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Chapter 3 Considerations of Sex Differences

in Musculoskeletal Anatomy

Phillip S. Sizer, PT, PhDPhillip S. Sizer, PT, PhD

andand

C. Roger James, PhD, FACSMC. Roger James, PhD, FACSM

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Learning Objectives• After completing this chapter, you should After completing this chapter, you should

understand:understand:• sexual dimorphism and how it applies to humanssexual dimorphism and how it applies to humans• sex differences in general morphologysex differences in general morphology• sex differences in skeletal geometrysex differences in skeletal geometry• sex differences in collagenous, cartilage, & bone tissuesex differences in collagenous, cartilage, & bone tissue• sex differences in upper extremity anatomy & sex differences in upper extremity anatomy &

mechanicsmechanics• sex differences in lower extremity anatomy & sex differences in lower extremity anatomy &

mechanicsmechanics• sex differences in spine anatomy & mechanicssex differences in spine anatomy & mechanics

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Musculoskeletal Anatomy of Men and Women

• Sexual dimorphism is Sexual dimorphism is prominent in many prominent in many species, but more species, but more subtle in humanssubtle in humans

• There are generally There are generally recognized differences recognized differences in body structurein body structure

Symbolic representation of men and women as depicted on the plaque of the Pioneer 10 spacecraft in 1972. Source: NASA. Adapted with permission.

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Differences in General Body Characteristics• Sex differences are age dependent:Sex differences are age dependent:

• Before puberty, boys and girls at the 50Before puberty, boys and girls at the 50 thth percentile are approximately the same height percentile are approximately the same height and weight.and weight.

• After puberty, men are approximately 14 cm After puberty, men are approximately 14 cm taller and have 12 kg more mass than women. taller and have 12 kg more mass than women.

• General appearance (body shape) changes, as General appearance (body shape) changes, as well.well.

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Selected Sex Differences in Skeletal Geometry: Pelvis

• Women haveWomen have• Larger inlet and outletLarger inlet and outlet• Greater interacetabular distanceGreater interacetabular distance• Greater hip width normalized to femur lengthGreater hip width normalized to femur length

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Selected Sex Differences in Skeletal Geometry: Femur

• Women haveWomen have• Greater femoral anteversionGreater femoral anteversion• Narrower intercondylar notch widthNarrower intercondylar notch width

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Selected Sex Differences in Skeletal Geometry: Knee, Tibia, and Foot

• Women haveWomen have• Greater genu recurvatumGreater genu recurvatum• Greater quadriceps (Q) angleGreater quadriceps (Q) angle• More lateral patellar alignmentMore lateral patellar alignment• Greater tibial torsion Greater tibial torsion • More bunions and deformities of the toesMore bunions and deformities of the toes

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Evidence of Sexual Dimorphism from Forensic Anthropology & Archeology

• Characteristics of skeletal geometry have Characteristics of skeletal geometry have been used to predict an individual’s sex been used to predict an individual’s sex from their skeletal remains.from their skeletal remains.

• The humerus, pelvis, femur, tibia, talus, and The humerus, pelvis, femur, tibia, talus, and calcaneus all have been used for this calcaneus all have been used for this purpose.purpose.

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Evidence of Sexual Dimorphism from Forensic Anthropology & Archeology

• The ability to predict an individual’s sex The ability to predict an individual’s sex from skeletal remains differs by bone.from skeletal remains differs by bone.

• The strongest predictors are the tibia, The strongest predictors are the tibia, femur, and calcaneus, followed by the femur, and calcaneus, followed by the pelvis and talus.pelvis and talus.

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Evidence of Sexual Dimorphism from Forensic Anthropology & Archeology

• Some anatomic characteristics of a bone are better Some anatomic characteristics of a bone are better predictors of sex than other characteristics.predictors of sex than other characteristics.

• The characteristics of the femur that best predict The characteristics of the femur that best predict sex include those that are associated with the sex include those that are associated with the femoral head.femoral head.

• Combinations of characteristics are the best Combinations of characteristics are the best predictors.predictors.

