Tibiofemoral kinematics following successful anterior cruciate ligament reconstruction using dynamic multiple resonance imaging

BACKGROUND: The aim of anterior cruciate ligament reconstruction is to reduce excess joint laxity, hoping to restore normal tibiofemoral kinematics and therefore improve joint stability. It remains unclear if successful ACL reconstruction restores normal tibiofemoral kinematics and whether it is this that is associated with a good result. STUDY: Case series. PURPOSE: To assess the kinematics of the anterior cruciate ligament-reconstructed knee using open-access MRI. METHODS: Tibiofemoral motion was assessed using open-access MRI, weightbearing through the arc of flexion from 0 degrees to 90 degrees in 10 patients with isolated reconstruction of the anterior cruciate ligament (hamstring autograft) in one knee and a normal contralateral knee. Midmedial and midlateral sagittal images were analyzed in all positions of flexion in both knees to assess the tibiofemoral relationship. Sagittal laxity was also assessed by performing the Lachman test while the knees were scanned dynamically using open-access MRI. RESULTS: The amount of excursion between the tibial and femoral joint surfaces was similar between the normal and reconstructed knees, but the relationship of tibia to femur was always different for each position of knee flexion assessed-the lateral tibia being about 5 mm more anterior in the anterior cruciate ligament-reconstructed knees. This anterior tibial position is statistically significantly different at 0 degrees (P <.0006), 20 degrees (P =.0004), 45 degrees (P =.002), and 90 degrees of flexion (P <.006). Anteroposterior laxity was similar between normal and anterior cruciate ligament-reconstructed knees. CONCLUSION: Anterior cruciate ligament reconstruction reduces sagittal laxity to within normal limits but does not restore normal tibiofemoral kinematics despite a successful outcome.     

How well do anatomical reconstructions of the posterolateral corner restore varus stability to the posterior cruciate ligament-reconstructed knee?

BACKGROUND: With grade 3 posterolateral injuries of the knee, reconstructions of the lateral collateral ligament, popliteus tendon, and popliteofibular ligament are commonly performed in conjunction with a posterior cruciate ligament reconstruction to restore knee stability. HYPOTHESIS: A lateral collateral ligament reconstruction, alone or with a popliteus tendon or popliteofibular ligament reconstruction, will produce normal varus rotation patterns and restore posterior cruciate ligament graft forces to normal levels in response to an applied varus moment. STUDY DESIGN: Controlled laboratory study. METHODS: Forces in the native posterior cruciate ligament were recorded for 15 intact knees during passive extension from 120 degrees to 0 degrees with an applied 5 N .m varus moment. The posterior cruciate ligament was removed and reconstructed with a single bundle inlay graft tensioned to restore intact knee laxity at 90 degrees . Posterior cruciate ligament graft force, varus rotation, and tibial rotation were recorded before and after a grade 3 posterolateral corner injury. Testing was repeated with lateral collateral ligament, lateral collateral ligament plus popliteus tendon, and lateral collateral ligament plus popliteofibular ligament graft reconstructions; all grafts were tensioned to 30 N at 30 degrees with the tibia locked in neutral rotation. RESULTS: All 3 posterolateral graft combinations rotated the tibia into slight valgus as the knee was taken through a passive range of motion. During the varus test, popliteus tendon and popliteofibular ligament reconstructions internally rotated the tibia from 1.5 degrees (0 degrees flexion) to approximately 12 degrees (45 degrees flexion). With an applied varus moment, mean varus rotations with a lateral collateral ligament graft were significantly less than those with the intact lateral collateral ligament beyond 0 degrees flexion; mean decreases ranged from 0.8 degrees (at 5 degrees flexion) to 5.6 degrees (at 120 degrees flexion). Addition of a popliteus tendon or popliteofibular ligament graft further reduced varus rotation (compared with a lateral collateral ligament graft) beyond 25 degrees of flexion; both grafts had equal effects. A lateral collateral ligament reconstruction alone restored posterior cruciate ligament graft forces to normal levels between 0 degrees and 100 degrees of flexion; lateral collateral ligament plus popliteus tendon and lateral collateral ligament plus popliteofibular ligament reconstructions reduced posterior cruciate ligament graft forces to below-normal levels-beyond 95 degrees and 85 degrees of flexion, respectively. CONCLUSIONS: With a grade 3 posterolateral corner injury, popliteus tendon or popliteofibular ligament reconstructions are commonly performed to limit external tibial rotation; we found that they also limited varus rotation. With the graft tensioning protocols used in this study, all posterolateral graft combinations tested overconstrained varus rotation. Further studies with posterolateral reconstructions are required to better restore normal kinematics and provide more optimum load sharing between the PCL graft and posterolateral grafts. CLINICAL RELEVANCE: A lower level of posterolateral graft tension, perhaps applied at a different flexion angle, may be indicated to better restore normal varus stability. The clinical implications of overconstraining varus rotation are unknown.     

