Sternal Instability and Non-Union Screening After Median Sternotomy

Median sternotomy remains the gold standard surgical incision for complex open-heart procedures, including coronary revascularisation and valvular reconstructions. While the vast majority of sternotomies achieve solid bony union within 8 to 12 weeks, approximately 1 to 3 percent develop sternal instability, pseudoarthrosis, or non-union. Sternal instability occurs when the divided bony halves fail to consolidate, permitting abnormal translational micromotion, clicking, and persistent anterior chest wall pain. Cardiopulmonary physiotherapists employ standardized clinical screening tools and physical palpation tests to detect early mechanical failure, preventing progression to deep sternal wound infection.

Domestic and Cultural Indian Realities

Certain clinical and lifestyle factors heighten sternal instability risk in the Indian patient demographic. High prevalence of poorly controlled type 2 diabetes mellitus compromises microvascular bone perfusion and impairs collagen synthesis. Post-menopausal Indian women with undiagnosed thoracic osteopenia are particularly prone to surgical wires cutting through brittle sternal cortical bone (wire cut-through). Domestically, premature resumption of heavy household tasks, such as hauling 20-litre water buckets, manually hand-washing heavy clothes, or grinding spices with a stone pestle, subjects the healing chest to shear forces that precipitate wire loosening.

Clinical Biomechanics and Sternal Non-Union Pathophysiology

Bone healing requires rigid mechanical fixation, intimate contact between cancellous surfaces, and adequate vascular supply. Stainless steel cerclage wires provide initial compression, but repetitive mechanical forces from coughing, upper limb movements, and respiratory excursions challenge this fixation. When asymmetric traction is applied through the pectoralis major muscles, shear stress across the sternotomy line disrupts capillary ingrowth and early osteoid bridging. If motion persists, fibrous tissue forms instead of lamellar bone, creating an unstable pseudoarthrosis. Chronic instability leads to wire fatigue, wire fracture, and chronic chest pain during breathing.

Bedside Clinical Evaluation and Risk Stratification

Clinical evaluation utilizes the validated Sternal Instability Scale (SIS), which grades stability from 0 to 3 based on manual palpation during specific upper limb and respiratory maneuvers. Grade 0 denotes a clinically stable sternum with no detectable motion. Grade 1 indicates minimal motion or clicking during deep breathing or coughing. Grade 2 represents moderate motion or marked separation with unilateral upper limb movement. Grade 3 signifies gross separation and movement of the sternal edges during quiet respiration. Clinicians palpate both sternal borders while the patient performs bilateral shoulder flexion, deep inspiration, and supported coughing.

Structured Rehabilitation and Movement Protocols

When mild sternal instability (Grade 1) is detected in the absence of active infection, conservative management focuses on external stabilization and activity restriction. Patients are fitted with a specialised rigid or elastic sternal support harness to limit lateral distraction. Upper extremity exercises are strictly modified: bilateral simultaneous reaching overhead is restricted, lifting weights is limited to under 2 kilograms, and all pushing and pulling actions are paused. Isometric core stabilization and gentle diaphragmatic breathing are maintained to prevent ventilatory deconditioning.

Red Flags and Specialist Escalation

Sternal instability complicated by signs of infection requires urgent surgical escalation. Clinicians and patients must watch for fever, chills, persistent purulent wound drainage, focal redness, wound dehiscence with exposed wires or bone, or a sudden increase in localized deep throbbing pain. The presence of paradoxical chest wall movement (flail sternum) or acute dyspnoea represents an emergency warranting immediate hospital admission to exclude deep mediastinitis.

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