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First published on September 16, 2005, doi:10.1177/0363546505278704
This version was published on January
1, 2006
The American Journal of Sports Medicine 34:24-28 (2006)
© 2006 American Orthopaedic Society for Sports Medicine
Structural Properties of Lateral Collateral Ligament Reconstruction at the Fibular Head
William J. Ciccone, II, MD,
Derek R. Bratton,
David M. Weinstein, MD,
David L. Walden, MD and
John J. Elias, PhD*
From the Medical Education and Research Institute of Colorado, Colorado Springs, Colorado
* Address correspondence to John J. Elias, PhD, Medical Education and Research Institute of Colorado, 3920 North Union Blvd, Suite 210, Colorado Springs, CO 80907(e-mail: elias{at}meric.info).
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ABSTRACT
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Background: Anatomical reconstruction of a ruptured lateral collateral ligament using allograft tissue secured within the fibular head with an interference screw has been described.
Hypothesis: Interference fixation at the fibular head does not reproduce the strength of the intact ligament.
Study Design: Controlled laboratory study.
Methods: Ten intact lateral collateral ligaments were tested to failure. The distal fixation of 11 ligaments reconstructed with a graft including a bone plug and 11 ligaments reconstructed with a graft without a bone plug were also tested.
Results: The reconstructed ligaments consistently failed at the fibular head. The intact specimens predominately failed through ligament rupture. The mean strength and stiffness values were 460 ± 163 N and 82 ± 25 N/mm, respectively, for the intact ligaments, 113 ± 40 N and 36 ± 10 N/mm, respectively, for reconstruction with a bone plug, and 135 ± 81 N and 34 ± 14 N/mm, respectively, for reconstruction without a bone plug. The strength and stiffness were significantly (P < .05) greater for the intact ligaments than for either reconstruction group. The variation in strength was significantly larger for reconstruction without a bone plug than for reconstruction with a bone plug.
Conclusion: Tension applied to lateral collateral ligaments reconstructed using fibular interference fixation should be limited immediately after surgery. Soft tissue fixation should be employed with care because of the inconsistency in the failure strength.
Clinical Relevance: Although fibular interference fixation is increasingly being described in the literature, the properties of reconstructed lateral collateral ligaments have not previously been quantified.
Key Words: lateral collateral ligament • reconstruction • interference fixation • strength
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INTRODUCTION
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The lateral collateral ligament (LCL) is the primary structure resisting varus angulation of the knee.5,10,18 Along with the other structures of the posterolateral corner, the LCL contributes to resisting external rotation of the knee.5,6,10,18,19 Injuries to the LCL are relatively uncommon.8,11,14 When LCL injuries occur, simultaneous injury to 1 of the cruciate ligaments is common,14,15,19 which further compromises knee stability. After complete rupture of the LCL, surgical intervention is necessary to restore knee stability.8
Although several surgical options are available to treat an injury to the LCL and the posterolateral corner, techniques that focus on restoring the function of the LCL have only recently been described.1,9,11,12,15,16 The LCL can be reconstructed using autograft or allograft tissue. Graft choices include hamstring tendons, biceps femoris tendons, Achilles tendons, and fascia lata, along with bone–patellar tendon–bone and quadriceps tendon–patellar bone grafts.1,9,11,15,16 One option for securing the graft to the fibula is interference fixation of the graft into the fibular head.1,11,15,16 Interference fixation can be used with both soft tissue grafts and grafts including a bone plug. Although clinical data related to this fixation technique have been promising,11 biomechanical data supporting this type of fixation are lacking. The current study was performed to characterize the mechanical properties of LCLs reconstructed using fibular interference fixation, for both soft tissue grafts and grafts including a bone plug, with a particular focus on the holding strength of the grafts within the fibular head. The hypothesis of the study is that interference fixation at the fibular head does not reproduce the strength of the intact LCL.
