Biomechanical Assessment of the Anterolateral Ligament of the Knee

Transcription

1 937 COPYRIGHT Ó 2016 BY THE OURNAL OF BONE AND OINT SURGERY, INCORPORATED Biomechanical Assessment of the Anterolateral Ligament of the Knee A Seconary Restraint in Simulate Tests of the Pivot Shift an of Anterior Stability Ran Thein, MD, ames Boorman-Pagett, BS, Kyle Stone, MS, Thomas L. Wickiewicz, MD, Carl W. Imhauser, PhD, an Anrew D. Pearle, MD Investigation performe at the Department of Biomechanics, Hospital for Special Surgery, New York, NY Backgroun: Injury to the lateral capsular tissues of the knee may accompany rupture of the anterior cruciate ligament (ACL). A istinct lateral structure, the anterolateral ligament, has been ientifie, an reconstruction strategies for this tissue in combination with ACL reconstruction have been propose. However, the biomechanical function of the anterolateral ligament is not well unerstoo. Thus, this stuy ha two research questions: (1) What is the contribution of the anterolateral ligament to knee stability in the ACL-sectione knee? (2) Does the anterolateral ligament bear increase loa in the absence of the ACL? Methos: Twelve caaveric knees from onors who were a mean (an stanar eviation) of 43 ± 15 years ol at the time of eath were loae using a robotic manipulator to simulate clinical tests of the pivot shift an anterior stability. Motions were recore with the ACL intact, with the ACL sectione, an with both the ACL an anterolateral ligament sectione. In situ loas borne by the ACL an anterolateral ligament in the ACL-intact knee an borne by the anterolateral ligament in the ACL-sectione knee were etermine. Results: Sectioning the anterolateral ligament in the ACL-sectione knee le to mean increases of 2 to 3 mm in anterior tibial translation in both anterior stability an simulate pivot-shift tests. In the ACL-intact knee, the loa borne by the anterolateral ligament was a mean of 10.2 N in response to anterior loas an <17 N in response to the simulate pivot shift. In the ACL-sectione knee, the loa borne by the anterolateral ligament increase on average to <55% of the loa normally borne by the ACL in the intact knee. However, in the ACL-sectione knee, the anterolateral ligament engage only after the tibia translate beyon the physiologic limits of motion of the ACL-intact knee. Conclusions: The anterolateral ligament is a seconary stabilizer compare with the ACL for the simulate Lachman, anterior rawer, an pivot shift examinations. Clinical Relevance: Since the anterolateral ligament engages only uring pathologic ranges of tibial translation, there is a limite nee for anatomical reconstruction of the anterolateral ligament in a well-functioning ACL-reconstructe knee. Peer Review: This article was reviewe by the Eitor-in-Chief an one Deputy Eitor, an it unerwent bline review by two or more outsie experts. It was also reviewe by an expert in methoology an statistics. The Deputy Eitor reviewe each revision of the article, an it unerwent a final review by the Eitor-in-Chief prior to publication. Final corrections an clarifications occurre uring one or more exchanges between the author(s) an copyeitors. Injury to the lateral capsular tissues of the knee may accompany anterior cruciate ligament (ACL) rupture in some patients 1-5. A istinct soft-tissue structure, the anterolateral ligament, has been ientifie within the lateral capsular envelope 6,7, an reconstruction strategies for this tissue in combination with ACL reconstruction have been propose 8,9. Proximally, the anterolateral ligament attaches ajacent to the lateral collateral ligament (LCL), an istally, it attaches to the proximal part of the tibia approximately halfway between Gery s tubercle an the fibular hea 6,7, Although the tensile Disclosure: This investigation was supporte by the Kirby Founation, the Clark Founation, the Institute for Sports Meicine Research, the Surgeon in Chief Fun at the Hospital for Special Surgery, an the Gosnell Family. On the Disclosure of Potential Conflicts of Interest forms, which are provie with the online version of the article, one or more of the authors checke yes to inicate that the author ha a relevant financial relationship in the biomeical arena outsie the submitte work. Bone oint Surg Am. 2016;98:

