Revision Hip Replacement: Causes, Failed Implants and Cases

Revision hip replacement removes and replaces some or all of a failed hip implant, one that has loosened, dislocated, fractured or become infected. Hips altered by an acetabular or femoral neck fracture that failed to heal, by avascular necrosis or by developmental dysplasia need complex primary replacement on the same principles. Each cause leaves a different pattern of damage, and each demands its own reconstruction.

Dr. Rakesh Mahajan, Vice Chairman & HOD - Orthopedics, BLK-Max Super Speciality Hospital, New Delhi, India, names dysplastic hips, avascular necrosis and post-traumatic arthritis as the most common indications for complex hip replacement. This article takes each cause in turn, explains what goes wrong in the joint and how he deals with it, and closes with the cases he presented. The complete guide to complex total hip arthroplasty gives the overview, and the article on acetabular reconstruction, implants and surgical approach explains the reconstruction techniques referred to here.

Hip replacement after an acetabular fracture

Severe fractures of the acetabulum, the socket of the hip, are a leading route to complex hip replacement. They can be stable or unstable and come in several patterns, and Dr. Mahajan stresses that they are not easy to hold in position. They may malunite (heal in the wrong position) or fail to unite at all, and either outcome can progress to established post-traumatic arthritis.

Replacing a hip after an acetabular fracture means dealing with the fracture first. Where the socket has split apart, a condition called diastasis, the walls must be restored before any cup can be seated. Where the posterior wall is the main problem and the anterior wall is intact, the wall can be fixed with a plate and screws and the replacement placed on that stable foundation. Where both walls have opened up, a cage is needed to carry the cup.

Hip replacement for avascular necrosis of the femoral head

Avascular necrosis (AVN), also called osteonecrosis, is death of bone caused by loss of its blood supply. The femoral head is especially vulnerable. Its blood arrives mainly through the retinacular (capsular) vessels, which arise from the medial circumflex femoral artery, a branch of the profunda femoris. When these vessels are damaged or thrombosed, the head loses its blood supply, the overlying cartilage is damaged and severe arthritis follows.

AVN after hip fractures

Fractures of the femoral neck, especially subcapital fractures just below the head, carry a high risk of AVN because the vessels to the head are so easily disrupted. Dr. Mahajan points out that the fracture can unite and still lead to AVN.

AVN in sickle cell disease

Sickle cell disease causes AVN of the femoral head in the same way: the blood supply to the head is damaged, the bone begins to die, and the hip progresses to arthritis. In adults, Dr. Mahajan plans surgery jointly with the haematology team. In his practice, once the sickle cell level in the blood (the proportion of sickle haemoglobin) is below 20%, the patient is fit for surgery, and most of these patients receive a primary hip replacement. Children are a separate question: Dr. Mahajan does not recommend hip replacement below 17 or 18 years of age, and the alternatives are set out in the complete guide.

Hip replacement after failed hip fracture fixation

Hip fractures that were fixed but healed badly are a common source of complex primary hip replacement. With failed intertrochanteric fractures, Dr. Mahajan sees a recurring pattern. The fracture has united, but the femoral neck has foreshortened and collapsed, leaving a varus deformity (the neck angled downwards) and secondary arthritis.

Hip replacement for developmental dysplasia of the hip (DDH)

Developmental dysplasia of the hip (DDH), formerly called congenital dislocation of the hip, describes a hip that is dislocated or unstable at birth. If it goes undetected, or proves difficult to keep reduced, the femoral head remains outside the acetabulum. The head keeps growing and becomes very large, while the socket fails to develop, leaving a mismatch between head and acetabular geometry.

For the replacement surgeon, DDH means a shallow or deficient socket, an abnormal femur and sometimes a canal too narrow for any standard stem. These are the cases in which 3D-printed custom implants, made to the patient's anatomy from a 3D CT scan, earn their place.

Other childhood and developmental causes

Childhood septic arthritis

An infection of the hip in early childhood can leave lasting damage, the condition historically known as Tom Smith's arthritis. Once sepsis has occurred, there can be osteolysis and osteonecrosis of the femoral head, a hip that has not grown, complex deformity with abnormal version (the hip may be retroverted or anteverted), and tight adductor muscles. Dr. Mahajan says such cases demand both experience and a knack for solving them.

Osteochondromas

Osteochondromas are benign bony outgrowths capped with cartilage. When they form around the hip, as in one of his patients in whom they were bilateral, they distort the anatomy and crowd the nerves and vessels. Before shaving them away, Dr. Mahajan obtains a 3D CT scan or MRI to confirm that no vessel or nerve is engulfed by the growth. In that patient the hip could still be replaced with primary implants once the growths were cleared, a complex primary replacement rather than a revision.

