Plain AP radiograph (a) and T2 coronal MRI (b) demonstrating advanced joint space narrowing and bone marrow edema around the AC joint
This patient presented with rotator cuff tendonitis, fraying of the undersurface of the supraspinatus tendon, and AC joint osteoarthritis. He attempted nonoperative management with physical therapy, NSAIDs, and steroid injections with only temporary improvement of his shoulder pain. Distinguishing AC joint pathology from rotator cuff tendonitis can be challenging. Pain localizing to the superior aspect of the shoulder, directly over the AC joint, with palpation or cross-chest adduction is typical of AC joint osteoarthritis. Conversely, pain with overhead activity or special tests such as Neer, Hawkins, or empty can (Jobe’s) test localizing to the anterolateral aspect of the shoulder may indicate rotator cuff tendonitis.
Our patient underwent a shoulder arthroscopy with subacromial decompression (SAD), debridement of articular sided supraspinatus tendon fraying, and arthroscopic distal clavicle resection (DCR). His immediate postoperative course was uncomplicated. He was discharged home on the day of surgery. The patient presented for follow-up and underwent a standardized physical therapy protocol, discontinuing sling immobilization within 10 days and starting active range of motion as tolerated.
Management of rotator cuff tendonitis with or without AC joint arthropathy begins with nonoperative treatment. Modalities include physical therapy, activity modification, immobilization, NSAIDs, and diagnostic or therapeutic injections. Injections into the subacromial space and/or the AC joint providing symptomatic relief are a prognostic indicator for successful surgical outcome. Physical therapy increases range of motion, flexibility, and periscapular strength . It does not reliably relieve arthritis pain. A brief period of immobilization and application of ice may reduce inflammation associated with acute exacerbations of AC joint arthropathy .
Operative indications for rotator cuff tendonitis with or without AC joint arthropathy include continued pain and loss of shoulder function despite at least 6 months of conservative management . Supraspinatus outlet impingement, which is the usual cause of rotator cuff tendonitis, typically begins with the anteroinferior aspect of the acromion and progresses to involve the AC joint. Therefore, surgical management involves adequate subacromial decompression including the subacromial bursa, coracoacromial ligament, and acromion. Specific indications for distal clavicle excision, which is a resection arthroplasty of the AC joint, include symptomatic arthritis from osteoarthritis, rheumatoid arthritis, and posttraumatic or atraumatic distal clavicle osteolysis. Absolute contraindications to SAD and DCR include active infection, while relative contraindications include neuroarthropathy, instability, and medical comorbidities precluding the patient from undergoing surgery.
Arthroscopic subacromial decompression with or without distal clavicle resection can be performed in the lateral decubitus or beach-chair position depending on surgeon preference. Our preference is lateral decubitus as it affords improved visualization and maneuverability around the subacromial space with an adjusted shoulder suspension device. The table should be placed in slight reverse Trendelenburg position to make the glenoid parallel to the floor. A bean bag is placed around the patient and suction applied to mold to the lateral position. A post on either side of the bean bag can be used to further stabilize the patient. For the lateral decubitus position, the operative arm should be placed in an apparatus consisting of a sleeve attached to a suspension of generally no more than 10 pounds. The shoulder should be in approximately 15° of forward flexion and no more than 45° abduction.
We recommend a diagnostic arthroscopy with particular attention to the supraspinatus tendon and debridement of fraying and partial-thickness tears of less than 50% of the tendon thickness in addition to subacromial decompression in the majority of patients. The most common way to approach the subacromial space and the AC joint arthroscopically is through a lateral transbursal portal located approximately 2 cm lateral to the edge of the lateral acromion as a working portal. We start the subacromial decompression by exposing the lateral and then the anterior margin of the acromion. A pilot trough is made at the anterolateral edge of the acromion using a 4 or 5.5 mm burr, and then extended across the anterior margin. We then taper the resection posteriorly over about two-thirds of the acromion undersurface using a “windshield wiper” motion. Care is taken to leave the acromion thicker as the resection proceeds posterior to minimize postoperative fracture (Fig. 1.2). For the distal clavicle excision a pilot trough is made in the anteroinferior aspect of the clavicle to guide resection. Approximately 5 mm of bone is resected, ensuring that the most posterior aspect of the clavicle is also resected (Fig. 1.2). A 4 or 5.5 mm burr is used to remove anywhere between 3 and 10 mm of distal clavicle using a “windshield wiper” motion. It can be challenging to decide how much to resect, as some authors advocate less than 5 mm of resection in the majority of cases so as not to disrupt the ligamentous structures [8, 9]. The majority of authors will agree that no more than 10 mm of distal clavicle should be resected [10–13]. The posterior inferior aspect of the AC joint may be difficult to visualize. An anterolateral portal or 70° arthroscope may help ensure that no bony contact remains between the acromion and clavicle. Care is taken to preserve the superior and posterior AC capsular ligaments to minimize anteroposterior instability and avoid release of the coracoclavicular ligaments to minimize superior instability postoperatively. To accomplish this, multiple viewing portals are used including the anterior portal through the rotator interval. We do not recommend coplaning the distal clavicle by removing the inferior 25% to match the acromioplasty as has been described. We advocate beginning patients on passive range-of-motion exercises immediately postoperatively as soon as the interscalene block wears off, including pendulum exercises unless concomitant rotator cuff repair is performed. Isometric, isokinetic, and active range-of-motion exercises are begun at the first postoperative visit, typically by 7–10 days. Return to sports is generally approximately 3 months; however it may be as early as 6 weeks for non-throwing athletes.