2 938 T HE OURNAL OF B ONE &OINT SURGERY BS. ORG TABLE I Anterior Translation an Internal Rotation of the Tibia in Response to the Simulate Pivot Shift Intact ACL* ACL Sectione* ACL an ALL Sectione* Anterior translation (mm) Flexion angle of ± 2.2 (21.2 to 1.4) 6.8 ± 2.6 (5.3 to 8.4) 8.7 ± 3.4 (6.7 to 10.7) Flexion angle of ± 2.4 (20.7 to 2.2) 6.9 ± 2.6 (5.3 to 8.5) 9.5 ± 3.2 (7.6 to 11.4) Internal rotation (eg) Flexion angle of ± 7.4 (14.3 to 23.0) 22.3 ± 6.9 (18.2 to 26.4) 24.9 ± 6.5 (21.0 to 28.7) Flexion angle of ± 9.1 (17.2 to 27.9) 25.3 ± 8.4 (20.3 to 30.2) 29.2 ± 8.0 (24.4 to 33.9) *The values are given as the mean an the stanar eviation, with the 95% confience interval in parentheses. ACL = anterior cruciate ligament, an ALL = anterolateral ligament. The ifference was significant (p < 0.05) relative to the ACL-intact conition. The ifference was significant (p < 0.05) relative to the ACL-sectione conition. properties of the anterolateral ligament have been quantifie 10, the in situ biomechanical function of the anterolateral ligament is not well unerstoo. It is known that the iliotibial ban an the soft tissues comprising the milateral capsule together resist rotational moments an anterior loas. A pioneering stuy by Segon reveale that the anterolateral capsular structures resist internal rotation of the tibia 11. Moreover, the iliotibial ban an the milateral capsule resist internal rotation an anterior translation from 30 to 90 of flexion in the ACL-sectione knee 13,14. What is not well explore, however, is the biomechanical function of the specific lateral soft tissue name the anterolateral ligament 6,7. In vitro experiments have shown that the istance between femoral an tibial insertions of the anterolateral ligament increase with internal rotation from 30 to 90 of flexion 6. However, those in vitro ata i not aress whether the anterolateral ligament bears loa. The anterolateral ligament provies limite resistance to anterior tibial loas in the ACL-intact knee in vitro; however, it bears about half of the applie internal rotation moment from 30 to 90 of flexion 12. Unfortunately, since the ata in that experiment were expresse as percentages of the applie moment, the magnitue of force borne by the anterolateral ligament was not reporte. It has been theorize that the anterolateral ligament may be an important stabilizer against the pivot-shift phenomenon 7, a critical preictor of instability an outcome 15,16.However, the role of the anterolateral ligament in resisting the complex multiplanar loas of the pivot shift has not been quantifie. Therefore, the goals of this stuy were (1) to etermine the contribution of the anterolateral ligament uring knee stability testing in the setting of an ACL-sectione knee an (2) to quantify the loas carrie by the anterolateral ligament in the ACL-intact knee an in the setting of the ACLsectione knee uring simulate clinical stability examinations. Materials an Methos Before biomechanical ata collection was begun, 10 knees were issecte to ensure that the anterolateral ligament coul be ientifie following previously publishe anatomical escriptions 6,7. After reflecting the iliotibial ban, the tibial insertion of the anterolateral ligament was ientifie in all 10 knees by flexing from 60 to 90 an applying varus an internal rotation (Fig. 1). The femoral insertion of the anterolateral ligament blene with or fanne aroun the femoral insertion of the LCL in most cases. Twelve aitional fresh-frozen human caaveric knees that were not use in the anatomical stuy (mean age of onors at the time of eath, 43 ± 15 years [range, 20 to 64 years]; 8 males an 5 right knees) were acquire. Specimens were strippe of surrouning skin an musculature except for the popliteal muscle-tenon complex, leaving all remaining ligamentous an capsular restraints intact. Then, the remaining proximal portion of the iliotibial ban was issecte to within 0.5 cm of its tibial insertion. Fig. 1 Lateral view of a caaveric knee with the anterolateral ligament isolate (star). The tibia is rotate internally an translate anteriorly to engage the lateral structures. The arrows near the femoral insertion highlight the combine, fan-like fibers of the proximal lateral collateral ligament (iamon) an anterolateral ligament.

