Pectoralis major tendon ‘landmarks’ humeral head position
By Sally Chapralis
Can be used for determining humeral length height
In proximal humerus fractures, the “landmarks” a surgeon can use to accurately position the humeral head during hemiarthroplasty are frequently lost due to fracture comminution. According to the authors of scientific paper 035, the pectoralis major tendon (PMT) can serve as such a landmark for determining humeral length and establishing the correct humeral height.
They found “that the distance between the upper edge of the pectoralis major tendon and the top of the humeral head (D-PMT) is a consistent reference for establishing the correct humeral height in the case of hemiarthroplasty for reconstruction of a proximal humerus fracture.”
This is significant because accurate restoration of the humeral head position is challenging, and if the prosthetic positioning is incorrect, the result may be a poor functional outcome.
Their study of 20 cadavers (40 shoulders) found that the D-PMT averaged 5.6 cm (± 0.5 cm, with a 95 percent confidence interval). “In only four of 40 shoulders did this distance exceed 6.0 cm, and there was no correlation between the size of the patient and this measurement,” they stated.
Researchers dissected 40 shoulders in 20 fresh cadavers: 11 males, 9 females; mean age 55 years old (range: 21 to 93 years old); mean patient height, 1.62 m (1.45 to 1.78 m). None had prior surgery or anatomic alteration of the shoulder.
The clinical team designated the distance between the “highest point in which the pectoralis tendon inserts on the humerus and the top of the humeral head” as the D-PMT. It was measured using a manual caliper while the shoulder was in neutral rotation. Right and left shoulders were analyzed independently.
Researchers found that the “average D-PMT was 5.6 cm (range: 5.0 to 7.0 cm; SD ± 0.5 cm).” The distance was greater than 6.0 cm in only four (10 percent) of the 40 shoulders studied. “The remaining 36 shoulders always had a D-PMT between 5.0 and 6.0cm.”
The fact that a consistent relationship exists between the upper edge of the pectoralis insertion and the top of the humeral head, even in shoulders of varying sizes, has significant clinical implications for hemiarthroplasty reconstruction of complex humerus fractures, noted the authors.
Previous studies have demonstrated that even a slight variation in proximal humeral geometry can result in severe functional impairment. Small variations on the head diameter can significantly decrease translation and rotation of the humerus. Placement of the prosthesis that results in a shorter humerus “increases the likelihood of poor tuberosity reduction. In addition, over-lengthening of the humerus may result in tuberosity displacement and poor function.”
Although several approaches can be used to determine retroversion and height of the prosthesis, the authors noted that these options all present some problems. For example, using preoperative templating of bilateral radiographs to show the entire humeral length requires controlled magnification. Jigs and other devices can be “bulky and awkward to use and only work with the specific prosthesis for which they were developed.”
Calculating humeral lengthening during surgery based on the medial diaphyseal calcar is not always possible, said the authors, because “in cases of chronic fracture or severe comminution, this (the medial diaphyseal calcar) may not be either available or accurate.”
Although correct prosthetic placement in terms of retroversion was not the subject of this anatomic study, the authors found the PMT to be a “useful landmark through which one might confirm proper height placement of a prosthesis in fracture.”
Based on these results, the presenters note that their “current approach to hemiarthroplasty uses this method in addition to preoperative radiographic templating. We believe that other surgeons may find this reference point useful when they perform these procedures.”
The research team included Joel Murachovsky, MD, Roberto Y. Ikemoto, MD, and Luis G.P. Nascimento, MD, all of Santo André, Brazil, and Jon J.P. Warner, MD, of Boston. The authors report no conflicts of interest.