A systematic review of the treatment of primary acromioclavicular joint osteoarthritis

Abstract

Background

This systematic review aims to comprehensively summarise and present the available evidence for the treatment of primary acromioclavicular joint (ACJ) osteoarthritis (OA).

Methods

Five databases were searched for studies investigating the management of ACJ OA. Included were studies with participants with clinical/radiological signs of primary ACJ OA, an intervention and included a functional outcome measure.

Results

Forty-eight studies were included. Treatments consisted of physiotherapy (n = 1 study), medical only (n = 11) and operative management (n = 36). Operative studies included five comparative trials – physiotherapy versus surgery (n = 1) and open versus arthroscopic resection (n = 4). A total of 1902 shoulders were treated for ACJ OA, mean age (51 years), 58% male and mean follow-up (28.5 months). Treatment with injection showed a mean improvement of 50% in pain levels at follow-up (mean = 7.5 months). The commonest surgical procedure was arthroscopic excision of the distal clavicle and operative studies averaged 6 months of conservative management and a mean functional outcome of 87.8%.

Conclusion

Studies varied in indication, intervention and quality but it did not provide evidence that both non-operative and operative interventions are effective. There was no significant difference between open or arthroscopic distal clavicle excision (DCE). Participants having between 0.5 and 2 cm of clavicle excised had good outcomes and those requiring concomitant shoulder procedures had similarly good outcomes.

Introduction

Shoulder pain is common, being the third most likely reason for presentation to primary care with a musculoskeletal complaint and an annual prevalence of over 40%.^1,2 Primary osteoarthritis (OA) of the acromioclavicular joint (ACJ) is a large contributor to this (up to one quarter ³ of primary care shoulder pain presentations). Initial treatment consists of oral analgesia, physiotherapy and joint injection, with surgical management for those with refractory symptoms, typically excision of the distal clavicle.^4,5 Other pathologies can exist concomitantly, thus providing diagnostic and management uncertainty. ⁶ These include glenohumeral or rotator cuff pathology, impingement syndromes and distal clavicle osteolysis, which tends to present in younger males who perform heavy lifting.^7,8

Several reviews have been published for ACJ pain, but none have provided a systematic, comprehensive overview of the evidence for the management strategies for primary ACJ OA, including conservative, medical and surgical treatments. Previous authors have reviewed the evidence for conservative or surgical management, ⁹ open versus arthroscopic distal clavicle excision (DCE),^5,10–12 as well as trends in surgical management and their outcomes. ¹³

There is no specific NICE, ¹⁴ BOA/BESS ¹⁵ or AAOS ¹⁶ secondary care pathway for the treatment of ACJ OA and a recent scoping review ⁶ of treatment of ACJ pain more generally reported a paucity of high-quality studies, concluding that there was no enough evidence to develop a treatment pathway. The aim of this systematic review is to identify the types, prevalence and effectiveness of different treatment modalities for ACJ arthritis, in order to inform potential treatment pathways.

Methods

The protocol for this review was registered with PROSPERO database (ID: CRD42021295185) to ensure transparency and no duplication of work. A systematic search of the literature was conducted by the authors in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) ¹⁷ checklist and protocols available at: http://www.prisma-statement.org/

On 29 November 2021, the following databases were systematically searched:

• MEDLINE;

• Ovid/HMIC/AMED/Embase;

• Cochrane Review Library;

• Trial registries:

  • ISRCTN and
  • ClinicalTrials.Gov.

Databases were searched using the search terms as shown in Table 1. A citation review, as well as a search of the grey literature (including non-peer reviewed and pre-print studies, manufacturers’ and healthcare organisations’ publications) and wider internet, was also performed.

Table 1.

Search strategy and terms used.

acromioclavicular OR acromioclavicular OR distal clavicle

AND

NOT osteolysis NOT dislocat* NOT septic NOT infection NOT reconstruct* NOT injur* NOT diagnos* NOT repair NOT diagnosis NOT report NOT fracture NOT fixation NOT stabili* NOT instablity NOT separation* NOT disrupt* NOT nonunion NOT ruptur* NOT imag* NOT radiog* NOT cadaver* NOT review* NOT editor* NOT cyst* NOT nerv* NOT osteochondroma

*indicates the wildcard term used for searching multiple characters or terms to give the widest search results for a given term.

