Biomechanical analysis of the effect of congruence, depth and radius on the stability ratio of a simplistic 'ball-and-socket' joint model

Anatomy and mobility in the adult cadaveric craniocervical junction

Genetic diseases with craniofacial malformations can be associated with anomalies of the craniocervical joint (CCJ). The functions of the CCJ are thus impaired, as mobility may be either limited by abnormal bone fusion causing headaches, or exaggerated in the case of hypermobility, which may cause irreparable damage to the spinal cord. Restoring the balance between mobility and stability requires surgical correction in children. The anatomy and biomechanics of the CCJ are quite unique, yet have been overlooked in the past decades. Pediatric evidence is so scarce, that investigating the adult CCJ is our best shot to disentangle the form-function relationships of this anatomical region. The motivation of the present study was to understand the morphological and functional basis of motion in the CCJ, in the hope to find morphological features accessible from medical imaging able to predict mobility. To do so, we have quantified the in-vitro kinematics of the CCJ in nine cadaveric asymptomatic adults, and estimated a wide range of mobility variables covering the complexity of spinal motion. We compared these variables with the shape of the occipital, the atlas and the axis, obtained using a dense geometric morphometric approach. Morphological joint congruence was also quantified. Our results suggest a strong relationship between bone shape and motion, with the overall geometry predicting best the primary movements, and the joint facets predicting best the secondary movements. We propose a functional hypothesis stating that the musculoligamental system determines movements of great amplitude, while the shape and congruence of joint facets determine the secondary and coupled movements, especially by varying the geometry of bone stops and the way ligaments are tensioned. We believe this work will provide valuable insights in understanding the biomechanics of the CCJ. Furthermore, it should help surgeons treating CCJ anomalies by enabling them to translate objectives of functional and clinical outcome into clear objectives of morphological outcome.

Correlation of Glenoid Concavity With Surgical Failure After Arthroscopic Stabilization for Recurrent Anterior Shoulder Instability

BACKGROUND

Glenoid concavity compression by rotator cuff muscle contraction is one of the key mechanisms in the stability of the glenohumeral joint.

PURPOSE/HYPOTHESIS

The purpose of this study was to evaluate the effects of glenoid concavity, as represented by the bony shoulder stability ratio (BSSR) and other factors, including glenoid bone defect size, on the surgical failure of arthroscopic stabilization procedures for recurrent anterior shoulder instability. The authors also aimed to determine the critical value of BSSR. It was hypothesized that both glenoid concavity and glenoid bone defect size would be correlated with surgical failure, with glenoid concavity having a stronger correlation.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

A total of 120 patients who underwent arthroscopic stabilization procedures for recurrent anterior shoulder instability were included. Patients with bony Bankart lesions were excluded to eliminate the postoperative effects of bony fragment restoration on the glenoid concavity. For each patient, variable factors including BSSR, glenoid bone defect size, presence of off-track Hill-Sachs lesions, and age at first dislocation were recorded. Chi-square analysis and Student t test were performed to analyze the effect of each variable on surgical failure. Multivariate logistic regression analysis was used to determine the combined effect of >2 variables on surgical failure. The critical value of BSSR was analyzed using a receiver operating characteristic curve.

RESULTS

Nine patients (7.5%) had recurrent instability requiring revision surgery. BSSR (patients with recurrence, 18.6% ± 19.4%; patients without recurrence, 41.8% ± 10.5%; P = .01), glenoid bone defect size (17.5% ± 3.6% vs 11.7% ± 7.0%; P = .02), age at the time of first dislocation (18.8 ± 3.9 years vs 22.0 ± 6.5 years; P = .04), and number of suture anchors used (4.1 ± 0.3 vs 5.8 ± 1.6; P < .001) showed significant differences between patients with and without surgical failure. Multivariate logistic regression analysis revealed surgical failure to be correlated with BSSR (odds ratio, 0.849; P = .02) and the number of suture anchors used (odds ratio, 0.070; P = .03). The critical value of BSSR was 29.3% (area under the curve, 0.84; 95% CI, 0.67-1.00; P < .001; sensitivity, 78%; specificity, 93%).

