An Experimental and Analytical Study of the Mechanism of Facet Load Transmission

Low-back pain has a complex and multi-faceted etiology. The articular facets have been shown to be load-bearing structures and may be a site for low-back pain. The aim of this study is to establish the mechanism for the transmission of axial load across a facet joint and to propose a facet-related hypothesis for low-back pain. The mechanism of load transmission was studied by two methods. Lumbar segments were instrumented with an intervertebral load cell (IVLC) to measure disc load so that facet load could be deduced. The applied load was moved 10 mm anteriorly and 12.5 mm posteriorly from the center of the vertebral body. The facets then were separated from the body and loaded axially to determine their stiffness in tension and compression and to observe the failure mode of the joint. It was shown optically that compressive loading of the isolated facet joints was equivalent to spinal extension and tensile loading to spinal flexion. Lastly, a finite element model of a lumbar motion segment was developed to simulate the transmission of facet load and to study the effects of the muscle tension.

Results of the study on six lumbar segments revealed that the normal facets carried 3-25% of the total load. If the facet joint was arthritic, the load could be as high as 47%. Experiments on isolated facet joints revealed that they behaved as a stiffening spring in compression and were weak in tension. When loaded to failure in compression, the inferior lumbar facets rotated posteriorly relative to the superior facets of the vertebra below and caused the capsule to rupture at about 6 kN without bony fracture. The transmission of compressive facet load occurs through contact of the tip of the inferior facet with the pars of the vertebra below. The data also show that an overloaded facet joint will cause rearward rotation of the inferior facet, resulting in the stretching of the joint capsule. The finite element model predicted an increase in facet load due to an increase in muscle force and posterior eccentricity. The following hypothesis is proposed: Excessive facet loads stretch the joint capsule and can be a cause of low-back pain. Further study is needed to prove this hypothesis.

Year	Entry
1970	Yamada H. Strength of Biological Materials. Evans FG, ed. Baltimore, MD: Williams & Wilkins Company; 1970.
1968	Tkaczuk H. Tensile properties of human lumbar longitudinal ligaments. Acta Orthop Scand. 1968;39(suppl 115):1-69.
1974	Prasad P, King AI, Ewing CL. The role of articular facets during +G_z acceleration. J Appl Mech. June 1974;41(2):321-326.
1967	Galante JO. Tensile properties of the human lumbar annulus fibrosus. Acta Orthop Scand. 1967;(suppl 100):1-91.
1979	Hakim NS, King AI. A three dimensional finite element dynamic response analysis of a vertebra with experimental verification. J Biomech. 1979;12(4):277-292.
1984	Yang KH, King AI. Mechanism of facet load transmission as a hypothesis for low-back pain. Spine. September 1984;9(6):557-565.
1976	Hakim NS, King AI. Static and dynamic articular facet loads. In: Proceedings of the 20th Stapp Car Crash Conference. October 18-20, 1976; Dearborn, MI. Warrendale, PA: Society of Automotive Engineers:609-639. SAE 760819.
1957	Brown T, Hansen RJ, Yorra AJ. Some mechanical tests on the lumbosacral spine with particular reference to the intervertebral discs: a preliminary report. J Bone Joint Surg. October 1957;39A(5):1135-1164.
1973	Belytschko TB, Andriacchi TP, Schultz AB, Galante JO. Analog studies of forces in the human spine: computational techniques. J Biomech. July 1973;6(4):361-371.
1984	Shirazi-Adl A. Three-Dimensional Nonlinear Finite Element Stress Analysis of a Lumbar Intervertebral Joint [PhD thesis]. McGill University; March 1984.
1974	Belytschko T, Kulak RF, Schultz AB, Galante JO. Finite element stress analysis of an intervertebral disc. J Biomech. May 1974;7(3):277-285.
1977	Carter DR, Hayes WC. The compressive behavior of bone as a two-phase porous structure. J Bone Joint Surg. 1977;59A(7):954-962.
1978	Lin HS, Lui YK, Ray G, Nikravesh P. Systems identification for material properties of the intervertebral joint. J Biomech. 1978;11(1-2):1-14.
1966	Rolander SD. Motion of the lumbar spine with special reference to the stabilizing effect of posterior fusion: an experimental study on autopsy specimens. Acta Orthop Scand. 1966;37(suppl 90):1-144.
1976	Wu H-C, Yao R-F. Mechanical behavior of the human annulus fibrosus. J Biomech. 1976;9(1):1-7.
1972	Markolf KL. Deformation of the thoracolumbar intervertebral joints in response to external loads: a biomechanical study using autopsy material. J Bone Joint Surg. April 1972;54A(3):511-533.
1981	Nachemson AL. Disc pressure measurements. Spine. January–February 1981;6(1):93-97.
1981	Horst M, Brinckmann P. Measurement of the distribution of axial stress on the end-plate of the vertebral body. Spine. May–June 1981;6(3):217-232.
1960	Nachemson A. Lumbar intradiscal pressure: experimental studies on post-mortem material. Acta Orthop Scand. 1960;31(suppl 43):1-104.
1963	Nachemson A. The influence of spinal movements on the lumbar intradiscal pressure and on the tensile stresses in the annulus fibrosus. Acta Orthop Scand. 1963;33(1-4):183-207.
1968	Nachemson AL, Evans JH. Some mechanical properties of the third human lumbar interlaminar ligament (ligamentum flavum). J Biomech. August 1968;1(3):211-220.
1976	Kulak RF, Belytschko TB, Schultz AB, Galante JO. Nonlinear behavior of the human intervertebral disc under axial load. J Biomech. 1976;9(6):377-386.
1982	Reuber M, Schultz A, Denis F, Spencer D. Bulging of lumbar intervertebral disks. J Biomech Eng. August 1982;104(3):187-192.
1982	Adams MA, Hutton WC. Prolapsed intervertebral disc: a hyperflexion injury. Spine. May 1982;7(3):184-191.
1969	Rockoff SD, Sweet E, Bleustein J. The relative contribution of trabecular and cortical bone to the strength of human lumbar vertebrae. Calcif Tiss Res. December 1969;3(1):163-175.
1980	Adams MA, Hutton WC. The effect of posture on the role of the apophysial joints in resisting intervertebral compressive forces. J Bone Joint Surg. August 1980;62B(3):358-362.
1981	Schultz AB, Andersson GBJ. Analysis of loads on the lumbar spine. Spine. January–February 1981;6(1):76-82.
1974	Prasad P, King AI. An experimentally validated dynamic model of the spine. J Appl Mech. September 1974;41(3):546-550.
1970	McElhaney J, Alem N, Roberts V. A porous block model for cancellous bones. Winter Annual Meeting of the American Society of Mechanical Engineers; November 29–December 3, 1970; New York, NY.1-9. ASME Publication 70-WA/BHF-2.

