Although some authors have reported favorable outcomes of posterior cruciate ligament (PCL) reconstruction performed with improved arthroscopic surgical techniques1,2, residual posterior laxity is the most common complication following PCL reconstruction3. In a review of the results of PCL reconstruction combined with other ligament reconstruction, the posterior drawer test was found to be normal in 37% to 70% of cases at the time of final follow-up4. The graft failure rate ranged from 2.3% to 30% following PCL reconstruction with or without other ligament reconstruction4. PCL injuries combined with other ligament injuries of the knee lead to more residual functional limitations5,6. In particular, posterolateral corner injuries are frequently associated with PCL injuries7, and untreated posterolateral corner injuries increase the force on the PCL graft, which increases the late failure rate of PCL reconstructions8-10.
The normal knee has some laxity in each direction, which is known clinically as physiological joint laxity11. However, some patients show excessive laxity of tibial external rotation on testing of the uninjured knee. We defined this excessive but not pathological external rotation as physiological posterolateral rotatory laxity.
The purpose of this study was to evaluate the influence of physiological posterolateral rotatory laxity on posterior knee stability and clinical outcomes following PCL reconstruction combined with simultaneous reconstruction of the posterolateral corner. We hypothesized that patients who had excessive tibial external rotation on the uninjured side at 90° of knee flexion would have more knee instability and an inferior clinical outcome in the reconstructed knee.
Materials and Methods
We retrospectively reviewed the records of 158 patients who had undergone arthroscopic PCL reconstruction with simultaneous reconstruction of the posterolateral corner from March 2004 to April 2009. The senior author of this study (S.-J.K.) performed all reconstructions. Subjects were selected according to the following criteria: (1) ≥8 mm of increased posterior translation compared with that of the normal, contralateral knee on posterior stress radiography12,13; (2) concomitant posterolateral rotatory instability on the reverse pivot-shift test and >10° of external rotation instability compared with the normal, contralateral knee at 30° and 90° flexion on the dial test; (3) a subjective functional deficit; and (4) a single-bundle anterolateral transtibial PCL reconstruction with an Achilles tendon-bone allograft, combined with anatomical reconstruction of the fibular collateral ligament and popliteus tendon with a tibialis posterior tendon allograft. Exclusion criteria included: (1) previous surgery on the affected knee; (2) instability of the contralateral knee; (3) isolated PCL injury without posterolateral corner insufficiency; (4) articular cartilage lesions greater than Outerbridge grade II at arthroscopic inspection14; (5) a subtotal or total meniscectomy; (6) a PCL avulsion fracture; (7) multiple ligament injuries, except for a combined PCL and posterolateral corner injury; (8) varus malalignment; and (9) inadequate follow-up (less than twenty-four months). Sixty-five patients met the inclusion and exclusion criteria.
Preoperatively, all patients were examined with the dial test while they were prone. The amount of external rotation of the tibia was determined by measuring the angle between the axis of the medial border of the foot and that of the femur with a goniometer. The dial test was positive if the side-to-side difference in external rotation was >10° at either 30° or 90° of knee flexion15.
In our literature review, the average amount of tibial external rotation of intact knees in the general population was found to be >40° at 90° of knee flexion16,17. We set ≥50° of tibial external rotation as the cutoff reference value for physiological posterolateral rotatory laxity and determined that posterolateral corner injury was possible if external rotation of the injured tibia exceeded 10° in a side-to-side comparison. To stratify physiological posterolateral rotatory laxity, patients were categorized into three groups according to the amount of tibial external rotation on the uninjured side at 90° of knee flexion: Group 1 (<40°), Group 2 (between 40° and 50°), and Group 3 (>50°). All patients gave informed consent to participate in the study, and institutional review board approval was obtained.
The patients were treated with an anterolateral transtibial single-bundle PCL reconstruction with use of an Achilles tendon-bone allograft with the one-incision technique. The center of the femoral socket was located at the 1:30 position for the right knee and the 10:30 position for the left knee. The bone plug of an Achilles tendon-bone allograft was trimmed to 25 mm in length and 11 mm in width. The Achilles tendon was prepared to be 60 mm in length and 11 mm in width. Posterolateral corner reconstructions consisted of an anatomical reconstruction of the fibular collateral ligament and popliteus tendon with a tibialis posterior tendon allograft. A more detailed description of the surgical technique has been published previously18,19.
