Hip

Question 1

What are femur bony features?

Answer 1

• Head (convex). 2/3 of a sphere. Articular cartilage covering is thickest on medial central surface
• Neck (anatomical and surgical) - 135 degree to shaft. Angle of inclination (neck to shaft) and torsion angle (angle between axis through femoral head and axis through femoral condyles) are important
• Intertrochanteric line - continues as pectineal line posteriorly
• Intertrochanteric crest
• Greater trochanter - attachment for gluteus medius, gluteus minimum, piriformis, vastus lateralis
• Lesser trochanter - attachment to iliopsoas
• Fovea capitis (dimple on the head of femur) - attachment for ligamentum teres (2 bands that originate at ischial and pubic sides of acetabular notch). Provides stability to joint and prevents subluxation during flexion and abduction. Connection of femoral head to pelvis

Question 2

What is the ligamentum teres?

Answer 2

• Intracapsular
• Serves as carrier for foveal artery which supplies femoral head in infant
• Injuries to the ligamentum teres can occur in dislocations which can cause lesions of foveal artery

Question 3

What are pelvis bony features?

Answer 3

• Ilium
• Ischium
• pubis
• Ischial spine
• Ischial tuberosity
• Inferior pubic ramus
• Superior public ramus
• Pubic symphysis
• Obturator foreman
• Greater and lesser sciatic notch
• Greater and lesser foreman
• ASIS, AIIS
• PSIS (back dimples), PIIS
• Anterior gluteal line
• Posterior gluteal line
• Inferior gluteal line
• Articular cartilage covers the surface of the acetabulum and thickens laterally and peripherally
• Articulation only occurs on the horseshoe shaped articular cartilage located peripherally
• Acetabular labrum (a fibrocartilage lip that deepens acetabulum) blends with transverse acetabular ligament

-Transverse acetabular ligament spans acetabular notch to prevent inferior dislocation of femoral head

Question 4

What is the hip joint?

Answer 4

• Ball and socket synovial joint
• Head of femur is 2/3 of a sphere
• Allows movement in triaxial joint (sagittal, frontal and transverse)
• Allows wide range of movement
• More stable than shoulder joint but reduced mobility. Reduced chances of dislocation
• Hip joint = socket is much deeper, and ligaments and muscles are bigger than in shoulder joint
• The socket (acetabulum) fully encompasses femoral head, making this joint stable, whereas humeral head is 4x larger than glenoid fossa
• The hip joint is controlled and protected by the acetabular labrum, the joint capsule and many powerful muscles
• Head of femur articulates with lunate surface of acetabulum. Covered by hyaline cartilage

Question 5

What are the motions available?

Answer 5

-Transverse, sagittal and frontal

• Transverse= allow internal and external rotation
• Sagittal = allow flexion and extension
• Frontal = abduction and adduction
• Motion is greatest in the sagittal plane.
• Flexion = 0 to 140 degrees
• Extension = 0 to 15
• Abduction = 0 to 30
• Adduction = 0 to 25
• External rotation = 0 to 90
• Internal rotation = 0 to 70

Important point: range of motion is influenced by age, speed of movement

• As people age, they use a progressively smaller portion of the range of motion
• With ageing, comes changes loss in motor control and decrease in fast twitch fibres
• Ageing muscles are unable to produce as much force per time compared to younger muscles
• Large deficits have been shown in the plantar flexor groups

Question 5

What is the acetabular labrum?

Answer 5

• Made up of fibrocartilage tissue
• Contains femoral head at extremes of motion, especially flexion
• Load bearing structure
• Blends with acetabular transverse ligament - provides support
• Increases stability of hip joint by deepening the acetabulum and increasing the area of articulation with head of femur
• Has a lot of vascular tissue in the internal articular surface within labrum so good healing
• sensitive shock absorber
• labrum helps stabilise and maintain congruence
• Labrum helps maintain a vacuum in the centre of the acetabulum fossa (depression at the centre created by peripheral cartilage thickening). Helps maintain stability
• Deficiency can lead to rotational instability and hypermobility which can cause abnormal load distribution

Question 7

What is the angle of Wiberg and angle of anteversion?