The biomechanical interdependence between the anterior cruciate ligament replacement graft and the medial meniscus

To establish a quantitative biomechanical relationship between the anterior cruciate ligament graft and the medial meniscus, 10 human cadaveric knees were examined using the robotic/universal force-moment sensor testing system. In response to a combined 134-N anterior and 200-N axial compressive tibial load, the resulting kinematics of the knee and the in situ forces in the anterior cruciate ligament, the anterior cruciate ligament graft, and the medial meniscus were measured. Anterior tibial translation significantly increased after anterior cruciate ligament transection, between 6.8 +/- 2.3 mm at full extension and 12.6 +/- 3.3 mm at 30 degrees of flexion. Consequently, the resultant forces on the medial meniscus, ranging from 52 +/- 30 N to 63 +/- 51 N between full extension and 90 degrees of knee flexion in the intact knee, were doubled as a result of anterior cruciate ligament deficiency. However, after anterior cruciate ligament reconstruction, anterior tibial translations were restored to the levels of the intact knee, and thus the forces on the medial meniscus were restored as well. Likewise, the in situ forces in the anterior cruciate ligament replacement graft increased between 33% and 50% after medial meniscectomy.     

Biomechanical analysis of femoral tunnel pull-out angles for anterior cruciate ligament reconstruction with bioabsorbable and metal interference screws

BACKGROUND: Fixation strength of metal and bioabsorbable interference screws has not been evaluated while varying the anterior cruciate ligament graft tension angle. HYPOTHESIS: There is no difference in fixation strength between 2 types of interference screws for anterior cruciate ligament graft fixation while the graft tension angle is varied relative to the femoral tunnel. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-eight anterior cruciate ligament reconstructions were performed using immature porcine femurs stripped of soft tissue and doubled-over porcine flexor digitorum profundus tendon grafts. Specimens were randomized to bioabsorbable or titanium interference screw fixation. Specimens were randomized to one of three pull angles (0 degrees , 30 degrees , 60 degrees ) representing loading at different knee flexion angles (n = 8/group). Reconstructed ligaments were tensioned to 10 N followed by 200 loading cycles between 10 and 150 N and a final failure test. Construct elongation (mm) at 100 and 200 cycles and failure load (N) were analyzed using a 2-way analysis of variance (P < .05). RESULTS: Screw material interacted significantly with graft tension angle, as the bioabsorbable screw specimens demonstrated significantly greater fixation strength when tensioned at greater angles. Specimens fixed with bioabsorbable screws showed significantly less elongation at both 100 and 200 cycles and significantly greater failure load compared with titanium screws. CONCLUSION: Bioabsorbable interference screws acutely have increased fixation strength compared with titanium interference screws for anterior cruciate ligament grafts loaded at greater tension angles. CLINICAL RELEVANCE: The strength of anterior cruciate ligament reconstruction fixation increases with increasing divergence between the tension angle and femoral tunnel, a condition seen when the knee approaches full extension.     

The position of the tibia during graft fixation affects knee kinematics and graft forces for anterior cruciate ligament reconstruction.

Ten cadaveric knees (donor ages, 36 to 66 years) were tested at full extension, 15 degrees, 30 degrees, and 90 degrees of flexion under a 134-N anterior tibial load. In each knee, the kinematics as well as in situ force in the graft were compared when the graft was fixed with the tibia in four different positions: full knee extension while the surgeon applied a posterior tibial load (Position 1), 30 degrees of flexion with the tibia at the neutral position of the intact knee (Position 2), 30 degrees of flexion with a 67-N posterior tibial load (Position 3), and 30 degrees of flexion with a 134-N posterior tibial load (Position 4). For Positions 1 and 2, the anterior tibial translation and the in situ forces were up to 60% greater and 36% smaller, respectively, than that of the intact knee. For Position 3, knee kinematics and in situ forces were closest to those observed in the intact knee. For Position 4, anterior tibial translation was significantly decreased by up to 2 mm and the in situ force increased up to 31 N. These results suggest that the position of the tibia during graft fixation is an important consideration for the biomechanical performance of an anterior cruciate ligament-reconstructed knee.     

