Orthopaedics - Hip Flashcards
What risk factors are associated with hip arthritis?
Loss of cartilage at the hip joint causes pain and stiffness as bony surfaces of the femoral head and the acetabulum come into contact.
More common in over 50s, with “wear and tear”. In some patients there are predisposing factors:
- inflammatory arthritis (RA, SLE, psoriatic arthritis) - systemic conditions that may affect multiple joints
- osteonecrosis - results in collapse of the femoral head
- previous septic arthritis - enzymes produced by bacteria destroy cartilage. Active infection is a contraindication to joint replacement
- abnormal hip shape - hip dysplasia, old slipped femoral epiphysis (SCFE), femoroacetabular impingment and old Perthe’s disease are developmental conditions that alter shape of the “ball and socket joint” causing increased wear. Patients develop OA in their 4th decade.
What signs and symptoms are associated with hip OA?
Pain: groin, buttock or thigh pain. Initially only present with movement but eventually becomes constant, even preventing sleep
Stiffness: typically patients are unable to cross their legs and getting out of a low chair or car is difficult
Limp: combination of pain, stiffness and weak muscles around hip result in a limp and the classic Trendelenburg gait
What are the key features on examination of a patient with hip OA?
Gait assessment and comment on stick or frame
Trendelenburg test whilst the patient is standing to assess hip ABDUCTORS
Range of movement - first do Thomas’ test to exclude a fixed flexion deformity, then assess all movements compared to the contralateral side: flexion, extension, abduction and adduction, internal and external rotation with the hip extended and in flexion
Leg length - erosion of the acetabulum may cause true shortening; fixed abduction contracture may cause apparent shortening
Neurovascular examination of the legs (feel for pulses and sensation), brief assessment of lumbar spine
What differential diagnoses should be considered in patients with suspected hip OA?
Spine: mechanical back pain may cause buttock or groin pain. Radiculopathy (root impingement) may cause shooting pains down the back of the leg, usually extending below the knee
Knee: pathology can cause thigh pain or limping
Tumour: primary bone tumours are rare, bony metastases are common. Weight loss, history of cancer (esp. breast and prostate), constant pain or night pain are red flags. Obtain full length femoral X rays or bone scan
Infection: septic arthritis and osteomyelitis, patient systemically unwell
Stress fracture of femora neck seen in runners; subtrochanteric fractures occur in elderly patients on bisphosphonates due to inhibition of bone remodelling
Greater trochanteric bursitis: inflammation of the bursa between iliotibial band and the greater trochanter may cause sharp localised pain. Patients typically cannot lie on their side.
What investigations should be requested in patients with suspected hip OA?
X rays - AP pelvis and lateral of the affected hip. Look for LOSS signs. Comment on leg length and the position of the femoral head in the acetabulum. Lumbar spine, full length femur and knee may also need X rays.
Bloods - routine pre op bloods if surgery is planned, CRP, ESR and RhF/ ANA if inflammatory arthritis suspected
CT/MRI - CT is good at assessing bone loss if acetabulum is severely eroded. MRI assesses soft tissues around the hip as well as the state of the cartilage if the diagnosis is not clear
What are the treatment options for OA?
Weight loss, analgesia, activity modification
Physiotherapy and use of a stick
Total hip replacement
What is osteonecrosis?
Loss of blood supply to bone is known as osteonecrosis. All joints can be affected but the femoral head is at risk because its blood supply is retrograde and tenuous.
What can cause femoral head osteonecrosis?
Idiopathic - most cases
Trauma - intracapsular neck of femur fractures disrupt the retinacular blood vessels that supply blood to the femoral head
Steroids - alterations in fat metabolism result in lipid globules in the blood, which block arterioles
Long term alcohol use
Haemaglobinopathies (e.g. sickle cell anaemia)
The bends - divers ascending too quickly develop nitrogen bubbles in the blood, which may block arterioles
What is the pathophysiology of avascular necrosis of the femoral head?
Bone just below the cartilage (subchondral bone) is the most susceptible to die if blood supply is disrupted. Initially patient complains of pain in the hip, but X rays appear normal. After a period of 3-6 months, dead subchrondral bone appears dense on X ray. Several weeks thereafter, the dead bone is resorbed and a linear lucency develops. This is known as the crescent sign. If the patient continues weight bearing, the femoral head collapses, losing its spherical shape and resulting in secondary osteoarthritis.
