Numeric simulation of time-dependent remodeling of bone around loaded oral implants

PURPOSE

The objective of this study was to investigate the time-dependent biomechanics of marginal bone around osseointegrated dental implants within physiologic loading conditions.

MATERIALS AND METHODS

The remodeling of marginal bone around a 4.1-mm-diameter, 10-mm-long implant was studied by implementing the Stanford theory into axisymmetric mathematical models simulating different bone support at the implant neck: 1-mm-thick cortical bone (model 1), 0.5-mm-thick cortical bone (model 2), absence of cortical bone (model 3), and absence of cortical bone with 0.5 mm of resorption of marginal trabecular bone (model 4). The results were examined separately for all models at five time intervals: the first loading after osseointegration and 3, 6, 9, and 12 months after osseointegration. Minimum principal stress, maximum principal stress, strain energy, total equivalent strain, displacement, average elastic modulus, and bone density were evaluated.

RESULTS

In models 1 and 2, the magnitude of the stresses increased during the 1-year period. The distributions of stresses in models 3 and 4 were less variable and lower than models with cortical bone. The region of high stresses enlarged during the first 3 months and then decreased over time. There was a time-dependent increase in strain energy density around the neck of the implant in models 1 and 2. The time-dependent displacement values of implants were almost constant over time (maximum 1 Mum change). The lowest implant displacement values were observed in model 1. There was a slight increase in the elastic modulus of cortical bone and a decrease in trabecular bone (maximum 1% change).

CONCLUSION

The time-dependent increase in stresses in the marginal zone of the implants with cortical bone support was higher than that of the implants supported solely by trabecular bone in the first year of function. Higher strain energy density around the implants with cortical bone support might indicate apposition and increase in interface stiffness, whereas lower strain energy density around implants supported solely by trabecular bone could be associated with skeletal tissue loss.

Axial rotation and mediolateral translation of the fibula during passive plantarflexion

BACKGROUND

Since the fibula is linked to the ankle as well as the knee joint, its importance for knee and ankle disabilities should be investigated. This study evaluates its movement during range of motion of the ankle.

MATERIALS AND METHODS

An instrument, together with the experimental protocol, was devised to determine the relative motion of the fibula in reference to the tibia with motion of the ankle joint on 20 paired lower extremity cadaver specimens.

RESULTS

It was demonstrated in all specimens that the fibula had a relative rotation around its longitudinal axis and mediolateral translation with reference to the tibia with ankle motion. The distal end of the fibula rotates more compared to the proximal end. The mediolateral translation of the proximal end of the fibula is rather close to that of the distal end. Although there was no consistent pattern for rotation, dorsiflexion caused lateral translation and plantarflexion caused medial displacement for most of the specimens.

CONCLUSION

A novel, invasive but relatively simple test setup was devised. Movement of the fibula which is important for the kinematics and kinetics of the knee and ankle joints was evaluated by this new device.

CLINICAL RELEVANCE

Evaluation of the fibula movement in normal lower extremities may lead to better understanding of its dynamic function which could have treatment implications for pathological conditions.

The annular ligament: an anatomical study

BACKGROUND

Despite documentations of ligamentous structures of the elbow, the anatomy and clinical and functional importance of the annular ligament has not been comprehensively defined in the orthopaedic literature.

HYPOTHESIS

The annular ligament is an important component of both the proximal radioulnar and humeroradial joints, as well as an important component of the neighboring muscles and ligaments.

STUDY DESIGN

Descriptive laboratory study.

MATERIALS AND METHODS

To investigate the annular ligament and its relationship with neighboring structures, macroscopic and microscopic dissections were performed on both upper extremities of 30 cadavers (12 female and 18 male) fixed in 10% formaldehyde and on 1 upper extremity of a fresh cadaver (male).

RESULTS

The distal ulnar insertion of discrete fibers on the supinator crest was defined as the inferior oblique band of the annular ligament, and the proximal insertion of the annular ligament was defined as the superior oblique band of the annular ligament. These patterns were noted in all specimens. It was difficult to distinguish the fibers of the supinator muscle in every specimen because they were intimately fused with the fibers of the annular ligament.

CONCLUSIONS

The superior and inferior oblique bands of the annular ligament attached proximally and distally onto the ulna, thus helping to secure the annular ligament in place.

Functional evaluation of intraarticular severely comminuted fractures of the calcaneus with gait analysis

Twenty-one patients (23 feet) treated nonsurgically for severely comminuted intraarticular fractures of the calcaneus were evaluated prospectively with a clinical scoring scale and computerized gait analysis. All patients had Sanders type III and type IV fractures. The treatment protocol consisted of no closed reduction, immobilization in removable splint, physiotherapy after edema subsided, and weightbearing after 8 weeks. All patients had a minimum follow-up of 2 years (mean, 38 months). Clinical results were good in 2 patients, fair in 3 patients, and poor in 16 patients. Gait analysis showed that patients were at high risk of gastrocnemius weakness and ankle and knee instability. These results may be useful for comparison with the results of other methods, such as open reduction and internal fixation, nonsurgical closed reduction, and arthrodesis.