Subpectoral proximal humeral anatomy: Guidance to decrease risk of fracture following subpectoral biceps tenodesis.

Background: Biceps tenodesis is used for a variety of shoulder and biceps pathologies. Humeral fracture is a significant complication of this procedure. This cadaveric anatomy study sought to determine the cortical thickness of the humeral proximal shaft to identify the optimal technique to decrease unicortical drilling and reduce the risk of fracture. Methods: A computed tomography (CT) of eight cadaveric humeral specimens was obtained with a metallic marker placed at the site of subpectoral tenodesis. These scans were examined to define the cortical thickness of the subpectoral region of the humerus and determine angular safe zones for reaming. Results: At the standard point of a subpectoral tenodesis, a mean angle relative to the coronal plane of 29.2° medially and 21.6° laterally from the deepest portion of the bicipital groove avoided unicortical drilling with a 7 mm reamer. These values varied slightly 1 cm proximal and distal to this level. The thickest regions of cortex in the subpectoral humerus correspond to the ridges of the bicipital groove. Discussion: To avoid unicortical tunnels, surgeons should limit deviation from the perpendicular approach to no more than 23° relative to the coronal plane medially and 11° relative to the coronal plane laterally.

The medial forearm fascia and lateral forearm fascia contribute to overhead elbow extension in displaced olecranon fractures: a biomechanical study.

BACKGROUND: In nonoperative management of displaced olecranon fractures, patients are able to maintain overhead extension despite a persistent nonunion. It has been hypothesized that this is feasible because of an intact lateral cubital retinaculum. The purpose of this biomechanical study was to determine the contribution of the medial and lateral cubital retinacula to overhead extension in the setting of a displaced olecranon fracture. METHODS: Eight fresh-frozen cadaveric upper-extremity specimens were used in this study. The triceps muscle was loaded through a pulley system operated by an Instron 8874 Biaxial Servohydraulic Fatigue Testing System at a rate of 10 mm/second to simulate overhead elbow extension. Each specimen was tested in 4 states: (1) native state with an intact olecranon; (2) transverse olecranon fracture; (3) transection of 1 cubital retinaculum (medial or lateral); and (4) transection of both medial and lateral cubital retinacula. The primary outcome was the ability to perform overhead extension. The secondary outcome was the force needed to generate extension. RESULTS: Elbow extension was noted in each specimen for trials 1, 2, and 3. Only when both the lateral fascia and medial fascia were transected was elbow extension not achieved. There was no significant difference in the force required to generate extension in the first 3 trials (P = .99). There was no significant difference in the change in the maximum force required to achieve extension between the specimens with only the medial side transected and the specimens with only the lateral side transected (P = .07). DISCUSSION: In the setting of an olecranon fracture, this biomechanical study suggests that if either the lateral or medial cubital retinaculum remains in continuity with the distal ulna, active overhead extension can be maintained. This finding may explain the positive clinical outcomes of nonoperative management of displaced olecranon fractures in the elderly patient population. Determining the integrity of the fascial structures preoperatively may help select candidates for nonoperative treatment of displaced olecranon fractures.

Negative Ulnar Variance Lessens DRUJ Instability After DRUJ Disruption: A Biomechanical Analysis.

BACKGROUND: The purpose of this study was to perform a biomechanical investigation on the effect of ulnar variance (UV) on the stability of the distal radioulnar joint (DRUJ) prior to and after DRUJ sectioning. METHODS: Ten cadaveric forearm specimens were included in the study and baseline UV was assessed radiographically. Radial motion relative to the ulna was evaluated using Intel real sense cameras and a custom developed program. The forearms were dissected, and a radial osteotomy was performed. Using a custom-made plate, radial stability was assessed with an UV of + 4, 0, and -4 mm by measuring the maximum and minimum radial position relative to the ulna during a simulated Shuck test. The volar radioulnar ligaments and triangular fibrocartilage complex (TFCC) were then sectioned, and testing was repeated at each UV state. RESULTS: Sectioning significantly increased radial translation at neutral (P = .008), +4 mm UV (P = .008), and -4 mm UV (P = .018). There were no significant differences in translation between the 3 UV groups with the DRUJ intact (P = .124). The ulnar negative (-4 mm) state had significantly lower translation compared to the positive (+4 mm) (P < .001) and the neutral (0 mm) (P = .026) UV states. There were no significant differences between the positive and neutral UV groups with the DRUJ sectioned. CONCLUSIONS: Fixating the radius in -4 mm of ulnar negativity significantly decreased radial translation after sectioning the volar radioulnar ligament and TFCC. Ulnar variance had no effect on stability with an intact DRUJ. STUDY TYPE: Biomechanical Study.