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Posterior Bone Block / Posterior Shoulder Instability

Posterior Bankart repair, bone block (Eden-Hybinette), and posterior capsulorrhaphy for posterior shoulder instability — FRCS/FRACS exam preparation

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Posterior approach | advanced

Surgical Imaging

Patient with shoulder immobilised in abduction orthosis after posterior shoulder dislocation surgery
Post-operative immobilisation after posterior shoulder stabilisation: the arm is held in neutral rotation and slight abduction using a body bandage with humeral sling. Immobilisation for 4–6 weeks in this position protects the posterior capsule repair and allows early graft or labral healing before progressive range-of-motion exercises.Credit: Naqvi G et al., Int J Shoulder Surg 2009 (PMC2904543) — CC BY-NC-SA 3.0
Two glenoid specimens comparing uninjured glenoid and injured glenoid with bone loss measurements H1 W1 and H2 W2
Glenoid bone loss quantification — critical for bone block decision: uninjured glenoid (left) shows normal width W1 and height H1; injured glenoid (right) demonstrates reduced W2 and H2 from posterior bone loss. When posterior glenoid bone loss exceeds 25% of the width, posterior bone block reconstruction (Eden-Hybinette) is preferred over soft-tissue repair alone.Credit: Tokish JM et al., Open Access J Sports Med 2014 (PMC3968087) — CC BY-NC 3.0
Posterior shoulder approach markings with three symbols showing portal and incision positions on draped operative field
Posterior shoulder approach surface markings: filled triangle = posterior acromion corner; filled circle = posterolateral portal (soft spot); open triangle = direct posterior portal (3cm medial to posterolateral corner). The axillary nerve runs 5–6cm inferior to the posterior acromion — all posterior incisions must stay within the safe zone above this level.Credit: Kim SH et al., J Shoulder Elbow Surg 2009 (PMC2708139) — CC BY 4.0

Critical Exam Topics — Posterior Instability

Posterior Bone Loss Threshold

Soft tissue procedures (less than 25% posterior glenoid bone loss):

  • Posterior Bankart repair (arthroscopic or open)
  • Posterior capsulorrhaphy

Bone block required (greater than 25% bone loss or engaging reverse Hill-Sachs):

  • Eden-Hybinette (iliac crest autograft to posterior glenoid)
  • Mead-Bain modification (coracoid transfer to posterior glenoid)
  • Glenoid track concept: off-track reverse Hill-Sachs lesion combined with bone loss mandates bony augmentation

Quantify bone loss on CT (3D reconstruction): Pico method or best-fit circle method. Express as percentage of inferior glenoid diameter.

Axillary Nerve — Posterior Approach Risk

Location: Exits quadrilateral space, winds around surgical neck of humerus from posterior to anterior. In the posterior approach, the nerve lies 5–6 cm from the posterolateral corner of the acromion.

At risk when: Placing inferior retractors aggressively, working too far distally on posterior capsule, rough retraction of deltoid.

Protection: Stay within 5 cm of acromion edge when placing retractors. Palpate nerve before dividing any posterior capsule inferiorly. Use blunt dissection inferiorly. Do NOT use self-retaining retractors beyond 5 cm from acromion.

Consequence of injury: Deltoid paralysis (catastrophic for shoulder function) and circumflex shoulder numbness.

Kim Lesion

Definition: An incomplete and concealed avulsion of the posteroinferior labrum. The superficial labral attachment looks intact (often only a shallow surface crack at the chondrolabral junction), but probing reveals detachment of the DEEP portion of the labrum, with loss of normal labral height and consequent chondrolabral retroversion (Kim SH et al. 2004, Arthroscopy, PMID 15346113).

Clinical significance: First described in a case series of 15 shoulders with posterior or multidirectional posteroinferior instability — it is a distinct lesion, not a prevalence figure. Missed on routine arthroscopy unless the labrum is probed carefully and elevated.

