1.3  Atraumatic Instability

• As mentioned in MODULE 1, atraumatic instability has no seemingly obvious mechanism
  of injury or cause of onset. Atraumatic shoulder instability is characterised by aberrant
  motor patterning of the scapula and humeral head superimposed on a background
  of congenital capsular hypermobility (Ref).
• This sub-group of instability is associated with a higher rate of congenital anomalies
  such as glenoid retroversion, glenoid hypoplasia, absent labral tissue, a voluminous
  joint capsule and wide rotator intervals (ref).
• There is a higher incidence of GLL and collagen disorders (Ehler’s Danlos and Marfan’s
  Syndrome) in patients with atraumatic shoulder instability.
• In atraumatic instability the patient may be aware that they have hypermobile shoulders
  as well other hypermobility in other synovial joints if generalized ligamentous laxity is
  present. In this case, they may report that they have always had clicking or clunking
  shoulders and may even be able to demonstrate spontaneous voluntary subluxations
  of the humeral head which called “volitional instability” (ref).
• In other situations, the patient may have no awareness of any hypermobility in their
  shoulder girdle.
• It is common for patients with atraumatic instability to report that they have always
  had poor posture as they typically sit with their scapula in depression and downward
  rotation at rest. This creates a “dropped” shoulder girdle position which contributes
  to poor posture.
• Hypermobile shoulders often have less shoulder girdle muscle bulk than other populations,
  (Simmonds & Keer, 2007) which is possibly due to alterations in hormonal
  (Denko & Boja, 2001), collagen(Malfait et al., 2006) (Child, 1986)and muscle fibre (ref)
  type proportions.
• Symptoms are typically a combination of pain, avoidance, feelings of “looseness”
  or that the joint is “out of place”, loss of control in certain motions and restriction of range
  of motion (due to uncontrolled and excessive HH translations blocking motion) (ref).
  Apprehension may be reported but is less common (ref). Shoulder range of motion
  (particularly those that cause symptoms) can produce GHJ clicking (see more in aggravating
  factors and symptomology section).
• As patients with atraumatic shoulder instability will typically have two or more directions
  of instability (ref) patients may report symptoms in multiple GHJ positions (ref). Most patients
  will have a primary direction of instability where their symptoms are more severe (ref)
• In some patients, spontaneous subluxations are reported that can be voluntary (controlled
  by the patient) or involuntary (uncontrolled by the patient) or a combination of both.
• Pain is often due to secondary rotator symptoms. The rotator cuff may be overloaded
  due to excessive fatigue from trying to control the HH (often in a poor length tension
  relationship due to poor scapula position),(ref) or the subluxing or translating HH causes
  excessive compression and/or traction on the rotor cuff tissues (particularly the articular
  surface) which generates pain (ref)
• Patients may also describe a deep, vague pain inside the GHJ that can hard to localize.
  This pain is often associated with a particular movement in which there is loss of HH control;
  such as reaching across the body in posterior dominant atraumatic instability (ref).
• The history of onset is usually associated with increased symptoms after an increase
  in activity level (such as swimming) or commencement of an unfamiliar activity such as
  taking on a new sport or gym which they have not previously done
• Onset can also occur with waking up one morning with pain after sleeping awkwardly
  on their shoulder
• It can be associated with increased fatigue levels such as carrying a heavy school
  bag or backpack
• Or there can be spontaneous onset of subluxation events that don’t seem to have
  any provocation factor – such picking up a school bag or taking off a tight top
• In atraumatic instability the patient will have symptoms in two directions (posterior-
  inferior or anterior-inferior) or all three directions (anterior, posterior and inferior).

Shifting sub-groups

• It is important to be aware that patients can shift sub-groups within their clinical history.
  For example, a patient may have a history of atraumatic instability (reporting they’ve
  always been “loose and clunky” since a child and been able to voluntarily sublux their shoulder
  free from pain). Later, they’ve fallen over in the shower, dislocated their shoulder (which
  required reduction) and sustained a structural lesion. The patient now presents with maco-
  traumatic instability superimposed on a background of atraumatic instability.
• Patients may also develop macro-traumatic instability on a background of mico-
  traumatic instability. For example, a swimmer that has been having significant shoulder
  pain from over training may have a sudden posterior subluxation event diving into the
  pool at the start of their race. This patient now has macro-traumatic instability superimposed
  on a previous history of micro-traumatic instability.
• Patients may develop micro-traumatic instability on a background of atraumatic instability.
  The hypermobile, MDI type patient may start a boot-camp or push up challenge in the gym
  and develop micro-traumatic instability (and possibly acquire structural lesions) over a period
  of weeks or months.