CONCLUSION

Glenoid concavity is strongly correlated with surgical failure after arthroscopic stabilization procedures for anterior shoulder instability. The value of BSSR reflects shoulder instability caused by glenoid bone morphology more accurately than glenoid bone defect size.

Native Glenoid Depth and Hill-Sachs Lesion Morphology in Traumatic Anterior Shoulder Instability

BACKGROUND

Although Hill-Sachs lesions (HSLs) are assumed to be influenced by glenoid characteristics in the context of bipolar bone loss, little is known about how glenoid concavity influences HSL morphology.

PURPOSE

To investigate the relationship between the native glenoid depth and HSL morphological characteristics.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Computed tomography images of bilateral shoulders from 151 consecutive patients with traumatic unilateral anterior shoulder instability were retrospectively reviewed. Patients were categorized into flat (<1 mm), moderate (1-2 mm), and deep (>2 mm) groups based on the native glenoid depth measured from the contralateral unaffected shoulder. The HSL morphological characteristics included size (depth, width, length, and volume), location (medial, superior, and inferior extent), and orientation (rim and center angle). The glenoid characteristics included diameter, depth, version, and bone loss. The patient, glenoid, and HSL morphological characteristics were compared among the 3 depth groups. Subsequently, the independent predictors of some critical HSL morphological characteristics were determined using multivariate stepwise regression.

RESULTS

After exclusion of 55 patients, a total of 96 patients were enrolled and classified into the flat group (n = 31), moderate group (n = 35), and deep group (n = 30). Compared with those in the flat group, patients in the deep group were more likely to have dislocation (38.7% vs 93.3%; P = .009) at the primary instability and had a significantly larger number of dislocations (1.1 ± 1.0 vs 2.2 ± 1.8; P = .010); moreover, patients in the deep group had significantly deeper, wider, larger volume, more medialized HSLs and higher incidences of off-track HSLs (all P≤ .025). No significant differences were detected among the 3 groups in HSL length, vertical position, and orientation (all P≥ .064). After adjustment for various radiological and patient factors in the multivariate regression model, native glenoid depth remained the strongest independent predictor for HSL depth (β = 0.346; P < .001), width (β = 0.262; P = .009), volume (β = 0.331; P = .001), and medialization (β = -0.297; P = .003).

CONCLUSION

The current study sheds light on the association between native glenoid depth and the morphology of HSLs in traumatic anterior shoulder instability. Native glenoid depth was independently and positively associated with HSL depth, width, volume, and medialization. Patients with deeper native glenoids were more likely to have off-track HSLs and thus require more attention in the process of diagnosis and treatment.

Effect of Glenohumeral Joint Bone Morphology on Anterior Shoulder Instability: A Case-Control Study

PURPOSE

Glenohumeral joint compatibility and bone morphology are among the most critical factors in shoulder stabilization. Our study investigated the effect of the bone morphological structure of the shoulder joint on anterior shoulder dislocation.

METHODS

In our study, people with a history of shoulder dislocation were selected as the patient group. In the control group, patients with shoulder MRIs for any reason and no history of shoulder dislocation were included. Those who have a fracture around the shoulder, a congenital deformity in the shoulder region, arthrosis of the shoulder, those whose MRI images cannot be measured, those with Hill-Sachs lesion, connective tissue diseases (such as Ehler Danlos), who are unsure of their diagnosis, or who have incomplete and incorrect suspicious information in their patient file have been excluded. In our retrospective case-control study, glenoid width, glenoid height, glenoid's height-to-width ratio, glenoid's depth, glenoid's version, glenoid's inclination, humerus radius of curvature, glenoid radius of curvature, and bony shoulder stability ratio were measured on MRI images of the patients. The sample size for each group was determined using a power analysis method. The intra-class coefficient (ICC) assessed interobserver and intraobserver reliability.

