Changes in knee kinematics from applied external Tibial torque: Implications for stabilizing an anterior cruciate ligament deficient knee.

BACKGROUND: Changes in knee kinematics from internal tibial torque under tibiofemoral compression force have been studied, but the potentially stabilizing effects of external tibial torque have not been reported. We hypothesized that for a given knee flexion angle, 1) external torque would significantly reduce anterior tibial translation, internal tibial rotation, and valgus tibial rotation before and after sectioning the anterior cruciate ligament and 2) changes in kinematics from applied external torque would be significantly greater with the cruciate cut. METHODS: A robotic test system was used to flex intact human knees continuously from 0° to 50° under 200 N compression, without and with 5 Nm external torque. Tests were repeated after cruciate section. FINDINGS: With the cruciate intact, external torque had no significant effect on anterior translation, and significantly reduced internal and valgus rotations at all flexion angles. With the cruciate cut, external torque significantly reduced anterior translation beyond 25° flexion, significantly reduced internal rotation at all flexion angles, and significantly reduced valgus rotation beyond 15° flexion. Although external torque had no significant effect on anterior translation with the ACL intact, external torque produced relatively large decreases in anterior translation with the cruciate sectioned (-11.6 mm at 50° flexion). Reductions in valgus rotation from applied external torque were significantly greater for cruciate deficient knees beyond 25° flexion. INTERPRETATION: We conclude that external tibial torque may be important for controlling the abnormal kinematics associated with an anterior cruciate ligament deficient knee, and possibly help stabilize the knee during in vivo activities.

Cyclic testing of tibialis tendon allografts for anterior cruciate ligament reconstruction using suture-post versus spiked washer tibial fixation.

BACKGROUND: The purpose of this study was to directly compare spiked washer and suture-post tibial-sided fixation techniques used for anterior cruciate ligament reconstruction by measuring anterior tibial translation during cyclic tests. METHODS: Fresh-frozen human knees were tested using a robotic system that applied 250 cycles of anterior-posterior tibial force (134 N) at 30° flexion, while recording tibial translation. Ten intact knees were tested to collect baseline data for native specimens. A single knee was selected to test ligament reconstructions using doubled tibialis tendon allografts. All grafts were fixed proximally using an EndoButton™, and the tibial end of the graft was fixed with either a spiked washer or with a suture post placed at two different locations (near and distant) relative to the tibial tunnel. FINDINGS: Mean first cycle translation for intact knees was 4.8 (sd 1.8) mm; means after reconstruction were 2.6 (sd 0.9) mm (spiked washer), 10.1 (sd 1.9) mm (suture post near), and 10.4 (sd 1.5) mm (suture post distant). Corresponding means for translation increase over 250 cycles were 0.3 (sd 0.2) mm, 3.6 (sd 1.3) mm, 7.2 mm (sd 0.9) mm, and 8.0 (sd 1.3) mm. All mean increases (first cycle and cyclic) after ACL reconstruction were significantly greater than those for the intact knees, and all means with a suture post were significantly greater than those with a spiked washer. There were no significant differences between mean translations for near and distant suture post locations. INTERPRETATION: Use of suture post fixation for anterior cruciate ligament reconstruction is questioned since increases in anterior tibial translation could lead to excessive post-operative knee laxity and possibly early clinical failure.

In vitro determination of the passive knee flexion axis: Effects of axis alignment on coupled tibiofemoral motions.

