Non-rigid fixation of the glenoid bone block for patients with recurrent anterior instability and major glenoid bone loss: A systematic review

Abstract

Background

New types of glenoid bone block fixation, involving suture buttons, suture anchors or even implant-free impaction of the graft, have been recently introduced. In contrast to screws which allow for a rigid fixation of the bone block, these alternative procedures provide a non-rigid type of fixation.

Methods

Two reviewers independently conducted the search in a systematic way (according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) using the MEDLINE/PubMed database and the Cochrane Database of Systematic Reviews. These databases were queried with the terms “Latarjet” OR “Eden-Hybbinette” OR “bone block” AND “anterior” AND “shoulder” AND “instability.”

Results

Eight out of the 325 initial studies were finally chosen according to our inclusion–exclusion criteria. In total, 750 patients were included in this review. The overall anterior instability recurrence rate for patients treated with non-rigid fixation was 2.6%, while the overall rate of non-union or graft osteolysis was 5.4%.

Conclusions

Regardless of the graft type, bone block non-rigid fixation showed satisfactory clinical and functional outcomes for the treatment of anterior shoulder instability with substantial glenoid bone deficiency. Furthermore, non-rigid fixation resulted in adequate bone graft healing and osseous incorporation. Lastly, given the relative lack of data, further prospective controlled studies are required to assess bone block non-rigid fixation procedures in comparison with the traditional rigid (with screws) fixation techniques.

Level

Systematic review, IV.

Introduction

The surgical treatment of recurrent anterior shoulder instability associated with severe glenoid defects and capsular deficiency remains challenging.^1,2 A possible therapeutic option for complex cases with substantial glenoid bone loss is the Latarjet technique which typically involves open or arthroscopic coracoid transfer with extra-articular fixation to the anterior-inferior glenoid surface via a horizontal split in the subscapularis muscle.³ The Eden-Hybinette procedure is another option with clinical outcomes very similar to the Latarjet technique.^4,5 It allows reconstruction of glenoid defects and restoration of shoulder stability with the use of an iliac crest autograft.⁶ Allogeneic bone grafts have also been used for the treatment of severe glenoid bone defects in patients with recurrent anterior instability to avoid donor site morbidity.⁷

Traditionally, in all the aforementioned techniques, the bone block is rigidly fixed onto the deficient glenoid surface with the use of one or two screws.^5,8,9 Despite stable fixation, metal screws have been associated with hardware complications.¹⁰ Particularly, screw failures are one of the most common complications, which have been reported and may compromise the results of these procedures.^11,12 In addition, increasing the angle between screws and glenoid articular surface could potentially result in impingement of the screw heads against the humeral head as well as jeopardizing the suprascapular nerve.¹³ As a result, new types of glenoid bone bock fixation, such as suture buttons and suture anchors or even implant-free impaction of the graft, have been recently introduced.¹⁰ In contrast to screws which allow for a rigid fixation of the bone block, these alternative procedures provide a non-rigid type of fixation. Although concerns have been raised regarding the strength and longevity of non-rigid fixation, a recent biomechanical study showed that the screw and suture button fixation techniques exhibited comparable biomechanical strength for coracoid bone block fixation.¹⁰ However, no systematic review has been published until now to focus on the clinical outcome of bone block non-rigid fixation for the treatment of anterior shoulder instability with substantial glenoid bone deficiency.

Our aim was to answer the following questions: (1) What are the clinical and functional outcomes of bone block non-rigid fixation for the treatment of anterior shoulder instability with glenoid bone deficiency? (2) Does non-rigid fixation result in adequate bone graft healing, union and osseous incorporation? (3) Do non-rigid fixation techniques result in similar clinical outcomes compared to rigid fixation techniques? Our hypothesis was that the bone block non-rigid fixation would be proven a safe and effective treatment for cases with anterior shoulder instability and substantial glenoid bone deficiency.

