Instability and Dislocation:
This is the most common complication leading to revision hip arthroplasty.
The incidence ranges from 0.3% to 10% after primary and 10% -28% after revision hip arthroplasty.
Posterior dislocation is more common than anterior with trauma and poor muscle tone as a risk factor.
Mal position of the surgical implant is an important surgical factor.
Plain radiograph is the investigation of choice and often occurs in the immediate post op period due to haematoma or a few years after the surgery due to wear of implant.
Osteolysis And Aseptic Loosening-
Second most common cause of morbidity and revision accounts for 19.7% of revision procedures.
The contributing factors include wear of prosthetic components,
poor initial position of implant and failure of fixation.
It is clinically associated with pain and discomfort.
Plain radiograph and CT supersede MRI in assessment of loosening.
The radiological features are
· Uniform periprosthetic radiolucency of more than 2mm- Aseptic loosening.
· New lucency less than 2 mm which is not visible on previous imaghing.
· Particle disease produces multifocal radiolucency related to localized osteolysis.
· Evidence of prosthesis movement- Varus orientation/rotation of component.
· Cement fracture.
Infection is the third most common cause that contributes to 14.8% of all revisions hip arthroplasties.
Infection can occur either early in the post operative period or present late in case of low grade infection.
Ultrasound is useful in assessment of collections or hip joint effusion.
Plain radiographs and CT are once again play the main role in diagnosis with loosening
· Infection can produce either pattern of radiolucency,
· Soft tissue abnormalities- such as joint distension and fluid collection (MR is superior but ultrasound may be easily accessible in certain circumstances)
· Arthrocentesis and synovial biopsy may be required to confirm the diagnosis in low grade infections.
· US guided aspiration and periarticular fluid assessment may be required.
· Nuclear medicine scan can be problem solving-
· Combined leucocyte-marrow imaging has 90% accuracy.
The incidence of periprosthetic fractures is less than 1% with femoral periprosthetic fracture being more common.
Vancouver classification is used for classification and has very good interobserver and intraobserver reliability.
Vancouver type A fracture is located in the trochanteric region,
type B fracture is located about the stem or the tip of the stem,
and a type C fracture is well distal to the tip of the stem.
In rare circumstances,
the metallic hardware can give way resulting in fracture of the femoral stem,
dissociation of the modular femoral component and fracture of acetabular liner,
which is more common with ceramic liners.
Wear of the poly liner is a common long term sequale/complication presenting with dislocation.
Heterotropic ossification is seen in 15%-50% of patients after the hip arthroplasty.
Patients typically present with hip stiffness.
Detectable calcification density can be seen on radiographs and CT within weeks after surgery and ankylosis seen as early as 12 weeks after the surgery.
A three phase bone scan is more sensitive and can be positive 4-6 weeks prior to calcification detected on plain radiograph or CT.
incipient HO can be detected on blood pool images as early as 2.5 weks after injury and the delayed phase become positive a week later.
Surgical excision is considered after maturation of HO and serial pre-operative bone scan can help quantify ratio of heterotropic to normal bone activity to avoid delay and subsequent risk of ankylosis.
Brooker classification is used for grading HO.
Grade 1 represent island of bone in soft tissue.
Grade 2 includes bone spur that arise from pelvis or proximal femur leaving >1cm between the opposing surfaces.
Grade 3 is similar to grade 2 but < 1cm between the opposing surfaces,
grade 4 is complete ankylosis.
Pseudobursae are irregular recesses that communicate with the joint and are typically detected at arthrography or cross sectional imaging.
Inflammation of the bursae can also be seen post hip arthroplasty due to altered dynamics of the joint.
Periprosthetic soft tissue adverse reaction to metal debris is another significant complication seen in metal on metal hip arthroplasties.
Increased local ion concentrations secondary to wear of implant can lead to hypersensitivity reactions and soft tissue derangement known as aseptic lymphocytic vasculitis associated lesion (ALVAL) or pseudotumour.
Pseudotumours have been classified by Hauptfleish et al as type 1 characterised by periprosthetic fluid collection with a thin smooth wall measuring <3mm in thickness.
type 2 have irregular wall with thickness of >3mm and contains multiple septations and debris whereas type 3 are predominantly solid mass.