The present study is a prospective comparative study conducted on 50 patients of all ages and both sexes for 1.5 years presenting with knee joint pain. After clinical evaluation, once the patient satisfied the inclusion and exclusion criteria for this study, he or she was taken for sonographic evaluation of the knee joint followed by MRI of the affected knee.

The inclusion criteria were patients with history of pain in the knee with or without swelling, patients with clinically suspected tears and patients with restriction of movement at the knee joint following trivial trauma. The exclusion criteria were patients not giving consent, claustrophobic patients, patient with metallic implant and post-operative cases.

50 patients with the complaint of knee joint pain were evaluated using ultrasound, which were further followed by MRI. Maximum patients (18) were in the age group of 21-30 years (36%) followed by below 20 years (22%) and minimum in the age group of above 50 years (12%). Of the 50 cases, 40 (80%) were males and 10 (20%) were females. While evaluating the different knee pathologies on USG and MRI, most common pathology detected on USG was joint effusion in 28 cases (56%) and most common pathology on MRI was ACL tear in 38 cases (76%). Of all the knee ligaments, most commonly involved was ACL.

Table 2

Sex	Number	%
Male	40	80%
Female	10	20%

Table 3

Findings	Frequency On USG (Percentage)	Frequency On MRI (Percentage)
ACL Tear	24 (48%)	38 (76%)
PCL Tear	5 (10%)	8 (16%)
MCL Injury	7 (14%)	6 (12%)
LCL Injury	7 (14%)	8 (16%)
MM Tear	17 (34%)	18 (36%)
LM Tear	14 (28%)	16 (32%)
Joint effusion	28 (56%)	30 (60%)
Soft tissue edema	19 (38%)	22 (44%)
Popliteal cyst	7 (14%)	7 (14%)
Osteoarthritis	6 (12%)	8(16%)

Table 4

Structures	Sensitivity %	Specificity %	PPV %	NPV %	Accuracy %
ACL	57.9%	83.3%	91.6%	38.4%	64%
PCL	50%	97.6%	80%	91.1%	90%
MCL	83%	95.4%	71.4%	97.7%	94%
LCL	75%	97.6%	85.7%	95.3%	94%
MM	83.3%	93.7%	88.2%	90.9%	90%
LM	75%	94.1%	85.7%	88.8%	88%
Joint effusion	93.3%	100%	100%	90.9%	96%
Soft tissue edema	86.3%	100%	100%	90.3%	94%
Popliteal / baker’s cyst	100%	100%	100%	100%	100%
Osteophytes / arthritis	75%	100%	100%	95.4%	96%

Figure 1 Figure 2 Figure 3 Figure 4

MRI is accepted as the gold standard technique for evaluation of various knee pathologies ^{7, 8}. However, in India MRI is not always available on demand especially in small hospitals. It also does not allow dynamic testing and is a rather lengthy and expensive imaging modality. The benefits of ultrasound include portability, low cost, high spatial resolution, dynamic imaging, and ability to guide percutaneous interventions when indicated. USG also allows direct patient contact, facilitating immediate clinical correlation and the ability to compare with the contralateral knee ⁹.

The study included 50 patients. The average age in this study was 33.2 years, with standard deviation of 10.6. The results were similar to study by EL-Monem SA and Enaba MM, whose average age was 28.4 years ¹⁰. Maximum cases were seen in the age range of 21-30 years, which suggest that young adults were more commonly involved in knee pathologies due to sports and athletic activities ¹¹.

The age distribution pattern observed in the present study was also comparable to the study of D S Shetty et al in which commonest age group was 21 to 30 years for both males and females ¹². Singh et al also found that majority of the patients with knee injury were in third decade ¹³.

