Saha's 1973 paper defines the biomechanical requirements for stable glenohumeral elevation using cadaveric surface measurements, simultaneous 8-channel EMG, and mathematical modeling. It establishes the concept of the 'zero-position' and the minimum muscular requirements for elevation. These principles are then applied directly to muscle transfer planning for flail shoulder and to design criteria for proximal humeral prostheses.
Managing a flail shoulder or designing a proximal humeral replacement requires more than restoring a prime mover. Without a vertical steerer and a horizontal steerer, the humeral head cannot be stabilized during elevation regardless of how strong the prime mover is.
When planning muscle transfers for brachial plexus palsy or poliomyelitis, map each transfer to one of three functional roles: prime mover (trapezius to distal humerus), vertical steerer (levator scapulae or SCM to greater tuberosity), and horizontal steerer (serratus anterior digitations or pectoralis minor to lesser tuberosity). If retrotorsion exceeds 30 degrees, add derotation osteotomy or the joint will dislocate anteriorly after transfer.
For proximal humeral prosthesis implantation, build in 5-10 degrees of retrotorsion and preserve tunnel attachment sites for at least one vertical and one horizontal steerer. An implant without steerer fixation points will be mechanically unstable regardless of fit.
Saha's glenohumeral index (vertical ~75, transverse ~58) gives you a quantitative sense of how much bony containment exists. The lower the index, the more the patient depends on muscular stabilization — relevant when counseling patients about rehabilitation expectations after reconstruction.
Saha's 1973 paper defines the biomechanical requirements for stable glenohumeral elevation using cadaveric surface measurements, simultaneous 8-channel EMG, and mathematical modeling. It establishes the concept of the 'zero-position' and the minimum muscular requirements for elevation. These principles are then applied directly to muscle transfer planning for flail shoulder and to design criteria for proximal humeral prostheses.
Managing a flail shoulder or designing a proximal humeral replacement requires more than restoring a prime mover. Without a vertical steerer and a horizontal steerer, the humeral head cannot be stabilized during elevation regardless of how strong the prime mover is.
When planning muscle transfers for brachial plexus palsy or poliomyelitis, map each transfer to one of three functional roles: prime mover (trapezius to distal humerus), vertical steerer (levator scapulae or SCM to greater tuberosity), and horizontal steerer (serratus anterior digitations or pectoralis minor to lesser tuberosity). If retrotorsion exceeds 30 degrees, add derotation osteotomy or the joint will dislocate anteriorly after transfer.
For proximal humeral prosthesis implantation, build in 5-10 degrees of retrotorsion and preserve tunnel attachment sites for at least one vertical and one horizontal steerer. An implant without steerer fixation points will be mechanically unstable regardless of fit.
Saha's glenohumeral index (vertical ~75, transverse ~58) gives you a quantitative sense of how much bony containment exists. The lower the index, the more the patient depends on muscular stabilization — relevant when counseling patients about rehabilitation expectations after reconstruction.