Orthopedic Teaching Cases 2023, Jan, 20 | 12:00 am

AC joint injuries

A 25-year-old, right-hand-dominant male presents to clinic complaining of right shoulder pain which started 1 week ago when he tried to open a jammed door with the point of his shoulder. He is tender over the acromioclavicular joint and has a bony prominence greater than the contralateral side. His radiograph is shown in Figure 6–3.

 

 

 

Figure 6–3

 

What is true of the anatomy of the AC joint?

  1. There is no synovial fluid associated with this joint.

  2. The posterior component of the acromioclavicular ligament is most important for this joint’s vertical stability.

  3. The trapezoid ligament inserts on the clavicle 3 cm proximal to the lateral border.

  4. The motion at the joint includes gliding and rotation.

 

Discussion

The correct answer is (C). The trapezoid ligament is the more lateral coracoclavicular ligament at 3 cm from the distal clavicle while the conoid ligament is 4.5 cm proximal to the lateral border of the clavicle. These two ligaments together provide the vertical stability of the joint. The AC joint is diarthrodial and does produce synovial fluid. The acromioclavicular ligament provides horizontal stability, and the strongest component is the superior ligament. Most of the motion is from the bones, and their ability to rotate, not the joint itself; the only movement at the AC joint is gliding.

Choose the correct pairing of an AC joint injury classification with its description.

  1. Type I: sprained AC and CC ligaments with slight vertical separation noted on radiographs

  2. Type II: torn AC and CC ligaments with a CC distance of 25% to 100% of the contralateral side

  3. Type IV: torn AC and CC ligaments with lateral clavicle displaced posteriorly

  4. Type V: torn AC and CC ligaments with distal clavicle under the conjoined tendon

Discussion

The correct answer is (C). Type I is a sprained acromioclavicular ligament only and shows no change on plain radiographs. Type II is sprained AC and CC ligaments with slight vertical separation noted on radiographs. A Type III sprain is torn AC and CC ligaments with a CC distance of 25% to 100% of the contralateral side. Type IV is torn AC and CC ligaments with lateral clavicle displaced posteriorly. A Type V sprain has torn acromioclavicular and coracoclavicular ligaments and a coracoclavicular distance >100% as compared to the contralateral side. A Type VI sprain is described in choice D; these are rare injuries, and the clavicle can either be subacromial or subcoracoid.

When considering operative intervention for an AC joint separation, which of the following statements is true?

  1. ORIF with CC suture fixation has an associated risk of hardware migration.

  2. Modified Weaver–Dunn uses a technique that only returns 20% strength of vertical stability compared to a free tendon graft.

  3. Primary AC joint fixation generally has a low incidence of complications.

  4. A hook plate is preferred for its low profile and low rate of soft tissue irritation.

 

Discussion

The correct answer is (B). The Modified Weaver–Dunn is a CC ligament reconstruction that uses a transfer of the coracoacromial ligament to the distal clavicle. This recreates the CC ligament but has only 20% strength as the normal CC ligament. A CC ligament reconstruction, which uses a free tendon graft, can more closely recreate the strength of the CC ligament. An ORIF with suture fixation does not have a risk of hardware failure or migration, but it can be associated with suture erosion, which can cause a clavicle fracture. Primary AC joint fixation is not routinely done due to pin migration and a high complication rate. Hook plate fixation requires a second surgery for hardware removal due to soft tissue irritations.

 

Objectives: Did you learn...?

 

The anatomy of the CC ligaments?

 

Then classification of AC joint injuries?

 

Advantages and disadvantages of various treatment options for AC joint injuries?