The Influence of Breast Reconstruction Choice on Functional Shoulder Biomechanics in Women Undergoing Mastectomy for Breast Cancer

Abstract

A majority of women that undergo mastectomy for breast cancer will choose to have reconstructive surgery performed to return the look and feel of healthy breast tissue. Common breast reconstruction techniques remove the pectoralis major and/or latissimus dorsi muscles from their skeletal attachments. This removal often leads to reductions in quality of life and self-reported shoulder function, but it is unclear how different breast reconstruction choices influence post-operative shoulder biomechanics. The purpose of this dissertation was to explore the pathophysiological mechanisms contributing to the physical and psychosocial deficits experienced by breast reconstruction patients. Ultrasound shear wave elastography, robot-assisted measures of shoulder joint biomechanics, and patient-reported outcomes surveys were utilized to examine the long-term effects of various breast reconstruction approaches on the integrity of the shoulder joint and patients’ self-reported physical and psychosocial well-being. Additionally, this dissertation includes a novel analysis of the neuromuscular compensation strategies adopted at the shoulder by breast reconstruction patients. Results from this dissertation suggest that breast reconstruction approaches requiring the disinsertion of shoulder musculature may lead to long-term and potentially chronic deficits in shoulder strength and stiffness. Our results also suggest that objective measures of shoulder biomechanics are predictive of self-reported physical and psychosocial well-being. Additionally, this dissertation provides evidence that the underlying function of the pectoralis major muscle is fundamentally altered following its disinsertion and the inclusion of radiotherapy. Finally, results from this dissertation suggest that patients who undergo bilateral breast reconstructions that disinsert the pectoralis major will adopt compensatory neuromuscular strategies only with their dominant arm. Investigations included in this dissertation provide several novel and innovative insights into the peri-operative care of breast cancer patients. This dissertation contains the first ever investigation into the influence of mastectomy and breast reconstruction on the underlying integrity of the shoulder joint and pectoralis major muscle using both robotic-assisted measures of shoulder biomechanics and ultrasound shear wave elastography. We also utilize novel mediation analyses to establish a causal relationship between the breast reconstruction approach, its influence on shoulder biomechanics, and the effect these shoulder biomechanics have on patient-reported well-being. Finally, this dissertation includes the first ever investigation into how the otherwise intact central nervous system adapts to breast reconstruction procedures requiring the disinsertion of shoulder musculature. These insights pave the way for impactful future research into the relationship between functional shoulder joint biomechanics and breast cancer patient quality of life, as well as into the neuromuscular implications of mastectomy and breast reconstruction. Findings from this dissertation have broad and significant clinical implications. This dissertation strengthens the surgical decision-making process for women choosing mastectomy and breast reconstruction. In particular, findings from this dissertation suggest that breast reconstructions requiring the disinsertion of shoulder musculature, in particular the combined disinsertion of shoulder musculature, should be avoided when possible. This dissertation also informs the development of optimal post-operative care. Specifically, that the restoration of shoulder adduction, abduction, internal rotation, and external rotation strength and adequate pectoralis major muscle function must be a focal point of post-operative care for patients undergoing mastectomy and breast reconstruction or breast-conserving therapy. Finally, findings from this dissertation apply to many clinical situations where musculature is surgically manipulated, such as in reconstructions of the head and neck using latissimus dorsi or serratus anterior muscle flaps or reconstructions of the lower extremity using rectus abdominis or gracilis muscle flaps.