Subsidence following surgical stabilization of acromioclavicular joint injuries: Should we be concerned?

Abstract

Subsidence, or loss of reduction, is a recognized concern following surgical stabilization of acromioclavicular joint injuries and remains a source of debate regarding its clinical importance and implications for revision. This minireview synthesizes the available evidence on the incidence of postoperative subsidence, the diverse radiological criteria used to define it, and its correlation with functional outcomes. Reported rates vary widely, from 15% to 80%, reflecting differences in fixation methods, surgical technique, and follow-up duration. Suspensory button systems and graft reconstructions are particularly prone to early loss of reduction, whereas hook plates tend to preserve initial alignment but are limited by implant-related complications such as subacromial erosion and the necessity for removal. Despite measurable subsidence, several studies demonstrate that global shoulder scores often remain satisfactory, although patients may experience persistent pain, cosmetic dissatisfaction, or functional impairment that can prompt revision surgery. Current evidence suggests that re-displacement alone should not be considered an indication for reoperation; revision is best reserved for symptomatic patients or those with device-related complications. Standardized definitions of subsidence and consistent use of acromioclavicular-specific patient-reported outcome measures are essential to determine its true clinical relevance and to refine surgical decision-making.

Key Words: Acromioclavicular joint; Acromioclavicular joint disruption; Acromioclavicular joint subsidence; Loss of reduction; Postoperative instability; Vertical stability; Horizontal stability; Coracoclavicular reconstruction; Tunnel malposition

Core Tip: Loss of reduction after surgical management of acromioclavicular joint injuries remains common across all fixation methods, yet its clinical relevance varies widely and is often poorly correlated with radiographic findings. This narrative minireview synthesizes current evidence to clarify how loss of reduction should be defined, why it occurs, which surgical and technical factors place patients at higher risk, and when revision reconstruction is truly justified. The minireview emphasizes that radiographs alone should not dictate management; instead, postoperative decision-making must integrate vertical and horizontal stability, tunnel accuracy, construct integrity, and the patient’s clinical symptoms and functional demands.

INTRODUCTION

The acromioclavicular joint (ACJ) plays a pivotal role in maintaining coordinated shoulder girdle motion and load transmission between the clavicle and scapula. Its stability relies on the balanced contribution of both vertical and horizontal restraints. The vertical plane is primarily governed by the coracoclavicular (CC) ligaments: The conoid and trapezoid, while the horizontal plane depends on the acromioclavicular (AC) capsule and the delto-trapezial fascia[1]. These elements act synergistically, allowing physiological gliding while preserving joint congruence during arm elevation. Disruption of these structures, whether partial or complete, alters normal scapulothoracic kinematics and can lead to pain, weakness, and a visible deformity of the shoulder contour[2,3].

The management of ACJ disruption remains one of the most debated topics in shoulder surgery. Treatment decisions are influenced by injury patterns, timing, patient activity level, and surgeon preference. Nonoperative care is generally reserved for low-grade injuries with intact vertical stability, whereas surgical intervention is advocated for displaced, high-grade, or symptomatic cases[4]. A wide spectrum of operative techniques has been described to restore both vertical and horizontal stability. These include rigid fixation methods such as hook plates and screws, suspensory button systems, tendon graft reconstructions, and various arthroscopic-assisted or minimally invasive procedures. Modern anatomic reconstructions aim to reproduce the native CC ligaments footprints, often using tendon grafts or synthetic materials to achieve durable stability[5,6].

Despite the substantial advances in implant design and surgical technique, postoperative complications remain frequent. Hardware irritation, infection, coracoid or clavicular fracture, and subacromial erosion are well-recognized concerns[7]. Among these complications, loss of reduction (LOR), often broadly referred to as postoperative subsidence in the literature, has emerged as the most prevalent and clinically relevant mode of failure following ACJ surgical stabilization. Notably, however, that true subsidence may reflect gradual implant-related settling within bone, whereas LOR more generally encompasses construct failure, recurrent ligamentous insufficiency, or loss of CC and or AC stability over time. Reported rates of LOR vary widely, ranging from approximately 15% to 80%[7-13], reflecting heterogeneity in surgical techniques, fixation constructs, rehabilitation protocols, and, importantly, the lack of a standardized definition of failure. This variability limits meaningful comparison across studies and complicates interpretation of outcomes.

The true clinical relevance of LOR, however, remains contentious. Several studies have demonstrated that radiographic displacement does not necessarily correlate with inferior shoulder function, with many patients achieving satisfactory clinical outcomes despite measurable LOR. Conversely, other patients may develop persistent pain, cosmetic dissatisfaction, or symptomatic instability that ultimately necessitates revision surgery. The challenge for the surgeon lies in discerning when radiographic findings are clinically meaningful and when observation is justified.

This narrative minireview explores the current understanding of postoperative LOR following surgical stabilization of the ACJ. It aims to clarify how this phenomenon has been defined and assessed in the literature, summarize its reported incidence across different fixation techniques, and examine its relationship to clinical outcomes. In addition, the minireview discusses whether revision surgery is warranted universally or should it be reserved for selected patients based on functional impairment. To ensure comprehensive coverage while preserving the narrative nature of the review, a structured literature search was conducted using PubMed, Scopus, and Web of Science databases for English-language articles published between 2000 and 2025, supplemented by manual cross-referencing of relevant bibliographies. Article selection was guided by relevance to the topic, with inclusion of studies that explicitly reported the incidence of postoperative LOR following ACJ surgery, clearly described the surgical technique employed, and provided an adequate duration of clinical and radiographic follow-up. Through this synthesis, we aim to provide practical insights into interpreting postoperative LOR and integrating radiographic findings into evidence-informed clinical decision-making.

