Interventional procedure overview of supercapsular percutaneously assisted total hip arthroplasty for osteoarthritis

Indications and current treatment

Osteoarthritis, also known as degenerative joint disease, is a disorder of synovial joints. It occurs when damage triggers repair processes leading to structural changes in a joint. There are 2 main types of osteoarthritis: primary (more generalised osteoarthritis with unknown aetiology) and secondary (osteoarthritis with a known cause, such as injury or inflammation in the joint). When it affects the hip, symptoms include joint stiffness, pain and reduced function, such as difficulty walking.

Care and management of osteoarthritis is described in NICE's clinical guideline on osteoarthritis. Current management of hip osteoarthritis includes lifestyle changes (such as weight loss), physical or occupational therapy, medications, and surgery (such as hip resurfacing, THA and osteotomy).

What the procedure involves

Supercapsular percutaneously assisted THA is also described as the 'SuperPath' approach. It is a minimally invasive approach to THA. The aim, as with standard posterior or direct lateral approaches, is to reconstruct the hip to reduce symptoms and improve hip function, but with smaller cuts and less tissue damage.

The procedure is done under general or regional anaesthesia. The patient is usually put in the standard lateral decubitus position with the hip in 45 degrees of flexion and 10 to 15 degrees of internal rotation. A cut is made superior to the greater trochanter. The gluteal fascia is cut, the gluteus maximus muscle is split, the gluteus medius and minimus muscles are retracted anteriorly, and the piriformis tendon is retracted posteriorly. Once the joint capsule is exposed, it is cut from the base of the greater trochanter to 1 cm proximal to the acetabular rim.

The femoral canal is then reamed and broached without dislocation. The femoral neck is osteotomised and the femoral head removed. The implant trial cup is placed into the acetabulum to allow access of instruments for its preparation. A second cut is made and using an external guide, a distal and posterior portal is then formed for acetabular reaming. Once the acetabulum is reamed, the definitive acetabular component and polyethylene liner are inserted and secured. Trial femoral components are reduced and tested for stability and tissue tension. Once the trial components are removed, the definitive femoral stem is inserted and the femoral head implanted. The hip joint capsule is preserved and closed with a suture. Then the gluteal fascia and skin are closed with sutures.

The procedure usually takes about 2 hours. Specific cementless implants and various specialised instruments are used. Postoperative rehabilitation is recommended for muscle strengthening and mobility.

Outcome measures

The Barthel Index consists of 10 items that measure a person's daily functioning, particularly the activities of daily living and mobility. The items include feeding, transfers from bed to wheelchair and to and from a toilet, grooming, walking on a level surface, going up and down stairs, dressing, and bowel and bladder continence. Scores range from 0 (totally dependent) to 100 (completely independent).

The HHS evaluates the results of hip arthroplasty. It covers pain (1 item, 0 to 44 points), function (7 items, 0 to 47 points), absence of deformity (1 item, 4 points), and ROM (2 items, 5 points). Scores range from 0 (maximum disability) to 100 (no disability).

The HOOS assesses the patient's opinion about their hip and associated problems, and evaluates symptoms and functional limitations related to the hip during a therapeutic process. It consists of 40 items assessing 5 subscales: pain, symptoms, activity limitations daily living, function in sport and recreation, and hip-related quality of life. Scores range from 0 (extreme symptoms) to 100 (no symptoms).

The HOS is a self-reported questionnaire, evaluating the outcomes of treatment for hip pathologies, divided into 2 subscales: activities of daily living (19 items) and sports (9 items). The activities of daily living and sports subscale scores are normalised to obtain a range between 0 and 100, with higher scores representing better function.

The Merle d'Aubigné Hip Score is a hip function evaluation instrument and includes the parameters for pain, mobility and ability to walk, with each rated from 0 (worst condition) to 6 (best condition).

The TUG test is a simple test that assesses a person's mobility and needs both static and dynamic balance. It uses the time that a person takes to rise from a chair, walk 3 meters, turn around 180 degrees, walk back to the chair and sit down while turning 180 degrees.

The TSC test is a measure of ability to ascend and descend a flight of stairs. It uses the time needed to go up and down a flight of 12 stairs.

The WOMAC is a disease-specific measure for hip and knee osteoarthritis. It consists of 24 items: 5 items about pain (score range 0 to 20), 2 items about stiffness (score range 0 to 8) and 17 items about physical functioning (score range 0 to 68). Higher scores on the WOMAC indicate worse pain, stiffness and functional limitation.

The iHOT-12 is a self-reported outcome used to evaluate quality of life in people with hip osteoarthritis. The questionnaire captures pain, symptoms and activity impairments. Scores range from 0 to 100, with lower scores representing greater impact.

The SF-12 is a self-reported outcome measure that assesses the impact of health on an individual's everyday life. It covers physical health-related domains (general health, physical functioning, role physical and body pain) and mental health-related scales (vitality, social functioning, role emotional and mental health). Scores range from 0 to 100, with higher scores indicating better physical and mental health functioning.

Safe zones for acetabular cup position, based on radiographs: