Biomechanical similarities among subscapularis repairs after shoulder arthroplasty.

HYPOTHESIS: Many authors suggest that subscapularis deficiency after shoulder arthroplasty has a negative effect on long-term outcomes. Thus, increasing emphasis has been placed on the technique for repair of the tendon. This study evaluated the biomechanical strength of 3 different repairs: osteotomy, tendon to bone, and a combined method. MATERIALS AND METHODS: Twenty-four paired shoulders from deceased donors were prepared for shoulder arthroplasty. The subscapularis tendon was removed/repaired with the lesser tuberosity in the osteotomy group, was removed periosteally in the bone-to-tendon group, and was tenotomized in the combined group. The tendon-to-bone repair used bone tunnels, and the combined construct added tendon-to-tendon fixation. A materials testing system machine was used for cycling. A digital motion analysis system with spatial markers was used for analysis. RESULTS: There were no significant differences (P > .05) in age, bone mineral density, or construct thickness. No statistically significant differences (P > .05) in elongation amplitude (P = .67) or cyclic elongation (P = .58) were detected within the constructs or between repair techniques. Failure testing revealed no differences in maximum load, stiffness, or mode of failure. DISCUSSION: There remains no consensus about the optimal method of repairing the subscapularis tendon during shoulder arthroplasty. Furthermore, the results of the current study do not support one technique over another with regard to initial fixation properties. All constructs investigated exhibited comparably robust biomechanical performance. Durability may, therefore, be more a result of healing potential than the specific construct chosen.

A biomechanical analysis of shoulder stabilization: posteroinferior glenohumeral capsular plication.

BACKGROUND: The use of posterior capsular plication to decrease capsular volume and address capsular laxity for treatment of posterior instability, multidirectional instability, or as an additional technique in the treatment of anterior instability is common. Multiple different suturing techniques have been described. HYPOTHESIS: The simple stitch will have inferior biomechanical properties compared with either the horizontal mattress or figure-of-8 stitches for suture plication of the posteroinferior quadrant of the glenoid. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty-one fresh-frozen shoulders with a mean age of 57.7 +/- 12.3 years were randomized into capsulolabral plication of the posteroinferior quadrant using either simple stitch configuration, horizontal mattress configuration, or figure-of-8 configuration. Each shoulder was mounted onto a materials testing machine, preloaded to 5 N for 2 minutes, cycled from 5 to 25 N for 100 cycles (1 Hz), and then loaded to failure at 15 mm/min. Capsular displacement from the glenoid was determined using digital video analysis. Data recorded included mode of failure, ultimate load to failure, load at 2 mm of displacement, as well as displacement during cyclical loading (during the entire 100 cycles and during the final cycle only). RESULTS: There was a statistically significant difference (P < .0001) in mechanism of failure among the 3 groups with the simple stitch group failing more often in the capsular tissue than in the mattress and figure-of-8 sutures, which more commonly failed at the capsulolabral junction. There was no statistically significant difference (P > .05) among the 3 groups in gapping (displacement) after cyclical loading, load at 2 mm of displacement, or in ultimate load to failure. Conclusion/ CLINICAL RELEVANCE: Based on these results, all 3 stitches can be used effectively for capsular plication, although the simple stitch may be preferred for the capsular plication because of technical ease and decreased trauma to the capsulolabral tissue.

Medial versus lateral supraspinatus tendon properties: implications for double-row rotator cuff repair.