3 939 T HE OURNAL OF B ONE &OINT SURGERY BS. ORG Fig. 2 Specimens were mounte to a six-egrees-of-freeom robot instrumente with a universal force-moment sensor (arrow). The femur was fixe to the groun through the peestal. Loas measure by the universal force-moment sensor were transforme to the anatomical coorinate system of the knee. A meial arthrotomy was performe to confirm that the specimens were free of gross joint egeneration an ligament amage an ha ha no prior surgery. The femur an tibia were strippe of soft tissue to within 10 cm of the joint line an were then potte in boning cement (Bono; 3M). The fibula was fixe to the tibia in their anatomical orientation, using a woo screw. Specimens were then mounte to a six-egrees-of-freeom robot (ZX165U; Kawasaki Robotics) instrumente with a universal force-moment sensor (Theta; ATI) (Fig. 2). The femur was fixe to the groun via a peestal. The tibia was aligne in full extension an was mounte to a fixture attache to the en effector of the robot. Specimens were wrappe in saline solutionsoake gauze to preserve the soft tissues throughout testing. The locations of anatomical lanmarks were efine using a 3-imensional igitizer with 0.23-mm accuracy (MicroScribe G2X; Solution Technologies). The lanmarks inclue the femoral epiconyles, the lateralmost aspect of the istal en of the tibia approximately 25 cm istal to the joint line, the most lateral an istal portion of the sulcus on the fibula where the LCL attaches, an the misubstance of the superficial meial collateral ligament approximately 2.5 cm istal to the meial joint line. On the basis of these anatomical lanmarks, a coorinate system was efine using previously escribe methos 18,20. The long axis of the tibia efine internal an external rotation. The femoral epiconyles efine the flexion axis. The common perpenicular to both of these axes provie a reference axis for measurement of anterior-posterior translation. Tibiofemoral translations were efine relative to a point bisecting the femoral conyles 18. Loas measure by the universal force-moment sensor were transforme to the anatomical coorinate system 21. The path of passive flexion was subsequently etermine from full extension to 90 of flexionin1 increments, using previously escribe algorithms 18,19,22. A 10-N compressive force was applie to the tibia, while loas in the remaining irections were minimize within specifie tolerances (5 N an 0.4 Nm, respectively). The knee positions along the flexion path were use as the starting points for stability testing. A pivot-shift examination was simulate by first applying a valgus moment of 8 Nm an then applying an aitional internal rotation moment of 4 Nm with the knee fixe at 15 an 30 of flexion 18,23,24.This2-torque moel of the pivot shift elicits anterior tibial subluxation in the ACL-sectione knee, which is a key aspect of the clinical examination The Lachman an anterior rawer examinations were simulate by applying a 134-N anterior tibialloawiththekneefixe at 30 an 90 offlexion, respectively. The orer of stability testing was varie from knee to knee. Before the stability testing was starte, the knee was preconitione for 10 cycles with anterior loas of 134 N at 30 of flexion an with pivoting loas at 15 of flexion 18. The tests were performe in five steps (Fig. 3). (1) The kinematic trajectories for each stability test were etermine with the ACL an anterolateral ligament intact. (2) Immeiately before an after sectioning the ACL, the previously recore kinematics of the intact knee were repeate an the loas at the knee were measure. (3) The net force carrie by the ACL was subsequently etermine using vector subtraction (i.e., the principle of superposition) 17. Next, the kinematics of the ACL-sectione knee were etermine. (4) The anterolateral ligament was ientifie as escribe above an was sectione starting at its tibial insertion. Immeiately before an after sectioning the anterolateral ligament, the previously recore kinematics of the ACL-intact an ACL-sectione knee were repeate an the loas at the knee were measure. (5) Vector subtraction was again employe to etermine the resultant force carrie by the anterolateral ligament in the ACL-intact an ACL-sectione states. Finally, stability tests were conucte in the knee lacking an ACL an an anterolateral ligament. Kinematic outcomes were the net anterior translation of the tibia in response to the simulate Lachman, anterior rawer, an pivot shift examinations, an the net internal rotation of the tibia in response to the simulate Fig. 3 Flow graph outlining the experimental protocol. Stability tests consiste of a simulate pivot-shift test, simulate Lachman test, an simulate anterior rawer test. Ligaments were sectione in the orer shown. The sequence of stability tests was varie from knee to knee within each ligament-sectioning state. ACL = anterior cruciate ligament, an ALL = anterolateral ligament.

