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

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.

The Effect of Varying Sizes of Ramp Lesions in the ACL-Deficient and Reconstructed Knee: A Biomechanical Robotic Investigation

BACKGROUND

Conflicting evidence has been reported regarding the biomechanical relevance of ramp lesions (RLs) on knee kinematics. Furthermore, the influence of the defect size of the RLs on anterior tibial translation (ATT) and external rotation (ER) is currently unknown.

PURPOSE

To evaluate the influence of RL defect size on knee kinematics in anterior cruciate ligament (ACL) deficiency and after simulated ACL reconstruction (sACLR).

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight cadaveric knee specimens were tested in a 6 degrees of freedom robotic test setup. Force-controlled clinical laxity tests were performed with 200 N of axial compression in 0°, 30°, 60°, and 90° of flexion: 5 N·m internal rotation (IR)/ER torque, 134 N ATT force, and an anteromedial drawer test consisting of 134 N ATT force under 5 N·m ER torque. After determining the native knee kinematics, the ACL was cut at the tibial insertion, followed by a transosseous refixation to simulate a surgical repair or reconstruction (simulated ACL reconstruction; sACLR). An RL was sequentially created with a length of 1, 2, and 3 cm. Each state of the RL was evaluated in the ACL-deficient state and after sACLR.

RESULTS

In the ACL-deficient state, only an RL of 3 cm length resulted in a significant increase of ATT in 30° of flexion (mean difference 0.73 mm; 95% CI, 0.36-1.1 mm). After sACLR, an RL had no significant effect. When looking at ER, an RL significantly increased ER in full extension in the ACL-deficient state in 2 cm (mean difference 0.9°; 95% CI, 0.08°-1.74°) and 3 cm length (mean difference 1.9°; 95% CI, 0.57-3.25). Furthermore, a 3-cm RL significantly increased IR in 0° of flexion in the ACL-deficient state (mean difference 1.9°; 95% CI, 0.2°-3.6°). No effect of ramp lesions on rotation was found after sACLR.

CONCLUSION

RLs result in a small increase in ATT, ER, and IR in ACL-deficient knees at early flexion angles, but not after sACLR.

CLINICAL RELEVANCE

Small RLs did not change time-zero knee kinematics and may, therefore, be left untreated, especially when the ACL is reconstructed.

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.

The Control of Anteromedial Rotatory Instability Is Improved With Combined Flat sMCL and Anteromedial Reconstruction

BACKGROUND

Both the superficial medial collateral ligament (sMCL) and the deep MCL (dMCL) contribute to the restraint of anteromedial (AM) rotatory instability (AMRI). Previous studies have not investigated how MCL reconstructions control AMRI.

PURPOSE/HYPOTHESIS

The purpose was to establish the optimal medial reconstruction for restoring normal knee kinematics in an sMCL- and dMCL-deficient knee. It was hypothesized that AMRI would be better controlled with the addition of an anatomically shaped (flat) sMCL reconstruction and with the addition of an AM reconstruction replicating the function of the dMCL.

STUDY DESIGN

Controlled laboratory study.

METHODS

A 6 degrees of freedom robotic system equipped with a force-torque sensor was used to test 8 unpaired knees in the intact, sMCL/dMCL sectioned, and reconstructed states. Four different reconstructions were assessed. The sMCL was reconstructed with either a single-bundle (SB) or a flattened hamstring graft aimed at better replicating the appearance of the native ligament. These reconstructions were tested with and without an additional AM reconstruction. Simulated laxity tests were performed at 0°, 30°, 60°, and 90° of flexion: 10 N·m valgus rotation, 5 N·m internal and external rotation (ER), and an AM drawer test (combined 134-N anterior tibial drawer in 5 N·m ER). The primary outcome measures of this force-controlled setup were anterior tibial translation (ATT; in mm) and axial tibial rotation (in degrees).

RESULTS

Sectioning the sMCL/dMCL increased valgus rotation, ER, and ATT with the simulated AM draw test at all flexion angles. SB sMCL reconstruction was unable to restore ATT, valgus rotation, and ER at 30°, 60°, and 90° of flexion to the intact state (P < .05). Flat MCL reconstruction restored valgus rotation at all flexion angles to the intact state (P > .05). ER was restored at all angles except at 90°, but ATT laxity in response to the AM drawer persisted. Addition of an AM reconstruction improved control of ATT relative to the intact state at all flexion angles (P > .05). Combined flat MCL and AM reconstruction restored knee kinematics closest to the intact state.

CONCLUSION

In a cadaveric model, AMRI resulting from an injured sMCL and dMCL complex could not be restored by an isolated SB sMCL reconstruction. A flat MCL reconstruction or an additional AM procedure, however, better restored medial knee stability.

CLINICAL RELEVANCE

In patients evaluated with a combined valgus and AM rotatory instability, a flat sMCL and an additional AM reconstruction may be superior to an isolated SB sMCL reconstruction.

Cartilage decisively shapes the glenoid concavity and contributes significantly to shoulder stability

PURPOSE

Glenohumeral joint injuries frequently result in shoulder instability. However, the biomechanical effect of cartilage loss on shoulder stability remains unknown. The aim of the current study was to investigate biomechanically the effect of two severity stages of cartilage loss in different dislocation directions on shoulder stability.

METHODS

Joint dislocation was provoked in 11 human cadaveric glenoids for 7 different directions between 3 o'clock (anterior) and 9 o'clock (posterior). Shoulder stability ratio (SSR) and concavity gradient were assessed in three states: intact, 3 mm and 6 mm simulated cartilage loss. The influence of cartilage loss on SSR and concavity gradient was statistically evaluated.

RESULTS

Both SSR and concavity gradient decreased significantly between intact state and 6 mm cartilage loss in every dislocation direction (p ≤ 0.038), except concavity gradient in 4 o'clock direction. Thereby, anterior-inferior dislocation directions were associated with the highest decrease in both SSR and concavity gradient of up to 59.0% and 49.4%, respectively, being significantly bigger for SSR compared with all other dislocation directions (p ≤ 0.040). Correlations between concavity gradient and SSR for pooled dislocation directions were significant in each separate specimen's state (p < 0.001).

CONCLUSION

From a biomechanical perspective, articular cartilage of the glenoid contributes significantly to the concavity gradient, correlating strongly with the associated loss in glenohumeral joint stability. The biggest effect of cartilage loss is observed in the most frequently occurring anterior-inferior dislocation directions, suggesting that surgical interventions to restore cartilage's surface and concavity should be considered for recurrent shoulder dislocations in presence of cartilage loss.