A clinical synthesis based on the Welch 2024 (Shoulder Elbow) and Rajagopalan 2023 (J Orthop) meta-analyses, Krill 2018 and the prospective 2024-2025 data on the overhead athlete.

Definition, epidemiology and risk factors

• 48 % of cadaveric specimens show AC osteoarthritic changes;
• 70 % of MRI scans of asymptomatic shoulders show signs of AC osteoarthritis;
• The association between age and prevalence is statistically significant.

• Overall prevalence: 83 % ;
• 75 % between 40 and 50;
• 100 % after 70;
• OR for age = 2.89 (95 % CI 2.30-3.63; p < 0.001).

• Age : the main non-modifiable factor. Degeneration of the fibrocartilaginous disc starts in the second decade; the osteoarthritis becomes almost universal after 70 (Rajagopalan 2023).⁵
• Previous trauma : a history of AC dislocation (Rockwood I to VI), subluxation or fracture of the distal third of the clavicle considerably raises the risk of post-traumatic osteoarthritis.⁷ The 2024 SR and meta-analysis (Caso 2024) concludes, however, that the choice of initial treatment for an AC dislocation should not be influenced by the risk of developing osteoarthritis, because the data are insufficient to predict that outcome.⁸
• Repeated microtrauma : occupational or sporting activities involving repetitive movements above the head (overhead activities) are a major risk factor. That includes construction workers and painters, as well as weightlifters, CrossFit athletes, rugby players and throwers.⁹
• Specific microtrauma from axial loading of the upper limb : bench press, dips, heavy dumbbell exercises, which are the origin of distal clavicular osteolysis (DCO, see chapter 5).¹⁰
• Anatomical variations : the size and orientation of the disc, the geometry of the acromion (Bigliani type I to III), although this area stays less agreed.¹¹

Pathophysiology and natural history

• Phase 1 : alteration of the fibrocartilaginous disc (fissuring, loss of height);
• Phase 2 : loss of articular cartilage thickness;
• Phase 3 : remodelling of the subchondral bone (sclerosis, cysts);
• Phase 4 : osteophyte formation, mainly on the inferior surface of the joint, which can compress the supraspinatus tendon and generate a secondary subacromial impingement syndrome.¹³

Focused history: the key questions to ask

• Aggravating activities : is the pain made worse by moving the arm across the body (horizontal adduction, such as reaching for the seat belt or washing the opposite armpit)?¹ Is it increased during overhead activities?³
• Night pain : does the patient feel pain when sleeping on the affected side? That position compresses the joint directly and is a frequently reported clinical sign.²
• History of trauma : is there a history of a fall onto the point of the shoulder (a cycling fall, a contact sport), of an AC dislocation even long ago, or of a distal clavicle fracture?⁴ This article covers the joint as a chronic degenerative ; if the trauma is recent and the question is one of grade, timescales and return, the dedicated article is the clavicle fracture and acromioclavicular separation.
• Occupational and sporting activities : heavy weight training (bench press, dips), heavy overhead loads, painter, plasterer, electrician.⁵
• Characteristics of the pain : cracking, catching sensations, localised swelling. These signs are not specific but can reinforce the clinical suspicion.¹

Clinical tests and differential diagnosis

• Cross-Body Adduction Test : passively bring the patient's arm into maximal horizontal adduction. Sensitivity 77 %, lower specificity because it can also load the subacromial structures (Chronopoulos 2004, AJSM, 35 patients).⁷
• Active Compression Test (O Brien) : arm at 90° of flexion, 10-15° of adduction, thumb down. Sensitivity 41 %, specificity 95 % (Chronopoulos 2004).⁷
• AC Resisted Extension Test : sensitivity 72 %, intermediate specificity (Chronopoulos 2004).⁷
• SAC test (Saccomanno 2014): a combination of palpation and AC stress. Overall accuracy 82 %, specificity 91.7 %, PPV 75 %. Reaches 98 % sensitivity combined with radiographs.⁸
• Paxinos sign : compression of the AC joint with the thumb under the acromion + the index finger on the clavicle. Specificity 100 % but sensitivity only 12 % in the original Saccomanno 2014 study, so a confirmatory test but not a screening one.⁸
• Direct palpation : firm pressure over the joint line. Good sensitivity but low specificity.⁶