All studies had to include participants with primary OA of the ACJ, as defined either nominally, clinically or radiographically, with at least one intervention and functional outcomes of the intervention. Studies include atraumatic ACJ pain with positive clinical tests such as cross-body arm adduction or compression tests (i.e. Paxinos test) or positive joint injection. These were included as they are defined as diagnostic in the current BESS/BOA guidance, ¹⁵ are widely validated and are sensitive (though not specific) to the joint.^18,19 Previous review articles assessing the ACJ have also used these criteria^5,6,9,20 Studies only assessing complication/revision rate or revision surgery were excluded. Studies that included only participants with post-traumatic OA and distal clavicular osteolysis were also specifically excluded, as these pathologies are different from primary OA and typically afflict at a younger age. No exclusions were made for age or language of studies.

Abstracts were screened independently by two of the authors using the inclusion and exclusion criteria listed in Tables 2 and 3, with the third author adjudicating in cases of disagreement over inclusion.

Table 2.

Inclusion criteria.

Inclusion criteria
ACJ arthritis +/− concomitant pathology – rotator cuff/impingement syndromes ACJ pain with CA adduction test + ve or radiographic degeneration At least one intervention – physiotherapy, joint injections, surgery Clinical studies – case series, RCTs Included QoL/functional/pain outcomes

ACJ: acromioclavicular joint; RCTs: randomised controlled trials.

Table 3.

Exclusion criteria.

Exclusion criteria
Studies including only participants with distal clavicular osteolysis Only studies for ACJ disruption/stabilisation/post-traumatic OA Revision surgery Biomechanical/cadaveric studies Reviews/knowledge summaries Case reports/letters Abstracts Purely complication or revision rate Unable to obtain complete study

ACJ: acromioclavicular joint; OA: osteoarthritis.

Studies were assessed for participant demographics, indications, follow-up length and pre-and post-interventional functional scores were extracted. If surgical, the length and type of initial conservative management and the types of surgery conducted were noted. Two screeners worked independently, and no data extraction tools were used. Mean functional scores (i.e. DASH, UCLA/Constant/ASES shoulder scores) were converted to a percentage of their total score to provide a method of comparison between varying scoring systems. This was used as there is no validated method to compare all of the numerous patient-related outcome measures. Whilst not used previously, this provides a simple way for the reader to assess between studies and allow quantitative comparison.

Figure 1 shows the PRISMA diagram with the number and outcomes of all studies found in the initial search.

Figure 1.

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) diagram showing the path of all papers found in the initial search.

Results

Forty-eight studies from 1968 to 2021 met the final inclusion criteria. One study included only physiotherapy as the sole intervention; 11 included joint injections but no operative management, with a majority being steroid/local anaesthetic, and 36 studies included operative procedures. Surgical studies included five comparative trials – four studied open versus arthroscopic resection and one physiotherapy versus surgery. Meta-analysis could not be performed due to the heterogeneity of the study’s methods and outcomes.

Demographics

Many studies included concomitant ACJ and shoulder disease, most often impingement or rotator cuff pathology as well as ACJ OA, but a majority of participants/joints in the studies had ACJ OA as their primary complaint. A total of 2324 joints were included in the studies with 1902 of them diagnosed as primary ACJ OA. The average age of participants was 51 years old, 60.3% were men and they had an average follow-up of 29 months. The majority (21/36) of operative studies originated in the United States whereas none of those studying only joint injection did, with these predominantly coming from Europe and Australia.

Physiotherapy (Appendix 1)

Only one study used physiotherapy as the sole intervention, though one study looked at physiotherapy versus surgical management in participants with ACJ OA and impingement. A case series looking at the effect of physiotherapy at a US military medical centre on participants with ACJ OA found that they had significantly improved functional outcomes at 6 months with physiotherapy alone. Another study ²¹ compared DCE with 3 months physiotherapy in participants with arthritis and impingement, finding that the operative group had significantly better functional outcomes at 1-year follow-up than the therapy group.

Joint injection (Appendix 2)

Eleven studies investigated 530 osteoarthritic joints treated with injection, the majority being steroid and local anaesthetic injection which is the accepted current non-operative treatment for ACJ OA. One studied prolotherapy and two looked at novel techniques including platelet-rich plasma (PRP) and radiosynoviorthesis. At an average of 7.5 months follow-up, all of the studies showed some positive effect on pain and/or function compared with baseline. There was an average pain reduction from a visual analog scale (VAS; out of 10) score from 6.4 to 3.0. When reported, functional scores improved from 51% to 79%. Three studies reported rates of progression to surgery of 59–67%,but with short follow-up from an injection of 1–5 months. In these studies, participants with a shorter response to joint injection were considered non-responders and offered surgery.

