Authors: Tyler Billings PT, DPT, Cert. MDT
Bryan Wright PT, DPT, Cert. MDT, OCS – Feb, 2017
Every human being can be classified within the broad spectrum of joint mobility. This spectrum begins and ends respectively with the especially loose (hypermobile) to excessively tight joints (hypomobile). Both hypermobility and hypomobility can lead to injury or be a result of injury. This article explores the definitions of stability and instability broadly. It also identifies implications of rehabilitation to the non-operative, unstable shoulder.
WHAT IS INSTABILITY
Stability is a combination of the function of your static and dynamic stabilizing systems. Static stabilizers include ligaments and capsules that surround the joint. The dynamic stabilizers include soft tissue muscular networks that work synergistically together in their timing to stabilize a joint.
Instability denotes excessive segmental motion of a specific area of the body that results in pain and possible subluxation or dislocation. It is critical to note that laxity and instability are not the same thing. While both laxity and instability consist of excessive joint motion in the body, only instability occurs symptomatically. Furthermore, where laxity is not a pathological syndrome and is considered a normal occurrence in the human body, instability is a pathology that affects either the static and/or dynamic stabilizers. Laxity, implies a degree of translation at a joint that falls within a physiological range of acceptable motion and is not symptomatic.
Instability can be found in multiple areas of the body with some areas having a much higher rate of incidence. The shoulder is the most moveable joint in the body and because of its tremendous amounts of motion it is the joint most prone to instability and dislocation.
TYPES OF SHOULDER INSTABILITY – TUBS and AMBRI
Shoulder instability is the inability to maintain the humeral head in its optimal placement in the glenoid fossa. When a joint has poor osseous congruency and capsular laxity, it greatly relies on the dynamic stabilizers and neuromuscular system to provide functional stability.
A wide range of shoulder instabilities exist from subtle subluxations to gross instability. These can be congenital multi-directional instabilities all the way to traumatic uni-directional dislocations. The glenohumeral joint is categorized into two broad categories of instability: Traumatic and Atraumatic.
Acronyms help us delineate these categories and assist in powerful rehab prescription. They are referred to as TUBS and AMBRI, and will be defined briefly in the following.
TUBS – (Traumatic Etiology, Unilateral Dislocation, Bankart lesion, Surgery often needed)
A traumatic complete shoulder dislocation in an anterior direction to one shoulder which often results in a bankart lesion. This lesion is where the anterior capsule of the shoulder avulses off the gleaned rim. Often, TUBS requires surgery, depending on the extent of damage that has occurred.
AMBRI – (Atraumatic Etiology, Mulit-directional instability, Bilateral, Rehab Potential, Inferior capsular shift)
A non- traumatic event usually consisting of both shoulders and normally does not involve dislocation. AMBRI has multi-directional instability, which means that it translates excessively in multiple planes of movement. This type of shoulder pathology more likely stems from congenital conditions and has high rehabilitation potential. The AMBRI shoulder will usually have inferior capsule laxity that causes that inferior portion of the capsule to shift. In the event the inferior shift is too excessive, it may require surgery to stabilize.
Based on the classification of shoulder instability, as well as several other factors, a non-operative rehabilitation program may be developed.
7 KEY FACTORS – A REHAB PROGRAM FOR AN UNSTABLE SHOULDER
1. ONSET OF PATHOLOGY
The first factor to consider is knowing if the shoulder instability resulted from a traumatic event or whether it is chronic with recurrent instability. The goals and the rehabilitation program may vary greatly based on the onset of mechanism of injury. Following a traumatic dislocation or subluxation the patient typically presents with significant soft tissue trauma, pain, and apprehension. The patient is progressed based on the patient’s symptoms with emphasis on early controlled range of motion (ROM), reduction of muscle spasm and guarding, and relief of symptoms.
Conversely, a patient that presents with atraumatic instability often has a history of repetitive injuries and symptomatic complaints. Often there is not a single instability episode but, a feeling of shoulder laxity or inability to perform tasks. Rehabilitation for this patient focuses on early proprioception training, dynamic stabilization drills, neuromuscular control, scapular muscle exercises, and muscle strengthening to enhance dynamic stability due to the unique characteristics of excessive capsular laxity.
2. DEGREE OF INSTABILITY
Various degrees of instability exist such as subtle subluxation or gross instability. These degrees of instability need to be assessed by a skilled examiner in order to first, determine the amount of translation between the humeral head and the glenoid. Second, to assess the end feel to each directional stress applied. Third, attempt to reproduce the patient’s symptoms and/or apprehension. With a proper assessment, the shoulder may be able to be classified with a specific type and degree of shoulder instability.
Subluxation refers to the complete separation of the articular surfaces with spontaneous reduction. Dislocation is a complete separation of the articular surfaces and requires an external force to relocate the joint, resulting in capsular tissue damage. The degree of tissue trauma can be great and with a subluxation or dislocation. If a dislocation occurs, majority of the time it is associated with a Bankart lesion. This is where the anterior capsule of the shoulder avulses from the glenoid rim. The rate of progression for a rehabilitation program will vary based upon the degree of instability and persistence of symptom
3. FREQUENCY OF DISLOCATION
A first time traumatic dislocation is often treated conservatively with physical therapy and immobilization in a sling with early controlled passive range of motion. Traditionally, immobilization has occurred with the shoulder in a sling by the person’s side. A study published in 2001 by Itoi in the Journal of Bone and Joint surgery suggests that the anterior capsule tissue was better approximated in the externally rotated position. The results in the study showed that there was increased recurrent instability rate in those immobilized in the traditional at the side sling position, compared to those immobilized in external rotation.
