Use of posteroanterior reference guides for bone block or coracoid process transfer in anterior glenohumeral instability: a cadaveric study of the relationship to the suprascapular nerve
Article information
Abstract
Background
Iatrogenic suprascapular nerve injury secondary to posterior drilling or screw penetration is a recognized complication of bone block or coracoid process transfers for anterior glenohumeral instability. We present the first cadaveric study that assesses the safety of posteroanterior reference guides and quantifies the relationship of the suprascapular nerve to posterior glenoid fixation with suture buttons.
Methods
Anterior glenoid bone block reconstruction with suture buttons utilizing a posteroanterior reference guide was performed in 10 fresh frozen cadavers via a posterior portal. Bullets were inserted in predefined superior and inferior guide holes via percutaneous incisions to facilitate posteroanterior drilling. Looped guide wires were used to deliver suture buttons from anterior to posterior positions. The shoulder joint was disarticulated and the infraspinatus sharply elevated until the suprascapular nerve was visualized. Four independent static measures of the shortest distance from the superior drill sleeve to the lateral aspect of the suprascapular nerve were recorded.
Results
The suprascapular nerve was not compromised utilizing the posteroanterior guide and suture button fixation technique in any specimen. The mean distance from superior sleeve tunnel to the suprascapular nerve was 5.00 mm (range, 3.25–8.00 mm) in females and 6.80 mm (range, 5.50–8.75 mm) in males. The shortest distance was 3.25 mm and the longest was 8.75 mm.
Conclusions
The use of posteroanterior reference guides for suture button fixation was not associated with iatrogenic suprascapular nerve injury in the specimens examined. However, the proximity of the suprascapular nerve underscores the need for caution. Comparative analysis with anteroposterior bone block techniques is required to establish the potential benefits of this procedure.
Level of evidence
V.
INTRODUCTION
Recurrent glenohumeral instability is a complex and common challenge faced in modern shoulder practice. Anterior glenoid deficiency is reported in 22% of traumatic anterior shoulder dislocations and in 90% of cases of recurrent anteroinferior instability [1]. Anterior bone block or coracoid process transfer procedures are commonly utilized to address anterior glenoid deficiency [2]. In the Latarjet procedure, the coracoid process and conjoint tendon are transferred to the anteroinferior glenoid rim via a split in the subscapularis, restoring anterior stability via a proposed triple-blocking mechanism that increases glenoid anteroposterior diameter, restores the sling effect of the conjoint tendon and lower subscapularis, and repairs the anterior joint capsule using the coracoacromial ligament [3]. An established complication of anterior bone block and coracoid transfer procedures is intraoperative injury to the terminal branch of the suprascapular nerve due to the proximity to the posterior glenoid rim and spinoglenoid notch during anteroposterior fixation of the bone block utilizing screws [4]. Injury to the suprascapular nerve causes denervation of infraspinatus resulting in debilitating weakness, loss of active external rotation, and/or chronic pain [4-7].
Cadaveric studies have established a safe zone for screw placement within 10º of the glenoid face in the axial plane [5]. However, accurate assessment of the axial plane is challenging following intraoperative insertion of the anterior bone block, with small errors in orientation potentially translating to significant variation in posterior exit points. Furthermore, plunging the drill beyond the posterior cortex may tether soft tissue adjacent to the suprascapular nerve; a mean plunge depth of 6.00 mm has been reported in even the most experienced surgeons [8]. Therefore, suprascapular nerve injury following anterior bone block procedures continues to be reported [4,6,7,9].
Taverna described an arthroscopic anterior stabilization technique utilizing tricortical iliac crest bone block, secured with posteroanterior suture button fixation through introduction of a posterior drill guide [10]. Similarly, arthroscopic techniques for performing a coracoid transfer have been described that utilize suture buttons to avoid the use of screws [11,12]. The relationship of the posterior glenoid bone tunnel and button placement thus far has not been established; however, we hypothesize the utilization of the posteroanterior reference guide instrumentation may reduce the risk of suprascapular nerve injury. We present the first cadaveric study to assess the relationship of the suprascapular nerve to posterior instrumentation utilizing a posteroanterior reference guide when performing bone block transfer for anterior glenohumeral joint instability.
METHODS
As this was a cadaveric study, consent and ethical approval were not required. However, all specimens were managed in accordance with the Human Tissue Act 2004, and the study adhered to the principles of the Helsinki Declaration 2013 revision.
