Acromioclavicular (AC) Joint Injury

Anatomy of the AC joint

The Acromioclavicular (AC) joint is the junction of part of the scapula called the acromion to the clavicle (collarbone), and this connection is how it is given its name.1,2 The AC joint functionally links the shoulder girdle to the torso and is important for shoulder mobility and stability.2 The joint is highly dependent upon ligament support to hold it together, preventing injury. The ligaments involved in supporting the AC joint are the acromioclavicular ligament, which connects the end of the clavicle to the acromion, and the coracoclavicular (CC) ligaments, which are composed of two ligaments (conoid and trapezoid ligaments) that connect another part of the scapula called the coracoid process to the clavicle.^1-3 There is also a capsule, which is a connective tissue surrounding the joint, helping provide support.^1,2 The deltoid and trapezius muscles also contribute dynamic support to the AC joint by helping maintain the clavicle’s position during movement. Damage to these muscles, which often occurs in higher-grade AC injuries, can worsen instability and complicate recovery.³˒⁴

An AC joint injury, often referred to as a shoulder separation, occurs when these ligaments are partially or completely torn, allowing the clavicle to separate from the acromion.⁴ The severity of separation is classified using the Rockwood scale (Grades I–VI), which is based on how much damage has occurred to the ligaments and supporting tissue.

• Grade I: Sprain of the AC ligament without complete tear, CC ligaments unharmed.⁴
• Grade II: Complete tear of the AC ligaments, sprain of the CC ligaments.⁴
• Grade III: Complete tear of the AC and CC ligaments, coracoclavicular interspace is 25%-100% greater than normal.⁴
• Grade IV: Avulsion of the CC ligament from the clavicle with upwards and backwards separation of the clavicle into the trapezius muscle.⁴
• Grade V: Complete tear of the AC and CC ligaments, coracoclavicular interspace is 100%-300% greater than normal (more exaggerated version of grade III).⁴
• Grade VI: Clavicle is separated downward towards the coracoid process.⁴

An important measurement in diagnosing AC injuries is the coracoclavicular (CC) interspace, the vertical distance between the clavicle and the coracoid process. An increase in this space (often seen on X-rays) indicates a more severe injury and helps differentiate between Grades II, III, and V.⁴

The AC joint must undergo controlled motion when the arm raises above the head, like throwing or reaching up to catch a pass.³ Because of this, injury to the AC joint may alter an athlete’s ability to throw and catch, making this injury relevant to all fantasy-eligible players.   

Cause of an AC joint Injury

The most common cause of an AC joint injury is direct trauma to the point of the shoulder, especially when the arm is positioned across the body.⁵ This often occurs during tackles, falls, or diving attempts to catch a ball. The force drives the acromion downward relative to the clavicle, stressing or tearing the stabilizing ligaments.¹˒². The second mechanism is a fall onto an outstretched arm, which causes an upward jamming force through the humerus into the shoulder complex. This compresses the AC joint and can disrupt the ligaments, especially if the fall involves rotation or twisting of the torso.¹˒²

AC joint injuries are very common in contact sports like football. Nearly 30% of all NFL shoulder injuries involve the AC joint, and up to 40% of NFL quarterbacks will sustain an AC joint injury during their careers, due to the combined overhead mechanics of throwing and increased risk of high-velocity hits.⁷

Wide receivers and running backs are also at elevated risk, particularly on sideline plays where diving or being tackled midair often results in a hard impact to the shoulder. In fantasy football, this is important to track, as even low-grade AC injuries can cause pain with reaching or catching, affecting target volume and catch rate.

In higher-grade injuries (Grade IV–VI), trauma is more severe and may involve tearing the ligaments from the bone (avulsion), causing significant displacement of the clavicle. These typically occur with violent collisions or when a player’s shoulder is pinned awkwardly beneath a defender or the ground.³˒⁴

AC joint surgical procedure

Consensus in the medical community agrees that grade IV-VI AC joint injuries require surgery to properly restore the stability and function of the AC joint.^2,3 Management of grade III AC joint injuries is much more complicated and often is trialed with conservative care; however, if unsuccessful will lead to surgery.^2,3

There are two broad categories of surgical AC joint reconstruction:

• Non-anatomic techniques: Use metal hardware (e.g., wires, pins, screws, plates) to manually hold the clavicle in place.
• Anatomic techniques: Use grafts to reconstruct the native ligamentous support structures and restore more natural biomechanics.⁸

Anatomic reconstructions are now considered the gold standard for athletes and high-demand individuals due to better outcomes in shoulder kinematics and long-term stability.⁸ These procedures often use either:

• Autograft (tissue harvested from the patient’s hamstring, semitendinosus, or palmaris longus)
• Allograft (donor tissue from a cadaver)

