Where Should Implants Be Anchored in the Humeral Head?

Abstract

To determine histomorphometric and bone strength distribution of the proximal humerus, analyses were done on 24 freshly harvested human cadaveric humeri. Median ages of 46 and 69 years were recorded respectively for the male group (n = 11; minimum, 34 years; maximum, 76 years) and the female group (n = 13; minimum, 46 years; maximum, 90 years). The humeral head was sliced into four equal horizontal levels (Levels 1-4). Five regions of interest were defined in each cutting plane: anterior, posterior, lateral, medial, and central. Histomorphometric analyses evaluated structural parameters (tissue volume to bone volume ratio, trabecular thickness), connectivity (number of nodes, node to node length), and trabecular orientation (mean bone length). The peak values of histomorphometric parameters and bone strength were identified for the cranial section and decreased caudally. The medial and dorsal aspects of the proximal humeral head were found to be the areas of highest bone strength. The trabecular network formed a pattern that connected the center of the gleaned cavity. The structural and connectivity parameters, bone strength, and trabecular orientation showed region- and level-related characteristics. Knowledge of distribution, microstructure, and quality of bone in the humeral head allows the remaining bone stock to be used effectively, even in elderly patients, with a minimally invasive approach and maximum mechanical stability.

The clinical benefit of medial support screws in locking plating of proximal humerus fractures: a prospective randomized study

“…Biomechanical studies have demonstrated a greater com- MSS medial support screw pressive stress on the medial region than on the lateral during normal shoulder motion [20,21]. Continuous varus stress of the rotator cuff may result in varus displacement of the humeral head and collapse of the articular surface during early rehabilitation, when the fracture fails to achieve anatomical reduction.…”

“…A cadaveric biomechanical study by Liew et al found that the grasping force of a screw placed under the subchondral bone of the medial and inferior region was comparably stronger than that of a screw placed either in the middle of the humeral head or in the lateral and superior region [22]. Another histomorphometric study by Hepp et al showed the highest bone strength to be in the medial and dorsal aspects of the proximal humeral head [21]. As a result, the optimal fixation of a screw is in the posterior-medial-inferior aspect of the humeral head to achieve mechanical stability by medial support for the fracture.…”

Locking Plate Fixation with and without Inferomedial Screws for Proximal Humeral Fractures: A Biomechanical Study

“…17 The inferomedial screws connect this trabecular network and decrease implant complications (such as screw penetration of the articular surface or plate breakage), and are of particular benefit in osteoporotic bone.…”

Grafting and fixation of proximal humeral aseptic non union: a prospective case series

“…Specimens failed primarily by plate bending as the humeral head was pushed down medially and distally (18). Analysis of the histomorphometry and microstructural architecture of the humeral head bone stock demonstrated that trabecular thickness and density are greater in the medial region (19). Liew et al (20) also found that the screws are significantly more resistant when they are placed into the medial subchondral bone and in the upper section of the humeral head.…”