Answer 7

• A malalagined acetabulum won’t adequately cover the femoral head, often leading to dislocation and osteoarthritis
• Angle of Wiberg (centre-edge angle) and angle of acetabular anteversion= describe the degree to which the acetabulum covers the femoral head
• Angle of Wiberg = extent to which the acetabulum covets femoral head in the frontal plane
• is usually 35-45 degrees. Provides a protective shelf over the femoral head
• A smaller angle contains less femoral head which increases the risk of dislocation
• Acetabular anteversion angle describes how much the acetabulum surrounds the femoral head within the horizontal plane
• Average value is 20 degrees
• Pathological increases in Acetabular anteversion decreases joint stability and liklihood of anterior dislocation

Question 8

What is a pincer? What is a cam?

Answer 8

• Pincer = extra bone extends out over normal rim of acetabulum (over coverage of acetabulum)
• Cam = bony protrusion in neck of femur. So femoral head grinds on cartilage inside acetabulum
• You can have both cam and pincer
• Leads to stiffness in thigh, hip or groin

Question 9

What is femoroacetabular impingement (FAI)?

Answer 9

• Abnormal inclination and torsion angles, as well as bony deformities can lead to FAIs
• This is a painful condition caused by the bone of the femoral neck bashing into or catching on the acetabulum during motion. Caused by bone overgrowth on femur or acetabulum
• Abnormal contact between the bony prominences leads to soft tissue damage in and around the joint
• This chronic repetitive trauma can lead to hip pain and decreased function
• Both Cam and pincer lesions can be present (seen on radiographs)
• this can cause labral and cartilage injury; hip osteoarthritis
• genetic factors may contribute to abnormal hip pathology e.g SNPs in HOX9

-Impingement test: doctor brings your knee up towards your chest and rotate it inwards towards your opposite shoulder. If this creates pain in the hip, it’s positive for impingement

Management:

• physical therapy and pain medication (NSAIDS)
• surgical: hip arthroscopy (minimises soft tissue disruption) use camera. Doctor can repair or clean out any damage to labrum or cartilage; correct FAI by trimming the bony rim of the acetabulum and also shaving down bump on femoral head
• pelvic osteotomies

For Cam lesion = cam resection or femoral osteoplasty is performed using a high speed burr to shave down excess bone

For pincer lesion = acetabular osteoplasty is performed

Question 10

What is the angle of inclination and the angle of torsion?

Answer 10

Angle of inclination:

• neck to shaft angle
• inclination angle is 140-150 degrees at birth but decreases to 125 degrees in adults
• An angle of greater than 125 degrees produces coxa valga
• An angle less than 125 degrees produces coxa vara
• Both coxa valga and cox vara have benefits but the negatives outweigh them
• Coxa valga: increase moment of hip abductor force to increase joint stability but increase sheer forces across femoral neck
• Coxa vara: decreases sheer forces across femoral neck but can increase the risk of dislocation as there’s less joint stability

Angle of torsion

• medial rotatory migration of lower limb bud during fetal development
• Commonly 40 degrees in neonates but decreases after 2 years to 10-20 degrees
• Less than 12 degrees = anteversion which causes portion of femoral head to be uncovered which increases the tendency for internal rotation during gait cycle to keep femoral head in Acetabulum
• More than 12 = retroversion. Tendency for external rotation during gait cycle

Question 11

Explain the gait cycle

Answer 11

• Joint is maximally flexed during the late swing phase of gait as limb moved forwards
• The joint extended as body moved forward at the beginning of stance phase
• Maximum extension is reached at heel off
• Abduction occurred during swing phase, reaching its maximum just after toe off
• At heel-strike, the hip joint reversed into adduction which is continued until late stance phase
• The hip joint was externally rotated throughout swing phase, rotating internally just before heel strike
• The joint remained internally rotated until late stance phase, at rotated externally

Question 13

What is the trabecular structure of the proximal femur?

Answer 13

• The interior of the femoral head and neck are composed of spongey bone with trabecular organised into medial and lateral systems
• Lateral trabecular system resists compression of the femoral head produced when the abductor muscles contract (resists compression forces on femoral head)
• Medial system resists joint reaction forces

Question 14

What are other joints of the pelvis?