Ten fresh frozen cadaveric specimens were used for this study, comprising six female specimens and four male specimens with a mean age of 72 years (range, 62–85 years). The use of 10 specimens reflects limited access to cadaveric specimens but is comparable to other cadaveric studies assessing anteroposterior bone block fixation [2]. Specimens were mounted in a simulated beach chair position at 45º with a clamp on the medial scapula. A deltopectoral approach was used before a standard posterior portal, 2 cm inferior and 2 cm medial to the posterolateral corner of the acromion, was created to introduce the posterior drill glenoid guide (Fig. 1), which was placed parallel to the glenoid face (Fig. 2) [10,13]. The guide was then rotated to secure the anterior edge of the glenoid under the hook between the 3 and 4 o’clock positions, representing the usual site of glenoid bone loss in anterior instability.
Per Taverna’s technique, bullets were placed in the superior and inferior guide holes and inserted via percutaneous incisions with blunt dissection of intervening soft tissue until firm contact with the posterior glenoid neck was established (Fig. 3) [10]. A 2.8-mm sleeved drill was inserted through each of the bullets and parallel drill holes were performed 10.0 mm apart and 5.0 mm posterior to the glenoid face as predefined by the guide. The inner drill was removed leaving the cannulated sleeve in situ. Flexible looped guide wires were inserted through the cannulated sleeve, retrieved anteriorly and used to deliver suture buttons from the anteroposterior, which were tied posteriorly utilizing Nice knots.
To identify the suprascapular nerve, the deltopectoral incision was extended superiorly and posteriorly to disarticulate the shoulder joint (Fig. 4). The infraspinatus and teres minor were sharply elevated from the greater tuberosity. The infraspinatus was further elevated from the infraspinous fossa until the suprascapular nerve could be visualized exiting the spinoglenoid notch. A standard protocol for arm positioning has not been established in other studies. Shoulder positioning was uniformly maintained at 0º adduction and 0º external rotation, per Taverna’s description of the technique [10]. No further release of infraspinatus was performed once visualization of the suprascapular nerve was confirmed, in order to minimize variable soft tissue tension affecting positioning of the nerve. Four independent static measures of the shortest distance from the superior drill sleeve to the lateral aspect of the suprascapular nerve were recorded (Figs. 5 and 6).

Disarticulation of the shoulder joint and elevation of the infraspinatus and teres minor (labelled) to identify the suprascapular nerve (asterisk).
As this was an anatomic study without a comparison group, no statistical analysis was performed. The study was conducted in accordance with the Human Tissue Act 2004 governing the use of cadaveric specimens. Posteroanterior fixation and measurements were performed by four post-fellowship shoulder surgeons. Specimens and laboratory facilities were provided by Smith and Nephew.
RESULTS
The suprascapular nerve was not compromised by posteroanterior bone block fixation for anterior shoulder stabilization in any of the specimens. The mean distance from the superior sleeve to suprascapular nerve was 5.00 mm in female specimens and 6.80 mm in male specimens. The shortest distance from the superior sleeve to suprascapular nerve was 3.25 mm, while the longest was 8.75 mm.
DISCUSSION
This cadaveric study explores the relationship between the suprascapular nerve and the posteroanterior reference guide in bone block transfer for anterior glenohumeral joint instability. Use of posteroanterior reference drill guides was not associated with iatrogenic suprascapular nerve injury, suggesting it is a relatively safe procedure. However, the proximity of the suprascapular nerve to the superior sleeve highlights the need for intraoperative caution.
The suprascapular nerve is a terminal branch of the upper trunk of the brachial plexus originating from the C5 and C6 nerve roots. The nerve runs laterally in the posterior cervical triangle parallel to the omohyoid before exiting posteriorly through the suprascapular notch and coursing obliquely along the floor of the supraspinous fossa toward the glenoid rim. During its descent through the supraspinous fossa, the nerve typically has two motor branches to supraspinatus and receives nociceptive fibers from the acromioclavicular joint and posterior glenohumeral joint capsule [14]. The nerve enters the infraspinous fossa via the spinoglenoid notch and runs inferomedially before terminating in three or four motor branches to the infraspinatus [14]. The suprascapular nerve is at closest proximity to the glenoid rim at the 9 o’clock position on the glenoid, with cadaveric studies reporting a distance of 18.74 mm [15]. This is particularly pertinent to anteroposterior drilling for anterior bone block procedures, where screws are oriented superiorly such that the last branch supplying infraspinatus is potentially at risk [4,6,7,9].
Multiple studies have described suprascapular nerve injury following anterior bone block procedures, with resulting denervation of the infraspinatus causing loss of active external rotation [4,6,7,9]. Two studies utilized postoperative electromyography, which confirmed acute suprascapular nerve iatrogenic injury [6,7]. Given the restrictions placed on patients following anterior stabilization, this complication may only be evident 6–12 weeks postoperatively. In two studies, removal of anteroposterior screws led to improvement in active external rotation, demonstrating that suprascapular nerve injury can occur secondary to screw placement as well as due to iatrogenic drill injury [7,16].