Exam relevance: Examiners test whether you would PROBE the posteroinferior labrum during arthroscopy — do NOT rely on visual inspection alone.

Treatment: Convert the concealed incomplete lesion to a complete tear ("unroof" the cleft), then perform labroplasty to restore labral height plus capsular shift, repairing to the posterior band of the inferior glenohumeral ligament. Failure to address the lesion results in persistent posterior instability.

Multidirectional Instability — Rehabilitation First

Definition: Glenohumeral instability in multiple planes (anterior, posterior, inferior) typically with global capsular laxity. Often bilateral. Classic demographic: young hypermobile patients, overhead athletes.

Cardinal sign: Sulcus sign greater than 2 cm with arm in neutral rotation that does NOT reduce with external rotation (sulcus sign reduced by ER in unidirectional inferior instability but persists in MDI due to rotator interval laxity).

Management first-line: Structured physiotherapy minimum 6 months (rotator cuff strengthening, periscapular stabilisation, proprioception training). 80–85% improve with rehabilitation alone.

Surgery only if: Failed 6 months supervised rehabilitation. Procedure: inferior capsular shift (Neer's open procedure or arthroscopic capsular plication) addressing global capsular redundancy. Do NOT perform bone block for MDI without bone loss.

Voluntary Dislocation — Psychosocial Workup

Definition: Patient deliberately dislocates shoulder using muscular contraction. May present as a learned behaviour, secondary gain, or symptom of underlying psychiatric disorder.

Screening: Ask directly: "Can you dislocate your shoulder yourself?" Observe for active muscular contraction pattern vs passive apprehension during examination.

Workup before any surgical consideration: Formal psychiatric/psychological evaluation. Assess for factitious disorder, somatisation, Munchausen syndrome, secondary gain (disability, insurance, attention-seeking). Rule out benign "trick shoulder" in athletes without psychological overlay.

Key principle: Surgery in voluntary dislocators with underlying psychopathology has uniformly poor outcomes (high recurrence, psychological non-compliance, chronic pain, litigation). Defer surgery until psychiatric clearance.

Glenoid Track Concept — Anterior Origin, Posterior Extrapolation

Origin (anterior instability): The glenoid track / "on-track vs off-track" paradigm was defined for ANTERIOR instability and the Hill-Sachs lesion (Di Giacomo, Itoi & Burkhart 2014, PMID 24384275). It quantifies whether a Hill-Sachs lesion will engage the anterior glenoid rim.

Anterior calculation: Glenoid track width = 0.83 × D − d, where D = glenoid diameter and d = anterior glenoid bone-loss width. If the Hill-Sachs interval (Hill-Sachs width + medial bony bridge) exceeds the track, the lesion is OFF-track.

Posterior extrapolation (use cautiously in the viva): By analogy a reverse Hill-Sachs lesion (anteromedial humeral head impaction) may engage the posterior rim during the posterior apprehension arc (flexion, adduction, internal rotation). This posterior application is biomechanically plausible but NOT formally validated — describe it as a bipolar (humeral plus glenoid) bone-loss assessment rather than quoting a validated posterior track number.

Practical message: A large engaging reverse Hill-Sachs combined with posterior glenoid loss is a bipolar problem that may require addressing both sides (posterior bone block plus a humeral-side or capsular procedure).

Mnemonic

POSTERIORPOSTERIOR — Assessment of Posterior Instability

Hook:POSTERIOR drives the entire clinical assessment pathway. Examiners expect a structured approach that correctly identifies the instability pattern before committing to any operative intervention. The most common error is failing to identify MDI or voluntary instability and proceeding to inappropriate surgery.

Mnemonic

BONEBONE — Posterior Bone Block Technique (Eden-Hybinette)

Hook:BONE block positioning is the critical technical determinant of success. Proud graft causes direct impingement on humeral head; recessed graft provides insufficient articular arc extension. Graft must sit flush with the posterior glenoid face. Axillary nerve protection during graft placement is mandatory.