4 940 T HE OURNAL OF B ONE &OINT SURGERY BS. ORG (p < 0.001) compare with the ACL-intact knee uring the simulate Lachman an anterior rawer examinations, respectively (Table II). Compare with the ACL-sectione knee, subsequent sectioning of the anterolateral ligament increase anterior tibial translation by a mean of 3.1 ± 2.1 mm (p = 0.003) an 2.8 ± 1.3 mm (p = 0.049) uring the simulate Lachman an anterior rawer examinations, respectively. This represents a 16.2% an 23.4% increase in anterior translation uring the Lachman an anterior rawer examinations, respectively, compare with the isolate ACL-sectione knee. Fig. 4 Mean force carrie by the anterior cruciate ligament (ACL) in the intact knee an the anterolateral ligament (ALL) in the intact an ACL-sectione knees in response to a simulate pivot-shift examination at 15 an 30 of flexion. Error bars inicate 1 stanar eviation. The plus sign inicates a significant ifference between the ACL an the anterolateral ligament in the ACL-intact knee (p < 0.05). The asterisk inicates a significant ifference between the anterolateral ligament in the intact knee an the anterolateral ligament in the ACL-sectione knee (p < 0.05). pivot shift. These outcomes were etermine for the ACL-intact, ACL-sectione, an combine ACL an anterolateral ligament-sectione conitions. To ientify ifferences in the kinematic ata, one-way repeate-measures analysis of variance (ANOVA) with Tukey post hoc testing was performe for the ACL-intact, ACLsectione, an combine ACL an anterolateral ligament-sectione conitions (p < 0.05). One-way repeate-measures ANOVA with Tukey post hoc testing was also use to ientify ifferences in loa borne by the A CL, an by the anterolateral ligament with an intact an a sectione ACL (p < 0.05). These comparisons were performe for each stability test at each flexion angle. Results Kinematics Sectioning the ACL an performing a simulate pivot-shift examination at 15 of flexion increase anterior tibial translation by a mean of 6.7 ± 1.9 mm compare with the ACLintact knee (p < 0.001) (Table I) an increase internal tibial rotation by a mean of 3.7 ± 1.3 (p < 0.001) (Table I). Subsequent sectioning of the anterolateral ligament resulte in a mean increase in anterior tibial translation of 1.9 ± 1.3 mm (a 27.6% increase; p = 0.009) an a mean increase in internal tibial rotation of 2.5 ± 1.3 (an 11.3% increase) (p < 0.001) compare with isolate ACL eficiency. Sectioning the ACL an performing a simulate pivotshift examination at 30 of flexion increase anterior tibial translation by a mean of 6.2 ± 1.6 mm compare with the ACLintact knee (p < 0.001) (Table I) an increase internal tibial rotation by a mean of 2.7 ± 1.6 (p < 0.001) (Table I). Subsequent sectioning of the anterolateral ligament resulte in a mean increase in anterior tibial translation of 2.6 ± 1.1 mm (a 38.0% increase; p < 0.001) an a mean increase in internal tibial rotation of 3.9 ± 1.5 (a 15.4% increase; p < 0.001) compare with the ACL-sectione knee. Sectioning the ACL increase anterior tibial translation by a mean of 12.3 ± 2.3 mm (p < 0.001) an 7.4 ± 4.2 mm Ligament Loas The loa carrie by the anterolateral ligament in the ACLintact knee in response to a simulate pivot shift was a mean of 13.5 ± 10.8 N at 15 an 16.6 ± 12.3 N at 30 (Fig. 4). These loas correspon to 13.7% an 16.6%, respectively, of those carrie by the ACL, which were 98.8 ± 24.8 N an ± 34.3 N at 15 an 30 flexion, respectively (p < for both) (Fig. 4). The loas carrie by the anterolateral ligament in the ACL-intact knee in response to the simulate Lachman an anterior rawer examinations were a mean of 10.2 ± 7.5 N an 7.2 ± 8.1 N, respectively (Fig. 5). These loas correspone to 6.4% an 5.9%, respectively, of those carrie by the ACL, which were a mean of ± 18.5 N an ± 16.1 N, in the simulate Lachman an anterior rawer examinations, respectively (p < in both cases) (Fig. 5). During the simulate pivot-shift examination at 15 an 30 of flexion, the loas in the anterolateral ligament after the ACL was sectione increase to a mean of 42.9 ± 30.2 N (p = 0.002) an 54.7 ± 25.0 N (p = 0.001), respectively. The magnitue of loa carrie by the anterolateral ligament was 43.4% Fig. 5 Mean force carrie by the anterior cruciate ligament (ACL) in the intact knee an the anterolateral ligament (ALL) in the intact an ACL-sectione knees in response to an applie anterior loa at 30 an 90 of flexion. Error bars inicate 1 stanar eviation. The plus sign inicates a significant ifference between the ACL an the anterolateral ligament in the ACL-intact knee (p < 0.05). The asterisk inicates a significant ifference between the anterolateral ligament in the intact knee an the anterolateral ligament in the ACL-sectione knee (p < 0.05).

