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Reestablishment of the posterior stability after the posterior cruciate ligament-released cruciate retaining total knee arthroplasty.

Abstract

Purpose: The cruciate retaining (CR) design was developed to obtain knee stability with the natural posterior cruciate ligament (PCL) in total knee arthroplasty (TKA). However, the preservation of the PCL can limit knee exposure and increase the technical challenge during the procedure. Knee exposure is easily achieved under the released PCL, and we hypothesized that the PCL naturally repairs after release, thus re-establishing the posterior stability. Accordingly, the objective of this study was to evaluate the varying of the posterior stability after the PCL-released CR TKA over time.

Methods: Eight consecutive patients received the CR TKA in which the entire PCL was subperiostealy released at its femoral insertion. Thereafter, the patients were examined with the Knee Society Score, the posterior drawer examination, and the knee ligament arthrometer postoperatively.

Results: Once the PCL was released, the tibia was easily subluxated, and the knee was clearly exposed intraoperatively. However, the posterior stability significantly improved with time postoperatively. We also had confirmed the reestablishment of the PCL directly at revision TKAs, one case of which is shown.

Conclusion: The reestablishment of the posterior stability after the PCL-released CR TKA was demonstrated. This procedure to release the entire PCL subperiostealy is recommended as a means of facilitating CR TKA.

Osteoarthritis (OA) is one of the common diseases for middle-aged and older people due to the degeneration of the articular cartilage. For severe OA patients, surgical procedures with artificial joints are the common treatment. In the USA, 615,050 total knee arthroplasty (TKA) were performed in 2008, (1) and the number of TKA performed more than tripled from 1993 to 2009. (2)

There are two major concepts for TKA: cruciate retaining design (CR) and posterior stabilized design (PS). The principle of the CR design is to maintain the posterior stability with the natural posterior cruciate ligament (PCL) whereas, the PCL is sacrificed in the PS design, and substituted functionally with a polyethylene tibial post that articulates against a metal femoral cam (post-cam mechanism). Because each TKA has benefits and detriments, it is controversial which should be selected for successful TKA. In 2013, 55% of TKAs were performed with stabilized implants (including posterior and cruciate stabilized), and 33% were CR TKAs. (3)

The benefits of the PS TKA are that the knee joint exposure and the soft tissue balancing are easier to perform due to the resected PCL. Moreover, the posterior femoral roll back is enforced by a post-cam mechanism. However, this structure has been associated with post wear, post fracture, post-cam dislocation, and less bone stock at the femoral cam site. (4)

Conversely, the CR TKA has been thought to better preserve normal kinematics with the PCL. (5) However, the knee joint exposure is limited, and the soft tissue balancing is difficult in the presence of the intact PCL. The quality of the PCL also varies among patients. Thus, the CR TKA procedure is technically more demanding and must be individualized in each case, more so than for the PS TKA. Besides that, it has been suggested that there is a "paradoxical" movement of the femur on the tibia with flexion in the CR knee. (6) Recently, it has been reported that the differences between the PCL-retained CR and the PCL-resected CR are not clinically relevant. (7) Thus, the importance of the PCL preservation in TKA remains controversial. (8) However, the delayed rupture of the PCL after the CR TKA has been reported, which eventually resulted in symptomatic flexion instability. (9,10) Therefore, the PCL function is again thought to be essential to achieve the kinematic knee movement for the CR TKA.

We believe that the maintaining of the PCL integrity together with the CR design assures better postoperative knee kinematics than is possible with the PS. However, the presence of the PCL truly obstructs the exposure of the knee during surgery.

The anterior cruciate ligament (ACL) and the PCL are very different in several regards. The cross section of the PCL is 1.5 times greater than that of the ACL. Most of the patients with PCL injuries have been reported to return to athletics at the same level with nonoperative treatment; however, some patients have shown deterioration of knee function over time and have required an operative treatment. Whereas, the ACL deficient knee is less incapacitated in activity of daily living, it has less possibility to return to sports activity with the nonoperative treatment. (11-13) By focusing on the difference of the natural healing capability, we hypothesized that the PCL by virtue of its location adjacent to the posterior joint capsule has a better propensity to recover than does the ACL, which is an intraarticular ligament and is not adjacent to the joint capsule. We considered that the PCL could be subperiostealy released from the intercondylar origin at the beginning of the surgery to facilitate exposure and proper component placements, and that the PCL integrity and function would be re-established by spontaneous healing of the PCL with the joint capsule.