Arthroscopic images while performing a subacromial decompression, during (a) and after (b) distal clavicle resection
Our patient had complete resolution of his pain by 2 months postoperatively so he was allowed to begin advanced strength training and he returned to work. Rotator cuff tendonitis and mil partial-thickness rotator cuff tears are common findings with AC joint arthropathy as they are part of a spectrum in supraspinatus outlet impingement. In our experience, more than 5 mm of distal clavicle resection is not needed, and patient outcomes depend more on the preservation of soft tissues and early rehabilitation. The patient in this clinical vignette had improvement of their anterolateral shoulder pain with physical therapy, with persistently symptomatic AC joint arthritis. He also responded to injection of the AC joint, which is a good prognostic sign. When appropriately indicated, distal clavicle resection can improve pain and function in patients with AC joint pathology.
Rotator cuff tendonitis associated with subacromial impingement begins with compression of the rotator cuff tendons causing tendonitis or bursitis. Chronic inflammation may lead to degeneration and, eventually, tendon rupture . Most commonly, rotator cuff fraying or partial-thickness tearing begins on the undersurface rather than the bursal side. Patients typically report pain over the anterolateral shoulder with or without radiation down the lateral humerus . Neer and Hawkins test combined has a negative predictive value of 90% . Subacromial decompression has long been the gold standard treatment for extrinsic impingement that has failed nonoperative management. Neer first described anterior acromioplasty in 1972. Since then, several arthroscopic techniques have been described to accomplish relieving direct compression of the rotator cuff. Ellman et al.  described an arthroscopic technique to resect the anterior undersurface of the acromion, bursal debridement, and coracoacromial ligament release. In contrast, McCallister et al.  proposed a “smooth-and-move” technique to perform extensive bursectomy and smoothing of the undersurface of the acromion without disruption of the coracoacromial ligament or avulsion of the deltoid.
Various pathologic processes can affect the AC joint, including, arthrosis, posttraumatic, or atraumatic distal clavicle osteolysis, and infections. Any resulting alteration of normal biomechanics and function of the AC joint may become symptomatic. The AC joint is also associated with subacromial impingement, originally described by Neer, as it forms the supraspinatus outlet along with the acromion and coracoacromial ligament . Osteophyte formation on the inferior aspect of the AC joint has been associated with narrowing of this space and the development of rotator cuff pathology [18–20]. Additionally, AC joint pathology has been correlated with rotator cuff tears [21, 22].
Patients with AC joint arthrosis typically present with pain that localizes to the AC joint or superior shoulder exacerbated by overhead or cross-chest activity. It can sometimes be referred to the anterolateral neck, deltoid, and trapezius . Mechanical symptoms may also be present, such as popping, catching, or grinding . Further complicating diagnosis, concomitant injuries include rotator cuff (up to 81%), biceps (22%), or labral pathology [5, 23].
The most sensitive physical exam test is the cross-chest adduction stress test with a sensitivity of 77% while the O’Brien active compression test is the most specific exam finding with a reported specificity of up to 95% [24, 25]. Imaging of the shoulder may show degenerative changes in the AC joint, best visualized on a Zanca view with 10° to 15° cephalic tilt. An “outlet view,” which is a scapular lateral projection with a 10° caudad tilt, allows visualization of inferior osteophytes emanating from the AC joint . Additionally, the axillary view allows visualization of osteophytes involving the anterior or posterior aspects of the AC joint.
Although plain radiographs are sufficient to diagnose AC joint degenerative arthrosis, advanced imaging can assist in identifying other pathologies contributing to shoulder pain. A diagnostic injection can be performed, although outcome is technique dependent and is more reliably done with the use of ultrasonography . A recent study by Wasserman et al. and the senior author (ASR) demonstrated that despite its superficial location, only two-thirds of in vivo AC joint injections performed were intra-articular or partial-articular .
Mumford in 1941 described an open resection of the distal clavicle for AC joint pathology . Since the advent of shoulder arthroscopy, several techniques have evolved to perform distal clavicle resection arthroscopically. While open techniques have shown good to excellent outcomes, arthroscopic techniques are associated with accelerated recovery, decreased pain postoperatively, improved cosmesis, and preservation of vital structures such as AC ligaments, joint capsule, and deltotrapezial fascia .
Case Presentation (Case 2—Os Acromiale)
A 25-year-old right-hand-dominant male presented with a 1-year history of right-shoulder pain with overhead activity that had failed nonoperative treatment including activity modification, physical therapy, nonsteroidal anti-inflammatory drugs (NSAIDs), and two subacromial corticosteroid injections. Physical examination revealed no restriction in shoulder range of motion, positive Hawkins and Neer impingement signs, point tenderness over the acromion, and pain with forward elevation. A magnetic resonance imaging (MRI) brought in by the patient demonstrated an os acromiale with associated bone marrow edema. Plain radiographs and a CT scan were also obtained and demonstrated a mesoacromion-type os acromiale (Fig. 1.3).
Plain AP radiograph (a) and CT scan with axial (b) and sagittal (c) views demonstrating a mesoacromion-type os acromiale
In so me cases, the underlying cause of rotator cuff tendonitis will be straightforward with a combination of clinical history, physical exam consistent with impingement, and imaging demonstrating inflammation of the tendons. In all cases, however, it is imperative to identify any and all sources of pain around the shoulder to ensure appropriate management. Shoulder pain can be difficult to localize which can be compounded by false-positive advanced imaging studies [30–32]. A thorough history and physical exam can usually lead clinicians to the correct diagnosis. Given the point tenderness over the acromion, pain with cross-chest adduction, and imaging demonstrating a mesoacromion, the patient was diagnosed with symptomatic os acromiale and underwent a trial of nonoperative management.