An in vivo comparison between intraoperative isometric measurement and local elongation of the graft after reconstruction of the anterior cruciate ligament

Anatomic anterior cruciate ligament reconstruction utilizing the double-bundle technique

The goal of every orthopaedic surgeon should be to restore anatomy as close as possible to normal. Intense research on reconstruction of the anterior cruciate ligament (ACL) and an advancing knowledge of the anatomy and function of the 2 primary bundles of the ACL have led to techniques of ACL reconstruction that more closely restore normal anatomy. Restoring the ACL footprint is one of the most important goals of the surgery, and the choice between anatomic single-bundle and double-bundle ACL reconstruction is determined by the anatomical features of each patient. After reconstruction, the graft undergoes a complex, lengthy process of remodeling; therefore, inappropriate (early), aggressive rehabilitation can lead to graft failure and compromise the patient's outcome. The purpose of this article is to provide an overview of the anatomy and function of the ACL, the methods for anatomic single-bundle and double-bundle ACL reconstruction, and our recommendations for postoperative rehabilitation.

In vitro evaluation of combined graft deformation in anterior cruciate ligament reconstructions

In this paper, we present a simple method of calculating deformation of an anterior cruciate ligament graft in combined elongation, bending and total twisting. We also report our results on these deformations for three types of ligament reconstruction in cadaver knees: two isometric reconstructions, using either a biological bone-patellar tendon-bone autograft or an artificial Trevira prosthesis, and modified over-the-top reconstruction with the prosthesis. The data show that the modified OTT technique produced elongation of the graft equivalent to that of the synthetic isometric technique, but significantly less than isometric reconstruction with the biological graft (p<0.05, ANOVA). Moreover, the grafts were subjected to bending and twisting.

Effects of notchplasty and femoral tunnel position on excursion patterns of an anterior cruciate ligament graft

PURPOSE

Errors in femoral tunnel placement in anterior cruciate ligament (ACL) reconstruction can cause excessive length changes in the graft during knee flexion and extension, resulting in graft elongation during the postoperative period. To improve the accuracy of tunnel placement and to avoid graft impingement, a notchplasty is commonly performed. The purpose of this study was to determine the effects of varying the position of the femoral tunnel and of performing a 2-mm notchplasty of the lateral femoral condyle and roof of the intercondylar notch on excursion patterns of a bone-patellar tendon-bone graft.

TYPE OF STUDY

Biomechanical cadaveric study.

METHODS

A cylindrical cap of bone, containing the tibial insertion of the ACL, was mechanically isolated in 15 fresh-frozen cadaveric specimens using a coring cutter. The bone cap was attached to an electronic isometer that recorded displacement of the bone cap relative to the tibia as the knee was taken through a 90 degrees range of motion. After native ACL testing, the proximal end of a 10-mm bone-patella tendon-bone graft was fixed within femoral tunnels drilled at the 10-, 11-, and 12-o'clock (or 2-, 1-, and 12-o'clock) positions within the notch. The distal end of the graft was attached to the isometer. Testing was then completed at each tunnel position before and after notchplasty.

RESULTS

Before notchplasty, mean graft excursions at the 10- or 2-, 11- or 1-, and 12-o'clock tunnels were not significantly different from the excursions of the native ACL or each other. After a 2-mm notchplasty, mean graft excursions at the 3 tunnel locations were not sigificantly different from each other but were greater than mean graft excursions before notchplasty. After notchplasty, all grafts tightened during knee flexion.

CONCLUSIONS

Although errors in placement along the arc of the intercondylar notch did not significantly affect graft excursion patterns, the apparent graft tightening with knee flexion that was observed for all 3 tunnel positions after notchplasty suggests that graft forces would increase with knee flexion over this range. This would indicate that as little amount of bone as possible should be removed from the posterior portion of the intercondylar notch in ACL reconstruction.