Methods

Two reviewers (MAM and LM) independently conducted the search in a systematic way (according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) using the MEDLINE/PubMed database and the Cochrane Database of Systematic Reviews. These databases were queried with the terms “Latarjet” OR “Eden-Hybbinette” OR “bone block” AND “anterior” AND “shoulder” AND “instability.” To maximize the search, backward chaining of reference lists from retrieved papers was also undertaken. A preliminary assessment of only the titles and abstracts of the search results was initially performed. The second stage involved a careful review of the full-text publications.

Inclusion criteria were clinical studies investigating adult patients, diagnosed with symptomatic anterior shoulder instability, who were treated with open or arthroscopic glenoid bone grafting (autograft or allograft) with non-rigid fixation (suture button, endobutton, or suture anchor fixation) and they had a minimum of 12 months clinical follow-up (with clinical tests and/or scores). These studies should have been written in English as full-text articles and they should have been published after 1 January 1990 and before 1 November 2018 (end of our search).

We excluded from our review all studies which were not dealing with glenoid bone grafting (regardless of the type of autograft or allograft), but they were describing only other means of operative or non-operative treatment for anterior shoulder instability, studies examining rigid fixation of the bone graft with the use of screws, studies assessing other types of shoulder instability (posterior, multidimensional), trials with follow-up less than 12 months, studies without clinical/functional outcome variables, abstracts, editorial comments, case reports, corrigendum, technical notes, literature reviews, preclinical studies, papers not written in English.

The two reviewers independently extracted data from each study and assessed variable reporting of outcome data. All reviewers compiled a list of articles not excluded after application of the inclusion and exclusion criteria. Differences between reviewers were discussed until agreement was achieved. In cases of disagreement the senior author (EA) had the final decision. Descriptive statistics were calculated for each study and parameters analyzed. The methodological quality of each study and the different types of detected bias were assessed independently by each reviewer and then they were combined synthetically. Selective reporting biases like publication biases were not included in the assessment. The primary outcome measures were the recurrence rate, osteolysis rate, non-union rate, rate of inadequate position of the graft, and graft healing rate. Secondary outcomes were the postoperative clinical and functional subjective scores, duration of surgery, postoperative glenohumeral osteoarthritis, postoperative subscapularis fatty infiltration, and postoperative positive subjective apprehension test.

Results

Eight out of the 325 initial studies were finally chosen according to our inclusion–exclusion criteria.^14–21 A summary flowchart of our literature search according to PRISMA guidelines can be found in Figure 1.

Figure 1.

PRISMA flow diagram.

There were four retrospective studies^14,18,20,21 and four prospective studies.^15–17,19 Amongst all, only two studies were controlled,^18,19 whereas the rest were case series.^{14–17,20,21} Specifically, Gendre et al.¹⁸ compared patients who underwent Bristow (standing position of the graft) and Latarjet procedures (lying position of the graft), while Metais et al.¹⁹ compared patients who underwent modified Latarjet-Patte procedure performed by open surgery, arthroscopic surgery with screw fixation, or arthroscopic surgery with endobutton fixation. All studies in this review^14–21 were published between 2014 and 2018 (Table 1).

Table 1.

Type of study, level of evidence, year of publication and modified Coleman methodology score.

Author(s)	Type of study	Level of evidence	Year of publication	Modified Coleman score
Taverna et al.14	Retrospective case series	IV	2018	57
Anderl et al.15	Prospective case series	IV	2016	70
Boileau et al.16	Prospective case series	IV	2015	60
Bonnevialle et al.17	Prospective case series	IV	2017	64
Gendre et al.18	Retrospective case–control	III	2016	64
Metais et al.19	Prospective case–control	III	2016	65
Zhao et al.20	Retrospective case series	IV	2014	65
Moroder et al.21	Retrospective case series	IV	2018	55

Six out of the eight studies of this review (75%) had a level of evidence IV^{14–17,20,21} and two studies (25%) were of level III.^18,19 The mean modified Coleman score for methodological deficiencies of the studies was 62.5/100, whereas it ranged from 55/100²¹ to 70/100 (Table 1).¹⁵

In total, 750 patients were included in this review (424 patients treated with non-rigid fixation and 326 patients who underwent rigid fixation). The gender was reported in seven out of eight studies^{14–18,20,21} and most (85%) of the patients were males. The mean age of the patients per study varied between 25¹⁵ and 30 years,^15,21 while the mean follow-up ranged from 1¹⁸ to 18 years.²¹ The dominant arm was the affected one in most patients of this review (417 out of 699 patients; 59.6%) (Table 2).^14–19,21

Table 2.

