Delivering a comprehensive knee assessment in athletes

Clínica CEMTRO, a leading healthcare provider in Madrid, Spain, performs over 13,000 surgeries and receives over 41,000 traumatological emergencies annually. Since its inception in 1998, the center has been at the forefront of innovation with the development of a wireless arthroscope and the pioneering development of cultured chondrocytes for joint repair. Clínica CEMTRO is an official FIFA Medical Centre of Excellence.

Complex cases that require a fast and accurate diagnosis are often referred to Clínica CEMTRO for optimal treatment and management. Anterior cruciate ligament (ACL) injuries are common and often result in instability. They may be caused by direct or indirect trauma, in which the most frequent mechanism is "noncontact," involving cutting, twisting, jumping and sudden deceleration1,2.

Meniscal tears occur frequently in the setting of ACL lesions, with rates reported as high as 79% after an acute injury3. Medial meniscal injuries are particularly concerning, as the posterior horn of the medial meniscus has been shown to be an important secondary stabilizer against anterior tibial translation4,5.

The ability to visualize these soft tissue lesions with MR imaging makes it a vital tool for determining treatment and the athlete’s return to sports activity. However, re-scans and patient call-backs due to suboptimal resolution, motion artifacts or incorrect patient positioning can impact the clinical service.

Patient history

A 19-year-old male athlete presents at the emergency room with an acute traumatic knee injury and instability after twisting his knee. Knee X-ray is normal with no fractures. A follow up MR exam was prescribed to exclude internal derangements of the knee.

Fortunately, the field of MR research and development is actively exploring alternatives to conventional MR reconstruction to address the tradeoffs between spatial resolution, SNR and scan time. AIR™ Recon DL, a novel deep-learning-based reconstruction algorithm, is a breakthrough that allows users to alleviate the delicate balance between these factors, saving time per exam with minimal impact on image quality, boosting SNR and reducing ringing artifacts6,7. AIR x™ Knee uses a trained, deep-learning algorithm to automatically detect and prescribe the acquisition slices for routine and challenging knee exams, delivering consistent and quantifiable results. The automated workflow optimizes technologist efficiency and reproducible planning to ensure exam consistency for a patient follow-up. Finally, oZTEo is a 3D radial acquisition that enables visualization of the cortical bone and gray soft-tissue background.

Technique

The MR study was performed on a SIGNA™ Voyager AIR™ IQ Edition 1.5T with a 16-channel knee T/R coil. This MR system includes AIR x™ Knee and AIR™ Recon DL, making it easier for each technologist to consistently achieve the desired image quality in the first scan.

In order to evaluate the potential impact of these technologies on a challenging patient, two different acquisition protocols – a high resolution and a fast protocol exam – were performed in this study (Table 1 and Figure 1).

In the fast protocol, a total scan time reduction of 65% was achieved (from 17 minutes to 6 minutes) without affecting diagnostic accuracy and image quality, according to Dr. Padrón.

"Both exams enable a proper diagnosis at the same degree of detail. This a great advantage for the clinical workflow, since it allows us to perform fast and accurate exams in urgent situations despite the MR system having a tight schedule. Moreover, AIR x™ Knee helps increase productivity by automating many manual steps, thus significantly reducing the time the technologist spends performing slice positioning," he says.

In addition, a Cartigram (T2 map) sequence is included in the protocol (Table 2) to assess the biochemical changes of the injured menisci in the affected condyle. Although validation studies of meniscal T2 mapping are limited, for this particular case study an independent assessment of the status of the menisci from a biochemical standpoint was conducted to determine if it was in accordance with the visual findings on the other MR sequences.

T2 values are sensitive to interactions between water molecules and the macromolecular concentration and structure of the extracellular matrix, which are based on the content, orientation and anisotropy of collagen. Therefore, tissue abnormalities translate into changes of the T2 values9.

By using GE Healthcare’s READYView advanced MR visualization platform, the Cartigram sequence can be directly post-processed on the MR operator console to generate the corresponding color-coded T2 maps (Figure 5).

The acquisition protocol was amended with the oZTEo sequence (Table 3) to explore the added value of MR bone imaging data in acute knee injury cases. oZTEo is based on a zero TE (ZTE) sequence, which samples the MR signal before any T2-relaxation decay occurs, making it particularly useful for very short T2 tissues, such as cortical bone that usually appears black in conventional MR.

The oZTEo sequence automatically generates an inverse contrast image for a CT-like appearance in which the bone surfaces are rendered bright (Figure 6).

Results

The T2 mapping technique demonstrates increased T2 relaxation times in the posterior horn of the medial meniscus tear (Figure 5B, ROI 1), indicating damage to the collagen network and an increase in water content10,11 in comparison to the low T2 value of the normal meniscus, which is mainly composed of fibrocartilage without any water content (Figure 5B, ROI 2).

oZTEo reveals the lack of discontinuity at the cortical bone, enhancing the subchondral bone sclerosis related to the bone bruises and bone marrow edema pattern seen on conventional MR pulse sequences (Figure 2). After a 3D volume rendering performed on READYView, "we could better appreciate the bone morphology similar to a CT image. Therefore, adding the oZTEo sequence to a conventional MR exam enabled a whole osteoarticular study even when no CT exam is acquired," says Dr. Padrón.

Discussion

Meniscal ramp lesions have important biomechanical consequences and occur more frequently than previously thought. These meniscal lesions remain significantly underdiagnosed and, therefore, are not promptly surgically repaired in standard knee arthroscopies because the diagnosis relies on anterior portals, limiting a full assessment of the posterior horn and attachment of the medial meniscus8.

In this case, the peripheral meniscal lesion must be repaired and the ruptured ACL needs reconstructive surgery to give support and stability back to the knee.

According to Dr. Padrón, as a result of the rapid and precise management of this case with AIR™ Recon DL, AIR x™ Knee and oZTEo, the patient’s prognosis was good. This athlete will likely recover his physical and sports activity after the meniscal suture and ACL replacement with hamstring tendons are performed.

References

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11. Arno S, Bell C, Xia D et al. Relationship between meniscal integrity and risk factors for cartilage degeneration. Knee. 2016;23(4):686-691. doi:10.1016/j.knee.2015.11.004.