RESULTS

A total of 80 patients, 40 each in the control and patient groups, were included in the study. Glenoid width was measured as 24.27 ± 1.58 in the patient group, 25.61 ± 1.72 in the control group; glenoid height was as measured 36.49 ± 2.26 in the patient group, 36.74 ± 1.99 in the control group; height-to-width ratio was measured as 1.5 ± 0.08 in the patient group, 1.43 ± 0.05 in the control group; glenoid version was as measured -0.53 ± 1.17 in the patient group, -1.44 ± 1.1 in the control group; glenoid inclination was measured as 1.44 ± 3.93 patient group, 2.64 ± 3.81 in the control group; glenoid depth was measured as 1.69 ± 0.41 in the patient group, 2.12 ± 0.53 in the control group; humerus radius of curvature was measured as 29.70 ± 6.76 in the patient group, 24.98 ± 3.22 in the control group; glenoid axial radius of curvature was measured as 61.8 ± 13.52 in the patient group, 52.53 ± 15.69 in the control group; glenoid coronal radius of curvature was measured as 43.01 ± 7.47 in the patient group, 37.74 ± 6.89 in the control group; the bony shoulder stability ratio was measured as 0.35 ± 0.06 in the patient group and 0.44 ± 0.06 in the control group. In the statistical evaluation, the glenoid width (p < 0.001), the glenoid height/width ratio (p < 0.001), the glenoid version (p < 0.001), the depth of the glenoid cavity (p < 0.001), and the radius of curvature measurements of the humeral head (p < 0.001) and the glenoid (axial, p < 0.007; coronal, p < 0.001) were found to be significantly different. Glenoid height and inclination were similar in both groups.

CONCLUSIONS

The detection of bone morphological features that constitute risk factors for shoulder dislocations plays an important role in preventing shoulder dislocations. In this way, it provides essential data on personalized rehabilitation programs and treatment selection for recurrent dislocations.

The Influence of Glenoid Bone Loss and Graft Positioning on Graft and Cartilage Contact Pressures After the Latarjet Procedure

BACKGROUND

Glenohumeral joint contact loading before and after glenoid bone grafting for recurrent anterior instability remains poorly understood.

PURPOSE

To develop a computational model to evaluate the influence of glenoid bone loss and graft positioning on graft and cartilage contact pressures after the Latarjet procedure.

STUDY DESIGN

Controlled laboratory study.

METHODS

A finite element model of the shoulder was developed using kinematics, muscle and glenohumeral joint loading of 6 male participants. Muscle and joint forces at 90° of abduction and external rotation were calculated and employed in simulations of the native shoulder, as well as the shoulder with a Bankart lesion, 10% and 25% glenoid bone loss, and after the Latarjet procedure.

RESULTS

A Bankart lesion as well as glenoid bone loss of 10% and 25% significantly increased glenoid and humeral cartilage contact pressures compared with the native shoulder (P < .05). The Latarjet procedure did not significantly increase glenoid cartilage contact pressure. With 25% glenoid bone loss, the Latarjet procedure with a graft flush with the glenoid and the humerus positioned at the glenoid half-width resulted in significantly increased humeral cartilage contact pressure compared with that preoperatively (P = .023). Under the same condition, medializing the graft by 1 mm resulted in humeral cartilage contact pressure comparable with that preoperatively (P = .097). Graft lateralization by 1 mm resulted in significantly increased humeral cartilage contact pressure in both glenoid bone loss conditions (P < .05).

CONCLUSION

This modeling study showed that labral damage and greater glenoid bone loss significantly increased glenoid and humeral cartilage contact pressures in the shoulder. The Latarjet procedure may mitigate this to an extent, although glenoid and humeral contact loading was sensitive to graft placement.