Real-time computerized in situ guidance system for ACL graft placement

A recent consensus within an international society for sports traumatology revealed that approximately 40% of ACL grafts are being surgically misplaced in current clinical practice. To help solve this problem, a computer-assisted system has been developed at the M.E. Müller Institute for Biomechanics to perform intraoperative planning and guidance of ACL replacement. Dynamic reference bases are fixed on the femur and tibia to track the knee's movement. No intraoperative imaging is required, and potential ligament attachment sites can be directly digitized using a computerized palpation hook in a minimally invasive fashion when used in conjunction with standard endoscopic tools. The palpation hook can be used by the surgeon to interactively define various anatomical structures and reference landmarks that are important for proper ligament positioning. The system can input a standard diagnostic X-ray (sagittal view of the femur) and allows intraoperative registration of this image with the patient to provide valuable X-ray landmarks for intraoperative guidance. The computer helps in situ planning of ligament placement by providing the surgeon with a 3D overview of the relevant anatomical landmarks and information on graft impingement and elongation for various simulated surgical insertions and graft sizes. After planning, the computer helps guide placement of the chosen insertion tunnels. This approach provides an augmented 3D view of knee anatomy and ligament function prior to drilling that is not possible with current procedures. The flexibility of the system in permitting surgeon-defined landmarks and free interpretation of functional factors allows it to support a variety of surgical workflows and techniques.

The elongation behavior of the anterior cruciate ligament graft in vivo. A long-term follow-up study

The relationship between the elongation values of an autogenous bone-patellar tendon-bone graft immediately after fixation and the anterior-posterior laxity of the knee 5 years later was studied in vivo. Immediately after fixation, the change in the graft midsubstance length during passive knee flexion-extension was measured using a Hall-effect transducer, and anterior-posterior knee laxity was measured with the KT-1000 arthrometer. Subjects were divided into group 1 (N = 6), with graft elongation values bounded by the 95% confidence intervals of the normal anterior cruciate ligament elongation values, and group 2 (N = 7), subjects with values outside these intervals. Immediately after reconstruction, the side-to-side difference in anterior-posterior laxity between the reconstructed and uninjured knees was not different between group 1 (-2.6 +/- 0.7 mm, mean +/- SEM) and group 2 (-1.7 +/- 1.0 mm) (P = 0.49). At 5-year follow-up, the difference was 1.2 +/- 0.7 mm for group 1, while for group 2 it was significantly greater at 4.7 +/- 0.6 mm (P = 0.004). At surgery, graft elongation values produced by flexion of the knee that are outside the limits of the anterior cruciate ligament result in significant increases in anterior knee laxity at long-term follow-up, while grafts with elongation values similar to the normal anterior cruciate ligament do not. Not only is restoration of anterior-posterior laxity values to within normal limits important, but the biomechanical behavior of the graft produced by flexion-extension of the knee should be appreciated.

In situ calibration of miniature sensors implanted into the anterior cruciate ligament part I: strain measurements

The goals of this study were to (a) evaluate the differential variable reluctance transducer as an instrument for measuring tissue strain in the anteromedial band of the anterior cruciate ligament, (b) develop a series of calibration curves (for simple states of knee loading) from which resultant force in the ligament could be estimated from measured strain levels in the anteromedial band of the ligament, and (c) study the effects of knee flexion angle and mode of applied loading on output from the transducer. Thirteen fresh-frozen cadaveric knee specimens underwent mechanical isolation of a bone cap containing the tibial insertion of the anterior cruciate ligament and attachment of a load cell to measure resultant force in the ligament. The transducer (with barbed prongs) was inserted into the anteromedial band of the anterior cruciate ligament to record local elongation of the instrumented fibers as resultant force was generated in the ligament. A series of calibration curves (anteromedial bundle strain versus resultant force in the anterior cruciate ligament) were determined at selected knee flexion angles as external loads were applied to the knee. During passive knee extension, strain readings did not always follow the pattern of resultant force in the ligament; erratic strain readings were often measured beyond 20 degrees of flexion, where the anteromedial band was slack. For anterior tibial loading, the anteromedial band was a more active contributor to resultant ligament force beyond 45 degrees of flexion and was less active near full extension; mean resultant forces in the range of 150-200 N produced strain levels on the order of 3-4%. The anteromedial band was also active during application of internal tibial torque; mean resultant forces on the order of 180-220 N produced strains on the order of 2%. Resultant forces generated by varus moment were relatively low, and the anteromedial band was not always strained. Mean coefficients of variation for resultant force in the ligament (five repeated measurements) ranged between 0.038 and 0.111. Mean coefficients of variation for five repeated placements of the strain transducer in the same site ranged from 0.209 to 0.342. Insertion and removal of this transducer at the anteromedial band produced observable damage to the ligament. In our study, repeatable measurements were possible only if both prongs of the transducer were sutured to the ligament fibers.

