Unicompartmental Knee Arthroplasty Surgery 10-Year Minimum Follow-up Period

Transcription

1 The Journal of Arthroplasty Vol. 11 No Unicompartmental Knee Arthroplasty Surgery 10-Year Minimum Follow-up Period Philippe Cartier, MD,* Jean-Louis Sanouiller, MD,* and Ronald R Grelsamer, MDJ- Abstract: Sixty knees in 54 patients were followed a minimum of 10 years after unicompartmental knee arthroplasty surgery. Follow-up periods ranged from 10 to 18 years (average, 12 years). In all cases, a Marmor prosthesis was used. TWo patients required arthroplasty surgery after the 10-year mark. Seven knees required revision prior to 10 years, and the 10- to 12-year survivorship for the entire cohort was 93%. Slight undercorrection of varus alignment and adequate polyethylene thickness of the tibial component appear to be important contributors to a successful outcome. Key words: unicompartmental knee arthroplasty, Marmor prosthesis. Unicompartmental knee arthroplasty (UKA) is one of the accepted modes of knee reconstruction for unicompartmental femorotibial arthrosis [1]. As with other forms of reconstruction such as high tibial osteotomy and total knee arthroplasty (TKA), a review of the literature reveals both favorable [2-18] and unfavorable reports [19-22]. A key parameter in evaluating the success of this or any other reconstructive procedure is long-term follow-up study. We present only the third review of UKA with a minimum 10-year follow-up evaluation and only the first such study not involving L. Marmot, MD, himself. Materials and Methods The cohort of 207 primary Marmor UKAs implanted in 197 patients (10 bilateral) between 1974 and 1984 was analyzed in Seventynine patients (83 knees) died prior to the 10-year follow-up mark, 49 cases were lost to follow-up evaluation within 10 years of surgery, 8 could be From *Clinique des Lilas, Paris, France, and ~-Maimonides Medical Center, New York, New York. Reprint requests: Philippe Cartier, MD, Clinique des Lilas, 41-49, Avenue du MarechaI Juin, Les Lilas, France. reviewed only by telephone, and 7 were revised prior to the 10-year mark. This left 54 patients who could be personally reviewed more than l0 years after the index procedure. Of note, 74 of the 132 knees lost to death or to follow-up evaluation had documentation that was adequate to justify inclusion in a survivorship study. For the remaining 58 cases, documentation was either no longer existent or too spotty for inclusion in the survivorship analysis. The seven patients requiring reoperation prior to the 10-year mark included three infections early in the series treated by arthrodesis, three femorotibial subluxations, and one degeneration of the opposite compartment treated by placement of a UKA in that compartment. Two of the three subluxations were the result of a technical error in positioning the components and the knees were converted to a TKA. The third patient was, in retrospect, a suboptimal candidate for a UKA as she had excessive medial laxity as a result of a valgus deformity and required treatment with a brace after surgery. The 54 patients reviewed at a minimum followup period of 10 years included 35 men and 19 women. The ratio of medial to lateral arthroplasty in this study was 7.5 to 1. There were 53 medial arthroplasties for medial arthritis on a varus knee and 7 lateral arthroplasties for lateral arthritis in a 782