CLASSIFICATION OF ACJ INJURIES

ACJ injuries can be broadly categorized according to timing and severity. From a temporal perspective, they are classified as acute or chronic disruptions. Acute injuries follow a recent traumatic event and are characterized by ligamentous failure of varying extent. In contrast, chronic ACJ instability develops when an acute injury is neglected or inadequately treated, leading to persistent pain, deformity, or functional limitation. The precise definition of chronicity remains controversial. Pathoanatomically, the chronic state reflects irreversible retraction and scarring of the disrupted ligaments, particularly the AC and CC ligamentous complexes. Once this occurs, spontaneous healing becomes unlikely, even if anatomic reduction is achieved. Although there is no universal consensus, most authors consider the transition to chronicity to occur after approximately three weeks following the initial injury. Beyond this period, the potential for biological healing diminishes substantially, though clinical differentiation between a subacute injury capable of recovery and a truly chronic disruption remains challenging[14-16].

Understanding the sequential mechanism of ligamentous injury is fundamental to interpreting these classifications. Typically, trauma causes sprain or rupture of the AC ligaments, compromising horizontal stability. With greater force, the CC ligaments fail, producing vertical instability. In the most severe injuries, detachment or tearing of the delto-trapezial fascia occur, resulting in gross deformity and functional compromise[3].

Several classification systems have been proposed to describe the spectrum of ACJ injuries. The early system by Tossy et al[17] divided injuries into three grades. Grade I represents a mild sprain with localized tenderness but no deformity or radiographic abnormality. Grade II involves partial disruption of the AC capsule and partial tearing of the CC ligaments, resulting in slight clavicular elevation and increased joint space. Grade III denotes complete dislocation with rupture of both the AC and CC ligaments, producing evident deformity and substantial widening of the CC interval. Subsequently, Allman[18] simplified the classification while maintaining its three-grade framework. In their model, grades I correspond to a simple sprain of the AC capsule, grades II to rupture of the AC ligaments with partial displacement of the clavicle, and grades III to complete disruption of both AC and CC ligaments, leading to full separation of the joint.

Recognizing that these systems could not fully capture the range of displacement patterns observed clinically, Rockwood and Green later expanded the classification to six distinct types. As illustrated in Figure 1, type I indicates a sprain of the AC ligaments with intact CC structures, while type II represents a complete tear of the AC ligaments with partial disruption of the CC ligaments, resulting in mild vertical displacement. Type III involves complete rupture of both AC and CC ligaments with 25%-100% superior migration of the distal clavicle relative to the contralateral side. Type IV is characterized by posterior displacement of the clavicle into the trapezius fascia. Type V signifies more extensive soft-tissue injury, with stripping of the delto-trapezial fascia from the distal clavicle and an increase in CC distance (CCD) of up to threefold. The rare type VI injury denotes inferior displacement of the distal clavicle beneath the coracoid process, often associated with high-energy trauma and severe soft-tissue disruption[19]. This expanded classification remains the most widely adopted in both clinical and research settings. It not only quantifies the extent of vertical and horizontal displacement but also guides treatment decisions and allows more consistent reporting of outcomes across studies.

Figure 1 Rockwood and Green classification for acromioclavicular joint injuries. Schematic representation of the six injury grades based on ligamentous disruption and clavicular displacement.

MANAGEMENT OF ACJ INJURIES

Conservative management remains the standard of care for lower-grade injuries in which structural integrity and vertical stability are largely preserved. These include types I, II, and III in selected cases. Nonetheless, surgical intervention is generally indicated for more complex or unstable injuries aiming to restore both anatomical alignment and functional stability of the shoulder girdle. Despite the diversity of available procedures, several foundational principles are shared across all surgical techniques. The initial priority is to achieve an accurate reduction of the joint to re-establish the normal relationship between the clavicle and the acromion. The second is to reconstruct or reinforce the torn ligamentous structures, particularly the AC and CC ligaments, using biological or synthetic grafts that replicate the native stabilizers. The third principle involves providing adequate mechanical stability during the healing period, either through inherently stable fixation or by temporary supplementary devices. Finally, when rigid fixation is used, implant removal after consolidation is generally recommended to minimize hardware-related complications[4].

Although these principles are widely acknowledged, significant variation exists regarding the timing of intervention, the type of fixation or reconstruction, and the surgical approach[5,6]. More than hundred techniques have been described, reflecting the ongoing search for the ideal balance between biomechanical strength and biological healing[20].

For acute ACJ disruptions, fixation options include pinning, hook plate, Bosworth screw, tension band wiring (TBW), and CC ligamentous reconstruction. These methods primarily aim to maintain reduction while the soft tissues heal. In chronic cases, management requires more complex reconstruction to address both vertical and horizontal instability. Procedures such as the modified Weaver-Dunn (WD), and anatomic CC ligamentous reconstruction, with distal clavicle excision in in selected situations have been reported to restore function and alleviate pain in the chronic setting.

Recent advances in arthroscopic technology have significantly influenced ACJ surgery. Enhanced visualization of the coracoid process allows accurate device placement while minimizing soft-tissue dissection and preserving the delto-trapezial fascia. This approach also reduces the risk of neurovascular injury[21]. Arthroscopic and arthroscopic-assisted techniques now include the Tight-Rope system, coracoid cerclage, and double-button constructs, all intended to provide stable fixation with less morbidity.