Classification of Posterior Shoulder Instability

Traumatic Posterior Instability: Single traumatic event (axial load in forward flexed, internally rotated arm — football tackle, fall on outstretched hand). Posterior labral tear (posterior Bankart lesion) or Kim lesion. Often missed clinically — posterior dislocations commonly missed on AP radiograph.

Atraumatic Posterior Instability: Insidious onset, repetitive microtrauma (bench pressing, swimming), generalised ligamentous laxity. Often associated with capsular redundancy rather than discrete labral tear.

Voluntary Instability: Patient deliberately dislocates using active muscle contraction. Must identify psychological overlay before any surgical consideration.

Unidirectional vs Multidirectional: Unidirectional (pure posterior) responds better to surgery. MDI requires rehabilitation first.

Epidemiology and Natural History

Incidence: Posterior instability constitutes 2–10% of all shoulder instability (far less common than anterior). Often underdiagnosed — posterior dislocation missed in up to 60% of cases on initial presentation.

Natural history: Traumatic posterior instability with labral tear has low spontaneous healing rate. Atraumatic instability with capsular laxity may respond to rehabilitation (up to 80–85% in MDI). Untreated engaging lesions progress to symptomatic instability.

Operative Indications

Posterior Bankart repair (soft tissue, less than 25% bone loss):

  • Traumatic posterior instability with posterior labral tear (Bankart or Kim lesion)
  • Failed 3–6 months physiotherapy in symptomatic patients
  • Athletes with functionally limiting instability
  • No significant bone loss (less than 25% glenoid diameter)

Posterior bone block (Eden-Hybinette or equivalent):

  • Posterior glenoid bone loss greater than 25% by CT measurement
  • Engaging reverse Hill-Sachs lesion (off-track by glenoid track calculation)
  • Failed previous soft tissue posterior stabilisation
  • Recurrent posterior instability after posterior Bankart repair

Evidence (all PMIDs verified against PubMed):

  • Kim SH et al. 2004 (PMID 15346113): original description of the Kim lesion (incomplete, concealed posteroinferior labral avulsion) in 15 shoulders treated by labroplasty and capsular shift
  • Bradley JP et al. 2006 (PMID 16567458): arthroscopic posterior capsulolabral reconstruction, 100 shoulders — mean ASES 50 to 86, 89% returned to sport at mean 27 months
  • Schwartz DG / Lafosse L et al. 2013 (PMID 23337111): arthroscopic posterior bone block (iliac crest), 19 shoulders — Rowe 18 to 82, radiographic union in all
  • Villefort / Gerber et al. 2022 (PMID 36911764): open posterior bone block, 14 patients, median 9-year follow-up — 31% tested recurrent instability, 62% major graft resorption, degenerative progression in 67%

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOAdvanced

Scenario 1: 20-Year-Old Gymnast — Multidirectional Instability

CLINICAL PROMPT

"A 20-year-old female gymnast presents with bilateral shoulder instability affecting both her performance and daily activities. Examination reveals a Beighton score of 7/9, bilateral sulcus sign of 2.5 cm (persisting with external rotation), positive anterior and posterior load-and-shift tests bilaterally, and diffuse shoulder apprehension in multiple planes. Plain radiographs are normal. How do you manage this patient?"