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MATERIALS AND METHODS
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In vitro testing was performed to characterize the strength and stiffness of intact LCLs, LCLs reconstructed with a soft tissue graft, and LCLs reconstructed with a graft including a bone plug. Thirteen intact LCL specimens, including the fibula and a block of the femur, were harvested from fresh-frozen cadaveric specimens. The dimensions of the midsubstance of each LCL were measured with a micrometer. Seven fibulas that were not damaged after testing of the intact LCL were reused for LCL reconstruction. Fibulas harvested from an additional 15 specimens were also used for LCL reconstruction. Six sets of paired fibulas were included in the specimens used for LCL reconstruction, with each pair split between the 2 types of reconstruction. The mean age ± SD for the specimens tested intact was 70 ± 10 years, compared with a mean age of 70 ± 11 years and 72 ± 11 years for the fibulas tested with grafts with and without a bone plug, respectively, although the specimen age was not available for 1 fibula used for reconstruction with a bone plug. Achilles tendon grafts, including a calcaneal bone block, were harvested for LCL reconstruction. Each graft was divided in half, with one half fashioned into a graft with a diameter of 9 mm at the distal end for soft tissue fixation and the other half fashioned into a graft including a bone plug with a diameter of 9 mm, a length of 20 mm, and a tapered tip. The dimensions of the midsubstance of each graft were also measured with a vernier caliper. All tissues were wrapped in saline-soaked gauze, stored at –20° C, and thawed to room temperature before reconstruction and testing.
Eleven LCL reconstructions were performed with a soft tissue graft, and 11 LCL reconstructions were performed with a graft including a bone plug. A 9-mm reamer was used to create a socket in each fibular head for interference fixation.11 Each soft tissue graft was inserted into a fibular head, and a 9 x 23-mm Bio-Tenodesis Screw (Arthrex, Naples, Fla) was driven into the hole beside the graft. Each graft including a bone plug was also inserted into a fibular head, and a 9 x 23-mm Bio-Interference Screw (Arthrex) was driven into the hole beside the graft (Figure 1
). All grafts were tested within 3 hours of fixation.
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Figure 1. Diagram of an allograft with a bone plug secured within the fibular head with an interference screw. Allografts with and without a bone plug were tested for the study.
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Each test specimen was inverted and mounted on a mechanical testing machine (858 Mini Bionix, MTS, Eden Prairie, Minn) using custom fixtures. The distal end of the fibula was secured in a cylinder attached to the actuator with screws passing through the bone (Figure 2). For the specimens reconstructed with soft tissue fixation, the block of the calcaneus still attached to the graft was potted in an aluminum tube fixed to the base of the testing machine using a low melting point metal alloy (Small Parts Inc, Miami Lakes, Fla). For the specimens reconstructed with a bone plug, the free end of the graft was whipstitched with No. 2 FiberWire (Arthrex) and fixed to a polyurethane foam block (Sawbones, Vashon, Wash) with tandem screws and spiked washers. For the intact specimens, the femoral bone block was also potted in the aluminum tube fixed to the base of the testing machine. The mean exposed graft or ligament length was approximately 55 mm for all 3 groups of specimens.
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Figure 2. The experimental test setup for a lateral collateral ligament reconstructed with an Achilles tendon graft with a bone plug. The fibula was inverted and fixed to the actuator of the materials testing machine. The free end of the graft was whipstitched and fixed to a polyurethane foam block with tandem screws and spiked washers.
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Each specimen underwent preconditioning followed by a test of ultimate strength. Preconditioning was performed by applying 5 loading cycles to a maximum load of 35 to 50 N at 0.5 Hz. One specimen reconstructed with soft tissue fixation failed during preconditioning. The remaining specimens were loaded to failure at a strain rate of 100% per second, based on the resting length of the graft.13 Load and displacement data were collected at 3 kHz to quantify ultimate strength and stiffness values for each specimen. The ultimate strength was recorded as the maximum force applied by the actuator. The stiffness was measured from the straightest portion of the force versus displacement curve. The region used for the stiffness measurement included a minimum of 50 points, with a minimum square of the correlation coefficient of .93, except for the specimen that failed during preconditioning, which had a correlation coefficient value of .87 for the stiffness measurement. A digital video camera recorded each test to identify the failure mode for each specimen.
Strength and stiffness measurements were compared between the intact LCLs and the 2 methods of LCL reconstruction. Because of the possibility of dissimilar variances for the 3 test groups, a nonparametric Kruskal-Wallis statistic and a nonparametric Dunn post hoc test were used to examine for statistically significant (P < .05) differences in the failure strength and stiffness between the 3 test groups. For groups that were not significantly different from one another, an F test was used to examine for statistically significant differences in the variances for the failure strength and stiffness. In addition, for the paired fibulas that were used for LCL reconstruction, a nonparametric Wilcoxon signed rank test was used to compare the strength and stiffness values between the 2 types of reconstruction, and an F test was used to examine for statistically significant differences in the variances for the failure strength and stiffness. To compare strength and stiffness values between fibulas that were tested intact and after reconstruction and fibulas that were tested only after reconstruction, t tests were also used.
