Advances in hip and knee surgery for arthritis
An ageing population and increased participation in sports by the general public has led to a significant clinical problem arthritis of the hip and knee. Adult reconstruction surgery has advanced in tandem to manage this ever-growing problem.
In the hip, there is recognition now that the majority of cases of previously labelled primary osteoarthritis of the hip is in fact the result of minor, and often not recognised, developmental abnormalities in the hip joint resulting in femoral-acetabular impingement and damage to the articular cartilage.
Harris and co-workers in Boston found that they could demonstrate the presence of these minor deformities in 80% of patient presenting with primary osteoarthritis of the hip that required hip replacements.
The work of Ganz and co-workers has elucidated the pathomechanism of osteoarthritis of the hip due to femoral acetabular impingement. In such cases, the repeated impingement between the femoral neck and the acetabular rim causes damage to the labrum and subsequent development of osteoarthritis. There are two varieties of femoral acetabular impingement (FAl). namely cam FAI and pincer FAI.
The cam FAI is due to an offset pathomorphology between the head and the neck of the femur, and often seen in the young athletic male. The pincer FAI, on the other hand, is caused by either retroversion of the acetabulum or over-coverage in cases of acetabular protrusion. This variety is more commonly seen in older females.
Careful history taking and physical examination together with radiographs, CT scans, bone scans and MRI with gadolinium arthrography are needed to assess the patients with hip pain in whom dysplasia or arthritis do not appear obvious. Understanding the pathomechanism of osteoarthritis allows the surgeon to treat it during the early stages and hopefully prevent late changes of osteoarthritis of the hip.
Open surgical dislocation of the hip followed by labral refixation, acetabular rim trimming and articular cartilage repair, correction of femoral head and neck offset, as well as arthroscopic surgery of the hip have been employed to treat FAI and prevent the onset of osteoarthritis. Although this is akin to procedures such as arthroscopy, osteotomy and cartilage repair of the knee joint, such hip procedures are relatively new and are technically difficult procedures.
In cases of severe dyplasia of the hip, pelvic and femoral osteotomies are employed in the young patient to prevent or delay development of severe arthritis. In patients with established advanced arthritis of the hips, many innovations to improve the quality, function and durability of the artificial hip replacement have been witnessed.
Standard total hip replacement using newer improved bearing surfaces include highly cross-linked polyethylene, ceramic-on-ceramic bearing, metal-on-metal bearing, surface replacement, and short stem femoral components. The durability of the artificial hip articulation can be improved by irradiating the polyethylene to produce cross-linking of the polymer that is more resistant to wear than non cross-linked polyethylene that has been used previously.
The new metal alloy, oxinium, for the femoral head, behaves like a ceramic surface, reducing wear by lowering the coefficient of friction between the head and the acetabular liner. Ceramic-on-ceramic and metal-on-metal bearings have much lower wear than conventional metal-on-cross-linked polyethylene bearings.
However, ceramic is brittle and thus a low risk of fracture exists, though the new Delta ceramic is much more durable and resistant to fracture. Metal-on-metal articulation has its problems of released metal ions into the blood stream and concerns of carcinogenic and renal toxicity exist. In some patients there can be a hypersensitivity to the released metal ions from the metal-on-metal articulations causing early osteolysis of the components. Therefore metal-on-metal articulation is not recommended in young female patients of childbearing age, and those with renal impairment and metal hypersensitivity.
Surface replacement of the hip has been reintroduced as a form of bone preserving operation for younger patients. By having a larger head compared to standard hip replacement, surface replacements have better motion and stability. This may enhance the lifestyle of younger patients. In a similar fashion, short stem femoral components are employed to reduce the amount of bone removed during hip replacement, and using extra large heads with metal-on-metal articulation may be preferred in young patients.
In the younger patient with knee arthritis, a biological solution to the problem of loss of cartilage is to employ the various techniques of cartilage transplantation and regeneration. This varies from simple micro fracture technique to stem cell research and growing cartilage cells in the laboratory before implanting them on to chondral defects in the knee. This has been successful for the smaller focal defects and can be combined with osteotomies to correct malalignments in the leg, which predisposes such patients to osteoarthritis. The classical closing wedge osteotomy is being replaced by the opening wedge osteotomy for varus knees in younger patients.
In older patients with established osteoarthritis requiring joint replacement, there are a variety of techniques of knee replacement available. The classical total knee replacement is now done with a minimally invasive technique to enhance
rehabilitation, and allows for early return to work and activities of daily living. There is also modification of the implant design and surgical techniques to improve the range of motion of the knee to permit squatting and kneeling in selected patients, which is viewed as an important factor in Asian patients.
The use of unicompartmental and bicompartmental prostheses for isolated unicompartmental arthritis with or without patellar arthritis is now advocated. Isolated patellafemoral arthritis can also be resurfaced with the appropriate isolated prosthesis sparing the non-involved tibia-femoral joint. The aims of these procedures are to conserve bone and being a less invasive technique, it also promotes quicker rehabilitation and earlier return to work.
It is well known that not all hip and knee replacement surgeries have the same results. Those that are done by a well trained and experienced adult reconstruction surgeon will certainly have significantly better results than those done by a less well trained and less experienced non sub-specialised orthopaedic surgeon. This is similar to the F1 professional racing driver versus the taxi driver comparison.
Computer-aided surgery for hip and knee replacement is done to improve the accuracy of the surgery and hopefully prolong the longevity of the artificial hip or knee joint. It is a useful tool in teaching younger surgeons to improve their surgical skills. Also computer navigation is helpful in minimally invasive surgery as vision is limited by the decreased incision size.
Another innovation in the recent years is the advancement of techniques to minimise the amount of soft tissue damage during the hip or knee replacement surgery. This will allow faster rehabilitation and recovery of the patient, a shorter hospital stay, and a faster return to work and normal activities.
Newer materials have also been fashioned. Trabecular metal, which is manufactured by spraying tantalum on to a carbon scaffold to produce a highly porous metal surface, allows for excellent bone in-growth and fixation of the hip and knee prosthesis. This is extremely useful in revision and primary hip and knee replacements where the implant is fixed to the bone by biological bone in-growth, obviating the use of the bone cement, methylmethacrylate, which has limited lifespan of 1 0 years in the hip replacements.
Trabecular metal has also been used to forge metal augments and prosthesis to replace areas of large bone defects in revision hip and knee replacements. It is superior to bone allografts as it does not undergo creeping substitutions and resorption when implanted. It is also readily available to fabricate on the spot in the operating room as opposed to using megaprostheses, which needs to be custom made and preordered well before the revision surgery.
Dr Lai Choon Hin is a senior consultant orthopaedic surgeon and the director of the Adult Reconstruction Service at Tan Tock Seng Hospital, Singapore.
Credit: orthopaedic SPOTLIGHT