5 941 T HE OURNAL OF B ONE &OINT SURGERY BS. ORG TABLE II Anterior Translation of the Tibia in Response to Anterior Loa During the Simulate Lachman an Anterior Drawer Examinations Anterior Translation* (mm) Flexion Angle Intact ACL ACL Sectione ACL an ALL Sectione ± 2.2 (5.5 to 8.0) 19.1 ± 2.4 (17.6 to 20.5) 22.2 ± 3.1 (20.4 to 24.0) ± 1.3 (4.0 to 5.5) 12.2 ± 4.0 (9.8 to 14.5) 15.0 ± 4.6 (12.3 to 17.7) *The values are given as the mean an the stanar eviation, with the 95% confience interval in parentheses. ACL = anterior cruciate ligament, an ALL = anterolateral ligament. The ifference was significant (p < 0.05) relative to the ACL-intact conition. The ifference was significant (p < 0.05) relative to the ACL-sectione conition. Fig. 6 Mean force carrie by the anterior cruciate ligament (ACL) in the ACL-intact knee an the anterolateral ligament (ALL) in the ACL-sectione knee as a function of anterior tibial translation uring a simulate Lachman examination. The thin lines bracketing the ligament engagement paths signify the ligament loa versus the anterior tibial translation of the iniviual specimens with the smallest an largest ligament loas. an 54.6% of that carrie by the ACL in the intact knee uring the pivot shift examination at 15 an 30, respectively (Fig. 4). The increase loa borne by the anterolateral ligament in the setting of the ACL-sectione knee occurre with the tibia translate anteriorly an aitional 6.7 an 6.2 mm beyon its position for the ACL-intact knee uring the simulate pivot shift examination at 15 an 30, respectively(table I). After the ACL was sectione, loas carrie by the anterolateral ligament increase to a mean of 61.1 ± 33.8 N in response to the simulate Lachman examination (p < 0.001) (Fig. 5) an increase to 43.1 ± 20.3 N in response to the anterior rawer examination (p < 0.001) (Fig. 5). The magnitue of loa carrie by the anterolateral ligament was 38.3% an 35.6% of that carrie by the ACL in the intact knee uring the Lachman an the anterior rawer examinations, respectively. The increase loa borne by the anterolateral ligament after the ACL was sectione occurre with the tibia translate anteriorly an aitional 12.3 an 7.4 mm beyon its position for the ACL-intact knee uring the Lachman an the anterior rawer examinations, respectively (Table II). During the simulate Lachman examination for the ACL-sectione knee, the anterolateral ligament carrie loa as the knee translate from 12 to 20 mm (Fig. 6). In contrast, the ACL bore loa as the knee translate from 3 to 7 mm anteriorly (Fig. 6). Discussion The most important finings were that (1) the loa borne by the anterolateral ligament in the ACL-intact knee was minimal, averaging 16.6 N in response to the simulate pivot shift an 10.2 N in response to anterior loas; (2) the loa borne by the anterolateral ligament increase in the ACL-sectione knee compare with the ACL-intact knee, with an increase of nearly five to sixfol in response to isolate anterior loas an more than threefol in response to the simulate pivot shift; an (3) sectioning the anterolateral ligament in the setting of ACL insufficiency le to 2 to 3 mm of aitional anterior translation in both the uniplanar anterior testing (Lachman an anterior rawer) an the multiplanar loaing (simulate pivot shift). These ata suggest that the anterolateral ligament is a seconary stabilizer to the ACL for the pivot shift, Lachman, an anterior rawer examination. Specifically, the anterolateral ligament experiences low loas uring these tests in the ACLintact knee, but bears increase loa an imparts some constraint to stability testing in the ACL-sectione state (Figs. 4 an 5). Somewhat surprisingly, the anterolateral ligament bears increase loa at the extremes of tibial translations in the ACLsectione knee, but fails to engage until the tibia has isplace beyon the physiologic bounaries that are present with an intact ACL (Figs. 6 an 7). For example, the tibia must translate approximately 10 to 12 mm anteriorly for the anterolateral ligament to bear at least 20 N of loa uring the Lachman test (Fig. 6). These ata suggest that the ACL an anterolateral ligament have istinct patterns of engagement uring the stability examination. The ACL is loae as the knee is maintaine within its normal, physiologic envelope of motion. In contrast, the anterolateral ligament engages only as the knee translates into a pathologic position encountere in the ACL-sectione knee (Figs. 6 an 7). Thus, the anterolateral ligament may bear loa in the setting of faile ACL reconstruction or chronic complete tears of the ACL in which patients may present with anterior tibial subluxation 27 of >15 mm 28. Our fining that the anterolateral ligament bears minimal loa in the ACL-intact knee in response to the Lachman

