2. Total Hip Replacement Today - Outstanding Problems

The outstanding problem is the young active patient with an arthritic hip. The problem is worse if the patient is male (higher loosening rates with THR), has an active job and wishes to play sport or engage in physical activity to keep himself healthy.

The most extreme and well known example of this is the American footballer and baseball star Bo Jackson, who had a total hip replacement and returned to sport only for his hip to fail in under one year. The best results of hip replacement in young patients are published from Wrightington.¹³

If we ignore the most crippled patients with rheumatoid arthritis and other debilitating conditions, and consider only the patients with osteoarthritis then the results of the Charnley THR at the premier centre of excellence show a 50% revision rate at 19 years. Several reports show worse results in young patients, and the young active patients with an arthritic hip is recognized by surgeons across the world as the problem.



1. What do surgeons do with the young active patient?

Following the lead by Charnley. and recognizing the problems of hip replacement in this group, the first option employed is to delay as long as possible. Patients are advised to change their employment to a more sedentary occupation. However this is not always easy, and it is common experience to see young patients with arthritic hips who are no longer able to work. The social consequences, to their families, are severe with profound economic consequences for the country.

Patients are advised to take anti-inflammatory medication in an attempt to dull the pain. These medicines cost money and have an array of side effects. The common problems are gastrointestinal complications, ranging from indigestion to ulcers, bleeding, perforation of the stomach or duodenum and strictures of the small intestine. It is common experience to see patients on anti-inflammatory medication for hip arthritis rushed into hospital with upper GI bleeding. Other complications seen are hypertension, congestive cardiac failure and renal damage.

The local effect of long term ingestion of anti-inflammatory medicines on the osteoarthritic hip are profound,^14,15,16,17 with destructive arthritis presenting as a major problem in these young patients. The consequences of damage to the peri-articular bone in these patients who require fixation of a hip arthroplasty are obvious.

As a final complication, patients who are on anti-inflammatory medication bleed excessively from their wounds at hip replacement. Excessive bleeding and haematoma formation increase die risk of deep infection. Eventually intolerable pain and disability drive the surgeon to carry out total hip replacement on the young patient. In order to prolong the life of the replacement, patients are advised not to engage in sport or manual work.

Not unreasonably, surgeons and design engineers have tried to improve the conventional hip replacement particularly for use in more active patients. These alterations in design have focused on improving fixation of components and improving wear of the articulating parts.

2. Excessive bone removal.

The one thing that a surgeon can be sure of when performing a total hip replacement in a young active patient is that sooner or later revision surgery will be necessary. When that revision surgery is performed, shortage of bone will be present and allograft bone grafting will be necessary, typically using 3-6 femoral heads at a cost of £250 per femoral head. Revision components for more elaborate fixation in the presence of severe bone loss are sometimes necessary at substantial extra cost compared to primary THR implants. It does seem conceptually unsound, therefore, to excise so much bone at the primary operation particularly in the young patient.

3. Dislocation.

Dislocation rates of 3-4% are reported as usual following total hip replacement.^11,12 These dislocations relate to problems of restoration of patient's anatomy with a limited range of "off the shelf" total hip replacement designs. In this regard, it is particularly difficult to restore offset in large male patients. Reduced prosthetic head size is considered by the authors to present an inevitable problem of dislocation in total hip replacement. This is disputed,¹⁸ and when the range of head size of 11 to 32 mm is considered, no difference in dislocation rates occur. However when the patient's femoral head is replaced by a prosthesis of the same size (38-58 mm) as will be presented later, then the dislocation rate is seen to be very low.



When dislocation occurs following total hip replacement, the patient requires re-admission to hospital (depending on time of dislocation) a further general anaesthetic, a variable time on traction in bed (up to three weeks), supply of a hinged orthosis to prevent re-dislocation and out patient physiotherapy to strengthen muscles. For the minority who go on to recurrent dislocation, the re-admissions are repeated and revision surgery is eventually performed with variable success. All of this comes at a cost to the health service and an inevitable economic and social cost to the patient.

4. Thrombo-embolic complications.

Total hip replacement has the highest rate of thrombo-embolic complications of any surgical procedure. In the most thorough study performed to date, Gardedri performed fibrinogen uptake tests daily on patients following THR and then performed a venogram to confirm positive results. 92% of patients following THR had deep venous thrombosis.¹⁹

Deep vein thrombosis (DVT) delays discharge from hospital by five days while pulmonary embolism necessitates an additional seven days of hospitalisation. ²⁰ Fortunately only a few patients develop a fatal pulmonary embolus following THR, but re-admission of patients to medical wards with non-fatal pulmonary embolus and swollen legs from DVT is not uncommon. In an analysis of 7,547 total hip replacements Seagroatt et al, determined that 208 patients had had emergency readmission within twenty-eight days after the procedure. Of these 208 patients, 54 were readmitted for DVT or pulmonary embolus. ²¹ Post-phlebitic limbs and leg ulcers are seen as a late complication. These complications often do not develop until five to ten years after the acute event but, when present, they tend to persist indefinitely. ²² These complications have obvious cost implications to the health service.