Answer 14

Pubic symphysis:

• Secondary cartilaginous joint
• Made from fibrocartilage and hyaline cartilage
• Connects pubic bones
• Supported by anterior arcuate ligaments

Sacroiliac joints:

• Synovial joint between ala of sacrum and articular surface of ilium
• reinforced anterior, posterior, long and short sacroiliac ligaments

Question 15

What are important pelvic ligaments?

Answer 15

• Anterior and posterior sacroiliac ligament (prevent anterior and inferior movement of sacrum)
• Sacrospinous ligament = assists external rotation of pelvis
• Sacrotuberous ligament = prevent sacrum tilting backwards
• Iliolumbar ligament = joints L4 and L5 to iliac bone crest. 5 bands
• Inguinal ligament = from ASIS to pubic tubercle. Attach oblique muscles to pelvis

Question 16

What is the iliofemoral ligament?

Answer 16

• Capsular ligament
• High tensile strength
• Y shaped
• Twisted during standing
• keeps femoral head in contact with acetabulum
• limits external rotation, adduction and medial rotation
• prevents hyperextension of hip joint when standing

Question 17

What is the pubofemoral ligament?

Answer 17

• Capsular ligament

- Limits extension and external hip rotation

Question 18

What is the joint capsule?

Answer 18

• The hip joint is enclosed by a strong fibrous capsule
• External fibrous layer of capsule is attached to acetabulum and transverse acetabulum ligament

There are 3 capsular ligaments:

• anterior = iliofemoral and pubofemoral —> provide anterior support
• posterior = ischiofemoral —> provide posterior support
• They are tightest in extension and medial rotation
• They are loose in flexion and lateral rotation

Muscles are important to assist the capsular complex

-Chronic knee hyperextension due to weak quadriceps and short ankle plantarflexors transmit an anterior force to head of femur - can compress femoral head in acetabulum

Question 19

What are the normal hip movements?

Answer 19

• Flexion= 140
• Extension = 20
• Adduction = 30
• Abduction = 90
• Internal rotation = 30
• External rotation = 60

Question 20

What are the hip flexors?

Answer 20

• Iliacus
• Psoas major
• Rectus femoris
• Sartorius

Question 21

What are hip extensors?

Answer 21

• Gluteus maximus
• Semimembranous
• Semitendinous
• Biceps femoris

Question 22

What are the hip abductors?

Answer 22

• Gluteus maximus
• Gluteus minimus
• Gluteus minimus
• Tensor fascia lata

Question 23

What are the hip adductors?

Answer 23

• Adductor longus, brevis, Magnus
• gracilis
• pectinus

Question 24

What are the medial and lateral rotators?

Answer 24

Medial rotators:

• tensor fascia lata
• Psoas major
• iliacus
• gluteus minimus

Lateral rotators:

• gluteus maximus
• gemellus superior and inferior
• obturstor internus and externus
• quadratus femoris
• piriformis

Question 25

What is the ischiofemoral ligament?

Answer 25

• Weakest capsular ligament

- Limits extension and internal hip rotation

Question 26

What is the neurovascular supply of the hip joint?

Answer 26

• Mainly medial and lateral circumflex femoris arteries (from profunda femoris)
• Medial circumflex artery is the major blood supply because the lateral circumflex artery must penetrate the thick iliofemoral ligament to reach the joint
• As a result, damage to the medial circumflex artery can cause avascular necrosis of the femoral head

Sciatic nerve (L4-S3), femoral nerve (L2-L4) and obturator nerve (L2-L4) supply sensation to your hip and knee. This can explain why hip and knee pain can be referred in a bidirectional manner

Question 27

What is avascular necrosis?

Answer 27

• Death of femoral head due to vascular disruption
• Results in pain around hip with insidious onset
• Potential causes: trauma, haematological disease, sickle cell anaemia

-Fractures and dislocations can disrupt or rupture the profunda femoris (medial/lateral femoral circumflex artery)

• Because the 2 arteries are from the profunda femoris, it leaves the femoral head vulnerable to avascular necrosis
• Foveal artery is also commonly disrupted during dislocation

Traumatic AVN:

• associated with damage to medial circumflex femoral artery (the main supply to femoral head)
• leads to death of cells in bony matrix and the reparative process begins, weakening the subchondral bone
• can lead to bony collapse and arthritic changes to joint