Demographic data, mean follow-up and type of surgery per study.

Author(s)	Number of patients	Sex	Mean age	Mean follow-up	Dominant arm	Type of surgery
Taverna et al.14	26	20 males 6 females	25.5 years (range 18–35)	29.6 months (range 24–33)	21/26 cases (80%)	Arthroscopic Iliac crest allograft Endobuttons
Anderl et al.15	14 (15 shoulders)	12 males 2 females	30 years (range 20–51)	Minimum of 2 years (range 25.9 ± 4.7 months)	8/14 cases (53%)	Arthroscopic J-bone iliac crest autograft Implant-free impaction of the graft into a vertical osteotomy of the anterior glenoid rim
Boileau et al.16	76	66 males 10 females	27 years (range 15–58)	14 months (range 6–24)	48/76 cases (64%)	Arthroscopic Latarjet (native coracoid transfer) Suture buttons
Bonnevialle et al.17	88	86% males 14% females	25 ±7 years (range 16–60)	12.6 months (range 6–24)	50/88 cases (57%)	Arthroscopic Latarjet (native coracoid transfer) Double-button fixation
Gendre et al.18	70 patients 35 Bristow (standing position) 35 Latarjet (lying position) Note: 19/70 smokers	61 males 9 females	27 years (range 15–58)	12 months (range 6–30)	45/70 cases (64%)	Arthroscopic Native coracoid transfer Suture button fixation
Metais et al.19	390 patients 3 groups L: 104, AS: 222 AB: 64	Not reported	27.8 years (mean: 26 ± 8.9, range 13.6–66.6)	22.7 ±4.1 months (range 13.3–31.5)	230/390 cases (59%)	Native coracoid transfer Open surgery (L group) with screw fixation or arthroscopic surgery either with screw (AS group) or endobutton fixation (AB group)
Zhao et al.20	52	39 males 13 females	26.3 ±4.4 years (range 19–35)	2–5 years (mean 38.8 ± 12.2 months, range 24–64 months)	Not reported	Arthroscopic Iliac crest allograft Anchors
Moroder et al.21	34 (35 shoulders)	30 males 4 females	30 ±10 years (range 19–54)	18 years (range 15–23)	15/35 cases (43%)	Open Iliac crest autograft Implant-free impaction of the graft into a vertical osteotomy of the anterior glenoid rim

L group: open modified Latarjet-Patte procedure with screw fixation; AS group: arthroscopic modified Latarjet-Patte procedure with screw fixation; AB group: arthroscopic modified Latarjet-Patte procedure with endobutton fixation.

Surgical technique

Suture buttons were used in five studies,^14,16–19 while one study utilized suture anchors²⁰ and two studies^15,21 described the impaction of a J-shape graft into a vertical osteotomy of the anterior glenoid rim by performing an implant-free technique (Table 2). Five studies used a system specifically indicated for securing bone graft to the glenoid through two double pairs of arthroscopic round Endobuttons (Double Round Endobutton system; Smith & Nephew Inc., Andover, MA, USA).^14,16–19 This system combined a Sz34 high-strength polyethylene double suture with two metallic buttons secured at each end.¹⁴ The pair of double round Endobuttons secured the bone graft against the glenoid neck at the level of the articular surface, while sequential fixation was obtained with a tensioner device.^14,16–19

