What are the management options for postoperative truncal shift and uneven shoulder level after surgical fixation of adolescent idiopathic scoliosis (AIS) and its effect on function?

Management of Postoperative Truncal Shift and Shoulder Imbalance After AIS Surgery

Postoperative truncal shift and shoulder imbalance are common iatrogenic complications occurring in approximately 9-58% of AIS patients after surgical correction, and while they typically improve spontaneously within 6 months, persistent deformities can significantly impact cosmetic appearance and patient satisfaction, requiring careful monitoring and potential revision surgery in severe cases.

Incidence and Natural History

• Iatrogenic truncal shift occurs in 8.8% of patients who had balanced trunks preoperatively, representing a true surgical complication 1
• Overall postoperative truncal shift prevalence is 13.6%, though surgery reduces the preoperative prevalence from 29.3% 1
• Shoulder imbalance is even more common, affecting up to 58% of patients postoperatively in Lenke 1C curves 2
• Lateral shoulder rebalancing occurs spontaneously up to 6 months after surgery, with radiographic shoulder height and coracoid height difference improving significantly during this period 3
• T1 tilt (medial shoulder asymmetry) does not change significantly postoperatively and may represent a more persistent problem 3

Primary Risk Factors for Persistent Deformity

For Truncal Shift:

• Undercorrection of the lumbar curve is the primary modifiable risk factor for postoperative truncal shift 1
• Higher preoperative thoracic apical vertebra-central sacral vertical line (AV-CSVL) translation increases risk 2
• Excessive thoracic deformity correction rate paradoxically increases trunk shift risk 2
• Shorter fusion constructs are associated with higher trunk shift rates 2

For Shoulder Imbalance:

• Postoperative apical vertebral translation (AVT) of the proximal thoracic curve is the strongest predictor of persistent shoulder imbalance 4
• Adding-on phenomenon (distal curve progression below the lowest instrumented vertebra) significantly contributes to shoulder imbalance 4
• A predictive index has been validated: PSI Index = 1.2 × postoperative AVT of PTC + 1.1 × adding-on angle, with a cutoff of 15 predicting shoulder imbalance with 80% positive and 87% negative predictive value 4

Functional Impact

• Radiographic indices correlate only weakly (r ≤ 0.7) with cosmetic appearance, meaning radiographs alone cannot fully assess the functional and psychological impact 2
• Cosmetic shoulder height and angle show particularly poor correlation with radiographic measurements 2
• Trunk shift on radiographs does significantly correlate with cosmetic trunk shift (P=0.004), making it a reliable indicator of visible deformity 2
• Posterior trunk symmetry index worsens significantly in patients with trunk shift (-7.94 vs. +16.53 improvement in balanced patients) 2

Management Algorithm

Immediate Postoperative Period (0-6 Months):

• Observe and reassure patients during the first 6 months, as spontaneous rebalancing occurs in the majority of cases 3
• Document baseline measurements including radiographic shoulder height, coracoid height difference, T1 tilt, and trunk shift 3
• Assess for adding-on phenomenon with serial radiographs 4
• Calculate PSI index if shoulder imbalance is present to predict likelihood of resolution 4

6-12 Months Postoperatively:

• If truncal shift or shoulder imbalance persists beyond 6 months, spontaneous improvement is unlikely 3
• Obtain clinical photographs to assess cosmetic impact, as radiographs underestimate cosmetic deformity 2
• Evaluate for specific red flags requiring intervention:
  • Trunk shift >2 cm from midline 1
  • PSI index >15 4
  • Progressive adding-on phenomenon 4
  • Significant cosmetic concerns affecting quality of life 5

Conservative Management Options:

• Core strengthening and postural awareness training should be initiated for all patients with persistent imbalance 6
• Physical therapy focusing on trunk stabilization 6
• Pain management strategies if discomfort develops 6

Surgical Revision Indications:

• Persistent truncal shift >2 cm with documented cosmetic concerns affecting quality of life 5, 1
• Documented adding-on progression requiring extension of fusion 4
• Development of functionally disruptive pain 6
• Severe cosmetic deformity with psychological impact 5

Surgical Prevention Strategies

Intraoperative Considerations:

• Ensure adequate correction of the lumbar curve to prevent postoperative truncal shift 1
• Minimize postoperative AVT of the proximal thoracic curve to reduce shoulder imbalance risk 4
• Consider hook constructs over all-screw constructs when shoulder balance is a primary concern, as hooks provide better postoperative shoulder symmetry (though at the cost of 14% less thoracic correction: 62.2% vs 76.0%) 3
• Avoid excessively short fusion constructs that increase trunk shift risk 2
• Select distal fusion level carefully to prevent adding-on, as this significantly contributes to shoulder imbalance 4

Construct Selection Trade-offs:

• Pedicle screw constructs achieve 76% correction versus 62% with hooks, but result in worse shoulder balance 3
• This represents a critical decision point: prioritize curve correction magnitude versus shoulder symmetry based on individual patient priorities 3

Critical Pitfalls to Avoid

• Do not rely solely on radiographic measurements to assess cosmetic outcome, as correlation is weak (r ≤ 0.7) 2
• Do not intervene surgically before 6 months unless progressive adding-on is documented, as spontaneous rebalancing is common 3
• Do not undercorrect the lumbar curve in pursuit of selective thoracic fusion, as this is the primary modifiable risk factor for trunk shift 1
• Do not ignore the PSI index calculation when shoulder imbalance is present, as it reliably predicts persistent deformity 4
• Do not dismiss patient cosmetic concerns even when radiographs appear acceptable, as clinical appearance may be significantly worse than radiographic measurements suggest 2

Monitoring Protocol

• Clinical and radiographic assessment at 6 weeks, 3 months, 6 months, and 12 months postoperatively 3
• Obtain clinical photographs at each visit to document cosmetic appearance separately from radiographic measurements 2
• Calculate PSI index at 3-month follow-up to predict need for intervention 4
• Assess for adding-on phenomenon on each radiograph 4
• After 12 months, transition to annual monitoring as recommended for all postoperative AIS patients 7