Last week we began exploring some of the factors that I think are most important in designing rehabilitation programs for nonoperative shoulder instability. As we discussed, shoulder instability covers a very large group of people, and different types of instability will require modifications to our rehabilitation and training programs.
Key Factors in Shoulder Instability
Check out part 1 of this series on my key factors in the nonoperative shoulder instability rehabilitation to see my first 3 factors. Below I will summarize my final 3 key points.
Factor # 4 – Direction of Shoulder Instability
The next factor to consider is the direction of shoulder instability present. The three most common forms include anterior, posterior and multidirectional. Anterior shoulder instability is the most common traumatic type of instability seen in the general orthopedic population. It has been reported that this type of instability represents approximately 95% of all traumatic shoulder instabilities. However, the incidence of posterior instabilities appears to be dependent on the patient population. For example, in professional or collegiate football, the incidence of posterior shoulder instability appears higher than the general population. This is especially true in linemen. Often, these posterior instability patients require surgery as Mair et al reported 75% required surgical stabilization.
Following a traumatic event in which the humeral head is forced into extremes of abduction and external rotation, or horizontal abduction, the glenolabral complex and capsule may become detached from the glenoid rim resulting in anterior instability, or a Bankart lesion as discussed in part 1. Conversely, rarely will a patient with atraumatic instability due to capsular redundancy dislocate their shoulder. These individuals are more likely to repeatedly sublux the joint without complete separation of the humerus from the glenoid rim.
Posterior shoulder instability occurs less frequently, only accounting for less than 5% of traumatic shoulder dislocations. This type of instability is often seen following a traumatic event such as falling onto an outstretched hand or from a pushing mechanism. However, patients with significant atraumatic laxity may complain of posterior instability especially with shoulder elevation, horizontal adduction and excessive internal rotation due to the strain placed on the posterior capsule in these positions.
Multidirectional instability (MDI) can be identified as shoulder instability in more than one plane of motion. Patients with MDI have a congenital predisposition and exhibit ligamentous laxity due to excessive collagen elasticity of the capsule.
One of the most simple tests you can perform to assess MDI is the sulcus sign. I would consider an inferior displacement of greater than 8-10mm during the sulcus maneuver with the arm adducted to the side as significant hypermobility, thus suggesting significant congenital laxity. You can see this pretty good in this photo to the right, the sulcus is clearly larger than my finger width.
Due to the atraumatic mechanism and lack of acute tissue damage with MDI, ROM is often normal to excessive. Patients with recurrent shoulder instability due to MDI generally have weakness in the rotator cuff, deltoid and scapular stabilizers with poor dynamic stabilization and inadequate static stabilizers. Initially, the focus is on maximizing dynamic stability, scapula positioning, proprioception and improving neuromuscular control in mid ROM. Also, rehabilitation should focus on improving the efficiency and effectiveness of glenohumeral joint force couples through co-contraction exercises, rhythmic stabilization and neuromuscular control drills. Isotonic strengthening exercises for the rotator cuff, deltoid and scapular muscles are also emphasized to enhance dynamic stability.
Factor #5 – Neuromuscular Control
The fifth factor to consider is the patient’s level of neuromuscular control, particularly at end range. Injury with resultant insufficient neuromuscular control could result in deleterious effects to the patient. As a result, the humeral head may not center itself within the glenoid thereby compromising the surrounding static stabilizers. The patient with poor neuromuscular control may exhibit excessive humeral head migration with the potential for injury, an inflammatory response, and reflexive inhibition of the dynamic stabilizers.
Several authors have reported that neuromuscular control of the glenohumeral joint may be negatively affected by joint instability. Several research articles have been published looking at this. Lephart et al compared the ability to detect passive motion and the ability to reproduce joint positions in normal, unstable and surgically repaired shoulders. The authors reported a significant decrease in proprioception and kinesthesia in the shoulders with instability when compared to both normal shoulders and shoulders undergoing surgical stabilization procedures. Smith and Brunoli reported a significant decrease in proprioception following a shoulder dislocation. Blasier et al reported that individuals with significant capsular laxity exhibited a decrease in proprioception compared to patients with normal laxity. Zuckerman et al noted that proprioception is affected by the patient’s age with older subjects exhibiting diminished proprioception than a comparably younger population. Thus, the patient presenting with traumatic or acquired instability may present with poor neuromuscular control that must be addressed.
Factor # 6 – Pre-Injury Activity Level
The final factor to consider in the nonoperative rehabilitation of the unstable shoulder is the arm dominance and the desired activity level of the patient. If the patient frequently performs an overhead motion or sporting activities such as a tennis, volleyball or a throwing sport, then the rehabilitation program should include sport specific dynamic stabilization exercises, neuromuscular control drills and plyometric exercises in the overhead position once full, pain free ROM and adequate strength has been achieved. Patients whose functional demands involve below shoulder level activities will follow a progressive exercise program to return full ROM and strength. The success rates of patients returning to overhead sports after a traumatic dislocation of their dominant arm are low. Arm dominance can also significantly influence the successful outcome. The recurrence rates of instabilities vary based on age, activity level and arm dominance. In athletes involved in collision sports, the recurrence rates have been reported between 86-94%.
To summarize, nonoperative rehabilitation of shoulder instability has many subtle variations. To simplify my thought process, I always think of these 6 key factors before I decide what I want to do. For more information on the rehabilitation of shoulder instability, check out 7-week online CEU program at ShoulderSeminar.com that includes an entire week dedicated to this topic.
I hope these factors help you too. What other factors do you consider when designing rehabilitation programs for shoulder instability?