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A Biomechanical Comparison of 3 Reconstruction Techniques for Posterolateral Instability of the Knee in a Cadaveric Model
A Biomechanical Comparison of 3 Reconstruction Techniques for Posterolateral Instability of the Knee in a Cadaveric Model Sung-Jae Kim, M.D., Ph.D., Hyoung-Sik Kim, M.D., Ph.D., Hong-Kyo Moon, M.D., Woo-Hyuk Chang, M.D., Sul-Gee Kim, M.D., and Yong-Min Chun, M.D., Ph.D.
Purpose: The objective of this study was to compare the varus and external rotatory laxity of reconstructed knees by use of 3 different reconstruction techniques that address posterolateral instability of the knee: popliteus tendon (PT) and lateral collateral ligament (LCL) reconstruction, PT and popliteofibular ligament (PFL) reconstruction, and PFL and LCL reconstruction. Methods: We divided 36 fresh-frozen cadaveric knees into 3 groups of 12, and each group was assigned to a reconstruction technique: PT-LCL reconstruction with the posterior tibialis tendon, PT-PFL reconstruction with the patellar tendon and bone (Warren technique), and PFL-LCL reconstruction with the semitendinosus tendon (Larson technique). Each specimen was fixed with an Ilizarov external fixator and mounted on a custom-designed apparatus that was made to measure posterolateral instability of the knee, that is, external rotatory and varus laxity in the intact state, after cutting, and in the postoperative state at every 30° from 0° to 90°. Results: There were no significant differences between the 3 techniques with external rotation and varus laxity in all specimens. Conclusions: PT-LCL reconstruction was comparable to the other 2 established techniques: PT-PFL reconstruction (Warren technique) and PFL-LCL reconstruction (Larson technique). However, the original strength of the native knee could not be achieved with any of the techniques. Clinical Relevance: All techniques restored the posterolateral stability of the knee to near normal, with none of them being superior.
T
he posterolateral complex is composed of dynamic and static components that act to ensure proper stability. Of these components, through numerous biomechanical and anatomic studies, it has been determined that the most consistent and important components are the lateral collateral ligament (LCL) and the popliteus
From the Department of Orthopaedic Surgery, Arthroscopy and Joint Research Institute, Yonsei University Health System, Seoul, South Korea. The authors report no conflict of interest. Received December 1, 2008; accepted August 20, 2009. Address correspondence and reprint requests to Yong-Min Chun, M.D., Ph.D., Department of Orthopaedic Surgery, Arthroscopy and Joint Research Institute, Yonsei University Health System, CPO Box 8044, 134, Shinchon-dong, Seodaemun-gu, Seoul 120-752, South Korea. E-mail: [email protected] Crown Copyright © 2010 Published by Elsevier Inc. on behalf of the Arthroscopy Association of North America. All rights reserved. 0749-8063/10/2603-8689$36.00/0 doi:10.1016/j.arthro.2009.08.010
complex, including the popliteofibular ligament (PFL), for varus and external rotatory stability.1-4 Posterolateral instabilities are more commonly associated with anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) injuries than with isolated injuries, so posterolateral instabilities are often neglected at the initial physical examination in both acute and chronic settings.1,5-8 Reconstructions of the ACL and PCL that do not address posterolateral rotatory instability deteriorate over time, which can predispose patients to subsequent failures of the reconstructed ligament.9,10 Recent in vitro studies have showed that untreated grade III injuries of the posterolateral structures contribute increased force to the reconstructed ACL or PCL in knees.8,11 There are several surgical procedures for posterolateral instabilities that have been designed to address both acute and chronic injuries and range from primary repair of the injured structure in the acute setting to various reconstructions of chronic injuries.5,12-19
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 26, No 3 (March), 2010: pp 335-341
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Despite the assorted biomechanical and clinical reports,5,12-21 however, no consensus on or approval of the optimal choice of treatment with long-term results has been achieved. In any reconstruction of the posterolateral corner, these principal structures, that is, LCL, popliteus tendon (PT), and PFL, should be addressed. Although it is still technically challenging to reconstruct all of these structures with isometry, there are several techniques that address varus and posterolateral rotatory instability by addressing 2 of these principal structures: PT-LCL reconstruction,12 PT-PFL reconstruction (Warren technique),14 and PFL-LCL reconstruction (Larson technique).13 The objective of this study is to compare the varus and external rotatory laxity of reconstructed knees by use of 3 different reconstruction techniques that address posterolateral instability: the PT-LCL reconstruction technique, which reconstructs the PT and the LCL with the posterior tibialis (Fig 1A); the Warren technique, which reconstructs the PT and the PFL with the patellar bone and tendon (Fig 1B); and the Larson technique, which reconstructs the PFL and the LCL with the semitendinosus (Fig 1C). It was hypothesized that the PT-LCL reconstruction would be comparable to the other 2 reconstruction techniques. METHODS Specimen Preparation and Mounting We used 36 fresh-frozen cadaveric knees ranging in age from 68 to 84 years (mean age, 75.7 years) in this
study. Institutional review board approval was obtained. All of the knees were intact macroscopically and showed no surgical wounds or instabilities on clinical examination. Each specimen was kept frozen at ⫺20°C and thawed at room temperature for 24 hours before testing. The 36 specimens were divided into 3 groups of 12 and assigned to each technique. To secure the graft to the bone, a biodegradable interference screw was used during all of the reconstruction techniques. The tibia and fibula were fixed in their anatomic position with a 36-mm cortical screw to compensate for the absence of the distal tibiofibular joint, and they were cut approximately 25 cm from the joint line. For dissection of the knees, the skin was stripped off and the plane between the biceps femoris and the posterior border of the iliotibial tract was developed. Then, the lateral head of the gastrocnemius muscle and the biceps femoris were stripped off to visualize the LCL, PFL, and PT. Once the LCL, PFL, and PT were exposed, the specimens were rigidly secured by an Ilizarov external fixator (JOYM, Seoul, South Korea) by use of half-pins. Half-pins were inserted perpendicular to the long axis of the femur and tibia so that the moving head of the apparatus was parallel to the epicondyle and joint line. We used 2 custom-designed apparatuses (Sunkyung sys-tech, Daejeon, South Korea) for measuring external rotatory laxity and varus laxity separately (Figs 2 and 3).22 After application of the Ilizarov external fixator, the specimens were first mounted on the apparatus to measure the external rotatory laxity.