COMPLICATIONS OF ACJ SURGERY

Complications following ACJ injuries may arise from the initial trauma or from the surgical procedure itself. Recognizing these complications is essential not only for understanding the underlying mode of failure but also for guiding revision strategies and improving long-term outcomes. Pain resulting from residual horizontal instability, failure of fixation[22], infection[23], distal clavicle osteolysis[24], or fractures involving the coracoid or clavicle[25,26] are among the most frequent sources of postoperative morbidity.

The most prevalent and clinically relevant postoperative complication remains the LOR, which continues to challenge surgeons and represents a principal determinant of patient satisfaction and functional recovery[7]. LOR can result from several mechanisms, including biological, mechanical, or combined failure. Careful identification of such patterns allows the surgeon to correct the primary cause and thereby increase the likelihood of success in subsequent interventions.

BIOMECHANICAL RATIONALE FOR POSTOPERATIVE SUBSIDENCE

Postoperative subsidence after ACJ reconstruction reflects the interaction of construct mechanics, tunnel geometry, biological healing, and early loading. The ACJ is exposed to significant vertical and horizontal forces during daily activities. Subsidence in the vertical plane often results from graft elongation, suture stretch, button slippage, or progressive widening of clavicular and coracoid tunnels under cyclic load[27,28]. Horizontal stability relies on the AC capsule and overlying fascia, and techniques that reconstruct only the CC ligaments may leave persistent anterior-posterior translation, allowing gradual mechanical drift despite apparent initial reduction[29,30].

Accurate tunnel placement is critical. Medialized or oversized tunnels concentrate stress and predispose to early tunnel enlargement, altered force vectors, and progressive LOR. Constructs that rely on cortical buttons or coracoid fixation are particularly sensitive to tunnel position and bone quality. Biological factors such as delayed graft incorporation, insufficient delto-trapezial healing, poor bone stock, and local tissue damage further reduce resistance to repetitive load[31-33]. Certain fixation strategies, such as hook plates, resist early displacement but shift stress to adjacent structures once motion is resumed[34]. Overall, postoperative subsidence represents a combined mechanical and biological compromise. Minor early settling may be clinically irrelevant, whereas progressive or bidirectional instability often reflects underlying construct or tunnel issues that affect long-term outcomes.

RADIOGRAPHIC CRITERIA FOR ANATOMIC / ACCEPTED REDUCTION

Radiographic evaluation remains the cornerstone for assessing the quality and maintenance of ACJ reduction following surgery. A successful reduction is characterized by restoration of the normal CCD, appropriate joint alignment, and stability throughout follow-up. Among available imaging modalities, the Zanca view is widely accepted as the standard projection for evaluating the ACJ. This specialized anteroposterior view, obtained with a 10°-15° cephalic tilt, minimizes overlap of the bony contours and allows accurate visualization of the joint space and CC interval. Because of its precision and reproducibility, it is preferred both for postoperative assessment and serial follow-up imaging[35].

Postoperative evaluation of ACJ alignment primarily relies on measuring the CCD, the side-to-side difference in CCD relative to the contralateral shoulder, and the CCD ratio between both sides. The CCD is defined as the perpendicular distance from the uppermost border of the coracoid process to the opposing inferior cortex of the clavicle (Figure 2A). Reported normal CCD values vary across studies depending on imaging technique, population characteristics, and measurement landmarks. While several authors describe a normal CCD range of approximately 11 mm to 13 mm, others report lower mean values, such as 8.6 ± 1.9 mm, and a side-to-side difference within 5 mm compared with the uninjured shoulder, being more reliable than absolute values. A stable reduction should demonstrate no re-dislocation, corresponding to less than a 50% increase in CCD relative to the contralateral side. These parameters collectively define an acceptable ACJ reduction[36].

Figure 2  Radiographic and anatomical measurements. A: Coracoclavicular interval measurements used to assess acromioclavicular joint (ACJ) reduction. Coracoclavicular distance (CCD) of the contralateral normal side (A) and the injured side (B) are demonstrated; CCD difference is calculated as (B minus A), and CCD ratio as (B divided by A); B: Assessment of clavicular tunnel positioning following ACJ reconstruction. The clavicular tunnel ratio is obtained by dividing the distance from the lateral clavicular border to the center of each bone tunnel by the total clavicular length; C: ACJ subluxation ratio. The ratio is determined as (D/A) × 100%, where D is the perpendicular distance from the inferior clavicle to the inferior acromial tangent line, and A is the perpendicular height of the acromion at its midline; D: Measurement of ACJ widening. Widening is calculated as the mean of the superior and inferior clavicle-to-acromion distances (A and B), compared with corresponding measurements on the contralateral shoulder. DCTP: Distance from the lateral clavicular border to the center of each bone tunnel.

Moreover, Apivatgaroon et al[37] defined an anatomical ACJ reduction, on immediate postoperative radiographs, as a CCD within 2 mm from the normal side with no over-reduction. Hence, anatomical restoration, avoidance of over-reduction, and maintenance of vertical alignment are the principal radiographic criteria defining a successful ACJ reduction and vertical stability[38].

The positioning and sizing of clavicular tunnels in anatomic CC ligament reconstruction are among the strongest predictors of sustained reduction. Accurate placement and maintained size of drilled tunnels can guarantee fixation strength without future re-displacement. Tunnel placement is quantified using the clavicular tunnel ratio, which is calculated by dividing the distance from the lateral border of the clavicle to the center of the tunnel by the total clavicular length (Figure 2B). Investigations demonstrated that placement of the conoid tunnel at approximately 25% of the clavicular length from the lateral edge is optimal for maintaining reduction[37,39].