2 Unicompartmental Knee Arthroplasty Cartier et al. 783 valgus knee. The average age at the time of surgery was 65 years (range, years). The average follow-up period was 12 years (range, years). Eleven patients had had prior surgery, including eight valgus tibial osteotomies (6 undercorrected), one UKA, with a 6-ram all-polyethylene plateau, one patellectomy, and one Elsmlie-Trillat tibial tuberosity transfer. The arthritis could be classified as osteoarthrosis in 37 cases, post-traumatic in 13, and secondary to avascular necrosis in 8. There was one case of Paget's disease and one of chondrocalcinosis. The selection criteria were as follows: for patients under age 70, those with unicompartmental osteoarthrosis were selected for UKA if they presented with a contraindication for a tibial osteotomy such as severe arthrosis, neutral limb alignment, absence of metaphyseal bowing, pagoda- shaped tibial plateaus (an upper tibia that has the shape of an inverted "V"), and pseudosubluxation in the.sagittal plane as a result of osteophystes or bone stock deficiency (on a standing lateral roentgenogram, the femur is displaced either anteriorly or posteriorly relative to the tibia)--all factors that we have found to be correlated with poor results after a realignment osteotomy. In patients over age 70, where the choice lies between a UKA and a TKA, rather than between a UKA and an osteotomy, we have routinely chosen the UKA. Our premise was that patients would be just as satisfied with the UKA as with the TKA, both in the short run and in the long run, and that the UKA would be less costly. Before and after surgery, all patients had roentgenograms, which included standing anteroposterior and standing lateral views in full extension; three-joint views of the hip, knee, and ankle; and axial views of the patella (Merchant type) in 30 and 60 of knee flexion. Surgical Technique In association with the UKA, all patients underwent a lateral retinacular release. At the time these cases were performed, it was the senior author's opinion that the patella could be an eventual source of problems and the lateral release was routinely performed prophylactically. At present, lateral releases are carried out only in select cases of patella malalignment. In 27 cases, part of the patellar cartilage was shaved, in 8 cases, a partial patellectomy in the frontal plane was carried out for moderate to severe arthritic changes (complete removal of the subchondral bone), and in 4 cases, a concurrent patellofemoral arthroplasty was carried out (this did not prejudice the results as these patients were doing well at the time of the last review). The technique used for implantation of the femorotibial arthroplasty has been previously described [23,24]. Its main features include centering of the femoral component on the tibial component throughout the range of motion (especially near extension), complete stability of the tibial component prior to cementing (absence of "yawning" in flexion), slight undercorrection (maintaining slight mechanical varus in a medial arthroplasty) [5,13,15,18,25], thorough removal of notch osteophytes (notchplasty), and protection from drying of the other compartments. Contrary to the original technique of Marmor, we sought to place the tibial component on the cortical rim of the plateau rather than within the cancellous bone. It has been the senior author's opinion that placing the tibial component in the cancellous bone has three potential disadvantages: the obliquity of the component is more difficult to control, the component is more likely to subside, and major bone defects of the types already described in the literature [22] are more likely to occur. Clinical Results Results The I989 Knee Society rating system was used to grade results, separating a knee score from patient function [26]. Specifically, the knee score assesses pain, stability, and range of motion, with a score of 100 being achieved with a well-aligned knee, no pain, minimal instability, and 125 of motion. Patient function assesses the ability to walk and climb stairs. A score of 100 is achieved when the patient can walk unlimited distances and negotiate stairs normally. The knee score was 75% excellent, 20% good, 3% fair, and 2% poor. The patient function score was 57% excellent, 20% good, 7% fair, and 16% poor. The discrepancy between the two scores could be accounted for by eight patients who developed pain elsewhere (ie, 1 other knee, I hip, 1 ankle, 5 radiculopathies) and, consequently, had difficulty climbing stairs. Fifty patients (56 knees) noted no pain, two noted only occasional pain, and two noted severe pain (representing failures). Of these two patients with severe pain, one developed pain in the opposite compartment as a result of overcorrection into valgus, and the other suffered from subsidence of both components presumed to be secondary to the onset of pathologic osteoporosis in both legs and spine.