In contrast, Zhao et al.²⁰ described a technique in which two 3.5-mm double-loaded titanium suture anchors (Twinfix; Smith & Nephew, Andover, MA, USA) were used. Specifically, they used two sets of grafting instruments which were developed by the senior author,²⁰ including a guide pin, a core bar, and a trocar. According to their description, after the graft was pushed along the suture into the trocar, and the guide sutures were passed through the respective holes in the core bar, the graft was pushed through the trocar into the joint.²⁰ As final step of the technique, the graft was completely released from the trocar and the two sutures were tied in their appropriate locations.²⁰

Moreover, two studies described a technique that did not make use of any foreign materials for fixing the graft in the glenoid.^15,21 As first step, they prepared a bicortical graft with a small oscillating saw in a J-shaped fashion, while two 1.6 mm pins were drilled into the short limb of the graft according to the holes of a custom-made impactor (Arthrex Inc).¹⁵ A 2 cm-wide osteotomy of the glenoid, 5 mm medial to the glenoid rim at an angle of approximately 30° to the glenoid plane, was performed with the use of a 15 mm–wide chisel (Lambotte; Limbeck), and a crevice of at least 15 mm depth was created to completely fit the graft.¹⁵ Then, the graft was impacted with a mallet until the keel reached the glenoid rim; once the graft was in place, the long drill pins were retracted through the openings of the impactor.¹⁵

Arthroscopic technique was used in seven out of eight studies,^14–20 while open technique was utilized in two studies (Table 2).^19,21 Variations of the Latarjet technique (use of native coracoid transfer) were applied in four studies,^16–19 while the rest of the studies used either iliac crest autograft^15,21 or allograft.^14,20 Metais et al.¹⁹ conducted a multicenter study to compare three groups of patients: group L was treated with open surgery using screws for the fixation of native coracoid, group AS underwent arthroscopic surgery with screws and group AB received arthroscopic surgery with endobutton (non-rigid group) (Table 2).

Finally, two out of the eight studies of this review (25%) reported the duration of the surgical procedure.^17,20 Bonnevialle et al.¹⁷ reported that the mean duration was adversely correlated to surgical experience.

Graft position

Graft position was reported in four out of eight studies (50%).^14,16–18 In terms of horizontal position, the graft position was optimal (flushed) in 80%¹⁷ to 100% of the patients.¹⁴ As for the vertical position of the graft, it was just or below the equator (optimal) in a percentage ranged from 92.3%¹⁴ to 96% of the treated patients.¹⁷

Recurrence rate

The overall anterior instability recurrence rate for patients treated with non-rigid fixation was 2.6% (11 out of 424 patients). Specifically, two studies reported no anterior re- dislocations or subluxations.^14,15 Boileau et al.¹⁶ reported one subluxation in a rugby player, while Bonnevialle et al.¹⁷ reported two subluxations. In addition, Gendre et al.¹⁸ reported two re-dislocations in patients who had non-union of the bone block, while Metais et al.¹⁹ reported four re-dislocations in the non-rigid fixation group (AB). Finally Zhao et al.²⁰ reported one re-dislocation and Moroder et al.²¹ found one traumatic re-dislocation due to bone graft fracture.

Postoperative positive apprehension test

Five out of the eight studies of this review (62.5%) documented postoperative apprehension test in patients treated with non-rigid fixation.^{14,17,19–21} Based on these studies, the overall rate of positive apprehension test was 9.5% (25 out of 264 patients). Particularly, Taverna et al.¹⁴ reported a patient with pain during apprehension test and Zhao et al.²⁰ reported two positive anterior apprehension tests. Bonnevialle et al.¹⁷ reported no positive apprehension test in 80 patients, while Moroder et al.²¹ reported positive apprehension test in eight shoulders. Finally, Metais et al.¹⁹ noted that six patients of the non-rigid fixation group had positive apprehension test for passive external rotation at 90° of abduction at final follow-up.