The natural passive flexion axis of human cadaveric knees was determined using a technique that minimized coupled tibiofemoral motions (translations and rotations), and the kinematic effects of mal-positioned flexion axes were determined. The femur was clamped in an apparatus that allowed unconstrained tibial motions as the knee was flexed from 0° to 90°. To establish the natural flexion axis, the femur's position was adjusted such that coupled tibiofemoral motions were minimized. Tests were repeated, first with the femur rotated internally and externally from its original position, and again after positioning the femur to flex the knee about the transepicondylar axis. Compared to the transepicondylar axis, flexion about the natural axis significantly reduced mean tibial translation by 66.4% (p < 0.01) and varus-valgus rotation by 70.1% (p <0.01). Mean varus-valgus rotation increased by 3.4° (factor of 4) when the femur was rotated 3° internally or externally from the optimum position. Differences in condylar location coordinates between the transepicondylar and natural flexion axes most likely indistinguishable clinically. Knee flexion about an axis that minimizes coupled tibiofemoral motions could be important for placement and orientation of a femoral total knee component and for specimen alignment during biomechanical knee testing.

Femoral Contact Forces in the Anterior Cruciate Ligament Deficient Knee: A Robotic Study.

PURPOSE: To measure contact forces (CFs) at standardized locations representative of clinical articular cartilage defects on the medial and lateral femoral condyles during robotic tests with simulated weightbearing knee flexion. METHODS: Eleven human knees had 20-mm-diameter cylinders of native bone/cartilage cored from both femoral condyles at standardized locations, with each cylinder attached to a custom-built load cell that maintained the plug in its precise anatomic position. A robotic test system was used to flex the knee from 0° to 50° under 200-N tibiofemoral compression without and with a 2 Nm internal tibial torque, 5 Nm external tibial torque, and 45 N anterior tibial force (AF). CFs and knee kinematics were recorded before and after cutting the anterior cruciate ligament (ACL). RESULTS: ACL sectioning did not significantly increase medial or lateral CFs for any loading condition, with the exception of AF, in which increases in medial CF ranged from 38 N (at 15° flexion, P < .01) to 77 N (at 50° flexion, P < .002). Compared with the intact condition, ACL sectioning significantly increased anterior tibial translation by 12.33 mm (at 15° flexion, P < .001) and 17.4 mm (at 50° flexion, P < .001), and increased valgus rotation by 2.4° (at 15° flexion, P < .001) and 3.8° (at 50° flexion, P < .001). CONCLUSIONS: Our hypothesis that CF would increase after ACL section was confirmed for the AF test condition only, and only for the medial condyle beyond 10° flexion. With the ACL sectioned, it appeared that the increased CF was owing to the medial condyle riding up over the posterior tibial plateau resulting from the large anterior tibial displacements. CLINICAL RELEVANCE: Aside from our limited finding with AF, we concluded that CFs were generally unaffected by ACL section.

Contact force between the tibial spine and medial femoral condyle: A biomechanical study.

BACKGROUND: Contact between the tibial spine and medial femoral condyle with internal tibial rotation (ITR) has been proposed as a factor for the development of osteochondritis dissecans lesions. We hypothesized that tibial spine contact force (CF) would increase significantly with applied internal tibial torque (IT). METHODS: A 20 mm diameter cylinder of bone encompassing the tibial spine was cored and attached to a load cell. The isolated bone cylinder included the tibial attachments of the anterior cruciate ligament (ACL) and anterior horn of the lateral meniscus (AHLM). Eleven human cadaveric knees were flexed from 0°-50° under 200 N of tibiofemoral compression (TFC), without and with 2 N-m IT. Tests were repeated with the AHLM cut, and again with both AHLM and ACL cut, where the load cell recorded CF alone without contributions from any ligamentous attachments. FINDINGS: There were no significant differences in CF, ITR, or valgus tibial rotation (VTR) after sectioning the AHLM, without or with applied IT. With no tibial torque, mean CFs were less than 20 N throughout the flexion range. Addition of IT significantly increased 1) mean CF by 44.4 N(SD 15.8 N) at 0°(+240%) and 27.2 N(SD 5.0 N) at 20°(+675%), 2), mean ITR by 10.2°(SD 0.8°) at 0° flexion and 18.6°(SD 2.0°) at 20° flexion, and 3) mean VTR by 1.3°(SD 0.4°) at 0° flexion and 4.4°(SD 0.8°) at 20° flexion. INTERPRETATION: Our hypothesis was confirmed only between 0° and 20° of knee flexion, where the intercondylar separation distance is relatively small and the possibility of tibial spine contact with ITR is greater.