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RESULTS
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The intact ligaments were stronger than the reconstructed ligaments. For 3 of the intact specimens, the fibula failed at a screw hole used to secure the fibula to the actuator. The data from these specimens were excluded from the study results. The mean failure strength ± SD was 460 ± 163 N for the intact ligaments, 113 ± 40 N for ligaments reconstructed with a bone plug, and 135 ± 81 N for ligaments reconstructed without a bone plug (Figure 3). The difference in failure strength between the intact ligaments and the 2 types of reconstruction was statistically significant (P < .01), with no significant difference between the 2 types of reconstruction. For grafts secured with soft tissue fixation, the failure strength ranged from 25 N to 267 N. For grafts that included a bone plug, the failure strength ranged from 50 N to 186 N. The variation in strength was significantly larger for soft tissue fixation than for fixation with a bone plug (P = .03).
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Figure 3. The mean failure strength ± SD for intact LCLs, LCLs reconstructed with a graft with a bone plug, and LCLs reconstructed with a soft tissue graft. The failure strength for the intact LCLs was significantly greater (P < .01) than the failure strength for the 2 types of reconstruction.
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The reconstructed ligaments consistently failed through the interference fixation in the fibular head, whereas the intact specimens predominately failed through ligament rupture. Seven of the intact specimens failed through ligament rupture, whereas 2 failed through bony avulsion of the fibula, and 1 failed through bony avulsion of the femur. For the intact LCLs, the mean major and minor diameters at the midpoint of the ligament were 3.7 ± 1.0 mm and 2.0 ± 0.4 mm, respectively. The failure mode for 10 of the 11 specimens reconstructed with a bone plug was the bone slipping between the screw and the fibular head. The other specimen reconstructed with a bone plug, which had a failure load of 90 N, failed when the tendon pulled off the bone plug. For 9 of the 11 specimens reconstructed with a soft tissue graft, failure occurred when the tendon slipped between the screw and the fibular head. The 2 other specimens, which had failure loads of 203 N and 156 N, failed from tendon rupture at the suture securing the tendon to the screw. For the reconstructed LCLs, the mean major and minor diameters at the midpoint of the graft were 8.4 ± 2.3 mm and 4.5 ± 1.6 mm, respectively.
The intact ligaments were stiffer than the reconstructed ligaments. The mean stiffness was 82 ± 25 N/mm for the intact ligaments, 36 ± 10 N/mm for ligaments reconstructed with a bone plug, and 34 ± 14 N/mm for ligaments reconstructed without a bone plug (Figure 4). The stiffness was significantly greater for the intact ligaments than for both types of reconstruction (P < .01), with no significant difference between the 2 types of reconstruction. The variance for the stiffness measurements also did not vary significantly between the 2 types of reconstruction.
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Figure 4. The mean stiffness ± SD for intact LCLs, LCLs reconstructed with a graft with a bone plug, and LCLs reconstructed with a soft tissue graft. The stiffness for the intact LCLs was significantly greater (P < .01) than the stiffness for the 2 types of reconstruction.
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The strength and stiffness measurements for the paired fibulas that were used for LCL reconstruction and the fibulas that were used for reconstruction after testing in the intact state were similar to the measurements for the entire group of specimens. For the paired fibulas, the mean failure strength was 115 ± 87 N for soft tissue fixation and 101 ± 32 N for reconstruction with a bone plug. The difference between the 2 types of reconstruction was not statistically significant, although the variation in strength was significantly larger for the soft tissue grafts than for the grafts that included a bone plug (P < .05). The stiffness values for the paired fibulas were also similar to those recorded for the entire group of specimens, with no significant differences in stiffness or variation in stiffness between the 2 types of reconstruction. The mean failure strength for the fibulas that were tested intact and after reconstruction was 119 ± 58 N, compared with 127 ± 68 N for fibulas that were tested only after reconstruction. No significant differences were found when comparing the strength or stiffness values between the reconstructions performed with a fibula that had been tested in the intact state and reconstructions performed with a fibula that had not been tested previously.
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DISCUSSION
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The current results indicate that a graft secured to the fibular head with interference fixation is dramatically weaker and less stiff than an intact LCL. The reconstructed LCLs typically failed at the fibular head, and the grafts had larger cross-sectional areas than the intact ligaments, indicating that the inferior strength and stiffness for the reconstructed ligaments reflect the properties of the interference fixation rather than the properties of the graft tissue. The failure strength for fixation of a soft tissue graft within the fibular head was similar to the failure strength for fixation of a graft including a bone plug within the fibular head. The failure strength was less consistent for soft tissue fixation, however. Therefore, soft tissue fixation causes a higher risk of the graft slipping out of the fibular head when applying minimal tensile load.