Year

Entry

1970

Yamada H. Strength of Biological Materials. Evans FG, ed. Baltimore, MD: Williams & Wilkins Company; 1970.

1968

Tkaczuk H. Tensile properties of human lumbar longitudinal ligaments. Acta Orthop Scand. 1968;39(suppl 115):1-69.

1974

Prasad P, King AI, Ewing CL. The role of articular facets during +G_z acceleration. J Appl Mech. June 1974;41(2):321-326.

1967

Galante JO. Tensile properties of the human lumbar annulus fibrosus. Acta Orthop Scand. 1967;(suppl 100):1-91.

1979

Hakim NS, King AI. A three dimensional finite element dynamic response analysis of a vertebra with experimental verification. J Biomech. 1979;12(4):277-292.

1984

Yang KH, King AI. Mechanism of facet load transmission as a hypothesis for low-back pain. Spine. September 1984;9(6):557-565.

1976

Hakim NS, King AI. Static and dynamic articular facet loads. In: Proceedings of the 20th Stapp Car Crash Conference. October 18-20, 1976; Dearborn, MI. Warrendale, PA: Society of Automotive Engineers:609-639. SAE 760819.

1957

Brown T, Hansen RJ, Yorra AJ. Some mechanical tests on the lumbosacral spine with particular reference to the intervertebral discs: a preliminary report. J Bone Joint Surg. October 1957;39A(5):1135-1164.

1973

Belytschko TB, Andriacchi TP, Schultz AB, Galante JO. Analog studies of forces in the human spine: computational techniques. J Biomech. July 1973;6(4):361-371.

1984

Shirazi-Adl A. Three-Dimensional Nonlinear Finite Element Stress Analysis of a Lumbar Intervertebral Joint [PhD thesis]. McGill University; March 1984.

1974

Belytschko T, Kulak RF, Schultz AB, Galante JO. Finite element stress analysis of an intervertebral disc. J Biomech. May 1974;7(3):277-285.

1977

Carter DR, Hayes WC. The compressive behavior of bone as a two-phase porous structure. J Bone Joint Surg. 1977;59A(7):954-962.