An alternative geometric method for evaluating tunnel position has been proposed by Mori et al[40]. In such approach, a circle is drawn around the coracoid process, and a line is traced along the superior surface of the clavicle on the Zanca view. A rectangle is then created using these two landmarks; when all tunnels fall within the rectangle, the position is considered satisfactory and associated with improved maintenance of reduction. Horizontal stability is assessed using the axillary view, which allows evaluation of anteroposterior translation of the lateral clavicle. The joint is considered horizontally stable if translation is less than 50% compared with the uninjured side[41,42].

RADIOGRAPHIC CRITERIA OF LOR

Both Spencer et al[8] and Milewski et al[9] defined radiographic failure or LOR as an increase in CCD greater than 5 mm compared with immediate postoperative measurements. Similarly, over-reduction is considered undesirable, as it produces a non-anatomical alignment[38]. Saccomanno et al[35] proposed a three-tier system for evaluating reduction maintenance based on side-to-side differences. Reduction was considered maintained when no difference was observed, partial loss when the displacement was less than the clavicular width, and complete loss when the displacement exceeded one clavicular width[43].

Similarly, Taft et al[44] categorized quality reduction using quantitative CCD differences: Anatomical reduction of 0 to 2 mm, slight loss of 2 mm to 4 mm, partial loss of 4 mm to 8 mm, and total loss of more than 8 mm. Martetschläger et al[45] considered a 10-millimeter side-to-side difference or increase in CCD as LOR, while Yoo et al[46] reported partial or complete loss according to whether the difference was less or greater than the clavicular width.

Yoo et al[47] defined vertical LOR as an increase in the CCD ratio greater than 25% percent, whereas in a later report they proposed a threshold of more than 50%. Madi et al[48], in concordance with Rockwood and Young, considered re-displacement to be present when the mean CCD reached or exceeded 100% of the contralateral shoulder, with values between 50% and 100% interpreted as subluxation[48]. Nonetheless, Clavert et al[49] described persistent dislocation when this ratio surpassed 150%. Given these varying criteria, the definitions of LOR remain inconsistent among studies. Some authors advocate for a stricter and more uniform definition: An increase in CCD of more than 25%, equivalent to approximately 2.3-millimeter-subsidence, assuming a mean contralateral normal CCD of 8.6 ± 1.9 mm[50].

The AC joint subluxation ratio provides another means to assess vertical displacement (Figure 2C). A line is drawn along the inferior border of the acromion, and a perpendicular line is extended from this reference to the superior acromial border to measure acromial height (A). A second perpendicular line is drawn from the inferior acromial border to the inferior clavicular border, and the length is recorded as (D). The subluxation ratio is calculated as (D/A) × 100, with values of 50% or greater indicating LOR[37,51]. The degree of ACJ widening can be assessed by measuring the mean distance between the superior borders of the acromion and clavicle and between their inferior borders (Figure 2D). Apivatgaroon et al[37] defined LOR as widening of 2 mm or more compared with the uninjured side.

A medial conoid tunnel placement, exceeding 25% of the total clavicular length from the lateral edge, has been identified as a significant risk factor for LOR[37,39]. When evaluated by the rectangular reference method, tunnel placement outside the defined rectangular zone correlates with higher likelihood of recurrent displacement[40]. Additionally, tunnel widening is a critical sign of mechanical insufficiency. When the ratio of the final tunnel diameter to the initial postoperative diameter exceeds 150% percent, the probability of LOR increases markedly. This measurement is performed by comparing immediate postoperative and final follow-up radiographs[37]. The ACJ is considered subluxated when translation of the lateral clavicle is between 50% and 100% and fully dislocated when translation exceeds 100% relative to the uninjured shoulder[41,42].

CLINICALLY RELEVANT LOR

Despite the previously mentioned radiographic criteria, there is no universally accepted definition of clinically meaningful LOR after ACJ stabilization. Many patients exhibit small degrees of postoperative settling, which often reflect graft remodeling, device adaptation, or early biological relaxation rather than true mechanical failure. Such changes are frequently asymptomatic and do not compromise functional recovery.

Clinically relevant LOR should therefore not be defined radiologically alone. Instead, it should be recognized when postoperative re-displacement is accompanied by symptoms that affect daily or athletic activities. These include persistent pain, subjective or objective instability, strength deficits during overhead tasks, or a deformity that the patient finds unacceptable[52].

A practical definition should integrate a measurable postoperative displacement, evidence for progressive or static instability, and clear correlation with patient-reported symptoms or functional limitations. This combined approach can avoid overinterpretation of benign radiographic changes and identifies the cases in which LOR reflects true biomechanical failure requiring further intervention.

INCIDENCE OF LOR FOLLOWING SURGICAL MANAGEMENT OF ACJ INJURIES

Reported rates of LOR vary markedly across the literature, ranging from 15% to 80%[7,10-13]. This wide discrepancy likely reflects differences in fixation constructs, injury chronicity, and definitions of radiographic failure. Tables 1, 2, 3, and 4 summarize the available evidence across major operative categories, including pinning[53,54], CC screw[55-57], TBW constructs[58-60], hook plate[61-66], graft-based reconstructions[67-75], arthroscopic and arthroscopic-assisted procedures[42,76-84], synthetic ligament augmentation[85-88], and anchor-based techniques[89,90].

Table 1 Incidence of loss of reduction after acromioclavicular joint pinning, coracoclavicular screw fixation, hook plate, and tension band wiring in acute acromioclavicular joint disruptions.

