Earl R. Bogoch, M.D., FRCSC
Toronto, ON

The ideal procedure for total hip or knee replacement would achieve superior clinical performance while minimizing surgical trauma, tissue dissection and scarring, facilitating rapid rehabilitation and lowering health care costs. To move closer to these goals, proponents of minimally invasive (M.I.) arthroplasty techniques are developing modified and new methods of implanting prostheses. Orthopaedic manufacturers introduce and distribute instruments for M.I. arthroplasty, which are being adopted by orthopaedic practitioners, while the popular press publishes accounts presenting the advantages of this approach.

I have observed the trend with interest but have not yet adopted M.I. arthroplasty techniques because, at this point, the advantages do not appear to justify the potential negative effects, particularly in the hip. There is reason for concern that, if M.I. arthroplasty surgery is widely adopted, as seems likely, patients will be exposed to the risk of complications and treatment failures, while seeking to gain benefits that are less than they might appear.

The paradigm of M.I. surgical technique in the musculoskeletal system is arthroscopic surgery of the knee, and comparison with hip and knee arthroplasty may be revealing. Are M.I. hip and knee arthroplasty comparable?

Let’s review the proposed benefits of M.I. hip and knee arthroplasty:

Less Tissue Dissection
Standard hip approaches are now performed relatively atraumatically. Approaches are smaller, muscle dissection is more controlled and skin incisions smaller than previously. A direct lateral approach to the hip in a normal sized patient can be accomplished through a 12 cm incision. Hip patients are usually unconcerned about the scar for THA, although TKA incision scars are sometimes an issue. Current M.I. hip techniques, while having shorter skin incisions, may have a more traumatic muscle dissection. Just as an open fracture of the femoral shaft with a 1 cm. skin laceration cannot be considered a Grade I fracture, two minimal incisions may be the outer manifestation of an operation requiring more tissue damage, not less, than a traditional total hip replacement. There is a risk that patients may misunderstand this, and consider the length of the skin incision to reflect the extent of the operation.

Shortened Hospital Stay And Rapid Rehabilitation
Total hip and knee replacement can commonly be performed with a two or three day hospital stay in selected patients, as is sometimes performed for out of country patients who pay high daily rates for hospital stay. U.S. HMOs are achieving mean length of stay of 4 days. It is possible that M.I. THA and TKA will be accomplished with very brief hospital length of stay but modified traditional methods may require only a day longer. Images of M.I. patients walking and climbing stairs on the day of surgery are not surprising. With traditional methods, patients commonly walk on postoperative day 1 and it would not be difficult to induce some of them to walk on the day of surgery. Any complications or failures that may result from the introduction of M.I. methods may reverse the small economic advantage.

Blood loss
It seems likely that intraoperative blood loss in M.I. arthroplasty will be lower than in standard techniques

Risk vs. Benefit
Innovative operations are best introduced where the existing procedure has low efficacy and high risk, where the “upside” is great and the standard procedure is problematic. Those conditions do not currently prevail. Total hip and knee replacement have evolved to become procedures that have 95% or higher positive outcomes after 5-10 years, which are among the most cost-effective interventions in all of medicine, generate high patient satisfaction rates and which have low levels of local complications. There is further improvement available as the standard procedure becomes simplified, and rehabilitation is shortened.

The introduction of M.I. arthroplasty provides the possibility of small gains in non-critical areas, as described above. There are however additional serious risks that may accompany this innovation, as with any new operation. In the hip, the risk of neurovascular injury, fracture, and unstable or malaligned prosthetic implantation is likely increased. Small calcar cracks, which are easily identified and managed in traditional surgery, could propagate to major femoral fractures before being identified.

In the knee, good results at 8 and 10 years have been reported with M.I. unicompartmental arthroplasty. However the popularization of M.I. knee arthroplasty would impose a new learning curve on a profession that has for the most part learned to do a good knee replacement, potentially creating complications and treatment failures that would not have otherwise occurred. Even a small increase in the complication rate would nullify and even reverse the small benefits to be obtained. Clinical investigators who design studies to determine if a new hip or knee implant is measurably superior to existing successful implants, know that the sample size is in the thousands. It will be difficult to create a series of M.I.implant patients, especially in the hip, whose mean objective outcome, including complicated or failed cases, is measurably superior to existing series.

We study and work to improve our implant positioning, especially in the hip, and we carefully train residents to do the same. It is likely that M.I. arthroplasty of the hip will result in increased rates of malposition and unstable fixation of implants, with clinical consequences.

In the knee, unicompartmental arthroplasty by standard methods was favoured only by a minority of knee surgeons but gained popularity in recent years due to M.I. methods. Unicompartmental arthroplasty procedures were associated with rapid recovery even before M.I. techniques were introduced. The challenge for the new methods will be to demonstrate, other than in specialized units dedicated to their development, low early failure rates and 10-year survival rates that compare to traditional bi- and tricompartmental arthroplasty. The risk of failures and complications appears to be lower in the knee than in the hip.

Finally, M.I. hip and knee arthroplasty techniques, which offer an easier and quicker rehabilitation, should not alter the indications or lower the threshold at which these procedures are considered. Patients need to understand that the two procedures which are being replaced, when they accept M.I. surgery, are among the best currently available surgical treatments.