|ESSR 2019 / P-0124||
|Postoperative Shoulder: widening one’s knowledge in the MRI era|
- Review the different surgical procedures used for the treatment of subacromial impingement, rotator cuff pathology and glenohumeral instability.
- Postoperative shoulder’s Magnetic Resonance findings and complications related to subacromial decompression, rotator cuff and labrum repair, and superior capsular reconstruction (SCR) are revisited.
Magnetic Resonance Imaging (MRI) has a fundamental role in the management of the postoperative shoulder and is regarded as a pivotal imaging technique for the differentiation between postoperative complications and expected findings after shoulder surgery.
However, when we are dealing with postoperative MRI, there could be some metallic susceptibility artifacts (figure 1A). These artifacts are more prominent with shoulder prothesis, screws and staples, but they can be produced by minor particles from the surgery, like in acromioplasty (figure 1B).
The transition from the metallic hardware to bioabsorbable and bioinert suture anchors used has led to less metallic susceptibility. Also, in order to minimize these artifacts, the radiologist can change some protocol settings, such as:
- increase the bandwidth;
- use fast spin-echo sequences instead of conventional spin-echo sequences;
- use short tau inversion recovery sequence (STIR) instead of fat suppression (FS) sequences, in order to achieve more homogeneous fat suppression;
- correct the direction of the slice-encoding metal artifact. These artifacts are more pronounced in the frequency-encoding direction, which should be orientated according to the direction of lesser expected findings;
- use new pulse sequences designed to reduced metallic artifacts: slice encoding for metal artifact correction (SEMAC), view angle tilting (VAT), multiple-acquisition with variable resonances image combination (MAVRIC) or the combination of SEMAC, VAT, and increased bandwidth, also referred to as the WARP sequence;
- scan at a lower magnetic field strength (prefer the 1,5 Tesla scanners).
The subacromial decompression, the rotator cuff repair and the repair of glenohumeral instability are the most common surgeries of the shoulder.
For the treatment of subacromial impingement the most common surgical procedures are:
- arthroscopic subacromial decompression: anterior and posterior acromion resection, bursectomy and resection of acromioclavicular joint osteophytes;
- resection of the acromioclavicular joint (ARAC);
- Mumford procedure that consist on resection of the distal clavicula;
- bursectomy and coraco-acromial ligament resection.
The postoperative imaging findings expected after subacromial impingement surgery are:
- morphological and bone marrow signal changes in the acromion (figure 2);
- widening of the acromioclavicular space (figures 2 and 3);
- absence or replacement of the coraco-clavicular ligament by fibrous tissue;
- presence of acromioclavicular osteoarthritis (figure 2 and 3);
- subacromial fluid is very common in asymptomatic patients and, can sometimes communicate with the acromioclavicular joint (geyser sign).
Rotator cuff lesions
The surgical management of rotator cuff lesions depends on multiple factors like the age and the activity of the patient; the depth and the size of the rupture, and the presence of other shoulder pathology.
The surgical procedures for rotator cuff lesions can be divided in three main types:
- arthroscopic: indicated in small full-thickness tears without tendon retraction and in partial bursal-sided tears that are usually associated with some degree of subacromial impingement (ASD is also performed in these surgeries);
- mini-open repairs: the deltoid muscle is not detached from the acromion so this is a less invasive surgery (compared to open surgery). The surgical procedures can vary from side-to-side suturing of the torn ends and reattachment of the tendon to the great tuberosity using variable sutured anchors (single and double row techniques);
- open surgery: indicated in full-thickness tears with tendon retraction. In these cases, the deltoid is detached from the acromion and the tear is repaired with tendon reinsertion to the bone by transosseous or anchored sutures.
The expected postoperative imaging findings after rotator cuff lesion surgical repair are:
- subacromial bursitis and humeral head’s signal changes: can be seen years after the surgery;
- the repaired tendon can appear thin, thickened, irregular and have low or high T2 signal due to fibrous tissue (figure 4);
- in asymptomatic patients, the postoperative MRI can show the repaired tendon with high T2 signal and a considerable amount of subacromial fluid.
The surgical management of glenohumeral instability comprehends open and arthroscopy surgeries. The surgical procedures vary with the type of lesion and the open surgery can be anatomic or non-anatomic.
There are some classic surgical procedures in glenohumeral instability surgical repair:
- labral tears: the anterior labrum, the joint capsule and the anterior band of the inferior glenohumeral ligament are attached to the glenoid rim by sutures;
- Bankart procedure: anteroinferior labral lesions with capsule tear are treated with reattachment of the anterior capsule to the glenoid in conjunction with anteroinferior labral repair;
- Remplissage technique: in Hill-Sachs lesions, the posterior capsule and the infraspinatus tendon are transferred to the Hill-Sachs lesion to prevent the lesion to be re-engaged with the glenoid rim.
The expected postoperative imaging findings in glenohumeral instability repair are:
- metallic susceptibility artifacts from the sutures, however the new bioabsorbable and bioinert anchors do not create a significant artifact (figure 5);
- irregular capsular thickening;
- truncated labrum or a labrum decreased in size.
The most common complication after shoulder surgery, usually in rotator cuff surgical repair, is a tendon retear and the diagnosis is considered when we have the following imaging findings on postoperative MRI:
- full-thickness tear > 11 mm;
- retracted tendon;
- displaced or broken sutures/anchors;
- superior displacement of the humeral head;
- small tears not visible on preoperative MRI or on previous postoperative MRI;
- extensive subacromial bursitis;
- muscle atrophy.
There are other postoperative complications related to the surgical procedure:
- deltoid muscle dehiscence is a rare complication of open surgery for rotator cuff repair. Often, we can see fluid extending through deltoid muscle from the acromial attachment;
- anchors/sutures failure in rotator cuff repair that can appear when they are pull-out from the bone;
- cystic, granulomatous and osteolysis bone reaction to bioabsorbable anchors and less frequently in bioinert anchors, when they are used;
- acromial fracture, heterotopic calcification and persistency of the subacromial impingement after subacromial impingement surgery (figure 6).
Although rare, there are some complications after shoulder surgery that can emerge in all surgical procedures:
- infection, which may lead to osteomyelitis;
- axillar or subscapular nerve injury, leading to deltoid and infraspinatus atrophy (figure 7);
- adhesive capsulitis;
- shoulder arthropathy, osteolysis and free articular bodies.