Anatomical double-bundle anterior cruciate ligament reconstruction after valgus high tibial osteotomy: a biomechanical study

BACKGROUND: Although anatomical double-bundle anterior cruciate ligament reconstruction can successfully restore normal knee biomechanics for knees with typical varus-valgus alignment, the efficacy of the same reconstruction method for knees after a valgus high tibial osteotomy is unclear. HYPOTHESIS: Anatomical double-bundle anterior cruciate ligament reconstruction for valgus knees after a high tibial osteotomy cannot restore normal knee kinematics and can result in abnormally high in situ forces in the ligament graft. STUDY DESIGN: Controlled laboratory study. METHODS: Ten cadaveric knees were subjected to valgus high tibial osteotomy followed by an anatomical double-bundle anterior cruciate ligament reconstruction. The valgus knees were tested using a robotic/universal force-moment sensor system before and after the ligament reconstruction. The knee kinematics in response to anterior tibial load and combined rotatory loads, as well as the corresponding in situ forces of the anterior cruciate ligament bundles and grafts, were compared between the ligament-intact and ligament-reconstructed valgus knees. RESULTS: After reconstruction, the anterior tibial translation and internal tibial rotation for the valgus knee decreased approximately 2 mm and 2 degrees , respectively, at low flexion angles compared with those of the anterior cruciate ligament-intact knee (P < .05). The in situ forces in the posterolateral graft became 56% to 200% higher than those in the posterolateral bundle of the intact anterior cruciate ligament (P < .05). CONCLUSION: Performing an anatomical double-bundle anterior cruciate ligament reconstruction on knees after valgus high tibial osteotomy may overconstrain the knee and result in high forces in the posterolateral graft, which could predispose it to failure. CLINICAL RELEVANCE: Modifications of anterior cruciate ligament reconstruction procedures to reduce posterolateral graft force may be needed for valgus knees after a high tibial osteotomy.     

The effect of femoral tunnel position on graft forces during inlay posterior cruciate ligament reconstruction

BACKGROUND: The femoral tunnel may be positioned centrally or eccentrically within the posterior cruciate ligament footprint during a single-bundle posterior cruciate ligament reconstruction. HYPOTHESIS: After reconstruction, graft forces are significantly different from those of the native posterior cruciate ligament and are affected by the position of the femoral tunnel. STUDY DESIGN: Controlled laboratory study. METHODS: The resultant force in the native posterior cruciate ligament was measured in nine cadaveric knees as the knee was flexed from -5 degrees to 120 degrees of flexion. Posterior cruciate ligament reconstruction was performed with the femoral side of the graft positioned centrally and then offset 5 mm eccentric to the central position. RESULTS: Mean graft forces were not significantly different between eccentric and central tunnel positions during passive knee extension between 120 degrees and 0 degrees of flexion; at 5 degrees of hyperextension, the eccentric position generated significantly lower graft forces. For both reconstruction techniques, mean graft forces were significantly higher than those for the native posterior cruciate ligament beyond approximately 90 degrees of flexion, for 5 N.m internal and external tibial torque; 5 N.m varus and valgus moment. CONCLUSIONS: Graft force reductions achieved with the eccentric femoral position appear to be relatively small compared with the forces expected during rehabilitation and activities of daily living. Clinical Relevance: After posterior cruciate ligament graft reconstruction, rehabilitation activities that load the knee at high degrees of flexion should be avoided to limit excessive forces on the maturing graft.     

Measurement of posterior tibial translation in the posterior cruciate ligament-reconstructed knee: significance of the shift in the reference position

