Differences in reconstruction of the anatomy with modern adjustable compared to second-generation shoulder prosthesis

Abstract

Reconstruction of the anatomy of the proximal humerus is a prerequisite to achieving good long-term clinical results after shoulder arthroplasty. Modern, adjustable prostheses have greater flexibility of inclination, retroversion, and medial and dorsal offset in comparison with older prostheses. Such improvements should allow for better reconstruction of the centre of rotation compared to older prostheses. Reconstruction of the humeral head centre was assessed in 106 modern adjustable (Affinis) and 47 second-generation prostheses. All reconstructions were compared both to the preoperative state and the unoperated shoulder. To describe the pre-and postoperative states, the geometry and position of the humeral head in relation to the glenoid were analysed on patient radiographs. Applying the defined parameters, modern adjustable prostheses showed better reconstruction than second generation prostheses. Parameter values measured in reconstructions using fourth generation prostheses were comparable to those of the unoperated shoulder, but differed significantly from the preoperative state. Second generation prostheses, in contrast, only show non-specific differences in parameter values. This suggests that an approximate reconstruction of normal anatomy can be achieved using a modern fourth generation prosthesis. Reconstruction of the complex anatomy of the proximal humerus is significantly better with modern adjustable prostheses compared to second generation prostheses. Improved clinical outcome can therefore be predicted in a functional and intact rotator cuff. The advantage of using modern prostheses systems over older models is clearly demonstrated in this study. IntroductionThe anatomy of the proximal humerus can vary with respect to inclination, retrotorsion and the medial and dorsal offsets (the offset of the centre of rotation in relation to the humeral axis) [1,6,9,14,17,20,21]. Due to this, many groups call for this anatomy to be repaired as precisely as possible when implanting a humeral prosthesis in order to achieve optimal postoperative joint function [1,4,5,7,8,10,13,15,16,18,20,22,23]. Others go further and insist on reconstruction of the centre of rotation specifically [17].In many cases of osteoarthritis, flattening of the humeral head can be identified (Fig. 1a, b), resulting in conditional lateral displacement of the centre of rotation in relation to shaft axis but causing a medial shift of the of the rotational centre in relation to the glenoid. Other patients show a primary osteoarthritis with no significant deformation of the humeral head (Fig. 1c). The technical demands for reconstruction of the rotational centre differ considerably in both cases.Modern prostheses allow adaptation to both the primary and also pathologically altered secondary anatomy. These prostheses generally allow eccentric adjustment of the prosthesis head in relation to the shaft. Some also feature variable, adjustable inclination.In order to reconstruct a shoulder as closely as possible to the contralateral side...

Variability of medial and posterior offset in patients with fourth-generation stemmed shoulder arthroplasty

“…The study showed that rotation centre restoration can be achieved with significantly more precision than with older, nonadjustable prostheses (Neer II, among others). The midterm clinical outcomes achieved with this prosthesis are similar to those reported in the literature for other modern prostheses; some parameters are even markedly superior [8].…”

Prospective study of double-eccentric hemi shoulder arthroplasty in different aetiologies: midterm results

“…The prosthesis allows for free placement of the head component; the surgeons focused on optimal transition from the humeral head to the insertion of the supraspinatus tendon. Thus, the prosthesis allows for optimal reconstruction of the humeral geometry, a prerequisite for good function of the prosthesis and something which has been requested by many authors [5,11,20,22,26].…”

“…Optimal reconstruction of anatomy results in optimised freedom of action and reduces the risk of subacromial impingement. In particular, the exact reconstruction of the centre of rotation is necessary to maintain normal function of the rotator cuff and to minimise eccentric loading of the glenoid [5,9,11,20]. Initial experimental and clinical results suggest that modern third and fourth generation prostheses are beneficial for later function [3].…”

Three-dimensional assessment of the dimensions of the osteoarthritic glenoid

“…[33][34][35] Modular sizes of the glenoid component have facilitated reasonable cover of the height and width of osteoarthritic glenoids. However, given the variability in the radius of curvature of osteoarthritic glenoids observed in our study, there is an argument for TSR systems to include modular reamers that allow for glenoid components with multiple backside radii of curvature.…”