FIGURE 1. Three reconstruction techniques to address posterolateral instability of knee. (A) Our technique of reconstructing PT and LCL. (B) Warren technique of reconstructing PFL and PT. (C) Larson technique of reconstructing PFL and LCL. The arrows indicate the interference screws.
POSTEROLATERAL KNEE INSTABILITY
FIGURE 2. Custom-designed apparatus for measuring external rotatory laxity with Ilizarov external fixator. (Reprinted with permission from Chun et al.22)
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ACL guide, we created a 7-mm tibial tunnel from the Gerdy tubercle to the point 10 mm inferior to the posterior joint line and 5 mm medial to the posterior aspect of the tibiofibular joint (Fig 1A). A 7-mm fibular tunnel was created from the anteroinferior aspect of the fibular head to the posteromedial side at an angle of 70°. The posterior tibialis tendon was harvested from the same leg, and both ends were prepared with leading sutures. From the anterior aspect, both ends were pulled out through the tibial and fibular tunnels, and then secured with 7-mm-diameter and 20-mm-long bioabsorbable interference screws (Smith & Nephew, Andover, MA) for the fibula and 7-mm-diameter and 25-mm-long bioabsorbable interference screws (Smith & Nephew) for the tibia to stabilize the proximal tibiofibular joint. A Kirschner wire was provisionally driven at a tentative isometric point for each structure. The isometric point for the
To measure external rotatory laxity in the intact state, specimens were subjected to an external rotatory torque of 5 Nm1-4,20 with a cable-and-pulley system at every 30° from 0° to 90° of knee flexion. The angles produced by external rotatory torque were displayed on a digital recorder (Fig 2). To measure varus laxity, the specimens were subjected to varus torque of 3 Nm with a cable-and-pulley system at every 30° from 0° to 90° of knee flexion (Fig 3). After assessing the intact state of these 3 groups, we severed the LCL, PFL, and PT at their midpoint to produce external rotatory laxity and varus laxity. Then, the varus laxity and external rotatory laxity were measured at every 30° from 0° to 90° of knee flexion in the same manner. After measurement of the deficient state, each specimen underwent surgery according to the assigned reconstruction technique. After the assigned reconstruction, the specimen was mounted on the apparatuses to measure both external rotatory laxity and varus laxity at every 30° from 0° to 90° of knee flexion under the same torque (5 Nm for external rotatory torque and 3 Nm for varus torque) as used before surgery. The difference between the intact and post-reconstruction states was calculated to determine how well each reconstruction technique restored posterolateral stability to the intact state of varus and external rotatory laxity. Surgical Techniques PT-LCL Reconstruction: Re-establishment of PT and LCL: After developing the interval between the iliotibial band and biceps femoris tendon, using an
FIGURE 3. Custom-designed apparatus for measuring varus laxity with Ilizarov external fixator. (Reprinted with permission from Chun et al.22)
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LCL was at approximately the anterosuperior border of the lateral femoral epicondyle, and for the PT, it was at the superior margin of the anterior one third of the popliteal sulcus. The isometry was checked in the context of graft wrapping around the Kirschner wire and excursion of less than 2 mm on the Kirschner wire through a range of motion. The femoral tunnels for both the LCL and PT were created in the anterosuperior direction. Both ends of the graft were threaded with a 7-mm EndoPearl (Linvatec, Largo, FL) attached to the tip, introduced into each tunnel. With 15 lb of graft tension on each strand, both ends of the graft were preconditioned and secured with 7-mmdiameter and 25-mm-long bioabsorbable interference screws (Smith & Nephew) at 30° of knee flexion. Larson Technique: Re-establishment of PFL and LCL: After procurement of the semitendinosus tendon from the same leg, the lateral femoral epicondyle and fibular head were exposed (Fig 1C). After a guide pin was introduced from anterior to posterior through the center of the fibular head at its area of maximum diameter, a 7-mm tunnel was created in the fibular head. One end of the graft was passed through the tunnel, causing the ends to exit at both the anterior and posterior aspects of the fibular head. The anteriorexiting band of the graft was the component for the LCL, and the posterior-exiting band was the component for the PFL. A guide pin was tentatively driven at the anterior edge of the lateral femoral epicondyle, and then the isometry was checked. Both ends of the graft were wrapped around the guide pin, with excursion of less than 2 mm on the guide pin through the range of motion. A 7-mm femoral tunnel was created over the guide pin, and both ends of the graft were delivered into the tunnel. With 15 lb of graft tension on each strand, both ends of the graft were preconditioned and secured with 7-mm-diameter and 25-mmlong bioabsorbable interference screws (Smith & Nephew) at 30° of knee flexion. Warren Technique: Re-establishment of PFL and PT: The patellar bone and tendon or Achilles bone and tendon can be harvested from the same leg as the knee being operated on (Fig 1B). In this study the patellar bone and tendon were used. The patellar bone–tendon construct has a bone plug in only 1 end of the patellar tendon, and the patellar tendon was split into 2 strands. After procurement of the patellar bone and tendon from the same leg, the interval between the iliotibial band and biceps femoris tendon was developed. With the ACL guide, a 7-mm tibial tunnel was created from the Gerdy tubercle to the point 2 cm
below the joint line. A 7-mm fibular tunnel was created in the fibular head from posterior to anterior, beginning distal and posterior to the fibular styloid. A Kirschner wire was tentatively drilled at the point that was considered to be the isometric point and placed proximal and posterior to the femoral attachment of the PT. A leading suture was passed from posterior to anterior through the tibial tunnel. A device measuring isometry was attached to the free end of the suture, and the isometry was checked. A 7-mm femoral tunnel was created on the isometric point. The patellar bone plug was driven into the femoral tunnel and secured with a 7-mm-diameter and 25-mm-long bioabsorbable interference screw (Smith & Nephew). Two strands of the tendon were introduced into the tibial and fibular tunnels. With 15 lb of graft tension on each strand, both ends of the graft were preconditioned and secured with a 7-mm-diameter and 20-mmlong bioabsorbable interference screw (Smith & Nephew) for the fibula and a 7-mm-diameter and 20-mm-long bioabsorbable interference screw (Smith & Nephew) for the tibia at 30° of knee flexion. Data Analysis The external rotary laxity and varus laxity were measured as angles at every 30° from 0° to 90° of knee flexion in the intact, deficient, and post-reconstruction states. In each state the laxities were measured twice, and the mean of the 2 trials was used for data analysis. To compare the mean values of the 3 different techniques (PT-LCL reconstruction, PFLLCL reconstruction, and PT-PFL reconstruction) in the intact state, deficient state, and post-reconstruction state, an analysis of variance with a post hoc comparison (Tukey) was used in the setting of a KolmogorovSmirnov analysis. To evaluate how closely each technique re-established the varus and external rotatory laxity to the intact state, we compared the difference in the mean values between intact and post-reconstruction laxity for the 3 different techniques. P ⬍ .05 was considered statistically significant. RESULTS External Rotatory Laxity In the intact state there were no differences in external rotatory laxity between the 3 groups at any angle of knee flexion (0°, P ⫽ .406; 30°, P ⫽ .383; 60°, P ⫽ .994; 90°, P ⫽ .651) (Table 1). In the deficient state after cutting of the structures, there
POSTEROLATERAL KNEE INSTABILITY TABLE 1.
