1. BIOMECHANICS OF THE LUMBER SPINE Dr. Fatima Zehra (Physical Therapist) School of Physiotherapy, IPMR Dow University of Health Sciences

2. Spine has 33 vertebrae; 7 Cervical 12 Thoracic 5 Lumbar 5 SACRAL 4 Coccygeal

3. CURVES OF SPINE o The normal spine has an "S"- like curve from the side view o Thoracic & sacral … Kyphosis o Cervical … Lordosis o Lumber … Lordosis

4. THE LUMBER SPINE  Principal function  To protect spinal cord  To transfer loads from head & trunk to the pelvis  Lumber spine stability  Intrinsic stability by IV discs & ligaments  Extrinsic stability by Spinal muscles

5. THE LUMBER SPINE  THE MOTION SEGMENT 1. Ant. Portion … 2 superimposed IV bodies, IV Disc, Ant. & Post. long. Ligaments 2. Port. Portion … corresponding Vertebral Arches, IV Joints /Facets, Trans. & Spinous processes and various ligaments 3. Vertebral canal … Arches & Vertebral bodies

6.  The Vertebral Bodies  Thicker, larger & wider than cervical / thoracic spines  Progressively larger caudally  Bear mainly compressive loads ANTERIOR PORTION OF THE MOTION SEGMENT

7.  The IV Disc  Bears/Distributes loads & Restrain excessive motion  Dual Function b/c of its location/unique composition  Nucleus Pulposus … A gelatin mass, Rich in hydrophilic glycosaminoglycans, Slightly posterior position in the disc, Bears compressive Loads  Annulus Fibrosus … A fibrocartilage structure, Criss-cross arrangement of collagen fibers Bears high bending & Torsional Loads ANTERIOR PORTION OF THE MOTION SEGMENT

8.  Loading of IV Disc during ADLs  Combination of Compression, Bending (tensile) and Torsion  Flexion, Extension & Lateral Flexion produce compressive & tensile loads in the disc  Rotation produces mainly shear or torsion loads in the disc  Annular tears display increased rotational moments during loading ANTERIOR PORTION OF THE MOTION SEGMENT

9.  Intradiscal Pressure (Intrinsic pressure)  In Normal Unloaded Disc  Approx. 10 N/cm² (Nachemson, 1960)  During Compressive Loading  NP acts Hydrostatically i.e. stores energy & distributes loads throughout the disc uniformly  Pressure is 1.5 times the externally applied load  Makes NP bulge laterally & exerts circumferential tensile stresses to Ann. Fib. ANTERIOR PORTION OF THE MOTION SEGMENT

10.  During Compressive Loading  Tensile stresses are 4-5 times the applied load in the post part of AF  Degenerated Disc has reduced hydrophilic capacity and reduced hydrostatic function  Degeneration makes the disc more vulnerable to stresses

11.  Guide the movement of motion segment  Orientation of Facets & Types of motions  C1–C2 Facets : Parallel to the transverse plane  C3–C7 Facets : 45˚ to Trans. plane & parallel to the frontal plane  Allows Flex., Ext., Lat. Flexion and Rotation  Thoracic Facet: 60˚ to Trans. & 20˚ to frontal planes  Allows Lat. Flex., Rot. & some Flex. - Ext. POSTERIOR PORTION OF THE MOTION SEGMENT

12. Orientation of Facets & Types of Motions  Lumber Facets: 90˚ to Trans. & 45˚ to frontal planes  Allows Flex., Ext., Lat. Flex. & almost No Rot.  But in LS Joints oblique orientation of facets allows considerable Rotation NOTE: Considerable variation is found in the values of orientation of facets within and among individuals. POSTERIOR PORTION OF THE MOTION SEGMENT

13.  Load bearing function of lumber facets  Varies with position of spine  Greatest load in hyperextension, Approx. 30% of the total load ( King et al., 1975)  Axial load is transferred to the annulus & Ant. Long. Lig. to support the spine, if facets are compromise (Haher et al., 1994)  High loading on facets during forward bending, coupled with Rotation (El-Bohy & king, 1986) POSTERIOR PORTION OF THE MOTION SEGMENT

14.  Load bearing function of lumber facets  Vertebral Arches & IV joints are important restrains for Shear Forces on spine  Patients with deranged arches & defective IV joints (Spondylolisis / Listhesis) are at increased risk for forward displacement of the vertebral body (Adams & Hutton, 1983; Miller et al., 1983)  Transverse & Spinous processes are for muscles attachment & provide extrinsic stability

