*6.4. Arthroplasty*

The problem with dislocation arthropathy is that these patients are younger than those with idiopathic OA and usually have substantial internal rotation contracture and posterior glenoid defects [62].

As with each OA, the preoperative clinical examination with determination of the rotation is essential. A limited external rotation is a prognostically negative criterion for the post-op result. The preoperative analysis of the glenoid constellation is often insufficient in the axial projection and is better investigated in the CT. The MRI is used to evaluate fatty atrophy and integrity of the subscapular muscle and the other portions of the rotator cuff.

During the approach, the mobilization with an anterior extension of the subscapular muscle is critical of particular importance. This can be achieved by completely separating the subscapular tendon and approximately 1 cm medial refixation. A medialization of around 1 cm corresponds to an external rotation gain of approximately 20◦. In case of

stronger contractions, a bifocal capsulotomy according to Habermeyer is preferred [63]. The incision begins at the rotator interval. After ligature of the anterior circumflex arteries and protection of the latissimus dorsi and teres major insertion, the subscapular muscle is wholly detached down to the metaphysis [64]. The medial mobilization behind the anterior margin of the coracobrachialis muscle is not recommended to preserve blood circulation and innervation and avoid secondary damage to the subscapular muscle.

The replacement on the humeral side depends on the size of the defect. In younger patients, a cup, stemless or short stem/stem prostheses are possible (Figure 5). In the cup prosthesis, the bony defect should not exceed 30%. Recent studies report comparable short-term results between a combination of humeral surface replacement with cemented glenoid component and conventional total shoulder arthroplasty [65].

Dorsal rolled out glenoids require excellent preoperative planning to define the glenoid form and version. After the good exposition, the axis and the glenoid center should be marked with, e.g., a K-wire to plan the correct inclination and version. The value of navigation still must be proven. In most cases, with sufficient bone substance, the higher edge of the glenoid is removed to create a correct version. In larger, usually posterior defects, a reconstruction by a bone graft ("contained defect") or accumulation of an iliac crest graft ("non contained defect") is necessary (Figure 6). Bone transplantation for reestablishment of the glenoid defects or correcting the version is already mentioned in small numbers by Neer [66] after introducing the unlinked prostheses. The simultaneous implantation of a cemented glenoid is problematic from a biological point of view. Here twostep procedures should be preferred. The fixation of anterior bone grafts is substantially more straightforward and unproblematic than that of posterior defects. The posterior bone grafts can be placed only sometimes from the anterior. If a dorsal defect without hold to the medial exists, the graft must be inserted from the posterior. The graft is fixed with two screws that should not affect the implantation of the glenoid (keel or pegs). If a strong posterior inclination of the glenoid is present and no sufficient correction of the version is possible, stability can be increased by adapting the version of the components against each other. If this is not possible, it is better to surrender the glenoidal component. In case of a simultaneous existing out-of-center rotator cuff lesion, the implantation of Reverse Shoulder Arthroplasty (RSA) is possible.