• The NPV is > 94 % for ALL the AC tests: a negative test does rule the condition out;
• The PPV is < 30 % for ALL the tests: a positive test on its own does not confirm the condition;
• The Paxinos + O Brien combination reaches a positive Likelihood Ratio of 2.71 , the best documented combination;
• The composite test palpation + cross-body + active compression all positive raises the post-test probability strongly.

Critical differential diagnoses to rule out

• Subacromial impingement and cuff tendinopathy : pain that is more diffuse over the side of the shoulder (deltoid), typically linked to active elevation. It frequently coexists with AC osteoarthritis.¹⁰
• Cervical pathology : a C4-C5 radiculopathy can cause pain referred to the shoulder and the trapezius. A cervical examination (Spurling, distraction) is essential.¹¹
• Long head of biceps tendinopathy : anterior pain, close to the AC joint. A positive Speed test.
• Residual post-traumatic AC instability : a type II or III dislocation that healed poorly, giving a chronic instability sometimes more symptomatic than the osteoarthritis itself.⁴
• SLAP lesion (superior labrum) : a presentation similar to O Brien; a CT or MR arthrogram may be needed.

Should patients be classified, and what are the benefits?

Criticism and controversy: the tyranny of the image

Hierarchy of recommended interventions

• Patient education : explaining the benign nature of AC osteoarthritis (the imaging norm after 40), the difference between image and symptom, the importance of self-management.³
• Temporary activity modification : limiting the triggering movements, in particular forced horizontal adduction, loaded full elevation, the heavy bench press and dips. A strategy of « relative rest » rather than complete stopping.¹,⁴
• First-line drug management : oral or topical NSAIDs over short periods (Cochrane Derry 2017, a moderate but real effect for acute musculoskeletal pain), paracetamol as an alternative.⁵

The place of exercise and the best-supported approaches

• Rotator cuff strengthening : strong, enduring muscles for dynamic glenohumeral stabilisation and an indirect reduction in AC stresses.⁹
• Control and strengthening of the scapular stabilisers : a particular focus on serratus anterior and the lower and middle trapezius. Scapular dyskinesis raises the risk of future shoulder pain by 43 % in the asymptomatic athlete (Hickey 2018 BJSM SR-MA).¹¹
• Upper thoracic mobility : an excessive thoracic kyphosis worsens scapular kinematics; build in thoracic extensions and pectoral opening.
• Avoiding painful provocation : at first modify or avoid the forced horizontal adduction exercises, heavy loads on the midline (heavy bench press, dips) and loaded full elevation. The principle of the optimal load (stimulating but not painful).¹²

Manual therapies, technologies and injections

• AC manual therapy : anteroposterior and inferosuperior mobilisation of the AC joint; thoracic and scapulothoracic mobilisation. They reduce pain in the short term and improve range. Their long-term efficacy in isolation is limited, so build them into a multimodal approach.¹³
• Taping : weak to moderate evidence, effects mainly very short-term, with a significant placebo contribution.
• Electrotherapy, ultrasound, laser : high-quality evidence against their routine use. The Cochrane SR Page 2016 (CD012225, 47 trials, 2,388 participants) shows no clinically relevant effect in rotator cuff disease. Pieters 2020 confirms: moderate evidence of NO effect for laser, shockwave and ultrasound.¹³,¹⁴
• Corticosteroid injections : a mean 50 % reduction in pain at 7.5 months (Welch 2024). Ultrasound guidance is essential: without it, up to 50 % of injections are misplaced.⁶ The Kompel 2019 limits: 44 % acceleration of OA progression and 17 % joint collapse in the hip and knee, so be cautious about repeating them.⁷
• PRP, hyaluronic acid : insufficient evidence to recommend them in AC osteoarthritis specifically (Welch 2024). To be kept for clinical research.¹