Non-union or osteolysis of the bone block

The overall non-union rate in the studies included in this review was 5.4% (23 out of 424 patients). Boileau et al.¹⁶ reported partial osteolysis of the graft in seven patients, whereas Gendre et al.¹⁸ reported 12 patients with non-union. Interestingly, all these cases concerned patients who were smoking.^16,18 Bonnevialle et al. found four early migrations of the bone graft which did not require revision.¹⁷ On the contrary, Zhao et al.²⁰ reported healing rates of up to 100% (Table 3).

Table 3.

Inadequate graft incorporation, graft osteolysis, and osteoarthritic progression after surgery.

Author(s)	Graft osteolysis/ inadequate union	Pre and post-operative osteoarthritis
Taverna et al.14	N/A	25/26 cases (96.2%). No sign 1/26 cases (3.8%) asymptomatic degenerative change
Anderl et al.15	N/A	10/15 shoulders (66.7%) pre-operative arthropathy—> No deterioration post-operatively
Boileau et al.16	Graft osteolysis: 7 patients (out of 76)	N/A
Bonnevialle et al.17	Early migration of the graft: 4 patients (out of 88)	N/A
Gendre et al.18	Non-union: 12 patients (out of 70)	N/A
Metais et al.19	N/A	N/A
Zhao et al.20	N/A	Pre-operatively: 36 shoulders no signs of arthrosis 14 shoulders mild arthrosis 2 shoulders moderate arthrosis No progression in 2 years
Moroder et al.21	N/A	Normal joint space in 27 shoulders (77%) Joint space narrowing in 8 shoulders (23%) 10 shoulders (29%) showed sclerosis or cysts Osteophytes (either the humeral head or the glenoid) in 25 shoulders (71%) Collective instability arthropathy score was 0.9 ± 0.7 vs. contralateral side 0.4 ± 0.8.

Other complications

Overall rates of postoperative hematomas (4 out of 424 patients), graft fractures (4 out of 424 patients), anchor failures (3 out of 116 patients), nerve injuries (5 out of 424 patients with hypesthesia from the donor site), and infections were very low. Both Taverna et al.¹⁴ and Moroder et al.²¹ reported two postoperative hematomas. In addition, Anderl et al.,¹⁵ Bonnevialle et al.¹⁷ and Moroder et al.²¹ mentioned one bone graft fracture each, while Gendre et al.¹⁸ documented one coracoid tip fracture.

Metais et al. diagnosed postoperative infection in two patients of the open rigid group and four patients of the arthroscopic rigid group.¹⁹ Nerve injury was found only in three patients of the arthroscopic rigid group.¹⁹ In addition, hematomas were reported in two patients of the open rigid group and screw removal was required in three patients of the open rigid group and six patients of the arthroscopic rigid group.¹⁹ In contrast, none of the patients who underwent an arthroscopic non-rigid fixation had any of the just-above mentioned complications (hematoma, graft fracture, infection, nerve injury).

Postoperative osteoarthritis

Four out of the eight studies (50%) reported rates of pre- and post-operative glenohumeral osteoarthritis^14,15,20,21 in the short- (15–18 months) to mid-term follow-up (5 years). Taverna et al.¹⁴ documented one case of asymptomatic post-operative degenerative change, after an arthroscopic bone block grafting (iliac crest allograft) which was fixed with endobuttons. Anderl et al.¹⁵ reported no postoperative radiographic deterioration in 10 out of 15 shoulders with pre-operative arthritis after arthroscopic implant-free grafting. Likewise, Zhao et al.²⁰ noted that there was no progression of glenohumeral osteoarthritis after arthroscopic grafting with suture anchors. In contrast, Moroder et al.²¹ showed joint space narrowing in 23% of the treated shoulders (8 out of 35), while 77% of the shoulders (27 out of 35) had normal joint space (Table 3).

