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David Lark
David Lark

Spacer (Extended Mix)


Articulating spacers are now popular due to their advantage of preserving a range of motion and maintaining muscle strength. However, these can have a high incidence of complications, including fractures, dislocations, and malalignment.4,5 Such articulating spacers must be balanced in a way similar to ordinary TKAs, but this can be difficult to achieve due to loss of bone stock and ligament laxity. A modified surgical technique, therefore, seems necessary not only to improve such balancing during first-stage revision but also to provide time to monitor higher risk patients for longer periods while maintaining their range of motion and mobility.




Spacer (Extended Mix)


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A comparison was then made between the groups based on the incidence of complications encountered including gap size, malalignment (defined as more than ten degrees of varus/valgus angulation), tilting, subluxation, and spacer fracture. The interval between the first and second stages was also determined, as well as those patients undergoing repeat first stages. Ambulatory status after first-stage revision surgery was also obtained.


Fixed, nonmobile cement spacers were inserted after debridement and removal of both infected components to occupy the remaining knee joint cavity, with extension into both femoral and tibial canals. Two 40 g bags of Palacos R (Heraeus Medical, Wehrheim, Germany) cement including 2 g gentamicin were used.


After removal of both infected knee components followed by irrigation and debridement of the femoral and tibial canals, the technique is carried out using Spacer-K and two 40 g bags of Palacos R cement which include 2 g gentamicin. The first mix of cement can be split into three phases: early, middle, and late. In the early phase, the tibial component of the cement spacer is cemented orthogonally at the height of the proximal fibula, and the remaining cement is then molded into a large cylinder [Figure 1].


In the late phase, when the cement is set, serial cuts to the cement protruding from the femur are made facilitating positioning of the femoral component of the spacer into a semi-stable situation. Care is taken to support the spacer posteriorly to avoid breakage of the flanges during testing. Adjustments to length, anteroposterior position, and rotation (keeping anatomical reference points visible) can be made at this juncture to optimize alignment, ligament tensions, and therefore, stability [Figure 3].


The second cement mix is used to fix the femoral component of the spacer in place [Figure 4]. Cement is carefully used to build up any commonly occurring deficiencies, the epicondylar ridges as well as buttressing the posterior flanges of the femoral component, which are prone to subsequent breakage.


Fewest complications were observed in the cement pedestal group, with no spacers having subluxed or tilted in this group. The longest followup was also observed in the pedestal group. Mobile spacers with no cement pedestal displayed a higher incidence of malalignment, subluxation, tilting, and spacer fracture. This is in addition to having the highest reinfection rate and the greatest number of cases with complications.


Management of an infected TKA remains one of the major challenges faced by a knee surgeon. Several options, including single-stage revision and chronic antibiotic suppression, exist to manage this particular severe clinical problem. However, two-stage revision is still considered to be the best way forward to monitor for recurrent infection and reduce the need for rerevision of fully cemented components while preserving knee function.2 The results of our series not only confirm this but also seem to safely extend the indication for an articulated spacer into a set of cases with more extensive bone loss which previously would have required a fixed spacer, as evidenced by the increased gap sizes in the first stage of revision observed in the cement pedestal group.


To only use a fixed spacer is still somewhat controversial, but some surgeons believe that the stabilized and nonmobile nature of the spacer provides a better environment for the eradication of infection.6 The main disadvantage of fixed spacers is, however, joint stiffness and poor range of motion after the second stage of the revision. Instability and wound healing problems have also been associated with fixed spacers although to a lesser extent compared to mobile spacers. In addition, some authors state that static spacers may not restore the normal anatomic joint contours, particularly in heavier patients, thus leading to significant bone loss associated with a higher risk of spacer displacement.7


Static spacers do, however, seem to have a role in patients with severe ligamentous instability, highly compromised extensor mechanisms, and massive bone loss after the infected prosthesis has been removed. They may also have a role to play when inadequate soft-tissue cover necessitates plastic surgical intervention.8 Johnson et al.9 discovered comparable reinfection rates among 115 total knee arthroplasties (34 articulating spacers and 81 static spacers). Six patients in the dynamic spacer cohort (17%) and 14 patients in the static spacer cohort (17%) became reinfected and underwent further debridement. Four complications were found in the dynamic spacer group (2 fractures, 1 subluxation, and 1 dislocation). However, the authors state these could all be explained by surgical technical errors or patient weight-bearing compliance.


As opposed to static spacers, some authors believe that articulating mobile spacers provide satisfactory infection control while also improving function and range of motion.10,11 This motion can maintain adequate length and preserve the extensor mechanism while preventing scar tissue formation around the knee joint, which contributes to quadricep shortening, capsular thickening, and contracture. Such motion seems to explain easier reimplantation noted during revision surgery following the use of such a technique.12


This study has shown the benefits of utilizing the cement pedestal technique for the first-stage revision knee arthroplasty. It is associated with fewer complications compared with both fixed and mobile nonpedestal spacers. A longer interval time between first- and second-stage revision surgeries is then possible to observe for recurrent infection in the cases at increased risk of recurrent infection as noted above. In this study, longer followup times before second-stage revision facilitated extended periods of observation for those patients most at risk of recurrence. Where surgical resources are limited, then longevity of a spacer can also be most useful. 041b061a72


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