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External Rotatory Laxity in Intact State, After Cutting, and in Postoperative State
Intact state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value After cutting PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value Postoperative state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value
0°
30°
60°
90°
9.5° ⫾ 2.9° 8.8° ⫾ 3.7° 9.6° ⫾ 3.6° .406
14.0° ⫾ 4.3° 13.5° ⫾ 6.7° 12.7° ⫾ 5.1° .383
12.4° ⫾ 5.3° 11.6° ⫾ 4.1° 12.3° ⫾ 5.8° .994
11.2° ⫾ 5.3° 11.0° ⫾ 6.1° 11.5° ⫾ 5.8° .651
15.6° ⫾ 4.2° 14.2° ⫾ 3.4° 14.7° ⫾ 3.1° .460
23.0° ⫾ 2.7° 21.4° ⫾ 3.2° 20.7° ⫾ 4.4° .372
19.4° ⫾ 4.7° 19.0° ⫾ 4.8° 20.4° ⫾ 3.9° .855
17.6° ⫾ 5.3° 17.6° ⫾ 4.9° 18.2° ⫾ 5.5° .506
12.8° ⫾ 2.7° 10.7° ⫾ 3.6° 11.5° ⫾ 3.2° .619
17.2° ⫾ 3.0° 15.3° ⫾ 5.1° 15.2° ⫾ 4.7° .378
16.0° ⫾ 3.8° 13.9° ⫾ 3.4° 14.7° ⫾ 5.1° .642
14.7° ⫾ 4.9° 14.0° ⫾ 5.1° 13.8° ⫾ 5.5° .216
were also no differences between the 3 groups at any angle of knee flexion (0°, P ⫽ .460; 30°, P ⫽ .372; 60°, P ⫽ .855; 90°, P ⫽ .506) (Table 1). In addition, there were no differences between the 3 groups in the post-reconstruction states at any angle of knee flexion (0°, P ⫽ .619; 30°, P ⫽ .378; 60°, P ⫽ .642; 90°, P ⫽ .216) (Table 1). Regarding the mean differences in external rotatory laxity between the intact and post-reconstruction knees, PT-LCL reconstruction and PT-PFL reconstruction (Warren technique) restored external rotatory stability more closely than PFL-LCL reconstruction (Larson technique), although there were no significant differences statistically (0°, P ⫽ .821, F ⫽ 0.449; 30°, P ⫽ .334, F ⫽ 1.046; 60°, P ⫽ .242, F ⫽ 1.724; 90°, P ⫽ .239, F ⫽ 0.475). TABLE 2.
Intact state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value After cutting PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value Postoperative state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value
Varus Laxity In the intact state there were no differences in varus laxity between the 3 groups at any angle of knee flexion (0°, P ⫽ .305; 30°, P ⫽ .849; 60°, P ⫽ .402; 90°, P ⫽ .971) (Table 2). In the deficient state after cutting of the structures, there were also no differences between the 3 groups at any angle of knee flexion (0°, P ⫽ .273; 30°, P ⫽ .463; 60°, P ⫽ .301; 90°, P ⫽ .814) (Table 2). In addition, in the postreconstruction state, there were no differences between the 3 groups at any angle of knee flexion (0°, P ⫽ .755; 30°, P ⫽ .127; 60°, P ⫽ .400; 90°, P ⫽ .319) (Table 2). Regarding the mean differences in varus laxity between the intact state and post-reconstruction knees,
Varus Laxity in Intact State, After Cutting, and in Postoperative State 0°
30°
60°
90°
2.4° ⫾ 1.7° 2.4° ⫾ 1.6° 3.1° ⫾ 1.6° .305
3.3° ⫾ 1.7° 3.5° ⫾ 0.9° 3.7° ⫾ 1.7° .849
3.7° ⫾ 1.4° 4.1° ⫾ 1.5° 3.8° ⫾ 1.7° .402
4.4° ⫾ 1.2° 4.7° ⫾ 0.6° 4.3° ⫾ 0.9° .971
11.2° ⫾ 0.9° 11.2° ⫾ 0.8° 12.8° ⫾ 1.6° .301
11.7° ⫾ 0.7° 12.6° ⫾ 1.5° 13.0° ⫾ 1.6° .814
4.5° ⫾ 0.9° 5.3° ⫾ 1.6° 10.0° ⫾ 1.6° .400
5.4° ⫾ 1.5° 5.9° ⫾ 1.5° 10.9° ⫾ 1.5° .319
8.2° ⫾ 1.5 8.7° ⫾ 1.2 9.5° ⫾ 1.2 .273 3.0° ⫾ 1.6° 2.8° ⫾ 1.5° 4.8° ⫾ 1.5° .755
10.3° ⫾ 1.4 10.6° ⫾ 1.5 11.7° ⫾ 1.5 .463 4.1° ⫾ 0.8° 4.3° ⫾ 1.6° 8.2° ⫾ 1.5° .127
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there were no significant differences statistically between the 3 groups, although PT-LCL reconstruction and PFL-LCL reconstruction (Larson technique) restored varus stability more closely than PT-PFL reconstruction (Warren technique) at every 30° of knee flexion (0°, P ⫽ .065, F ⫽ 1.970; 30°, P ⫽ .102, F ⫽ 2.004; 60°, P ⫽ .088, F ⫽ 2.283; 90°, P ⫽ .090, F ⫽ 1.673).