A common technique is the anatomic coracoclavicular ligament reconstruction with a figure-of-eight loop using a tendon graft. Some procedures also include synthetic suture augmentation (like FiberTape or TightRope systems) to provide immediate stability while the graft biologically incorporates.⁸. Surgical success depends on restoring both vertical and horizontal stability. Studies show that while vertical displacement is easier to correct, horizontal instability (front-to-back motion) remains a challenge post-op and may contribute to long-term symptoms if not addressed.⁸

For elite athletes, surgical selection is influenced by:

• Severity of separation (especially Grade IV+)
• Time in season (early-season injuries allow more time for return)
• Contract status and positional demands (e.g., QB throwing mechanics)
• Surgeon’s experience and preference⁸

While most surgical patients return to daily activity within 3–4 months, a full return to contact sports often takes 5–7 months and may result in season-ending IR status depending on injury timing.⁸ For fantasy football managers, understanding that surgical AC injuries occurring during or after training camp should typically be considered long-term absences.

AC joint rehab process

The rehab timeline for an AC joint injury depends on the severity (grade) and whether surgery is performed.¹³˒⁵

• Grades I & II are treated conservatively.
• Grades IV–VI are treated surgically.
• Grade III is the gray area—rehab is typically tried first, but if instability or pain persists, surgery may follow.¹–³˒⁵

For non-surgical management (Grades I–II and some III), the athlete progresses through four key phases based on symptoms, not strict timeframes.⁵˒⁹˒¹⁰

Phase 1: Acute Pain and Inflammation Management

• Sling immobilization (1–7 days) to reduce stress on the AC joint
• Ice, NSAIDs, and gentle movement of the elbow, wrist, and hand to prevent stiffness¹˒³
• Prolonged sling use is discouraged as it can lead to shoulder capsule tightening and muscle atrophy, delaying return to function.⁵
• The sling is typically removed when the athlete can tolerate the arm hanging without pain.

Phase 2: Mobility and Early Strengthening

• Passive and assisted shoulder ROM (flexion and abduction first)
• Avoid horizontal adduction (arm across the body) and internal rotation early on, as these stress the healing ligaments⁵
• Gentle rotator cuff and scapular stabilizer strengthening begins, often with isometrics and light bands
• Supportive positions (hand on table, wall-assisted) are useful to offload the joint during initial strengthening

Phase 3: Strength and Stability

• Active, full ROM in all planes without pain
• Strength progression: resistance bands → cables → dumbbells
• Emphasis on:
  • Rotator cuff strength (external rotators especially)
  • Scapular control (serratus anterior, middle/lower trap)
• Closed-chain loading (e.g., wall pushups, quadruped shoulder taps) builds joint compression and functional control

Phase 4: Return to Sport Progression

• Begin plyometrics: medicine ball tosses, clap pushups, reactive drills
• Functional pressing progressions (bench press, overhead press) are introduced cautiously
• For QBs: A gradual throwing program begins with low-velocity, short-distance throws before advancing to full-intensity passes⁵
• Skill players begin catch drills, blocking/contact prep, and position-specific agility once strength and stability are normalized

Surgical Cases (Grades IV–VI and some III)

Surgical recovery follows a 4-phase rehab protocol that can last 4–6+ months:¹¹˒¹²

1. Protection (0–6 weeks): sling use, passive ROM only
2. Mobility/Strength Phase (6–12 weeks): gradually restore motion, light resistance
3. Advanced Strength (3–4 months): reintroduce load-bearing and dynamic drills
4. Return to Play (4–6+ months): full-contact clearance after passing strength and functional testing

NFL athletes who undergo in-season surgery typically miss the remainder of the year. If surgery occurs in the offseason, players can return in time for training camp.

Conservative AC Joint Rehab

Rehab Phases5,9,10	Treatments5,9,10
Phase I	Immobilized in sling. Rest, ice, anti-inflammatories. Elbow, wrist, hand range of motion exercise.
Phase II	Theraband, cable, and light dumbbell exercises for shoulder blade and rotator cuff strength. Progress weight bearing exercises. Full body exercises incorporating the legs and core.
Phase III	Theraband, cable, and light dumbbell exercises for shoulder blade and rotator cuff strength. Progress weight-bearing exercises. Full body exercises incorporating the legs and core.
Phase IV	Passive and active-assisted shoulder range of motion into elevated and lateral directions. Shoulder blade and rotator cuff strengthening in pain-free positions. Initiate exercises bearing weight on hands. Progress to range of motion in all directions and active motion.

Often, Grade III AC joint injuries are initially managed non-operatively. However, athletes may experience persistent pain, functional limitations, or aesthetic deformity, such as the visible bump seen on Keenan Allen’s shoulder during Hard Knocks.⁸

Studies show that although anatomical alignment may never fully normalize after conservative care, many athletes regain sufficient functional strength and motion to return to pre-injury levels.⁸ Conservative care may still be the best option for skill position players if surgery would delay the return to play past the season.

