Rockwood Adults CH34

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CHAPTER 34 • Glenohumeral Instability

Gyftopoulos et al. 80 recently evaluated the diagnostic accu- racy of using the circle method on MRI in calculating glenoid bone loss compared to the standard 3D CT imaging. They found MRI accuracy was only 1.3% different overall compared with the CT imaging and concluded that using the circle method with MRI can be an accurate alternative to 3D CT. Owens et al. 173 pro- posed an equation for predicting the normal glenoid width in both males and females for calculating glenoid bone loss. They evaluated 1,264 MR images and found that glenoid width was correlated to the glenoid height measurements and that males and females were different in their respective measurements. The formula for normal glenoid width in males is (1/3 height) + 15 mm and in females is (1/3 height + 13 mm). With this stan- dardized formula, it is possible to make accurate calculations of the amount of glenoid bone loss with only a digital ruler and an MRI of the injured shoulder. Critical Glenoid Defect Size The size of the glenoid bone defect is a major risk factor for fail- ure after arthroscopic repair due to altered mechanics and the effect on the stability of the shoulder. 137 The prevalence of glenoid rim lesions has been reported as high as 90%, including 50% of bony Bankart lesions and 40% erosion of the anterior glenoid in patients with recurrent shoulder instability. 227 Recurrence rate after arthroscopic stabilization is unacceptable in patients with significant bone loss or an inverted pear glenoid morphology. 31 Lo et al. 137 demonstrated in a cadaver study that the inverted pear glenoid indicated at least 25% to 27% loss to the anterior-infe- rior glenoid width. It is essential for surgeons to look for and accurately calculate the amount of anterior glenoid bone loss to properly indicate patients for surgery between arthroscopic repair and bony procedures (Latarjet, bone grafting, etc.). Historically, 20% to 25% of anterior glenoid bone loss was defined as the “Critical” cutoff that needs to be addressed with a bone procedure at the primary operation. 31,32 Recently, the idea of “Subcritical” bone loss was introduced by Shaha et al. 209 in a study that reported significantly worse outcomes in patients with > 13.5% glenoid bone loss after arthroscopic Bankart repair and recommended addressing these patients with either Latarjet or an additional combined procedure to further stabilize the shoul- der and decrease the risk of recurrence. The authors evaluated 75 anterior instability patients who underwent arthroscopic repair in a military institution. The cohort was divided into quartiles based on bone loss. In patients who failed with recurrent insta- bility, the amount of glenoid bone loss was significantly higher than the group that did not fail (25% vs. 13%). Furthermore, the authors also found that bone loss greater than 13.5% led to a clinically significant increase in the Western Ontario Shoulder Instability scores consistent with unacceptable outcome even in the subset of patients who did not sustain a recurrent disloca- tion. Shin et al., 211 in a similar study, reported 17.3% bone loss as the “critical” value that led to surgical failure and recurrence of instability after arthroscopic repair. In the patient group with less than 17.3% bone loss, the failure rate was 3.7% compared with a 42.9% failure rate in the group with over 17.3% bone loss. Bio- mechanically, a recent study also reported glenoid defects of over 15% or more of the largest anteroposterior glenoid width as the

“critical” bone loss amount in which a soft tissue repair cannot restore normal glenohumeral translation. This restricts rotational ROM and leads to abnormal humeral head translation. 212 CLASSIFICATION OF GLENOHUMERAL INSTABILITY The spectrum of shoulder instability ranges from subluxation to locked-dislocation. Subluxation is defined as the translation of the humeral head against the glenoid without complete separa- tion of the articular surfaces and spontaneous reduction occurs when the abnormal force is removed and the humeral head reduces back to the normal anatomic position. A subluxation can occur in one of three types or directions: anterior, posterior, or inferior. The other end of the spectrum is dislocation where excessive translation of the humeral head results in complete sep- aration of the articular surfaces. In these instances, the humeral head does not self-reduce when the abnormal force is removed. These patients often require manual reduction maneuvers with either conscious sedation or muscle paralysis (usually in the operating room) to the humeral head to the anatomic position. Owens et al. 178 prospectively evaluated shoulder instability in 38 patients who sustained a first-time anterior glenohumeral sub- luxation event and proposed a new spectrum of injury termed “Transient luxation.” Transient luxation is between a subluxation and a dislocation as these patients experience a subluxation event that momentarily causes a separation of the articular surfaces but self-reduces. Furthermore, these patients will present with either a Bankart lesion on the anterior glenoid or a Hill–Sachs lesion on the posterior superior humeral head. A variety of classification systems for glenohumeral insta- bility have been proposed by various authors throughout the years. However, there is currently no universally accepted clas- sification system for glenohumeral instability. It is difficult to develop a comprehensive classification system for shoulder instability that can define the relevant etiology, mechanism, and pathology in every patient. Furthermore, none of these proposed classifications has undergone validation or reliability testing. Additionally, trying to define the appropriate treatment for each group within a classification has proven to be difficult. A well-defined classification system for glenohumeral insta- bility should help identify the pathology by the direction of instability, subluxation or dislocation, whether it is traumatic or atraumatic, primary or recurrent, the anatomic structures that are involved, the presence or absence of generalized joint lax- ity, voluntary or involuntary dislocations, and any underlying collagen or neuromuscular disorder. Furthermore, the classifi- cation should provide us with information regarding the natural history and prognosis as it relates to the instability event and offer recommendations regarding the treatment.

Glenohumeral Instability: FEDS SYSTEM CLASSIFICATION

FREQUENCY—Patient is asked, “How many episodes have you had in the last year?” a. Solitary—“1 Episode” b. Occasional—“2 to 5 Episodes” c. Frequent— “ > 5 Episodes”