CLINICAL RELEVANCE

The Latarjet procedure with a correctly positioned graft should not lead to increased glenohumeral joint contact loading. The present study suggests that lateral graft overhang should be avoided, and in the situation of large glenoid bone defects, slight medialization (ie, 1 mm) of the graft may help to mitigate glenohumeral joint contact overloading.

Patients with recurrent anterior shoulder instability exhibit altered glenohumeral and scapulothoracic joint kinematics during upper limb movement: A prospective comparative study

BACKGROUND

Altered shoulder kinematics in patients with recurrent anterior shoulder instability remains poorly understood. This prospective study aimed to quantify in vivo glenohumeral and scapulothoracic joint kinematics and joint-contact positions in patients with shoulder instability and healthy controls.

METHODS

Twenty patients with recurrent anterior shoulder instability (mean 28 years) and five patients without shoulder pathology (mean 39 years) were scanned using open CT in six static upper limb positions including 90° of abduction, combined abduction and external rotation, 90° of flexion, lift-off position (i.e. reaching behind the back) and the neutral shoulder with external rotation. Image datasets were digitally reconstructed to quantify shoulder joint kinematics and glenohumeral translation.

FINDINGS

At 90° of abduction, instability patients demonstrated significantly less glenohumeral abduction and a reciprocal increase in upward scapulothoracic rotation compared to controls (mean difference: 13.3°, p = 0.038). With the shoulder in combined abduction and external rotation, instability patients showed a significant increase in glenohumeral rotation and a reciprocal decrease in scapulothoracic rotation compared to controls (mean difference: 5.0°, p = 0.042). There were no significant differences in humeral head translation in the sagittal plane (anterior-posterior axis) for all motions tested (p > 0.05).

INTERPRETATION

Scapulothoracic and glenohumeral kinematics are significantly different between patients with recurrent anterior shoulder instability and those with a healthy shoulder. Instability patients compensate for reduced glenohumeral function during abduction by increasing scapular rotation. With the shoulder in combined abduction and external rotation position, greater glenohumeral joint angles without significantly increased humeral head translation suggest altered neuromuscular control in the unstable shoulder.

Biomechanical Analysis of Posterior Open-Wedge Osteotomy and Glenoid Concavity Reconstruction Using an Implant-Free, J-Shaped Iliac Crest Bone Graft

BACKGROUND

Posterior open-wedge osteotomy and glenoid reconstruction using a J-shaped iliac crest bone graft showed promising clinical results for the treatment of posterior instability with excessive glenoid retroversion and posteroinferior glenoid deficiency.

PURPOSE

To evaluate the biomechanical performance of the posterior J-shaped graft to restore glenoid retroversion and posteroinferior deficiency in a cadaveric shoulder instability model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A posterior glenoid open-wedge osteotomy was performed in 6 fresh-frozen shoulders, allowing the glenoid retroversion to be set at 0°, 10°, and 20°. At each of these 3 preset angles of glenoid retroversion, the following conditions were simulated: (1) intact joint, (2) posterior Bankart lesion, (3) 20% posteroinferior glenoid deficiency, and (4) posterior J-shaped graft (at 0° of retroversion). With the humerus in the Jerk position (60° of glenohumeral anteflexion, 60° of internal rotation), stability was evaluated by measuring posterior humeral head (HH) translation (in mm) and peak translational force (in N) to translate the HH over 25% of the glenoid width. Glenohumeral contact patterns were measured using pressure-sensitive sensors. Fixation of the posterior J-graft was analyzed by recording graft micromovements during 3000 cycles of 5-mm anteroposterior HH translations.

RESULTS

Reconstructing the glenoid with a posterior J-graft to 0° of retroversion significantly increased stability compared with a posterior Bankart lesion and posteroinferior glenoid deficiency in all 3 preset degrees of retroversion (P < .05). There was no significant difference in joint stability comparing the posterior J-graft with an intact joint at 0° of retroversion. The posterior J-graft restored mean contact area and contact pressure comparable with that of the intact condition with 0° of retroversion (222 vs 223 mm², P = .980; and 0.450 vs 0.550 MPa, P = .203). The mean total graft displacement after 3000 cycles of loading was 43 ± 84 µm, and the mean maximal mediolateral graft bending was 508 ± 488 µm.

