Preoperative MRI and Intraoperative Arthroscopic Evaluation of Chondral Pathology at the Hip Chondrolabral Junction

Abstract

Background:

Previous literature has found that hip magnetic resonance imaging (MRI) has lower accuracy and reliability in preoperative diagnosis of cartilage and labral pathology compared with knee and shoulder MRI. This is a notable limitation, as MRI findings play a significant role in the determination for surgical intervention in femoroacetabular impingement syndrome (FAIS) and aid in surgical planning, intraoperative cartilage management, and in postoperative rehabilitation expectations.

Indications:

Hip arthroscopy is most commonly utilized for the treatment of FAIS and associated labral tears and chondral pathology of varying grades, particularly at the chondrolabral junction. Given the difficulty in assessing chondrolabral pathology on preoperative MRI, we present our preferred method of correlating MRI to intraoperative findings at the chondrolabral junction.

Technique Description:

Using preoperative MRI and the Outerbridge classification system, we describe our method to assess cartilage injuries and chondrolabral junction pathology in patients who undergo hip arthroscopy for FAIS. We correlate chondral injuries with preoperative MRI to aid surgeons in interpreting the degree of chondral injury from MRI and corresponding surgical findings.

Results:

Given that MRI of the hip is neither as accurate nor as reliable as MRI of the knee or shoulder, an understanding of how to correlate preoperative MRI with intraoperative appearance can better prepare the surgeon for findings at the chondrolabral junction of the hip. The absence of findings on MRI does not rule out the possibility of cartilage or labral pathology.

Discussion/Conclusion:

Intraoperatively, hip cartilage is assessed using either the Outerbridge or Beck classification systems. These classification systems require direct visualization of the hip joint, and full assessment of the chondrolabral junction and associated pathology may not be possible until intra-articular work is complete. While MRI evaluation of the hip is difficult due to the depth of the hip joint, location of the hip relative to the MR magnet, and thinness of the acetabular cartilage, it is a useful tool for preoperative hip joint cartilage assessment, though not as accurate as knee and shoulder MRIs. Understanding the correlation between preoperative hip MRI and intraoperative chondrolabral pathology can aid the surgeon in preparation for hip arthroscopy in the treatment of FAIS.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

Today, we are going to discuss preoperative magnetic resonance imaging (MRI) and intraoperative arthroscopic evaluation of chondral pathology at the hip chondrolabral junction. Here are our disclosures.

Femoroacetabular impingement (FAI) is believed to be one etiology of early hip osteoarthritis and is the most common indication for hip arthroscopy. Patients who undergo hip arthroscopy for FAI will have varying degrees of chondral pathology. Chondrolabral pathology is typically managed alongside labral repair or reconstruction and correction of cam and/or pincer morphology at the time of arthroscopic surgery. Previous literature has found that, in comparison to knee and shoulder imaging, hip MRI imaging has lower accuracy and reliability in preoperative diagnosis of cartilage and labral pathology. There is also poor interrater reliability among arthroscopists performing intraoperative cartilage and labral damage classification. Therefore, it is important to understand the relationship between preoperative MRI and intraoperative appearance, as this can aid the surgeon in preoperative planning and in setting postoperative rehabilitation expectations. In general, we evaluate the coronal and sagittal images from a non-contrast hip MRI to assess the acetabular dome and use the axial sequences to assess the anterior and posterior acetabulum. We look for uniform surface contour and signal homogeneity. Some signal variation is expected and normally the signal becomes darker near the subchondral bone plate.

This can be quite difficult to evaluate in the hip as the cartilage is normally <2 mm thick. Any fluid signal extending into or undermining the cartilage is suspicious for a defect or delamination. Previous studies have shown that dark signal in the cartilage can correlate with cartilage delamination.

In this patient, a 16-year-old female with 8 months of hip pain, MRI of the left hip demonstrates a dark signal in the cartilage consistent with possible delamination. Here, as the back of the radiofrequency ablation device is used to push on the top of the labrum, the cartilage demonstrates what is called a “wave sign” or “carpet sign” representing intact but delaminated cartilage. Here, the area of cartilage delamination is defined by the arthroscopic probe. It extends approximately 8 mm inferior to the labrum into the acetabular cartilage. After labral repair, the area of the delaminated cartilage within the “wave” became more evident, as indicated by the blue arrows.