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Factors Influencing Sex Differences in Skeletal Geometry

• Skeletal maturitySkeletal maturity• Environmental stressesEnvironmental stresses• GeneticsGenetics

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Sex Differences in Musculoskeletal Tissues: Collagenous Tissues• There are several sex differences in collagenous There are several sex differences in collagenous

tissues (e.g., tendon, ligament, skin):tissues (e.g., tendon, ligament, skin):• Collagen thicknessCollagen thickness• Collagen orientationCollagen orientation• Collagen contentCollagen content• Collagen diameterCollagen diameter• Collagen volumeCollagen volume• Collagen metabolismCollagen metabolism

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Sex Differences in Musculoskeletal Tissues: Cartilage Tissue• Women have 1.5-4 times greater risk of Women have 1.5-4 times greater risk of

osteoarthritisosteoarthritis• There are several sex differences in cartilage, There are several sex differences in cartilage,

women having:women having:• Less cartilage volumeLess cartilage volume• Less cartilage thicknessLess cartilage thickness• Less cartilage surface areaLess cartilage surface area• Slower cartilage accrual rate in youthSlower cartilage accrual rate in youth• Greater cartilage degradation in older ageGreater cartilage degradation in older age

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Sex Differences in Musculoskeletal Tissues: Bone Tissue• Women have greater risk of bone fracture, Women have greater risk of bone fracture,

especially after menopause.especially after menopause.• There are several sex differences in bone, women There are several sex differences in bone, women

having:having:• Slower bone accrual rate in youthSlower bone accrual rate in youth• Less peak bone mass in adulthoodLess peak bone mass in adulthood• Slower bone turn-over in adulthoodSlower bone turn-over in adulthood• Less volumetric bone mineral density at some sitesLess volumetric bone mineral density at some sites• Less bone area at some sitesLess bone area at some sites• Less cortical thickness at some sitesLess cortical thickness at some sites• Less compressive and bending strength at some sitesLess compressive and bending strength at some sites

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Shoulder Anatomy Sex-Based Differences

• Incidence of external impingement is likely Incidence of external impingement is likely related to differences in:related to differences in:• Acromion process shapeAcromion process shape• Posterior capsule shorteningPosterior capsule shortening

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Shoulder Anatomy Sex-Based Differences• Increased incidence of glenohumeral Increased incidence of glenohumeral

instability in women is likely related to instability in women is likely related to differences in:differences in:• Glenoid fossa inclinationGlenoid fossa inclination• Anterior capsular laxityAnterior capsular laxity• Decreased joint stiffnessDecreased joint stiffness

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Shoulder Anatomy Sex-Based Differences• Increased incidence of idiopathic capsulitis Increased incidence of idiopathic capsulitis

in women is likely related to differences in:in women is likely related to differences in:• Increased thickening of the anterior-superior Increased thickening of the anterior-superior

joint capsule at the coracohumeral ligamentjoint capsule at the coracohumeral ligament• Non-inflammatory synovial reaction in the area Non-inflammatory synovial reaction in the area

of the subscapularis tendonof the subscapularis tendon• Active fibroblastic proliferation and tissue Active fibroblastic proliferation and tissue

transformationtransformation

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Elbow Anatomy Sex-Based Differences• Increased incidence of tennis elbow in Increased incidence of tennis elbow in

women is likely related to differences in:women is likely related to differences in:• Decreases in estrogen productionDecreases in estrogen production• Mesenchymal changes in the tendon structureMesenchymal changes in the tendon structure

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Wrist & Hand Anatomy Sex-Based Differences• Increased incidence of carpal tunnel Increased incidence of carpal tunnel

syndrome in women is likely related to syndrome in women is likely related to differences in:differences in:• Tunnel architecture and volumeTunnel architecture and volume• Shape of the hamate hookShape of the hamate hook• Digital featuresDigital features• Hand-length ratiosHand-length ratios• Body mass indexBody mass index

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Wrist & Hand Anatomy Sex-Based Differences• Female architectural differences likely Female architectural differences likely

result in the following Carpal Tunnel result in the following Carpal Tunnel Syndrome precipitating factors:Syndrome precipitating factors:• Increased tunnel pressureIncreased tunnel pressure• Perineural edema & fibrosisPerineural edema & fibrosis• Deficits in neurophysiological functionDeficits in neurophysiological function• Autonomic disturbancesAutonomic disturbances

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Hip Joint Anatomy Sex-Based Differences• A woman’s predisposition to stress & frank A woman’s predisposition to stress & frank

fracture at the hip are likely related to:fracture at the hip are likely related to:• Architectural differences in the hip & pelvisArchitectural differences in the hip & pelvis• Reduced acetabular depth and femoral head Reduced acetabular depth and femoral head

widthwidth• Narrowed CD angleNarrowed CD angle• Decreased femoral neck strengthDecreased femoral neck strength• Decreased bone massDecreased bone mass

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Hip Joint Anatomy Sex-Based Differences• A woman’s predisposition to labral tears at A woman’s predisposition to labral tears at

the hip are likely related to:the hip are likely related to:• Decreased labral tensile strengthDecreased labral tensile strength• Increased femoral neck thicknessIncreased femoral neck thickness• Decreased CD angulationDecreased CD angulation

