Monocortical fixation of the coracoid in the Latarjet procedure is significantly weaker than bicortical fixation.

PURPOSE: A crucial step of the Latarjet procedure is the fixation of the coracoid process onto the glenoid. Multiple problems associated with the fixation have been described, including lesions of the suprascapular nerve due to prominence of the screw or bicortical drilling. The purpose of the present study was to evaluate whether monocortical fixation, without perforating the posterior glenoid cortex, would provide sufficient graft stability. METHODS: Coracoid transfer was performed in 14 scapula models (Sawbones®, Composite Scapula, 4th generation). Two groups were assigned: in one group, fixation was achieved with two screws that did not perforate the posterior cortex of the glenoid neck (monocortical fixation), in the other group, fixation was achieved with perforation of the posterior cortex (bicortical fixation). The ultimate failure load and mode of failure were evaluated biomechanically. RESULTS: Monocortical fixation was a significantly weaker construct than bicortical fixation (median failure load 221 N, interquartile range 211-297 vs. median failure load 423 N, interquartile range 273-497; p = 0.017). Failure was either due to a pullout of the screws from the socket or a fracture of the glenoid. There was no significant difference in the mode of failure between the two groups (n.s.). CONCLUSION: Monocortical fixation was significantly weaker than bicortical fixation. However, bicortical drilling and overly long screws may jeopardize the suprascapular nerve. Thus, anatomic knowledge about the safe zone at the posterior rim of the glenoid is crucial. Until further research has evaluated, if the inferior stability is clinically relevant, clinicians should be cautious to use a monocortical fixation technique for the coracoid graft.

The effect of rotator cuff malreduction on tendon tension: an evaluation of a custom-made digital tensiometer clamp.

INTRODUCTION: Rotator cuff tears are common and good-to-excellent clinical outcome is reported after subsequent repair. However, the retear rate of rotator cuff repairs has been shown to be as high as 20%. The reasons for retear seem to be multifactorial, mainly comprised by mechanical and biological aspects. Regarding mechanical causes, the role of the tendon tension and malreduction is so far unknown. First, we hypothesized that the tendon tension depends on the technique of tendon reposition and that malreduction of the tendon results in an increased tendon tension. Second, we aimed to demonstrate the inter- and intraobserver reliability of a novel custom-made digital tensiometer clamp. MATERIALS AND METHODS: A tendon defect of posterosuperior rotator cuff (reverse L-shaped) was simulated in seven cadaveric human shoulder specimens. By use of a custom-made tensiometer clamp, the supraspinatus tendon was reduced by pulling it in (1) an anterolateral direction (anatomical reduction) and (2) in a straight lateral direction (malreduction) until the footprint was completely covered. The reduction procedure was consecutively repeated to evaluate the inter- and intraobserver reliability. RESULTS: The mean traction forces for anatomical reduction and malreduction were 16.02 N (SD 8.06) and 19.52 N (SD 9.95), respectively. The difference between the two groups was statistically significant (p = 0.028). The interobserver reliability showed a correlation of r = 0.757 [95% confidence interval (CI) 0.092-0.955]. The intraobserver reliability of the three surgeons was observed to be between r = 0.905 and 0.986. CONCLUSIONS: The malreduction of the rotator cuff has a significant influence on the tendon tension and may therefore affect the healing rate of the tendon after the repair, so that a tension-balanced repair could improve the clinical results. Furthermore, the application of a novel custom-made tensiometer clamp showed good interobserver and excellent intraobserver reliabilities.

Design considerations for patient-specific surgical templates for total hip arthroplasty with respect to acetabular cartilage.

Patient-specific instruments (PSIs) are clinically used to support the surgeon during a planned intervention. The planning is typically done based on volumetric image data from medical imaging systems, e.g. computed tomography (CT). The PSI uses the known surface structure of a bone for orientation during the intervention. Some surfaces of human bone are covered with a layer of cartilage which is hardly visible in clinically applied CT-imaging. This experimental study investigates ten different PSI designs and their effect to the overall accuracy when neglecting the cartilage in the design process. Therefore, a model of an acetabulum is used to simulate the use case of PSI in total hip arthroplasty. The concept of the different designs is to create structural elasticities in the PSI to avoid shifting of the whole instrument and rather have a small part of it deformed by cartilage. A needle array structure, for instance, should also be able to oust or penetrate remaining soft tissue in the acetabulum.