CONCLUSION

Biomechanical analysis of the posterior J-graft demonstrated reliable restoration of initial glenohumeral joint stability, normalization of contact patterns comparable with that of an intact shoulder joint with neutral retroversion, and secure initial graft fixation in the cadaveric model.

CLINICAL RELEVANCE

This study confirms that the posterior J-graft can restore stability and glenohumeral loading conditions comparable with those of an intact shoulder.

Open-Full-Jaw: An open-access dataset and pipeline for finite element models of human jaw

BACKGROUND

State-of-the-art finite element studies on human jaws are mostly limited to the geometry of a single patient. In general, developing accurate patient-specific computational models of the human jaw acquired from cone-beam computed tomography (CBCT) scans is labor-intensive and non-trivial, which involves time-consuming human-in-the-loop procedures, such as segmentation, geometry reconstruction, and re-meshing tasks. Therefore, with the current practice, researchers need to spend considerable time and effort to produce finite element models (FEMs) to get to the point where they can use the models to answer clinically-interesting questions. Besides, any manual task involved in the process makes it difficult for the researchers to reproduce identical models generated in the literature. Hence, a quantitative comparison is not attainable due to the lack of surface/volumetric meshes and FEMs.

METHODS

We share an open-access repository composed of 17 patient-specific computational models of human jaws and the utilized pipeline for generating them for reproducibility of our work. The used pipeline minimizes the required time for processing and any potential biases in the model generation process caused by human intervention. It gets the segmented geometries with irregular and dense surface meshes and provides reduced, adaptive, watertight, and conformal surface/volumetric meshes, which can directly be used in finite element (FE) analysis.

RESULTS

We have quantified the variability of our 17 models and assessed the accuracy of the developed models from three different aspects; (1) the maximum deviations from the input meshes using the Hausdorff distance as an error measurement, (2) the quality of the developed volumetric meshes, and (3) the stability of the FE models under two different scenarios of tipping and biting.

CONCLUSIONS

The obtained results indicate that the developed computational models are precise, and they consist of quality meshes suitable for various FE scenarios. We believe the provided dataset of models including a high geometrical variation obtained from 17 different models will pave the way for population studies focusing on the biomechanical behavior of human jaws.

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 Biomechanical Effect of Bone Grafting and Bone Graft Remodeling in Patients With Anterior Shoulder Instability

BACKGROUND

Individual constitutional differences in glenoid shape and bone remodeling require a patient-specific and longitudinal approach to evaluate the biomechanical effects of glenoid bone grafting in patients with anterior shoulder instability.

PURPOSE

To quantify the longitudinal, in vivo, biomechanical effects of bone grafting, bone graft remodeling, and glenoid shape in patients with anterior shoulder instability by means of patient-specific finite element models.

STUDY DESIGN

Descriptive laboratory study.

METHODS

In total, 25 shoulders of 24 patients with anterior shoulder instability and anterior glenoid bone loss underwent an arthroscopic iliac crest bone graft transfer (ICBGT) procedure with either autologous or allogenic bone. Patient-specific finite element simulations based on preoperative, postoperative, and follow-up computed tomography scans were used to quantify the bone-mediated stability ratio (SR) and the distance to dislocation. Additionally, the relationship between glenoid morphological parameters and the SR was assessed.

RESULTS

The ICBGT procedure significantly increased the SR and distance to dislocation in the 2-, 3-, and 4-o'clock directions immediately after the surgical intervention (P < .01) in both the autograft and the allograft groups. Although the SR and distance to dislocation decreased subsequently, autografts showed long-term effects on SR and dislocation distance in the 3-o'clock direction (P < .01) and on SR in the 4-o'clock direction (P < .01). Allografts showed no significant effect on SR and dislocation distance in long-term follow-up (P > .05). Overall, glenoid retroversion as well as cavity depth predicted stability in all 4 dislocation directions, with glenoid cavity depth showing the highest correlation coefficients (R = 0.71, 0.8, 0.73, and 0.7 for 2-, 3-, 4-, and 5-o'clock, respectively).