DISCUSSION The aim of this study was to compare 3 posterolateral reconstruction techniques in the knee to evaluate how closely each technique restores external rotatory and varus laxity to the intact state. All of these techniques address only 2 components of 3 principal structures supporting posterolateral stability, and it remains a challenge to address all 3 components with isometry. Whereas LaPrade et al.15 showed anatomic reconstruction of all 3 principal components, they did not perform isometric testing. Warren14 indicated that in addition to reconstruction of the PT and PFL, the LCL could be reconstructed with a strip of the biceps femoris tendon and the isometric point for the PT and PFL should be proximal and posterior to the femoral attachment of the PT. It appears, however, that this location may not be correct for the popliteus muscle– tendon unit (PFL or PT). In resisting varus laxity, we found that PFL-LCL reconstruction and PT-LCL reconstruction did not yield better results than PT-PFL reconstruction. Given the fact that the LCL component was not reconstructed in PT-PFL reconstruction, this result is interesting. In PT-PFL reconstruction, the reconstructed PFL courses from the posterior aspect of the fibular head to a point proximal and posterior to the femoral attachment of the PT, which appears to be close to the femoral epicondyle.14 Thus we suggest that the reconstructed PFL might partially act as the LCL. Markolf et al.23 also reported that PT or PFL reconstruction had significant effects on controlling varus rotation as well as external rotation. Markolf et al.24 indicated that the PT and PFL had a similar effect in resisting external rotation, and we found no significant difference between PT-LCL reconstruction and PFL-LCL reconstruction in resisting external rotatory laxity. On the other hand, Nau et al.25 reported that reconstructing both the PT and PFL did not yield an advantage in resisting external rotation. In our study, PT-PFL reconstruction did not show superiority over the other 2 techniques.
PT-LCL reconstruction addresses only 2 components: the PT and LCL. Although some authors have reported that the PFL has a longer lever arm than the PT, enabling the PFL to more efficiently restrain the external tibial rotation,14,16 LaPrade et al.26 documented that when an external rotation torque was applied to these 2 structures, there was no significant difference in mean load response measured in each structure. Other authors have reported that the PT resists external rotatory laxity to the same extent as the PFL.20,22 Despite its inferiority in terms of lacking a lever arm, the reconstruction of the PT has several benefits over that of the PFL.22 As Sugita and Amis27 indicated, reconstructing the PFL could be influenced by diversity in the position of the fibular head around the posterolateral aspect of the tibia, which can lead to various success rates. Thus, in the context of a relatively posteriorly placed fibular head with regard to the lateral femoral condyle only, a reconstructed PFL can have a less steep angle in the sagittal plane and can efficiently resist external rotation as well as posterior translation of the tibia.27 Chun et al.22 proposed the possibility of concomitant injury at the proximal tibiofibular joint in the setting of a posterolateral corner injury of the knee. As they described, the reconstruction of the PFL should be performed based on the premise that the proximal tibiofibular joint is intact. In PT-LCL reconstruction, which addresses the PT and LCL, the proximal tibiofibular joint is statically stabilized by the posterior tibialis and a biodegradable interference screw.12 Typically, there is well-controlled movement between the proximal fibula and tibia mediated by static and dynamic stabilizers around an intact knee.28 In reconstruction of the posterolateral corner of the knee by PT-LCL reconstruction, we expect that the reconstructed LCL complements the absence of the PFL in the setting of a stabilized proximal tibiofibular joint.22 In particular, if the patient has a concomitant unstable proximal tibiofibular joint because of trauma or generalized laxity, we suggest that the PT-LCL reconstruction technique can be recommended because the proximal tibiofibular joint is stabilized with this technique. There are some limitations to our study. First, the grafts used were different for the 3 different techniques, which may have influenced our results. However, we wanted to follow the original technique. Second, this in vitro study gives only time-zero information and cannot predict in vivo results in human beings. Third, this study lacks statistical power because of the small number of specimens in each group.
POSTEROLATERAL KNEE INSTABILITY According to the power calculation before testing, the adequate sample size was determined to be 42 knees (14 for each group), but we had only 36 knees, yielding a power of 0.7. Fourth, we did not investigate the contribution of dynamic structures such as the iliotibial band and biceps femoris, because other in vitro studies did not evaluate these structures. Furthermore, we stripped off the biceps femoris and lateral head of the gastrocnemius muscle to identify the PFL clearly and verify the transection. CONCLUSIONS PT-LCL reconstruction was comparable to the other 2 established techniques: PT-PFL reconstruction (Warren technique) and PFL-LCL reconstruction (Larson technique). However, the original strength of the native knee could not be achieved with any of the techniques. Acknowledgment: The authors thank Young-Jun Cho, our research assistant, for helping with the experiments as well as illustrations.
