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Orthopaedic Proceedings
Vol. 90-B, Issue SUPP_I | Pages 98 - 99
1 Mar 2008
Dickey I Hugate R Reach J Zobitz M Zhang R G M
Full Access

Trabecular materials show great promise for soft-tissue attachment to prosthetic implants. Results with Tantalum have been very encouraging, however, it remains unclear if this in-growth is secondary to the specific metal or its generic structure,. If structure, is there a specific tolerance with respect to porosity and pore size? In a canine model, bulk blocks of porous alumina ceramic were shown to be completely ingrown by four weeks. The type material was not a factor, and effect of pore size revealed that there is a wide tolerance in facilitating in-growth with the larger pores having the greatest attachment strength (p=0.004).

This study examines the in-vivo soft tissue in-growth potential of porous alumina ceramic and the effect of three distinct pore size ranges on this process.

Alumina ceramic implants of fixed porosity (~ 85%) were designed in three pore size ranges (100–200, 250–400 and 600–800 μM). Using an established canine model, six implants (two of each type) were implanted in the dorsal subcutaneous tissues of tweleve mature canines and examined histologically and mechanically at four, eight and sixteen weeks with respect to type, amount and strength of soft tissue in-growth.

Soft tissue in-growth was grossly evident in all implants at each time interval, and in each pore size. Microscopic examination revealed neo-vascularized in-growth throughout the implant, without evidence of inflammation or foreign body reaction. Numerous blood vessels were visible at the implant interface and within the porous alumina ceramic structure. With peel testing, the weakest attachment strength was with the small pore size with no differences between the medium and large pore sizes. An increase of attachment strength in each pore size was observed over time.

This study suggests that architecture of porous structures in general, and not the type of material used, confers the biologic activity and that there is a wide tolerance for pore size in facilitating this process in soft tissue in-growth. Further study of other inert foam structures will be useful in further defining the assets and limitations of this genre of trabecular materials as a whole.

Funding: Stryker Orthopaedics, Mahwah, NJ

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Orthopaedic Proceedings
Vol. 90-B, Issue SUPP_I | Pages 99 - 99
1 Mar 2008
Dickey I Reach J Talac R Zobitz M Adams J Scully S Lewallen D
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Reliable soft tissue attachment to prosthetic implants remains a great clinical challenge in adult reconstruction and oncology. Past efforts using tendon alone have been universally disappointing. With the introduction of trabecular metals, new possibilities present them selves in dealing with this problem. Using an established canine supraspinatus tendon model, reliable and physiologic soft tissue attachment to a trabecular metal prosthesis was achieved, with near normal strength and function. This suggests that this new genre of material can possibly provide better options in dealing with this difficult problem.

Direct attachment of tendon to an endoprothesis has applications throughout the field of orthopaedics. The purpose of this study was to devise a soft-tissue attachment device using tantalum foam metal which would allow for early soft tissue reconstruction strength and long term biologic in-growth fixation.

A foam metal tendon attachment prosthesis was designed. Using a validated tendon attachment model, twenty-three skeletally-mature canine supraspinatus tendons were sharply detached and then reattached to the greater tuberosity. Ultimate strength, stiffness and gross morphological changes were recorded immediately after surgery and at three and six weeks.

Tendon-implant strength as percent of normal rose from thirty-nine percent at surgery, to sixty-seven percent at three weeks, and ninety-nine percent at six weeks (standard deviations thirteen, nineteen, and eighteen percent). Stiffness of construct also approached normal tendon: forty-seven percent at surgery, sixty-two percent at three weeks, and ninety-four percent at six weeks (standard deviations seventy-seven, nineteen, and eighteen percent). Supraspinatus muscle volume decreased from ninety seven (percent of normal) at surgery, to seventy-nine percent at three weeks. By six weeks, the muscle had recovered to ninety percent of normal volume. Gross and histologic analysis revealed complete tendon in-growth and attachment to the prosthesis with the formation of Sharpey’s fibers

This study suggests that tendon attachment to a metallic endoprothesis is possible. Near normal physiologic strength and stiffness was achieved six weeks post surgery. Future study should ascertain the micro-anatomy of this attachment and delineate the mechanical conditions necessary for soft tissue in-growth.

Funding: Zimmer, Inc., Warsaw, IN

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Orthopaedic Proceedings
Vol. 86-B, Issue SUPP_III | Pages 252 - 252
1 Mar 2004
Halder A Zobitz M An K Neumann W
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Aims: Although the glenohumeral joint is the most mobile articulation of the human body it is known to exhibit ball-and-socket-kinematics. Compression into the glenoid concavity keeps the humeral head centered. The purpose of this study was to determine the effects of joint position on glenohumeral stability through concavity-compression. Methods: Ten cadaver shoulders were tested. The glenoid was mounted horizontally onto a six-component load cell while the humerus was clamped to a vertically unconstrained slide. An x-y-stage translated the load cell with the glenoid underneath the humeral head in eight different directions. Compressive loads of twenty, forty and sixty Newtons were applied. The tests were repeated in 0, 30, 60 and 90 degrees of glenohumeral abduction with and without labrum. Translation distances and the forces resisting translation were recorded and the stability ratio calculated. Results: The average stability ratio was higher in hanging arm position than in glenohumeral abduction. With intact labrum the highest stability ratio was detected in inferior direction (59.8±7.7 percent), without labrum in superior direction (53.3±7.9 percent). In both conditions the anterior direction showed the lowest stability ratio (32.0±4.4 percent; 30.4±4.1 percent). Resection of the labrum resulted in a decrease in stability ratio of 9.6 ±1.7 percent. With increasing compressive load the stability ratio slightly decreased. Conclusions: Anterior shoulder dislocation may be facilitated by the lower stability in glenohumeral abduction and anterior direction. The labrum may not contribute as much as previously assumed to glenohumeral stability. Even moderate compressive forces are sufficient to provide stability through concavity-compression.