Postoperatively, patients were regularly followed with outpatient clinic visits at two weeks, three months, six months, and then annually. The grafts were protected by immobilization with a hinged knee brace in extension for the first four to six weeks. Although the patients wore the hinged knee brace all day for four weeks, protected range-of-motion exercises such as prone passive flexion exercises, three times a day, were started at two to four weeks as pain allowed. Isometric quadriceps strengthening exercises and mobilization of the patella were initiated immediately after surgery. Only minimal weight-bearing, such as toe-touching, was allowed, with a locked brace, during this period.
After the first four to six weeks, the knee was kept in an unlocked hinged knee brace for six more weeks. Patients were initially allowed to bear weight and flex their knees as tolerated, and then knee flexion was progressively increased up to 90°. At eight weeks postoperatively, closed-chain kinetic exercises were started. At twelve weeks, use of a stationary bicycle, stair-stepping, and single-leg stances were allowed. Full flexion or squatting was prohibited for three months postoperatively. After six months, when the limb symmetry index was seen to be ≥90% in a single-leg hop test, the patients were allowed to return to their preinjury sports activity or full activity.
Clinical assessment of posterior knee stability and functional outcomes was performed preoperatively and postoperatively. The results of the dial test were categorized into four levels according to the International Knee Document Committee (IKDC) knee evaluation form (grade 0, ≤5°; grade 1+, 6° to 10°; grade 2+, 11° to 19°; and grade 3+, ≥20°).
Posterior knee instability was evaluated with posterior stress radiography with use of a Telos device (Telos, Marburg, Germany) with a 150-N posterior load applied to the proximal part of the tibia at 90° of knee flexion and in neutral rotation. When analyzing the posterior stress radiograph, we used the peripheral osseous landmarks suggested by Stäubli and Jakob20. The posterior displacement was measured between the femoral and tibial vertical midpoint lines with use of a computerized radiographic system (Centricity Enterprise Web version 2.0; GE Medical Systems, Waukesha, Wisconsin). Each of the femoral and tibial vertical midpoints was a crossing point of the two lines; a line parallel to the tibial plateau and a vertical line at the midpoint of two lines were drawn from the most posterior outlines of the medial and lateral condyles of the tibia and femur20-22.
To evaluate varus instability, a varus stress radiograph was obtained at 30° of knee flexion with a Telos device and the application of a 150-N varus load23. Varus instability was quantified according to the method described by Jacobsen24. One horizontal line tangential to the portion of the most distal subchondral bone of both tibial plateaus was drawn, and another horizontal line tangential to both femoral condyles was drawn in the same manner. One line perpendicular to the tibial-side horizontal line was drawn tangential to the most lateral side of the tibia. The distance between the two horizontal lines on this perpendicular line was regarded as varus laxity.
Interobserver variability was calculated to enhance the reliability of measurements. Every stress view obtained to evaluate posterior translation was independently measured twice by two orthopaedic surgeons; the mean values of each examiner’s two measurements were determined and used in the analysis to calculate interobserver variability. Means of the values measured on the varus stress views and with the dial tests were obtained in the same manner.
The average of the two individual mean values was used. Functional outcomes were assessed with the Lysholm score and the IKDC score.
Statistical analysis was performed with use of PASW software (version 19.0; SPSS, Chicago, Illinois). Analysis of variance (ANOVA) was used to compare the three groups with regard to the side-to-side difference seen on posterior stress radiography and varus stress radiographs (continuous data). The Mantel-Haenszel chi-square test was used to compare groups with regard to the differences in the grades on the dial test and the IKDC scores (categorical ordinal data). The differences in the Lysholm scores (ranked continuous data) were analyzed with the Kruskal-Wallis test. The interobserver reliability of measurement of the instability on stress radiography and the external rotation of the tibia was evaluated with use of the intraclass correlation (ICC) set at a 95% confidence interval (CI). The level of significance was set at p < 0.05.
Source of Funding
There was no external funding for this study.
This study included sixty-five patients, fifty-five males and ten females. The mean age of the patients at the time of surgery was 37.2 years (range, sixteen to sixty-four years). There were twenty-three males and three females in Group 1, eighteen males and three females in Group 2, and fourteen males and four females in Group 3. The mean age at the time of surgery was 38.9 years (range, sixteen to sixty-three years) in Group 1, 36.1 years (range, twenty to sixty-four years) in Group 2, and 36.1 years (range, eighteen to fifty-eight years) in Group 3. There were no significant differences among the groups with regard to age at the time of surgery, body mass index, mean follow-up duration, or time to surgery. The average tibial external rotation of the uninjured knee at 90° of knee flexion was 33.6° in Group 1 (ICC, 0.697), 44.8° in Group 2 (ICC, 0.683), and 55.4° in Group 3 (ICC, 0.689) (see Appendix).