This is a short-term clinical study to evaluate the varying of posterior stability after the PCL-released CR TKA. A case report of a secondary look during a revision TKA additionally proves the potential of the released PCL to reattach to the lateral aspect of the medial femoral condyle from which it had been released.

Patients and Methods

The inclusion criteria of this study were patients who had been diagnosed with primary osteoarthritis and had been indicated for TKA. Eight consecutive cases in five patients were enrolled, and all TKAs were carried out by a single surgeon (JFF) under spinal anesthesia between August and October 2014. The exclusion criteria were patients with revision TKAs.

Operative procedures involved midline skin incision with medial parapatellar arthrotomy. After subperiosteal soft tissue release from the proximal tibia, the ACL was divided. Following that, the entire PCL was subperiostealy released at its femoral insertion within the intercondylar notch with a surgical scalpel (Fig. 1A). The patella was resurfaced in all cases, and the fixed bearing CR design system (3DKnee, DJO Global, Vista, CA) was implanted (Fig. 2). After the fixation of the implants with bone cement, the released PCL was returned into its original position without any adjunctive fixation (Fig. 1B). Then, joint capsule, fascia, subcutaneous tissues, and skin were sutured by layers. The patients were allowed to walk with a walker or a cane with full weight-bearing on the first postoperative day.

Postoperative recovery status was evaluated twice with the Knee Society Score (KSS knee and function scores) (14) at the second postoperative visit (1 to 2 months postoperatively) and at the third visit (3 to 5 months postoperatively). Anterior and posterior stability of the knee was also examined by manual evaluation of anterior and posterior drawer tests. Additionally, the anteroposterior laxity, which was defined as the total amount of anterior motion and posterior motion in this study, was measured by the KT-2000 knee ligament arthrometer (MedMetric Corp., San Diego, CA). All physical examinations were performed with the patients in a supine position.

Statistical Analysis

Paired sample t-tests were used to compare the difference in KSS knee and function scores and anteroposterior laxity. All statistical analyses were performed with SPSS version 19.0 software (SPSS Inc., Chicago, IL) and the significance level was set at p < 0.05.

Results

One female and two male patients underwent simultaneous bilateral TKAs, and these cases were examined separately. Then, there were eight cases in one female and four males, mean age was 63.3 [+ or -] 11.1 (range: 51 to 79), and mean BMI was 34.5 [+ or -] 7.6 (range: 26.8 to 43.1). All cases were diagnosed as primary osteoarthritis of the knee. The preoperative KSS knee score was 37.0 [+ or -] 9.4 (25 to 50), and the function score was 35.6 [+ or -] 19.9 (5 to 55), (Fig. 4).

The first postoperative evaluation was performed between 3 weeks and 7 weeks after surgery. The knee score was 74.4 [+ or -] 10.7 (range: 59 to 90), and the function score was 24.4 [+ or -] 12.2 (range: 20 to 55). The knee joints were still swollen, and the endpoint by manual posterior drawer test was not detected. The joint laxity was 5.2 [+ or -] 1.9 mm (range: 3 to 7.5). The knee score was significantly improved compared to the preoperative score (p < 0.001).

The second evaluation was performed between 12 weeks and 20 weeks after surgery. The knee score was 89.4 [+ or -] 11.6 (range: 70 to 100), and the function score was 82.5 [+ or -] 14.1 (range: 65 to 100). The knee conditions were improved, but slight swelling remained. The posterior stability with a firm endpoint by manual evaluation was detected in all cases. The anteroposterior laxity was 3.6 [+ or -] 1.2 mm (range: 2 to 5). The knee and function scores were significantly improved compared to the preoperative score (p < 0.001). The anteroposterior laxity was also improved compared to the first evaluation (p < 0.046).