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10. Harner CD, Vogrin TM, Hoher J, Ma CB, Woo SL. Biomechanical analysis of a posterior cruciate ligament reconstruction. Deficiency of the posterolateral structures as a cause of graft failure. Am J Sports Med 2000;28:32-39. 11. LaPrade RF, Resig S, Wentorf F, Lewis JL. The effects of grade III posterolateral knee complex injuries on anterior cruciate ligament graft force. A biomechanical analysis. Am J Sports Med 1999;27:469-475. 12. Kim SJ, Park IS, Cheon YM, Ryu SW. New technique for chronic posterolateral instability of the knee: Posterolateral reconstruction using the tibialis posterior tendon allograft. Arthroscopy 2004;20:195-200 (Suppl 2). 13. Larson R. Isometry of the lateral collateral and popliteofibular ligaments and techniques for reconstruction using a free semitendinous tendon graft. Oper Tech Sports Med 2001;9:84-90. 14. Veltri DM, Warren RF. Operative treatment of posterolateral instability of the knee. Clin Sports Med 1994;13:615-627. 15. LaPrade RF, Johansen S, Wentorf FA, Engebretsen L, Esterberg JL, Tso A. An analysis of an anatomical posterolateral knee reconstruction: An in vitro biomechanical study and development of a surgical technique. Am J Sports Med 2004; 32:1405-1414. 16. Fanelli GC, Larson RV. Practical management of posterolateral instability of the knee. Arthroscopy 2002;18:1-8. 17. Stannard JP, Brown SL, Farris RC, McGwin G Jr, Volgas DA. The posterolateral corner of the knee: Repair versus reconstruction. Am J Sports Med 2005;33:881-888. 18. Baker CL Jr, Norwood LA, Hughston JC. Acute posterolateral rotatory instability of the knee. J Bone Joint Surg Am 1983; 65:614-618. 19. Noyes FR, Barber-Westin SD. Surgical restoration to treat chronic deficiency of the posterolateral complex and cruciate ligaments of the knee joint. Am J Sports Med 1996;24:415426. 20. Pasque C, Noyes FR, Gibbons M, Levy M, Grood E. The role of the popliteofibular ligament and the tendon of popliteus in providing stability in the human knee. J Bone Joint Surg Br 2003;85:292-298. 21. Covey DC. Injuries of the posterolateral corner of the knee. J Bone Joint Surg Am 2001;83:106-118. 22. Chun YM, Kim SJ, Kim HS. Evaluation of the mechanical properties of posterolateral structures and supporting posterolateral instability of the knee. J Orthop Res 2008;26:13711376. 23. Markolf KL, Graves BR, Sigward SM, Jackson SR, McAllister DR. How well do anatomical reconstructions of the posterolateral corner restore varus stability to the posterior cruciate ligament-reconstructed knee? Am J Sports Med 2007;35:11171122. 24. Markolf KL, Graves BR, Sigward SM, Jackson SR, McAllister DR. Effects of posterolateral reconstructions on external tibial rotation and forces in a posterior cruciate ligament graft. J Bone Joint Surg Am 2007;89:2351-2358. 25. Nau T, Chevalier Y, Hagemeister N, Deguise JA, Duval N. Comparison of 2 surgical techniques of posterolateral corner reconstruction of the knee. Am J Sports Med 2005;33:18381845. 26. LaPrade RF, Tso A, Wentorf FA. Force measurements on the fibular collateral ligament, popliteofibular ligament, and popliteus tendon to applied loads. Am J Sports Med 2004;32:16951701. 27. Sugita T, Amis AA. Anatomic and biomechanical study of the lateral collateral and popliteofibular ligaments. Am J Sports Med 2001;29:466-472. 28. Espregueira-Mendes JD, da Silva MV. Anatomy of the proximal tibiofibular joint. Knee Surg Sports Traumatol Arthrosc 2006;14:241-249.
Purpose: The objective of this study was to compare the varus and external rotatory laxity of reconstructed knees by use of 3 different reconstruction techniques that address posterolateral instability of the knee: popliteus tendon (PT) and lateral collateral ligament (LCL) reconstruction, PT and popliteofibular ligament (PFL) reconstruction, and PFL and LCL reconstruction. Methods: We divided 36 fresh-frozen cadaveric knees into 3 groups of 12, and each group was assigned to a reconstruction technique: PT-LCL reconstruction with the posterior tibialis tendon, PT-PFL reconstruction with the patellar tendon and bone (Warren technique), and PFL-LCL reconstruction with the semitendinosus tendon (Larson technique). Each specimen was fixed with an Ilizarov external fixator and mounted on a custom-designed apparatus that was made to measure posterolateral instability of the knee, that is, external rotatory and varus laxity in the intact state, after cutting, and in the postoperative state at every 30° from 0° to 90°. Results: There were no significant differences between the 3 techniques with external rotation and varus laxity in all specimens. Conclusions: PT-LCL reconstruction was comparable to the other 2 established techniques: PT-PFL reconstruction (Warren technique) and PFL-LCL reconstruction (Larson technique). However, the original strength of the native knee could not be achieved with any of the techniques. Clinical Relevance: All techniques restored the posterolateral stability of the knee to near normal, with none of them being superior.
T
he posterolateral complex is composed of dynamic and static components that act to ensure proper stability. Of these components, through numerous biomechanical and anatomic studies, it has been determined that the most consistent and important components are the lateral collateral ligament (LCL) and the popliteus
From the Department of Orthopaedic Surgery, Arthroscopy and Joint Research Institute, Yonsei University Health System, Seoul, South Korea. The authors report no conflict of interest. Received December 1, 2008; accepted August 20, 2009. Address correspondence and reprint requests to Yong-Min Chun, M.D., Ph.D., Department of Orthopaedic Surgery, Arthroscopy and Joint Research Institute, Yonsei University Health System, CPO Box 8044, 134, Shinchon-dong, Seodaemun-gu, Seoul 120-752, South Korea. E-mail: [email protected] Crown Copyright © 2010 Published by Elsevier Inc. on behalf of the Arthroscopy Association of North America. All rights reserved. 0749-8063/10/2603-8689$36.00/0 doi:10.1016/j.arthro.2009.08.010
complex, including the popliteofibular ligament (PFL), for varus and external rotatory stability.1-4 Posterolateral instabilities are more commonly associated with anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) injuries than with isolated injuries, so posterolateral instabilities are often neglected at the initial physical examination in both acute and chronic settings.1,5-8 Reconstructions of the ACL and PCL that do not address posterolateral rotatory instability deteriorate over time, which can predispose patients to subsequent failures of the reconstructed ligament.9,10 Recent in vitro studies have showed that untreated grade III injuries of the posterolateral structures contribute increased force to the reconstructed ACL or PCL in knees.8,11 There are several surgical procedures for posterolateral instabilities that have been designed to address both acute and chronic injuries and range from primary repair of the injured structure in the acute setting to various reconstructions of chronic injuries.5,12-19
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Despite the assorted biomechanical and clinical reports,5,12-21 however, no consensus on or approval of the optimal choice of treatment with long-term results has been achieved. In any reconstruction of the posterolateral corner, these principal structures, that is, LCL, popliteus tendon (PT), and PFL, should be addressed. Although it is still technically challenging to reconstruct all of these structures with isometry, there are several techniques that address varus and posterolateral rotatory instability by addressing 2 of these principal structures: PT-LCL reconstruction,12 PT-PFL reconstruction (Warren technique),14 and PFL-LCL reconstruction (Larson technique).13 The objective of this study is to compare the varus and external rotatory laxity of reconstructed knees by use of 3 different reconstruction techniques that address posterolateral instability: the PT-LCL reconstruction technique, which reconstructs the PT and the LCL with the posterior tibialis (Fig 1A); the Warren technique, which reconstructs the PT and the PFL with the patellar bone and tendon (Fig 1B); and the Larson technique, which reconstructs the PFL and the LCL with the semitendinosus (Fig 1C). It was hypothesized that the PT-LCL reconstruction would be comparable to the other 2 reconstruction techniques. METHODS Specimen Preparation and Mounting We used 36 fresh-frozen cadaveric knees ranging in age from 68 to 84 years (mean age, 75.7 years) in this
study. Institutional review board approval was obtained. All of the knees were intact macroscopically and showed no surgical wounds or instabilities on clinical examination. Each specimen was kept frozen at ⫺20°C and thawed at room temperature for 24 hours before testing. The 36 specimens were divided into 3 groups of 12 and assigned to each technique. To secure the graft to the bone, a biodegradable interference screw was used during all of the reconstruction techniques. The tibia and fibula were fixed in their anatomic position with a 36-mm cortical screw to compensate for the absence of the distal tibiofibular joint, and they were cut approximately 25 cm from the joint line. For dissection of the knees, the skin was stripped off and the plane between the biceps femoris and the posterior border of the iliotibial tract was developed. Then, the lateral head of the gastrocnemius muscle and the biceps femoris were stripped off to visualize the LCL, PFL, and PT. Once the LCL, PFL, and PT were exposed, the specimens were rigidly secured by an Ilizarov external fixator (JOYM, Seoul, South Korea) by use of half-pins. Half-pins were inserted perpendicular to the long axis of the femur and tibia so that the moving head of the apparatus was parallel to the epicondyle and joint line. We used 2 custom-designed apparatuses (Sunkyung sys-tech, Daejeon, South Korea) for measuring external rotatory laxity and varus laxity separately (Figs 2 and 3).22 After application of the Ilizarov external fixator, the specimens were first mounted on the apparatus to measure the external rotatory laxity.