Anterior cruciate ligament strain in-vivo: a review of previous work

Disruption of the anterior cruciate ligament (ACL), a primary stabilizer of the knee, can produce disability. The purpose of our work has been to study the normal ACL in humans, in the presence of normal muscle function and body weight, and develop clinical criteria for reconstruction, establish a basis for rehabilitation programs, and evaluate how knee braces protect this important ligament. The strain behavior of the ACL has been measured by arthroscopic implantation of the Differential Variable Reluctance Transducer while subjects are under local anesthesia. Movement of the knee from a flexed to an extended position, either passively or through contraction of the leg muscles, produces an increase in ACL strain values. Isolated contraction of the dominant quadriceps with the knee between 50 degrees and extension creates substantial increases in strain. In contrast, isolated contraction of the hamstrings at any knee position does not increase strain. With the knee un-weighted, the protective strain shielding effect of a functional knee brace decreases as the magnitude of anterior shear load applied to the tibia increases. A different behavior occurs during weight bearing, the strain shielding effect of the brace remains constant as the magnitude of anterior load increases. Our approach is novel in that it can be used to measure on important portion of the ACLs strain distribution while clinically relevant loads are applied to the knee, subjects perform rehabilitation exercises, or in the presence of different orthoses such as functional knee braces.

Can an isometer predict the tensile behavior of a double-looped hamstring graft during anterior cruciate ligament reconstruction?

An isometer, a highly compliant spring-scale device for measuring suture displacement, has been used intraoperatively by surgeons to select the optimal placement of the femoral tunnel for an anterior cruciate ligament graft. The isometer measures the displacement of a suture centered in a tibial tunnel and attached to an intraarticular location on the femur before the femoral tunnel is drilled. Because the placement of the femoral tunnel strongly impacts the tensile behavior of an anterior cruciate ligament graft and because surgeons have used the amount of suture displacement to guide the placement of the femoral tunnel, the objective of this study was to determine the ability of an isometer to predict graft tension. In 14 patients undergoing reconstructive surgery of the anterior cruciate ligament, an isometer was used to measure suture displacement during passive knee motion for a provisional femoral tunnel location. An electrogoniometer recorded the flexion angle of the knee. The femoral tunnel was drilled. A double-looped semitendinosus and gracilis autograft was inserted around a post in the femoral tunnel, and the tension in the four limbs of the graft exiting the tibial tunnel was measured during passive knee motion. Graft-tension versus knee-flexion-angle curves revealed that each knee exhibited one of two distinct curve shapes: L-shaped, characterized by the maximum tension occurring at full extension and a nearly flat profile from 35 to 90 degrees of flexion, or U-shaped, with elevated tensions at 80-90 degrees of flexion (p < 0.001) reaching at least half of the tension in full extension. Because the shapes of the suture-displacement versus flexion-angle curves were more consistently L-shaped, the intraoperative measurement of suture displacement was not a useful predictor of either the increase in tension in the graft with flexion or the maximum tension in the graft.

The strain behavior of the anterior cruciate ligament during bicycling. An in vivo study

Stationary bicycling is commonly prescribed after anterior cruciate ligament injury or reconstruction; however, the strains on the ligament or ligament graft during stationary bicycling remain unknown. In this study we measured ligament strain on eight patients who were candidates for arthroscopic meniscectomy under local anesthesia. Six different riding conditions were evaluated: three power levels (75, 125, and 175 W), each of which was performed at two cadences (60 and 90 rpm). The peak ligament strain values ranged from 1.2% for the 175-W, 90-rpm, condition to 2.1% for the 125-W, 60-rpm, condition. No significant differences were found in peak strain values due to changes in power level or cadence. Thus, the strain values were pooled across the six riding conditions tested. The mean peak strain value was 1.7%, a value that is relatively low compared with other rehabilitation activities previously tested. These data suggest that knee rehabilitation programs can be designed to include this selection of power and cadence levels without significantly changing ligament strain values. Thus, stationary bicycling is a rehabilitation exercise that permits the patient to increase muscle activity by increasing the power level or decreasing the cadence without subjecting the ligament or ligament graft to higher strain values.