In the present study, 80% of the patients were male and 20% were female with male to female ratio 4:1. This corresponded with the sex distribution pattern reported in the study by Anil Madurwar et al where authors noted, out of 50 patients of knee trauma examined, 42 patients (76%) were males and 8 of them were females. Similar results were shown by Singh et al ¹³ and D S Shetty et al ¹². This could be explained by the fact that the males are the one who are physically active, engaged in increased various outdoor activities and sports events while females are more vulnerable to meniscal degeneration resulting from weight bearing due to obesity and less involvement in outdoor activities ¹⁴.

In the present study, 25 patients (50%) had injury in the left knee and 25 patients (50%) had injury in the right knee. Thus, both knees were involved equally. This is in contradiction to a study conducted by Amandeep et al where left knee was involved more frequently than right knee.

Most common pathology detected on USG was knee joint effusion in 28 cases (56%) and on MRI was ACL tear in 38 cases (76%).

Effusion was also seen as most common ultrasound finding in other studies by Singh B et al ¹³ and Yousuf et al. Knee effusion is commonly seen in various knee pathologies and can be detected by ultrasound. In our study near perfect agreement was noted between ultrasound and MRI in detection of effusion. Ultrasound also demonstrated sensitivity of 93.3%, specificity of 100%, and accuracy of 96%. Similar sensitivity and specificity of ultrasound was also seen in study by Draghi F et al ¹⁵. In recent study by Singh B et al ¹³ ultrasound showed sensitivity, specificity and accuracy of 100% for detecting knee effusion.

Meniscal lesions are a major cause of knee pain and have adverse effects on the proper functioning of the knee joint. Tears and degenerations constitute the majority of meniscal lesions. In our study, almost substantial agreement was noted between USG and MRI in detection of medial meniscus tears. Ultrasound in comparison to MRI in our study showed a sensitivity of 83.3%, specificity of 93.7% and accuracy of 90%. Unlu EN et al in their study showed moderate agreement between US and MRI in detection of tears ¹⁶. Similarly, in study by Singh A et al sensitivity of ultrasound in detecting medial meniscal tears was 77.7%, specificity was 90.4% and accuracy was 86.6% with MRI as gold standard ¹⁷. However, in study by Ghosh N et al ultrasound showed sensitivity of 100% but lower specificity of 40% as compared to our study ¹⁸.

For detecting lateral meniscus tears substantial agreement was noted between ultrasound and MRI in our study and in study by Unlu EN et al ¹⁶. In our study the sensitivity, specificity and accuracy of ultrasound in detection of lateral meniscal tears were 75%, 94.1% and 88% respectively. Similar results were seen in studies by Singh B et al , Unlu EN et al and Singh A et al who evaluated various knee pathologies on ultrasound and used MRI as gold standard ^{13, 16, 17}.

Collateral ligaments are also commonly injured during sports or traffic injuries. In our study substantial agreement was noted between ultrasound and MRI in detection of medial collateral ligament tear. Ultrasound demonstrated sensitivity of 83%, specificity of 95.4% and accuracy of 94%. Compared to our study Singh B et al and Singh A et al showed sensitivity (83.3% and 84.6%) and similar specificity (97.7% and 98%) and accuracy (96% and 96.6%) of ultrasound for detecting medial collateral ligaments tears ^{13, 17}. Ghosh N et al showed lower sensitivity of 67.0% and specificity of 83.0% for ultrasound in their study ¹⁸. For detecting lateral collateral ligament tear substantial agreement was noted between ultrasound and MRI in our study. Ultrasound also demonstrated sensitivity of 75%, specificity of 97.6% and accuracy of 94% in our study. In study done by Singh B et al sensitivity, specificity and accuracy of USG in diagnosing lateral collateral ligament tears were 84.6%, 97.8% and 95.0% respectively ¹³. Thus ultrasound can be an effective imaging modality for evaluating patients with collateral ligament injuries.

