical history, a comprehensive clinical examination
was conducted, wherein various tests were performed to assess the extent of knee injury.
Specifically, the Lachman and anterior drawer tests were employed to evaluate the
anterior cruciate ligament (ACL) injury, whereas the Godfrey sag sign and posterior
drawer tests were employed to evaluate the posterior cruciate ligament (PCL) injuries.
Magnetic resonance imaging (MRI) was then performed using the 1.5 Tesla MR protocol
on a General Electric Healthcare Company (GE Signa Voyager 1.5T, Waukesha, Wisconsin,
USA) 1.5 T MRI machine. T1 and T2 weighted sequences were performed on axial, coronal,
and sagittal planes. The MR films were meticulously assessed by a highly skilled radiologist,
who carefully documented the status of the cruciate ligaments.
Subsequently, arthroscopic surgery was performed under spinal anesthesia, with the
patient placed in a supine position, with lateral support to the proximal thigh. A
proximal thigh tourniquet was utilized for each case. The operating surgeon was not
apprised of the MRI findings.
The acquired data were analyzed using the sophisticated statistical tool SPSS software
Statistics 28.0, IBM Corporation (Armonk, New York, USA). Continuous variables were
analyzed by computing the sensitivity, specificity, positive predictive value (PPV),
and negative predictive value (NPV). A P-value lower than 0.05 was deemed statistically significant.
To ascertain the sensitivity, specificity, and accuracy of magnetic resonance imaging
(MRI), the outcomes obtained through arthroscopic examination were considered to represent
the true diagnosis. Sensitivity, which represents the ability of the MRI to identify
individuals with the condition, was computed as the ratio of true positive results
to the sum of true positive and false negative results.
Specificity, which reflects the MRI's capacity to accurately identify those without
the condition, was determined as the ratio of true negative results to the sum of
true negative and false positive results.
Accuracy, which represents the overall ability of the MRI to identify both positive
and negative cases correctly, was calculated as the summation of true positive and
true negative results divided by the total number of patients who underwent arthroscopy.
The combined data was meticulously compiled and categorized into four distinct groups,
based on their correlation with the MRI findings. These categories included the following:
First, the true-positive result signified instances in which the MRI diagnosis was
accurately confirmed by arthroscopy.
Second, the true-negative result, which pertained to cases in which the MRI yielded
a negative finding for the lesion, and this was corroborated by the arthroscopic examination.
Third, the false-positive result, which represented situations in which the MRI indicated
the presence of a lesion, but arthroscopy failed to confirm its existence.
Lastly, the false-negative result, which referred to cases in which arthroscopy detected
the presence of the lesion, but the MRI failed to reveal any indication of it.
Results
A total of 200 patients who exhibited traumatic ACL and PCL injuries were carefully
identified and examined through a retrospective and prospective approach, wherein
MRI evaluation was followed by arthroscopic surgery. Specifically, patients who demonstrated
suspected ACL and PCL injuries and fulfilled the predetermined inclusion criteria
were carefully selected for inclusion in the study.
Notably, individuals who displayed degenerative changes or evidence of loose bodies
in plain radiographs, those who were deemed unfit for anesthesia, and those who had
undergone non-operative treatments were all carefully excluded from the study to ensure
its validity.
The collected data was meticulously analyzed to determine the true positives, true
negatives, false positives, and false negatives associated with the study. Using specificity
and sensitivity measures, PPV and NPV were then calculated with the aid of arthroscopic
examination, which served as the gold standard for comparison.
Age Distribution
This study was conducted on patients aged 18 to 60, with a mean age of 35.7 years
at admission.
The highest frequency and percentage are observed in the 20-to-24 age group with 60
individuals, which accounts for 30% of the total sample. The remaining age groups
range from 7 to 13% in frequency and 4 to 6% in percentage.
Mode of Injury
Road traffic accidents were our study's most common mode of injury, accounting for
∼ 60%.
Anterior Cruciate Ligament
Sensitivity: TP / (TP + FN) = 138 / (138 + 16) = 0.896 or 89.6%
Specificity: TN / (TN + FP) = 37 / (37 + 9) = 0.804 or 80.4%
PPV: TP / (TP + FP) = 138 / (138 + 9) = 0.939 or 93.9%
NPV: TN / (TN + FN) = 37 / (37 + 16) = 0.698 or 69.8%
Accuracy: (TP + TN) / (TP + TN + FP + FN) = (138 + 37) / 200 = 0.875 or 87.5%
Therefore, the MRI test has a high sensitivity (89.6%), indicating that it correctly
identifies the majority of arthroscopically positive cases, but a lower specificity
(80.4%), indicating that it also identifies some arthroscopically negative cases as
positive. The PPV of the test is high (93.9%), meaning that if the MRI test is positive,
there is a high probability that the patient is truly arthroscopically positive. However,
the NPV is lower (69.8%), indicating that if the MRI test is negative, there is still
a significant probability that the patient is arthroscopically positive. Overall,
the MRI test has an accuracy of 87.5%, which is relatively good but not perfect.