CONCLUSION

The autologous ICBGT procedure biomechanically improved anterior shoulder stability in long-term follow-up, whereas the use of allografts did not show any bone-mediated biomechanical effect at follow-up due to resorption. Furthermore, in addition to measurements of defect extent, the glenoid depth and version seem to be useful parameters to determine the biomechanical effect and need for glenoid bone grafting in patients with shoulder instability.

CLINICAL RELEVANCE

This study proposes the use of autologous bone grafts for a successful long-term stabilization effect. Additionally, this study proposes additional glenoid morphological measures to predict shoulder stability.

Long-term Results of the Open Latarjet Procedure for Recurrent Anterior Shoulder Instability in Patients Older Than 40 Years

BACKGROUND

Subgroup analyses of the Latarjet procedure have suggested that age over 40 years is a risk factor for dislocation arthropathy.

PURPOSE

To analyze long-term results of the open Latarjet procedure for recurrent anterior shoulder dislocation in patients at least 40 years of age.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A total of 39 consecutive patients (40 shoulders) with a mean age of 48 years (range, 40-66 years) at surgery were evaluated at a mean follow-up of 11.0 years (range, 8-16 years). Of these, 15 patients (38%) had undergone previous soft tissue stabilization surgery. Long-term results were assessed clinically and radiographically, including computed tomography scanning at final follow-up.

RESULTS

No recurrence of dislocation was noted. Subluxation had occurred in 3 patients (8%), and apprehension persisted in 5 patients (13%). The total Walch-Duplay score averaged 89 points at the final follow-up, and the mean Subjective Shoulder Value (60%-91%) had improved significantly (P < .001). In total, 36 patients rated their result as excellent, 3 as good. Further, 6 patients (15%) underwent joint-preserving reoperation, and 1 patient (3%) had reverse total shoulder arthroplasty for severe dislocation arthropathy. Dislocation arthropathy was severe in 14 patients (37%) and had progressed by at least 2 grades in 17 patients (45%). Patients with severe dislocation arthropathy had already shown degenerative changes preoperatively as opposed to those who ultimately had no or moderate dislocation arthropathy (n = 24) (P < .001). Progression of dislocation arthropathy was associated with lateral (>1 mm) graft positioning (P < .001) and older age at surgery (r = 0.58; P < .001).

CONCLUSION

The open Latarjet procedure for recurrent anterior shoulder instability in patients older than 40 years reliably restores stability and leads to high patient satisfaction. This procedure is, however, associated with a substantial rate of advanced but clinically mild symptomatic dislocation arthropathy, which is associated with the degree of preoperative joint degeneration, older age at surgery, and lateral graft placement.

Posterior Acromial Morphology Is Significantly Associated with Posterior Shoulder Instability

BACKGROUND

The purpose of this paper was to determine whether acromial morphology influences anteroposterior shoulder stability. We hypothesized that a more horizontal and higher position of the acromion in the sagittal plane would be associated with posterior instability.

METHODS

In this retrospective study, patients with unidirectional posterior instability were age and sex-matched to a cohort of patients with unidirectional anterior instability. Both cohorts were compared with a control group of patients with no instability and no degenerative glenohumeral (rotator cuff and/or joint surface) or acromial changes. Measurements on radiographs included posterior acromial tilt, anterior and posterior acromial coverage (AAC and PAC), posterior acromial height (PAH), and the critical shoulder angle (CSA).