A Case Report

An 84-year-old male underwent a PCL-released CR TKA in his right knee 7 years earlier. The patient was satisfied with the outcome and was without complaint. He also had suffered from cardiac dysfunction and had undergone cardiac surgery prior to the TKA. His general medical condition worsened with age post-TKA, attended with aggravation of his cardiac condition. Finally, the patient developed septicemia, which hematologically seeded the right knee. An open debridement was then required.

The operative findings showed that the knee joint was filled with an opaque yellowish liquid and hypertrophic synovitis consistent with infection. However, the PCL, which had been released at the primary TKA 7 years earlier, was confirmed to be re-attached to the intercondylar notch (Fig. 3A). The PCL was released again (Fig. 3B) to facilitate exposure and joint debridement. The polyethylene insert was revised, and the PCL was left at the original site without any additional fixation.

Discussion

The CR TKA was performed with the subperiosteal release of the PCL in order to facilitate the knee exposure. Reestablishment of the posterior stability was confirmed with both subjective study by the KSS function score and with objective study by the KSS knee score, posterior drawer test, and knee ligament arthrometer measurement within 20 weeks post-TKA. An example of the restoration of the PCL integrity was documented at the time of a prosthesis joint infection debridement 7 years after a primary TKA was performed.

Instability of the knee is one of the failure mechanisms in TKA. (15) Excessive anteroposterior motion results in limited femoral rollback and range of motion. (16) Therefore, the reproduction of the anteroposterior stability is crucial for successful TKA. However, the ACL is almost universally divided in typical CR and PS TKA, and thus the knee behaves as an ACL-deficient knee after TKA. (17) In the CR knee, the tibia is subluxated anteriorly on the femur during knee extension, and the femur slides anteriorly during knee flexion.

To compensate for this pathologic condition, the 3DKnee components (Fig. 2A) in which a tibial insert is anteroposteriorly curved medially and spherically congruent laterally have been developed. This lateral congruency constrains the lateral condyle to a central anteroposterior position in extension (Fig. 2B), but it is relatively lax and allows posterior translation in flexion (Fig. 2B). Thus, there is rough analogy with the location and stabilizing role of the ACL, which is called "ACL-substituting," compared to the traditional sagittally curved symmetric articular configuration. (18) However, it is still the fixed bearing CR design, and therefore, the posterior stability was theoretically dependent on the PCL function instead of the post-cam mechanism.

The PCL originates from an anterolateral aspect of the medial femoral condyle in the intracondylar notch and inserts into the PCL fossa beneath the posterior capsule on the proximal tibia. (12,13) The PCL is the primary restraint to posterior translocation of the proximal tibia at all flexion angles greater than 30[degrees] and is a secondary restraint to varusvalgus and external rotation forces.

Regarding anteroposterior stability, the PS design has been implicated as being correlated with mid-flexion instability, which is suffered before the engagement of the post-cam mechanisms. (19) Conversely, the CR TKA is believed to provide more stable knee kinematics with a sufficient joint stability under the significant role of the PCL. However, the exposure of the knee is definitely limited under the presence of an intact PCL. The flexion gap was widened after the PCL recession, and thus it became easy to subluxate the tibia in the PS TKA, which facilitated the precise positioning of the implants with the clearly exposed knee. Moreover, intraoperative management is required in the CR TKA for a "tight" PCL with referring to the lift off of the anterior tibial component. Options are the PCL retention, the partial recession of the PCL, the complete excision of the PCL, or the conversion to the stabilized prosthesis. (20) Therefore, it is a technical benefit of the PS TKA to simply cut the entire PCL at the beginning of the surgery.

For these reasons, the entire PCL was released at the primary CR TKA to obtain the same knee exposure as with the PS TKA. Compared to the ACL injury, most cases of nonoperative treatment of acute PCL injuries have acceptable subjective results. (11) We have focused on this capability of the PCL and relied on the natural healing of the PCL following subperiosteal release from the femur. Anatomically, the proximal insertion of the PCL to the femur is more accessible than its distal insertion to the tibia. Therefore, we chose to release the PCL from the femur. After the release process, the posterior aspect involving the PCL insertion of the tibia was clearly exposed.

Because of the long insertion of the PCL onto the proximal tibia, a considerable part of the tibial PCL attachment was reported to be removed with the proximal tibial resection in the CR TKA if the PCL was not spared in the bone block during resection. (21) However, our procedure enables surgeons to easily visualize the PCL insertion and protect it with a Hohmann retractor without damage to the PCL.