6 942 T HE OURNAL OF B ONE &OINT SURGERY BS. ORG Fig. 7 Lateral view of a caaveric knee with the anterolateral ligament (star) isolate. The femur is fixe while the tibia is manipulate manually. In Fig. 7-A, the tibia is hel at a neutral position in 90 of flexion. In Fig. 7-B, the tibia is in varus an internally rotate to a subluxate position to engage the lateral soft-tissue envelope incluing the anterolateral ligament. The lateral collateral ligament (iamon) an anterolateral ligament appear more taught in this subluxate position. an anterior rawer examinations corroborates previous work 12. Our fining of a tibial isplacement increase of approximately 3 mm in response to anterior stability tests after anterolateral ligament sectioning agrees with a previously reporte increase of 4 mm after sectioning the anterolateral structures 13. In contrast, Spencer et al. foun more mute changes in anterior translation after sectioning the anterolateral ligament in the ACLsectione knee, with only a 1.9-mm increase uring Lachman an anterior rawer examinations; this may be ue to arthritic changes note in their oler cohort of specimens or ifferences in the constraints of their test apparatus 29.Theanterolateralligament was previously foun to resist isolate internal rotation moments in the ACL-intact knee at >30 of flexion, but less so at < Similarly, our ata inicate that the anterolateral ligament plays a minimal role in resisting rotatory multiplanar loas in the ACL-intact knee at 15 an 30 of flexion. Some knees may be more epenent on the anterolateral ligament to maintain stability. One ACL-sectione knee in our stuy ha an increase in anterior translation of 5.5 mm an 7.2 mm uring the pivot shift an Lachman examinations, respectively, after sectioning of the anterolateral ligament. This was >2.3 times the mean increase of either test. Wroble et al. also reporte high interspecimen variability in the stabilizing role of the anterolateral structures 14. Clinical examinations ientifying iniviuals who are more epenent on their lateral soft tissues may help to target those who woul most benefit from lateral stabilizing proceures with ACL reconstruction. This stuy has limitations. First, tissues superficial to the anterolateral ligament, incluing the istal portion of the iliotibial ban, were remove prior to testing. This portion of the iliotibial ban might contribute to knee stability even though it lacke a proximal attachment. However, our measurements of anterior tibial translation in the Lachman an anterior rawer examinations agree with previous stuies in which the anterolateral tissues an iliotibial ban were sectione together 13,14. Therefore, this portion of the iliotibial ban oes not appear to play a major role. In any case, our finings are a worst-case scenario of the maximum contributions of the anterolateral ligament to knee stability, since the iliotibial ban is not there to share loa with it. Secon, the isolate contribution of the anterolateral ligament to knee stability in an ACL-intact knee was not assesse, since anterolateral ligament injury is primarily observe in combination with ACL rupture 1,2,11.The orer of stability testing was varie to mitigate bias cause by first sectioning the ACL an then sectioning the anterolateral ligament. Nonetheless, if repeate loaing increase knee rotations an translations, our ata are an upper boun of the contribution of the anterolateral ligament to knee stability. Finally, the clinical pivot-shift examination consists of applie valgus, internal rotation, an anterior loas with flexion 30. Although the 2-torque moel of the pivot shift consists of only a subset of these loas, it causes anterior subluxation of the tibia 23,25,26, which is a critical aspect of the clinical pivot shift. In conclusion, the anterolateral ligament is a seconary stabilizer to simulate pivot shift, Lachman, an anterior rawer tests. In the ACL-intact knee, the anterolateral ligament carries minimal loa uring these stability tests. With the ACL sectione, the anterolateral ligament resists anterior translation an axial tibial rotation, but bears loa only beyon the physiologic ranges of the ACL-intact knee. Thus, the nee for anterolateral ligament reconstruction in a well-functioning ACL-reconstructe knee appears to be limite. n NOTE: The authors thank Danyal Nawabi, MD, for his insightful feeback on the manuscript.