Analysis of a semitendinosus autograft in a rabbit model

The purpose of this study was to evaluate the histologic and biomechanical changes that occur between 12 and 52 weeks in an intraarticular, semitendinosus autograft placed through tibial and femoral drill holes in a rabbit model. The results of this study show that, in this rabbit model, the soft tissue graft maintained its biologic fixation in the osseous tunnel when stressed to failure at 1 year. The bony fixation occurred by the formation of an indirect tendon insertion, and this formation was complete by 26 weeks. At 52 weeks, large differences persisted in the strength and stiffness of the graft compared with the normal semitendinosus tendon and anterior cruciate ligament. Based on the results of this study, we support a cautious approach in returning patients to early full activity, including sports, after anterior cruciate ligament reconstruction with a semitendinosus autograft.

Isometry measurements in the knee with the anterior cruciate ligament intact, sectioned, and reconstructed

When assessing isometry during anterior cruciate ligament surgery, it is assumed that points determined to be isometric remain so after reconstruction. We sought to evaluate if isometric measurements vary with the status of the anterior cruciate ligament. A computerized electronic isometer was used to measure the magnitude and pattern of change in separation distance between a constant point in the tibial insertion of the anterior cruciate ligament and five positions within the femoral insertion with the anterior cruciate ligament intact, sectioned, and reconstructed. For the center position, the magnitude and pattern of the change in separation distance was physiologically isometric in all conditions (maximal length change, 3.0 mm). For the posterior position, the isometry pattern remained physiologic in each condition, and the magnitude of the separation distance was nearly isometric in all conditions (maximal length change, 3.7 mm). The superior and inferior positions had similar isometric measurements in the intact and sectioned conditions but significantly different measurements after anterior cruciate ligament reconstruction. Intraoperative assessment of isometry at positions in the center or posterior portion of the anterior cruciate ligament's femoral insertion provides useful information that is not altered by reconstruction. For superior and inferior positions, however, points found to be isometric in the anterior cruciate ligament-deficient knee did not remain isometric after reconstruction.

The effect of intraoperative isometric measurement on the outcome of anterior cruciate ligament reconstruction: a clinical analysis

The concept of isometry is based on the measurement of displacement between potential femoral and tibial anterior cruciate ligament (ACL) graft attachment sites while the knee is taken through a range of motion. To evaluate the clinical benefit of intraoperative isometry measurements in ACL reconstruction, we prospectively compared 59 patients (58% acute) in whom isometry was tested (group I) with 35 patients (77% acute) in whom isometry was not tested (group II). All patients underwent arthroscopically assisted ACL reconstruction using autogenous bone-patella tendon-bone graft and interference screw fixation, and were followed-up for a minimum of 24 months (mean, 30 months). With 88% follow-up, no significant differences were found in objective testing, which included the pivot shift test, the Lachman test, KT-1000 arthrometer measurements, and range of motion. A significant difference was found between the two groups when Lysholm scores (P = .04) and Tegner Scores (P = .02) were compared, with group II having higher scores. In addition, one of 15 visual analog scales, "gives way," showed a significant difference between the two groups (P = .01). On a scale of 1 to 10 with 1 being "no giving way" and 10 being "very frequent giving way", group I had an average of 1.68 and group II had an average of 0.58. These differences were related to the greater percentage of chronic cases in group I. Analysis of only those patients with acute injuries from each group showed no significant differences in any objective or subjective measurement. Group I had an overall failure rate of 13%, and group II had a failure rate of 6.7% (chi 2 = .848). These results indicate that, in the hands of a surgeon experienced in ACL reconstruction, intraoperative assessment of isometry has little effect on the clinical outcome.

