Chapter 3 Considerations of Sex Differences in Musculoskeletal Anatomy Phillip S. Sizer, PT, PhD and C. Roger James, PhD, FACSM 1 Learning Objectives • After completing this chapter, you should understand: • • • • • • • sexual dimorphism and how it applies to humans sex differences in general morphology sex differences in skeletal geometry sex differences in collagenous, cartilage, & bone tissue sex differences in upper extremity anatomy & mechanics sex differences in lower extremity anatomy & mechanics sex differences in spine anatomy & mechanics 2 Musculoskeletal Anatomy of Men and Women • Sexual dimorphism is prominent in many species, but more subtle in humans • There are generally recognized differences in 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. 3 Differences in General Body Characteristics • Sex differences are age dependent: • Before puberty, boys and girls at the 50th percentile are approximately the same height and weight. • After puberty, men are approximately 14 cm taller and have 12 kg more mass than women. • General appearance (body shape) changes, as well. 4 Selected Sex Differences in Skeletal Geometry: Pelvis • Women have • Larger inlet and outlet • Greater interacetabular distance • Greater hip width normalized to femur length 5 Selected Sex Differences in Skeletal Geometry: Femur • Women have • Greater femoral anteversion • Narrower intercondylar notch width 6 Selected Sex Differences in Skeletal Geometry: Knee, Tibia, and Foot • Women have • Greater genu recurvatum • Greater quadriceps (Q) angle • More lateral patellar alignment • Greater tibial torsion • More bunions and deformities of the toes 7 Evidence of Sexual Dimorphism from Forensic Anthropology & Archeology • Characteristics of skeletal geometry have been used to predict an individual’s sex from their skeletal remains. • The humerus, pelvis, femur, tibia, talus, and calcaneus all have been used for this purpose. 8 Evidence of Sexual Dimorphism from Forensic Anthropology & Archeology • The ability to predict an individual’s sex from skeletal remains differs by bone. • The strongest predictors are the tibia, femur, and calcaneus, followed by the pelvis and talus. 9 Evidence of Sexual Dimorphism from Forensic Anthropology & Archeology • Some anatomic characteristics of a bone are better predictors of sex than other characteristics. • The characteristics of the femur that best predict sex include those that are associated with the femoral head. • Combinations of characteristics are the best predictors. 10 Factors Influencing Sex Differences in Skeletal Geometry • Skeletal maturity • Environmental stresses • Genetics 11 Sex Differences in Musculoskeletal Tissues: Collagenous Tissues • There are several sex differences in collagenous tissues (e.g., tendon, ligament, skin): • • • • • • Collagen thickness Collagen orientation Collagen content Collagen diameter Collagen volume Collagen metabolism 12 Sex Differences in Musculoskeletal Tissues: Cartilage Tissue • Women have 1.5-4 times greater risk of osteoarthritis • There are several sex differences in cartilage, women having: • • • • • Less cartilage volume Less cartilage thickness Less cartilage surface area Slower cartilage accrual rate in youth Greater cartilage degradation in older age 13 Sex Differences in Musculoskeletal Tissues: Bone Tissue • Women have greater risk of bone fracture, especially after menopause. • There are several sex differences in bone, women having: • • • • • • • Slower bone accrual rate in youth Less peak bone mass in adulthood Slower bone turn-over in adulthood Less volumetric bone mineral density at some sites Less bone area at some sites Less cortical thickness at some sites Less compressive and bending strength at some sites 14 Shoulder Anatomy Sex-Based Differences • Incidence of external impingement is likely related to differences in: • Acromion process shape • Posterior capsule shortening 15 Shoulder Anatomy Sex-Based Differences • Increased incidence of glenohumeral instability in women is likely related to differences in: • Glenoid fossa inclination • Anterior capsular laxity • Decreased joint stiffness 16 Shoulder Anatomy Sex-Based Differences • Increased incidence of idiopathic capsulitis in women is likely related to differences in: • Increased thickening of the anterior-superior joint