Sternal instability results from infection and /or disruption of the wires connecting the surgically divided sternum resulting in separation, pain and excessive motion of the sternal edges. Factors that significantly increase the risk of sternal infection or instability in patients following median sternotomy include: female gender with large breasts, diabetes mellitus, obesity, bilateral internal mammary artery harvesting, reoperation procedures, increased blood product requirement and excessive coughing.
Sternal instability is often reported by patients as a clicking, clunking or increased movement of the sternum that results in pain and discomfort with activities of daily living (ADL) such as reaching, rolling over in bed and getting up out of a chair. The clinical sequence of sternal instability is illustrated below. As sternal non-union may lead to mediastinitis or deep sternal wound infection, early detection and management are essential.
Sternal stability assessment
The diagnosis of sternal instability can be reliably made by Real-Time Ultrasound Imaging, or physical assessment of the sternum employing the Sternal Instability Scale (SIS).
As part of the assessment process, clinicians should ask patients about the following:
- Pain quality and location– intermittent/constant, dull/sharp, hot/cold, deep/superficial
- Feelings of instability or excessive motion – e.g., patient reports that their chest 'feels like it is going fall open'
- Sounds – ‘clicking’, ‘clunking’
- Activities that provoke symptoms (‘unstable feeling’, pain, clicking or crepitus)
- State of the wound or scar including the colour, sensitivity to temperature, discharge (serous or coloured), hypersensitivity, and presence of keloid scarring or adhesions
Modified Sternal Instability Scale (SIS)
The Modified Sternal Instability Scale (SIS), (see table below), is a reliable scale for physical assessment of the sternum for stability. This scale prompts health professional to assess and grade sternal instability to ensure consistent in reporting of this complication and to prompt timely referral and management to the cardiac surgeon if warranted.
||Clinically stable sternum (no detectable motion) – normal
||Minimally separated sternum (slight increase in motion)
||Partially separated sternum – regional (moderate increase in movement)
||Completely separated sternum – entire length (marked increase in motion)
The upper and lower regions of the sternum should be assessed separately as the lower sternum is often more unstable than the upper region. Palpate between the sternal halves using the 2nd, 3rd and 4th digits (as shown in the figure below) during:
- Shoulder flexion (unilaterally and/or bilaterally)
- Trunk lateral flexion and/or rotation
- Coughing and deep inspiration/expiration
Select the grade that corresponds with the findings of the physical examination. If the SIS grade is 2 or 3, notify the medical practitioner to ensure timely medical management if required (e.g., surgical re-wiring).
It is recommended that the sternum be assessed i) 3 to 5 days post-cardiac surgery, ii) at the commencement of cardiac rehabilitation (3 to 6 weeks post surgery) and iii) prior to commencing exercise involving upper limb advanced stretches and weights or pulleys (unilateral). Patients diagnosed with sternal instability will need monitoring every 3 to 4 weeks.
Figure: Physical assessment of sternal instability
Management of Sternal Instability
For those with established sternal instability, a return to theatre for surgical re-wiring is often necessary. At times, this option is not available if bone quality is poor or confounding risk factors for re-operation exist.
Patients with sternal instability should continue to follow the “Keep Your Move in the Tube” method to ensure safe performance of transfers and daily tasks.
A medication review may be necessary for those with a dry, non-productive cough secondary to medications (e.g., ACE inhibitors) to minimise risk of sternal instability.
In some instances, external bracing, such as the “Qualibreath” (see figure below), may be recommended to:
- Provide an interim measure prior to surgical repair
- Minimise symptoms of pain
- Prevent the progression of a minimally unstable sternum
All women should be encouraged to wear a supportive bra, with wide straps and no underwire, early in the post-operative period to ensure support for their breasts and to minimise undue stress on the healing sternum and associated wound. Whilst many women use a standard firm fitting sports bra, commercial options which are specifically designed for this purpose, are available. An example of this is the “Qualibra” (shown below).
Reproduced with permission from HjorthHealth Pty Ltd, 2012
The table below summarises recommended management approaches for patients with sternal instability.
||Clinically stable sternum (no motion) - normal
||Minimally separated sternum (sligh increase in motion)
||Record in the medical record and continue to monitor if the patient is symptomatic
||Partially separated sternum - regional (moderate incrase in movement)
Referral to medical practitioner for review
Regular monitoring of sternal instability +/- orthopaedic bracing (sternal brace)
||Completely separated sternum - entire length (marked increase in motion)
||Referral to medical practitioner and/or cardiothoracic surgeon for review +/- orthopaedic bracing (sternal brace)