The effect of defect orientation and size on glenohumeral instability: a biomechanical analysis

Glenoid Concavity Affects Anterior Shoulder Stability in an Active-Assisted Biomechanical Model

Background

The treatment of bony glenoid defects after anteroinferior shoulder dislocation currently depends on the amount of glenoid bone loss (GBL). Recent studies have described the glenoid concavity as an essential factor for glenohumeral stability. The role of glenoid concavity in the presence of soft tissue and muscle forces is still unknown.

Hypothesis

Glenoid concavity would have a major impact on glenohumeral stability in an active-assisted biomechanical model including soft tissue and the rotator cuff's compression forces.

Study Design

Controlled laboratory study.

Methods

In 8 human shoulder specimens, individual coordinate systems were calculated based on anatomic landmarks. The glenoid concavity was measured biomechanically and based on computed tomography. Static load was applied to the rotator cuff tendons and the deltoid muscle. In a robotic test setup, anteriorly directed force was applied to the humeral head until translation of 5 mm (Nant) was achieved. Nant was used as a parameter indicating shoulder stability. This was performed in the following testing stages: (1) intact joint, (2) labral lesion, (3) 10% GBL, and (4) 20% GBL. The 8 specimens were divided equally into 2 subgroups (low concavity [LC] versus high concavity [HC]), with 4 specimens each, according to the previously measured concavity.

Results

Anterior glenohumeral stability was highly correlated with the native glenoid concavity (R 2 = 0.8). In the testing stages 1 to 3, we found a significantly higher mean stability in the HC subgroup compared with the LC subgroup (P≤ .0142). The HC subgroup still showed higher absolute Nant values with 20% GBL; however, there was no significant difference from the LC subgroup. The loss of stability in 20% GBL was correlated with the initial concavity (R 2 = 0.86). Thus, a higher loss of Nant in the HC subgroup was observed (P = .0049).

Conclusion

In an active-assisted model with intact soft tissue surrounding and muscular compression forces, the glenoid concavity correlates with shoulder stability. In bony defects, loss of concavity is an essential factor causing instability. Due to their significantly higher native stability, glenoids with HC can tolerate a higher amount of GBL.

Clinical Relevance

Glenoid concavity should be considered in an individualized treatment of bony glenoid defects. Further studies are required to establish reference values and develop therapeutic algorithms.

A review of bone grafting techniques for glenoid reconstruction

BACKGROUND

Traumatic anterior shoulder dislocations can cause bony defects of the anterior glenoid rim and are often associated with recurrent shoulder instability. For large glenoid defects of 20-30% without a mobile bony fragment, glenoid reconstruction with bone grafts is often recommended. This review describes two broad categories of glenoid reconstruction procedures found in literature: coracoid transfers involving the Bristow and Latarjet procedures, and free bone grafting techniques.

METHODS

An electronic search of MEDLINE and PubMed was conducted to find original articles that described glenoid reconstruction techniques or modifications to existing techniques.

RESULTS

Coracoid transfers involve the Bristow and Latarjet procedures. Modifications to these procedures such as arthroscopic execution, method of graft attachment and orientation have been described. Free bone grafts have been obtained from the iliac crest, distal tibia, acromion, distal clavicle and femoral condyle.

CONCLUSION

Both coracoid transfers and free bone grafting procedures are options for reconstructing large bony defects of the anterior glenoid rim and have had similar clinical outcomes. Free bone grafts may offer greater flexibility in graft shaping and choice of graft size depending on the bone stock chosen. Novel developments tend towards minimising invasiveness using arthroscopic approaches and examining alternative non-rigid graft fixation techniques.

How does anterior glenoid bone loss affect shoulder stability? A cadaveric analysis of glenoid concavity and bony shoulder stability ratio

BACKGROUND

Concavity compression is an important glenohumeral stabilizing factor, and recent studies have suggested that peripheral glenoid bone loss creates the most relevant change in stability. This study analyzed changes in the bony shoulder stability ratio (BSSR) with sequential anterior glenoid bone loss (0%-40% width) and with reconstructive bone graft procedures. The aim was to quantify the critical bone defect size that would significantly alter the BSSR and determine restoration of the BSSR with the Latarjet procedure.