Clinical/functional outcome variables

The mean preoperative Instability Severity Index Score was reported in three out of eight studies,^14,15,17 while it ranged from 4.1¹⁴ to 6.¹⁵

All studies which compared preoperative and postoperative clinical or functional subjective scores noted significant postoperative improvement. The Rowe score was applied in all except for one study (87.5%).^{14–17,19–21} The mean postoperative Rowe score per study ranged from 81¹⁷ to 98.6,¹⁵ demonstrating a significant improvement compared to preoperative mean values.^15,17 Walch-Duplay Score was documented in four out of eight studies (50%)^14,16,17,19 ranging from 80¹⁷ to 96.¹⁶ In addition, the Subjective Shoulder Value (SSV) was noted in three studies.^14,15,21 It ranged between 87.4¹⁴ and 95.6.¹⁵ Finally, one study reported the mean Constant score¹⁵ and another one the mean Oxford Shoulder Score.²⁰

Three studies documented patients’ satisfaction after surgery.^14,20,21 Specifically, Taverna et al.¹⁴ reported that 88.5% of patients were satisfied with their treatment, whereas Zhao et al.²⁰ and Moroder et al.²¹ noted satisfaction rates of 92.3% and 94%, respectively (Table 4).

Table 4.

The clinical and functional outcomes of non-rigid bone block fixation.

Author(s)	Clinical/functional scores	ROM	Patient satisfaction
Taverna et al.14	Pre-op Instability Severity Index Score: 4.1 (range: 3–6) Walch-Duplay score: 93.2 (SD: 7.8) Rowe score: 96.4 (SD: 6.5) Subjective Shoulder Value: 87.4 (SD: 12.1)	Average loss of external rotation, 4.4 (SD: 8.7)	Satisfaction rate: 88.5%
Anderl et al.15	Mean pre-op Instability Severity Index Score: 6 (SD: 1.6) Postopertive scores Rowe score: 98.6 (SD: 1.5) (Improved) Constant score: 96.3 (SD: 3.9) (Improved) Subjective outcome using Visual Analog Scale (VAS) for pain: 0.2 (SD: 0.6) (Improved) Subjective Shoulder Value for Sports (SSVS): 95.6 (SD: 3.8) (Improved)	Forward flexion: 167.9 (SD: 6.3) pre-op → 176.8 (SD: 4.6) post-op (Improved) Abduction: 158.6 (SD: 25.4) pre-op → 175.7 (SD: 5.1) post-op (Improved) External rotation: 58.9 (SD: 14.2) pre-op → 72.1 (SD: 7.3 post-op) (Improved)	N/A
Boileau et al.16	Postoperative scores Rowe score: 95 (range 84–100) Walch-Duplay score: 96 (range 86–100)	N/A	High rate (without further clarification)
Bonnevialle et al.17	Pre-op Instability Severity Index score: 5 (SD: 1.6) Walch-Duplay score: 80 (SD: 12) Rowe score: 81 (SD: 13)	Average active mobility: 170 (SD: 11) in forward elevation (n.s.) 66 (SD: 18) in external rotation with elbow at side (Improved) 88 (SD: 6) in external rotation in abduction (Improved) T12 (range L1–T7) in internal rotation	N/A
Gendre et al.18	N/A	N/A	N/A