Differences in the Radius of Curvature Between Femoral Condyles: Implications for Osteochondral Allograft Matching.

BACKGROUND: The radius of curvature (ROC) is an important variable related to potential cartilage incongruities in the transplantation of a large femoral osteochondral allograft. The anterior-posterior length (APL) of a condyle is used as a criterion for donor-graft acceptance. We hypothesized that there would be a linear correlation between the ROC and APL of a condyle, that the ROC and APL would differ significantly between the medial femoral condyle (MFC) and the lateral femoral condyle (LFC), and that a donor graft from the LFC would be suitable for an MFC defect. METHODS: Knee magnetic resonance imaging scans of 147 patients with no cartilage defects were analyzed. Best-fit circles in the sagittal plane were determined at standardized locations on each condyle. Assuming the use of a 20-mm graft that was flush to the edges of the native cartilage, the central graft prominence was calculated for potential donor-host differences in the ROC. RESULTS: There was a linear correlation between the ROC and APL. There were significant differences in the mean ROC and APL between the MFC and LFC. Based on calculations of the central graft prominence among all ROC combinations within the patient group, 100% of potential medial-to-medial, 97.8% of lateral-to-lateral, and 92.5% of lateral-to-medial transplantations would produce a central graft prominence of <1 mm. On average, an allograft harvested from an LFC (mean ROC, 25.7 mm; mean APL, 69.8 mm) implanted into an MFC defect site (mean ROC, 31.9 mm; mean APL, 66.6 mm) would have a central graft prominence of 0.4 ± 0.3 mm. CONCLUSIONS: Assuming a maximum central graft prominence tolerance of +1 mm, our findings demonstrate that matching the ROC or APL would not be necessary for potential medial-to-medial or lateral-to-lateral allograft transplants within this patient group. Implantation of an LFC donor allograft into an MFC defect is also supported by our findings.

Effects of Proud Large Osteochondral Plugs on Contact Forces and Knee Kinematics: A Robotic Study.

BACKGROUND: Osteochondral allograft (OCA) transplantation is used to treat large focal femoral condylar articular cartilage defects. A proud plug could affect graft survival by altering contact forces (CFs) and knee kinematics. HYPOTHESIS: A proud OCA plug will significantly increase CF and significantly alter knee kinematics throughout controlled knee flexion. STUDY DESIGN: Controlled laboratory study. METHODS: Human cadaver knees had miniature load cells, each with a 20-mm-diameter cylinder of native bone/cartilage attached at its exact anatomic position, installed in both femoral condyles at standardized locations representative of clinical defects. Spacers were inserted to create proud plug conditions of +0.5, +1.0, and +1.5 mm. CFs and knee kinematics were recorded as a robot flexed the knee continuously from 0° to 50° under 1000 N of tibiofemoral compression. RESULTS: CFs were increased significantly (vs flush) for all proudness conditions between 0° and 45° of flexion (medial) and 0° to 50° of flexion (lateral). At 20°, the average increases in medial CF for +0.5-mm, +1-mm, and +1.5-mm proudness were +80 N (+36%), +155 N (+70%), and +193 N (+87%), respectively. Corresponding increases with proud lateral plugs were +44 N (+14%), +90 N (+29%), and +118 N (+38%). CF increases for medial plugs at 20° of flexion were significantly greater than those for lateral plugs at all proudness conditions. At 50°, a 1-mm proud lateral plug significantly decreased internal tibial rotation by 15.4° and decreased valgus rotation by 2.5°. CONCLUSION: A proud medial or lateral plug significantly increased CF between 0° and 45° of flexion. Our results suggest that a medial plug at 20° may be more sensitive to graft incongruity than a lateral plug. The changes in rotational kinematics with proud lateral plugs were attributed to earlier contact between the proud plug's surface and the lateral meniscus, leading to rim impingement with decreased tibial rotation. CLINICAL RELEVANCE: Increased CF and altered knee kinematics from a proud femoral plug could affect graft viability. Plug proudness of only 0.5 mm produced significant changes in CF and knee kinematics, and the clinically accepted 1-mm tolerance may need to be reexamined in view of our findings.

