An evaluation was made of results of follow-up studies, ranging from nine months to about 3 1/2 years, of six patients who had mandibular ridge augmentations at the University of Minnesota Hospitals. Clinical observations, patients' subjective feelings, and measurements of vertical loss of the original graft were the main considerations in the studies. Although there was almost continual resorption of the bone grafts after surgery patients were satisfied with the procedure and the current dental function.

Alveolar Process↗

PubMed1970

[Remote results of Perthes' disease under fixation in a relaxed position (Imhäuser) (results of 17 years)].

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Age Factors↗

PubMedDate not supplied

[Computer-based motion simulation of total hip prostheses with ceramic-on-ceramic wear couple. Analysis of implant design andorientation as influence parameters].

OBJECTIVE: In THA, ceramic-on-ceramic wear couples are increasingly used. A restricted range of motion (ROM) due to unfavourable implant design or positioning may cause impingement or dislocation, which can result in failure of ceramic inserts. METHODS: By means of a 3-D CAD program different hip joint movements were simulated and the effects of ceramic hip implant design and position on the range of motion were analysed. RESULTS: To offer sufficient ROM and to minimise risk of impingement and dislocation, inclination angle of the acetabular cup should be 45 degrees, cup anteversion 15 degrees and stem antetorsion 0 degrees to 10 degrees. In regard to implant design, acetabular cups with slightly- recessed ceramic inserts should be used. Prosthetic systems with an elevated liner or with a mushroom-shaped femoral head are associated with limited ROM and increased risk of mechanical failure. The ratio of head to neck diameter should never be less than 2 : 1. Larger heads not only increase ROM, but also the stability of the prosthesis against dislocation. Thereby, the wear rate of ceramic-on-ceramic couples is not increased, in contrast to polyethylene. CONCLUSION: Considering certain criteria for ceramic hip implants regarding implant positioning, design and handling, ceramic-on-ceramic couples can be used with low risk of revision surgery and they can also reduce the prosthesis loosening associated with wear in young and active patients.

Ceramics↗

PubMedDate not supplied

[Calculation of hallux bending moments from plantar pressure distribution measurement].

PURPOSE: The following study aims to demonstrate the bending stress on a hallux valgus during normal gait. The bending axis was related to the position of an open wedge osteotomy. The moments were calculated from plantar pressure measurements. METHOD: In the gait analysis laboratory plantar pressure distribution measurement was done with healthy adult volunteers during barefoot gait. From the plantar pressure distribution the vertical forces were derived just for the region hallux metatarsal I. The following calculation of the bending stress regarding to the hypothetic region of the osteotomy was done by integrating the pressure distribution multiplicated with the distance to the osteotomy. The measurements are compared with theoretical values derived from the anatomy of the foot under some plausible assumptions. RESULTS: The results of the mean values of the bending stress were 15.8 +/- 4.8 Nm for the female subjects and 21.6 +/- 5.6 Nm for the male subjects. The amount of the bending moments depended with low significance on the weight. More important is the individual type of gait. CONCLUSION: The measurements show the size of bending stress the plate stabilizing the osteosynthesis has to resist under unfavorable circumstances (for example if the plantar foot muscles are not adequately activated) and if no external stabilization (for example, cast) is used.

Adolescent↗

PubMedDate not supplied

[Experimental analysis of neutral, asymmetric and constraint liners for total hip replacement: investigation of range of motion and protection against joint instability].

AIM: Recurrent dislocation after total hip replacement is a severe complication, which requires specific treatment and implants. The purpose of the present study was to compare a constraint liner with an elevated rim and standard liner regarding their range of motion and dislocation stability. METHOD: With a test device, range of motion until impingement (ROM (Imp)) and dislocation (ROM (Lux)) were experimentally analyzed using the above-mentioned insert types of a commercial total hip system. On the basis of movement combinations associated with dislocation, the ROM was determined. Further measuring parameter was the resisting moment against subluxation of the femoral head. RESULTS: The constraint liners showed clear restriction of the movements "internal rotation combined with 90 degrees flexion and 0 degrees adduction" and "external rotation with 10 degrees extension and 15 degrees adduction" of up to 20 degrees compared to the neutral liner. ROM (Imp) was only decreased by about 8 degrees with the elevated-rim liner. The constraint liners revealed the highest resisting moments in subluxation, however, at adequate orientation in the acetabular cup the elevated-rim liners provided a higher ROM (Lux) of up to 12 degrees. Both designs were superior to the neutral liner at retroversion and steep cup position regarding resisting moment and ROM (Lux). CONCLUSION: In case of insufficient soft tissue tension the use of constraint liners may increase the dislocation stability, however, in contrast to elevated-rim liners the impingement-free movement interval is clearly reduced. Thus, material damage and high shear stress in the bone interface can result. Therefore, constraint liners should only be used in exceptional cases.

Equipment Failure Analysis↗

PubMedDate not supplied

[Influence on load transfer of different femoral neck endoprostheses].

AIM: Aiming to reduce known complications of stemmed implants, such as resorptive bone remodeling or bone damage in revision, implants with only epi-metaphyseal anchorage have been developed. In the following study the influence of three different femoral neck endoprostheses, CUT, CIGAR (ESKA Implants Lübeck) and TPP (SulzerMedica) on the postoperative load transfer to the femur was investigated in comparison to a cementless hip stem. METHODS: Using a composite femur model and photoelastic coating technique, the pre- and postoperative osseous strain was measured under static loading. The load corresponded to the absolute maximum of the hip joint load during walking. Statistical analysis was based on the interval of 99 % confidence which was generated by the preoperative measurements. RESULTS: The different anchorage concepts of the femoral neck endoprostheses exhibited a significant influence on the load transfer, especially along the medial and lateral cortical bone. But, in comparison, the cementless hip stem caused more pronounced stress-shielding which can induce resorptive bone remodelling. CONCLUSION: One specific femoral neck anchorage concept led to a change from preoperative tension to postoperative compression at the lateral cortical bone. This regionally limited effect may influence in the mid- or long-term the local bone remodeling in a negative manner.

Cementation↗

PubMedDate not supplied

[Comparative static biomechanical studies of tripod surface structures of cementless endoprostheses].

AIM: While the importance of stability of endoprosthetic surface structures has been recognized for some time there is a lack of comparative surveys and assessment indices that would permit comparison and improvement of surfaces on cementless endoprostheses. METHOD: Using separately produced, systematically mounted specimen pieces of endoprosthetic surfaces with isolated non-linked elements of varying shapes and sizes, stability parameters and stability behaviour are described. Results of tripode-structures are compared to spherical surfaces. RESULT: These investigations show clearly that geometrical attributes, the orientation and the contact of surface elements to the endoprosthetic stem influence the stability considerably more than the size of these surface elements. CONCLUSION: Using tripode-elements with different orientation, size and density, a differentiated formation of cementless endoprosthetic surfaces is possible.

Biomechanical Phenomena↗