BACKGROUND: The measurement of anterior or posterior tibial translation depends on the existence of a repeatable and accurate reference position of the knee from which the corresponding translation is measured. HYPOTHESIS: Clinical measurements of posterior tibial translation alone do not accurately reflect the laxity of posterior cruciate ligament-reconstructed knees. STUDY DESIGN: Controlled laboratory study. METHODS: Ten human cadaveric knees were tested by using a robotic/universal force-moment sensor testing system. The reference positions and the resulting kinematics in response to a 134-N anterior-posterior tibial load were determined for the intact and reconstructed knees. Posterior cruciate ligament reconstruction was performed with the graft tensioned and fixed at two different positions: 1) 90 degrees of knee flexion with a 134-N anterior tibial load and 2) full extension with no load. RESULTS: Posterior cruciate ligament reconstruction with graft fixation at full extension with no load resulted in anterior shift of the reference position by 1.5 to 3.2 mm. The reconstruction resulted in an overconstrained knee with significantly decreased total anterior-posterior translation of 2.6 to 3.2 mm. However, the posterior tibial translation measured was not significantly different from that of the intact knee. Posterior cruciate ligament reconstruction with graft fixation performed at 90 degrees of flexion with a 134-N anterior tibial load resulted in kinematics similar to those of the intact knee. CONCLUSION: Posterior tibial translations that are measured clinically can be misleading because the reference position of the knee can be shifted significantly after posterior cruciate ligament reconstruction. Clinical Relevance: The measurement of total anterior-posterior translation may be a more accurate way to assess kinematics of the reconstructed knee.     

Change in meniscal strain with anterior cruciate ligament injury and after reconstruction

Meniscal injury has been well documented in association with injury to the anterior cruciate ligament. The purpose of this study was to evaluate the effect of anterior cruciate ligament transection and reconstruction on meniscal strain. Four differential variable reluctance transducer strain gauges were placed in the medial and lateral menisci of nine cadaveric knees. Each specimen was mounted to a six-degree-of-freedom knee testing device. Testing was conducted with the knee fully extended and at 45 degrees and 90 degrees of flexion, both with and without applied axial load. At each angle of flexion, an anterior and posterior tibial load was applied. Next, the anterior cruciate ligament was transected and the testing sequence was repeated. Finally, the ligament was reconstructed using a central one-third patellar tendon graft and the testing sequence was repeated. The results demonstrated statistically significant increases in meniscal strain in ligament-transected knees compared with intact specimens. A reduction in meniscal strain to a level similar to that detected in the ligament-intact knees was observed after anterior cruciate ligament reconstruction. These results have important clinical implications regarding the potentially deleterious effect of the anterior cruciate ligament-deficient knee on meniscal strain and the potential benefit of anterior cruciate ligament reconstruction.     

The effect of anterior cruciate ligament reconstruction on knee joint kinematics under simulated muscle loads

BACKGROUND: Numerous studies have investigated anterior stability of the knee during the anterior drawer test after anterior cruciate ligament reconstruction. Few studies have evaluated anterior cruciate ligament reconstruction under physiological loads. PURPOSE: To determine whether anterior cruciate ligament reconstruction reproduced knee motion under simulated muscle loads. STUDY DESIGN: Controlled laboratory study. METHODS: Eight human cadaveric knees were tested with the anterior cruciate ligament intact, transected, and reconstructed (using a bone-patellar tendon-bone graft) on a robotic testing system. Tibial translation and rotation were measured at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion under anterior drawer loading (130 N), quadriceps muscle loading (400 N), and combined quadriceps and hamstring muscle loading (400 N and 200 N, respectively). Repeated-measures analysis of variance and the Student-Newman-Keuls test were used to detect statistically significant differences between knee states. RESULTS: Anterior cruciate ligament reconstruction resulted in a clinically satisfactory anterior tibial translation. The anterior tibial translation of the reconstructed knee was 1.93 mm larger than the intact knee at 30 degrees of flexion under anterior load. Anterior cruciate ligament reconstruction overconstrained tibial rotation, causing significantly less internal tibial rotation in the reconstructed knee at low flexion angles (0 degrees-30 degrees) under muscle loads (P < .05). At 30 degrees of flexion, under muscle loads, the tibia of the reconstructed knee was 1.9 degrees externally rotated compared to the intact knee. CONCLUSIONS: Anterior cruciate ligament reconstruction may not restore the rotational kinematics of the intact knee under muscle loads, even though anterior tibial translation was restored to a clinically satisfactory level under anterior drawer loads. These data suggest that reproducing anterior stability under anterior tibial loads may not ensure that knee joint kinematics is restored under physiological loading conditions. CLINICAL RELEVANCE: Decreased internal rotation of the knee after anterior cruciate ligament reconstruction may lead to increased patellofemoral joint contact pressures. Future anterior cruciate ligament reconstruction techniques should aim at restoring 3-dimensional knee kinematics under physiological loads.     