The preoperative mean side-to-side difference (and standard deviation) in posterior tibial translation measured with the Telos device were 12.6 ± 3.9 mm in Group 1, 13.2 ± 3.7 mm in Group 2, and 13.5 ± 3.3 mm in Group 3. At the last follow-up visit, the mean side-to-side difference was 3.6 ± 1.3 mm (ICC, 0.854) in Group 1, 3.3 ± 1.6 mm (ICC, 0.857) in Group 2, and 4.3 ± 1.6 mm (ICC, 0.852) in Group 3. There was no significant difference among the groups preoperatively or at the last follow-up evaluation. Two patients (8%) in Group 1, one patient (5%) in Group 2, and three patients (17%) in Group 3 had a 6 to 10-mm increase in posterior translation compared with that of the contralateral, intact knee at the time of the last follow-up (Table I).
The preoperative mean side-to-side difference seen on the varus stress radiograph was 5.0 ± 0.8 mm in Group 1, 4.8 ± 1.2 mm in Group 2, and 5.5 ± 0.9 mm in Group 3. At the last follow-up visit, the mean side-to-side difference was 1.6 ± 0.7 mm in Group 1 (ICC, 0.875), 1.7 ± 0.7 mm in Group 2 (ICC, 0.887), and 2.0 ± 0.5 mm in Group 3 (ICC, 0.896). There was no difference among the groups with regard to varus instability preoperatively or at the last follow-up visit. Twelve patients (four in Group 1, five in Group 2, and three in Group 3) had an increase in varus laxity of ≥3 mm, compared with the normal side, at the last follow-up visit (mean side-to-side difference, 3.4 ± 0.7 mm [95% CI, 3.1 to 3.5 mm]) (Table II).
On the dial test, there were no significant differences among the groups at either 30° or 90° of knee flexion preoperatively or at the time of the last follow-up (Table III). One patient in Group 3 showed decreased external rotation by up to 5° compared with that of the normal, contralateral knee at both 30° and 90° of knee flexion.
The average Lysholm score improved from 60.2 ± 5.3 preoperatively to 85.8 ± 7.9 at the last follow-up evaluation in Group 1, from 58.3 ± 6.7 to 88.7 ± 6.9 in Group 2, and from 57.4 ± 7.3 to 84.1 ± 6.7 in Group 3. There was no significant difference among the groups preoperatively or at the last follow-up visit (Table IV).
Preoperatively, the IKDC knee score was C (abnormal) in eleven patients (42%) and D (severely abnormal) in fifteen patients (58%) in Group 1. At the last follow-up visit, four patients (15%) in Group 1 had a score of A (normal); eighteen patients (69%), B (nearly normal); and four patients (15%), C. In Group 2, eleven patients (52%) had a preoperative IKDC knee score of C and ten patients (48%) had a score of D. At the last follow-up visit, four patients (19%) in Group 2 had a score of A (normal); fourteen (67%), B; two (10%), C; and one (5%), D. In Group 3, six patients (33%) had a preoperative score of C and twelve patients (67%) had a score of D. At the last follow-up visit, the score was A for two patients (11%) in Group 3, B for nine (50%), C for six (33%), and D for one (6%). There was no significant difference in the IKDC score among the groups preoperatively at the time of the last follow-up (Table V).
In Group 1, one patient had a suspected cortical break of the fibular head at the site of the reconstruction of the posterolateral corner such that the bioabsorbable interference screw was not firmly seated in the fibular tunnel. Immobilization was prolonged for six weeks for this patient. There were no infections or neurovascular complications in any of the groups.
Varus load as well as posterior drawer force combined with external rotation torque is one of the most important joint-loading conditions that increase the force on the PCL graft10. Recent biomechanical analysis supports the clinical theory that untreated injuries to the posterolateral corner cause PCL graft failure8,10. Therefore, we suspected that excessive physiological posterolateral rotatory laxity would affect the postoperative results of PCL reconstruction even though it was not pathological. In this study of PCL reconstruction, however, there was no significant difference in knee instability or functional outcomes among three groups according to the amount of tibial external rotation at 90° of knee flexion on the uninjured side. Therefore, these data suggest that physiological posterolateral rotatory laxity should not be considered a risk factor that may cause abnormal knee laxity after PCL reconstruction and successful reconstruction of the posterolateral corner.