Patient education and psychological factors

• Pain neuroscience education : explain that pain does not mean tissue damage; target catastrophic beliefs. A documented reduction in kinesiophobia (fear of movement) and an improvement in function (Louw 2016, a meta-analysis).¹⁵
• Specific demystification of AC osteoarthritis : explain that the image is the norm after 40 (Rajagopalan 2023, 75-100 %), and that a positive image does not predict the intensity of the symptoms.
• Setting SMART goals (Specific, Measurable, Achievable, Realistic, Time-bound): for example « getting back to a 60 kg bench press without pain in 8 weeks ».
• Identifying yellow flags : anxiety, depression, catastrophising (PCS), fear of movement (TSK-11). These factors are major predictors of chronicity. If they predominate, psychological collaboration is indicated.¹⁶

Criticism and controversy

1. Corticosteroid injections: how many and how often? No international consensus. The Kompel 2019 data (hip and knee) call for caution. PRP and hyaluronic acid injections stay embryonic for the AC joint.⁷,¹
2. The research-practice gap : passive modalities with no evidence (laser, ultrasound) stay widely used in the clinic, despite the Pieters 2020 and Page 2016 evidence.¹³,¹⁴
3. Heterogeneity of the exercise protocols : no optimal protocol validated for AC osteoarthritis. Individualisation is needed, but it makes studies hard to compare.⁹

Self-management and patient empowerment

• Ergonomic modification of activities : adapt the technique rather than avoiding the activities completely. Concrete examples:
  • Bench press: reduce the load, widen the grip, use a limited range, build in a unilateral dumbbell variant;
  • Dips: replace with push-ups or ring dips at a limited depth;
  • Overhead work: adapt the posture, alternate sides, break the sessions up;
  • Sleep: a triangular pillow to relieve the affected side, a semi-lateral position.
• Self-monitoring of the symptoms : keeping a simple diary (daily VAS pain, activities done, sleep quality). It makes progress objective and allows proactive adjustment.³
• A home exercise programme personalised and evolving, focused on scapular motor control (lower trapezius, serratus anterior, infraspinatus). Regularity > intensity: 10-15 min a day is better than 1 h a week.⁴,⁵
• Managing flare-ups : a « toolbox » for inflammatory flares: ice 15-20 min 3-4 times a day, a short course of NSAIDs, relative rest, relaxation techniques.⁶

A safe return to sport and to activity

1. Prerequisite criteria :
   • Full active range, pain-free , in flexion, abduction and rotation;
   • No pain on direct palpation of the AC joint;
   • Strength of the rotators and scapular stabilisers ≥ 90 % of the other side (hand-held dynamometer);⁸
   • A DASH score < 15 or a significant MCID improvement (≥ 10.2 points against baseline);
   • A specific test: Cross-body adduction tolerated under increasing load (a 2 kg then a 5 kg dumbbell).
2. Progressive load resumption on the Gabbett principle (the training-injury paradox, BJSM 2016): +10-15 % of load a week, watching the acute to chronic workload ratio. Any significant increase in pain or stiffness the day after the effort must lead to a temporary reduction.⁹
3. Reintroducing sport-specific movements : start with analytical exercises at low speed and without load, then progress to more complex movements (throwing, the tennis serve, the snatch, the clean) under increasing load. Build in exercises of proprioception and neuromuscular control.¹⁰
4. End-of-rehabilitation functional tests :
   • Upper Quarter Y-Balance Test (UQYBT): asymmetry < 4 cm;
   • Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST): > 21 touches in 15 sec in the athlete;
   • Repeated throwing tests (the Athletic Shoulder Test, ASH) for throwing sports;
   • Bench press 1RM ≥ 90 % of the healthy side.
5. Psychological assessment of apprehension : the Shoulder Activity Scale + TSK-11 (kinesiophobia). A full return only if apprehension is low and confidence restored.¹¹