5. Lengthening of the leg after total hip replacement.
Lengthening of the leg at total hip replacement is a consequence of surgeons trying to achieve a tight reduction in order to prevent post-operative dislocation. Love & Wright²³ recorded mean lengthening of 15mm in 18% of cases, Williamson and Reckling²⁴ 16mm and Turula²⁵ 9mm. 27% of cases in the latter two series required a shoe-raise to be worn on the opposite leg. In the past, patients accepted the wearing of a raised shoe on the opposite leg but in recent years have followed the trend in the USA and litigation is commonly pursued. An inevitable cost to the health service results. As will be shown later, it is virtually impossible to lengthen the leg at hip resurfacing.

6. Proprioception and function.

Patients are grateful for the pain relief afforded by total hip replacement but are aware that the hip neither feels like a normal hip nor functions tike a normal hip. Comments like "It's not part of my body" are common. Although these feeling are, of necessity, subjective, we have been impressed that hip resurfacing patients have no such feelings and many patients return to recreational sport, and some to competitive sport.

Resurfacing patients have participated in the 1998 Soccer World Cup, the London Marathon, the World Masters Judo Championships, the World Masters Badminton Championships and the World Seniors Squash Championships. The most interesting group of patients are those with a total hip replacement on one side and a resurfacing on the other. Almost invariably they volunteer that the resurfaced side feels more normal and is stronger that the replaced side.



7. Loosening and osteolysis.

Loosening of components has both a mechanical and biological basis. With regard to the femoral component of conventional total hip replacement, resection of the femoral head and part of the neck has the inevitable consequence that the point of loading is at a distance from the point of fixation, thus subjecting the femoral component to high bending and torque forces. With resurfacing of the hip, on the femoral side, the point of loading is coincident with the point of fixation. On the acetabular side, it is recognized that the acetabulum is a mobile structure. With cemented cups, it may be this micro-motion that leads to the inevitable appearance of pseudomembrane at the cement bone interface.

In an autopsy study of the Chamley THR, Malcolm²⁶ found that every single cemented acetabular component was histologically loose with pseudomembrane at the cement bone interface. Uncemented porous ingrowth acetabular components can certainly address this issue of cup fixation, and two autopsy studies have shown bone ingrowth and solidly fixed uncemented sockets. ^27,28 However, the uncemented total hip replacement cup comes with significant problems. It has been shown that the use of uncemented cups doubles the polyethylene wear of the liner. ²⁹ Whilst osteolysis in the cemented acetabular component presents as a linear pattern with component loosening, osteolysis in the uncemented cup presents late, with severe cavitary retro-acetabular bone loss.

This is widely appreciated in the USA, ^30,31 but this presentation of osteolysis is only just appearing in the UK and will present formidable revision problems in the future. We use an uncemented porous ingrowth socket with the Birmingham Hip Resurfacing (BHR), fixation is a non-problem, and in the future, osteolysis is not expected, as no polyethylene is present in the system and the metal on metal bearing has a 40-year benign clinical history.

Osteolysis in the femur may be linear or focal. With cemented femoral components the linear pattern predominates and the clinical and radiographic presentation is of loosening. Loosening of components is the one failure pattern in the Chamley THR performed in young patients. ^12,13

With uncemented femoral components, the focal pattern of osteolysis predominates. 10 year survivorship of 68% for the PCA and 69% for the Harris-Galante designs have been reported, using clinical or radiographic failure as the end point.³²

Polyethylene particles have been identified as the main cause of osteolysis, most of these particles are submicron size and ingested by macrophages, which initiate a complex cellular response, including release of substances such as cytokines, growth factors and inflammatory mediators, ultimately resulting in bone resorption, mainly by osteoclasts.³²


8. Stress Shielding.

Stress shielding of the proximal femur occurs when a metallic stem is inserted as part of conventional total hip replacement. There are now reports showing between 30% and 45% proximal femoral bone loss following stemmed total hip replacement. ^34,35

It is unknown whether this proximal femoral bone loss contributes to loosening of the femoral component of a total hip replacement but when revision surgery is required then the bone loss from the primary surgery and the bone loss from the osteolysis and loosening is added to by bone loss due to stress shielding. With hip resurfacing loading of the existing femoral head occurs and stress shielding is not seen in the proximal femur.

9. Scientific Explanation for Stress Shielding following THR (from Kit Huiskes).

Following THR the stem takes pan of the load away from cortices. (Mid-frontal section through 3-D F.E.model.) Stress protection osteopaenia in proximal femur will follow. Distribution of elastic energy in intact femur. Load mainly transferred through cortices.


10. Difficulty with Revision.

Revision of conventional total joint replacement whether cemented or cementless is an arduous task and is of far greater magnitude than the initial total joint replacement. Revision of conventional joint replacement requires specialist techniques and solutions and this is expensive for the NHS. A multitude of techniques are utilized to address the problems at revision surgery but the common factor is high expense and consumption of time.

In the small number of revisions of surface replacement arthropiasties that have been carried out, the revision procedure is essentially a primary total hip replacement with similar technology, expense and post-operative recovery to a conventional primary total joint replacement.