Operative management (Appendix 3)

Thirty-six studies reporting on operative outcomes in ACJ OA included 1386 osteoarthritic joints with an average follow-up of 37.4 months. Twenty-six studies looked at arthroscopic DCE and 14 open DCEs with 4 studies comparing open and arthroscopic. One study presented the findings from percutaneous DCE performed radiologically without the use of an arthroscope. ²² Nine studies also carried out subacromial decompression (SAD) for impingement and seven studies rotator cuff repair (RCR) for rotator cuff tears.

Functional scores improved from an average of 52.1% before the operation to 87.8% afterwards. This remained consistent whether RCR or SAD was carried out. All three interventions carried out together had a lower functional outcome score, but in only three studies with a small cohort of participants. This may be due to a combination of factors including poorer functional baseline but must be taken in the context of small numbers (Figure 2).

Figure 2.

Venn diagram showing numbers of operative studies including distal clavicle excision (DCE) +/− different interventions and numbers of shoulders within them. (% score indicates the average functional outcome score at final follow-up).

There was no association between age and functional outcome or between functional outcome and length of final follow-up. There was a large variation in the average mean participant age between studies. This may be partly due to the inclusion of studies that included other pathologies such as distal clavicle osteolysis or post-traumatic OA, as well as ACJ OA as these commonly present at an earlier age.

Quality of studies

Studies were quality assessed using the Cochrane Risk of Bias 2 (RoB2) tool ²³ and the results can be found in Appendix 4. There was significant variation in the methodology, quality, outcomes and reporting of the studies. There were two randomised controlled trials (RCTs)^24,25 within the injection category and three within the operative studies^26–28 which are classified as level 2 evidence. ²⁹ The other studies were a mixture of cohort studies and case series which are level 4 evidence. A majority (33/48) of the studies used a validated functional outcome score (i.e. ASES, UCLA and Constant), several used pain rating such as the VAS score (five studies) or another form (five studies) and the remainder used subjective or created scoring systems. Four studies failed to give key demographics such as age, sex distribution or number of participants.

Discussion

The evidence from this systematic review showed that when receiving treatment – whether this be physiotherapy, medical management or surgery – participants showed considerable improvement in their patient-related outcome measures including pain.

Non-operative management

There is a dearth of evidence for physiotherapy alone, with only one study looking at this despite it being a mainstay of treatment for a majority of participants with ACJ OA. The single study following participants undergoing only physiotherapy had short follow-up and was from a military health centre which may make the findings less applicable to the wider population. Studies looking at joint injections had a relatively short follow-up period and high rates of conversion to operative management. One UK ³⁰ study, however, found significantly improved functional scores at 5-year follow-up and correlation between younger age and greater improvement. Studies reporting duration of improvement of symptoms had large variation between them; Jacob and Sallay ³¹ reported 21 days of improvement whereas Kurta et al., ³² Bain et al. ³³ and Hossain et al. ³⁰ reported 3, 19.5 and 240 months respectively.

Operative management

Arthroscopic versus open DCE

Four studies looked at look at open versus arthroscopic DCE with differences in outcome. Two studies^26,34 found a non-significant increase in pain with open operations, another a significant increase ³⁵ and another ³⁶ conversely found significantly decreased pain with an open DCE. There were no apparent differences in participant demographics, numbers, methods or follow-up period to account for the contradictory findings. One reason posited for this is an open operation may be quicker and may allow greater adequacy of excision when compared with an arthroscopic approach but that arthroscopic is less invasive, as well as easier concomitant acromioplasty.

SAD/acromioplasty

Eight studies included concomitant SAD as well as DCE, all with positive outcomes. Dragoo et al., ³⁷ Levine et al. ³⁸ and Daluga and Dobozi ³⁹ all found good outcomes including whether a direct or bursal approach was used. Brix et al. ⁴⁰ found persistent pain at 6 months after the operation in approximately one-third of participants, with associations to compensation cases and a propensity to anxiety amongst those suffering ongoing symptoms.