Biomechanical consequences of replacement of the anterior cruciate ligament with a patellar ligament allograft. Part I: insertion of the graft and anterior-posterior testing

Nineteen fresh-frozen knee specimens from cadavera were tested for anterior-posterior laxity with 200 newtons of force applied to the tibia. A cylindrical cap of subchondral bone containing the tibial insertion of the anterior cruciate ligament was isolated with a coring cutter and was potted in acrylic. A thin wire was connected to the undersurface of the cap, and relative displacement between the cap and the tibia was measured with an isometer as the knee was extended. The cap of bone was connected to a load-cell that recorded force in the intact ligament during anterior-posterior testing with the tibia locked in neutral, internal rotation, and external rotation. The anterior cruciate ligament was then resected, and a femoral tunnel was drilled at the site where the isometer readings from the wire were the same as those obtained for the intact anterior cruciate ligament. A bone-patellar ligament-bone graft was used to reconstruct the anterior cruciate ligament, and the isometer measurements were repeated with the graft in place. The graft was pre-tensioned at 30 degrees of flexion to restore normal anterior-posterior laxity. Anterior-posterior laxity tests were repeated at this level of pre-tension (laxity-matched pre-tension) as well as at a level that was forty-five newtons greater (over-tension). The moment required to extend the knee was measured before and after insertion of the graft at both levels of pre-tension. When the tibia was locked in positions of internal and external rotation, the anterior-posterior laxities and the forces in the anterior cruciate ligament (generated by an anterior force applied to the tibia) were significantly less than the corresponding values with the tibia in neutral rotation at 20, 30, and 45 degrees of flexion (p < or = 0.05). Isometer readings for the intact anterior cruciate ligament indicated that the cap of bone retracted into the joint a mean and standard deviation of 3.1 +/- 0.8 millimeters as the knee was extended from 30 degrees of flexion to full extension. For each specimen, the isometer measurements for the trial wire and for the graft were within 1.5 millimeters of those for the intact anterior cruciate ligament. At laxity-matched pre-tension (mean, 28.2 +/- 16.8 newtons), the mean anterior-posterior laxities of the reconstructed knees were within 1.0 millimeter of the corresponding means for the intact knees between 0 and 45 degrees of flexion. Over-tensioning of the graft by forty-five newtons decreased the anterior-posterior laxity a mean of 1.2 millimeters at 30 degrees of flexion. Over-tensioning of the graft did not change the moment required to bring the knee to full extension.

The effect of anterior cruciate ligament graft elongation at the time of implantation on the biomechanical behavior of the graft and knee

This investigation determined the effect that anterior cruciate ligament graft elongation at the time of surgical reconstruction has on the long-term biomechanical behavior of the graft and knee joint. We chose the canine model for anterior cruciate ligament reconstruction, using the medial third of the patellar tendon with attached proximal bone block. Elongation of the graft was measured immediately after graft fixation during passive knee flexion using the Hall effect transducer. The dogs were divided into either Group 1 (graft elongation behavior within the 95% confidence limits of the normal anterior cruciate ligament) or Group 2 (graft elongation behavior more than the 95% confidence limits of the normal anterior cruciate ligament). All of the dogs were sacrificed 18 months postoperatively, and we evaluated anteroposterior load displacement (i.e., anteroposterior laxity) of the knee and the structural properties of the graft. The anteroposterior laxity behavior of the reconstructed knees in Group 2 was significantly more than that of Group 1. Group 2 had significantly less linear stiffness of the graft than Group 1. There was no difference in the ultimate failure load and absorbed energy at failure values of the grafts between Groups 1 and 2. The findings from this investigation indicate that the graft elongation behavior at the time of reconstruction is a critical factor that influences the long-term success of anterior cruciate ligament reconstruction.