15. CASE STUDY  30-year-old male gymnast  H/o severe back pain radiating to both legs  Aggravating by Strenuous training & Relieved by Rest / Restriction of activity  Clinical Exam./MRI Finding: L5-S1 Spondylolisthesis with Bilateral PI defect of L5  PI Fatigue # due to physiological loads during repeated flex.- ext. of LS leading to ant. slipping of L5 onto S1

16.  Biomechanical Effects  Displacement of COG of the body anteriorly  Hyperextension of lumber spine above the lesion in compensation  Backward displacement of upper trunk  Abnormal forces on IV Disc  Herniation of disc into neural foramina  Moderate stenosis of both L5-S1 Nerve Roots CASE STUDY

17. POSTERIOR PORTION OF THE MOTION SEGMENT  Ligament Flavum  Under constant tension in neutral spine  Contracts during extension of spine  Elongates during flexion of spine  Pre-stresses the disc b/c of its location  Hypertrophy of LF in Disc Degeneration, Traction Spurs, Spondylolisthesis conditions

18.  During Flexion of spine … IS Ligaments bear greatest strains, Followed by capsular ligament & LF  During Extension of spine … AL Ligament bears the greatest strain  During Lateral Flexion of spine … Contra-lateral transverse ligament bears the highest strains, Followed by LF & Capsular Ligaments  During Rotation of spine … Capsular ligaments of the facet joints bear the most strain POSTERIOR PORTION OF THE MOTION SEGMENT

19. KINEMATICS  Agonist Muscles … Initiate / Carry out motion  Antagonist muscles … Control / Modify motion  ROMs … Depends on the orientation of IV Joints facets  The Rib cage … Limits thoracic motion  The pelvis … Augments trunk movement by tilting

20.  Flexion - Extension ROMs  Approx. 4˚ in each upper thoracic motion segment  Approx. 6˚ in mid thoracic region  Approx. 12˚ in two lower thoracic segment  Approx. 20˚ at the lumbo-sacral level KINEMATICS

21.  Lateral Flexion ROMs  8 to 9˚ in lower thoracic segments  6˚ in the upper thoracic region  6˚ in all lumber thoracic region  Only 3˚ in lumbo-sacral segment  Rotation ROMs  9˚ in upper thoracic region  2˚ in lower segments of lumber spine  5˚ in the lumbo-sacral segment KINEMATICS

22.  Surface Joint Motion  Coupled with flexion, extension and lateral flexion  Analyzed by instant center method of Reuleaux  The instantaneous center of motion for the motion segments of the lumber spine usually lies within the lumber disc  The instantaneous center pathway will be altered in pronounced disc degeneration KINEMATICS

23.  Functional motion of the spine  A combined action of several motion segments  ROM is strongly age-dependent (decreases 30% from youth to old-age)  Flexion & Lateral Bending decreases with age while rotation is maintained  Flexion – Extension is more in male while lateral flexion is more in female KINEMATICS

24. FLEXION – EXTENSION  During Unloaded Flexion – Extension  First 50 – 60˚ of flexion occurs in lumber spine (lower motion segments)  Forward pelvic tilting allows further flexion  Little contribution in flexion from thoracic spine b/c of oblique orientation of facets and rib cage

25.  Initiated by abdominal muscles & vertebral portion of psoas muscle  Upper body weight allows further flexion  Erector spinae muscles control the flexion  Post. hip muscles control the forward pelvic tilting  In full flexion, the erector spinae muscle are fully stretched & become inactive (flexion-relaxation phenomenon)  Flex. moment is controlled passively by ES & post. spinal ligaments FLEXION

26.  Backward tilting of pelvis:  By GM activity together with hamstring muscles  Initiates extension of spine  Paraspinous muscles … activates until the upright positioning of the trunk is achieved  In hyperextension of trunk from upright position:  Ext. muscles activates during the initial phase & decreases during further Ext.  Abdominal muscles control this moment  Extreme/Forced Ext. … Ext. activity is again required EXTENSION

27. LATERAL FLEXION & ROTATION  Lat. Flex. occurs in thoracic and lumber spine  Rib cage restriction at thoracic level  Errector spinae and abdominal muscles are active during Lat. Flex. (ipsilateral & contralateral contraction)  Rotation occurs at thoracic & lumbosacral levels mainly  Rotation is coupled with lateral flexion of spine, most marked in upper thoracic region (vertebral bodies Rot.)  Back & abd. Muscles are active on both sides during Rotation

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