Hip abductor moment arm--a mathematical analysis for proximal femoral replacement.
BACKGROUND
Patients undergoing proximal femoral replacement for tumor resection often have compromised hip abductor muscles resulting in a Trendelenberg limp and hip instability. Commercially available proximal femoral prostheses offer several designs with varying sites of attachment for the abductor muscles, however, no analyses of these configurations have been performed to determine which design provides the longest moment arm for the hip abductor muscles during normal function.


METHODS
This study analyzed hip abductor moment arm through hip adduction and abduction with a trigonometric mathematical model to evaluate the effects of alterations in anatomy and proximal femoral prosthesis design. Prosthesis dimensions were taken from technical schematics that were obtained from the prosthesis manufacturers. Manufacturers who contributed schematics for this investigation were Stryker Orthopaedics and Biomet.


RESULTS
Superior and lateral displacement of the greater trochanter increased the hip abductor mechanical advantage for single-leg stance and adduction and preserved moment arm in the setting of Trendelenberg gait. Hip joint medialization resulted in less variance of the abductor moment arm through coronal motion. The Stryker GMRS endoprosthesis provided the longest moment arm in single-leg stance.


CONCLUSIONS
Hip abductor moment arm varies substantially throughout the hip's range of motion in the coronal plane. Selection of a proximal femur endoprosthesis with an abductor muscle insertion that is located superiorly and laterally will optimize hip abductor moment arm in single-leg stance compared to one located inferiorly or medially.
Department of Orthopaedics and Sports Medicine, 13220 Laurel Drive, University of South Florida, Tampa, Florida 33612, USA. eric.r.henderson@gmail.com
Eric R
ER
Henderson
German A
GA
Marulanda
David
D
Cheong
H Thomas
HT
Temple
G Douglas
GD
Letson
D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005684:Gait / Q000502:physiology; D006621:Hip Joint / Q000502:physiology* / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D008962:Models, Theoretical; D018482:Muscle, Skeletal / Q000502:physiology* / Q000601:surgery; D011474:Prosthesis Design; D016059:Range of Motion, Articular / Q000502:physiology*; D012984:Software
Acta Orthop Belg. 1994;60(4):374-7
7847085
Orthopedics. 1986 Dec;9(12):1639-52
3469635
J Biomech. 1978;11(1-2):75-85
659458
J Bone Joint Surg Br. 1992 Jan;74(1):33-8
1732261
J Biomech. 1975 Mar;8(2):103-10
1150676
Arch Orthop Trauma Surg. 1995;114(2):76-8
7734237
Acta Orthop Scand. 1992 Aug;63(4):411-2
1529691
Phys Ther. 1972 Feb;52(2):149-58
5008294
Arch Phys Med Rehabil. 1990 Sep;71(10):739-41
2403279
J Bone Joint Surg Am. 1947 Jul;29(3):607-19
20253034
J Bone Joint Surg Am. 1979 Jul;61(5):639-52
457709
Clin Orthop Relat Res. 1977 Nov-Dec;(129):313-8
608292
Clin Orthop Relat Res. 1985 Jan-Feb;(192):159-67
3855392
J Bone Joint Surg Br. 2001 Nov;83(8):1156-60
11764431
Z Orthop Ihre Grenzgeb. 1991 Jul-Aug;129(4):285-94
1833916
J Am Geriatr Soc. 1987 Jan;35(1):13-20
3794141
J Bone Joint Surg Am. 1981 Oct;63(8):1228-39
7287793
Clin Orthop Relat Res. 1996 Jan;(322):207-23
8542698
Acta Orthop Scand. 1994 Jun;65(3):315-8
8042485
Acta Orthop Scand. 1996 Feb;67(1):37-42
8615100
J Biomech. 1981;14(11):803-12
7334040
J Bone Joint Surg Am. 1973 Dec;55(8):1698-720
4804991
N Engl J Med. 1995 Mar 2;332(9):556-61
7838189