What is the treatment for avascular necrosis of the femoral head?
Initially, make patient non weight bearing to prevent femoral head collapse. Physio maintains ROM
Core decompression: early cases, before crescent sign appears, tunnel is drilled up the femoral neck and into the head, relieves pressure, improves blood flow and may stimulate bone healing. Results not guaranteed
THR: once head has collapsed this is the only surgical option
When is total hip replacement indicated?
Usual indication is treatment of hip OA when conservative treatment has failed and symptoms are severe enough to warrant surgery.
How many types of hip replacement are there?
3 types:
1) Total hip replacement - femoral head is replaced with a prosthetic ball and the acetabulum is relined with a prosthetic cup
2) Resurfacing - technique in which the patients femoral head is preserved and resurfaced with a metal shell. The acetabulum is relined in the same way as THR. Preservation of bone makes future revision easier, but realignment very sensitive to errors with even small deviations resulting in femoral neck fractures. Failure rates are high and technique is not as popular
3) Hemi-arthroplasty - replacement of the femoral head only, without addressing acetabulum. Used for treatment of femoral neck fractures
What is the difference between a cemented and an uncemented hip replacement?
Prosthesis may be secured to bone using bone cement. This is a polymer called polymethylmethacrylate. It acts as a grout and is injected into the femoral canal under pressure to ensure it becomes deeply embedded into the prepared bone surface. Pressurisation may force fat out of the marrow and into the bloodstream, can cause intraoperative hypotension and cardiovascular collapse during the procedure.
Alternatively an uncemented prosthesis may be used. These prosthesis are coated in hydroxyapetite (same chemical compound as calcium and phosphate found in bone) and have a roughened surface to encourage bone to integrate with the prosthesis creating a “biological bond”. Theoretically this is longer lasting than cement and avoids the issues associated with fat embolism. But the tight fit required may result in fractures of the femur or pelvis as the prosthesis is implanted.
What is a bearing surface?
The interface between the ball of the femoral head and the cup of the acetabulum is known as the bearing. The bearing carries significant load and must be low friction and hard wearing. If the bearing wears out then the hip has to be revised.
What different materials can be used for bearing surfaces?
1) Polyethylene - used in the acetabulum, cheap and low friction. Wear out with time, producing debris in the form of polyethylene particles. These small particles are the same size as bacteria, and this similarity stimulates white blood cells to produce inflammatory cytokines. Cytokines stimulate osteoclast to resorb bone around the prosthesis, causing loosening and premature failure. This is called osteolysis.
2) Metal - cheap and works well with polyethylene acetabular liners. Metal was used as the acetabular bearing, but resulted in large amounts of metal wear debris being produced and caused problems with systemic toxicity and local inflammation
3) Ceramic - hard wearing and extremely low friction. Good material for both acetabular liners and femoral heads. So hard that there is virtually no wear, making it good for young patients. It is expensive and can fracture if exposed to sudden shock loading
What complications are associated with total hip replacement?
1) Nerve injury - sciatic nerve is particularly at risk resulting in foot drop and numbness in the foot. Common causes include traction on the nerve or compression by retractor placement
2) Bleeding - average is 250ml
3) DVT - without prophylactic anticoagulation DVT is common after THR. Chemical and mechanical thromboprophylaxis should be used
4) Infection - clean air supply in theatre, antibiotic loaded cement and perioperative antibiotics. If the prosthesis becomes infected a two stage revision may be indicated in which the hip is removed, the patient is given antibiotics for 6 weeks before a new prosthesis is inserted
5) Dislocation - may occur if soft tissues are not balanced or the prosthesis is malpositioned intraoperatively. Precautions including avoidance of crossed legs, bending over and sitting in low chairs
6) Leg length discrepancy - if the acetabulum has been severely eroded or the hip is an abnormal shape, leg length differences are more common. Up to 15mm difference is usually well tolerated.
How should a painful THR be investigated?
Infection - this is the first diagnosis to exclude. Infection may occur many years after surgery. It may be due to bacteria introduced at the time of surgery, or haematogenous spread of bacteria in conjunction with an infection elsewhere in the body such as a dental abscess. Check CRP and ESR and get a bone scan, which will show increased uptake around the prosthesis.
