a Departamento de Ortopedia, Santa Casa de São Paulo, São Paulo, SP, Brasil
b Serviço de Ortopedia e Traumatologia, Hospital Israelita Albert Einstein, Universidade Federal de São Paulo (Unifesp), São Paulo, SP,Brasil
c Instituto de Ortopedia, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (USP), São Paulo, SP, Brasil
d Escola Paulista de Medicina, Universidade Federal de São Paulo (Unifesp), São Paulo, SP, Brasil
Introduction
The concept of knee arthroplasty with mobile tibial weight-bearing was introduced by Goodfellow and O'Connor in 1978.1This innovation was based on the need to adapt the compo-nents of the prosthesis to different angles during flexion andextension.2Its aim was to increase the physiological move-ment in the joint and thus diminish abrasion and wear onthe polyethylene component, formation of particles, occur-rences of osteolysis3and, especially, patients' complaints ofpain. This greater durability has not been proven in mediumand long-term clinical studies.4-7However, some authors haveachieved better results from prostheses with mobile weight-bearing, in relation to stability and the action of going upstairs.
Biomechanical studies have shown that prostheses withmobile tibial weight-bearing reduce the incongruence createdby non-physiological rotation in implanting the femoral com-ponent. Several studies have shown good long-term resultsfrom using these implants. However, some authors have indi-cated that there is a need for studies with long-term follow-upand have proven that this technique has clinical and survivaladvantages, in comparison with implants with fixed tibialweight-bearing.
The objective of this paper was to present the medium andlong-term clinical results from using prostheses with mobiletibial weight-bearing in patients attended by the Knee SurgeryGroup of the Department of Orthopedics and Traumatology ofSanta Casa de São Paulo.
Sample
Between January 2000 and July 2007, 162 patients underwenttotal knee arthroplasty in which polyethylene tibial compo-nents with rotary movement were used (Fig. 1). These patientswere initially invited to return for medium-term assessmentof the clinical results (mean follow-up of 4 years). On that occa-sion, 96 patients responded to the invitation, and a total of117 knees were evaluated.13The present study consisted ofreassessment of these same patients after a minimum post-operative period of 5 years.
Out of the 96 patients who were assessed in the previousstudy, 69 responded to the invitation of the present study. Ten
of these had undergone bilateral arthroplasty, and therefore 79knees were evaluated. There were 10 men and 59 women, withages ranging from 53 to 87 years (mean of 75.7) and postoper-ative follow-up ranging from 5.5 to 13 years (mean of 8 yearsand 8 months). The deformities that formed the indications forsurgery are described in Table 1. Out of the 27 patients whowere lost from the follow-up, it was found that ten patientshad died for reasons unrelated to the surgery, while the otherlosses (17) were due to our failure to locate the patient or topatients' non-attendance even after receiving the invitation.
Methods
This was an observational study on a cohort of patients froma previous investigation.13It was conducted in a public uni-versity hospital (Santa Casa de São Paulo). The study wasapproved by the institution's ethics committee.
Before the surgery, the patients were evaluated usingsemiological data, frontal-view panoramic radiographs withweight-bearing and also lateral and axial radiographs on thepatellofemoral joint, and a diagnosis of osteoarthrosis wasmade. The patients underwent preoperative evaluations sothat the procedure could be implemented with the lowestrisk possible. The following were considered to be exclu-sion factors: diaphyseal deformities that made correction viaarthroplasty impossible, major bone losses due to osteolysis,ligament laxity that required implants with stabilizing mech-anisms (not present in the model that would be used) andosteoarticular infections. In cases of bilateral treatment, therewas always an interval of 2-4 months between the operationson one knee and the other.
For this study, the patients were invited to come fora new clinical and functional assessment. The functionalassessment was made in accordance with the objective cri-teria established by the Knee Society Clinical Rating System(KSRS),14as shown in Table 2.
As established in the assessment system (KSRS), the finalscores ranged from 0 to 100. Results with scores greater than84 were considered to be excellent; from 70 to 84, good; from 60to 69, fair; and less than 60, poor. Patients who had to undergorevision of the arthroplasty were considered to be treatmentfailures and received the score of zero.