Several cadaveric studies have sought to define safe zones for anteroposterior bone block fixation. Shishido and Kikuchi [17] proposed that the risk of iatrogenic suprascapular nerve injury could be mitigated utilizing a drilling angle within 28º of the glenoid face in the axial plane. Lädermann et al. [5] expanded on this by evaluating the distance from the suprascapular nerve to the superior and inferior screws following an open Latarjet procedure in 10 cadaveric specimens. Screws were not in contact with the suprascapular nerve if the angle relative to the glenoid was less than or equal to 10º, reflecting the specific inferior-to-superior sagittal plane drilling direction required for bone block fixation in anterior instability [5]. Longo described dynamic techniques to displace the suprascapular nerve from the surgical field to reduce risk of injury: in a cadaveric study, the median distance between the glenoid and suprascapular nerve was 12.00 mm with 90º of shoulder internal rotation compared to 19.00 mm at 90º of external rotation [2]. However, while dynamic techniques may reduce risk of iatrogenic injury during drilling, this does not reduce risk of nerve irritation secondary to screw placement [7,16]. Our study utilizes a fixed angle posterior referencing guide with suture button fixation instead of screws.
There are technical and anatomic factors during anteroposterior bone block fixation for anterior instability that can explain the intra-operative difficulty of maintaining a drilling angle within 10º of the glenoid face in the axial plane. Firstly, the entry point for fixation on the anterior surface of the glenoid is typically only 7.00 mm from the glenoid rim [18]. Further, the intraoperative determination of a precise axial angle is complicated by the glenoid's concave surface. The glenoid version can lie between –4º and 4º in the axial plane, whilst in the scapular plane it is oriented 30 º anterior to the true coronal plane [19].
Our study suggests that posteroanterior bone block fixation for anterior shoulder stabilization is relatively safe and not associated with iatrogenic suprascapular nerve injury in cadaveric specimens. By bluntly dissecting through soft tissue until bony contact with the posterior glenoid neck is established and utilizing protective drill sleeves throughout, we theorize that the risk of iatrogenic suprascapular nerve injury is likely to be reduced compared to blind anteroposterior drilling, as the posteroanterior reference guides prevent medialization of any posterior glenoid instrumentation. Taverna’s technique demonstrated excellent short-term results, with no recurrent dislocation, 92.3% healing rate on computed topography scans, and no neurological injury at the 2-year follow-up in 26 patients [20].
However, this study highlights the need for a high index of caution throughout the procedure. The mean distance from the superior sleeve to suprascapular nerve was 5.00 mm in female specimens and 6.80 mm in male specimens. Therefore, it is imperative that blunt dissection is meticulously performed until the glenoid neck is encountered and drill sleeves are left in situ throughout to avoid entrapment of the suprascapular nerve within the fixation construct.
There are several limitations to this study. Only 10 cadaveric specimens were available for analysis, a small sample size, although the same number was used in comparable anatomic studies of the suprascapular nerve during anteroposterior bone block fixation [5]. Posteroanterior bone block fixation was performed in specimens without the anatomic sequelae of anterior shoulder instability, and the height of cadaveric specimens was not recorded. Although there is potential for surgeon bias when performing the procedure, we aimed to reduce this by utilizing four independent measures. In addition, variation in suprascapular nerve positioning during dynamic and static positioning was not considered. Furthermore, this study solely analyzed the use of posteroanterior reference guide instrumentation during anterior bone block fixation; therefore, comparative analysis versus anteroposterior reference bone block fixation could not be conducted.
CONCLUSIONS
The suprascapular nerve is at risk during bone block fixation for anterior shoulder stabilization. In this small anatomic series, use of posteroanterior reference drill guides was not associated with iatrogenic suprascapular nerve injury. However, the proximity of the suprascapular nerve to the drill sleeve underscores the need for a high index of caution throughout the procedure.
Notes
Author contributions
Conceptualization: AC, LDM. Data curation: OO, MT, AC, LDM. Formal analysis: RC, OO, AC, LDM.
Investigation: OO, MT, AC, LDM. Methodology: OO, MT, AC, LDM. Supervision: AC, LDM. Writing – original draft: MRB, OO. Writing – review & editing: MRB, RC, CAJD, AC, LDM.
Conflict of interest
None.
Funding
None.
Data availability
Contact the corresponding author for data availability.
Acknowledgments
None.