Anterior stability of the reverse shoulder arthroplasty depending on implant configuration and rotator cuff condition.

INTRODUCTION: The aim of this study was to investigate the stabilizing influence of the rotator cuff as well as the importance of glenosphere and onlay configuration on the anterior stability of the reverse total shoulder replacement (RTSR). MATERIALS AND METHODS: A reverse total shoulder replacement was implanted into eight human cadaveric shoulders, and biomechanical testing was performed under three conditions: after implantation of the RTSR, after additional dissection of the subscapularis tendon, and after additional dissection of the infraspinatus and teres minor tendon. Testing was performed in 30° of abduction and three rotational positions: 30° internal rotation, neutral rotation, and 30° external rotation. Furthermore, the 38-mm and 42-mm glenospheres were tested in combination with a standard and a high-mobility humeral onlay. A gradually increased force was applied to the glenohumeral joint in anterior direction until the RTSR dislocated. RESULTS: The 42-mm glenosphere showed superior stability compared with the 38-mm glenosphere. The standard humeral onlay required significantly higher anterior dislocation forces than the more shallow high-mobility onlay. External rotation was the most stable position. Furthermore, isolated detachment of the subscapularis and combined dissection of the infraspinatus, teres minor, and subscapularis tendon increased anterior instability. CONCLUSIONS: This study showed superior stability with the 42-mm glenosphere and the more conforming standard onlay. External rotation was the most stable position. Detachment of the subscapularis as well as dissection of the complete rotator cuff decreased anterior stability.

The lasso-loop, lasso-mattress and simple-cinch stitch for arthroscopic rotator cuff repair: are there biomechanical differences?

PURPOSE: Various stitching techniques have been described to facilitate arthroscopic repair of rotator cuff tears. The aim of the present study was to compare the biomechanical properties of the lasso-loop, lasso-mattress and simple-cinch stitch for rotator cuff repair. METHODS: Twelve infraspinatus tendons were harvested from sheep and split in half. The tendons were randomized into three different stitch configuration groups for biomechanical testing: lasso-loop, lasso-mattress and simple-cinch stitch. Each specimen was first cyclically loaded on a universal materials testing machine under force control from 5 to 30 N at 0.25 Hz for twenty cycles. Then, each specimen was loaded to failure under displacement control at a rate of 1 mm/s. Cyclic elongation, peak-to-peak displacement and ultimate tensile load were reported as mean ± standard error and compared using one way analysis of variance. The type of failure was recorded. RESULTS: No differences in cyclic elongation (1.31 ± 0.09 mm for the simple-cinch vs. 1.49 ± 0.07 mm for the lasso-mattress vs. 1.61 ± 0.09 mm for the lasso-loop stitch, p = 0.063) or peak-to-peak displacement (0.58 ± 0.04 mm for the simple-cinch, 0.50 ± 0.03 mm for the lasso-mattress and 0.62 ± 0.06 mm for the lasso-loop stitch, p = 0.141) were seen between all tested stitch configurations. In the load-to-failure test, the simple cinch stitch (149.38 ± 11.89 N) and the lasso-mattress (149.38 ± 10.33 N) stitch demonstrated significantly higher ultimate load than the lasso-loop stitch (65.88 ± 4.75 N, p < 0.001). All stitch configurations failed with suture pull out. CONCLUSIONS: The lasso-mattress and the simple-cinch stitch showed similar biomechanical properties with significant higher tensile loads needed for failure than the lasso-loop stitch.

Biomechanical evaluation of the simple cinch stitch for arthroscopic rotator cuff repair.