Statistical analysis
The data obtained were subjected to statistical evaluation. Thechi-square test was applied for qualitative variables, or the
Fisher exact test if necessary. To quantitative variables versusqualitative variables, the Mann-Whitney nonparametric testwas used. The Statistical Package for the Social Sciences (SPSS)software version 13 was used, and the significance level wasset at 5%. The analysis was conducted under guidance fromstatisticians from the publication support committee of theSchool of Medical Sciences, Santa Casa de São Paulo.
Results
Out of the 96 patients evaluated in the previous study,1369attended the invitation. Surgery had been performed bilater-ally in ten of these patients. Thus, 79 knees were evaluated,with a mean follow-up period of 8 years and 8 months.
The arthroplasties that required revision received scoresof zero. Among the patients who did not undergo revision, theminimum score found was 40 points and the maximum was99. The mean score was 74.41 points.
With regard to surgical complications (Table 3), one caseof fracturing of the femoral condyle was seen during cemen-tation, and this was fixed using Steinmann wires, whichrequired subsequent revision because of aseptic loosening.There were three cases of patellar fractures: one during thesurgery and two after the operation. The fracture that occurredduring the surgery was marginal and did not require fixation.
Among the others, one was comminutive (patellectomy wasperformed) and the other was a transverse fracture that wastreated conservatively and evolved without consolidationand pain. Subsequently, this latter case was treated withpartial patellectomy. Three patients presented neuropraxiaof the fibular nerve. Two of them presented spontaneousrecovery and the third underwent neurolysis 2 months laterand evolved with total recovery. There was also one case ofdehiscence of a skin suture. Surgical cleaning and suturingwere performed, and the case evolved without infection andwith a good clinical result. Five cases of infection occurred, allof them before reaching 5 years after the operation. One caseoccurred after a repair that was performed on the extensormechanism because of a fall to the ground that evolvedwith infection and loosening of the prosthesis. In this case,the patient underwent removal of the prosthesis and thenarthrodesis after the infection had been resolved. In the otherfour cases, revision of the arthroplasty was performed intwo procedures, with use of a spacer. There were five casesof aseptic loosening of the prosthesis, and revision of thearthroplasty was performed in these cases.
The KSRS results were distributed as excellent (KSRSgreater than 84), in 55.7% of the cases (44 knees); good(between 70 and 84), in 22.8% (18 knees); fair (between 60 and69), in 7.6% (six knees); and poor (less than 60), in 13.9% (11knees).
The relationship between the presence of complicationsand whether unilateral or bilateral arthroplasty had been per-formed, and no statistically significant association was found(p = 0.058; Fisher exact test).
The relationships between the patient's sex and occur-rences of complications and between sex and results werealso evaluated. Neither of these showed any statistical differ-ence (p = 1, Fisher exact test; and p = 0.610, Mann-Whitney test,respectively).
The relationship between the etiology of the arthrosisand the presence of complications was evaluated. Greaterincidence of complications was found in cases of secondaryarthrosis, and this was statistically significant (p = 0.044; Fisherexact test). In evaluating the relationship between the resultsand whether the etiology was primary or secondary, betterresults were observed in the group of patients with pri-mary osteoarthrosis, although without statistical significance(p = 0.210; Mann-Whitney test).
Discussion
Prostheses with mobile tibial weight-bearing emerged throughthe study by Goodfellow and O'Connor in 1979. They defendedthe concept that the mobile tibial component, acting solidlywith the femoral condyle, would represent a congruent pros-thesis without restrictions at any moment during flexion andextension.1Subsequent studies showed that this implant hadhigh durability and enabled movements similar to those ofnormal knees, with regard to kinematics, and its indicationsexpanded to include younger patients.1,15,16Some studieshave indicated that the survival of the implant is greaterthan 20 years in 97.7% of the cases.17,15Nonetheless, otherauthors have not seen advantages of one model over the other, since they found similar results regarding patient satisfactionand implant durability. Studies comparing bilateral arthro-plasties, in which one knee received a prosthesis with fixedweight-bearing and the other received a prosthesis with rotaryweight-bearing have been conducted, and no significant dif-ferences were found.