Atraumatic AVN:

• coagulation of intraosseous microcirculation causes venous thrombosis
• leads to arterial occlusion due to lack of venous outflow
• this increases pressure within bone, compressing capillary beds and decreasing blood flow to the femoral head
• this leads to cell death and repair, as in traumatic AVN

Physical examination:

• inspection of hip, skin and greater trochanter
• thorough neurovascular exam is required to assess sensory and motor function
• leg roll test: specific test for hip. Patient is supine, gently rolling thigh internally and externally
• stinchfield test: involves resisted hip flexion - a positive test elicits pain which is likely to be associated with intraarticular hip pathology
• Use MRI. It’s 98% sensitive

Treatment:
Non-operative=
-bisphosphonates (limited to small lesions)
Operative=
-core depression of femoral head with or without stem cell injection: Drilling holes into femoral head. Relieves increase in pressure within femoral head, allowing blood flow and healing. Creates channels for new blood vessels to nourish the affected areas of the hip

• Osteochondral (bone and cartilage grafting): used with core depression to help regenerate healthy bone and support cartilage at the hip joint. A bone graft is healthy bone tissue that is transplanted to where it is need. It can be autograft or allograft.
• vascularised fibula graft: segment of fibula is taken along with its blood supply. This graft is transplanted into a hole created in the femoral head and neck, and the artery and vein are reattached to help heal the area of AVN.
• total hip resurfacing: requires adequate bone stock to support resurfacing component. Metal on metal articulation
• total hip replacement: most reliable pain relief. Both the head of femur and acetabulum are replaced with an artificial device. Doctor also removes damaged bone and cartilage

Question 28

What is developmental dysplasia of hip (DDH)?

Answer 28

• abnormal hip development. Ball is loose in socket. In all cases, acetabulum is shallow
• risk factors: female sex, first born infant, family history (genes such as HOX9 and DKK1)
• There are different grades of classification: always dislocated, disloctable, subluxatable (mild case)- ball is loose in socket but won’t move out
• Any interference with proper contact between femur and acetabulum in utero or infancy leads to DHH
• Lower limb buds develop around 4 weeks; chondroblasts aggregate to form future bones of the hip
• femoral head grows faster than acetabulum which results in under coverage of femoral head leading to abnormal development
• The acetabulum continues to grow up to the age of 5 hence DHH may develop at any time from embryogenesis to 5 years
• Malaligned contact for prolonged periods leads to chronic changes like hypertrophy of capsule, ligamentum teres —> preventing relocation of femoral head

Examinations:
-Ortolani manoeuvre: infant in supine position with hip flexed at 90 degrees and neutral position. Apply anterior force on the greater trochanter and abduct hip. If the hip is dislocated, one would feel a jerk or clunk

-Barlow manoeuvre: same position as ortolani manoeuvre. Apply posterior force to trochanter, adduct hip

Use ultrasound for abnormal hip examination with plain radiographs

Management:

• adolescent/adult hip preservation surgery - periacteabular osteotomy is an option for those with pain and shallow acetabulum
• abduction splints (Pavlik harness) can be tried at an early stage for new borns. Holds the hip in position whilst allowing free movement of legs. Also tightens ligaments and promotes normal hip socket formation
• For infants who fail the splints, a closed reduction with a hip spica cast is preferred
• Open surgery: incision is made at the baby’s hip and femur is sometimes shortened to help fit the bone into the acetabulum. Also realigns hip

Question 29

What are hip fractures?

Answer 29

• Occurs in proximal femur
• Most hip fractures occur in elderly patients whose bones have become weakened by osteoporosis
• In young patients, it’s caused by high energy event

-Hip fracture can occur in femoral neck, femoral head, Intertrochanteric area, subtrochanteric area

Symptoms:

• pain in groin and upper part of thigh
• pain will be elicited on pin-rolling the leg

1) Femoral neck fracture (intracapsular - within capsule and extracapsular)
- intracapsular = subdivided into capital, subcapital and transcervical
- extracapsular = occur outside capsule. encompass Intertrochanteric(between the greater and lesser trochanter), intratrochanteric and subtrochanter fractures (found anywhere between the lesser trochanter to 5cm distally)
- usually require surgery