Although no other study that the authors are aware of has addressed the mechanical properties of reconstructed LCLs, the strength and stiffness of intact LCLs have been measured previously. One study reported a mean failure strength of 747 N for the LCL,13 compared with the 460 N mean failure strength recorded for the current study. The difference in failure strength could be because of the contribution of the popliteofibular ligament, which was also loaded for the previous study. For another previous study, the mean failure strength for an isolated LCL was 309 N,17 which is closer to that reported for the current study. Similarly, the mean stiffness recorded for the intact LCLs for the current study was 82 N/mm, compared with 97 N/mm for the study with the largest failure strength13 and 58 N/mm for the study with the smallest failure strength.17 Neither this study nor the previous studies addressed the properties of an intact or reconstructed LCL for cyclic loading, which is a clinically relevant loading scenario.
The 3 primary contributors to static stability of the posterolateral knee are the LCL, the popliteus tendon, and the popliteofibular ligament. Although all 3 structures act to resist external rotation,5,6,10,18,19 application of a varus moment primarily loads the LCL.5,10,18 With the knee at full extension, the LCL is oriented posteriorly from proximal to distal, but in deep flexion, the LCL is oriented anteriorly from proximal to distal.14,17 During midflexion, when the LCL has the greatest influence on varus stability,5,6,18,19 the LCL is nearly parallel to the long axis of the fibula.14,17 Therefore, although off-axis loads can be applied to the LCL in vivo, the applied load is primarily along the axis of the fibula when resisting a varus moment. A previous study estimated that in a patient with a varus thrust gait, a 471 N tensile force can be applied to the LCL.10 Although the prediction seems to be an overestimation of in vivo loading based on the mean failure loads of 460 N and 309 N reported for the current study and a previous study,17 respectively, the prediction gives an indication of the large tensile force carried by an intact or reconstructed LCL when resisting a varus moment.
The current study focused on the properties of interference fixation of a reconstructed LCL within the fibular head. The proximal insertion of the graft into the femur was not incorporated into the study. When using a graft to reconstruct the LCL, the proximal end of the graft is typically fixed to the lateral epicondylar insertion of the femur with interference fixation.1,9,11,12 The interference screws inserted into the femur are nearly perpendicular to the long axis of the femur. For application of a tensile force, the interference fixation at the fibular head is assumed to be weaker than the interference fixation at the femur because of the orientation of the screw. In some cases, however, a reconstructed graft could possibly fail at the proximal interface within the femur before failure at the fibular head.
Several surgical options are available to treat an injury to the LCL and posterolateral corner. Early surgical techniques relied on advancement of the femoral attachment of the posterolateral structures.4,7 Tenodesis of the long head of the biceps femoris tendon subsequently became popular.2,3 Reconstruction of the LCL has gained in popularity as the understanding of the role of the ligament for maintaining knee stability has grown.11 One option for securing the graft to the fibula is through interference fixation of the graft into the fibular head.1,11,15,16 In a retrospective study including 10 patients, reconstruction of the LCL using interference fixation with allograft tissue was shown to improve knee stability and lead to improved patient function beyond 2 years postoperatively.11 Biomechanical evaluation of this technique provides a scientific basis for prescribed postoperative protocols after surgical reconstruction.
The current study used relatively old cadaveric specimens to measure the failure strength of the intact and reconstructed ligaments. Injuries to the LCL typically occur in a relatively young patient population. For the anterior cruciate ligament, specimens from 20- to 30-year-olds are 2.5 times stronger than specimens from 70-year-olds.20 A similar increase in the strength of the LCL would be likely if the specimens came from younger specimens. An increase in the fixation strength for reconstructed ligaments would also be probable, although an increase large enough to overcome the difference between the intact and reconstructed LCLs recorded for the current study is unlikely.
The test conditions used for the current study represent a reconstructed LCL immediately after surgery. Good clinical results have been obtained for interference fixation into the fibular head, despite the fact that the reconstructed ligaments are initially dramatically weaker than intact LCLs.11 To help protect the reconstructed LCL during the healing process, the knee is typically immobilized for 2 to 3 weeks.1,11,16 Postoperative bracing greatly reduces the varus torque on the knee, thereby minimizing the tension applied to the reconstructed ligament. Based on the results of the current study, the protection to the graft provided by bracing the knee is justified.