Metais et al.19	Walch-Duplay score: Improved from 46 pre-operatively to 90.6 Modified Rowe score: Improved from 46 pre-operatively to 91.1	Flexion: 1. Pre-op mean 179.1° unaffected side vs. 175.4° affected side 2. Post-op mean 175.5° affected side 3. No significant difference across groups at 6 months. 4. Significant difference (P = 0.001) at last follow-up External rotation at 0° of abduction (ER1): 1. Pre-op mean 75.3° unaffected side vs. 71° affected side 2. Post-op mean 66.8° affected side 3. Significant difference (P = 0.001) across groups at 6 months 4. No significant difference across groups at last follow-up External rotation at 90° of abduction (ER2): 1. Pre-op mean 89.5° unaffected side vs. 82.9° affected side 2. Post-op mean 80.2° affected side 3. No significant difference across groups at 6 months 4. Significant difference across groups at last follow-up Internal rotation, hand behind the back (IR1): 1. Pre-op mean 9.6° unaffected side vs. 10.1° affected side 2. Significant difference (P < 0.0001) across groups at 6 months. 3. Significant difference (P = 0.0004) at last follow-up Internal rotation at 90° of abduction (ER2): 1. Pre-op mean 70.9° (unaffected side) vs. 68.5° (affected side) 2. No significant difference across groups at 6 months 3. No significant difference across groups at last follow-up Gagey hyperabduction test: 1. Pre-op mean 101.6° (unaffected side) vs. 104.4° (affected side) 2. No significant difference across groups at 6 months 3. Significant difference (P < 0.0001) across groups at last follow-up Motion range restriction: minimal with all techniques— > improved throughout follow-up External rotation at 90° of abduction and internal rotation at 0° of abduction: better after open surgery	Not reported
Zhao et al.20	Oxford score: Improved from 29.7 ± 5.6 pre-op to 42.4 ± 3.3 (2 years post-op) Rowe score: Improved from 34.7 ± 6.1 pre-op to 91.8 ± 2.8 (2 years post-op)	>10° external rotation limitation at 0° of abduction in 17, 9, and 2 patients at 3, 6, and 12 months, respectively External rotation at 0° of abduction in the normal range in 50 patients (5° limitation compared with the contralateral side in 1 patient and a 15° limitation in 1 patient) External rotation at 90° of abduction normal in 47 patients (<5° limitation compared with the contralateral side in 3 patients, 5° to 10° limitation in 2 patients, and a 15° limitation in 1 patient) 50 patients restored internal rotation (2 patients had limitations) No clinical signs of subscapularis insufficiency	48 patients satisfied 4 dissatisfied
Moroder et al.21	Western Ontario Shoulder Instability Index (WOSI): 295 ± 344 (range 0–1765) Rowe Score: 94 ± 10 (range 55–100) Subjective Shoulder Value (SSV): 90 ± 15 (range 20–100) Collective Instability Arthropathy score: 0.9 ± 0.7 vs. contralateral side: 0.4 No significant differences in clinical outcome scores between patients without or with prior surgery No correlations between preoperative factors and clinical outcome scores	Slight differences were detected in active range of motion between the affected and the contralateral side: 1. Flexion 178° vs. 179° (P = .325) 2. Abduction 177° vs. 179° (P = .225) 3. External rotation 63° vs. 67° (P = .048) 4. High external rotation 77° vs. 82° (P = .007) 5. Internal rotation 8.8 vs. 9.4 points (P = .017) 6. High internal rotation 70° vs. 74° (P = .026) No significant strength deficit of the affected side was noticed	33 patients (94%) very satisfied 2 patients (6%) satisfied