PRACTICAL APPROACH
This is a classic presentation of multidirectional instability (MDI) in a hypermobile athlete — one of the most nuanced management challenges in shoulder surgery. The key features confirming MDI: bilateral involvement, Beighton score 7/9 (generalised hypermobility), sulcus sign greater than 2 cm that does NOT reduce with external rotation (persistence of sulcus in ER distinguishes MDI with rotator interval laxity from unidirectional inferior instability), and instability in multiple planes. My management is primarily non-operative. First-line treatment — structured physiotherapy program minimum 6 months: (1) Rotator cuff strengthening — emphasise ER (infraspinatus, teres minor) to dynamically stabilise the posterosuperior capsule, and subscapularis to stabilise anteroinferiorly. (2) Periscapular stabilisation — serratus anterior and lower trapezius to improve scapular kinematics, which normalises the glenoid orientation during overhead activities. (3) Proprioception retraining — essential component often overlooked; closed-chain exercises, balance board, perturbation training. (4) Avoid activities that reinforce instability (hypermobile gymnastic manoeuvres that exploit voluntary laxity). Evidence: 80–85% of MDI patients improve with structured rehabilitation. Surgical options are reserved for the 15–20% who fail 6 months of supervised rehabilitation with continued severe functional limitation. If surgery required: Neer's open inferior capsular shift (or arthroscopic capsular plication with pan-directional capsular volume reduction). Procedure addresses global capsular redundancy. The surgeon shifts the inferior capsule superiorly (inferior leaf up, superior leaf down over it — T-plasty). Critical points: (1) Do NOT perform a bone block — there is no bone loss in MDI. (2) Do NOT perform isolated posterior Bankart repair — there is usually no discrete labral tear. (3) Do NOT operate on the dominant shoulder in isolation — bilateral capsular shift may eventually be required. For this gymnast specifically: her career aspirations and hypermobility profile make surgical outcomes unpredictable. Tighten capsule too much — she loses the laxity that gives her competitive advantage. Too little — instability persists. I would strongly recommend a minimum 12-month trial of supervised rehabilitation specific to gymnastics demands before considering surgery, and involve a sports physiotherapist experienced with hypermobile athletes.
CLINICAL SCENARIOAdvanced

Scenario 2: 30% Posterior Glenoid Bone Loss — Bone Block Decision

CLINICAL PROMPT

"A 28-year-old rugby player has a 3-year history of recurrent posterior shoulder instability after an initial tackle injury. He has had one episode of reduction in the emergency department and multiple subluxation episodes. CT scan shows 30% posterior glenoid bone loss and a large anteromedial humeral head impaction (reverse Hill-Sachs lesion). Plain films show no acute fracture. Arthroscopic posterior Bankart repair was performed 18 months ago and failed. What is your operative plan?"

PRACTICAL APPROACH
This patient has failed arthroscopic soft tissue repair and now has CT-confirmed 30% posterior glenoid bone loss — this is a clear indication for posterior bone block procedure. The management is a posterior bone block (Eden-Hybinette technique) with concurrent assessment of the reverse Hill-Sachs lesion. My operative planning: (1) Preoperative CT planning: measure bone loss precisely (Pico method or best-fit circle): 30% confirmed. Assess glenoid track — glenoid track = 0.83 × glenoid diameter − posterior bone loss. Compare to reverse Hill-Sachs lesion width on CT. If reverse Hill-Sachs is off-track (engages posteriorly during apprehension arc): bone block alone may suffice to convert lesion to on-track by extending the posterior articular arc. (2) Patient counselling: consent for Eden-Hybinette bone block with iliac crest autograft harvest, possible open revision of previous repair, possible reverse Hill-Sachs filling procedure (remplissage equivalent for posterior instability — posterior capsulodesis to fill the anteromedial defect) if off-track engaging. (3) Operative technique: Lateral decubitus. Posterior approach — deltoid split, infraspinatus interval. Mark axillary nerve at 5 cm landmark. Visualise posterior glenoid defect. Harvest tricortical iliac crest graft (approximately 2.5 × 1.5 × 1 cm, sized to defect on preoperative CT template). Prepare posterior glenoid surface (burr to bleeding cancellous bone). Position graft flush with posterior glenoid articular surface — neither proud nor recessed. Fix with two 3.5 mm cortical screws (or cannulated screws over guide wires for accuracy). Confirm position fluoroscopically. Repair infraspinatus and capsule over graft (graft lies extra-articular). (4) Addressing the reverse Hill-Sachs: If glenoid track assessment shows lesion converts from off-track to on-track after bone block — no additional humeral procedure needed. If still off-track despite bone block: consider posterior remplissage (infraspinatus tenodesis into anteromedial defect to prevent engagement) or humeral head rotation osteotomy (rarely needed). (5) Expected outcomes and honest counselling: short-term arthroscopic bone block series report good score gains and reliable union (Schwartz/Lafosse 2013, PMID 23337111), but long-term open data are sobering — around 30% tested recurrent instability, 62% major graft resorption, and arthrosis progression in two-thirds at median 9 years (Villefort/Gerber 2022, PMID 36911764). I would counsel this rugby player that posterior bone block is salvage surgery, less predictable than an anterior Latarjet, with a real chance of residual instability and progressive arthritis. Postoperatively: sling about 6 weeks, CT at around 3 months to assess graft position and union, return to contact sport no earlier than 6 months and only once stable.
CLINICAL SCENARIOStandard

