| Abstract|| |
Methods: A retrospective study was done to compare the results of PCL sparing with PCL retaining designs of TKR in patients with similar types of deformities, with special reference to ease of surgery, post operative motion range and functional outcome. Group 1 consisted of 10 PCL substituting knees, with a mean follow up of 5.76 years, and group 2 consisted of 10 PCL retaining knees with a mean follow up of 6.31 years. We only included those cases which could be matched preoperatively with regard to age, sex, diagnosis, deformity, knee score and functional status.
Results: Postoperative evaluation was done by using the Knee Society's clinical and functional scoring system, and follow up radiographs were obtained and analysed. The knee score had improved from average of 43.3 points to 90.10 points in group 1 and from 46.10 points to an average of 84.6 points in group 2. The function scores improved from 17 to 66.5 in group 1 and from 17 to 72 points in group 2. There was no difference in the post operative radiological grades. Our results showed no difference in the change in parameters in these two groups, with all cases having similar improvement vis- a- vis function and motion range.
Conclusion: We noted that in cases with similar deformities, no significant improvement was achieved by sacrificing the PCL. However, specific indications do exists for excising the PCL; even if the implant is more expensive, it may be better for some cases with severe deformity, which may be difficult to correct intraoperatively without excising the PCL.
Keywords: Total knee replacement; Posterior cruciate ligament
|How to cite this article:|
Nagi O N, Dhillon MS, Kumar V. Comparison of PCL sparing and PCL substituting implants for total knee replacement. Indian J Orthop 2004;38:80-3
|How to cite this URL:|
Nagi O N, Dhillon MS, Kumar V. Comparison of PCL sparing and PCL substituting implants for total knee replacement. Indian J Orthop [serial online] 2004 [cited 2019 Dec 12];38:80-3. Available from: http://www.ijoonline.com/text.asp?2004/38/2/80/40905
| Introduction|| |
Total Knee arthroplasty(TKA) has now become accepted universally as the treatment for a severely arthritic knee with end stage disease. It provides good pain relief satisfactory restoration of the function in patients with advanced degenerative changes.
The role of the posterior cruciate ligament (PCL) in primary total knee arthroplasty has been under study for several years.  Proponents of saving the PCL argue that in addition to enhancing stability, allowing femoral roll back and increased flexion, it also absorbs shearing forces that would otherwise be imparted to the implant bone interface. Additionally the PCL may have a role in improved post operative proprioception  . On the other hand, the policy at some centers is to routinely resect the PCL to facilitate deformity correction and improve component fixation; this allows the use of a prosthesis with more congruent articulations that imparts less stress to their polyethylene inserts  .
A variety of prostheses have been designed, with most of the implants either substituting a resected PCL or allow for its preservation  . Clinical success and satisfactory survivorship have been reported with both these procedures. There are several advantages in implanting a PCL substituting prosthesis; the surgical technique is easier to perform, the surgeon can get away with minimal tibial resection allowing placement of tibial component in stronger host bone, and polyethylene wear is decreased when a conforming articular surface is implanted. Additionally the deformity can be corrected more easily 
Advocates of PCL retention in TKA cite an increase range of flexion extension motion , however other published studies cite the problem of a tight PCL as one which restricts flexion  . Additionally, the normal mechanism of femoral roll back is facilitated by the PCL, which increases the moment arm of the quadriceps. This can be compensated with a post or cam tibial design  . The PCL also acts as a secondary stabilizer to varus/valgus knee stability  and controls external rotation in flexion; on the other hand a tight PCL can make collateral ligament balancing difficult in cases of significant knee deformity.
Keeping the fact in mind that the PCL may have significant advantages if retained, and a tight PCL may also create surgical and post surgical problems on the other hand, it was proposed to evaluate the functional and radiological results of these two types of TKA in two similar subsets of patients. In one group a PCL substituting design was used for TKA and in the second group PCL retaining design was employed.[Figure 1],[Figure 2]
| Materials and Methods|| |
Over a 6 month period, a retrospective review was done of 20 cases that had undergone TKA a minimum of 4 year prior to evaluation; the chosen cases were called for examination and radiological assessment. These patients were selected from the data base of the PGIMER; ten cases with PCL retaining TKA and ten cases with a PCL substituting design TKA were invited for follow up. The records were carefully examined to try and include similar preoperative knees (age, sex matched, with somewhat similar indications for surgery and similar pre-operative deformities), so that comparative data would be relevant. All the TKAs were performed by the principal author, and all follow up cases were examined by at least 2 of the three authors of this study.
The clinical examination was done on the basis of the Knee Society clinical rating system  and the radiological examination was done according to the Knee Society radiological evaluation  form respectively. Group 1 (PCL substituting) TKA was done using IB two implants (Zimmer), and Group 2 (PCL retaining) employed IB one (Zimmer) implants.