Currently, MRI and arthroscopy are the reference standards for diagnosing an ACL injury. Due to its deep location and oblique orientation, the anterior cruciate ligament is partially visible with ultrasound, thus it is still not possible to directly visualize the complete ACL using sonography ¹⁹. Various direct and indirect methods are described in various studies to look at anterior cruciate ligament. Ultrasound had shown high sensitivity and specificity in diagnosing ACL tear in these studies ^{20, 21, 22}. We used anterior approach to look for anterior cruciate ligament tear. In our study, out of 50 cases, 24 cases were positive by USG, out of which 22 cases proved to be positive by MRI, other 2 were normal. Ultrasound demonstrated sensitivity of 57.9%, specificity of 83.3% and accuracy of 64% in our study. There was fair agreement noted. Compared to our study Sharma VK et al showed only slight agreement between ultrasound and MRI in detecting anterior cruciate ligaments tears ²³. But this was lower as compared to other studies. Attya MSA conducted a study in which he recorded an accuracy of 83.3 %, sensitivity of 81.2% and specificity of 84.2% of USG in diagnosis of ACL injury ²⁴. According to study done by Abdel el Monem S and Enaba MM the sensitivity and specificity of USG for ACL tears was 81% and 84% respectively ²⁵.

Posterior cruciate ligament is depicted on ultrasound by posterior approach. The intermediate and distal portion of posterior cruciate ligament is demonstrated by ultrasound. The proximal portion of this ligament and its insertion into femur cannot be demonstrated ²⁶. We used posterior approach to look at PCL injuries. In present study, the sensitivity, specificity and accuracy of USG in diagnosing PCL tears are 50 %, 97.6 % and 90% and moderate agreement noted between USG and MRI. Compared to our study Sharma VK et al showed moderate agreement between ultrasound and MRI in detecting anterior cruciate ligaments tears ²³. According to Wang C et al., sonographic examination had a sensitivity of 83.3%, a specificity of 87.0% and an accuracy of 85.7% in detecting PCL tears ²⁷. Specificity and accuracy are comparable; however sensitivity is lesser then latter study. Ultrasound showed low sensitivity in our study which is quiet consistent with study done by Singh A et al who showed sensitivity of 33.3% in their study ¹⁷.

For detecting Baker’s cyst ultrasound in our study showed sensitivity, specificity and accuracy of 100%. Perfect agreement was noted between USG and MRI in detecting Baker’s cyst. In study by Singh B et all, Sharma VK et al and Ward EE et al ultrasound showed similar sensitivity, specificity and accuracy of 100% in detecting baker’s cyst ^{13, 23, 28.}

For detecting osteophytes almost perfect agreement was noted between ultrasound and MRI. Ultrasound showed sensitivity of 75%, specificity of 100% and accuracy of 96% for detecting osteophytes compared to MRI as gold standard. Nearly similar results were seen in study by Podlipská, J. et al ²⁹. For detecting soft tissue edema almost perfect agreement was noted between ultrasound and MRI. Ultrasound showed sensitivity of 86.3%, specificity of 100% and accuracy of 94% for detecting soft tissue edema compared to MRI as gold standard.

The present study has a limitation of sample size. We recommend that the study should be done on large number of patients as well as at multiple centers.

Based on our results, it can be concluded that USG is an effective imaging modality that has a positive effect on the management of many patients presenting with knee pain & injuries. Knee USG has high accuracy in diagnosing collateral ligament and meniscal tears. A wide availability, lower cost and better tolerability of USG make it a modality of first choice for evaluation of knee ligamentous and meniscal tears. MRI can be reserved for patients with suspicious USG results. If there is a patient with history of knee trauma and clinical suspicion of cruciate ligaments injuries, we recommend starting with high resolution ultrasound examination as screening tool. For negative examinations, follow up if there is no improvement the second step is MRI examination to rule out cruciate injuries. For positive results MRI examination is recommended to confirm cruciate ligaments injuries and for getting more details. For pathologies like knee joint effusion, synovitis, popliteal cysts, soft tissue edema and arthritic changes, the accuracy of ultrasound is almost comparable to MRI. Hence, USG should be used as first line modality for detecting these modalities.