Regarding our sample, out of the original 162 patients,96 responded to the invitation at the time of the first data-gathering made by our group (mean follow-up of 5 years).Sixty-nine of these responded to the present invitation. Thisloss was greater than those in the literature consulted12,20andwas due to a variety of factors, such as changes in address andtelephone number, death or socioeconomic factors. It can besupposed that patients with good results from the proceduremight have neglected to return because they considered this tobe unimportant. We also noted that the loss from the follow-up was variable among the other studies consulted. Argensonet al. found a loss of 7% from their minimum follow-up of 10years among their patients.20On the other hand, in a studywith a similar length of follow-up, Meftah et al.11presented aloss of 23% among their patients.
In our group's first assessment, the mean final KSRS scorewas 78.22 points. In comparing this with the present results(mean final score of 74.41), we consider that this decrease wasto be expected. It would have been caused by the expectedwear on the implant and the aging of the patient sample.However, we did not find any data in the literature compar-ing the same group of patients over medium and long-termfollow-ups.
In relation to complications, paralysis of the fibular nerveoccurred in three cases that had all presented preoperativevalgus deformity, and all of them presented total resolution.The data in the literature show that neuropraxia of the fibularnerve is more common in knees with valgus deviation, giventhat at the time of correction of the axis, through section-ing capsule, tendon and ligament structures, tension may begenerated in the nerve and consequently, neuropraxia.
Initially, the patellar component was fixed to the bone onlyusing a wide circular orifice. All of the three cases of patellarfracture occurred with implants of this type. After changingthe implant such that there would be three small orifices, therewere no further postoperative cases of patellar fracture.
Prostheses with tibial weight-bearing have been implantedeither with preservation or with replacement of the posteriorcruciate ligament, with similar results. In our cases, the pos-terior cruciate ligament was replaced with the aim of avoidingasymmetrical tension and the possibility of rotary dislocationof the mobile platform (spin-out), which never occurred inour cases. There were five cases of aseptic loosening (6.3%).In none of our cases was there any postoperative misalign-ment of the axis that might have accelerated the looseningprocess. These five cases underwent revision operations andevolved satisfactorily.
In relation to the number of infections, the incidence in oursample was greater (6.1%) than what was seen in the world-wide literature (1.8-2.3%).11,20We can suppose that this wasdue to social factors, such as postoperative care, along withthe fact that all of our patients underwent surgery in a publicteaching institute, in which greater numbers of professionalsundergoing training are present in the operating theater. Ong
et al.23identified that surgery performed in public services andlengthy duration of procedures (>210 min) were risk factors forprosthetic infections (in hip arthroplasty procedures).
In a case series with follow-up of greater than 10 years,Meftah et al.11found that 96% of their results were good andexcellent, with a mean functional KSRS score of 89.1 points.Argenson et al.20showed similar results, with a mean func-tional KSRS score of 88. We conclude that our sample showeda lower mean score because we included cases that underwentrevision, which lowered the mean score because we gave thesecases the minimum score. In analyzing our results with exclu-sion of these cases with scores of zero, we obtained a meanscore of 85 points and considerably diminished the differenceencountered. Another result that should be noted is that 78.5%of the patients obtained KSRS scores >70, i.e. good or excellent.
The limitations of this study consist of the lack of controlgroup for comparing the results and the difficulty in com-paring patients for reevaluation after a long postoperativeperiod. There is a need for new studies that compare func-tion, symptoms and satisfaction among patients undergoingtotal knee arthroplasty with mobile and fixed weight-bearing,with follow-ups of more than 10 years.
Conclusion
The total knee prostheses with mobile tibial weight-bearingsubjected to analysis using the Knee Society Clinical RatingSystem achieved good results with a mean of 74.41 points.
Conflicts of interest
The authors declare no conflicts of interest.
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