METHODS

Anterior glenoid defects were created with sequential osteotomies (10%-40%), and defects were reconstructed using 2 Latarjet modifications (classic Latarjet procedure and congruent-arc Latarjet [CAL] procedure). We obtained 108 computed tomography scans of (1) intact scapulae (n = 12), (2) after each bone defect (n = 48), and (3) after each reconstruction (n = 48). The glenoid concavity depth and concavity radius were measured, and the BSSR was determined using a validated mathematical formula. Statistical analysis was performed to determine significant differences between the intact state and each of the deficient and reconstructed glenoids.

RESULTS

The glenoid concavity radius increased by approximately 30% (14 mm) and the glenoid concavity depth decreased by 50% (1.5 mm) from the 0% to 40% defect. The maximal sequential change in depth (1.2 mm, 44%; P < .001) and radius (6 mm, 12%; P < .001) occurred at the 10% glenoid defect. The overall BSSR decreased by approximately 40% (0.15) from the intact glenoid to the 40% defect. This change in the BSSR was most profound (0.11, 30%; P < .001) at the 10% glenoid defect and was only marginal thereafter between the 20% and 40% defects (0.24, 0.22, and 0.21). The Latarjet procedure adequately restored glenoid concavity; however, the CAL procedure significantly overcorrected all 3 parameters at 10% defect.

CONCLUSION

The glenoid concavity depth and BSSR undergo progressive deformation with sequential bone loss, and 90% of this change occurs with a 10% glenoid defect. Articular concavity and the BSSR are adequately restored with the Latarjet procedure, and the CAL procedure significantly overcorrects concavity in mild (0%-10%) defects.

The Glenolabral Articular Disruption Lesion Is a Biomechanical Risk Factor for Recurrent Shoulder Instability

Purpose

To investigate the biomechanical effect of a glenolabral articular disruption (GLAD) lesion on glenohumeral laxity.

Methods

Human cadaveric glenoids (n = 10) were excised of soft tissue, including the labrum to focus on the biomechanical effects of osteochondral surfaces. Glenohumeral dislocations were performed in a robotic test setup, while displacement forces and three-dimensional morphometric properties were measured. The stability ratio (SR), a biomechanical characteristic for glenohumeral stability, was used as an outcome parameter, as well as the path of least resistance, determined by a hybrid robot displacement. The impacts of chondral and bony defects were analyzed related to the intact glenoid. Statistical comparison of the defect states on SR and the path of least resistance was performed using repeated-measures ANOVA and Tukey’s post hoc test for multiple comparisons (P < .05). The relationship between concavity depth and SR was approximated in a nonlinear regression.

Results

The initial SR of the intact glenoid (28.3 ± 7.8%) decreased significantly by 4.7 ± 3% in case of a chondral defect (P = .002). An additional loss of 3.2 ± 2.3% was provoked by a 20% bony defect (P = .004). The path of least resistance was deflected significantly more inferiorly by a GLAD lesion (2.9 ± 1.8°, P = .002) and even more by a bony defect (2.5 ± 2.9°, P = .002). The nonlinear regression with concavity depth as predictor for the SR resulted in a high correlation coefficient (r = .81).

Conclusions

Chondral integrity is an important contributor to the SR. Chondral defects as present in GLAD lesions may cause increased laxity, influence the humeral track on the glenoid during dislocation, and represent a biomechanical risk factor for a recurrent instability.

Clinical Relevance

Cartilage deficiency corresponding to GLAD lesions may be a risk factor for impaired surgical outcomes.

Glenoid concavity has a higher impact on shoulder stability than the size of a bony defect

PURPOSE

Surgical treatment of shoulder instability caused by anterior glenoid bone loss is based on a critical threshold of the defect size. Recent studies indicate that the glenoid concavity is essential for glenohumeral stability. However, biomechanical proof of this principle is lacking. The aim of this study was to evaluate whether glenoid concavity allows a more precise assessment of glenohumeral stability than the defect size alone.

