Minimally invasive balloon-reduction of acute Hill-Sachs-lesions and impression fractures after shoulder dislocation - an experimental approach

Background: The shoulder is the joint most often affected by dislocations. It is known that bony defects of the glenoid and/or humerus can lead to recurrent dislocations even after arthroscopic shoulder stabilization. To prevent recurrent instability, it appears reasonable to reduce fresh and larger Hill-Sachs lesions (off-track lesions). In spine surgery, balloon kyphoplasty is widely used for fracture reduction. The aim of this study was to determine whether the balloon dilatation procedure is transferable to the humeral head and under which conditions it can be successful.

Methods: In this biomechanical proof-of-concept study, a preformed "impression stamp" was used to create standardized Hill-Sachs impressions (Calandra grade III lesion) on 13 human humeral specimens. A kyphoplasty balloon was then placed intraosseously and close to the defect using a special monolateral trocar and the defect was reduced by balloon dilatation. CT imaging was performed on the native specimens, after defect placement and after reduction. Both the defect size and the extent of reduction were measured radiologically, as well as the bone density. Also, the pressure and volume necessary for reduction were measured.

Results: 13 proximal humerus specimens were examined. The mean age of the 7 body donors (3 female) was 85 years (SD ±8.1). The average bone density was 49.0 mg/ml (SD ±26.9) and therefore defined as osteoporotic. The average defect depth (difference to native, measured from a best-fit circle) was 4.1 mm (SD ±1.4), corresponding to an average defect volume of 1203 mm³ (SD ±949). After balloon dilatation, the average achieved reduction (difference to the defect) was 4.3 mm (SD ±1.9) or 1223 mm³ (SD ±1059). This results in an average difference from native to reduced of -0,2 mm (SD ±0.5) or 20 mm³ (SD ±212) and represents no significant difference compared to baseline values (p = 0.90 or p = 0,75, respective), but a slight overreduction in the volumetric measurements. In all humeral specimens, a reduction of at least 2.6 mm or 221 mm³ compared to the defect situation was achieved. An average volume of 3.4 ml (SD ±1,1) and pressure of 271 psi (SD ±81) were required for reduction.

Conclusion: The present results demonstrate, that minimally invasive balloon reposition of large acute Hill-Sachs lesions appears methodologically feasible. The required pressure for reduction seems to be higher compared to previous studies. Further studies are necessary for the development of this technique and its reproducible translation into clinical practice.