Both groups were compared for preoperative and post operative parameters. Detailed functional and radiological data was compiled using the above mentioned scores, and these were compared to see for any differences in the post operative function.
| Results|| |
The demographic data is given in [Table 1]. The mean ages of both the groups of patients were comparable. There were no statistically significant difference in the age, sex, diagnosis, duration of follow up and pre-operative deformity.
The detailed clinical assessment scores of both groups are given in [Table 2],[Table 3]. Clinical scores taking into account pain (mean score increased by 32.50 points and by 34.00 points in groups 1 and 2 respectively), range of movement (mean score changed from 18.30 points to 19.10 points and from 17.70 points to 16.90 points) were not statistically different in both groups of patients. In Group I stability in A-P and medio-lateral direction, increased by 4 points (mean) each, and in Group II, by 2.00 points (mean) and 1.50 points (mean) respectively. The difference in stability change in both groups was not statistically significant.
In Group I ability to use stairs increased by 21.00 points (mean), in Group II by 31.00 points (mean) and walking ability increase in both groups was the same (27.00 points mean).
In Group-I Knee score increased by 47.28 points (mean) and in Group-II by 44.60 points (mean) and functional score in Group-I increased by 49.50 points (mean) and in Group-II by 55 points (mean), as shown in [Table 2] b and [Table 3]b.
Radiological evaluation using the femur flexion angle, tibia angle and tibia valgus angle in A-P X-ray and femur flexion angle and tibia angle in lateral X-ray and patellar position were not significant between both the group and there were no radiolucencies in any of the TKAs [Table 4].
Analysis of the above data showed that there was no significant difference in knee score, functional score and radiological data between the TKA using either PCL substituting or PCL retaining designs.
| Discussion|| |
The role of the PCL in primary TKA has been debated for several years , . The PCL is the strongest ligament in the knee and can be responsible for absorbing a significant amount of force. As in the normal knee, the prosthetic knee can achieve greater flexion if the implanted prosthesis allows the femur to glide posteriorly on the tibia, cleaning the posterior structures. Moreover, this posterior roll back enhances the efficiency of the quadriceps muscles by lengthening the lever arm from the point of joint contact to the quadriceps tendon.
Freeman et al  have shown that the knee represents a crossed four-bar linkage, the upper and lower elements of which are represented by the femur and tibia and the crossed linkage is represented by the ACL and the PCL. If the ACL is excised (as is done in routine TKA), then the crossed linkage effect of the PCL in isolation becomes ineffective. Additionally surgical difficulties encountered due to contracted PCLs and the restricted flexion postoperatively with PCL retention lead many surgeons to change routinely to PCL substituting designs. This was refuted by many who found that preplanned PCL resection and PCL retention did not show significant alterations in function  . Backer et al conducted a study of bilateral TKAs where they used patients as their own control by carrying out a PCL substituting TKA in one knee and a PCL retaining TKA in the contralateral knee. The results were identical as judged by patient satisfaction.
Pereira et al  revealed no difference in clinical or early radiological outcome between PCL sacrificing and PCL substituting and retaining TKA; they however supported the argument that PCL sacrifice should be considered in cases in which extensive releases and complex ligamentous balancing are required, and this would not alter the functional and result.
The controversy in the literature regarding choosing to save or sacrifice the PCL at time of TKA is made more confusing by reports that advocate the advantages of both procedures. In an attempt to clarify the surgical indications, Laskin et al  found that in 15 o or more of varus contracture the PCL was partly responsible for the deformity, and unless excised, the deformity could not be corrected by medial release alone. Hirbch et al  have observed that preserving the PCL does not consistently lead to improved functional range of movement. The PCL substituting implant, when implanted with the correct indications, has demonstrated excellent survivor ship in some hands, and appears to offer greater range of movement  . On the other hand the prosthesis is more expensive and needs more specialized equipment, adding significantly to the cost.
As a counter argument, Vinchiguerra et al  found that functional outcome seems to be the same whenever a PCL substituting or a PCL retaining total knee prosthesis was used, regardless of the indications.
In the Indian scenario these are important arguments. Cost and prosthesis availability may influences decisions to some extent, but this should not be at the expense of post operative results. With this in mind, we analyzed similarly deformed knees in age and sex matched cases to see if the end results were different at the early follow up periods. Increases in all parameters in both groups were almost similar and there was no statistically significant difference between both the groups.
It is difficult to explain why the results have not been improved by the use of more recent type of prosthesis (PCL substituting design) which have been designed or modified to overcome recognized causes of failure in earlier designs, or by their implantation with the aid of more advanced instrumentation. The present study seems to find no short term benefit. However, it is wise to understand that perhaps the two types of prostheses have different indications, and may not be applicable in similar situations. We believe that if the contractures are significant, and the PCL is adding to the deformity, it should be excised and a PCL substituting implant should be used. On the other hand, if the PCL seems adequate and does not hinder the surgical procedure, and seems to be adding to the stability, it should preferably be retained, as it has significant stabilizing function. The biggest disadvantages in this protocol would be the added cost of having both types of implants as well as relevant instrumentation available in the OT.
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O N Nagi
1027, Sector 24-B, Chandigarh
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]