The 6 degrees of freedom kinematics of the knee after anterior cruciate ligament deficiency: an in vivo imaging analysis

BACKGROUND: Previous studies of knee joint function after anterior cruciate ligament deficiency have focused on measuring anterior-posterior translation and internal-external rotation. Few studies have measured the effects of anterior cruciate ligament deficiency on 6 degrees of freedom knee kinematics in vivo. OBJECTIVE: To measure the 6 degrees of freedom knee kinematics of patients with anterior cruciate ligament deficiency. STUDY DESIGN: Controlled laboratory study. METHODS: The knee joint kinematics of 8 patients with unilateral anterior cruciate ligament rupture was measured during a quasi-static lunge. Kinematics was measured from full extension to 90 degrees of flexion using imaging and 3-dimensional modeling techniques. The healthy, contralateral knee of each patient served as a control. RESULTS: Anterior cruciate ligament deficiency caused a statistically significant anterior shift (approximately 3 mm) and internal rotation of the tibia (approximately 2 degrees ) at low flexion angles. However, ligament deficiency also caused a medial translation of the tibia (approximately 1 mm) between 15 degrees and 90 degrees of flexion. CONCLUSION: The medial shift of the tibia after anterior cruciate ligament deficiency might alter contact stress distributions in the tibiofemoral cartilage near the medial tibial spine. These findings correlate with the observation that osteoarthritis in patients with anterior cruciate ligament injuries is likely to occur in this region. CLINICAL RELEVANCE: The data from this study suggest that future anterior cruciate ligament reconstruction techniques should reproduce not only anterior stability but also medial-lateral stability.     

Injury to the anterior cruciate ligament during alpine skiing: a biomechanical analysis of tibial torque and knee flexion angle

BACKGROUND: The anterior cruciate ligament has been shown to be particularly susceptible to injury during alpine skiing. Tibial torque is an important injury mechanism, especially when applied to a fully extended or fully flexed knee. PURPOSE: We wanted to record the forces generated in the anterior cruciate ligament with application of tibial torque to cadaveric knees in different positions. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-seven fresh-frozen cadaveric knees were instrumented with a tibial load cell that measured resultant force in the anterior cruciate ligament while internal and external tibial torques were applied to the tibia at full extension, 90 degrees of flexion, full flexion, and forced hyperflexion. RESULTS: At each knee flexion position, mean force generated by 10 N.m of internal tibial torque was significantly higher than the mean generated by 10 N.m of external tibial torque. Mean forces generated by tibial torque at 90 degrees of flexion were relatively low. During flexion-extension without tibial torque applied mean forces were highest (193 N) when the knee was hyperflexed. CONCLUSIONS: Application of internal tibial torque to a fully extended or fully flexed knee represents the most dangerous loading condition for injury from twisting falls during skiing. CLINICAL RELEVANCE: Understanding of the mechanisms of falls can be used to design better equipment and to better prevent or treat injury.     

Tibiofemoral kinematics of the anterior cruciate ligament (ACL)-deficient weightbearing, living knee employing vertical access open "interventional" multiple resonance imaging

BACKGROUND: Our current understanding of tibiofemoral kinematics in the anterior cruciate ligament (ACL)-deficient knee is very limited. Using vertical open-access MRI, it is possible to accurately analyze tibiofemoral motion in patients with isolated rupture of the ACL. STUDY: Prospective cohort study. PURPOSE: To assess if ACL rupture alters normal knee weightbearing kinematics. METHODS: Tibiofemoral motion was assessed through the arc of flexion from 0 degrees to 90 degrees in 10 patients with isolated rupture of the ACL in one knee and a normal contralateral knee. Midmedial and midlateral sagittal images were analyzed in all positions of flexion in both knees to assess the tibiofemoral relationship. RESULTS: In the lateral compartment of the knee, the tibial plateau is persistently subluxed anteriorly throughout the arc of flexion from 0 degrees to 90 degrees (flexion facet center to posterior tibial cortex distance of 15.8 mm +/- 2.9 in ACL-deficient knees compared to 21.4 mm +/- 1.4 in normal knees at 0 degrees extension, P <.0001) when compared to normal knees. The medial tibiofemoral relationship is unchanged compared to normal knees. CONCLUSION: Rupture of the ACL changes tibiofemoral kinematics producing anterior subluxation of the lateral tibial plateau. CLINICAL SIGNIFICANCE: Altered kinematics may explain, at least in part, the increased incidence of secondary osteoarthritis in patients with ACL rupture.     

