Biomechanical investigation of arm position on deforming muscular forces in proximal humerus fractures

Abstract

Background: Muscular forces drive proximal humeral fracture deformity, yet it is unknown if arm position can help mitigate such forces. Our hypothesis was that glenohumeral abduction and humeral internal rotation decrease the pull of the supraspinatus and subscapularis muscles, minimizing varus fracture deformity.Methods: A medial wedge osteotomy was performed in eight cadaveric shoulders to simulate a two-part fracture. The specimens were tested on a custom shoulder testing system. Humeral head varus was measured following physiologic muscle loading at neutral and 20° humeral internal rotation at both 0° and 20° glenohumeral abduction. Results: There was a significant decrease in varus deformity caused by the subscapularis (p<0.05) at 20° abduction. Significantly increasing humeral internal rotation decreased varus deformity caused by the subscapularis (p<0.05) at both abduction angles and that caused by the supraspinatus (p<0.05) and infraspinatus (p<0.05) at 0° abduction only.Conclusions: Postoperative shoulder abduction and internal rotation can be protective against varus failure following proximal humeral fracture fixation as these positions decrease tension on the supraspinatus and subscapularis muscles. Use of a resting sling that places the shoulder in this position should be considered.

Optimal immobilization position for conservative treatment of proximal humerus fractures by fracture type: a biomechanical cadaveric study

“…At our tertiary hospital, we frequently encounter cases of failed conservative treatment for PHFs due to suboptimal immobilization position. Upon reviewing previous studies 14 , 15 , 19 , 25 , 26 , many kinds of slings or braces that achieve internal rotation of the shoulder have been conventionally utilized for conservative treatment of PHFs. In recent studies 20 , 21 , 27 , however, there has been a proposal to immobilize the arm in the neutral position in PHFs.…”

“…In recent studies 20 , 21 , 27 , however, there has been a proposal to immobilize the arm in the neutral position in PHFs. On the other hand, Chalmers et al 14 , 15 suggested shoulder abduction and internal rotation for the immobilization position in surgical neck fractures to decrease deformation by muscular force. As described in previous studies, there is still no consensus on optimal immobilization position for conservative treatment in different types of PHFs.…”

“…There has been little research on the immobilization position of the affected arm with consideration of fracture type. In the few studies touching on this topic, most of the focus was on varus collapse associated with SN fracture type 14 , 15 . There have been several cases where initial suboptimal immobilization positioning worsened the condition compared to the initial fracture 12 , 13 .…”

Neglected subscapularis apophyseal plate avulsion fracture in skeletal immaturity: a case report

“…These sports-related injuries have been reported in hockey, lacrosse, baseball, football, wrestling, judo, and soccer [2][3][4]. The most common mechanism of injury involves remnant subscapularis apophyseal plate avulsion while some are a combination of abduction, external rotation, and extension in the shoulder [2][3][4][5][6]. The incidence of these injuries has increased among younger patients with increased participation in athletic activities.…”

Optimal immobilization position for conservative treatment of proximal humerus fractures by fracture type: A biomechanical cadaveric study

“…There has been little research on the immobilization position of the affected arm with consideration of fracture type. In the few studies touching on this topic, most of the focus was on varus collapse associated with SN fracture type [12,13]. Among patients referred to our hospital, there have been many cases where initial suboptimal immobilization positioning worsened the condition compared to the initial fracture.…”