Scenario 3: Post-op Loss of External Rotation — What Happened?

CLINICAL PROMPT

"A 25-year-old competitive swimmer underwent arthroscopic posterior capsulolabral repair 4 months ago for posterior instability. She now returns with persistent posterior shoulder pain and inability to externally rotate her shoulder beyond neutral (0°). Preoperatively she had 60° ER bilaterally. What is your diagnosis, its mechanism, and management?"

PRACTICAL APPROACH
This clinical picture — progressive loss of ER to 0° after posterior capsulolabral repair — is consistent with overtightening of the posterior capsule during capsulorrhaphy/plication. The patient has gone from 60° ER bilaterally to 0° ER on the operated side — a loss of 60°, which is severe and functionally devastating for a competitive swimmer who requires significant ER for freestyle and butterfly mechanics. Mechanism of injury: The posterior capsule is a primary static restraint to glenohumeral internal rotation. When the posterior capsule is plicated/shortened excessively during arthroscopic repair, it limits external rotation. The tightened posterior capsule creates the equivalent of a posterior contracture — the humeral head is forced into relative anterior superior translation as ER is attempted (similar to but opposite to the GIRD phenomenon). Additionally, excessive posterior capsular tightening may cause abnormal glenohumeral joint reaction forces with secondary pain. Clinical assessment: (1) Range of motion: document ER at 0° and 90° abduction, IR in both positions. Confirm posterior capsular tightness (firm end-feel in ER vs springy/soft normal). (2) Examine for anterior impingement signs (positive Neer, Hawkins) — posterior tightening drives humeral head anteriorly. (3) Rotator cuff strength — particularly IR strength (subscapularis) and ER strength (infraspinatus) to detect any concurrent deficiency. (4) Imaging: radiographs (confirm no glenohumeral arthritis, confirm hardware position/no anchor migration). MRI — assess labral repair status and posterior capsule thickness. Management options: (1) Initial conservative: intensive physiotherapy programme targeting posterior capsular stretching (modified cross-body stretch, horizontal adduction stretching). Continue minimum 3–6 months. In anterior instability, posterior capsular stretching resolves GIRD; here, the capsule should gradually stretch if not excessively scarred. (2) If no improvement at 6 months: surgical posterior capsular release — arthroscopic. The posterior capsular plication sutures are identified and released under direct vision. Take care to avoid axillary nerve inferiorly during release. (3) Return-to-sport: this swimmer cannot compete at less than 45° ER — swimming mechanics require full glenohumeral rotation. Surgical release of overtightened capsule allows return to function. Outcome: arthroscopic posterior capsular release for post-operative stiffness has good outcomes (75–80% recovery of ER) if performed before significant secondary glenohumeral arthritic changes develop (within 18–24 months of surgery).

