Rockwood Adults CH34

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CHAPTER 34 • Glenohumeral Instability

Evaluation of Glenoid Bone Loss The amount of glenoid bone loss significantly impacts the out- come and recurrence rate after arthroscopic Bankart repair. Burkhart et al. 31 reported a high recurrence rate of 67% after arthroscopic Bankart repair in patients with more than 25% preoperative glenoid bone loss. However, in patients without significant bone loss, the recurrence rate was 4%. Biomechani- cal studies have also confirmed the above findings and showed that an osseous defect that is > 21% of the glenoid length caused instability and limitation of shoulder ROM after Bankart repair. 107 Thus, it is critical to evaluate the exact amount of glenoid bone loss preoperatively to indicate patients for either arthroscopic repair or bone procedure. Once a critical threshold is met for bone loss, there is a higher failure rate of arthroscopic Bankart repair; other repair options, such as a Latarjet, should be consid- ered for surgical management. Various methods, including calculating the glenoid width, length, and surface area, have been developed to measure the amount of bone loss in a standardized fashion. Burkhart et al. proposed a unique method of quantifying glenoid bone loss arthroscopically using the center of the glenoid or the bare spot. Using a probe of 3 mm, the distance from both the anterior (Da) and the posterior margin to the bare spot (Dp) is measured. Amount of glenoid bone loss is defined as (Dp − Da)/2 × Dp × 100. However, the bare spot was not con- sistently located at the center of the glenoid. Miyatake et al. 156 evaluated the accuracy of using the bare spot arthroscopically and found that in 29% of patients (10 shoulders), there was a greater than 5% difference from the standard 3D CT mea- surements. Several authors have described different methods of using either unilateral 2D CT images or 3D CT utilizing an assumed inferior circle of the glenoid on the affected side comparing it

rapidly acquired, and provide excellent fine bony detail. Ante- rior shoulder dislocations can often lead to glenoid bone rim fractures (bony Bankart lesion), and repeated subluxations or dislocations can remodel the anterior-inferior glenoid. 226 Such pathology is well imaged by CT, as the imaging can detect the smallest osseous fragments and glenoid asymmetry. When acquired with high resolution and thin slices, 3D volume-rendered reformats can also be created with the humeral head digitally subtracted providing further visualization of the glenoid fossa for preoperative planning and measurement or calculation of the amount of bone loss. In the evaluation of the posterolateral humeral head com- pression fracture, also called the Hill–Sachs lesion, CT scans with 3D reconstruction images provided a similar diagnostic accuracy to arthroscopy. However, a purely cartilaginous defect of the posterior superior humeral head was difficult to diagnose with CT imaging. The prevalence and size of the Hill–Sachs lesions was also directly related to the number of subluxations or dislocations. 179 While isolated Hill–Sachs lesions or those associated with small Bankart lesions may be less clinically significant, bipolar lesions (Hill–Sachs and Bankart lesions occurring together) may require the surgeon to address both- sided pathology with arthroscopic Bankart repair and humeral head remplissage to maintain stability and minimize failure. 147 Nakagawa et al. 161 found that the prevalence of bipolar lesions was 33% in shoulder with primary instability and 62% in shoul- ders with recurrent instability. The size of the Hill–Sachs lesion was directly correlated with the size of the glenoid lesion. Post- operative recurrence of instability or failure of surgery was 29% in patients with bipolar lesions. Thus, if such bipolar lesions are suspected, CT scan with 3D reconstruction is critical for the identification and sizing of these lesions to direct surgical management and improve outcome in patients with shoulder instability (Fig. 34-23).

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Figure 34-23.  Bipolar lesion with CT to show both glenoid bone loss and humeral head bone loss or Hill– Sachs lesion. A: Axial CT image shows the large Hill–Sachs lesion on the posterior humeral head ( arrow ). B: Axial CT image shows the large anterior bony Bankart lesion with glenoid bone loss. ( continues )