Do Intramedullary Screws Provide Adequate Fixation for Humeral and Ulnar Components in Total Elbow Arthroplasty? A Cadaveric Analysis.

PURPOSE: The objective of this study was to determine the structural properties of the cadaver bone-screw interface for cementless intramedullary screw fixation in the context of total elbow arthroplasty. METHODS: The intramedullary canals of seven humerus and seven ulna specimens from fresh-frozen cadavers were drilled using custom drill bits until the inner cortex was reached and then hand tapped for the corresponding thread size. Titanium screws were advanced into the tapped holes until securely seated. The bones were potted and then mounted on a uniaxial material testing machine. A tensile load was applied, and end-of-test elongation, failure load, energy absorbed, and stiffness were determined. End-of-test load and elongation were defined as the elongation and load experienced by the structure at 3,000 N or failure. Each specimen was inspected for evidence of pullout, loosening, or visible fractures. RESULTS: The end-of-test load and elongation for the humerus specimens were 2721 ± 738 N and 3.0 ± 0.9 mm, respectively. The ulna specimens reached 92% of the humerus specimens' end-of-test load at 2,514 ± 678 N and 120% of their end-of-test elongation (3.6 ± 0.6 mm). The stiffness of the humerus specimens was 1,077 ± 336 N/mm, which was 1.3 times greater than the stiffness of the ulna specimens (790 ± 211 N/mm). Lastly, the energy absorbed by the humerus samples was 3.6 ± 1.6 J, which was 92% of the energy absorbed by the ulna samples at 3.9 ± 1.1 J. One humerus and three ulnas failed before the end-of-test load of 3,000 N. Two failures were caused by screw pullout and two by bone fracture. CONCLUSIONS: Our findings demonstrate that intramedullary screw fixation is successful in withstanding forces that are greater than required for osseointegration. CLINICAL RELEVANCE: Uncemented fixation may be beneficial in elbow arthroplasty.

Comparing Static Stability of Native Elbow With Static Stability of Novel Bidirectional Ligament Reconstruction at Different Degrees of Elbow Flexion.

Purpose: The treatment of bidirectional ligament instability is proposed using a method that simultaneously tensions medial and lateral ligaments. Graft tension is maintained via plates that apply compression between the graft and bone. Methods: We tested static varus and valgus elbow stability in six cadaver elbows with intact ligaments and capsules at five positions, and then created gross instability by dividing all soft tissue attachments. A ligament reconstruction was subsequently performed with and without nonabsorbable ligament augmentation. Elbow stability was measured and compared with the native state. Results: The augmented and the nonaugmented ligament reconstructions provided stability to the lateral side with only 1.0 mm of increased deflection recorded for the augmented ligaments and 0.6 mm for the nonaugmented when compared with the native state. On the medial side, the deflection was greater after reconstruction compared with the native state with the augmented ligaments ranging between 1.0 and 1.8 mm and the nonaugmented ligament reconstruction ranging between 2.4 and 3.3 mm. Conclusions: This novel ligament reconstruction maintained secure fixation between ligament and bone and allowed for maintenance of static stability at different degrees of elbow flexion. Clinical Relevance: Restoring elbow stability using a method that minimizes ligament graft and which may not need to be removed could benefit management of bidirectionally unstable elbows, such as following interposition arthroplasty or substantial trauma.

Cadaveric Biomechanical Analysis of 3 Lateral Ulnar Collateral Ligament Reconstructions.

OBJECTIVE: To biomechanically assess the angular stability provided by 3 techniques for reconstruction of the lateral ulnar collateral ligament. METHODS: Eight cadaveric elbows were tested with the lateral collateral ligament complex intact, disrupted from the origin at the lateral epicondyle, and reconstructed with 3 different techniques using ulnar bone tunnels: a suture "lasso" or palmaris longus tendon "lasso" both docked with a metal button at the origin, and a doubled-over palmaris longus tendon docked with metal buttons at both the origin and ulnar insertion. Elbows were tested with a physiologic elbow simulator, and varus angular position was quantified with an optical tracking system. Statistical analysis was performed using a repeated measures analysis of variance test to determine whether significance existed, and a Tukey post hoc analysis to compare statistical difference between native, disrupted, and repair states. RESULTS: There was a statistically significant difference between all repairs and the disrupted state (P < 0.05). The varus angulation after the repairs showed that the suture reconstruction was closest to the native case. The tendon reconstructions were similar to each other but less similar to the native elbow. Quantitatively, the suture reconstruction was within an average of 0.86 degrees of the native elbow throughout range of motion. CONCLUSIONS: A suture reconstruction was most similar to a native elbow, but both tendon reconstructions significantly improved angular stability under varus gravitational loads.

Unique model evokes the supination/pronation deficits found after Mason II fractures.

A rapid prototyping model of Mason II fracture was used to investigate baseline recommendations for surgical intervention founded on kinematic forearm rotational blockage. Exact replicas of the radial heads in nine cadaveric specimens were produced and specimens were tested in a physiologic elbow simulator. After testing supination/pronation, the rotations were repeated with native replicas and with replicas modeling 3 mm depressed Mason II fractures with and without a gap of 1 mm between the body and fragment. The fragments were located circumferentially around the radial head at 10, 2 and 6 o'clock positions. There was no statistical difference between the range of motion of the native case and the native replica without fracture. After inclusion of the fracture, seven of the nine specimens showed rotational blockages. A two-way ANOVA found no statistical difference due to type of Mason II fracture (p > 0.87) or fracture location (p > 0.27). A χ-square analysis showed that presence of a kinematic deficit with a fractured radial head was significant (p < 0.03). The results support continued surgical intervention for a 3 mm depressed fracture and also establish the use of the rapid prototype as a model for kinematic investigation of fractures in a cadaveric model when ligamentous attachments are preserved.

Extensor tendon injuries in athletes.

Extensor tendon injuries of the hand and wrist in high-level athletes can cause a delay in return to play and permanently affect their performance. Given the inherent demand for a speedy and complete recovery, orthopedic surgeons must have an understanding of how to best direct an athlete's treatment for these injuries. The extensor anatomy is very intricate and a thorough understanding of the anatomy can help with both diagnosis and treatment. However, untreated or poorly managed injuries are at risk of leading to chronic deformities. We will discuss the diagnosis and management of the most common extensor tendon injuries and tendinopathies of the hand found in athletes: mallet fingers, swan-neck deformities, boutonniere deformities, central slip ruptures, sagittal band ruptures, intersection syndrome, extensor carpi ulnaris tendinitis, and extensor carpi ulnaris subluxation.