However, in cases of persistent symptoms, especially instability during overhead activity or blocking, delayed surgical repair is considered. Elite athletes whose game requires full upper-body strength and control (e.g., offensive linemen, linebackers, QBs) may be steered toward surgery to reduce the risk of recurrence and maximize joint stability.⁸

Post-Op AC Joint Rehab

Phase of Rehab11,12	Goals and Precautions11,12	Rehab11,12
Phase I: Protection, Pain, and Swelling Control. Post-Op Weeks 1-6	Goals Protect Surgery. Reduce pain and swelling. Begin restoring ROM. Prevent muscle atrophy. Precautions Sling worn at all times other than showering and exercises. Do not elevate arm past 90°. Avoid lifting objects >5lbs. Avoid placing hand behind back or arm across body.	Ice 4-5 times/day. Neck, elbow, wrist, hand range of motion. Shoulder pendulums. Passive stretching to 90° elevation, rotation to tolerance (with arm by side). Gentle muscle isometrics to tolerance.
Phase II: Protection, ROM, and Initiation of Strength. Post-Op Weeks 6-12	Goals Protect surgery. Reduce pain and swelling. Continue progressing ROM. Gradually increase strength. Precautions No pushups or pushing movements. No lifting weighted objects overhead or across body.	Wean out of sling. Continue icing 4-5 times/day. Slowly progress ROM in all directions (increase ~15°/week as tolerable). Begin active assisted ROM progressing to active ROM when able. Continue with muscle isometrics progressing to active shoulder exercises without weight and theraband exercises when tolerable. Scapular strength exercises.
Phase III: Full ROM and Strengthening. Post-Op Weeks 12-18	Goals Full ROM. Improve strength, power, endurance, and control. Precautions No deadlifts of pressing exercises. No contact.	Continue ROM until full. Continue progressing shoulder and scapular exercises beginning to add resistance via bands, cable, light dumbbells. Begin wall pushups at 12 weeks. True weight training beginning at 16 weeks.
Phase IV: Advancing Strength and Sports Specific. Post-Op Weeks 18+	Goals Restore full strength, mobility, stability. Return to sport.	Continue stretching as needed. Unrestricted strength training. Upper body plyometrics. Sports-specific training (throwing program, catching, running)

References

1. Sueki D, Brechter J. Orthopedic Rehabilitation Clinical Advisor. 1st ed. Maryland Heights, MO. Elsevier Inc.; 2010.
2. Nolte P, Lacheta L, Dekker T, Elrick B, Millett P. Optimal Management of Acromioclavicular Dislocation: Current Perspectives. Orthop Res Rev. 2020;12:27-44.
3. Deans C, Gentile J, Tao M. Acromioclavicular joint injuries in overhead athletes: a concise review of injury mechanisms, treatment options, and outcomes. Curr Rev Musculoskelet Med. 2019;12(2):80-86.
4. Rockwood C, Williams G, Young D. Disorders of the acromioclavicular joint. 2nd ed. Philadelphia: WB Saunders; 1990.
5. LeVasseur M, Mancini M, Berthold D, et al. Acromioclavicular Joint Injuries: Effective Rehabilitation. Open Access J. Sports Med. 2021:12;73-85.
6. Lynch TS, Saltzman MD, Ghodasra JH, Bilimoria KY, Bowen MK, Nuber GW. Acromioclavicular joint injuries in the National Football League: epidemiology and management. Am J Sports Med. 2013;41(12):2904–2908.
7. Kelly BT, Barnes RP, Powell JW, Warren RF. Shoulder injuries to quarterbacks in the National Football League. Am J Sports Med. 2004;32:328–331.
8. Virk M.S, Apostolakos J, Cote M.P, Baker B, Beitzel K, Mazzocca A.D. Operative and Nonoperative Treatment of Acromioclavicular Dislocation. J Bone Joint Surg. 2015;3(10).
9. Gladstone JN, Wilk KE, Andrews JR. Nonoperative treatment of acromioclavicular joint injuries. Oper Tech Sports Med. 1997;5:78–87.
10. Cote MP, Wojcik KE, Gomlinski G, Mazzocca AD. Rehabilitation of acromioclavicular joint separations: operative and nonoperative considerations. Clin Sports Med. 2010;29:213–228.
11. Massachusetts General Hospital Orthopedics.  Shoulder Separation and Acromioclavicular Joint Injury.  Massachusetts General Hospital Orthopedics. https://www.massgeneral.org/assets/MGH/pdf/orthopaedics/sports-medicine/physical-therapy/rehabilitation-protocol-for-AC-joint-reconstruction.pdf.  Accessed April 17 2022.
12. Northwestern Medical Center.  AC Joint Reconstruction Protocol.  Northwestern Medical Center. https://www.northwesternmedicalcenter.org/pdf/ac-joint-reconstruction-protocol/.  Published December 2016.  Updated December 2016.  Accessed April 17 2022.