Ref.	Study design	n	Rockwood type	Technique	Mean follow-up	LOR/re-dislocation
Horst et al[53], 2013	Retrospective	11	Acute (III)	ACJ pinning	6-21 weeks	9.1% LOR
Leidel et al[54], 2009	Retrospective	70	Acute (III)	ACJ pinning	1-10 years	11% re-dislocation, 4% migration
Cetinkaya et al[56], 2017	Retrospective	32 (16 vs 16)	Acute (III)	Bosworth screw vs modified Phemister	93-96 months	Bosworth: 2/16; Phemister: 1/16
Darabos et al[57], 2015	RCT	68 (34 vs 34)	Acute (III)	Bosworth screw vs AC tight-rope	6 months	Bosworth: 11.8%; tight-rope: 5.9%
Bektaşer et al[55], 2004	Prospective	34	Acute (III)	Bosworth screw	35 months	8.8%
El-Shennawy et al[58], 2021	Retrospective	30	Acute (III-V)	TBW	1 year	6.8% partial LOR
Ozan et al[60], 2020	Retrospective	24	Acute (III)	TBW	3.5 years	45.8% residual subluxation
Lateur et al[59], 2016	Retrospective	25	Acute (IV, V)	TBW	12 years	2% LOR
Wang et al[65], 2024	Retrospective	58 (35 vs 23)	Acute (III, V)	Hook plate vs tight-rope	15.4 months	Hook plate: 2.9%; tight-rope: 4.3%
Ko et al[62], 2023	Prospective	61 (36 vs 25)	Acute (III-V)	Hook plate vs tight-rope	7 years	Hook plate: 16.7%; tight-rope: 28%
Amr[66], 2021	Prospective	64 (32 vs 32)	Acute (III-VI)	Hook plate vs reconstruction	64 months	Hook plate: 21.8%; reconstruction: 6.2% subluxation
Nie and Lan[63], 2021	Retrospective	112 (84 vs 28)	Acute (III-V)	Hook plate vs tight-rope	34 months	Hook plate: 11.9%; tight-rope: 7.1%
Shen et al[64], 2021	Retrospective	35 (19 vs 16)	Acute (III-V)	Hook plate vs tight-rope	27-30 months	Hook plate: 0%; tight-rope: 6.3%
Cai et al[61], 2018	Prospective	69 (39 vs 30)	Acute (III)	Hook plate vs tight-rope	12 months	Hook plate: 0%; tight-rope: 10%

LOR: Loss of reduction; RCT: Randomized controlled trial; ACJ: Acromioclavicular joint; AC: Acromioclavicular; TBW: Tension band wiring.

Table 2 Loss of reduction rates following modified Weaver-Dunn procedures and anatomic coracoclavicular ligament reconstructions.

Ref.	Study design	n	Rockwood type	Technique	Mean follow-up	LOR/re-dislocation
Hegazy et al[67], 2016	Prospective	20 (10 vs 10)	Chronic (III)	Reconstruction by semitendinosus autograft vs modified WD	27.8 months	ST graft: 0%; WD: 30% early failures
Kibler et al[69], 2017	Retrospective	15	Acute and chronic (III-V)	Reconstruction with allograft + AC ligament docking	36 months	7%
Kumar et al[70], 2014	Retrospective	55 (31 vs 24)	Chronic (III-V)	Reconstruction by synthetic ligament vs Modified WD + CC sling	40 months	WD: 9.7%; synthetic ligament: 4.2% with rupture
Fauci et al[68], 2013	RCT	40 (20 vs 20)	Chronic (III, IV)	Reconstruction by biological allograft vs synthetic ligament	4 years	Biologic: 5% LOR, 5% subluxation; synthetic: 10% LOR, 30% subluxations
Boström Windhamre et al[72], 2010	Retrospective	45 (23 vs 22)	Chronic (III-V)	WD augmented with hook plate vs with PDS-braid fixation	7-9 years	Hook plate: 17.4%; PDS-braid: 13.6%
Millett et al[71], 2009	Prospective	17	Acute and chronic (IV-V)	Coracoacromial ligament transfer using docking technique (modified WD)	29 months	6% re-dislocation after trauma
Tauber et al[75], 2009	Prospective	24 (12 vs 12)	Chronic (III-V)	Reconstruction by semitendinosus autograft vs modified WD	37 months	WD: 41.7%; ST graft: 8.3%
Law et al[73], 2007	Retrospective	5	Acute (III)	Reconstruction by gracilis tendon autograft	26 months	20% subluxation
Pavlik et al[74], 2001	Retrospective	17	Chronic (III)	Modified WD + CC screw	36.6 months	Slight loss: 35%; partial loss: 12%

LOR: Loss of reduction; RCT: Randomized controlled trial; WD: Weaver-Dunn; AC: Acromioclavicular; CC: Coracoclavicular; PDS: Polydioxanone suture; ST: Semitendinosus tendon.

Table 3 Loss of reduction rates associated with arthroscopic and arthroscopic-assisted acromioclavicular joint reconstruction techniques.

Ref.	Study design	n	Rockwood type	Technique	Mean follow-up	LOR/re-dislocation
Çarkçı et al[77], 2020	Retrospective	36	Acute (III and V)	Arthroscopic double-button	31.4 months	25%
Lee et al[79], 2017	Retrospective	47	Acute (III-V)	Arthroscopic assisted single button	24 months	38.3%
Spoliti et al[83], 2014	Prospective	19	Acute (III-V)	Arthroscopic tight-rope (button + fiber wire)	12 months	15.8%
Tauber et al[42], 2016	Retrospective	26 (12 vs 14)	Chronic (III-V)	Arthroscopic TB vs SB CC reconstruction	29 months	TB: 8% vs SB: 21% recurrence
Nordin et al[81], 2015	Prospective	8	Chronic (III-V)	Arthroscopic assisted Graft-rope	12 months	50% early LOR
Murena et al[80], 2009	Prospective	16	Acute (III-V)	Arthroscopic double-button	31 months	25% partial LOR
Chernchujit et al[84], 2006	Retrospective	13	Acute (IV-V)	Arthroscopic reconstruction with suture anchors + titanium plate	18 months	15% subluxation; 8% re-dislocation

LOR: Loss of reduction; TB: Triple-bundle; SB: Single-bundle; CC: Coracoclavicular.