METHODS

The stability ratio (SR) is a biomechanical estimate of glenohumeral stability. It is defined as the maximum dislocating force the joint can resist related to a medial compression force. This ratio was determined for 17 human cadaveric glenoids in a robotic test setup depending on osteochondral concavity and anterior defect size. Bony defects were created gradually, and a 3D measuring arm was used for morphometric measurements. The influence of defect size and concavity on the SR was examined using linear models. In addition, the morphometrical-based bony shoulder stability ratio (BSSR) was evaluated to prove its suitability for estimation of glenohumeral stability independent of defect size.

RESULTS

Glenoid concavity is a significant predictor for the SR, while the defect size provides minor informative value. The linear model featured a high goodness of fit with a determination coefficient of R² = 0.98, indicating that 98% of the SR is predictable by concavity and defect size. The low mean squared error (MSE) of 4.2% proved a precise estimation of the SR. Defect size as an exclusive predictor in the linear model reduced R² to 0.9 and increased the MSE to 25.7%. Furthermore, the loss of SR with increasing defect size was shown to be significantly dependent on the initial concavity. The BSSR as a single predictor for glenohumeral stability led to highest precision with MSE = 3.4%.

CONCLUSION

Glenoid concavity is a crucial factor for the SR. Independent of the defect size, the computable BSSR is a precise biomechanical estimate of the measured SR. The inclusion of glenoid concavity has the potential to influence clinical decision-making for an improved and personalised treatment of glenohumeral instability with anterior glenoid bone loss.

Arthroscopic Glenoid Bone Grafting With Soft Fixation for Recurrent Anterior Shoulder Dislocation

Glenoid bone defect is a common structural deficiency in cases of recurrent anterior shoulder dislocation. Glenoid bone grafting is an effective method to address glenoid defect and promote labrum regeneration. In most previous reports, firm fixation of the bone grafts was conducted, but with obvious inconvenience. Thus, we introduce a special glenoid bone-grafting technique in which the bone fragments are placed to the anterior side of the glenoid through the rotator interval, with 1 inferior graft free of fixation and 1 superior graft fixed to the glenoid by suture suspension. This technique is indicated in patients with recurrent anterior shoulder dislocation with glenoid defect or needing osseous stimulation for labrum regeneration. The critical point of this technique is the proper use of special glenoid bone grafting instruments. We believe this technique will provide a special choice in the treatment of recurrent anterior shoulder dislocation.

Benefits of bone graft augmentation to arthroscopic Bankart repair for recurrent anterior shoulder instability with glenoid bone loss

PURPOSE

Glenoid bone loss contributes to recurrent instability after arthroscopic Bankart repair alone. With significant glenoid bone loss, better results have been reported after arthroscopic Bankart repair with glenoid arc reconstruction. However, no reports compare augmentation using bone graft with non-augmentation for glenoid bone loss. The purpose of this study was to assess clinical results of an arthroscopic Bankart repair with or without arthroscopic bone graft augmentation. It was hypothesized that such bone graft augmentation would restore shoulder stability, and lead to excellent outcomes.

METHODS

Of 552 patients treated for anterior glenohumeral instability with arthroscopic Bankart repair, 68 met this study's inclusion criteria of glenoid bone loss over 20% and follow-up of at least 2 years. Patients were divided into 2 groups based on whether with bone graft augmentation for glenoid bone loss [Group A: n = 35, median age; 21 years (range 13-72 years)], or not (Group B: n = 33, median age; 21 years (range 13-50 years)]. For grafting, either autologous iliac bone or artificial bone made of hydroxyapatite was used. Rowe score, recurrence rate, and return to sport were used to assess the results.

RESULTS

Mean Rowe score was 95.0 (SD 10.6) in Group A and 69.7 (SD 27.2) in Group B (p < 0.05). The recurrence rate was 2.9% (1/36) in Group A and 48.5% (16/33) in Group B (p < 0.05). Regarding contact/collision athletes, 24 were contained in Group A and 22 in Group B. Of the patients with recurrence in Group B, 13 (59.1%) were contact/collision athletes. Finally, 50% of the contact/collision sports athletes for both groups returned to their sports at the same as pre-injury level. Of the 11 patients who returned to the same level of contact/collision sports in Group B, seven returned with residual instability. Nine athletes in Group A and 3 in Group B quit their sports for personal or social reasons.