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Knee Joint Anatomy Sex-Based Differences• A woman’s predisposition to ACL Injuries A woman’s predisposition to ACL Injuries

at the knee are likely related to:at the knee are likely related to:• Reduced femoral intercondylar notch width Reduced femoral intercondylar notch width

(controversial) (controversial) • Altered biomechanical behaviorsAltered biomechanical behaviors• Altered motor control strategiesAltered motor control strategies

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Knee Joint Anatomy Sex-Based Differences• Biomechanical differences in women Biomechanical differences in women

during landing and cutting:during landing and cutting:• Reduced knee flexion angle at contactReduced knee flexion angle at contact• Increased knee valgus motionIncreased knee valgus motion• Increased knee joint laxity and anterior tibial Increased knee joint laxity and anterior tibial

translation translation • Increased subtalar joint pronationIncreased subtalar joint pronation• Greater ACL ligament creepGreater ACL ligament creep

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Knee Joint Anatomy Sex-Based Differences• Control strategy differences in women Control strategy differences in women

during landing and cutting:during landing and cutting:• Reduced protective hamstring activityReduced protective hamstring activity• Increased quadriceps activityIncreased quadriceps activity• Decreased cocontractive controlDecreased cocontractive control

• Increased soleus and gastrocnemius activityIncreased soleus and gastrocnemius activity

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Knee Joint Anatomy Sex-Based Differences• Hormonal differences in women during Hormonal differences in women during

landing and cutting:landing and cutting:• Menstrual fluctuations in estrogen and Menstrual fluctuations in estrogen and

progesterone concentrations and receptorsprogesterone concentrations and receptors• Resultant fluctuations in metallomatrix protease Resultant fluctuations in metallomatrix protease

activity and decrease fibroblastic activity within activity and decrease fibroblastic activity within the ligamentthe ligament

• Resultant ligament laxityResultant ligament laxity

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Ankle & Foot Anatomy Sex-Based Differences• Women differ from men in the incidence ofWomen differ from men in the incidence of

• Achilles tendopathyAchilles tendopathy• Inversion traumaInversion trauma

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Ankle & Foot Anatomy Sex-Based Differences• A woman’s predisposition related to A woman’s predisposition related to

differences in:differences in:• Cartilage thickness differencesCartilage thickness differences• Architectural differences, such as the obliquity Architectural differences, such as the obliquity

of the 1of the 1stst MT base MT base• Tissue property differencesTissue property differences

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Cervical Spine Anatomy Sex-Based Differences• A woman’s predisposition to cervical spine A woman’s predisposition to cervical spine

affliction related to differences in:affliction related to differences in:• Architectural differences, such as the shape of Architectural differences, such as the shape of

the pedicles, laminae, and cartilage coverage on the pedicles, laminae, and cartilage coverage on articular processesarticular processes

• Tissue property differences, such as loading Tissue property differences, such as loading response of the intervertebral discresponse of the intervertebral disc

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Thoracic Spine Anatomy Sex-Based Differences• A girl’s predisposition to adolescent A girl’s predisposition to adolescent

idiopathic scoliosis (AIS) related to:idiopathic scoliosis (AIS) related to:• GeneticsGenetics• Skeletal maturationSkeletal maturation• Postmenarchal statusPostmenarchal status• Psychosocial factors that include self-esteem Psychosocial factors that include self-esteem

and body imageand body image

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Lumbar Spine Sex-Based Differences• A woman’s predisposition to lumbar A woman’s predisposition to lumbar

affliction may be related to:affliction may be related to:• Increased lordosisIncreased lordosis• Structural differences in the articular facetsStructural differences in the articular facets• Cross-sectional diameter of musclesCross-sectional diameter of muscles• Control strategy differences during static Control strategy differences during static

posture, transition, and loadingposture, transition, and loading• Increased segmental motion and decreased Increased segmental motion and decreased

segmental stiffnesssegmental stiffness

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Sacroiliac Joint Anatomy Sex-Based Differences• A woman’s predisposition to Sacroiliac A woman’s predisposition to Sacroiliac

joint affliction is related to:joint affliction is related to:• Hormone fluctuationHormone fluctuation• Architectural differencesArchitectural differences• Tissue responsesTissue responses

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Conclusion

• The musculoskeletal anatomy of men and The musculoskeletal anatomy of men and women is grossly similar, yet important women is grossly similar, yet important differences exist that may influence the way differences exist that may influence the way in which the general public views and in which the general public views and health care professionals respond to health care professionals respond to women’s musculoskeletal health issues. women’s musculoskeletal health issues.