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Superior displacement of the hip in total joint replacement: Effects of prosthetic neck length, neck‐stem angle, and anteversion angle on the moment‐generating capacity of the muscles
Author(s) -
Delp Scott L.,
Komattu Abraham V.,
Wixson Richard L.
Publication year - 1994
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.1100120614
Subject(s) - isometric exercise , displacement (psychology) , range of motion , moment (physics) , valgus , neck muscles , anatomy , orthodontics , medicine , surgery , physics , physical therapy , psychology , classical mechanics , psychotherapist
The purpose of this study was to determine the effects of superior displacement of the hip center and changes in three prosthetic parameters (neck length, neck‐stem angle, and anteversion angle) on the capacity of muscles to generate force and moment about the hip. A three‐dimensional model that calculates the maximum isometric forces and moments generated by 25 muscles crossing the hip over a wide range of body positions was used to evaluate the effects of a 2 cm elevation of the hip center and changes in the prosthetic parameters. After superior displacement of the hip center, the neck length was increased from 0 to 3 cm, the neck‐stem angle was varied between 110 and 150°, and the anteversion angle was varied between 0 and 40°. Our analysis showed that a 2 cm superior displacement of the hip center would decrease the moment‐generating capacity of the four muscle groups studied (abductors, adductors, flexors, and extensors) if neck length were not increased to compensate for decreased muscle length. In the computer model of an adult man that we used, a 2 cm increase in neck length restored the moment‐generating capacity of the muscles by increasing muscle length and force‐generating capacity. However, a 3 cm increase in neck length increased passive muscle forces substantially, which potentially could limit joint motion. An increased neck‐stem angle (i.e., a valgus neck) decreased the abduction moment arm but increased the moment‐generating capacity of the other muscle groups. A change in the anteversion angle from 0 to 40° had a relatively small effect on the isometric moment‐generating capacity of the muscles studied.