3 784 The Journal of Arthroplasty Vol. 11 No. 7 October 1996 Of the two failures that occurred after 10 years, one was believed to be secondary to overcorrelation into valgus with subsequent deterioration of the opposite compartment, and the other was due to the development of severe, diffuse osteoporosis about the knee with subsidence of both components. Postoperative knee flexion averaged 126 (up from an average of 118 before surgery). A slight flexion contracture was noted after surgery and averaged 3 throughout the cohort, an improvement over the 9 average before surgery. Thirty-nine patients could walk unlimited distances without rest; 14 were limited to 1,500 m. Only the patient with loosening was clearly limited to indoor ambulation. Before surgery, just 12 patients climbed stairs normally (reciprocal gait without holding onto a railing). After surgery, 45 of the 60 patients could climb stairs normally. After surgery, two patients demonstrated slight anterolateral instability as a result of a chronic anterior cruciate ligament insufficiently and one patient exhibited quadriceps weakness as a result of a prior patellectomy. This contrasts with a slight instability noted in 12 cases and a major instability noted on 26 knees before surgery (see Discussion). Of the 10 patients with anterior cruciate ligament insufficiency before surgery, 7 remained asymptomatic, 1 underwent a subsequent extraarticular Lemaire reconstruction, and 2, as noted, demonstrated slight clinical instability. Roentgenographic Results The anatomic placement of the implants was studied. In three cases (all medial arthroplasties), we beleived that the femoral component gradually came too close to the tibial spines as a result of the tibial cut: the plateau was perpendicular to the axis of the tibial shaft rather than being perpendicular to the epiphyseal axis (see Discussion and Fig. 1). In one case, we were displeased with the obliquity of the femoral component as we believed that there was edge contact with the tibial plateau, and in another case, we were displeased with the obliquity of the final component. We also evaluated postoperative alignment. As noted, slight undercorrection was sought in all cases. This was confirmed roentgenographically in all cases but one. The average postoperative alignment for medial arthroplasties was 5 of mechanical varus (approximately zero degrees of anatomic, femorotibial varus). The one case that was not undercorrected--and in fact was overcorrected to about 5 of valgus--required surgical revision. The alignment for the lateral arthroplasties averaged 7 of mechanical valgus (12 of anatomic valgus). Fifteen cases were, in our opinion, too severely undercor- Fig. 1. Unicompartmental arthroplasty for medial unicompartmental arthrosis. The prosthetic tibial plateau is not perpendicular to the femoral shaft. Contrary to the situation in TKA, we have found this to be a desirable feature, especially in the face of metaphyseal bowing. rected, and these cases averaged 9 of mechanical varus (approximately 4 of anatomic varus). Interestingly, 9-mm tibial plateaus were used in all of the cases of this study, and neither undue polyethylene wear nor loosening was noted. Evaluation of the contralateral compartment revealed a normal roentgenographic appearance in 49 cases, subchondral irregularity and osteophytes in 6 cases, and joint space narrowing in 5 cases. Only one of the latter was symptomatic and this was the one varus knee that we failed to undercorrect. Four knees had had some roentgenographic features of arthrosis in the contralateral compartment before surgery, but none of those (all slightly undercorrected) had any further deterioration during the study period. Finally, the roentgenographic studies were analyzed for the presence, nature, and progression of radiolucent lines. One UKA was completely surrounded by a radiolucent line about both the femoral and tibial components (the one case of clear clinical loosening). Four femoral components were incompletely surrounded by a radiolucent line, 23 tibial components incompletely surrounded by a radiolucent line, and 6 tibial components completely surrounded by a radiolucent line. The latter was always less than 2 mm wide and did not progress over the length of the study.

4 Unicompartmental Knee Arthroplasty Cartier et al. 785 Complications There were three infections. There was one case of arthrofibrosis requiring open lysis of adhesions, one case of patellar catching addressed by arthroscopic debridement, and one pes tendinitis, which was operated on with success. The patients received a heparin derivative (fraxiparine) and there were no thromboembolic complications. Survivorship Analysis A survival table was created in a manner previously described [27,28]. The cases were grouped into intervals of 1 year, with failure defined as revision or need for revision. The table was carried out until 12 years, after which the confidence limits became too low. As with all such survivorship analyses, the patients lost to follow-up evaluation were assumed at each interval to be doing no better or worse than the cohort still available for study. As such, the survivorship at 10 years was calculated to be 93% (95% confidence interval, 80.7%-100%) (Fig. 2). Discussion It appears to us that the long-term results of UKA can be quite satisfactory. We still prefer to carry out an osteotomy in younger patients who meet our criteria, but the results in the younger patients of our study were no worse than those of the older patients, and as such, it seems to us that the younger patients who do not meet these criteria are reasonable candidates for a UKA. The older patients did not require conversion to a TKA, and as such, the UKA in our hands can truly be said to be the more cost-effective procedure. Our results would appear to validate the principle of slight undercorrection as there does not seem to have been loosening or clinically significant wear in the undercorrected patients. Interestingly, contrary to Sarangi et al. [29], we did not Fig. 2. Surv~orship % 'ooi~ " o-i ,,, t0 tl 12 Yu0rs Survivorship curve for cohort in this study. even note clinical problems with the 15 cases that were undercorrected more than the few degrees we would have liked. In all 15 cases the allpolyethylene tibial component was at least 9 mm thick. We currently believe that an adequate thickness contributed to the success of these cases and we agree with Engh et al. [30] and with Ryd et al. [31] that the thickness of the tibial component plays a role in the survivorship of the implant. This of course is consistent with the trend in TKA. The presence of degenerative lesions in the opposite compartment could naturally be thought of as a relative contraindication to a UKA; however, our four patients with such lesions had no further deterioration of that compartment, and we tend to agree with Corpe and Engh [32] that scattered focal changes in the contralateral compartment are not a contraindication to UKA. The radiolucencies noted about many of the implants in this series are of interest to us. For the most part they do not seem to have been related to loosening. We speculate that they are the result of operating without a tourniquet, as we have seen fewer radiolucencies since we have started inflating the tourniquet during the cementing portions of the procedure. Revision of a UKA to a TKA has been a subject of controversy [22,33]. The revision to a TKA in three of our cases and the revision to a UKA in two cases did not present any particular technical difficulties. This tends to confirm our opinion that if a resurfacing type of UKA is used and if the failure is noted in a timely fashion, revision of a UKA need not be problematic. By resurfacing type, we mean a femoral implant requiring only a small posterior condylar resection. The distal femur is shaved down to bleeding subchondral bone rather than being subject to a "distal" cut, and no anterior chamfer cut is performed. In all our cases, care was taken to use the least amount of cement possible. Ligamentous laxity plays an important part in the discussion of UKA surgery. This can be divided into collateral laxity and cruciate laxity. Collateral ligament laxity can itself be a true laxity as a result of a stretched or torn ligament or can be a pseudolaxity whereby bone erosion or a bone defect compromises the effectiveness of a collateral ligament (Fig. 3). The two types of laxity can occasionally be differentiated before surgery with stress views, and can be readily differentiated at the time of surgery when the bony defect is addressed by the implant. Should the instability disappear, a UKA can be implanted as planned. Should the instability persist even after placement of the appropriate trial implant, one is dealing with true

