Early shoulder replacement designs by Krueger [1] and Neer [2] established a venue for replacing the proximal humerus in the event of complex fractures or degenerative arthritis. As further pathologies evolved, requiring improved stability, more constrained and semi-constrained devices were developed [3] [4] . Fenlin developed a reverse-type shoulder replacement using a “ball & socket” mechanism in 1973 [3] . DePalma, the chairman of the orthopaedic department at NJ Medical School, recruited a mechanical engineer, Michael J Pappas, PhD, in 1974 to collaborate with his research resident, Frederick F Buechel, MD, to evaluate his initial constrained designs and develop a semi-constrained TSR that they called the “floating socket”, since it was comprised of a sphere within a sphere with an offset pivot center, creating a “floating socket”! (See Figure 1). This patented device had 120˚ of motion and was attached by snap rings to a fixed glenoid component; making it one of the first “reverse” TSR’s [5] [6] (see Figure 2). It was successful in both chimpanzee [7] and human [5] in the short term, but in the intermediate term (>3 years) it failed by glenoid component loosening, even though one device lasted for 17 years in a rheumatoid female patient, see Figure 3.

The lesson learned from the “floating-socket” device was that even semi-constrained devices can loosen by repetitive torque on glenoid fixation. This knowledge gave rise to minimizing or eliminating torque on fixation elements in our future designs. By uncoupling the humeral component from the glenoid component, and minimizing constraint in favor of soft tissue stabilization, component loosening in either cemented or cementless fixation was minimized.

Of interest, our initial cementless cobalt chrome resurfacing TSR, implanted in 1982, remained functional for over 26 years, until wear through of the ultra high molecular weight polyethylene (UHMWPe) bearing caused osteolysis and failure, see Figure 4.

In 1989, we changed from cobalt-chromium alloy to titanium nitride (TiN) ceramic coated titanium alloy resurfacing and stem-type components with porous coating for cementless fixation and created a system of stem-type and revision component as well (B-P Shoulder System, Figure 5). These highly polished and biocompatible components gave reasonable congruity to the arthritic glenoid surface and were surprisingly pain free. After observing wear failures of total stem-type TSR after 15 years using standard UHMWPe, see Figure 6, it stimulated the concept of hemiarthroplasty rather than TSR to avoid glenoid bearing

revision. This appealing concept allowed minimal contouring of the proximal humerus and gave long term (>10 years) results that were equal to or superior to TSR, see Figure 7 and Figure 8.

This historical context of design rationale and reviewing clinical results was essential to our understanding of loading concepts in the pursuit of refining implant design to compensate for stable or compromised rotator cuff mechanisms. Also, salvage situations required proximally porous coated stem-type fixation components to avoid stress shielding the humeral shaft. Overall, our early experience with constrained and semi-constrained devices led to loosening failures, which logically led us to unconstrain our implants in favor of soft tissue and anatomical constraints, rather than mechanical constraints.

The B-P Shoulder Replacement System, see Figure 5, evolved from the “floating socket” TSR, see Figure 2, developed in 1974 [5] [6] . This initial device was modified and implanted in an adult male chimpanzee in 1975 (see Figure 9), and followed for 3 years, when the animal died from complications of Crohn’s disease; the device was retrieved from the primate center post-mortem. The first human “floating socket” TSR was implanted in 1975 and was also followed for 3 years, when the 60 year old osteoarthritic male patient died from complications of liver cirrhosis; the device was retrieved with permission post-mortem.

B-P Resurfacing shoulder replacements were extensively studied by Pritchett [8] [9] in both anatomic hemiarthroplasty and full proximal humeral hemiarthroplasty conditions, using femoral resurfacing implants, see Figure 10. Bipolar shoulder replacements were studied by Worland [10] [11] and used in salvage situations involved in loss of proximal humeral bone stock (see Figures 11-12).

Resurfacing Shoulder Arthroplasty, using polished TiN ceramic coated implants, has been extensively studied by Pritchett [8] [9] . He recently reported on 428 patients with intact or reconstructable rotator cuff mechanisms that received a hemiarthroplasty and were followed for 5 to 30 years (mean 11 years), as well as 67 patients with rotator cuff arthropathy that received a hemiarthroplasty using a femoral resurfacing component, and were followed for a minimum of five years. He found that 94% of the former group had good to excellent results, while 90% preferred their resurfacing arthroplasty to a stem-type prosthesis already implanted in their contralateral shoulder. In the latter group, there were 9 patients with a reverse TSR in their opposite shoulder; 6 of 9 patients preferred their femoral resurfacing implant, stating that “it felt more natural”. Bipolar shoulder replacements were quite useful for severe proximal humeral deficiency or rotator cuff arthropathy, since the outer shell of the bipolar component filled the subacromial space, which provided stability and a fulcrum to allow stable abduction, see Figure 13. No glenoid component was

needed for this articulation, in contrast to the “Reverse TSR” [4] that uses a semi-constrained large gleno-sphere, stabilized by multiple screws, which are constantly exposed to torquing forces.

Resurfacing shoulder replacement has been proven to be an effective surgical procedure to restore function and relieve pain. Extensive studies by Pritchett [8] have shown that polished TiN ceramic implants cause minimal wear on the native glenoid surface and are more wear-resistant than similar cobalt chromium devices, based on simulator and retrieval analyses.

His comparative studies of patients with bilateral shoulder replacements demonstrate the superiority of resurfacing implants over stem-type implants by patient preference [9] .

The journey of implant design from “floating-socket” to stem-type to the simplistic resurfacing type has required diligence and engineering expertise. The specific details of fabrication of the resurfacing humeral component and the resurfacing femoral component (Biocore9, Whippany, NJ) are shown in Figure 14. Both devices have been cleared by the FDA 510K process [12] [13] [14] .

Despite the complexity of resurfacing surgery, it is less invasive than implanting stem-type or reverse-type shoulder prostheses. There is also a lower infection rate and less overall complications using resurfacing implants [8] . In surgery, the old adage of “doing the least to gain the most” certainly applies to resurfacing shoulder hemiarthroplasty.

Resurfacing shoulder hemiarthroplasty in patients with intact or reconstructable rotator cuff mechanisms had 94% good or excellent results at 5 - 30 years, mean 11 years.

Rotator cuff arthropathy patients that were reconstructed with femoral resurfacing components had results that were equal to, or better than, reverse TSR at a minimum of 5 years.

Resurfacing shoulder replacement surgery was observed to have fewer infections and fewer complications than stem-type shoulder replacements.

The authors declare no conflicts of interest regarding the publication of this paper.

Buechel, F.F. and Pappas, M.J. (2024) Buechel Pappas Resurfacing Shoulder Replacement: Evolution and Over 40 Years of Clinical Experience. Open Journal of Orthopedics, 14, 218-228. https://doi.org/10.4236/ojo.2024.145020