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Commentary & Perspective | ||||||||
Commentary
to: The evaluation and management of the patient with a stiff, painful or clicking total knee replacement presents a challenge to the orthopaedic surgeon. While there are many non-invasive diagnostic tools which may aid in this evaluation, such as a carefully recorded history and physical examination, plain radiography, scintigraphy, computerized tomography, thermography, intraarticular anesthetic injections and selective spinal blocks, not all patients will be successfully diagnosed. In these cases, direct visualization of the prosthetic components, interfaces and intraarticular soft tissues may be required. While this can often be accomplished only by a knee arthrotomy, there are many situations where a less invasive arthroscopic procedure can be successfully employed. Arthroscopy of the knee in which there is a prosthetic replacement has received scant attention in the literature. While there are several reports describing the outcome in small series1-8, little attention has been directed toward potential complications and adverse long-term outcomes. In our own experience, the most feared complication of this procedure is prosthetic sepsis (two of fifteen cases in the setting of severe arthrofibrosis, unpublished data) which may ultimately require a two-stage reimplantation procedure. Sepsis following arthroscopy, although uncommon, may be even more likely with a knee prosthesis in situ due to the presence of a large foreign body. In this study the authors address another adverse outcome of knee arthroscopy following total knee replacement - damage to the metallic femoral component. The authors' concern with this complication is justified by the known occurence of damage to the native femoral condyle during arthroscopic manipulation (so-called articular scuffing) as well as the observation that abrasive damage to the metallic femoral component may lead to accelerated abrasive or three-body wear of the polyethylene tibial articular surface, the polyethylene patellar articular surface, and the femoral component itself. Using a simple mechanical model, the authors demonstrated that even at loads as low as 4 N (approximately1 lb) stainless steel particles from the arthroscopic cannula can be transferred to a polished cobalt-chromium femoral component surface, thereby creating a rougher counterface for the polyethylene surfaces. In addition, at loads as low as 8 N, scratching of the cobalt-chromium surface can be identified. In contrast, no damage was observed on the femoral component when a plastic cannula was used, although at higher loads the cannula itself was damaged. These findings led the authors to the obvious recommendation of using plastic cannulae for arthroscopic surgery in the setting of a prior total knee replacement. In general, we would support the authors' conclusion and recommendation. However, there are certain limitations of this study, and there are important caveats for the use of arthroscopic surgery following total knee replacement. Regarding the study, the extent to which the experimental set-up mimics the actual arthroscopic procedure is not clear. The authors do acknowledge that there were no clinical references for the range of forces (magnitude and direction) encountered during arthroscopic surgery. We would also note that surface damage to the femoral component may vary as a function of the heat treatment, alloy composition, surface finish and surface treatment (e.g., passivation) of both the femoral component and the stainless steel cannula. Therefore, these results may not be strictly generalizable. For example, the damage pattern induced by both plastic and metal cannulae on titanium alloy femoral components may be entirely different than that reported here for cobalt-chromium alloy components. From the data presented in this manuscript, the case could also be made to harden the stainless steel cannulae in order to minimize the amount of material transfer; however, this solution must be weighed against the potential for increased abrasive wear of the femoral component. Although the plastic cannula may afford some degree of protection, it should be realized that, in practice, the tip of the metallic arthroscope and the glass lens will protrude beyond the plastic cannula. Therefore, the surgeon should not be lulled into a false sense of security when using plastic cannulae - the tip of the arthroscope may still cause damage. Not mentioned in this article was the potential for cannula-induced damage to the polyethylene surfaces of the tibial and patellar components, which may also be problematic. As the authors have acknowledged, the long-term effects of the damage modes observed in this study could not be ascertained. In fact, there are no intermediate or long-term studies that have established a direct relationship between femoral component damage and implant survivorship, nor are there studies which establish tolerance limits for the degree of surface roughness. In other words, how much surface damage is too much? The surgeon is often faced with this dilemma when revising only one component of a joint reconstruction, for example, in the setting of a failed metal-backed patellar component with concomitant scratching of the femoral trochlear counterface. Nonetheless, it stands to reason that less damage is better and that the surgeon should assiduously avoid any femoral, tibial or patellar damage during arthroscopic manipulation. These considerations lead us to conclude that arthroscopy following total knee replacement is not a trivial procedure, and should only be performed for specific indications where there has been a favorable track record. At our institution, these indications include patellar clunk syndrome, arthrofibrosis, certain cases of recurrent synovitis and rare cases of unexplained mechanical symptoms of catching or locking. Arthoscopic treatment of the problematic total knee replacement has been most effective in patients with localized soft-tissue disorders with success ranging from 73% to 100%2,4. We are reluctant to recommend arthroscopy in the patient with unexplained pain since only modest benefits have been reported in these patients1-8. Finally, it is critical to emphasize the importance of meticulous surgical and aseptic techniques to avoid the pitfalls of prosthetic sepsis and damage to the prosthetic components. Careful selection of portals, the avoidance of sharp metallic trocars, the use of plastic cannulae and gentle handling of the instruments will minimize the risks inherent in this procedure. Joshua
J. Jacobs, MD
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