7 943 T HE OURNAL OF B ONE &OINT SURGERY BS. ORG Ran Thein, MD 1 ames Boorman-Pagett, BS 2 Kyle Stone, MS 2 Thomas L. Wickiewicz, MD 2 Carl W. Imhauser, PhD 2 Anrew D. Pearle, MD 2 1 Department of Orthopeic Surgery, Sheba Meical Center, Tel-Hashomer, Israel 2 Departments of Biomechanics (.B.-P., K.S., an C.W.I.) an Orthopeic Surgery (T.L.W. an A.D.P), Hospital for Special Surgery, New York, NY aress for R. Thein: ranthein@gmail.com aress for. Boorman-Pagett: BoormanPagett@hss.eu aress for K. Stone: kstone3@binghamton.eu aress for T.L. Wickiewicz: WickiewiczT@hss.eu aress for C.W. Imhauser: ImhauserC@hss.eu aress for A.D. Pearle: PearleA@hss.eu References 1. Irvine GB, Dias, Finlay DB. Segon fractures of the lateral tibial conyle: brief report. Bone oint Surg Br Aug;69(4): Hess T, Rupp S, Hopf T, Gleitz M, Liebler. Lateral tibial avulsion fractures an isruptions to the anterior cruciate ligament. A clinical stuy of their incience an correlation. Clin Orthop Relat Res un;303: Dietz GW, Wilcox DM, Montgomery B. Segon tibial conyle fracture: lateral capsular ligament avulsion. Raiology May;159(2): Claes S, Luyckx T, Vereecke E, Bellemans. The Segon fracture: a bony injury of the anterolateral ligament of the knee. Arthroscopy Nov;30(11): Epub 2014 Aug Campos C, Chung CB, Lektrakul N, Peowitz R, Truell D, Yu, Resnick D. Pathogenesis of the Segon fracture: anatomic an MR imaging evience of an iliotibial tract or anterior oblique ban avulsion. Raiology May;219(2): Dos AL, Halewoo C, Gupte CM, Williams A, Amis AA. The anterolateral ligament: anatomy, length changes an association with the Segon fracture. Bone oint Mar;96(3): Claes S, Vereecke E, Maes M, Victor, Veronk P, Bellemans. Anatomy of the anterolateral ligament of the knee. Anat Oct;223(4): Epub 2013 Aug Rezansoff A, Caterine S, Spencer L, Tran MN, Litchfiel RB, Getgoo AM. Raiographic lanmarks for surgical reconstruction of the anterolateral ligament of the knee. Knee Surg Sports Traumatol Arthrosc Nov;23(11): Epub 2014 un Sonnery-Cottet B, Thaunat M, Freychet B, Pupim BH, Murphy CG, Claes S. Outcome of a combine anterior cruciate ligament an anterolateral ligament reconstruction technique with a minimum 2-year follow-up. Am Sports Me Mar 4 ul;43(7): Epub 2015 Mar Kenney MI, Claes S, Fuso FA, Williams BT, Golsmith MT, Turnbull TL, Wijicks CA, LaPrae RF. The anterolateral ligament: an anatomic, raiographic, an biomechanical analysis. Am Sports Me Apr 17 ul;43(7): Segon P. Recherches cliniques et expérimentales sur les épanchements sanguins u genou par entorse. Progres Me. 1879(7):297-9, , Parsons EM, Gee AO, Spiekerman C, Cavanagh PR. The biomechanical function of the anterolateral ligament of the knee. Am Sports Me Mar;43(3): Epub 2015 an Samuelson M, Draganich LF, Zhou X, Krumins P, Reier B. The effects of knee reconstruction on combine anterior cruciate ligament an anterolateral capsular eficiencies. Am Sports Me ul-aug;24(4): Wroble RR, Groo ES, Cummings S, Henerson M, Noyes FR. The role of the lateral extraarticular restraints in the anterior cruciate ligament-eficient knee. Am Sports Me Mar-Apr;21(2):257-62; iscussion Kocher