Posterior Bone Block / Posterior Instability — Exam Summary

Clinical summary

Key Evidence

Kim's lesion — original description of the concealed posteroinferior labral avulsion

Level IV
Kim SH, Ha KI, Yoo JC, Noh KC • Arthroscopy (2004)
Clinical Implication: In posterior instability you must PROBE and elevate the posteroinferior labrum — visual inspection alone misses the Kim lesion, and an unaddressed lesion causes persistent instability.
Verify on PubMed (PMID 15346113)

Arthroscopic capsulolabral reconstruction for posterior instability — 100 shoulders

Level II
Bradley JP, Baker CL, Kline AJ, Armfield DR, Chhabra A • Am J Sports Med (2006)
Clinical Implication: Arthroscopic posterior capsulolabral repair is a reliable first-line operation for symptomatic unidirectional posterior instability without significant bone loss, even in contact athletes.
Verify on PubMed (PMID 16567458)

Arthroscopic posterior bone block augmentation with iliac crest graft

Level IV
Schwartz DG, Goebel S, Piper K, Kordasiewicz B, Boyle S, Lafosse L • J Shoulder Elbow Surg (2013)
Clinical Implication: Posterior bone block can stabilise shoulders that fail soft-tissue repair or have posterior glenoid deficiency, but it is technically demanding and not uniformly pain-free; flush graft and attention to hardware matter.
Verify on PubMed (PMID 23337111)

Mid-to-long-term results of open posterior bone block — the cautionary data

Level IV
Villefort C, Stern C, Gerber C, Wyss S, Ernstbrunner L, Wieser K • JSES Int (2022)
Clinical Implication: Counsel realistically: posterior bone block is salvage surgery with high resorption, recurrence and arthrosis rates, especially in atraumatic instability — outcomes are far less predictable than an anterior Latarjet.
Verify on PubMed (PMID 36911764)

Glenoid track and on-track / off-track concept (anterior instability)

Level V
Di Giacomo G, Itoi E, Burkhart SS • Arthroscopy (2014)
Clinical Implication: The track concept is validated for ANTERIOR instability; apply it to posterior instability only by analogy as a bipolar bone-loss assessment, not as a validated posterior threshold.
Verify on PubMed (PMID 24384275)

References

  1. Kim SH, Ha KI, Yoo JC, Noh KC (2004). Kim's lesion: an incomplete and concealed avulsion of the posteroinferior labrum in posterior or multidirectional posteroinferior instability of the shoulder. Arthroscopy. 20(7):712–720. PMID: 15346113. DOI: 10.1016/j.arthro.2004.06.012

  2. Bradley JP, Baker CL 3rd, Kline AJ, Armfield DR, Chhabra A (2006). Arthroscopic capsulolabral reconstruction for posterior instability of the shoulder: a prospective study of 100 shoulders. Am J Sports Med. 34(7):1061–1071. PMID: 16567458. DOI: 10.1177/0363546505285585

  3. Schwartz DG, Goebel S, Piper K, Kordasiewicz B, Boyle S, Lafosse L (2013). Arthroscopic posterior bone block augmentation in posterior shoulder instability. J Shoulder Elbow Surg. 22(8):1092–1101. PMID: 23337111. DOI: 10.1016/j.jse.2012.09.011

  4. Villefort C, Stern C, Gerber C, Wyss S, Ernstbrunner L, Wieser K (2022). Mid-term to long-term results of open posterior bone block grafting in recurrent posterior shoulder instability: a clinical and CT-based analysis. JSES Int. 7(2):211–217. PMID: 36911764. DOI: 10.1016/j.jseint.2022.12.008

  5. Di Giacomo G, Itoi E, Burkhart SS (2014). Evolving concept of bipolar bone loss and the Hill-Sachs lesion: from "engaging/non-engaging" lesion to "on-track/off-track" lesion. Arthroscopy. 30(1):90–98. PMID: 24384275. DOI: 10.1016/j.arthro.2013.10.004

  6. Burkhead WZ Jr, Rockwood CA Jr (1992). Treatment of instability of the shoulder with an exercise program. J Bone Joint Surg Am. 74(6):890–896. PMID: 1634579

  7. Neer CS 2nd, Foster CR (1980). Inferior capsular shift for involuntary inferior and multidirectional instability of the shoulder. J Bone Joint Surg Am. 62(6):897–908.