Total shoulder - does the CT measurement of glenohumeral offset matter?

A reliable method of determining glenohumeral offset in anatomic total shoulder arthroplasty

These authors obtained preoperative and postoperative CT scans on 37 patients having total shoulder arthroplasty to measure glenohumeral offset (GHO) to determine its effect on shoulder function. 

They found a mean increase in GHO of 4.3 mm (standard deviation, 4.6; range, from  -10.6 to +10.8) after surgery. No associations were observed between change in offset and functional or strength scores. 

Comment: Two observations are worth making about this study. (1) the range in offset was huge, varying from 1 cm of increased medicalization to 1 cm of lateralization. (2)  the change in offset did not significantly effect the change in Constant score.

In our practice, we routinely insert a standard thickness all polyethylene glenoid component with minimal reaming of the glenoid bone. This may result in an increase of 2 to 3 millimeters of lateral offset. On the humeral side, the thickness of the humeral head component is selected to allow internal rotation to 60 degrees with the arm abducted to 90 degrees, 50% posterior translation on the drawer test. and 150 degrees of flexion. Thus the net change in glenohumeral offset is determined by the preoperative pathoanatomy and the soft tissue balance.

Determining the change position of the tuberosity in relation to the scapula can be a helpful tool for assessing (a) the degree of medial erosion preoperatively and (b) the degree to which the tuberosity is lateralized after surgery (recognizing that excessive tuberosity lateralization can placed increased tension on the rotator cuff, "overstuffing").

Rather than obtaining CT scans we use the lateral acromial line on the plain film AP in the plane of the scapula (Grashey view) to indicate the relative position of the tuberosity and scapula as shown in the images below.

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Lateral humeral offset in shoulder arthroplasty

Association of lateral humeral offset with functional outcome and geometric restoration in stemless total shoulder arthroplasty

These authors obtained three CT scans on each of 44 patients having stemless total shoulder arthroplasty: (1) preoperative for the osteoarthritic shoulder, (2) for the contralateral healthy shoulder and (3) for the operated shoulder after surgery. They also obtained preoperative and postoperative clinical outcome measures at a minimum follow-up of 12 months (range, 12-50 months).

They measured lateral humeral offset (LHO) as the distance between the medial edge of the base

of the coracoid process and the most lateral border of the greater tubercle. 

                             

 

 The postoperative difference in LHO between the operated shoulder after surgery and contralateral healthy shoulder was 1.3 ± 4.6 mm. Lengthening of LHO was associated with worsening shoulder function at 3 months but not at 12 months. 

Comment: Determining the position of the tuberosity in relation to the scapula is a helpful tool for assessing (a) the degree of medial erosion preoperatively and (b) the degree to which the tuberosity is lateralized after surgery (recognizing that excessive tuberosity lateralization can placed increased tension on the rotator cuff, "overstuffing").

Rather than obtaining CT scans we use the lateral acromial line on the plain film AP in the plane of the scapula (Grashey view) to indicate the relative position of the tuberosity and scapula as shown in two different patients below.

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