Effects of Anterior Closing Wedge Tibial Osteotomy on Anterior Cruciate Ligament Force and Knee Kinematics.

BACKGROUND: A certain percentage of patients undergoing anterior cruciate ligament (ACL) reconstruction will experience graft failure, and there is mounting evidence that an increased posterior tibial slope (PTS) may be a predisposing factor. Theoretically, under tibiofemoral compression force (TFC), a reduced PTS would induce less anterior tibial translation (ATT) and lower ACL force. HYPOTHESIS: Ten-degree anterior closing wedge osteotomy of the proximal tibia will significantly reduce ACL force and alter knee kinematics during robotic testing. STUDY DESIGN: Controlled laboratory study. METHODS: Eleven fresh-frozen human knees were instrumented with a load cell that measured ACL force as the knee was flexing continuously from 0° to 50° under 200-N TFC as our initial testing condition, followed by the addition of the following tibial loads: 45-N anterior force (AF), 5-N·m valgus moment (VM), 2-N·m internal torque (IT), and all loads combined. ACL force and knee kinematics were recorded before and after osteotomy. RESULTS: Osteotomy produced significant changes in the tibiofemoral position at full extension (as defined by a 2-N·m knee extension moment). This resulted in apparent knee hyperextension (9.4° ± 1.9°), posterior tibial translation (7.9 mm ± 1.6 mm), internal tibial rotation (3.2° ± 2.3°), and valgus tibial rotation (3.2° ± 1.5°). During straight knee flexion with TFC alone, osteotomy reduced ACL force to 0 N beyond 5° of flexion, and ATT was reduced between 0° and 45° ( P < .05). With TFC + AF, ACL force was reduced beyond 5° of flexion, and ATT was reduced between 5° and 45° ( P < .05). With TFC + VM, ACL force was less than 10 N beyond 5° of flexion, and ATT was reduced at all flexion angles ( P < .05). Under the loading conditions TFC + IT and TFC + IT + AF + VM, osteotomy did not significantly change ACL force or ATT at any flexion angle. CONCLUSION: In general, osteotomy lowered ACL force and reduced ATT when IT was not present. The benefits of osteotomy were negated when IT was included possibly because the dominant mechanism of ACL force generation was cruciate impingement from internal winding and not ATT. CLINICAL RELEVANCE: PTS-reducing osteotomy significantly decreased ACL force and reduced ATT for knee loads that did not include IT.

Contact Forces Acting on Large Femoral Osteochondral Allografts During Forced Knee Extension.