RCR

Seven studies looking at DCE with RCR showed good results and used only the arthroscopic technique. A key finding was a RCT ²⁸ randomising participants with ACJ OA and 50–100% rotator cuff tears to DCE or DCE and RCR which showed no clinical difference in the outcome. Another RCT ²⁷ randomised participants with radiological ACJ OA and rotator cuff tears to RCR or RCR and DCE, also with no clinical difference in outcome. However, a larger case series ⁴¹ found that participants undergoing RCR who did not undergo a DCE had significantly worse functional outcomes. Three other studies^39,42,43 which included groups having concomitant RCR and DCE all found positive outcomes including reduction of pain, return to previous sporting level and participant satisfaction.

The results above from participants having concomitant surgery such as RCR or SAD show the need to ensure concomitant pathology is diagnosed prior to surgery. An arthroscopic approach to DCE allows SAD to be performed in the same operation with minimal additional time and procedure.

Patient selection

There were a small number of participants (>10%) who did not have good outcomes from surgery. Several studies also commented that participants who fared badly from surgery were worker compensation cases or those with predisposition to altered pain experience. Brix ⁴⁰ with 6 months follow-up, found that 36% of participants had persistent pain with significant associations of unemployment, insurance/compensation and anxiety traits to a worse outcome. A number of other studies^41,44,45 found that work-related injury participants had a significantly decreased functional score post-surgery or worse outcomes.^46–48 Many studies excluded participants with ongoing compensation claims.

Though this review covers primary ACJ OA, some included studies included other aetiologies. The studies which include OA with trauma as a causative agent show these participants to have poorer outcomes. Novak et al. ⁴⁵ found 4/5 ‘poor’ results had traumatic onset. Another study ⁴⁹ found only reasonable outcomes overall and warn ‘it is difficult to advocate this procedure as a common treatment for chronic pain of the ACJ due to a … degenerative condition.’ This study included a large proportion of participants with traumatic aetiology and found poorer outcomes in this subgroup.

Length of clavicular excision

There is varying evidence on the significance of the length of clavicle excised, with studies suggesting poorer outcomes if too little or too much clavicle is removed. A small study ⁴⁴ (n = 18) used a CT scan to quantify clavicular excision and found a mean resection length of 6.6 mm in ‘good’ results and 4 mm in ‘moderate or poor” results.’ Whilst this finding was not statistically significant, it may aid in advising a minimum resection length.

Another ⁴² measured average excision to be 9 mm and all participants were satisfied with a large majority returning to their previous level of sport. Eskola et al. ⁴⁹ in a study (n = 73) with 9 years average follow-up, and an average of 16 mm excision length found a significant association between increased excision length and pain, with participants who over 1 cm resected to have significantly more pain than those under 1 cm. They still found reasonable functional outcomes in those participants treated for primary ACJ OA. Duindam et al. ³⁶ compared arthroscopic and open excision finding a shorter average excision length in the arthroscopic group (3.2 mm) compared to 7.1 mm in the open group but no difference in the functional outcomes. Table 4 shows the length of DCE versus functional outcome in studies which included this information. There was no association between excision length and functional outcome score.

Table 4.

Length of excision versus functional outcome.

	Average clavicular excision (cm)	Functional outcome score
Kay 1994 50	1–1.5	90%
Snyder et al. 47	1.5–2.1	89.1%
Dragoo et al. 37	1.5	91.8%
Flatow 1995 51	0.6–1.25	NS (‘Satisfactory in 83%’)
Duindam et al. 36		78.3%
- Open	0.32	79%
- Arthroscopic	0.71	78%
Kim et al. 44	0.55	70.2%
Park 2016 52	0.4–0.7	95.4%
Ringshawl 2021 53	0.75	84.6%

The UK study looking at revision ⁵⁴ of DCE found that incomplete excision was the primary reason for revision ACJ excision, followed by heterotopic ossification. It also found that functional outcomes did not significantly improve, and satisfaction scores remained low in revision participants. Blazar et al. ⁵⁵ found increased pain in participants with greater translation of their remaining distal clavicle after excision.

BESS and BOA recommend the following pathway for non-operative treatment of ACJ OA as part of wider guidance for shoulder pain in primary care (Figure 3). Conservative measures and steroid injections are recommended along with radiographs if there is no improvement.

Figure 3.