Postoperative range of motion

Six out of eight studies (75%)^{14,15,17,19–21} assessed the postoperative range of motion (ROM). Taverna et al.¹⁴ reported a mean loss of 4.4° in postoperative external rotation after bone block surgery. Anderl et al.¹⁵ showed a significant postoperative improvement in terms of forward flexion, abduction, external and internal rotation. In contrast, Bonnevialle et al.¹⁷ found no significant differences between pre- and post-operative mean values of forward flexion, while the difference was significant in terms of external rotation with the elbow positioned in 0° and 90° abduction. Metais et al.¹⁹ reported that motion range restriction was minimal with all techniques used and improved throughout follow-up, while external rotation at 90° of abduction and internal rotation at 0° of abduction were significantly better after open rigid surgery. Finally, Moroder et al.²¹ reported no significant differences in active ROM between the affected and the contralateral side and no significant strength deficit of the affected side, whereas Zhao et al.²⁰ reported normal range of external rotation at 0° and 90° of abduction in almost all treated patients. According to Zhao et al.,²⁰ no clinical signs of subscapularis insufficiency were found (Table 4).

Discussion

The key finding of this analysis was that bone block non-rigid (without screws) fixation was a satisfactory treatment for cases with recurrent anterior instability and substantial glenoid bone deficiency. Regardless of the type of graft that was used, bone block non-rigid fixation resulted in very low recurrence rates of instability as well as revision rates. All mean postoperative clinical and functional subjective scores were significantly improved compared to the preoperative respective values, while postoperative ROM was satisfactory with none to minimal rotational loss. In addition, complications’ rates were also very low, while specific types of complications which have been related to bone block rigid fixation (with screws), such as screw breakage, posterior protrusion or inadequate orientation of the screws as well as suprascapular nerve injuries, were absent in patients treated with non-rigid fixation. Therefore, we suggest that the use of non-rigid types of fixation (suture buttons, suture anchors or implant-free impaction technique) without the use of screws might be a safe and effective alternative for patients with substantial glenoid bone deficiency.

However, concerns have been raised regarding the reliability of allograft incorporation into the glenoid without resorption.²² Concerning our analysis, cases of non-union, graft osteolysis or graft resorption were rare and the vast majority of patients had uneventful bone healing with adequate osseointegration of the graft. Furthermore, graft positioning was optimal in both the vertical and horizontal axis as for most patients included in this analysis. Finally, postoperative progression of osteoarthritis in the short- to mid-term was also very low in all studies that examined this radiographic variable. Since there was a complete lack of evidence regarding potential progression of osteoarthritis in the long term, we feel that further studies are required to lead to definitive conclusions concerning the association between bone block non-rigid fixation and potential degenerative changes in the glenohumeral joint.

Furthermore, there was only one study to compare arthroscopic rigid (with screws) and non-rigid (without screws) fixation.¹⁹ In this multicenter study conducted by the French Arthroscopic Society, Metais et al. found that arthroscopic rigid and arthroscopic non-rigid fixation produced similar clinical outcomes, with good shoulder stability and near-normal range of motion, thus allowing the patients to return to their sports activities under favorable conditions.¹⁹ Taking into account the lack of randomized controlled trials on this field, we suggest that further studies of higher quality will be needed to assess the therapeutic value of non-rigid fixation techniques compared to the traditional rigid fixation techniques (Latarjet, Eden-Hybinette).

Our review included various types of grafts, such as native coracoid bone transfer, iliac crest autograft or allograft. Regardless of the type of graft, all studies depicted satisfactory clinical and functional outcomes with low complications’ rates. However, there were only two studies to examine the outcome of allograft non-rigid fixation, while all other studies used autologous bone grafting (native coracoids or iliac crest). Therefore, further evidence is required to establish the use of bone block allograft in conjunction with non-rigid fixation techniques.

Overall, we feel that it is rather the surgical experience that mostly affects the outcomes of this technique and not the specific type of implant that it is utilized. Both arthroscopic bone block rigid and non-rigid techniques are considered technically demanding with steep learning curve for the treating physicians.^17,23 As minimally invasive procedures, bone block techniques involving suture buttons or anchors instead of screws and subscapularis split might favor an arthroscopic approach.

This review was not without limitations. The studies included in this analysis were mainly single series of patients without any controlled group. As a matter of fact, there was a complete lack of level I and II controlled trials, while there were only two case–control studies.^18,19 The “quality assessment” of the studies for methodological deficiencies, as a common alternative to “risk of bias” was examined by the modified Coleman methodology Score²⁴ and it was found low to moderate. The study design, including type of graft, type of fixation, follow-up, and type of surgery (open or arthroscopic), was relatively heterogeneous. However, all studies examined a bone block technique performed with a specific type of fixation (non-rigid), which has gained increasing attention amongst physicians the last years (all publications were from 2014 to 2018). In addition, the results of all studies were towards the same direction, since they all depicted that bone block non-rigid fixation produced satisfactory clinical outcomes with very low failure rates.

Conclusions

Regardless of the graft type, bone block non-rigid (without screws) fixation showed satisfactory clinical and functional outcomes for the treatment of anterior shoulder instability with substantial glenoid bone deficiency. Furthermore, non-rigid fixation resulted in adequate bone graft healing and osseous incorporation. Lastly, given the relative lack of data, further prospective controlled studies are required to assess bone block non-rigid fixation procedures in comparison with the traditional rigid (with screws) fixation techniques.