FIGURE 1. Three reconstruction techniques to address posterolateral instability of knee. (A) Our technique of reconstructing PT and LCL. (B) Warren technique of reconstructing PFL and PT. (C) Larson technique of reconstructing PFL and LCL. The arrows indicate the interference screws.
POSTEROLATERAL KNEE INSTABILITY
FIGURE 2. Custom-designed apparatus for measuring external rotatory laxity with Ilizarov external fixator. (Reprinted with permission from Chun et al.22)
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ACL guide, we created a 7-mm tibial tunnel from the Gerdy tubercle to the point 10 mm inferior to the posterior joint line and 5 mm medial to the posterior aspect of the tibiofibular joint (Fig 1A). A 7-mm fibular tunnel was created from the anteroinferior aspect of the fibular head to the posteromedial side at an angle of 70°. The posterior tibialis tendon was harvested from the same leg, and both ends were prepared with leading sutures. From the anterior aspect, both ends were pulled out through the tibial and fibular tunnels, and then secured with 7-mm-diameter and 20-mm-long bioabsorbable interference screws (Smith & Nephew, Andover, MA) for the fibula and 7-mm-diameter and 25-mm-long bioabsorbable interference screws (Smith & Nephew) for the tibia to stabilize the proximal tibiofibular joint. A Kirschner wire was provisionally driven at a tentative isometric point for each structure. The isometric point for the
To measure external rotatory laxity in the intact state, specimens were subjected to an external rotatory torque of 5 Nm1-4,20 with a cable-and-pulley system at every 30° from 0° to 90° of knee flexion. The angles produced by external rotatory torque were displayed on a digital recorder (Fig 2). To measure varus laxity, the specimens were subjected to varus torque of 3 Nm with a cable-and-pulley system at every 30° from 0° to 90° of knee flexion (Fig 3). After assessing the intact state of these 3 groups, we severed the LCL, PFL, and PT at their midpoint to produce external rotatory laxity and varus laxity. Then, the varus laxity and external rotatory laxity were measured at every 30° from 0° to 90° of knee flexion in the same manner. After measurement of the deficient state, each specimen underwent surgery according to the assigned reconstruction technique. After the assigned reconstruction, the specimen was mounted on the apparatuses to measure both external rotatory laxity and varus laxity at every 30° from 0° to 90° of knee flexion under the same torque (5 Nm for external rotatory torque and 3 Nm for varus torque) as used before surgery. The difference between the intact and post-reconstruction states was calculated to determine how well each reconstruction technique restored posterolateral stability to the intact state of varus and external rotatory laxity. Surgical Techniques PT-LCL Reconstruction: Re-establishment of PT and LCL: After developing the interval between the iliotibial band and biceps femoris tendon, using an
FIGURE 3. Custom-designed apparatus for measuring varus laxity with Ilizarov external fixator. (Reprinted with permission from Chun et al.22)
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LCL was at approximately the anterosuperior border of the lateral femoral epicondyle, and for the PT, it was at the superior margin of the anterior one third of the popliteal sulcus. The isometry was checked in the context of graft wrapping around the Kirschner wire and excursion of less than 2 mm on the Kirschner wire through a range of motion. The femoral tunnels for both the LCL and PT were created in the anterosuperior direction. Both ends of the graft were threaded with a 7-mm EndoPearl (Linvatec, Largo, FL) attached to the tip, introduced into each tunnel. With 15 lb of graft tension on each strand, both ends of the graft were preconditioned and secured with 7-mmdiameter and 25-mm-long bioabsorbable interference screws (Smith & Nephew) at 30° of knee flexion. Larson Technique: Re-establishment of PFL and LCL: After procurement of the semitendinosus tendon from the same leg, the lateral femoral epicondyle and fibular head were exposed (Fig 1C). After a guide pin was introduced from anterior to posterior through the center of the fibular head at its area of maximum diameter, a 7-mm tunnel was created in the fibular head. One end of the graft was passed through the tunnel, causing the ends to exit at both the anterior and posterior aspects of the fibular head. The anteriorexiting band of the graft was the component for the LCL, and the posterior-exiting band was the component for the PFL. A guide pin was tentatively driven at the anterior edge of the lateral femoral epicondyle, and then the isometry was checked. Both ends of the graft were wrapped around the guide pin, with excursion of less than 2 mm on the guide pin through the range of motion. A 7-mm femoral tunnel was created over the guide