Diagnosis and treatment of shoulder pain in primary care. ⁶⁰

Image-guided injection

Joint injections may be freehand or use image guidance, normally in the form of ultrasound. Bain et al. ³³ showed that the initial needle position without (fluoroscopic) guidance was only intra-articular 50% of the time. Park et al. ⁵⁶ directly compared palpation and ultrasound-guided injection in 100 participants, finding some functional outcomes to be significantly improved at 6 months in the ultrasound-guided group, but not at 1 or 3 months. Sabeti-Aschraf et al.^24,25 conversely found no difference between palpation and ultrasound-guided injections, as well as no difference between ultrasound-guided intra- or peri-articular injection at relatively short (3 weeks) follow-up. Another study ⁵⁷ proved joint entry in 96% using ultrasound and that the anterior superior aspect of the joint was the widest target even in advanced degeneration. Cadaveric studies have shown image guidance to improve needle aim and joint penetration.^58,59 Despite ultrasound guidance being shown to improve the accuracy of intra-articular injection, it is not clear that it improves clinical outcomes and the authors therefore do not recommend its use routinely.

Imaging

Many of the more recent studies in this review used pre-operative MRI, following radiographs to form an initial radiological diagnosis. MRI can provide knowledge of those likely to benefit most from other interventions with capsular hypertrophy shown to be the most significant finding related to (short-term) pain relief from injection. ⁶¹ In an asymptomatic cohort, Frigg et al. ⁶² found MRI-proven ACJ OA ‘remained asymptomatic in 83% of cases … 10% turned worse.’ Whilst not routinely recommended, the authors contend that MRI may be useful in a small cohort of patients for whom clinical tests are positive but radiographs normal or equivocal. In this case, MRI scan may help to distinguish between arthritis and temporary inflammation or pain due to other causes. For a majority of patients, MRI will be unnecessary and a strain on limited healthcare resources. Ultrasound can be used to confirm the presence of other causative aetiologies such as rotator cuff or biceps tendon pathology. ¹⁵

Pre-operative management

Eighteen studies (see Appendix 5) specified their initial non-operative management with an average of 6.4 months between commencing conservative management (including joint injection) and surgery. The studies gave ubiquitously positive outcomes for surgery with functional scores, pain and return to activity all improved in participants who had undergone an initial trial of non-operative treatment. After this period with steroid injection and other non-operative modalities, operative management should be considered for patients with ongoing symptoms with a high likelihood of benefit from surgery. Some patients will present more acutely and require more urgent operative management at the surgeon's discretion.

Strengths

This review was systematic, using the PRISMA guidelines, and made no exclusions for age or language. It captured a large number of participants with primary ACJ OA and used a pragmatic approach to ensure studies including participants with concomitant or different pathology were captured. The authors have ensured the findings are placed in a clinically relevant context with respect to UK practice.

Limitations

One of the key limitations of this review is that we only used English-language/Western databases and registers. Though no exclusions were made for language (and a non-English-language paper was included) studies in other languages, notably Chinese languages, may not have been captured as they may not be indexed in the databases used. A majority of operative studies were from the United States and, though the demographics of the patients were broadly similar to the author’s experience of those in the UK, they may not be generalisable to other populations. The quality and heterogeneity of studies within the review is a limitation with multiple measures of functional outcomes and variation in their report.

Conclusions

A large body of evidence for the treatment of primary ACJ OA was found. The quality of studies and outcomes was varied, as well as studies including mixed indications and interventions. Participants have improved functional outcomes from joint injection (over a limited period) and operative management after a period of non-operative management which averaged 6 months. There was no significant difference between open or arthroscopic DCE and patients having between 0.5 and 2 cm of clavicle excised had good outcomes. Participants requiring concomitant RCR or SAD had similarly good outcomes. Patients with specific factors (workers’ compensation claims, anxiety or altered pain perception) may have poorer outcomes.

Ultrasound-guided injection improves the accuracy of penetration of the joint with the needle but there is not good evidence to suggest this improves functional outcome. It is therefore not recommended routinely. MRI is not recommended routinely for patients with clinical and radiological OA.

The authors have collated all the available information on ACJ OA treatment and provided practical interpretation of the evidence regarding treatment.

Appendix 1.

Studies including conservative management of acromioclavicular joint (ACJ) osteoarthritis (OA).