5 786 The Journal of Arthroplasty Vol. 11 No. 7 October 1996 Fig. 3. Pseudoinstability. With severe bony defects, there can be apparent collateral instability. When the bony defect is adequately filled, the apparent instability disappears. This patient's apparent varus (lateral collateral ligament) instability resolved with placement of a medial component. collateral laxity and only a TKA would address the situation. With respect to anterior cruciate ligament deficiencies, we are a little more reserved than Marmor [13] and a little less so than Deschamps and Lapeyre [34] when it comes to performing a UKA. When the ligament has been gradually eroded by intercondylar osteophytes, this is not a contraindication to a UKA because there has been no other soft tissue disruption and the knee is clinically stable. Empirically, we have found that in these cases it is best to set the tibial component more posteriorly that usual; however, when the knee is lax as a result of a prior injury and the joint has been gradually stabilized by the arthrosis, it is our opinion that an intra- or extraarticular cruciate reconstruction should be carried out. Indeed, in our experience, these knees tend to become clinically unstable again once the stabilizing defects and osteophytes are removed. The obliquity of the tibial component as noted on an anteroposterior roentgenogram has not received much attention in the literature. It was originally our impression that as with TKAs, the tibial cut should be essentially perpendicular to the longitudinal axis of the tibia and, in cases of bowing, should be perpendicular to a line drawn from the center of the tibial spines to the center of the ankle joint. This would mirror the TKA technique; however, based on some early failures in patients with a bowed tibia, we now feel that in the presence of metaphyseal bowing the mediai tibial plateau should be perpendicular to the upper tibia (epiphyseal axis) so as to remain parallel to the lateral tibial plateau (Fig. 1), which in our opinion remains the major reference point. When the metaphyseal tibial deformity is more than 6, we currently carry out an osteotomy, usually prior to the UKA. The survivorship analysis assumes--as do all such analyses--that the patients lost to follow-up evaluation are surviving and patients are still available for study. We believe that this is optimistic but no more so in this study than in other survivorship analyses with which this study can be compared. The Marmor prosthesis is clearly an acceptable implant as evidenced by our results, but the instrumentation has been imprecise and may have contributed to uneven results in the hands of other surgeons. As such, we now favor an offshoot of the Marmor prosthesis, the instrumentation of which we hope can give reproducible results. Moreover, we also favor modularity in the sense of being able to choose different thicknesses of polyethylene for a given metal tray, whereas the Marmor was termed modular in the simple sense that the surgeon had more than one tibial thickness to choose from. We attribute our relative success to the surgical principles outlined above and, following the personal advice of L. Marmor, MD, to our avoidance of 6-mm tibial components (Fig. 4). At issue is still the question of whether the tibial component should be metal-backed or not. The nonmetal-backed, all-polyethylene component has the advantage of offering more polyethylene for a given tibial component thickness. The metalbacked component offers a stiffer base and allows for easier removal of excess cement posteriorly, last-minute fine tuning of the plateau thickness, and the option of screw fixation. A prospective study is underway comparing an all-polyethylene tibial component with the modular metal-backed component of the same design. Conclusion This series is one of the first to report on unicompartmental surgery with a minimum followup period of 10 years. We believe that the good results reported herein justify giving unicompartmental surgery an important role in reconstructive surgery of the knee and have encouraged us to make the procedure accessible to all reconstructive knee surgeons. References 1. Grelsamer RP: Unicompartmental osteoarthrosis of the knee: current concepts review. J Bone Joint Surg 77A:278, I995

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