The effect of knee flexion angle and application of an anterior tibial load at the time of graft fixation on the biomechanics of a posterior cruciate ligament-reconstructed knee

Ten knees were studied using a robotic testing system under a 134-N posterior tibial load at five flexion angles. Three knee positions were used to study the effect of flexion angle at the time of graft fixation (full extension, 60 degrees, and 90 degrees) and two were used to study the effect of anterior tibial load (60 degrees and 90 degrees). Knee kinematics and in situ forces were determined for the intact ligament and the graft for each reconstruction. Graft fixation at full extension significantly decreased posterior tibial translation compared with the intact knee by up to 2.9 +/- 2.9 mm at 30 degrees, while in situ forces in the graft were up to 18 +/- 35 N greater than for the intact ligament. Conversely, posterior tibial translation for graft fixation at 90 degrees was significantly greater than that of the intact knee by up to 2.2 +/- 1.1 mm at all flexion angles; in situ forces decreased as much as 33 +/- 30 N. When an anterior tibial load was applied before graft fixation at 90 degrees of flexion, posterior tibial translation did not differ from the intact knee from 30 degrees to 120 degrees, while the in situ force in the graft did not differ from the intact ligament at full extension, 60 degrees, and 120 degrees of flexion. These data suggest that graft fixation at full extension may overconstrain the knee and elevate in situ graft forces. Conversely, fixation with the knee in flexion and an anterior tibial load best restored intact knee biomechanics.     

Knee biomechanics of the dynamic squat exercise

PURPOSE: Because a strong and stable knee is paramount to an athlete's or patient's success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise. METHODS: Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation. RESULTS: Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles. Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 60 degrees knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between 0 and 50 degrees knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100 degrees knee flexion. Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee. CONCLUSIONS: The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat.     

The effect of femoral attachment location on anterior cruciate ligament reconstruction: graft tension patterns and restoration of normal anterior–posterior laxity patterns

The issue of the best place to attach an anterior cruciate ligament graft to the femur is controversial, and different anatomic or isometric points have been recommended. It was hypothesised that one attachment site could be identified that would be best for restoring normal anterior–posterior laxity throughout the range of knee flexion. It was also hypothesised that these different attachment sites would cause different graft tension patterns during knee flexion. Using six cadaver knees, an isometric point was found 3 mm distal to the posterior edge of Blumensaats line, at the 10:30–11:00 oclock position in right knees, at the antero-proximal edge of the anatomic ACL attachment. Anterior–posterior laxity was measured at ±150 N draw force at 20–120° flexion with the knee intact and after anterior cruciate ligament transection. The graft was placed at the isometric point, and AP laxity was restored to normal at 20° flexion, then measured at other angles. Graft tension was measured throughout, and also during passive flexion–extension. This was repeated for four other graft positions around the isometric point in every knee. Laxity was restored best by grafts tensioned to a mean of 9±14 N, positioned isometrically and 3 mm posterior to the isometric point. Their tension remained low until terminal extension. Grafts 3 mm anterior to the isometric point caused significant overconstraint, and had higher tension beyond 80° knee flexion. Small changes in attachment site had large effects on laxity and tension patterns. These results support an isometric/posterior anatomic femoral graft attachment, which restored knee laxity to normal from 20 to 120° flexion and did not induce high graft tension as the knee flexed. Grafts attached to the roof of the intercondylar notch caused overconstraint and higher tension in the flexed knee.     

The remains of anterior cruciate ligament graft tension after cyclic knee motion

BACKGROUND: There is sometimes a return of excess knee laxity after anterior cruciate ligament reconstruction. One of the contributing factors might be a loss in graft tension. It is unknown whether the tension imposed on an anterior cruciate ligament graft degrades with time and, if so, the effect of that loss of tension on knee laxity. HYPOTHESES: The pretension in the anterior cruciate ligament graft reduces significantly within the first 500 motion cycles, and this decrease in graft tension causes an increase in knee laxity. STUDY DESIGN: Controlled laboratory study. METHODS: This study measured the remains of bone-patellar tendon-bone graft pretension after cyclical flexion-extension and the effect of any tension loss on knee laxity, using 8 cadaveric knees. A tension transducer was inserted into the graft and calibrated in situ. The reconstruction tension was 40 N at 20 degrees of flexion. In test 1, the graft tension was measured under cyclical flexion-extension in a motorized rig up to 1500 cycles. Test 2, with a new graft, also included anteroposterior and internal-external rotational knee laxity measurements at 0, 500, and 1500 cycles. RESULTS: The graft tension at 0 degrees of flexion dropped from 208 N, by 25% after 50 cycles, 41% by 500, and 46% by 1500 cycles. Anterior laxity increased from +1.4 to +2.8 mm by 500 cycles, and performing these laxity tests also caused significant tension losses. CLINICAL RELEVANCE: These results provide one possible explanation for early slackening of anterior cruciate ligament reconstructions.     