Author	Year	Study type	Indication	Intervention	Participants	Joints	Mean age	Male sex	Average follow-up (months)	Outcome measures	Pre-score	Post-score
Harris	2012	Prospective cohort	ACJ OA	Physiotherapy	13	13	41.1	85%	6	SPADI ASES	34.6 59.5	4.8 92

Appendix 2.

Studies including ACJ injection.

Author	Year	Study type	Indication	Intervention	Participants	Joints	Mean age	Male sex	Average follow-up (months)	Outcome measures	Pre-score	Post-score
Kurta	2005	Prospective case series	ACJ OA (n = 13) Osteolysis (n = 4) Disruption (n = 1)	SI + LA	18	18	46.3	88.9%	0.5	VAS Duration of pain relief	7	3.6 14.3 weeks
Bain	2007	Case–control study	ACJ OA	USS-guided versus blind SI	44	44	46	25.0%	0	VAS Progression to surgery	6	2 (immediate) 59% at 5 months
Hossain	2008	Prospective case series	ACJ OA	SI	20	25	55	40%	12	Constant	60	87
Sabeti-Aschraf	2010	Prospective RCT	ACJ OA	USS versus palpation SI	20	20	51.3	55%	0.75	VAS-rest CMS	7.0 50.0	6.3 61.3
van Riet	2012	Prospective case series	ACJ OA	SI + LA	58	58	48	60%	42	VAS ASES UCLA		0.5 94.1 33.9
Sabeti-Aschraf	2013	Prospective RCT	ACJ OA	Intra versus peri-articular SI	101	106	53.1	NS	0.75	VAS-n VAS-p Constant-Murley COAT	5.22 5.76 54.5 2.25	2.42 2.68 73.3 1.1
Edelson	2014	Prospective case series	ACJ OA (n = 15) +/− RC tears +/− other pathology (n = 18)	SI + LA	48	48	53	46%	6	VAS	8 8	2.5 6.5
Park	2015	Retrospective case series	ACJ OA	USS-guided versus blind SI	100	100	58.5	23%	6	SPADI VNSar	52.9 5.09	29.0 2.38
Hsieh	2018	Prospective case series	ACJ OA/enthesopathy	Prolotherapy (dextrose + LA)	31	31	57.4	32.30%	2	VAS		delta = −4.3
Vereb	2018	Prospective case series	ACJ OA	Radiosynoviorthesis using erbium-169	51	85	64.3	35%	6	VAS	6.4	3.4
Ramesh Raja	2021	Prospective case series	ACJ OA	PRP injection	13	16	51	62%	6	Constant	45	89

ACJ: primary acromioclavicular joint; LA: local anaesthetic; OA: osteoarthritis; RC tear: rotator cuff tear; SI: steroid injection.

Appendix 3.

Studies including operative management of ACJ arthritis.