RESULTS

The number of patients enrolled in each instability group was 41, based on a priori power analysis. The control group consisted of 53 shoulders. Of the measured anatomic factors, PAH showed the most significant association with posterior instability (odds ratio [OR] = 1.8; p < 0.001) in the logistic regression model. PAH was significantly greater in the posterior instability group compared with the anterior instability group (30.9 versus 19.5 mm; p < 0.001). With a cutoff value of PAH of 23 mm, the OR for posterior instability was 39. Shoulders with posterior instability were also significantly different from normal shoulders with regard to PAH (p < 0.001), AAC (p < 0.001), and PAC (p < 0.001) whereas, in the shoulders with anterior instability, all of these values except the AAC (p = 0.011) did not differ from those of normal shoulders.

CONCLUSIONS

Specific acromial morphology is significantly associated with the direction of glenohumeral instability. In shoulders with posterior instability, the acromion is situated higher and is oriented more horizontally in the sagittal plane than in normal shoulders and those with anterior instability; this acromial position may provide less osseous restraint against posterior humeral head translation. A steep "Swiss chalet roof-type" acromion virtually excluded recurrent posterior instability in an albeit relatively small cohort of patients. Additional investigation is needed to determine the relevance of these findings for future treatment.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Editorial Commentary: Computed Tomography-based Analysis of the Arthroscopic Latarjet Procedure Suggests Graft Positioning Is More Variable than Expected

The Latarjet operation is one of the most successful techniques for the treatment of recurrent anterior shoulder instability, which has recently been translated into the arthroscopic field. Several studies suggest that its arthroscopic variant is safe and reproducible and report promising short-term and mid-term results. Some authors claim that, in addition to less soft tissue damage, positioning of the coracoid graft is more accurate during arthroscopic control. There is currently no evidence of superiority of the arthroscopic or the open technique. As with the open procedure, the arthroscopic Latarjet operation requires a substantial learning curve; therefore the arthroscopic technique should be reserved for experienced arthroscopists treating a large number of shoulder instabilities.

Arthroscopic Versus Open Iliac Crest Bone Grafting in Recurrent Anterior Shoulder Instability With Glenoid Bone Loss: A Computed Tomography-Based Quantitative Assessment

PURPOSE

To assess the iliac crest bone graft (ICBG) position in the en-face view and axial plane comparing arthroscopic with open procedures.

METHODS

A total of 40 consecutive patients with recurrent anterior shoulder instability and glenoid bone loss over 10% treated by 2 independent orthopaedic departments were included. Two independent observers analyzed preoperative and immediate postoperative computed tomography scans of 20 open (group O) and 20 arthroscopic (group A) procedures. Defect and ICBG characteristics of the J-shaped graft in the en-face view and axial plane were manually assessed by multiplanar reconstructed computed tomography scans. Variances in terms of graft positioning were analyzed.

RESULTS

No significant variances in arthroscopic graft positioning were observed. The graft position in the en-face view was comparable in both groups, with the superior extent of the arthroscopic graft (40° ± 9° [inferior extent, 139° ± 16°]) lying significantly higher than the superior extent in group O (50° ± 13°, P = .005 [inferior extent, 147° ± 21°; P = .178]). The covered glenoid defect size was above 95% (98% ± 1% in group O vs 95% ± 2% in group A, P = .001). The arthroscopic graft in the axial plane showed a significantly steeper impaction angle (34.8° ± 7.8° vs 26.9° ± 9.9°, P = .010), with a significantly increased medial offset compared with group O (6.6 ± 1.7 mm vs 5.4 ± 1.3 mm, P = .024). The mediolateral step formation, however, was not significantly different (2.9 ± 1.1 mm in group A vs 3.2 ± 0.8 mm in group O, P = .289). The interobserver reliability was very good for all measurements (R = 0.969; 95% confidence interval, 0.965-0.972).

CONCLUSIONS

Positioning of the arthroscopic ICBG in the en-face view and axial plane is comparable to that of the open technique. Good glenoid defect coverage and glenoid concavity reconstruction can be achieved with the arthroscopic technique. The main difference compared with the open procedure is the significantly steeper impaction angle.

LEVEL OF EVIDENCE

Level III, case-control study.