This is a 40-year-old male with a 1 year history of left hip pain. On this coronal T2 fat suppressed sequence a hypointense line (marked with the white arrow) within the acetabular cartilage/chondrolabral junction is noted medial to the labral tear (identified with the red arrow). Here, we demonstrate the grade 1 changes noted at the chondrolabral junction. One suture anchor has been placed at the far lateral extent of the labral tear, and the anchor drill guide is in position. Prior to labral repair, grade 1 chondromalacia can be seen here at the chondrolabral junction. As the labrum is being repaired, the labrum is more anatomically reapproximated to the acetabular rim, thus exposing the underlying delaminated cartilage at the chondrolabral junction, marked here with an asterisk.

After labral repair, the area of delamination and grade 1 changes appear more prominent here. The arthroscopic probe demonstrates that this area measures approximately 6 mm inferior from the edge of the labrum. This is a 35-year-old female with years of ongoing right hip pain. On the sagittal proton density fat suppressed sequence, her acetabular cartilage looks normal. After the capsule has been separated from the labrum, we can see labral tissue and grade 2 chondromalacia at the chondrolabral junction. Labral repair was performed, and loose cartilage at the chondrolabral junction was removed with the shaver. While the area of grade 2 chondromalacia was relatively focal, the adjacent, more lateral chondrolabral junction demonstrated undersurface delamination, as highlighted by the arthroscopic probe. In this 22-year-old male with 1 year of right hip pain, we see on this coronal T2 fat suppressed sequence an ill-defined hypointense signal (noted with the white arrow) at the chondrolabral junction in zone 3. Here, the cartilage at the chondrolabral junction demonstrates grade 3 changes. With the shaver, the loose cartilage flaps are debrided prior to labral repair. Of note, this was not nearly as impressive on preoperative MRI as what we found intraoperatively. This mismatch of the appearance of the chondrolabral junction on preoperative MRI and what is seen intraoperatively is relatively common given the difficulty in evaluating hip MRIs. In this case, it is possible that arthrogram may have defined this more clearly, but it is our protocol to obtain a noncontrast hip MRI in all hips that have not had a prior hip surgery. Once the labral repair was completed, the area of grade 3 chondromalacia is more clearly identified, as shown here with arrows. Upon close inspection of the chondrolabral junction, a thin layer of cartilage remained overlying the bone, with fissuring to the level of subchondral bone in an area with a diameter more than 1.5 cm consistent with the Outerbridge definition of grade 3 chondromalacia.

This is a 38-year-old active male with many years of left hip pain. On these coronal T2 fat suppressed and sagittal proton density fat suppressed sequences, we can see full thickness cartilage defects (noted with the white arrows) at the chondrolabral junction. In this example of grade 4 chondromalacia, the chondrolabral junction is not initially clearly visible given the significant detachment of the labrum. Posteriorly, an area of grade 3 cartilage wear consistent with the contrecoup phenomenon is noted. As we inspect the labrum more anteriorly, the significant detachment of the labral tissue is appreciated. Here, the extent of cartilage damage at the chondrolabral junction is covered by the unstable labral tissue. The labral repair is performed and elevates the labrum into its anatomic position. In doing so, the chondrolabral junction is more clearly visible, and the extent of cartilage damage is better appreciated. The shaver is utilized to debride loose cartilage flaps from the impaction zone.

Here, the area of cartilage damage measures approximately 1 cm inferior to the inferior aspect of the labrum. It is the senior authors’ preference to perform an abrasion chondroplasty in the setting of grade 4 chondromalacia in lieu of performing a microfracture, based on recent literature demonstrating similar outcomes in patients with microfracture and abrasion chondroplasty. ¹⁰ With abrasion chondroplasty, no change in postoperative protocol is necessary, which is especially beneficial when grade 4 chondromalacia was not expected based on preoperative MRI.

Our standard postoperative protocol includes 2-3 weeks of 20% body weight weightbearing, with some motion restrictions for the first 6 weeks. Impact activity typically begins around 3 months postoperatively. Heterotopic ossification prophylaxis includes indomethacin for 4 days, followed by naproxen for 4 weeks.

In summary, preoperative assessment of the hip cartilage is difficult even with advanced imaging due to the depth of the hip joint within the body, location of the hip joint relative to the MRI magnet, and the fact that the cartilage of the acetabulum is very thin. MRI may identify labral tears and chondral pathology preoperatively, but the absence of those findings on preoperative imaging may not sufficiently rule them out. Understanding this limitation of hip MR imaging can better prepare the surgeon for possible intraoperative findings.

We find that the coronal and sagittal MR sequences are the best to assess for chondrolabral pathology, and axial sequences can assess the anterior and posterior acetabulum. Intraoperatively, the true extent of chondral damage may be more apparent after labral repair. Understanding how preoperative MRI correlates with intraoperative chondrolabral pathology aids the surgeon in preoperative planning, intraoperative cartilage management, and in setting appropriate postoperative rehabilitation and recovery expectations.

Thank you.