Smart intramedullary rod for correction of pediatric bone deformity: a preliminary study.

We were interested in determining if a smart intramedullary rod made of nitinol shape-memory alloy is capable of correcting deformed immature long bones. Because of limitations in our study design the process was reversed in that we examined the smart rod's ability to create a deformity rather than to correct one. Smart rods of different lengths and diameters were heat-treated to resume a radius of curvature of 30 to 110 mm. The low and high temperature phases of the smart rods were set, respectively, at 0 degrees C to 4 degrees C and 36 degrees C to 38 degrees C. The preshaped smart intramedullary rods were implanted in the cooled martensite phase in the medullary canal of the tibia in eight rabbits, where they restored their austenite form, causing a continuous bending force. On a weekly basis anteroposterior and lateral radiographs of the surgically treated tibia and the contralateral tibia were obtained for comparison. Rabbits were euthanized 6 weeks after surgery and computed tomography scans of both tibias were used for image analysis. Smart rods with a larger radius of curvature showed only minimal signs of remodeling; however, rods with a radius of curvature of 50 and 70 mm generated enough force history to create bone remodeling and deformation. The amount of bone deformation was highly magnified when unicortical corticotomy on the tension side was done. Based on this preliminary study the technology of the smart intramedullary rod may provide a valuable alternative method to correct pediatric skeletal deformities.

A study of ulnar collateral ligament of the thumb metacarpophalangeal joint.

The current study examined the biomechanical properties of intact and repaired ulnar collateral ligaments of the metacarpophalangeal joint of the thumb to determine a safe rehabilitation protocol after repair. In the first part of the study mechanical properties of the ligament were examined and the induced stress and strain were determined during simulated pinch and grip. In the second part of the study the strength and limitations of ulnar collateral ligament repair using a mini-Mitek bone suture anchor was determined. The biomechanical study was done on 16 fresh-frozen thumbs from male cadavers. Failure load, maximum stress, and Young's modulus of intact ulnar collateral ligament were 294.3 +/- 28.2 N, 11.4 +/- 1.2 MPa, and 37.3 +/- 5.1 MPa, respectively. There was no significant correlation between the low grip force and the ligament strain. There was, however, a significant correlation between the pinch force and the ligament strain. The failure load and joint rigidity of intact ulnar collateral ligaments were significantly higher (3.1 and 2.3 times, respectively) than the mini-Mitek repaired ligaments. The current study suggests that pinch activity during the rehabilitative process after repair or reattachment of the ulnar collateral ligament should be eliminated. Repaired ligaments with mini-Mitek bone suture anchors may be able to do a moderate range of motion during postoperative rehabilitation; however, additional in vivo studies are necessary before any clinical recommendation is made.