Concerning the evaluation position of the knee, the ACL function with anterior stability has been examined at 15[degrees], 30[degrees], and 90[degrees] in flexion. (22,23) Meanwhile, the PCL function with posterior stability has been examined at 70[degrees] and 90[degrees] in flexion. (24) Because of the knee pain, the knee swelling, and the limitation of the knee flexion, especially at the first evaluation time period, 30[degrees] in flexion was selected to evaluate the anteroposterior laxity in this study. However, at the second evaluation, the patients were also manually examined at 90[degrees] in flexion for posterior stability as well as the quality of the endpoint resistance perceived with the posterior drawer test.

Excellent functional outcomes have been reported with this ACL-substituting implant with and without PCL for the mid-term follow-up. (16) Ritter and coworkers had also examined the PCL-retained, the PCL-recessed, and the PCL-excised CR TKAs. They concluded that the CR TKA without PCL needs not be converted to the PS TKA as long as stability in the anteroposterior and coronal planes was achieved. (20) However, because of the difference in the stair-stepping outcomes and the knee flexion, they discussed that the PCL might be necessary for obtaining optimum function after TKA. Although the PCL was released at the primary TKA in our procedure, the regeneration of the PCL was also detected. Therefore, the function of the PCL as a posterior stabilizer was considered to be re-acquired with time.

Several limitations were included in this study. The number of the patients was small, and the follow-up period was short. However, the PCL-released CR TKA procedure has been performed for many cases in our institution, and the results were typically excellent without any posterior instability. In fact, we had confirmed the regeneration of the PCL directly at revision TKAs of which one of the cases was shown.

Because of the entire release of the PCL in the CR TKA, the flexion gap was thought to be increased compared with the traditional surgical technique in the CR TKA with the presence of the intact PCL. This might affect knee function; however, no patients have complained of joint instability after the surgery. In that regard, the posterior stability was confirmed to be re-established with time. Moreover, the 3DKnee design has been developed to provide anterior stability. Thus, we believed that anteroposterior stability could be achieved after the PCL-released CR TKA with the 3DKnee design.

Conclusion

The entire PCL was released in the CR TKA to facilitate the knee exposure. However, the released PCL has been shown to naturally heal and re-establish the posterior stability with time. Because of the technical benefit for the surgery and absence of detriment of posterior instability, the subperiosteal PCL release at the femoral insertion is recommended as a useful surgical technique in performing the CR TKA.

Disclosure Statement

None of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.

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Caption: Figure 1 A, The PCL was released with a surgical scalpel at the left knee. B, The PCL insertion to the proximal tibia was exposed. To view this figure in color, see www.hjdbulletin.org.

Caption: Figure 2 The right ACL-substituting tibial insert is an anteroposteriorly curved medially and spherically congruent laterally prosthesis (A). The lateral views show the lateral condyle constrains in extension (B), but relatively lax in flexion (C). To view this figure in color, see www.hjdbulletin.org.

Caption: Figure 3 A, The PCL was regenerated with the posterior capsule in the intrachondylar notch at the right knee. B, The PCL was re-released. To view this figure in color, see www.hjdbulletin.org.

Caption: Figure 4 A, The KSS knee score, B, the function score, and C, the anteroposterior laxity (pre-op: preoperation, 1st: the first evaluation, 2nd: the second evaluation, bars: standard deviation, *statistical difference).

Yasushi Oshima, M.D., Ph.D., and Joseph F. Fetto, M.D.

Yasushi Oshima, M.D., Ph.D., and Joseph F. Fetto, M.D., Division of Adult Reconstructive Surgery, Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York.

Correspondence: Yasushi Oshima, M.D., Ph.D., Division of Adult Reconstructive Surgery, Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, 1040 First Avenue 345, New York, New York 10022; yasuortho@yahoo.com.
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Author:Oshima, Yasushi; Fetto, Joseph F.
Publication:Bulletin of the NYU Hospital for Joint Diseases
Article Type:Report
Geographic Code:1USA
Date:Jul 1, 2017
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