• The blood supply to the neck of femur is retrograde (passing from distal to proximal along the femoral neck to the femoral head)
• The predominant supply is from the medial circumflex femoral artery which lies directly on the intracapsular femoral neck
• The lateral circumflex artery provides less blood as it has to pierce the thick iliofemoral ligament
• So a displaced intracapsular neck of femur can disrupt the blood supply to the femoral head, causing avascular necrosis
• Any patients with a displaced intracapsular fracture will require arthroplasty, as opposed to fixation

Investigations:

• Plain film imaging (AP and lateral views of affected views)
• Full length femoral radiographs
• Basic blood tests in case transfusion is needed in surgery

Management:

• opioid analgesia for pain
• physiotherapy
• total hip replacement for displaced intracapsular fracture
• open reduction: make incision over hip joint, put the bone back into place and hold the bone with pins and screws - does carry the risk of avascular necrosis

Intertrochanteric fractures
-treated surgically with either a sliding compression hip screw and side plate or an intramedullary nail

Question 30

What is osteoarthritis?

Answer 30

• Degenerative disease of synovial joints that causes progressive loss of articular cartilage
• Increase in water content in articular cartilage and alternations in proteoglycans and collagen abnormalities
• mild inflammation which progresses to moderate inflammation and hypervascularity
• in the late stage of osteoarthritis, the synovium becomes thickened excessively vascular, with subchondral bone attempting to remodel damage —> this results in lytic lesions and sclerotic edges
• proteolytic enzymes and cytokines increase the inflammation

-Mainly occurs in people 50 years of age

Symptoms:

• stiffness
• pain in groin or thigh that radiates to buttocks or knee
• mechanical instability (e.g locking)

Cause:

• increasing age
• family history of osteoarthritis
• obesity
• improper formation of the hip joint at birth (developmental dysplasia of the hip)

Use radiographs

Non-operative management:

• NSAIDs
• Walking stick
• Weight loss, activity modification and exercise
• Corticosteroid joint injections

Operative management:

• arthroscopic debridement (used to clean up arthritic joints - used for degenerative labral tears)
• periacetabular osteotomy with or without femoral osteotomy (indicated in young adults with reduced hip and mild to moderate arthritis
• femoral head resection (for pathological hip lesions and painful head subluxation)
• Hip resurfacing (damaged bone and cartilage is removed and replaced with metal shell. Head of femur isn’t removed but instead it is called with a smooth metal covering)
• Total hip arthroplasty (indicated in end stage, preferred for older patients). Doctor will remove damaged acetabulum and femoral head, then position a new metal or plastic joint surfaces to restore the function of the hip

Question 31

What is slipped upper capital femoral epiphysis (SUFE)?

Answer 31

Aetiology:

• when proximal femur epiphysis is displaced posterinferiorly to the head and neck
• hypothesised that displacement occurs due to high physiological axial load transmitted across a weak physis
• endocrine disorders can weaken the physis
• exact mechanism is unclear
• idiopathic

Symptoms

• pain in hip, groin, thigh or knee
• limited internal rotation. Internal rotation may elicit pain
• may have Drehmann sign = external rotation and passive flexion of hip at 90 degrees
• thigh atrophy may or may not be present

Investigations

• Use radiographs
• MRI can be done
• Use lab testing for endocrine or renal disorders

Management:
-analgesia for pain

• In situ fixation: for mild cases. Doctor makes small incision near the hip, then inserts a metal screw across the growth plate to maintain the position of the femoral head and prevent any further slippage
• Open reduction: doctor makes an open incision in the hip, then gently manipulates/reduce the head of femur back into its normal anatomical position
• Dunn’s procedure: removing greater trochanter, screwing through the physis to align it with the head of the femur, then screwing greater trochanter back on —> this process can lead to avascular necrosis if arteries are disrupted

Question 32

What are the kinetics of the hip?

Answer 32

• Hip flexion of at least 120 degrees, abduction of at least 20 degrees and internal and external rotation are required for daily activities
• Gait involves motion in all 3 planes (sagittal, frontal and transverse)
• Use of cane on the contralateral side of the affected hip or a brace can substantially alter and frequently decrease magnitude of the hip joint reaction force