Total Shoulder Arthroplasty: Glenoid Component - Wheeless' Textbook of Orthopaedics

- Discussion:
- indications are controversial;
    - increased glenoid loosening rates from eccentric loading & excessive wear can be expected with w/ rotator cuff arthropathy;
    - component design:
           - Radiographic comparison of pegged and keeled glenoid components.
           - The radiographic evaluation of keeled and pegged glenoid component insertion.
           - A study of micromovement of pegged and keeled glenoid components compared using radiostereometric analysis.
           - Three-D element analysis of glenoid replacement prostheses: a comparison of keeled and pegged anchorage systems.
           - Stability of Cemented in-Line Pegged Glenoid Compared with Keeled Glenoid Components in Total Shoulder Arthroplasty

    - glenoid version:
- in the report by RS Churchill MD et al, 344 human scapular bones (172 matched pairs) were measured for their glenoid height, width, inclination, and version;
           - overall glenoid version for the entire study group was 1.23° of retroversion;
           - average glenoid version for black and white patients measured 0.20° and 2.65° of retroversion, respectively (P = .000014);
           - no statistical difference in glenoid version was found between men and women of the same race;
- ref: Glenoid size, inclination, and version: An anatomic study. R. Sean Churchill, MD. J Shoulder Elbow Surg 2001;10:327-32
- bone loss:
- posterior bone loss:
    - many w/ osteoarthritis have posterior glenoid bone loss, where as pts w/ rheumatoid arthritis may have central (medial) erosion;
      - if postior glenoid erosion is present, it may be necessary to alter amount of humeral retroversion from nl 35 deg to a less retroverted position;
    - hence the glenoid will be positioned in more retroversion than normal, but the humeral head will be in less retroversion, and therefore the two
      will balance each other out;
    - w/ more substantial posteior erosion, then a glenoid component w/ posterior augmentation will be necessary;
- central bone loss:
      - in many cases, can be managed w/ bone grafting or use of a larger portion of cement;
                  - references:
    - Glenoid bone-grafting in total shoulder arthroplasty.
    - bone grafting for glenoid components:

    - center point for reaming:
           - center point: lateral aspect of the subscapularis fossa at a point midway between the superior and lateral borders of the scapula;
           - true center of the glenoid is slightly inferior to midpoint - this is the point of slippage of the humeral head during concentric motion;

    - cement mixing technique:
            - The effect of cementing technique on structural fixation of pegged glenoid components in total shoulder arthroplasty.

- Complications:
- excessive offset (over stuffing the shoulder):
- "over-stuffing the shoulder" with placement of a glenoid component will lateralize the humeral component and will place the subscapularis
tendon under increased tension and risk rupture;
- avoid excessively large components and neck lengths since this will increase capsular tension and will result in decrease in motion and increase instability;
- surgeon should be able to pass one finger between the acromion and the prosthetic head, should be able to inferiorly translate the humeral
head so that one half of the glenoid is exposed;
- humeral head component should allow enough posterior translation in order to allow exposure of anterior half of glenoid (15 mm of posterior translation);
- the abducted arm should allow 70 deg of internal rotation and 40 deg of external rotation;
- overstuffing the joint is more likely with total shoulder replacement (rather than hemiarthroplasty) because the glenoid component will add to the offset;
- glenoid lossening:
- radiolucencies around the glenoid component will eventually be seen in 60% of patients;
- some authors note that in many cases radiographs may fail to show loosening because xray beam is not perpendicular to the bone-component interface;
- flouroscopically positioned radiographs may improve radiographic diagnosis of loosening;

Total shoulder arthroplasty versus hemiarthroplasty for rheumatoid arthritis of the shoulder: Results of 303 consecutive cases