The incidence of recurrent dislocation ranges from 17%-96% with a mean of 67% in patient populations between ages 21-30 years old. Therefore, the rehabilitation program in young athletes should progress cautiously. Hovelius et al demonstrated that the rate of recurrent dislocations is based on the patient’s age and not affected by the length of post-injury immobilization. Individuals between ages 19-29 are the most likely to experience multiple episodes of instability. Hovelius et al noted patients in their 20’s had a recurrence of 60% whereas, patients in their 30’s to 40’s had less than 20% recurrence rate. In an adolescent, the recurrence rate is as high as 92% and 100% with an open physes.
Chronic subluxations, as seen in the atraumatic category may by treated more aggressively due the the lack of acute tissue damage and less muscular guarding and inflammation. Caution is always placed on excessive stretching of the involved joint capsule.
4. DIRECTION OF INSTABILITY
The three most common forms of instability are anterior, posterior, or multi-directional. Anterior instability is the most common traumatic type of instability that is seen in the general orthopedic population, representing 95% of all traumatic shoulder instabilities. Following a traumatic event in which the humeral head is forced into extremes of abduction and external rotation, the glenolabral complex and capsule may become detached from the glenoid rim resulting in anterior instability. This type of detachment is referred to as a Bankart lesion. The drawing to the left illustrates a Bankart lesion. The arrow denotes the avulsed capsule from the glenoid.
Posterior instability occurs less frequently and only accounts for 5% of traumatic shoulder dislocations. This type of instability is often seen following a traumatic event of an outstretched hand or from a pushing mechanism. However, patients with significant atruamatic laxity may complain of posterior instability, especially with shoulder elevation.
Multi-directional instability (MDI) can be identified as shoulder instability in more than one plane of motion that is atraumatic. Patients with MDI have congenital predisposition and exhibit ligamentous laxity due to excessive collagen elasticity of the capsule. This patient will usually display greater than 8-10 mm during the sulcus maneuver, suggesting congenital laxity (See picture).
Due to the atraumatic mechanism and lack of tissue damage, ROM is often normal to excessive with inadequate static stabilizers. The rehabilitation focus for those with MDI is on progressively maximizing dynamic stability by gaining balance in the RTC, scapular positioning, proprioception, and improving neuromuscular control in multiple planes of motion.
5. CONCOMITANT PATHOLOGIES
Disruption of the anterior capsulolabral complex occurs during a traumatic injury resulting in an anterior Bankart lesion. Often an osseous lesion occurs such as a Hill Sach’s lesion which is caused by compression impact on the posterolateral aspect of the humeral head as it relocates back into the glenoid. Occasionally, a bone bruise may be present in individuals who have sustained a shoulder dislocation as well as pathology to the RTC. Other common injuries involve the superior labrum (SLAP lesion). These concomitant lesions may significantly slow down the rehabilitation program and return to function.
6. NEUROMUSCULAR CONTROL
Neuromuscular control is defined as the efferent, or motor, output in reaction to an afferent, or sensory input. The afferent input is the ability to detect the glenohumeral joint position and motion in space with resultant efferent response by the dynamic stabilizers to assist in stabilization of the humeral head. An injury that results in insufficient neuromuscular control could result in deleterious effects to the patient. As a result, the humeral head many not center itself within the glenoid, thus compromising the surrounding static stabilizers. Lephart et al compared the ability to detect passive motion and the ability to reproduce joint positions in patients with normal, unstable, and surgically repaired shoulders. The author reports a significant decrease in proprioception and kinesthesia in unstable shoulders.
Proprioception is the unconscious perception of movement and spatial orientation arising from stimuli within the body system that is detected by the nervous system. The unstable shoulder patients require neuromuscular control and proprioceptive training to reduce further injury and to aide in full recovery of function.
7. ACTIVITY LEVEL
The final factor to consider in the non-operative rehabilitation of an unstable shoulder is the arm dominance and the desired activity level of the patient. If the patient frequently performs overhead activity/sports such as tennis or volleyball, then the rehabilitation program should include sport specific dynamic stabilization exercises, plyometrics, and neuromuscular control drills in the overhead position once full, pain free ROM and adequate criteria are met. The success rates of patients returning to an overhead sport after dislocating their dominant shoulder are low with non-operative treatment. The recurrence rates of instabilities of the shoulder vary based on age, activity level, and arm dominance.
The glenohumeral joint is a less stable joint that relies on the interaction of both the dynamic (muscular) and static stabilizers (ligaments/capsule) in order to maintain congruency in the joint and maintain stability. Patients may be classified into two types of shoulder instability – Traumatic (TUBS) and Atraumatic (AMBRI). Rehabilitation will vary based on the type of stability present and the 7 key principles discussed. Disruption of how the stabilizers interact or poor development of any of these factors may result in instability, pain, and loss of function.
We are commonly asked how we maintain a high level of attention to these factors across all of our clinics. We frequently gather together with all of our doctors of physical therapy to better integrate the examination and the 7 key factors of treating the unstable shoulder. We look forward to collaborating with you in helping your patients achieve life changing outcomes. Please email firstname.lastname@example.org with any questions or call us at any of our 6 Magic Valley locations.