Criticism and controversy

1. A lack of standardised criteria for the AC joint : there is no test battery validated specifically for AC osteoarthritis. The thresholds (90 % strength, < 4 cm UQYBT) come from other shoulder conditions.
2. An underestimated role for the psychosocial factors : kinesiophobia, catastrophic beliefs (PCS), a mistaken perception of « irreversible » wear. Major predictors of chronicity and of poor functional results.¹¹
3. Heterogeneity of the « return to sport » : competitive CrossFit does not demand the same capacities as recreational golf. Individualisation is essential; the criteria must be adapted to the specific demand of the sport.¹⁰

Distal osteolysis (DCO): the « weightlifter s shoulder »

• General population: 5 % (a study of 7,000+ patients, of whom only 9 % were women);
• Weightlifters: up to 28 % (Cahill 1982);
• Adolescent and young adult patients: 6.5 % (mean age 15.9, of whom 24 % women, Roedl 2015).³

• Insidious, deep pain localised to the distal clavicle and the AC joint;
• Increased by the triggering activities (bench, dips, overhead);
• Tenderness on direct palpation of the AC joint and the distal clavicle;
• Cross-body adduction reproduces the pain;
• Systemic checks (weight, fever) normal, a discriminating element against inflammatory or infectious causes.¹

• Radiographs : often normal at first; later, resorption of the distal clavicle is seen, with widening of the AC joint space and sometimes micro-cysts.⁴
• MRI (the gold standard): marrow oedema of the distal clavicle (high T2/STIR signal), subchondral microfractures, thickening of the superior AC ligament, joint erosions, sometimes a periosteal reaction on the clavicle and the acromion.¹,⁴

A clinical stratification tool for the athlete

1. The acute phase (2-6 weeks) : stop the triggering activities (bench, dips, heavy overhead). Keep up alternative activities (cardio, lower body, pain-free movements). A short course of NSAIDs. Ice 15-20 min after effort.
2. The intermediate phase (6-12 weeks) : gradual reintroduction of the exercises, technical modifications (a wider grip for the bench, reduced depth for the dips, replacement by push-ups for a period). A structured scapular programme (Y, T, W, full-can, push-up plus).
3. The return phase : load progression +10-15 % a week (Gabbett 2016). If it fails after 3-6 months of well-conducted conservative care -> consider a guided corticosteroid injection, then a surgical discussion (Mumford).⁵

Criticism and controversy

• Should the young athlete be injected? The Kompel 2019 data (hip and knee) call for caution, in the young athlete in particular where joint life expectancy is long. To be kept for refractory cases after 3 months of conservative care.⁶
• Early surgery or prolonged conservative care? No consensus. The Welch 2024 SR does not show the superiority of early surgery over watchful waiting.⁵
• The role of bench press technique in prevention : a wider grip (1.5× shoulder width), a reduced range (no chest touch if symptomatic), a reduced incline, offer promising leads but have not been rigorously studied.

Classic case: assessment and conservative resolution

• Exquisite tenderness on direct palpation of the AC joint line;
• A positive cross-body adduction test (reproducing the familiar pain);
• A positive active compression test (O Brien) at the AC joint, negative deep (ruling out a SLAP);
• Full active range but painful at the end of elevation;
• No red flag.

