There are challenges associated with the commonly used methods for the fixation of humeral components with short or standard length stems:
(1) The anatomy of inside of the humeral cortex is not regular or constant among shoulders
As a result, as pointed out by the authors of Intramedullary reaming for press-fit fixation of a humeral component removes cortical bone asymmetrically the cylindrical reaming that is commonly used in shoulder arthroplasty perferentially removes bone from the anterior and posterior cortices, a phenomenon that is not visible on anteroposterior radiographs.
(2) The anatomy of the inside of the humeral cortex is not matched by any implant
(3) Reaming and broaching the bone to fit the implant risks weakening of the humerus (endosteal notching)
(4) Stress shielding results from non-uniform distribution of loads from the humeral component to the humeral bone (for example in the cases below, most of the load transfer takes place at the distal end of the implant which is tightly wedged in the canal leading to resportion of the more proximal bone).
(5) The surgeon may not be able to completely seat the component.
(6) A well fixed but malpositioned "platform" stem precludes easy conversion to reverse total shoulder
(6) The fixation may be inadequate to withstand the loads applied to the component
(7) Safe revision requiring implant removal is challenging after cement fixation or with the use of bone ingrowth/ongrowth stems
This technique avoids removing endosteal bone with reamers (these are only used to size the canal by inserting progressively larger medullary reamers until there is a slight cortical purchase on rotation: "love at first bite". The volumetric gaps between the humeral implant are filled with morcellized cancellous bone from the resected humeral head that is sequentially impacted into the metaphyseal and proximal diaphyseal regions of the proximal humerus until the implant is stable to rotation of the impactor.
The authors named this technique the “Procrustean technique” after the mythical innkeeper, Procrustes, who either stretched out or cut the legs off his guests so that they would fit exactly in his guest bed. Like Procrustes, they preferred to modify the patient's endosteal anatomy to achieve the perfect of the implant rather than accepting an inadequate fit.
They performed cadaver studies to demonstrate that impaction grafting optimized the "fit and fill" at the implant-humerus interface.
In their paper, they presented an assessment of different humeral fixation techniques.
For three decades, this approach has been our standard approach for fixation of short and standard length humeral stems. We found impaction grafting serves to
1) preserve and augment bone stock (i.e. it is "canal sparing") and provide secure fixation for both short and standard length humeral stems (see recent case below of an anatomic total shoulder in a woman with severe osteoporosis; note the increased density of cancellous bone around the short stem implant which was securely fixed by impaction autografting)
2) accommodate variations in proximal humeral geometry,
3) allow for optimization of implant position by selective placement of graft,
5) enable the use of relatively thin smooth stems resulting in a lower filling ratio,
and 6) avoid the considerable risks associated with removing a cemented or bone ingrowth stem.
The authors of Impaction grafting improves the fit of uncemented humeral arthroplasty tested the hypothesis that the quality of the fit between a humeral prosthesis and the humerus could be optimized by impaction grafting with cancellous bone. Ten paired human humeri were prepared for insertion of a humeral implant by a standard surgical technique. One humerus from each pair was randomized to receive a 10-mm humeral component with cancellous impaction autografting, whereas the other was inserted without grafting. After insertion of a polymethylmethacrylate model of the prosthesis, computed tomography scans were obtained with 3-mm sections and the void areas of each section measured by use of NIH Image. The data demonstrated that cancellous impaction grafting significantly reduced the void between the prosthesis and the humerus. The effect was most marked in the proximal and middle thirds of the implant.
The authors of Impaction autografting: bone-preserving, secure fixation of a standard humeral component pointed out that when fixed with bone ingrowth, a tight diaphyseal press fit, or cement, the humeral component of a shoulder arthroplasty may present problems of malposition, stress shielding, periprosthetic fracture or difficulty with removal at revision arthroplasty. They attempted to avoid these fixation methods by using impaction cancellous autografting of the humeral stem, minimizing contact between the prosthetic stem and the humeral cortex.
They reviewed 286 primary anatomic shoulder arthroplasties having an average follow-up of 4.9± 2.7 years.
Of the 286 stems, 267 (93.4%) had not subsided at a minimum of two years after surgery.
The authors concluded that impaction autografting provides a secure, durable, bone-preserving means of humeral component fixation in anatomic shoulder arthroplasty.
Comment: Impaction autografting is an inexpensive method readily at hand in primary arthroplasty. It is safe and effective in managing the challenges of humeral component fixation in shoulder arthroplasty while avoiding the costs and risks of ingrowth or ongrowth implants and bone cement. In our practice it routinely used during implantation of short and standard length stemmed humeral components. We also use it in stemless humeral arthroplasty if there is any question about the quality of bone, as was the recently case in a 71 year old women. After reinvesting some of the bone from her resected humeral head into the humeral neck, the fixation moved from being marginal to robust.
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