Author	Year	Study type	Indication	Intervention	Participants	Joints	Mean age	Male sex	Final follow-up (months)	Outcome measures	Pre-score	Post-score
Worcester and Green	1968	Retrospective case series	ACJ OA (n = 56)	Open DCE	56	56	54	63%	54	Pain ROM		Majority pain free and full ROM by 4 months
Daluga	1989	Retrospective case series	Imp +/− ACJ OA +/− RC Imp, ACJ OA (n = 13) Imp, ACJ OA, RC (n = 10) Imp (n = 18) Imp + RC (n = 9)	SAD + Open DCE SAD + Open DCE + RCR SAD SAD + RCR	50	50	53	76%	45	Loyola Shoulder Evaluation	NS	Excellent = 32, good = 14, average = 2, poor = 2
Bigliani	1993	Retrospective case series	ACJ OA Osteolysis Traumatic OA	Arthro DCE	NS	42	NS	NS	21	Resolution of pain/return to full activity		93% (37% in traumatic OA)
Gartsman	1993	Retrospective case series	ACJ OA	Arthro DCE SI	20	20	51.3	65%	24	ASES -Pain -Work -ADLs -Sports	2.1 2.1 1.9 1.1	4.5 3.5 3.8 3.6
Jerosch	1993	Prospective case series	ACJ OA (n = 35) Post-traumatic (n = 16)	Arthro DCE	51	51	48.4	52.9%	13.4	homemade QOL (pain, movement, strength, ROM)	67.8	93.3
Tolin	1993	Retrospective case series	ACJ OA	Arthro DCE	33	33	39	82.0%	25	UCLA		Excellent = 9, Good = 11, Fair = 3 22 returned to pre-injury level of sport
Kay	1994	Prospective case series	ACJ OA	Arthro DCE	10	10	44	80%	14	UCLA	All pain on movement. 9 had ADL/night pain	All ‘good or excellent result(s)’
Petchell	1994	Retrospective case series	ACJ OA (n = 10) Post-traumatic OA (n = 7) Osteolysis (n = 1)	Open DCE	18	18	38	83%	36	UCLA	NS	Excellent = 4, Good = 9, Fair = 5
Flatow	1995	Retrospective case series	ACJ OA (n = 16) Osteolysis (n = 13) ACJ seperation (n = 8) Hypermobility (n = 4)	Arthro DCE	41	41	32	76%	31	NS	NS	‘41 shoulders were excellent in 18 (44%), good in 16 (39%), and poor in seven (17%). Therefore satisfactory results were noted in 83% of this overall treatment group.’
Novak	1995	Retrospective case series	ACJ OA (n = 10) Osteolysis (n = 1)	Open DCE	21	23	36	NS	30	HSS	NS	87 ‘12 excellent, 6 good, 4 fair, 1 poor’
Snyder	1995	Retrospective case series	ACJ OA	Arthro DCE	46	50	42	84.8%	24	Pain UCLA	7.7 24	1.7 34, 94% high/excellent
Eskola	1996	Retrospective cohort	ACJ OA (n = 33) Traumatic OA (n = 40)	Open DCE	73	73	43	64%	108	Subjective	NS	11 – good; 13 – satisfactory; 9 – poor
Blazar	1998	Retrospective case series	ACJ OA	Open DCE	16	17	39	75%	12	University of Pennsylvania Shoulder Score	NS	90.9
Gürbuz	1998	Prospective case series	ACJ OA + impingement	DCE +/− ant acromioplasty +/− RCR (n = 12) Physio (n = 14)	27	27	57.6	37.0%	13	UCLA	13 10	28 13
Jacob	1998		ACJ OA	SI + LA Arthro DCE	27	27	38	77.4%	19	ASES	NS	81 95
Levine	1998	Retrospective case series	ACJ OA	Arthro DCE + SAD	24	24	55	58%	32.5	Pain (1–5, 5 = no pain)	1.8	4.3
Lesko	1999	Prospective case series	ACJ OA (n = 57)	Artho DCE +/− RCR	57	57	NS	NS	NS	Pain	NS	‘Improvement or elimination of the distal clavicle pain was reported in all subjects’
Martin	2001	Prospective case series	ACJ pain + Imp ACJ OA (n = 13) Osteolysis (n = 3) Joint injury (n = 15)	DCE + RCR	31	32	36	93.5%	24	Functional ADLs score	2.7	3.9
Kay	2003		ACJ OA (n = 16) Osteolysis (n = 4)	Arthro DCE + SAD	20	20	NS	85%	72	UCLA Constant	17.5 70.5	29.8 98.5
Barber	2006	Prospective case series	Impingement +/− ACJ OA + OA (n = 23)	SAD +/− Arthro DCE	81	81	46	69.1%	73	Constant ASES	NS	96.0 97.7
Levine	2006	Retrospective case series	ACJ OA (n = 58) Osteolysis (n = 5) Both (3)	Bursal-approach Arthro DCE + SAD Direct-approach Arthro DCE + SAD	60	66	46	75%	72	ASES	NS	90 94
Freedman	2007	Prospective RCT	OA (n = 8) Osteolysis (n = 4) Traumatic OA (n = 5)	Arthro DCE Open DCE	17	17	40	94%	12	VAS SF36 – bodily pain subscale	4 43	1.4 69
Cheung	2009	Prospective cohort study	ACJ OA (n = 57) Osteolysis (n = 7)	Open DCE +/− ant/inf. acromioplasty	58	64	48	74.1%	99.6	Pain (1–5, 5 = worst) ASES	4.7	2.3 88.3
Elhassan	2009	Retrospective case series	ACJ OA (n = 102) Osteolysis (n = 3)	Arthro DCE Open DCE	103	105	45	46%	50	VAS Constant	7.7 48	1.8 88
teStroet	2010	Prospective case series	ACJ OA (n = 13) Traumatic OA (n = 10)	Open DCE	22	23	44	45.5%	12	VAS Constant	70 64	25 86
Robertson	2011	Retrospective cohort	ACJ OA (n = 44) Osteolysis (n = 5)	Arthro DCE Open DCE	48	49	49	52%	57	VAS ASES VAS ASES	NS	0.61 94.6 1.59 87.5
Duindam	2014	Retrospective cohort	ACJ OA (n = 145) Traumatic OA (n = 4)	Arthro DCE Open DCE	143	149	53.5	37%	38	VAS (0–100) DASH	NS	17.2 21.7
Kim	2014	Retrospective cohort	ACJ OA (n = 10) Traumatic OA (n = 8)	Arthro DCE	18	18	49	83%	32	Constant	57.7	70.2
Oh	2014	Prospective RCT	Asymptomatic ACJ OA + RC tears	RCR +/− DCE	78	78	63.8	69%	29	VAS Constant ASES	6.7 74.0 48.9	0.6 96.0 93.0
Park	2015	Prospective RCT	ACJ OA + RC tears	RCR +/− DCE	56	58	62.6	19%	44	VAS Constant ASES	5.3 44.5 39.5	1.8 74.5 81
Razmjou	2015	Prospective case series	ACJ OA + RC tears	144 DCE + RCR 40 RCR	184	184	62	60.9%	24	ASES RCMS ASES RCMS	49 51 44 47	86 96 77 85
Gokkus	2016	Retrospective case series	ACJ OA	Open DCE	30	30	52.5	40%	27	VAS UCLA	83.6 11.5	26.6 29.2
Park	2016	Prospective case series	ACJ OA	Arthro DCE	20	20	56	50%	74	UCLA	13.7	33.4
Brix	2019	Prospective case series	ACJ OA	Arthro ACJ resection +/− SAD	101	101	56	39.0%	6	No pain	NS	64.40%
Ng	2020	Prospective case series	ACJ OA	Percutaneous DCE	15	15	61.7	73%	27	VAS Constant SF-36	6.2 51.7 59.8	0 87.3 94.9
Ringshawl	2021	Prospective case series	ACJ OA 92% OA 8% traumatic OA	Arthro DCE	50	50	49.7	36.0%	36	UCLA	13.2	29.6