BACKGROUND: A single cylindrical graft plug is commonly used for large focal femoral defects during osteochondral allograft (OCA) transplantation. Excessive contact force (CF) on a proud plug could compromise initial healing. CFs during forced knee extension are of particular interest because this maneuver is used by therapists to restore early postoperative range of motion. HYPOTHESIS: A proud OCA plug will significantly increase the CF and significantly decrease the knee extension angle (KEA). STUDY DESIGN: Controlled laboratory study. METHODS: Eleven human knee specimens had miniature load cells installed in both femoral condyles at standardized locations representative of clinical defects. Each load cell had a 20-mm-diameter cylinder of native bone/cartilage attached at its precise anatomic location. Four spacers, 0.5 mm in thickness, were inserted sequentially between each load cell and its mounting bracket to create proud plug conditions of 0.5 to 2 mm. Measurements of the CF and KEA were recorded at extension moment levels up to 8 N·m. RESULTS: At 8 N·m, the mean CFs for flush plugs were 149 ± 18 N (lateral) and 34 ± 13 N (medial). The mean increases in the medial CF (compared with flush) for 0.5-mm, 1-mm, 1.5-mm, and 2-mm proud conditions were 31 N (+91%), 64 N (+188%), 111 N (+325%), and 154 N (+451%), respectively. Corresponding increases for lateral proud plugs were 55 N (+37%), 120 N (+81%), 162 N (+109%), and 210 N (+141%), respectively. The CFs (and CF increases) for lateral grafts were significantly ( P < .05) higher than corresponding values for medial grafts at each proudness condition. Medial plug proudness had no consistent effect on the KEA. A 1-mm proud lateral plug significantly reduced the KEA by -1.6° (0 N·m) and -0.9° (2 N·m). CONCLUSION: Graft proudness of only 0.5 mm significantly increased CFs during forced knee extension, emphasizing the surgical precision necessary to achieve normal CF levels. CLINICAL RELEVANCE: It is believed that some amount of CF is beneficial in the early stages of graft healing, and our findings suggest that forced knee extension may be well suited for this purpose. However, the surgeon should be aware that large extension moments can also generate relatively high CFs, especially if the plug is proud.

Location of the natural knee axis for internal-external tibial rotation.

BACKGROUND: Rotating hinge and mobile bearing tray knee replacement designs utilize a single fixed axis for tibial rotation, yet there is little published information regarding the natural internal-external axis (IEA) for tibial rotation. Identifying the IEA should provide an opportunity for reproducing normal knee kinematics and maintaining the balance of forces in the soft tissues that help control rotation of the tibia. METHODS: The location and orientation of the IEA relative to the tibial plateau were calculated in 46 fresh frozen human cadaveric specimens using an instant center of rotation analysis at fixed knee flexion angles ranging from five degrees to 105°. RESULTS: IEA location ranged from 4.0 to 4.9mm medial and 1.7 to 5.5mm posterior to the center of the tibial plateau (from 5° to 105° of knee flexion). IEA orientation was reported relative to a reference axis perpendicular to the plane of the tibial plateau. In the frontal plane, the IEA was not significantly different from the reference axis from five degrees to 45° flexion, and 2.0° to 2.7° valgus to the reference axis from 60° to 105° flexion. In the sagittal plane, the IEA was not significantly different from the reference axis from 5° to 15° flexion, and 3.0° to 7.0° extended from the reference axis from 30° to 105° flexion. CONCLUSIONS: The IEA moves posteriorly with increasing knee flexion on the tibial plateau. Placement of the IEA relative to the tibial plateau for a rotating hinge or mobile bearing tray implant may represent a compromise between design objectives for moderate and deeper knee flexion. CLINICAL RELEVANCE: This study has relevance for future knee implant designs.

Plate Versus Intramedullary Nail Fixation of Anterior Tibial Stress Fractures: A Biomechanical Study.