Why grafts fail

Significant advances in anterior cruciate ligament reconstructive surgery have been made in the past decade and, as a result, the number of anterior cruciate ligament reconstructive procedures being done have increased. Unfortunately, graft failure continues to occur and has resulted in an emphasis on revision surgery. Successful anterior cruciate ligament reconstruction is dependent on a number of factors including: patient selection, surgical technique, postoperative rehabilitation, and associated secondary restraint ligamentous instability. A particular emphasis both in scientific and clinical research has been placed on surgical technique. Errors in graft selection, tunnel placement, tensioning, or fixation methods chosen may lead to graft failure. Improper postoperative rehabilitation may lead to graft failure; however, current protocols seem to minimize its occurrence. Finally, failure to recognize or treat a significant secondary restraint instability can place excessive stress on the anterior cruciate ligament graft which may lead to failure. Care must be taken at every step of the process to ensure graft failure does not occur, because revision anterior cruciate ligament surgery results are not as predictable as primary anterior cruciate ligament reconstruction.

Use of an endoscopic aimer for femoral tunnel placement in anterior cruciate ligament reconstruction

Accurate placement of the femoral tunnel is a technically difficult aspect of anterior cruciate ligament reconstruction. Various drill guides have been developed to aid in the selection of this site. The purpose of this article is to describe a new drill guide designed to ensure anatomic placement of the femoral tunnel. The guide is used as part of a single-incision arthroscopic anterior cruciate ligament reconstruction technique with a bone-patellar tendon-bone graft secured with interference screws. An intraoperative check of the "pretunnel footprint" can be made to verify correct placement by the remaining cortical margins measurement within an acceptable 1 to 2 mm range before drilling the tunnel to depth. If necessary, minor adjustments to the guidepin location can be made to prevent posterior tunnel margin dimensions of less than 1 mm (troughing) or greater than 2 mm.

Recurrent acute hemarthrosis after anterior cruciate ligament reconstruction. Report of an unusual complication and a review of the literature

Arthroscopic-assisted and endoscopic operative techniques have allowed for less and less restrictive postoperative rehabilitation programs after cruciate ligament reconstruction. Accelerated rehabilitation programs may, however, also provoke mechanical problems at the transplant-bone interface, as reports in the literature of loosened fixation devices and loosened or even fractured bone pegs with subsequent hemarthrosis and recurrent instability have shown. We describe the case of a patient who presented with recurrent acute hemarthrosis after anterior cruciate ligament reconstruction without additional trauma and without instability. However, the symptoms and signs were clearly related to the fixation method employed.

Isometry testing for anterior cruciate ligament reconstruction revisited

The purpose of this study was to determine the effect, if any, that varying the distal testing position (tibial level) has on isometry data produced with a common anatomic proximal testing position at the native anterior cruciate ligament (ACL) origin. During ACL reconstruction in 25 knees, in vivo isometry measurements were recorded using two different isometry testing methods, which differed in the tibial level of the distal fixation testing point. Method 1 tested distally at a point 13 cm peripheral to the native ACL insertion on a vector in line with the tibial tunnel. Method 2 tested distally at a point central in the native ACL insertion at the level of the intercondylar floor. All tibial tunnels were standardized with similar sagittal tunnel-plateau angles and similar tunnel lengths. The proximal testing point was standardized at a point that was anatomically located at or near the central ACL origin 7 mm anterior to "over the top" in all knees. Using these methods, length changes between the proximal and distal testing points were recorded in each knee with each testing method, with the knee ranged from 70 degrees of flexion to full extension and from 70 degrees to 140 degrees of flexion. From these data, a total excursion from 0 degree to 140 degrees of flexion was calculated. A nonanatomic distal testing point (Method 1) produced a 6 mm +/- 1 mm total excursion, whereas anatomic testing points (Method 2) in the same knees produced a 1 mm +/- 1 mm total excursion. From these data, the authors conclude that the tibial level of the distal isometry testing point has a significant effect on the resultant isometry measurement such that anatomic testing points are most isometric. Isometers that produce data between nonanatomic testing points should not be used to position tunnels for ACL reconstruction and should not be used to assume the elongation forces an ACL substitute will see when fixed at different points. Conversely, the clinical relevance of this study is that both anatomic graft position and anatomic graft fixation position are important and, when achieved, should result in minimal graft elongation with early postoperative range of motion, leading to a more stable long-term result.