Table 4 Incidence of loss of reduction following acromioclavicular joint reconstruction using suture anchors or ligament advanced reinforcement system in acute and chronic injuries.

Ref.	Study design	n	Rockwood type	Technique	Mean follow-up	LOR/re-dislocation
Ben-Ari et al[89]1, 2024	Retrospective	3	Chronic (III, V)	Open reconstruction with 2 coracoid suture anchors + semitendinosus allograft	6 weeks-12 months	100% early LOR
Mendes Júnior et al[90], 2019	Prospective	30	Acute (V)	Open reconstruction with 2 metallic anchors + CA ligament transfer	≥ 6 months	High rate of subluxation (not quantified)
Tiefenboeck et al[87], 2018	Retrospective	47	Acute (III-V)	LARS reconstruction	7.4 years	17% slight LOR; 11% partial LOR; 2% total LOR
Muccioli et al[88], 2016	Prospective	43	Chronic (III-V)	LARS reconstruction	≥ 24 months	2% re-dislocation; 21% slight LOR
Lu et al[86], 2014	Prospective	24	Acute (IV-V)	LARS reconstruction	36 months	16.7% slight LOR

¹It should be noted that isolated case series with extremely small sample sizes, such as the study by Ben-Ari et al[90], should be interpreted cautiously and not extrapolated to broader clinical populations.

LOR: Loss of reduction; LARS: Ligament advanced reinforcement system; CA: Coracoacromial.

CONTRIBUTING FACTORS TO POSTOPERATIVE LOR

Multiple investigations have outlined a range of factors that predispose to postoperative LOR following surgical stabilization of the ACJ. These mechanisms vary according to the fixation construct used and the specific technical or biological challenges associated with each procedure. Early work by Lateur et al[59] emphasized that TBW is particularly vulnerable to reduction loss, with K wire migration identified as the primary mechanical failure mode. Their findings highlight intrinsic limitations of this fixation strategy, including insufficient resistance to combined vertical and horizontal forces and the absence of any CC support to maintain long term stability. Similar concerns have been reported with the Bosworth CC screw. Loosening or breakage of the screw is commonly cited, especially when patients begin shoulder elevation above ninety degrees before adequate healing. Migration or breakage of adjunctive AC K-wires further contributes to the early LOR associated with this fixation strategy[91].

Several patient and injury related factors also appear to influence outcomes with hook plate fixation. Lee et al[34] identified female sex as a risk factor, possibly related to reduced muscle mass, increased ligamentous laxity, and differences in biological healing capacity. Delayed surgery beyond the first week following injury, as well as higher grade injuries such as type IV disruptions, were likewise associated with a greater likelihood of recurrent subsidence following plate removal, presumably due to the extent of soft tissue damage present at baseline.

In the context of modified WD reconstructions, LOR has been observed more in chronic cases that operated after three months from injury. Extensive intraoperative mobilization in the presence of mature scar tissue and premature postoperative shoulder loading further increases the probability of LOR[11]. For suture button techniques, Lee et al[34] identified several technical parameters that correlated strongly with re-displacement. These included malalignment of the buttons, differences between double and triple button constructs, suboptimal coracoid or clavicular tunnel positioning, potential repair of AC ligament, and osteoporosis.

Anatomic CC reconstruction using dual clavicular tunnels and tendon grafts is similarly not immune to failure. The literature consistently shows that the most critical determinants of success are tunnel placement and surgical timing rather than graft selection or supplemental fixation. Medialized tunnels are strongly associated with recurrent displacement. Conoid tunnels positioned 7-9 mm more medial than ideal and conoid tunnel ratios of at least 0.3 markedly increase the likelihood of failure, whereas ratios below 0.25 are associated with excellent maintenance of reduction. Delayed reconstruction beyond two months from injury further compounds the risk[31]. Kibler et al[69], using a technique that integrates reconstruction of both the CC and AC ligaments with graft docking, reported LOR following a significant traumatic episode, accompanied by distal clavicle osteolysis. They suggested that with proper postoperative precautions, such fixation construct can yield durable biomechanical stability.

LOR with ligament advanced reinforcement system device has also been associated with specific technical pitfalls. Improper drill hole positioning and excessive early postoperative loading represent the main contributors to failure, rather than any inherent deficiency of the synthetic material when compared with biological grafts[92]. Cook et al[13], evaluating the graft rope construct, demonstrated that most failures resulted from suture rupture or slippage. They additionally observed substantial clavicular tunnel widening, with a mean increase of 3.6 mm relative to the immediate postoperative diameter. Moreover, Chernchujit et al[84] noted that the use of small diameter suture anchors, particularly the 2.8 mm size, contributed to postoperative subluxations and re-dislocations following arthroscopic anchor based fixation.

POSTOPERATIVE LOR AND ITS RELATIONSHIP TO CLINICAL OUTCOMES

The wide variability in reported LOR rates, whether presenting as subtle subluxation or complete re-displacement, naturally raises the question of how radiographic changes translate into clinical performance. Across the literature, the association between LOR and functional recovery is far from uniform, and its clinical relevance differs markedly between surgical constructs.