pin, and both ends of the graft were delivered into the tunnel. With 15 lb of graft tension on each strand, both ends of the graft were preconditioned and secured with 7-mm-diameter and 25-mmlong bioabsorbable interference screws (Smith & Nephew) at 30° of knee flexion. Warren Technique: Re-establishment of PFL and PT: The patellar bone and tendon or Achilles bone and tendon can be harvested from the same leg as the knee being operated on (Fig 1B). In this study the patellar bone and tendon were used. The patellar bone–tendon construct has a bone plug in only 1 end of the patellar tendon, and the patellar tendon was split into 2 strands. After procurement of the patellar bone and tendon from the same leg, the interval between the iliotibial band and biceps femoris tendon was developed. With the ACL guide, a 7-mm tibial tunnel was created from the Gerdy tubercle to the point 2 cm
below the joint line. A 7-mm fibular tunnel was created in the fibular head from posterior to anterior, beginning distal and posterior to the fibular styloid. A Kirschner wire was tentatively drilled at the point that was considered to be the isometric point and placed proximal and posterior to the femoral attachment of the PT. A leading suture was passed from posterior to anterior through the tibial tunnel. A device measuring isometry was attached to the free end of the suture, and the isometry was checked. A 7-mm femoral tunnel was created on the isometric point. The patellar bone plug was driven into the femoral tunnel and secured with a 7-mm-diameter and 25-mm-long bioabsorbable interference screw (Smith & Nephew). Two strands of the tendon were introduced into the tibial and fibular tunnels. With 15 lb of graft tension on each strand, both ends of the graft were preconditioned and secured with a 7-mm-diameter and 20-mmlong bioabsorbable interference screw (Smith & Nephew) for the fibula and a 7-mm-diameter and 20-mm-long bioabsorbable interference screw (Smith & Nephew) for the tibia at 30° of knee flexion. Data Analysis The external rotary laxity and varus laxity were measured as angles at every 30° from 0° to 90° of knee flexion in the intact, deficient, and post-reconstruction states. In each state the laxities were measured twice, and the mean of the 2 trials was used for data analysis. To compare the mean values of the 3 different techniques (PT-LCL reconstruction, PFLLCL reconstruction, and PT-PFL reconstruction) in the intact state, deficient state, and post-reconstruction state, an analysis of variance with a post hoc comparison (Tukey) was used in the setting of a KolmogorovSmirnov analysis. To evaluate how closely each technique re-established the varus and external rotatory laxity to the intact state, we compared the difference in the mean values between intact and post-reconstruction laxity for the 3 different techniques. P ⬍ .05 was considered statistically significant. RESULTS External Rotatory Laxity In the intact state there were no differences in external rotatory laxity between the 3 groups at any angle of knee flexion (0°, P ⫽ .406; 30°, P ⫽ .383; 60°, P ⫽ .994; 90°, P ⫽ .651) (Table 1). In the deficient state after cutting of the structures, there
POSTEROLATERAL KNEE INSTABILITY TABLE 1.
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External Rotatory Laxity in Intact State, After Cutting, and in Postoperative State
Intact state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value After cutting PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value Postoperative state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value
0°
30°
60°
90°
9.5° ⫾ 2.9° 8.8° ⫾ 3.7° 9.6° ⫾ 3.6° .406
14.0° ⫾ 4.3° 13.5° ⫾ 6.7° 12.7° ⫾ 5.1° .383
12.4° ⫾ 5.3° 11.6° ⫾ 4.1° 12.3° ⫾ 5.8° .994
11.2° ⫾ 5.3° 11.0° ⫾ 6.1° 11.5° ⫾ 5.8° .651
15.6° ⫾ 4.2° 14.2° ⫾ 3.4° 14.7° ⫾ 3.1° .460
23.0° ⫾ 2.7° 21.4° ⫾ 3.2° 20.7° ⫾ 4.4° .372
19.4° ⫾ 4.7° 19.0° ⫾ 4.8° 20.4° ⫾ 3.9° .855
17.6° ⫾ 5.3° 17.6° ⫾ 4.9° 18.2° ⫾ 5.5° .506
12.8° ⫾ 2.7° 10.7° ⫾ 3.6° 11.5° ⫾ 3.2° .619
17.2° ⫾ 3.0° 15.3° ⫾ 5.1° 15.2° ⫾ 4.7° .378
16.0° ⫾ 3.8° 13.9° ⫾ 3.4° 14.7° ⫾ 5.1° .642
14.7° ⫾ 4.9° 14.0° ⫾ 5.1° 13.8° ⫾ 5.5° .216
were also no differences between the 3 groups at any angle of knee flexion (0°, P ⫽ .460; 30°, P ⫽ .372; 60°, P ⫽ .855; 90°, P ⫽ .506) (Table 1). In addition, there were no differences between the 3 groups in the post-reconstruction states at any angle of knee flexion (0°, P ⫽ .619; 30°, P ⫽ .378; 60°, P ⫽ .642; 90°, P ⫽ .216) (Table 1). Regarding the mean differences in external rotatory laxity between the intact and post-reconstruction knees, PT-LCL reconstruction and PT-PFL reconstruction (Warren technique) restored external rotatory stability more closely than PFL-LCL reconstruction (Larson technique), although there were no significant differences statistically (0°, P ⫽ .821, F ⫽ 0.449; 30°, P ⫽ .334, F ⫽ 1.046; 60°, P ⫽ .242, F ⫽ 1.724; 90°, P ⫽ .239, F ⫽ 0.475). TABLE 2.