BACKGROUND: Anterior midtibial stress fractures are an important clinical problem for patients engaged in high-intensity military activities or athletic training activities. When nonoperative treatment has failed, intramedullary (IM) nail and plate fixation are 2 surgical options used to arrest the progression of a fatigue fracture and allow bone healing. HYPOTHESIS: A plate will be more effective than an IM nail in preventing the opening of a simulated anterior midtibial stress fracture from tibial bending. STUDY DESIGN: Controlled laboratory study. METHODS: Fresh-frozen human tibias were loaded by applying a pure bending moment in the sagittal plane. Thin transverse saw cuts, 50% and 75% of the depth of the anterior tibial cortex, were created at the midtibia to simulate a fatigue fracture. An extensometer spanning the defect was used to measure the fracture opening displacement (FOD) before and after the application of IM nail and plate fixation constructs. IM nails were tested without locking screws, with a proximal screw only, and with proximal and distal screws. Plates were tested with unlocked bicortical screws (standard compression plate) and locked bicortical screws; both plate constructs were tested with the plate edge placed 1 mm from the anterior tibial crest (anterior location) and 5 mm posterior to the crest. RESULTS: For the 75% saw cut depth, the mean FOD values for all IM nail constructs were 13% to 17% less than those for the saw cut alone; the use of locking screws had no significant effect on the FOD. The mean FOD values for all plate constructs were significantly less than those for all IM nail constructs. The mean FOD values for all plates were 28% to 46% less than those for the saw cut alone. Anterior plate placement significantly decreased mean FOD values for both compression and locked plate constructs, but the mean percentage reductions for locked and unlocked plates were not significantly different from each other for either plate placement. The percentage FOD reductions for all plate constructs and the unlocked IM nail were significantly less with a 50% saw cut depth. CONCLUSION: Plate fixation was superior to IM nail fixation in limiting the opening of a simulated midtibial stress fracture, and anterior-posterior placement of the plate was an important variable for this construct. CLINICAL RELEVANCE: Results from these tests can help guide the selection of fixation hardware for patients requiring surgical treatment for a midtibial stress fracture.

Right-Left Differences in Knee Extension Stiffness for the Normal Rat Knee: In Vitro Measurements Using a New Testing Apparatus.

Knee stiffness following joint injury or immobilization is a common clinical problem, and the rat has been used as a model for studies related to joint stiffness and limitation of motion. Knee stiffness measurements have been reported for the anesthetized rat, but it is difficult to separate the contributions of muscular and ligamentous restraints to the recorded values. in vitro testing of isolated rat knees devoid of musculature allows measurement of joint structural properties alone. In order to measure the effects of therapeutic or surgical interventions designed to alter joint stiffness, the opposite extremity is often used as a control. However, right-left stiffness differences for the normal rat knee have not been reported in the literature. If stiffness changes observed for a treatment group are within the normal right-left variation, validity of the results could be questioned. The objectives of this study were to utilize a new testing apparatus to measure right-left stiffness differences during knee extension in a population of normal rat knees and to document repeatability of the stiffness measurements on successive testing days. Moment versus rotation curves were recorded for 15 right-left pairs of normal rat knees on three consecutive days, with overnight specimen storage in a refrigerator. Each knee was subjected to ten loading-unloading cycles, with the last loading curve used for analysis. Angular rotation (AR), defined here as the change in flexion-extension angle from a specified applied joint moment, is commonly used as a measure of overall joint stiffness. For these tests, ARs were measured from the recorded test curves with a maximum applied extension moment of 100 g cm. Mean rotations for testing days 2 and 3 were 0.81-1.25 deg lower (p < 0.001) than for day 1, but were not significantly different from each other. For each testing day, mean rotations for right knees were 1.12-1.30 deg greater (p < 0.001) than left knees. These right-left stiffness differences should be considered when interpreting the results of knee treatment studies designed to alter knee stiffness when using the opposite extremity as a control.

Male-Female Differences in Knee Laxity and Stiffness: A Cadaveric Study.