Despite the relatively high rates of radiographic subsidence reported following TBW, most studies describe patients achieving good to excellent shoulder function at final follow-up. This apparent discrepancy can be partly attributed to methodological limitations of the available evidence. Radiographic assessment was typically based on Zanca, anteroposterior, and stress views evaluating CCD relative to the contralateral shoulder; however, the precise timing at which LOR occurred during follow-up was rarely reported. Most studies relied on retrospective designs with single-point radiographic and clinical assessments at the final follow-up visit, which varied substantially across cohorts, ranging from short-term to more than a decade. In addition, the timing of TBW construct removal was inconsistent, further limiting the ability to correlate radiographic changes with symptom progression. Consequently, radiographic loss of alignment does not necessarily reflect a degree of mechanical failure sufficient to impair daily function, particularly once temporary fixation has been removed and patients have adapted functionally[58-60].

In their long-term evaluation of CC screw fixation, Tiefenboeck et al[93] reported instances of early construct loosening that necessitated premature hardware removal, in some cases as early as 18 days postoperatively. Importantly, no further surgical interventions were required thereafter, and patients demonstrated high levels of satisfaction and sustained functional recovery at a mean follow-up of 7.8 years. These findings suggest that early mechanical compromise or loss of rigid fixation does not inevitably translate into persistent functional impairment, particularly once symptomatic hardware is removed, and soft-tissue healing has occurred[91].

Outcomes following the modified WD procedure reveal a more nuanced relationship between reduction maintenance and clinical performance. Patients experiencing partial LOR often remained functionally compensated without clinically meaningful deficits, whereas complete re-dislocation was more consistently associated with persistent pain and the need for revision surgery, suggesting a threshold beyond which structural failure becomes clinically significant. Notably, these conclusions are derived from retrospective series in which outcomes were evaluated at a mean follow-up of approximately four years, without documentation of the precise timing or progression of reduction loss during follow-up. Consequently, while complete re-dislocation appears more reliably linked to inferior clinical outcomes, the literature does not define a specific temporal or radiographic threshold at which partial LOR transitions from a compensated finding to a functionally relevant failure[11].

In anatomic CC reconstructions using one or two clavicular tunnels with tendon grafts, the correlation between radiographic and clinical failure appears more consistent. At a mean follow-up of 16 months, Hou et al[94] reported that patients with postoperative subluxation or re-dislocation experienced inferior clinical scores, persistent discomfort, subjective weakness, and a higher likelihood of requiring revision fixation. These findings suggest that anatomic reconstruction, although biomechanically robust, may be more sensitive to postoperative displacement.

Conversely, in the cohort reported by Kibler et al[69], LOR combined reconstruction of the CC and AC ligaments with graft docking did not translate into clinical deterioration over a mean follow-up of 3 years. The affected patient demonstrated preserved strength, symmetric shoulder function, and no scapular dyskinesis, with no need for revision. While reassuring, this observation reflects a single instance and cannot be broadly applied without further prospective evidence.

Synthetic augmentations such as the ligament advanced reinforcement system ligament show a gradient of clinical impact. Patients with mild postoperative subsidence generally maintained good shoulder function with minimal pain, whereas complete re-displacements resulted in significantly poorer functional outcomes after a mean follow-up of 12 months. Notably, even after revision, functional scores remained below those of patients whose initial reduction was preserved, indicating that complete LOR in this context may have lasting consequences[92].

Experience with the graft rope device also demonstrates heterogeneous outcomes. Cook et al[13] reported early alarming high failure rates at an average of only 7 weeks postoperative. Complete LOR typically resulted in unfavorable clinical profiles characterized by persistent pain, limited motion, and the need for further intervention. Partial subsidence, however, was often tolerated with acceptable function, despite visible deformity. Similarly, in their analysis of ACJ stability following suture anchor fixation with a mean follow-up period of 18 months, Chernchujit et al[84] reported chronic pain, restricted motion in patient with complete re-dislocation, and ultimately required revision surgery. In contrast, individuals exhibiting only minor subluxation were generally satisfied, as these radiographic deviations produced minimal functional impairment and were well tolerated.

REHABILITATION CONSIDERATIONS IN PREVENTING POSTOPERATIVE LOR

Postoperative rehabilitation plays a decisive role in preserving reduction integrity after ACJ reconstruction. Although surgical technique determines the initial stability, early loading, unprotected overhead activity, and premature return to work or sport remain major contributors to postoperative stretch-out and recurrent displacement. The early phase should emphasize strict protection of the construct, with sling immobilization and avoidance of active or passive elevation above shoulder height to prevent undue strain on both the AC and CC stabilizers[95].

Gradual motion with controlled progression is essential once early healing has occurred. Premature strengthening or aggressive range of motion therapy risks graft elongation, tunnel widening, or suture-button migration, especially following biologic reconstructions. Horizontal stability must also be considered; early cross-body activities or weight-bearing across the arm may compromise the AC capsule and posterior restraints. Return to heavy labor or contact sports should be delayed until both radiographic stability and symptom control are achieved[96]. Tailoring rehabilitation to the fixation method is critical, as constructs relying on biological healing require longer protection than those with stiffer mechanical devices. Ultimately, a well-structured rehabilitation protocol serves as a key adjunct to surgical technique in minimizing the risk of postoperative LOR.

WHEN TO CONSIDER REVISION SURGERY AFTER LOR IN ACJ RECONSTRUCTION

Determining whether a patient requires revision surgery after LOR of the ACJ demands a thoughtful, multifaceted assessment. Revision procedures are inherently complex and should be undertaken only after carefully evaluating the patient’s symptoms, functional demands, and radiographic findings, as well as identifying the precise mechanism that contributed to failure of the primary reconstruction. Common causes include mal-positioned tunnels, hardware-related complications, graft rupture, biological failure of healing, or persistent vertical and horizontal instability.