Cartilage loss and bone loss in young, active patients

Young patients can develop symptomatic, irreparable cartilage loss from sports and from femoroacetabular impingement, and active gym-goers and sportspeople can suffer bone loss, acetabular erosion or collapse of the femoral head. Where the cartilage is still salvageable, Dr. Mahajan prefers joint preservation, described in the complete guide; where it is not, these hips join the complex replacement pathway.

Revision hip replacement: why implants fail

Revision hip replacement means removing and replacing some or all of the original implant, and it is the other major source of complex hip surgery. Each mode of failure has its own logic.

Aseptic loosening

Aseptic loosening is loosening of the implant without infection. In cemented implants it occurs at the interface between implant, cement and bone; in uncemented implants, shear forces cause bony erosion and loosening. The work-up uses X-ray, MRI and CT, and its first task is to establish whether the loosening is truly aseptic or septic, and whether it involves the acetabular cup or the femoral stem. A loose stem shows subsidence: it sinks into the femur. Dr. Mahajan sees this especially in older patients with weak, osteoporotic bone.

Osteolysis

Osteolysis, the progressive loss of bone around an implant, can be seen around the femoral stem or the acetabular cup, and erodes the bone stock that any revision will have to rebuild.

Dislocation and instability

A well-fixed primary hip replacement can last 30 to 35 years, but if its geometry is wrong, particularly the version of the components, the hip will dislocate early. Around 90 percent of dislocations after primary hip replacement occur within the first three months, which points to a problem with the geometry, the fit of the components or the patient.

Instability can also come from weak abductors. The gluteus medius and gluteus minimus are the hip's main abductors, and they may be weakened by polio, other neurological conditions, injury or infection. In these patients Dr. Mahajan turns to a dual mobility, or tripolar, hip.

How dual mobility hips work

A dual mobility hip has three parts: the femoral head, two liners and the acetabular shell. Motion takes place at two articulations instead of one, which greatly reduces the chance of dislocation or instability. The range of movement becomes somewhat less, a price Dr. Mahajan considers acceptable: the patient wants a pain-free hip and a stable one.

Periprosthetic fracture

An implant can be involved in a fracture after a trivial fall or some other injury. A fracture around a previous implant turns a straightforward operation into a complex revision.

Infection

Infection of the implant is a serious cause of revision. Dr. Mahajan notes that the risk and incidence of infection are particularly high in patients with diabetes.

Retained hardware

Old plates, screws and nails from earlier fracture surgery can cause pathological stress fractures, including after the hardware is removed. These patients also need complex revision.

Complex and revision hip replacement cases

The cases he presented show how these causes combine in real patients.

1. Failed fixation of a trochanteric fracture. A young woman had been treated elsewhere with a dynamic hip screw for a fracture through the trochanteric region of the femur. The neck had foreshortened, with about an inch (more than 2 cm) of shortening; the head had collapsed with AVN and become sclerotic, and the screw was impinging on surrounding structures. A hip replacement restored the joint, but the anatomy was so disturbed that preparing the femoral canal was the hardest part.
2. Failed primary hip with a wandering acetabulum. A patient arrived with a failed primary replacement and acetabular bone loss so severe that neither the posterior nor the anterior wall remained, and the socket had migrated. The femoral anatomy had also changed. A Burch-Schneider cage restored stability to the acetabular shell.
3. Acetabular fracture with diastasis. The socket had opened up, but mainly at the posterior wall, with the anterior wall intact. Dr. Mahajan first fixed the wall with a plate and screws and placed the hip replacement once the acetabulum was stable.
4. Bilateral osteochondromas. A complex primary replacement achieved with primary implants after careful removal of the growths, guided by 3D CT and MRI.
5. Failed screw fixation of a femoral neck fracture. A young patient's fracture had been fixed with multiple cancellous screws but had not united. The implants had loosened and the neck had shortened. In such hips, Dr. Mahajan notes, the anatomy is always altered because the version, the rotational alignment of the femoral neck, has changed. The hip was painful. Because the patient's budget was limited, Dr. Mahajan used a cemented hip, which costs less than an uncemented one.
6. Complete diastasis of the acetabulum. Both the anterior and the posterior walls had opened up, with osteochondral damage to the femoral head. A Burch-Schneider shell stabilised the socket before the total hip replacement.
7. Old central fracture-dislocation. This patient had been operated on elsewhere for a central fracture-dislocation of the hip. Over time the femoral head became avascular and collapsed, the femur migrated upwards, and the limb became fixed in external rotation. The first step in such a hip is to locate the sciatic nerve.
8. Destroyed acetabulum fixed before replacement. In a similar case the acetabulum was severely damaged; once it had been fixed with a plate and screws, stability allowed a primary hip implant.

Why these operations need an experienced team

Dr. Mahajan's summary of these cases is that they are not straightforward, and a great deal of experience has to be brought to them. The surgeon must have every tool at hand, plan in advance and accept that the operation will take time. Patients and doctors can review the questions raised during the session in the Live Discussion, and indicative prices are on the cost page for other hip and knee replacement procedures.