BACKGROUND: Rotator cuff repair retear rates range from 25% to 90%, necessitating methods to improve repair strength. Although numerous laboratory studies have compared single-row with double-row fixation properties, little is known regarding regional (ie, medial vs lateral) suture retention properties in intact and torn tendons. HYPOTHESIS: A torn supraspinatus tendon will have reduced suture retention properties on the lateral aspect of the tendon compared with the more medial musculotendinous junction. STUDY DESIGN: Controlled laboratory study. METHODS: Human supraspinatus tendons (torn and intact) were randomly assigned for suture retention mechanical testing, ultrastructural collagen fibril analysis, or histologic testing after suture pullout testing. For biomechanical evaluation, sutures were placed either at the musculotendinous junction (medial) or 10 mm from the free margin (lateral), and tendons were elongated to failure. Collagen fibril assessments were performed using transmission electron microscopy. RESULTS: Intact tendons showed no regional differences with respect to suture retention properties. In contrast, among torn tendons, the medial region exhibited significantly higher stiffness and work values relative to the lateral region. For the lateral region, work to 10-mm displacement (1592 ± 261 N-mm) and maximum load (265 ± 44 N) for intact tendons were significantly higher (P < .05) than that of torn tendons (1086 ± 388 N-mm and 177 ± 71 N, respectively). For medial suture placement, maximum load, stiffness, and work of intact and torn tendons were similar (P > .05). Regression analyses for the intact and torn groups revealed generally low correlations between donor age and the 3 biomechanical indices. For both intact and torn tendons, the mean fibril diameter and area density were greater in the medial region relative to the lateral (P ≤ .05). In the lateral tendon, but not the medial region, torn specimens showed a significantly lower fibril area fraction (48.3% ± 3.8%) than intact specimens (56.7% ± 3.6%, P < .05). CONCLUSION: Superior pullout resistance of medially placed sutures may provide a strain shielding effect for the lateral row after double-row repair. Larger diameter collagen fibrils as well as greater fibril area fraction in the medial supraspinatus tendon may provide greater resistance to suture migration. CLINICAL RELEVANCE: While clinical factors such as musculotendinous integrity warrant strong consideration for surgical decision making, the present ultrastructural and biomechanical results appear to provide a scientific rationale for double-row rotator cuff repair where sutures are placed more medially at the muscle-tendon junction.

A biomechanical analysis of anterior Bankart repair using suture anchors.

BACKGROUND: Arthroscopic repair of anterior Bankart lesions is typically done with single-loaded suture anchors tied with simple stitch configuration. HYPOTHESIS: The knotless suture anchor will have similar biomechanical properties compared with two types of conventional suture anchors. STUDY DESIGN: Controlled laboratory study. METHODS: Fresh-frozen shoulders were dissected and an anteroinferior Bankart lesion was created. For phase 1, specimens were randomized into either simple stitch (SSA) or knotless suture anchors (KSA) and loaded to failure. For phase 2, specimens were randomized into 1 of 4 repair techniques and cyclically loaded then loaded to failure: (1) SSA, (2) suture anchor with horizontal mattress configuration, (3) double-loaded suture anchor with simple stitch configuration, or (4) KSA. Data recorded included mode of failure, ultimate load to failure, load at 2 mm of displacement, as well as displacement during cyclical loading. RESULTS: For phase 1, the load required to 2 mm displacement of the repair construct was significantly greater in SSA (66.5 +/- 21.7 N) than KSA (35.0 +/- 12.5 N, P = .02). For phase 2, there was a statistically significant difference in ultimate load to failure among the 4groups, with both the single-loaded suture anchor with simple stitch (184.0 +/- 64.5 N), horizontal mattress stitch (189.0 +/- 65.3N), and double-loaded suture anchor with simple stitch (216.7 +/- 61.7 N) groups having significantly (P < .05) higher loads than the knotless group (103.9 +/- 52.8 N). There was no statistically significant difference (P > .05) among the 4 groups in displacement after cyclical loading or load at 2 mm of displacement. CONCLUSION: Both knotless and simple anchor configurations demonstrated similar single loads to failure (without cycling); however, the knotless device required less single load to displace 2 mm. All repair stitches, including simple, horizontal, and double-loaded performed similarly. CLINICAL RELEVANCE: The findings may suggest that with cyclical loading up to 25 N there is no difference in gapping greater than 2mm, but a macrotraumatic event may demonstrate a difference in fixation during the initial postoperative period. Additional in vivo studies are needed to determine whether these differences affect the integrity of the repair construct and, ultimately, the clinical outcome.