Intact state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value After cutting PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value Postoperative state PFL-LCL (Larson technique) PT-LCL PT-PFL (Warren technique) P value
Varus Laxity In the intact state there were no differences in varus laxity between the 3 groups at any angle of knee flexion (0°, P ⫽ .305; 30°, P ⫽ .849; 60°, P ⫽ .402; 90°, P ⫽ .971) (Table 2). In the deficient state after cutting of the structures, there were also no differences between the 3 groups at any angle of knee flexion (0°, P ⫽ .273; 30°, P ⫽ .463; 60°, P ⫽ .301; 90°, P ⫽ .814) (Table 2). In addition, in the postreconstruction state, there were no differences between the 3 groups at any angle of knee flexion (0°, P ⫽ .755; 30°, P ⫽ .127; 60°, P ⫽ .400; 90°, P ⫽ .319) (Table 2). Regarding the mean differences in varus laxity between the intact state and post-reconstruction knees,
Varus Laxity in Intact State, After Cutting, and in Postoperative State 0°
30°
60°
90°
2.4° ⫾ 1.7° 2.4° ⫾ 1.6° 3.1° ⫾ 1.6° .305
3.3° ⫾ 1.7° 3.5° ⫾ 0.9° 3.7° ⫾ 1.7° .849
3.7° ⫾ 1.4° 4.1° ⫾ 1.5° 3.8° ⫾ 1.7° .402
4.4° ⫾ 1.2° 4.7° ⫾ 0.6° 4.3° ⫾ 0.9° .971
11.2° ⫾ 0.9° 11.2° ⫾ 0.8° 12.8° ⫾ 1.6° .301
11.7° ⫾ 0.7° 12.6° ⫾ 1.5° 13.0° ⫾ 1.6° .814
4.5° ⫾ 0.9° 5.3° ⫾ 1.6° 10.0° ⫾ 1.6° .400
5.4° ⫾ 1.5° 5.9° ⫾ 1.5° 10.9° ⫾ 1.5° .319
8.2° ⫾ 1.5 8.7° ⫾ 1.2 9.5° ⫾ 1.2 .273 3.0° ⫾ 1.6° 2.8° ⫾ 1.5° 4.8° ⫾ 1.5° .755
10.3° ⫾ 1.4 10.6° ⫾ 1.5 11.7° ⫾ 1.5 .463 4.1° ⫾ 0.8° 4.3° ⫾ 1.6° 8.2° ⫾ 1.5° .127
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there were no significant differences statistically between the 3 groups, although PT-LCL reconstruction and PFL-LCL reconstruction (Larson technique) restored varus stability more closely than PT-PFL reconstruction (Warren technique) at every 30° of knee flexion (0°, P ⫽ .065, F ⫽ 1.970; 30°, P ⫽ .102, F ⫽ 2.004; 60°, P ⫽ .088, F ⫽ 2.283; 90°, P ⫽ .090, F ⫽ 1.673).
DISCUSSION The aim of this study was to compare 3 posterolateral reconstruction techniques in the knee to evaluate how closely each technique restores external rotatory and varus laxity to the intact state. All of these techniques address only 2 components of 3 principal structures supporting posterolateral stability, and it remains a challenge to address all 3 components with isometry. Whereas LaPrade et al.15 showed anatomic reconstruction of all 3 principal components, they did not perform isometric testing. Warren14 indicated that in addition to reconstruction of the PT and PFL, the LCL could be reconstructed with a strip of the biceps femoris tendon and the isometric point for the PT and PFL should be proximal and posterior to the femoral attachment of the PT. It appears, however, that this location may not be correct for the popliteus muscle– tendon unit (PFL or PT). In resisting varus laxity, we found that PFL-LCL reconstruction and PT-LCL reconstruction did not yield better results than PT-PFL reconstruction. Given the fact that the LCL component was not reconstructed in PT-PFL reconstruction, this result is interesting. In PT-PFL reconstruction, the reconstructed PFL courses from the posterior aspect of the fibular head to a point proximal and posterior to the femoral attachment of the PT, which appears to be close to the femoral epicondyle.14 Thus we suggest that the reconstructed PFL might partially act as the LCL. Markolf et al.23 also reported that PT or PFL reconstruction had significant effects on controlling varus rotation as well as external rotation. Markolf et al.24 indicated that the PT and PFL had a similar effect in resisting external rotation, and we found no significant difference between PT-LCL reconstruction and PFL-LCL reconstruction in resisting external rotatory laxity. On the other hand, Nau et al.25 reported that reconstructing both the PT and PFL did not yield an advantage in resisting external rotation. In our study, PT-PFL reconstruction did not show superiority over the other 2 techniques.
PT-LCL reconstruction addresses only 2 components: the PT and LCL. Although some authors have reported that the PFL has a longer lever arm than the PT, enabling the PFL to more efficiently restrain the external tibial rotation,14,16 LaPrade et al.26 documented that when an external rotation torque was applied to these 2 structures, there was no significant difference in mean load response measured in each structure. Other authors have reported that the PT resists external rotatory laxity to the same extent as the PFL.20,22 Despite its inferiority in terms of lacking a lever arm, the reconstruction of the PT has several benefits over that of the PFL.22 As Sugita and Amis27 indicated, reconstructing the PFL could be influenced by diversity in the position of the fibular head around the posterolateral aspect of the tibia, which can lead to various success rates. Thus, in the context of a relatively posteriorly placed fibular head with regard to the lateral femoral condyle only, a reconstructed PFL can have a less steep angle in the sagittal plane and can efficiently resist external rotation as well as posterior translation of the tibia.27 Chun et al.22 proposed the possibility of concomitant injury at the proximal tibiofibular joint in the setting of a posterolateral corner injury of the knee. As they described, the reconstruction of the PFL should be performed based on the premise that the proximal tibiofibular joint is intact. In PT-LCL reconstruction, which addresses the PT and LCL, the proximal tibiofibular joint is statically stabilized by the posterior tibialis and a biodegradable interference screw.12 Typically, there is well-controlled movement between the proximal fibula and tibia mediated by static and dynamic stabilizers around an intact knee.28 In reconstruction of the posterolateral corner of the knee by PT-LCL reconstruction, we expect that the reconstructed LCL complements the absence of the PFL in the setting of a stabilized proximal tibiofibular joint.22 In particular, if the patient has a concomitant unstable proximal tibiofibular joint because of trauma or generalized laxity, we suggest that the PT-LCL reconstruction technique can be recommended because the proximal tibiofibular joint is stabilized with this technique. There are some limitations to our study. First, the grafts used were different for the 3 different techniques, which may have influenced our results. However, we wanted to follow the original technique. Second, this in vitro study gives only time-zero information and cannot predict in vivo results in human beings. Third, this study lacks statistical power because of the small number of specimens in each group.
POSTEROLATERAL KNEE INSTABILITY According to the power calculation before testing, the adequate sample size was determined to be 42 knees (14 for each group), but we had only 36 knees, yielding a power of 0.7. Fourth, we did not investigate the contribution of dynamic structures such as the iliotibial band and biceps femoris, because other in vitro studies did not evaluate these structures. Furthermore, we stripped off the biceps femoris and lateral head of the gastrocnemius muscle to identify the PFL clearly and verify the transection. CONCLUSIONS PT-LCL reconstruction was comparable to the other 2 established techniques: PT-PFL reconstruction (Warren technique) and PFL-LCL reconstruction (Larson technique). However, the original strength of the native knee could not be achieved with any of the techniques. Acknowledgment: The authors thank Young-Jun Cho, our research assistant, for helping with the experiments as well as illustrations.
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