CONCLUSIONS

Bone graft augmentation was beneficial when used with Arthroscopic Bankart repair for recurrent anterior shoulder instability with glenoid bone loss. Especially, for recurrent anterior shoulder instability with glenoid bone loss in contact/collision sports athletes, bone graft augmentation should be strongly considered as beneficial.

LEVEL OF EVIDENCE

Level IV.

Return to play and performance after shoulder instability in National Basketball Association athletes

HYPOTHESIS

We hypothesized that players in the National Basketball Association (NBA) who sustained a shoulder destabilizing injury could return to play (RTP) successfully at a high rate regardless of treatment type.

METHODS

We used publicly available data to identify and evaluate 50 players who sustained an in-season shoulder instability event (subluxation/dislocation) while playing in the NBA. Demographic variables, return to NBA gameplay, incidence of surgery, time to RTP, recurrent instability events, and player efficiency rating (PER) were collected. Overall RTP was determined, and players were compared by type of injury and mode of treatment.

RESULTS

All players (50/50) returned to game play after sustaining a shoulder instability event. In those treated nonoperatively, athletes who sustained shoulder subluxations returned after an average of 3.6 weeks, compared with 7.6 weeks in those who sustained a shoulder dislocation (P = .037). Players who underwent operative management returned after an average of 19 weeks. Athletes treated operatively were found to have a longer time interval between a recurrent instability event (70 weeks vs. 28.5 weeks, P = .001).

CONCLUSION

We found 100% rate of RTP after a shoulder instability event in an NBA athlete. Players who experience shoulder dislocations were found to miss more time before RTP and were more likely to undergo surgical intervention compared with those who experienced a subluxation. Surgical repair maintained a longer interval between recurrent instability. Future investigations should aim to evaluate outcomes based on surgical procedures and identify possible risk factors predictive of recurrent instability or failure to RTP.

[Recurrent instability and instability arthropathy]

Capsulolabral reconstruction (Bankart repair) is recommended as the first line treatment in young and functionally demanding active patients with anteroinferior shoulder instability, due to the high tendency to recurrent dislocation. This has become established both for arthroscopic and open primary shoulder stabilization with good clinical outcome; nevertheless, recurrence of dislocation is reported in up to 25% of patients. Risk factors for failed surgery are patient (e.g. young age, male gender and contact sports) and surgery (e.g. primarily underestimated glenoid bone loss, Hill-Sachs lesion, non-treatment of bipolar defects or malpositioned anchors) related. In the management of recurrent instability, it is necessary to carry out a thorough clinical investigation in addition to extended diagnostics with X‑ray and computed tomography. A second Bankart repair is only indicated in patients with low demands and without any glenoid bone loss. In the majority of patients, bony augmentation of the glenoid is necessary and realized by coracoid or iliac crest bone block transfer. The Latarjet procedure is biomechanically advantageous due to the additional sling effect of the conjoined tendons and both techniques show good clinical outcomes and a low recurrence rate. Furthermore, engaging Hill-Sachs lesions also require additional treatment. Remplissage of the infraspinatus muscle, iliac crest bone block transfer and partial joint replacement are viable options. A final consensus for treatment of Hill-Sachs lesions has yet to be defined. Dislocation arthropathy is an underestimated complication as a result of frequent recurrent dislocations. After development of dislocation arthropathy, patients reported a painful restriction of range of motion rather than instability. Arthroscopic arthrolysis and comprehensive arthroscopic management (CAM procedure) are possible joint-preserving treatment options.

The critical size of a defect in the glenoid causing anterior instability of the shoulder after a Bankart repair, under physiological joint loading

Aims

Patients with recurrent anterior dislocation of the shoulder commonly have an anterior osseous defect of the glenoid. Once the defect reaches a critical size, stability may be restored by bone grafting. The critical size of this defect under non-physiological loading conditions has previously been identified as 20% of the length of the glenoid. As the stability of the shoulder is load-dependent, with higher joint forces leading to a loss of stability, the aim of this study was to determine the critical size of an osseous defect that leads to further anterior instability of the shoulder under physiological loading despite a Bankart repair.

Patients and Methods

Two finite element (FE) models were used to determine the risk of dislocation of the shoulder during 30 activities of daily living (ADLs) for the intact glenoid and after creating anterior osseous defects of increasing magnitudes. A Bankart repair was simulated for each size of defect, and the shoulder was tested under loading conditions that replicate in vivo forces during these ADLs. The critical size of a defect was defined as the smallest osseous defect that leads to dislocation.