Loosening - may be due to polyethylene debris osteolysis or infection. X ray signs of loosening include a lucent line around the prosthesis or migration of the prosthesis on serial views
Fracture - may occur intraoperatively, especially with uncemented implants, or post operatively following a fall. If the femoral stem is loose it needs to be revised; if it remains fixed in the femur, cables and a plate can be used to reconstruct the bone around the stem
Other diagnosis - if the patients pain has not got better after THR was it the right diagnosis?
What is developmental dysplasia of the hip?
DDH is a condition in which the femoral head does not lie within the acetabulum. It is a spectrum of disease ranging from a femoral head that sits reduced for most of the time but can be pushed out of the acetabulum, often with a palpable or audible “clunk” (known as “clicking hip”) to a hip that is subluxed (partial contact remains between the head and acetabulum), to the most severe form where the hip is dislocated and irreducible.
Failure to obtain congruent reduction in a child means that the femoral head will not grow spherically and the acetabulum will not form properly. In later life this can lead to leg length discrepancy, abnormal gait, arthritis and pain.
What risk factors are associated with DDH?
Breech position
First born
Oligohydramnios - these three risk factors restrict the space in the uterus for foetal development
Female sex - higher levels of oestrogen result in increased ligamentous laxity
Family history - 6% if normal parent, 12% if affected parent, 36% if affected sibling AND parent
DDH is commonest in the left hip because this is usually the side of the foetus that presses against the mothers spine. DDH is also associated with torticolis and metatarsus adductus. Collectively these conditions are known as packaging disorders, resulting from restricted uterine space. It is thought that 1 in 60 neonates in the UK may have a degree of DDH, but most of it resolves spontaneously by 6 weeks.
What clinical signs are associated with DDH?
Gluteal fold asymmetry - poor sensitivity but sometimes noted by healthcare workers or parents when changing nappies
Abduction range - a very simple test to check the range of abduction of both hips. Asymmetry raises concerns
Barlow’s test - detects a hip that can be dislocated posteriorly. Flex hip and knee to 90 degrees and gently axially load, feeling for a clunk. Barlow’s push Backwards!
Ortolani’s test - this test detects a hip that is already dislocated and can be reduced. Flex the hip and knee to 90 degrees and keep your index finger on the greater trochanter. Abduct the hip gently and exert gentle forward pressure with your finger, feeling for the hip popping back into the joint. Ortolani’s Open legs!
Galeazzi test - flex hip and knees to 90 degrees and look from side for difference in patellar height indicating leg length discrepancy
What imaging is required in DDH?
The superior ossific nucleus of the femur, which will go on to form the femoral head, does not appear on x ray until around 6 months of age, therefore X rays are of limited use for this age group.
Ultrasound: not only does it detect cartilagenous structures, it is dynamic, meaning that real time screening can be performed as the hip is moved around. The scans can be difficult to interpret but the key measurement is the angle between the the bony roof of the acetabulum and the iliac wing. This is known as the alpha angle. Normal values should be greater than 60 degrees. An angle less than this indicates the acetabulum is shallow and is less likely to keep the femoral head in the joint.
Arthrogram - if doubt remains about whether the hip is transiently dislocating, subluxed or permanently dislocated, an arthrogram can be performed. Under anaesthetic, contrast is injected into the joint space and the hip is screened under fluoroscopy in a variety of positions
When are X rays useful in DDH?
In children over 6 months of age, the femoral head can be seen as a small dot. Two lines are drawn on X ray; Hilgenreiner’s line across the triradiate cartilages of the acetabulae; Perkin’s line perpendicular to Hilgenreiner’s line passing through the lateral edge of the roof of the acetabulum. The head should be in the inferomedial quadrant formed by these two lines. Shenton’s line can be traced and should be unbroken.
How should DDH be treated in a child of under 6 months of age?
A Pavlik harness is a device that holds the hips reduced. Straps keep the hip flexed and abducted. Too much flexion risks femoral nerve injury, too much abduction risks avascular necrosis of the femoral head. The harness should be worn for 23 hours per day. Reduction should be confirmed with USS. The usual duration of treatment is 6 months.
How should DDH be treated in a child between 6 months and 2 years?
In this age bracket ALL children should have an examination under anaesthetic and arthrogram in order to determine if any structures are blocking concentric reduction.
If the hip is reduced with the leg in a safe position (avoiding extremes of abduction or flexion) a hip spica cast can be applied for a total of 3 months. If the hip is irreducible or only reduced in an extreme position, open reduction may be required. Most surgeons will defer this until the child is 18 months of age because the risk of surgery is less in older children.
