# Chapter 3 Instability

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CHAPTER 3 | Instability

probe to measure the distance from the bare spot of the glenoid to the posterior glenoid rim. This measurement gives us the radius (R) of the glenoid. The diameter of the inferior glenoid is then calculated by doubling the radius: D R = 2 To calculate the glenoid bone loss (d), we measure two distances: the distance from the glenoid bare spot to the posterior glenoid rim (R 1 ) and the distance from the bare spot to the anterior glenoid rim (R 2 ). Glenoid bone loss (d) is then calculated: d R R = − 1 2 (Fig. 3-39) The glenoid track width is: GT D d = − 0 83. Since D = 30 and d = 5 in this case, GT = 0.83(30) − 5, or GT = 19.9 mm. Next, we arthroscopically determine the width of the Hill-Sachs interval (HSI) by measuring the width of the Hill-Sachs lesion (HS) and adding it to the width of the bone bridge (BB) at the same level: HSI HS BB = + (Fig. 3-40) Since HS = 12 and BB = 12 HSI = 24 mm. Once again, we compare the width of the glenoid track (GT) to the width of the Hill-Sachs interval (HSI). If HSI > GT, the Hill-Sachs lesion is off-track and will engage the anterior glenoid, and an arthroscopic remplissage must be performed in addition to an arthroscopic Bankart repair to prevent

engagement. However, if HSI < GT, an arthroscopic Bankart repair alone will suffice. In this case, HSI (24 mm) > GT (19.9 mm). Therefore, this Hill-Sachs lesion is off-track and will require arthroscopic remplissage in addition to arthroscopic FIGURE 3-39  Left shoulder, anterosuperolateral viewing portal. The calibrated probe, with 5-mm hash marks, has been introduced through a posterior portal. The radius of the glenoid is the distance from the bare spot of the glenoid to the posterior glenoid rim, or 15 mm (three hash marks). There has been some anterior bone loss, and the distance from the bare spot to the anterior glenoid rim is only 10 mm, indicating that there has been a 5-mm anterior glenoid bone loss.

FIGURE 3-40  A: The width of the Hill-Sachs lesion is measured sequentially by the 4-mm tip of the probe. The Hill-Sachs lesion has a width equal to three probe tips: 3 × 4 mm = 12 mm. B: The width of the bone bridge between the posterior cuff attachments and the Hill-Sachs lesion (H-S) is found to span three probe tips: 3 × 4 mm = 12 mm. G, glenoid.

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