capsule at the coracohumeral ligament • Non-inflammatory synovial reaction in the area of the subscapularis tendon • Active fibroblastic proliferation and tissue transformation 17 Elbow Anatomy Sex-Based Differences • Increased incidence of tennis elbow in women is likely related to differences in: • Decreases in estrogen production • Mesenchymal changes in the tendon structure 18 Wrist & Hand Anatomy Sex-Based Differences • Increased incidence of carpal tunnel syndrome in women is likely related to differences in: • • • • • Tunnel architecture and volume Shape of the hamate hook Digital features Hand-length ratios Body mass index 19 Wrist & Hand Anatomy Sex-Based Differences • Female architectural differences likely result in the following Carpal Tunnel Syndrome precipitating factors: • • • • Increased tunnel pressure Perineural edema & fibrosis Deficits in neurophysiological function Autonomic disturbances 20 Hip Joint Anatomy Sex-Based Differences • A woman’s predisposition to stress & frank fracture at the hip are likely related to: • Architectural differences in the hip & pelvis • Reduced acetabular depth and femoral head width • Narrowed CD angle • Decreased femoral neck strength • Decreased bone mass 21 Hip Joint Anatomy Sex-Based Differences • A woman’s predisposition to labral tears at the hip are likely related to: • Decreased labral tensile strength • Increased femoral neck thickness • Decreased CD angulation 22 Knee Joint Anatomy Sex-Based Differences • A woman’s predisposition to ACL Injuries at the knee are likely related to: • Reduced femoral intercondylar notch width (controversial) • Altered biomechanical behaviors • Altered motor control strategies 23 Knee Joint Anatomy Sex-Based Differences • Biomechanical differences in women during landing and cutting: • Reduced knee flexion angle at contact • Increased knee valgus motion • Increased knee joint laxity and anterior tibial translation • Increased subtalar joint pronation • Greater ACL ligament creep 24 Knee Joint Anatomy Sex-Based Differences • Control strategy differences in women during landing and cutting: • Reduced protective hamstring activity • Increased quadriceps activity • Decreased cocontractive control • Increased soleus and gastrocnemius activity 25 Knee Joint Anatomy Sex-Based Differences • Hormonal differences in women during landing and cutting: • Menstrual fluctuations in estrogen and progesterone concentrations and receptors • Resultant fluctuations in metallomatrix protease activity and decrease fibroblastic activity within the ligament • Resultant ligament laxity 26 Ankle & Foot Anatomy Sex-Based Differences • Women differ from men in the incidence of • Achilles tendopathy • Inversion trauma 27 Ankle & Foot Anatomy Sex-Based Differences • A woman’s predisposition related to differences in: • Cartilage thickness differences • Architectural differences, such as the obliquity of the 1st MT base • Tissue property differences 28 Cervical Spine Anatomy Sex-Based Differences • A woman’s predisposition to cervical spine affliction related to differences in: • Architectural differences, such as the shape of the pedicles, laminae, and cartilage coverage on articular processes • Tissue property differences, such as loading response of the intervertebral disc 29 Thoracic Spine Anatomy Sex-Based Differences • A girl’s predisposition to adolescent idiopathic scoliosis (AIS) related to: • • • • Genetics Skeletal maturation Postmenarchal status Psychosocial factors that include self-esteem and body image 30 Lumbar Spine Sex-Based Differences • A woman’s predisposition to lumbar affliction may be related to: • • • • Increased lordosis Structural differences in the articular facets Cross-sectional diameter of muscles Control strategy differences during static posture, transition, and loading • Increased segmental motion and decreased segmental stiffness 31 Sacroiliac Joint Anatomy Sex-Based Differences • A woman’s predisposition to Sacroiliac joint affliction is related to: • Hormone fluctuation • Architectural differences • Tissue responses 32 Conclusion • The musculoskeletal anatomy of men and women is grossly similar, yet important differences exist that may influence the way in which the general public views and health care professionals respond to women’s musculoskeletal health issues. 33