Posterior Cruciate Ligament
Sensitivity: TP / (TP + FN) = 45 / (45 + 15) = 0.75 or 75%
Specificity: TN / (TN + FP) = 123 / (123 + 17) = 0.878 or 87.8%
PPV: TP / (TP + FP) = 45 / (45 + 17) = 0.726 or 72.6%
NPV: TN / (TN + FN) = 123 / (123 + 15) = 0.891 or 89.1%
Accuracy: (TP + TN) / (TP + TN + FP + FN) = (45 + 123) / 200 = 0.84 or 84%
Therefore, the MRI test has a sensitivity of 75%, indicating that it correctly identifies
75% of arthroscopically positive cases. The specificity is higher at 87.8%, indicating
that it correctly identifies a higher proportion of arthroscopically negative cases.
The PPV is 72.6%, meaning that if the MRI test is positive, there is a 72.6% probability
that the patient is truly arthroscopically positive. The NPV is higher at 89.1%, indicating
that if the MRI test is negative, there is a higher probability that the patient is
truly arthroscopically negative. Overall, the MRI test has an accuracy of 84%, which
is moderately good but not perfect.
Discussion
The knee joint's MRI scan is considered an efficacious non-invasive diagnostic tool
and a preferred alternative to diagnostic arthroscopy. In current clinical practice,
MRI scans are routinely performed to confirm the diagnosis of anterior cruciate ligament
(ACL) and posterior cruciate ligament (PCL) injuries. Nonetheless, discerning partial
tears may pose challenges and vary based on the observer and the scanner's sensitivity.
The current study aims to compare and correlate the MRI and arthroscopic findings
in diagnosing ACL and PCL injuries. The study cohort encompassed individuals aged
18 to 60 years, with the youngest male patient being 18 years old, and the oldest
female being 60 years old. Males were more prone to knee injuries and underwent surgery
at a younger age, primarily due to their active involvement in sports. Furthermore,
the right knee was more commonly injured than the left.[3]
Prior studies have reported high sensitivity and specificity in diagnosing ACL tears
using MRI scans. Rubin et al.[4] reported 93% sensitivity for diagnosing isolated ACL tears. A sensitivity of 92
to 100% and specificity of 93–100% for the MR imaging diagnosis of ACL tears has been
reported by similar studies in the past.[5] The current study attested to a sensitivity of 90.90% and a specificity of 78.26%
for MRI in diagnosing ACL tears, displaying a fair correlation with arthroscopy. The
accuracy of MRI in detecting ACL tears was 88%, categorizing it in the “very good”
interpretation group (80–90%). The results were consistent with prior literature,
suggesting an 80-to-94% accuracy range in detecting crucial ligament tears. The PPV
of MRI was 93.33%, whereas the NPV was 72%.
The interpretation of MRI results is highly reliant on the experience and training
of the radiologist.[6]
[7]
[8] Arthroscopy serves as the reference point in most knee MRI studies owing to its
technical demands, and the results are subject to the surgeon's experience, primarily
in challenging cases. Magnetic resonance imaging remains the quintessential diagnostic
tool for ACL and PCL injuries, with reported accuracy ranging from 70 to 100%.[9] However, arthroscopy should be considered an adjunct to a comprehensive clinical
examination, including a thorough history, physical examination, and appropriate radiographs.
Surgical alternatives are thoroughly discussed with the patient before the procedure,
and the definitive surgical procedure is performed during an arthroscopic examination.
Several studies have validated the utility of MRI scans in diagnosing ACL and PCL
injuries. Despite the observer variability in interpreting MRI results, it remains
an indispensable diagnostic tool in current clinical practice.[10] Arthroscopy, however, should be used in conjunction with a comprehensive clinical
examination, providing a definitive diagnosis and treatment plan for patients.
Conclusion
Our research has conclusively demonstrated that MRI is an exceedingly reliable tool
in the diagnosis of ACL and PCL injuries in the knee joint. The sensitivity, specificity,
and overall accuracy of MRI are exceptionally high, thus affirming its indispensable
role in identifying such injuries. As such, it is an ideal screening tool, rendering
diagnostic arthroscopy unnecessary for diagnosis in the vast majority of patients.
Notably, MRI is both accurate and non-invasive, making it an optimal modality for
assessing ligamentous injuries. In light of these findings, we conclude that MRI should
be the first-line investigation for patients presenting with a knee injury, in whom
ligamentous injury is suspected.