Biomechanical effects of femoral notchplasty in anterior cruciate ligament reconstruction.

Notchplasty is frequently performed in conjunction with anterior cruciate ligament reconstruction. Bench loading tests were performed on 26 fresh-frozen knee specimens to measure excursion of a bone-patellar tendon-bone graft, anterior-posterior laxity of the knee, and graft forces before and after performing a 2-mm and a 4-mm notchplasty. The mean intraarticular pretension required to restore normal anterior-posterior laxity at 30 degrees of flexion (laxity-matched pretension level) was 27 N before notchplasty, 48 N after 2-mm notchplasty, and 65 N after 4-mm notchplasty. The mean graft pretension decreased 53% and 58%, respectively, on completion of a loading test series involving anterior-posterior and constant tibial loading forces. Mean laxity increased 1.4 mm at full extension and decreased 1.8 mm at 90 degrees of flexion after a 2-mm notchplasty. Mean graft forces increased markedly between 30 degrees and 90 degrees of passive flexion after notchplasty. Our results show that after a notchplasty, a higher level of graft pretension will be necessary to restore normal laxity at 30 degrees of flexion. This increased level of pretension, combined with changes in graft excursion, produced dramatic increases in graft force when the knee was flexed to 90 degrees. These relatively high forces would be detrimental to a remodeling graft and could lead to subsequent failure of the reconstruction.     

Dynamic joint forces during knee isokinetic exercise

This study analyzed forces in the tibiofemoral and patellofemoral joints during isokinetic exercise using an analytical biomechanical model. The results show that isokinetic exercise can produce large loads on these joints, especially during extension exercises. The tibiofemoral compressive force (4.0 body weight) is approximately equal to that obtained during walking but it occurs at 55 degrees of knee flexion. Anterior shear forces (resisting force to anterior drawer) exist during extension exercise at less than 40 degrees of knee flexion, with a maximum of 0.3 body weight. Posterior shear forces (resisting force to posterior drawer) exist during extension exercise at knee joint angles greater than 40 degrees and during the flexion portion of isokinetic exercise. The maximum posterior shear force is 1.7 body weight. The patellofemoral joint can encounter loads as high as 5.1 body weight which are 10 times higher than during straight leg raises. These results suggest that isokinetic exercise should be used cautiously in patients with knee lesions.     

The normal anterior cruciate ligament as a model for tensioning strategies in anterior cruciate ligament grafts

BACKGROUND: There is some confusion about the relationship between the tension placed on the graft and the joint position used in the fixation of anterior cruciate ligament grafts. This is because of deficiency in accurate basic science about this important interaction in the normal and reconstructed anterior cruciate ligament. HYPOTHESIS: If the normal femoral attachment of the anterior cruciate ligament can be preserved and the tibial insertion isolated and tested, an accurate force-flexion curve of the human anterior cruciate ligament can be mapped out and used as a standard for proper graft tensioning protocols in anterior cruciate ligament reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: In 10 fresh-frozen human cadaveric knees, an isolated bone plug containing the tibial anterior cruciate ligament insertion was connected with a custom-made tensiometer. The knees were moved through the whole range of motion; the starting point chosen was an anterior cruciate ligament tension of 10 N, which was applied at 10 degrees of knee flexion and resulted in a baseline curve. This curve was compared with the results recorded when the starting point was below the baseline curve, similar to, or above it. RESULTS: The anterior cruciate ligament showed low tension close to slackness in midflexion after starting with 10 N at 10 degrees of flexion. Starting points below the baseline curve shifted the whole curve downward; those above the baseline curve increased the force in the anterior cruciate ligament, resulting in a tight anterior cruciate ligament in midflexion. CLINICAL RELEVANCE: The normal anterior cruciate ligament shows a physiological laxity in midflexion. This study gives guidelines for tensioning protocols in anterior cruciate ligament grafts to replicate the force-flexion curve characteristics of the normal anterior cruciate ligament.