1. Education + activity modification + a topical NSAID: 4 weeks;
2. Scapular rehabilitation + adjunct manual therapy: 6-8 weeks;
3. A significant reduction in pain (~50-60 % VAS) in most patients;
4. For the non-responders: an ultrasound-guided corticosteroid injection, giving ~50 % further relief for 6 to 12 months (Welch 2024).²

The diagnostic challenge: when AC osteoarthritis mimics another condition

• C4-C5 cervical radiculopathy : the Iyer & Kim 2016 SR (Curr Rev MSK Med) recalls that C4 or C5 involvement can give isolated pain at the top of the shoulder, mimicking AC osteoarthritis perfectly.⁵ The presence of neurological signs (paraesthesia, biceps weakness, a reduced biceps reflex), a positive Spurling or pain that is not reproduced by horizontal adduction must raise the cervical spine.
• Cuff tendinopathy : more diffuse pain, over the side of the deltoid, increased on active abduction at 60-120°.
• Long head of biceps tendinopathy : a positive Speed test, anterior pain more medially.
• Residual post-traumatic AC instability : a feeling of instability, sometimes a clunk on movement, a history of a fall onto the point of the shoulder.

A complex case: the geyser sign, massive AC cysts and rare complications

• A massive full-thickness cuff tear (supraspinatus + infraspinatus);
• Severe AC osteoarthritis with destruction of the disc;
• A massive synovial cyst extravasating through the AC joint into the superficial soft tissues (the « geyser » sign on the historical arthrogram).⁷

• Radiographs: clear resorption of the distal clavicle, widening of the AC joint space;
• MRI: intense marrow oedema of the distal clavicle (high T2/STIR signal), subchondral microfractures, thickening of the superior AC ligament;
• No glenohumeral effusion and no cuff involvement.

• Brachial plexus compression by an exuberant callus or a massive AC osteophyte (very rare but described cases);¹¹
• Compression secondary to chronic AC instability or to a clavicular non-union callus (the Wilkin 2017 case, PMC 5610820).¹²

A critique of how clinical cases are read

When, and to whom, should you refer?

• Fever with a painful AC joint or a hot, red swelling -> suspect infection (septic arthritis);
• A firm, painless mass over the clavicle -> an oncological work-up;
• A known history of cancer + new bone pain -> suspect a metastasis;
• Unexplained weight loss + persistent pain -> a general work-up;
• Progressive neurological deficit (paraesthesia, motor weakness) -> suspect nerve compression;
• High-energy trauma recently with a deformity -> an urgent radiological work-up;
• Polyarticular involvement + systemic signs -> suspect inflammatory rheumatic disease (RA, SpA).

• GP or rheumatologist : diagnosis, drug management (NSAIDs, paracetamol), an inflammatory work-up if systemic rheumatic disease is suspected.⁴
• Orthopaedic shoulder surgeon : if conservative care fails at > 3-6 months, a surgical indication (Mumford), major post-traumatic instability.⁵
• Interventional radiologist : an ultrasound-guided corticosteroid injection, essential for reliable intra-articular delivery (a failure rate of ~50 % without guidance).⁶
• Occupational therapist : adapting the workstation (painter, plasterer, handler) to reduce repetitive overhead stresses.
• Strength and conditioning coach : for the athlete, adapting the programme and modifying bench press, dip and overhead press technique.
• Pain psychologist : if a high TSK-11 and PCS persist despite education.

Measuring outcomes and overcoming barriers

• Lack of time : the most cited constraint, tied to administrative pressure and patient volume;
• Lack of critical appraisal skills : difficulty appraising and synthesising the literature;
• Lack of organisational support : limited access to databases, no mentoring;
• Resistance to change : a preference for traditional methods or entrenched beliefs (for example the routine use of ultrasound despite the absence of evidence).

A critique: beyond the guidelines

• The RCTs are run on homogeneous populations under ideal conditions, rarely representative of real patients (comorbidities, age, psychosocial complexity).
• Extrapolating the data from subacromial pain syndrome (SAPS/RCRSP) to isolated AC osteoarthritis stays an approximation; the grade A recommendations for exercise (Pieters 2020) are based on SAPS, not on the AC joint strictly speaking.⁷
• The « de-implementation » of passive modalities with no evidence (laser, shockwave, routine ultrasound) stays slow, held back by patient expectations and practitioner habits.⁸