MS, Steaman R, Briggs KK, Sterett WI, Hawkins R. Relationships between objective assessment of ligament stability an subjective assessment of symptoms an function after anterior cruciate ligament reconstruction. Am Sports Me Apr-May;32(3): Leitze Z, Losee RE, okl P, ohnson TR, Feagin A. Implications of the pivot shift in the ACL-eficient knee. Clin Orthop Relat Res ul;436: Woo SL, Fox R, Sakane M, Livesay GA, Ruy TW, Fu FH. Biomechanics of the ACL: measurements of in situ force in the ACL an knee kinematics. Knee. 1998; 5(4): Imhauser C, Mauro C, Choi D, Rosenberg E, Mathew S, Nguyen, Ma Y, Wickiewicz T. Abnormal tibiofemoral contact stress an its association with altere kinematics after center-center anterior cruciate ligament reconstruction: an in vitro stuy. Am Sports Me Apr;41(4): Epub 2013 Mar Fujie H, Mabuchi K, Woo SL, Livesay GA, Arai S, Tsukamoto Y. The use of robotics technology to stuy human joint kinematics: a new methoology. Biomech Eng Aug;115(3): Groo ES, Suntay W. A joint coorinate system for the clinical escription of three-imensional motions: application to the knee. Biomech Eng May; 105(2): Yoshikawa T. Founations of robotics analysis an control. Cambrige: MIT Press; Prisk VR, Imhauser CW, O Loughlin PF, Kenney G. Lateral ligament repair an reconstruction restore neither contact mechanics of the ankle joint nor motion patterns of the hinfoot. Bone oint Surg Am Oct 20;92(14): Kanamori A, Zeminski, Ruy TW, Li G, Fu FH, Woo SL. The effect of axial tibial torque on the function of the anterior cruciate ligament: a biomechanical stuy of a simulate pivot shift test. Arthroscopy Apr;18(4): Kanamori A, Woo SL, Ma CB, Zeminski, Ruy TW, Li G, Livesay GA. The forces in the anterior cruciate ligament an knee kinematics uring a simulate pivot shift test: a human caaveric stuy using robotic technology. Arthroscopy Sep; 16(6): Engebretsen L, Wijicks CA, Anerson C, Westerhaus B, LaPrae RF. Evaluation of a simulate pivot shift test: a biomechanical stuy. Knee Surg Sports Traumatol Arthrosc Apr;20(4): Epub 2011 Nov Noyes FR, etter AW, Groo ES, Harms SP, Garner E, Levy MS. Anterior cruciate ligament function in proviing rotational stability assesse by meial an lateral tibiofemoral compartment translations an subluxations. Am Sports Me Mar;43(3): Epub 2014 Dec Almekiners LC, Panarinath R, Rahusen FT. Knee stability following anterior cruciate ligament rupture an surgery. The contribution of irreucible tibial subluxation. Bone oint Surg Am May;86(5): Tanaka M, ones K, Gargiulo AM, Delos D, Wickiewicz TL, Potter HG, Pearle AD. Passive anterior tibial subluxation in anterior cruciate ligament-eficient knees. Am Sports Me Oct;41(10): Epub 2013 Aug Spencer L, Burkhart TA, Tran MN, Rezansoff A, Deo S, Caterine S, Getgoo AM. Biomechanical analysis of simulate clinical testing an reconstruction of the anterolateral ligament of the knee. Am Sports Me Sep;43(9): Epub 2015 un Pathare NP, Nicholas S, Colbrunn R, McHugh MP. Kinematic analysis of the inirect femoral insertion of the anterior cruciate ligament: implications for anatomic femoral tunnel placement. Arthroscopy Nov;30(11): Epub 2014 Sep 16.