1978

Lin HS, Lui YK, Ray G, Nikravesh P. Systems identification for material properties of the intervertebral joint. J Biomech. 1978;11(1-2):1-14.

1966

Rolander SD. Motion of the lumbar spine with special reference to the stabilizing effect of posterior fusion: an experimental study on autopsy specimens. Acta Orthop Scand. 1966;37(suppl 90):1-144.

1976

Wu H-C, Yao R-F. Mechanical behavior of the human annulus fibrosus. J Biomech. 1976;9(1):1-7.

1972

Markolf KL. Deformation of the thoracolumbar intervertebral joints in response to external loads: a biomechanical study using autopsy material. J Bone Joint Surg. April 1972;54A(3):511-533.

1981

Nachemson AL. Disc pressure measurements. Spine. January–February 1981;6(1):93-97.

1981

Horst M, Brinckmann P. Measurement of the distribution of axial stress on the end-plate of the vertebral body. Spine. May–June 1981;6(3):217-232.

1960

Nachemson A. Lumbar intradiscal pressure: experimental studies on post-mortem material. Acta Orthop Scand. 1960;31(suppl 43):1-104.

1963

Nachemson A. The influence of spinal movements on the lumbar intradiscal pressure and on the tensile stresses in the annulus fibrosus. Acta Orthop Scand. 1963;33(1-4):183-207.

1968

Nachemson AL, Evans JH. Some mechanical properties of the third human lumbar interlaminar ligament (ligamentum flavum). J Biomech. August 1968;1(3):211-220.

1976

Kulak RF, Belytschko TB, Schultz AB, Galante JO. Nonlinear behavior of the human intervertebral disc under axial load. J Biomech. 1976;9(6):377-386.

1982

Reuber M, Schultz A, Denis F, Spencer D. Bulging of lumbar intervertebral disks. J Biomech Eng. August 1982;104(3):187-192.

1982

Adams MA, Hutton WC. Prolapsed intervertebral disc: a hyperflexion injury. Spine. May 1982;7(3):184-191.

1969

Rockoff SD, Sweet E, Bleustein J. The relative contribution of trabecular and cortical bone to the strength of human lumbar vertebrae. Calcif Tiss Res. December 1969;3(1):163-175.

1980

Adams MA, Hutton WC. The effect of posture on the role of the apophysial joints in resisting intervertebral compressive forces. J Bone Joint Surg. August 1980;62B(3):358-362.

1981

Schultz AB, Andersson GBJ. Analysis of loads on the lumbar spine. Spine. January–February 1981;6(1):76-82.

1974

Prasad P, King AI. An experimentally validated dynamic model of the spine. J Appl Mech. September 1974;41(3):546-550.

1970

McElhaney J, Alem N, Roberts V. A porous block model for cancellous bones. Winter Annual Meeting of the American Society of Mechanical Engineers; November 29–December 3, 1970; New York, NY.1-9. ASME Publication 70-WA/BHF-2.

Year	Entry
1989	El-Bohy AA, Yang K-H, King AI. Experimental verification of facet load transmission by direct measurement of facet lamina contact pressure. J Biomech. 1989;22(8-9):931-941.
1992	Avramov AI, Cavanaugh JM, Ozaktay CA, Getchell TV, King AI. The effects of controlled mechanical loading on group-II, III, and IV afferent units from the lumbar facet joint and surrounding tissue: an in vitro study. J Bone Joint Surg. December 1992;74A(10):1464-1471.
1989	Cavanaugh JM, El‐Bohy A, Hardy WN, Getchell TV, Getchell ML, King AI. Sensory innervation of soft tissues of the lumbar spine in the rat. J Orthop Res. May 1989;7(3):378-388.

Year

Entry

1989

El-Bohy AA, Yang K-H, King AI. Experimental verification of facet load transmission by direct measurement of facet lamina contact pressure. J Biomech. 1989;22(8-9):931-941.

1992

Avramov AI, Cavanaugh JM, Ozaktay CA, Getchell TV, King AI. The effects of controlled mechanical loading on group-II, III, and IV afferent units from the lumbar facet joint and surrounding tissue: an in vitro study. J Bone Joint Surg. December 1992;74A(10):1464-1471.

1989

Cavanaugh JM, El‐Bohy A, Hardy WN, Getchell TV, Getchell ML, King AI. Sensory innervation of soft tissues of the lumbar spine in the rat. J Orthop Res. May 1989;7(3):378-388.