Results

The FE models showed a high risk of dislocation during ADLs after a Bankart repair for anterior defects corresponding to 16% of the length of the glenoid.

Conclusion

This computational study suggests that bone grafting should be undertaken for an anterior osseous defect in the glenoid of more than 16% of its length rather than a solely soft-tissue procedure, in order to optimize stability by restoring the concavity of the glenoid.

Bone Loss and Glenohumeral Instability

Glenohumeral instability secondary to glenohumeral bone loss presents a complex problem to the treating surgeon because of the complex biomechanics of the glenohumeral joint and its reliance on numerous dynamic and static stabilizers. The role of glenoid bone loss, specifically inferior-anterior glenoid bone loss, has been well characterized in the setting of recurrent unidirectional instability with greatly improved clinical results when following an algorithmic reconstructive approach to the location and percentage of overall bone loss. Furthermore, as the role of bipolar bone loss in the setting of glenohumeral engagement becomes more apparent, surgeons can more effectively address those lesions contributing to the recurrent instability. As such, surgeons should carefully and critically asses patients with recurrent anterior instability to optimize patient clinical outcomes.

Editorial Commentary: Arthroscopic Latarjet Shoulder Stabilization: Where Are We? Where Are We Going?

Arthroscopic Latarjet procedure has shown satisfactory clinical outcomes in the treatment of anteroinferior shoulder instability. Although as of today there is no proven advantage of the arthroscopic procedure over an open one, it is too early to give up. At the same time, crucial to understand the causes of failure, to find the solutions to every single difficulty to simplify this surgery and to make it as accessible as possible.

What Is the Critical Value of Glenoid Bone Loss at Which Soft Tissue Bankart Repair Does Not Restore Glenohumeral Translation, Restricts Range of Motion, and Leads to Abnormal Humeral Head Position?

BACKGROUND

A general consensus has been formed that glenoid bone loss greater than 20% to 25% is the critical amount at which bony augmentation procedures are needed; however, recent clinical results suggest that the critical levels must be reconsidered to lower values.

PURPOSE

This study aimed to find the critical value of anterior glenoid bone loss when a soft tissue repair is not adequate to restore anterior-inferior glenohumeral translation, rotational range of motion, or humeral head position using a biomechanical anterior shoulder instability model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight cadaveric shoulders were tested with a customized shoulder testing system. Range of motion, translation, and humeral head position were measured at 60° of glenohumeral abduction in the scapular plane under a total of 40-N rotator cuff muscle loading in the following 11 conditions: intact; soft tissue Bankart lesion and repair; Bankart lesion with 10%, 15%, 20%, and 25% glenoid bone defects based on the largest anteroposterior width of the glenoid; and soft tissue Bankart repair for each respective glenoid defect. Serial osteotomies for each percentage of bone loss were made parallel to the long axis of the glenoid.

RESULTS

There was significantly decreased external rotation (121.2° ± 2.8° to 113.5° ± 3.3°; P = .004), increased anteroinferior translation with an externally applied load (3.0 ± 1.2 mm to 7.5 ± 1.1 mm at 20 N; P = .008), and increased posterior (0.2 ± 0.6 mm to 2.7 ± 0.8 mm; P = .049) and inferior shift (2.9 ± 0.7 mm to 6.6 ± 1.1 mm; P = .018) of the humeral head apex in the position of maximum external rotation after soft tissue Bankart repair of a 15% glenoid defect compared with the repair of a Bankart lesion without a glenoid defect, respectively.

CONCLUSION

Glenoid defects of 15% or more of the largest anteroposterior glenoid width should be considered the critical bone loss amount at which soft tissue repair cannot restore glenohumeral translation, restricts rotational range of motion, and leads to abnormal humeral head position.

CLINICAL RELEVANCE

The critical level of anterior glenoid bone loss at which bony restorations should be considered is closer to 15% of the largest anteroposterior width of glenoid for defects perpendicular to the superoinferior glenoid axis, which is lower than the commonly accepted threshold of 20% to 25%.