BACKGROUND: The tissue-suture interface is described as the most vulnerable and susceptible area in the muscle-tendon-bone construction of arthroscopic rotator cuff repair. Various stitching techniques have been described to enhance the strength, fixation and stability of the repair, but technical and biomechanical challenges remain. Purpose was to examine the biomechanical properties of the simple cinch stitch in comparison to other stitches commonly used for rotator cuff repair. METHODS: Infraspinatus tendons were harvested from sheep and split in half. The tendons were randomized into five different stitch configuration groups for biomechanical testing: simple stitch; horizontal stitch; FiberChain®; simple cinch stitch; and modified Mason-Allen stitch. Each specimen was first cyclically loaded on a universal materials testing machine under force control from 5 to 30N at 0.25Hz for twenty cycles. Then, each specimen was loaded to failure under displacement control at a rate of 1mm/s. Cyclic elongation, peak-to-peak displacement and ultimate tensile load were measured. The type of failure was recorded. FINDINGS: No differences in cyclic elongation or peak-to-peak displacement were seen between stitch configurations. In the load-to-failure test, the simple cinch stitch demonstrated significantly higher ultimate load than the simple and the horizontal stitch configurations. The comparison to the FiberChain® Suture revealed no statistical significant differences. The FiberChain® Suture demonstrated significantly higher ultimate load than the simple stitch. No statistical significance could be demonstrated in comparison to the horizontal stitch or the simple cinch stitch. The ultimate tensile load of the modified Mason-Allen stitch was significantly higher than that of the other stitch configurations. INTERPRETATION: The simple cinch stitch has an ultimate tensile load comparable to the FiberChain® suture and is superior to the simple stitch and the horizontal stitch. The major advantage of the simple cinch technique is that it is possible to perform the stitch entirely arthroscopically, without the need to perforate the tissue a second time or to use special suture materials. STUDY DESIGN: Controlled laboratory study.

Influence of defect size and localization on the engagement of reverse Hill-Sachs lesions.

BACKGROUND: Reverse Hill-Sachs (RHS) lesions can cause recurrent posterior shoulder instability because of engagement with the posterior glenoid rim; however, the effect of defect size and localization have yet to be determined. HYPOTHESIS: Both size and localization are critical for the engagement of an RHS defect with the posterior glenoid rim. STUDY DESIGN: Controlled laboratory study. METHODS: Ten RHS defects with predefined extent and localization were created through an anterolateral rotator cuff sparing approach in 10 fresh-frozen cadaveric shoulder specimens using a custom-made saw guide. Computed tomography scans of all specimens were completed, and standardized measurements were performed to determine the size (alpha angle) and localization (beta angle) of the defect as well as a combination of both parameters (gamma angle). Internal rotation motions were imposed on the shoulder joint in different arm positions and with varying amount of posterior translation by means of a robot-assisted shoulder simulator. The association between engagement of the defects and the defined parameters (alpha, beta, and gamma angles) was analyzed. RESULTS: In 0° of abduction, a cutoff value between engaging and nonengaging defects of 37.5° for the alpha angle (100% sensitivity; 75% specificity; area under the curve [AUC], 0.875; P = .055) and 36.5° for the beta angle (100% sensitivity; 25% specificity; AUC, 0.708; P = .286) was determined. The gamma angle showed the highest discriminatory power (AUC, 0.938; P = .025) with a cutoff value of 85.5° rendering 100% sensitivity and 75% specificity in the prediction of engagement. An increase in the applied posterior translation force decreased the degrees of internal rotation necessary before engagement occurred. No engagement occurred during internal rotation with the arm in 60° of abduction or 60° of flexion. CONCLUSION: The size and localization of RHS defects are both critical factors for engagement. The combination of both parameters in terms of the gamma angle measurement might be a helpful tool to identify defects prone to engagement. CLINICAL RELEVANCE: Not only the size but also the localization is decisive for engagement of RHS defects. The standardized measurement of the gamma angle combines both factors and might be a helpful tool to identify defects prone to engagement warranting surgical treatment.