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ACKNOWLEDGMENTS
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Equipment used for this study was provided by Arthrex, Naples, Florida.
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FOOTNOTES
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One or more of these authors has declared a potential conflict of interest: equipment for the study was donated by Arthrex.
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REFERENCES
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- Chen CH, Chen WJ, Shih CH. Lateral collateral ligament reconstruction using quadriceps tendon-patellar bone autograft with bioscrew fixation. Arthroscopy. 2001;17:551–554.[ISI][Medline][Order article via Infotrieve]
- Clancy WG. Posterolateral reconstruction for rotatory instability of the knee. Video J Orthop. 1992;7:3.
- Fanelli GC, Giannotti BF, Edson CJ. Arthroscopically assisted combined posterior cruciate ligament/posterior lateral complex reconstruction. Arthroscopy. 1996;12:521–530.[ISI][Medline][Order article via Infotrieve]
- Fleming RE Jr, Blatz DJ, McCarroll JR. Posterior problems in the knee: posterior cruciate insufficiency and posterolateral rotatory insufficiency. Am J Sports Med. 1981;9:107–113.[Abstract/Free Full Text]
- Gollehon DL, Torzilli PA, Warren RF. The role of the posterolateral and cruciate ligaments in the stability of the human knee: a biomechanical study. J Bone Joint Surg Am. 1987;69:233–242.[Abstract/Free Full Text]
- Grood ES, Stowers SF, Noyes FR. Limits of movement in the human knee: effect of sectioning the posterior cruciate ligament and posterolateral structures. J Bone Joint Surg Am. 1988;70:88–97.[Abstract/Free Full Text]
- Hughston JC, Jacobson KE. Chronic posterolateral rotatory instability of the knee. J Bone Joint Surg Am. 1985;67:351–359.[Abstract/Free Full Text]
- Kannus P. Nonoperative treatment of grade II and III sprains of the lateral ligament compartment of the knee. Am J Sports Med. 1989;17:83–88.[Abstract/Free Full Text]
- 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.[Abstract/Free Full Text]
- 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;32:1695–1701.[Abstract/Free Full Text]
- Latimer HA, Tibone JE, ElAttrache NS, McMahon PJ. Reconstruction of the lateral collateral ligament of the knee with patellar tendon allo-graft: report of a new technique in combined ligament injuries. Am J Sports Med. 1998;26:656–662.[Abstract/Free Full Text]
- Lill H, Glasmacher S, Korner J, Rose T, Verheyden P, Josten C. Arthroscopic-assisted simultaneous reconstruction of the posterior cruciate ligament and the lateral collateral ligament using hamstrings and absorbable screws. Arthroscopy. 2001;17:892–897.[ISI][Medline][Order article via Infotrieve]
- Maynard MJ, Deng X, Wickiewicz TL, Warren RF. The popliteofibular ligament: rediscovery of a key element in posterolateral stability. Am J Sports Med. 1996;24:311–316.[Abstract/Free Full Text]
- Meister BR, Michael SP, Moyer RA, Kelly JD, Schneck CD. Anatomy and kinematics of the lateral collateral ligament of the knee. Am J Sports Med. 2000;28:869–878.[Abstract/Free Full Text]
- 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;24:415–426.[Abstract/Free Full Text]
- Rihn JA, Groff YJ, Harner CD, Cha PS. The acutely dislocated knee: evaluation and management. J Am Acad Orthop Surg. 2004;12:334–346.[Abstract/Free Full Text]
- Sugita T, Amis AA. Anatomic and biomechanical study of the lateral collateral and popliteofibular ligaments. Am J Sports Med. 2001;29:466–472.[Abstract/Free Full Text]
- Veltri DM, Deng XH, Torzilli PA, Maynard MJ, Warren RF. The role of the popliteofibular ligament in stability of the human knee: a biomechanical study. Am J Sports Med. 1996;24:19–27.[Abstract/Free Full Text]
- Veltri DM, Deng XH, Torzilli PA, Warren RF, Maynard MJ. The role of the cruciate and posterolateral ligaments in stability of the knee: a biomechanical study. Am J Sports Med. 1995;23:436–443.[Abstract/Free Full Text]
- Woo SL, Hollis JM, Adams DJ, Lyon RM, Takai S. Tensile properties of the human femur-anterior cruciate ligament-tibia complex: the effects of specimen age and orientation. Am J Sports Med. 1991;19:217–225.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