Due to the fibular collateral ligament and popliteus complex being more effective in restraining external rotation at 30° of flexion than at 90°25, the degree of external rotation is the greatest at 30° of flexion in a knee with an isolated posterolateral corner injury. Cooper16 demonstrated that external rotation of a normal knee was greater at 90° of flexion than it was at 30°. We thought that, in the case of physiological but not pathological rotatory laxity of the knee, the degree of external rotation at 90° of knee flexion is more representative of the knee rotatory laxity. Therefore, we categorized patients according to the amount of tibial external rotation at 90° of knee flexion but not at 30°.
In this study, there was no significant difference in knee instability or functional outcomes among the three groups according to the amount of tibial external rotation at 90° of knee flexion on the uninjured side. However, the p values for the side-to-side difference approached significance for posterior tibial translation (p = 0.098) (Table I), varus instability (p = 0.078) (Table II), and the average Lysholm score (p = 0.068) (Table IV). With the numbers studied, the differences among the groups with regard to these values at the last follow-up evaluation did not reach significance. There is the possibility of a Type-II error secondary to insufficient sample size.
The PCL reconstruction was considered a failure if >8 mm of increased posterior tibial displacement, compared with that on the normal side, was found on the stress radiographs13,26. In the current study, eight patients (12%) had an increase in posterior translation of ≥6 mm but <8 mm on the stress radiographs. Meanwhile, in the cadaveric study of LaPrade et al.27, an approximately 2.7-mm increase in opening was seen on clinician-applied varus stress radiographs of knees with an isolated fibular collateral ligament injury and an approximately 4.0-mm increase was observed in cases with a grade-III posterolateral corner injury. In this study, external rotation was controlled well by reconstruction of the posterolateral corner as no patient had more than a 10° increase in external rotation compared with that of the intact knee on the postoperative dial test. However, twelve patients (18%) had an increase in varus instability of ≥3 mm compared with that in the intact knee as seen on the stress radiographs. Wang et al.28 reported that, in a study of twenty-five patients who had undergone PCL reconstruction (with an allograft in eighteen and an autograft in seven) combined with reconstruction of the posterolateral corner, the mean Lysholm scores improved from 64 points preoperatively to 86 points at an average of forty months postoperatively. Despite functional improvement, 20% of the patients had ≥5 mm of posterior ligament laxity and 46% of the patients had ≥5 mm of varus angulation. Khanduja et al.29 analyzed the outcomes of nineteen patients who had undergone a combined reconstruction of the PCL and posterolateral corner. After the time of follow-up at a mean of 66.8 months, the mean Lysholm score had improved to 76.5 points (from 41.2 points preoperatively); there was a grade-II posterior sag in 5% of the patients and residual minimal posterolateral laxity in 26% of the patients. Khanduja et al. also used both allografts (sixteen) and autografts (three) for the PCL reconstructions. Although it is difficult to directly compare those studies with ours because both allografts and autografts were used for PCL reconstruction in those studies, the outcomes of our study do not seem to be inferior to those in the others.
There were some inherent limitations in this study. First, we were unable to evaluate the effect of physiological posterolateral rotatory laxity on the results of the PCL reconstruction in the patients with an isolated PCL injury because only a small number of patients had an isolated PCL injury. Second, the examiners manually applied external rotational force to the tibia for the dial test. The force may have varied depending on the examiner, although two orthopaedic surgeons measured the laxity twice and the mean of their individual means was determined. Third, this study has a relatively low power for statistical analysis because the sample size of each group was small. Fourth, residual varus laxity occurred in some patients. This laxity could affect the result of PCL reconstruction combined with reconstruction of the posterolateral corner. Fifth, we used Jacobsen’s method24 to measure varus instability. This method relies on manual measurements, which are not as accurate as digital measurement.
In conclusion, this study suggests that knee instability in patients with PCL and posterolateral corner injuries with physiological posterolateral rotatory laxity can be controlled successfully with PCL reconstruction with simultaneous reconstruction of the posterolateral corner. Physiological posterolateral rotatory laxity should not be considered a risk factor that causes abnormal knee laxity after PCL reconstruction with simultaneous reconstruction of the posterolateral corner.
A table showing patient demographics is available with the online version of this article as a data supplement at jbjs.org.
Investigation performed at the Department of Orthopaedic Surgery and the Arthroscopy and Joint Research Institute, Yonsei University College of Medicine, Seoul, South Korea
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Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution (s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.