ACJ: primary acromioclavicular joint; Arthro DCE: arthroscopic distal clavicle excision; Imp: sub-acromial impingement; NS: not specified; OA: osteoarthritis; Open DCE: open distal clavicle excision; RC: rotator cuff tear; RCR: rotator cuff repair; SAD: subacromial decompression; Trauma: post-traumatic OA.

Appendix 4.

Cochrane Risk of Bias 2 (ROB2) quality assessment of studies.

Non-operative study	Year	Bias arising from randomisation	Bias due to deviation from intended interventions	Bias due to missing outcome data	Bias in the measurement of the outcome	Bias in the selection of the reported result	Overall risk of bias
Harris	2012	–
Kurta	2005	–
Bain	2007	–
Hossain	2008	–
Sabeti-Aschraf	2010
Van Riet	2012	–
Sabeti-Aschraf	2013
Edelson	2014	–
Park	2015	–
Hsieh	2018	–
Vereb	2018	–
Ramesh Raja	2021	–

 = low risk of bias;  = some concerns about bias;  = high risk of bias.

Appendix 5.

Length and form of conservative management prior to operative management in surgical studies.

Author	Initial conservative management (months)	Form of conservative management	Joints
Gartsman	12.2	NSAIDs;SI	20
Jerosch	9.8	Not specified	51
Tolin	6	NSAIDs; PT; maximum 2 × SI	33
Kay	4	NSAIDs; lidocaine injection	10
Flatow	10.5	NSAIDs, heat, activity modification and SI	41
Novak	6	Not specified	23
Blazar	6	Not specified	17
Gürbuz	4.5	Not specified	27
Levine	6	NSAIDs; heat; activity modification; confirmatory SI	24
Martin	10	Not specified	32
Kay	6	Not specified	20
Freedman	6	NSAIDs; cryotherapy; activity modification	17
Elhassan	3	Not specified	105
Robertson	6	NSAIDs; PT; SI	49
Gokkus	3	NSAIDs; electrotherapy; activity modification; SI	30
Park	5	Not specified	20
Ng	3	NSAIDs; activity modification	15
Ringshawl	6	Not specified	50
	Average: 6.4		Total: 584

PT: physiotherapy; SI: steroid/local anaesthetic injection.