Importantly, radiographic subsidence alone is not an indication for revision. Numerous studies have shown that recurrence rates vary widely across surgical techniques, yet the degree of radiographic displacement often bears little relationship to clinical performance[34]. Many patients with partial or even complete LOR remain functionally compensated and experience minimal pain, allowing for satisfactory outcomes without further intervention. In these cases, continued observation, activity modification, physiotherapy, and reassurance may be sufficient[97].

Revision reconstruction becomes appropriate only when radiographic findings correspond with clinically meaningful symptoms. These typically include persistent pain that interferes with daily or athletic activities, subjective or objective instability, strength deficits that impair overhead function, or deformity that is cosmetically unacceptable to the patient. When such symptoms are present, and when the cause of the initial failure is clearly understood and correctable, revision surgery can provide substantial benefit[16]. Several authors have documented favorable outcomes when revision is performed for sound indications. Tauber et al[97] demonstrated that revision using a semitendinosus autograft produced significant improvements in pain and shoulder function. Similarly, Berthold et al[98] reported durable long-term results with an anatomic revision technique, noting graft survivorship exceeding ten years in most patients.

Nevertheless, the literature consistently indicates that revision procedures do not achieve the same reliability or satisfaction rates as primary surgery. Complications are more common, recurrent instability is more likely, and postoperative results tend to be more variable. Success hinges on two critical factors: A precise understanding of why the initial reconstruction failed and selection of the most appropriate revision strategy for the individual patient. Ultimately, the decision to pursue revision must be tailored to the patient’s symptoms, expectations, functional goals, and the feasibility of addressing the underlying mechanical problem.

DECISION-MAKING FOR MANAGING POSTOPERATIVE LOR

Management of postoperative LOR must be individualized, as radiographic displacement alone is not a definitive indication for revision. Figure 3 demonstrates clinical decision flowchart for postoperative LOR after ACJ stabilization.

Figure 3 Clinical decision algorithm for evaluating and managing postoperative loss of reduction after acromioclavicular joint stabilization. A stepwise flowchart guiding assessment of symptoms, radiographic thresholds, and indications for revision. ROM: Range of motion.

FUTURE DIRECTIONS

Current evidence addressing postoperative LOR after AC joint stabilization remains limited by heterogeneous study designs, inconsistent radiographic definitions, and small sample sizes that hinder direct comparison across techniques. High-quality prospective trials are needed to clarify the relative performance of modern anatomic and arthroscopic reconstructions, particularly regarding tunnel placement, device configuration, and biological graft behavior. The influence of patient-specific factors such as bone quality, ligamentous laxity, and rehabilitation protocols also remains insufficiently explored, despite their likely contribution to early and late instability. Furthermore, the relationship between radiographic recurrence and true clinical impairment is not well defined, underscoring the need for studies that integrate standardized imaging with patient-reported outcomes and functional measures. Addressing these gaps through multicenter cohorts with unified definitions and long-term follow-up will be essential to establish clearer treatment algorithms and more reliable indications for revision surgery following ACJ reconstruction. Emerging technologies, including artificial intelligence and deep learning-based image analysis, may offer automated, reproducible assessment of CCD, tunnel positioning, and reduction maintenance. Such tools hold promises for reducing observer variability and improving longitudinal monitoring of postoperative stability, thereby facilitating more consistent definitions of LOR across future investigations.

CLINICAL RECOMMENDATIONS

Effective ACJ stabilization depends on restoring both vertical and horizontal stability using precise implant positioning, durable fixation/reconstruction, and strict protection from early loading. Although radiographs can effectively guide follow-up, decisions regarding revision must be based on symptoms rather than radiographic displacement alone. Revision surgery is reserved for patients with persistent pain, functional impairment, or symptomatic instability, and anatomic graft-based reconstruction remains the most reliable option.

CLINICAL PEARLS AND PITFALLS IN POSTOPERATIVE ACJ LOR

Key surgical pearls and pitfalls relevant to preventing postoperative LOR are summarized in Table 5.

Table 5 Clinical pearls and pitfalls related to postoperative loss of reduction after acromioclavicular joint stabilization.

Clinical pearls and pitfalls
Pearls
	LOR must be interpreted with symptoms, not radiographs alone
	Horizontal stability is equally important as vertical alignment
	Functional deficit and overhead pain are the most reliable indicators of true failure
	Identify the mechanism of failure before planning revision
	Combined CC and AC reconstruction enhances revision durability
	Protect the repair during the early healing phase
Pitfalls
	Treating radiographic LOR without clinical relevance
	Misinterpreting mild subsidence as failure
	Reliance on CCD alone without assessing horizontal stability
	Allowing early loading leading to graft stretch or hardware failure
	Failing to correlate radiographic findings with symptoms
	Overlooking coracoid or clavicular fractures

LOR: Loss of reduction; CC: Coracoclavicular; AC: Acromioclavicular; CCD: Coracoclavicular distance.

CONCLUSION

LOR is common after surgical management of ACJ disruptions, yet its clinical relevance varies and does not uniformly predict poor outcomes. Technical accuracy, appropriate fixation, and careful postoperative management are the strongest determinants of success. When LOR becomes symptomatic, revision with an anatomic reconstructive strategy can restore function, but results are consistently inferior to primary repair. Clearer, standardized criteria for defining LOR are needed to improve evidence quality and guide future practice.