BACKGROUND: It has been reported that over 70% of anterior cruciate ligament (ACL) injuries occur in noncontact situations and that females are at 2 to 8 times greater risk of ACL injury than males. Increased joint laxity and reduced knee stiffness in female knees have been suggested as possible explanations for the higher ACL injury rates in females. HYPOTHESIS: Compared with male knees, female knees will demonstrate increased laxity and reduced stiffness along the anterior-posterior (AP), internal-external (IE), and varus-valgus (VV) directions. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-seven fresh-frozen human cadaveric knees were tested (22 male and 25 female) by use of a robotic system. Mean ages were 34.6 years (range, 19-45 years) for males and 28.4 years (range, 16-42 years) for females. Joint laxity and stiffness were measured from force-vs-displacement or torque-vs-rotation curves recorded for 3 modes of testing: ± 134 N AP force, ± 5 N · m IE torque, and ± 10 N · m VV moment. RESULTS: Compared with male knees, female knees had greater internal laxity from 0° to 50° flexion (P < .01; maximum difference of 8.3° at 50° of flexion) and greater valgus laxity from 0° to 50° of flexion (P < .05; maximum difference of 1.6° at 50° of flexion). However, female knees exhibited greater anterior laxity only at 50° of flexion (P < .03; difference of 1.3 mm). No significant male-female differences in anterior or posterior stiffness were found. Male knees had 42% greater internal stiffness from 0° to 30° of flexion (P < .03), 35% greater valgus stiffness at 10° of flexion (P < .03), and 19% greater varus stiffness at 50° of flexion (P < .03). CONCLUSION: Female knees demonstrated significantly increased laxity and reduced stiffness compared with males. This finding was not uniform but was dependent on the direction tested and the knee flexion angle. CLINICAL RELEVANCE: Understanding the risk factors for noncontact ACL injury is important for injury prevention. In combination with other female-specific risk factors, increased knee laxity may be a contributing factor associated with the higher rate of female ACL injuries.

Effect of Different Preconditioning Protocols on Anterior Knee Laxity After ACL Reconstruction with Four Commonly Used Grafts.

BACKGROUND: It is currently unknown if preconditioning an anterior cruciate ligament (ACL) graft prior to fixation is helpful in eliminating possible increases in anterior knee laxity. The purpose of this study was to measure cyclic increases in anterior tibial translation of four commonly used graft tissues subjected to four preconditioning protocols. METHODS: A robotic system was used to apply 250 cycles of anteroposterior force (134 N of anterior force followed by 134 N of posterior force) to ten intact knees (ACL controls) and then to a single knee reconstructed, for separate tests, with bone-patellar tendon-bone, bone-Achilles tendon, hamstring tendon, and tibialis tendon grafts following (1) no preconditioning, (2) preconditioning on a tension board (89 N of initial force held for twenty minutes), (3) preconditioning in situ (89 N of force applied to the tibial end of the graft during twenty-five flexion-extension cycles), and (4) a combination of protocols 2 and 3. RESULTS: Over the 250 cycles, all grafts were associated with a progressive increase in anterior tibial translation that was approximately an order of magnitude greater than that of the ACL, and preconditioning had no significant effect on this increase in translation. There were some significant differences in the progressive anterior tibial translation increase among the graft tissues within a given preconditioning protocol, but these differences were no greater than 1.1 mm. First-cycle and cycle-250 anterior tibial translation varied among the graft tissue types, possibly reflecting an initial "settling in" process. Regardless of the tissue type, ≥75% of the total increase in the anterior tibial translation occurred within the first 125 cycles. CONCLUSIONS: Preconditioning had no significant effect on the progressive increase of anterior tibial translation from the first cycle to cycle 250 for any of the graft tissues tested. CLINICAL RELEVANCE: On the basis of these results, current preconditioning methods appear to be ineffective in reducing progressive increases in anterior knee laxity from cyclic loading.

Use of inertial sensors to predict pivot-shift grade and diagnose an ACL injury during preoperative testing.

BACKGROUND: The pivot-shift (PS) examination is used to demonstrate knee instability and detect anterior cruciate ligament (ACL) injury. Prior studies using inertial sensors identified the ACL-deficient knee with reasonable accuracy, but none addressed the more difficult problem of using these sensors to determine whether a subject has an ACL deficiency and to correctly assign a PS grade to a patient's knee. HYPOTHESIS: Inertial sensor data recorded during a PS examination can accurately predict ACL deficiency and the PS score assigned by the examining physician. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: A total of 32 patients with unilateral ACL deficiency and 29 with intact ACLs in both knees had inertial sensor modules strapped to the tibia and femur of each limb for preoperative PS testing under anesthesia. Support vector machine (SVM) methods assessed PS grades on the basis of these data, with the examiner's clinical grading shift used as ground truth. A fusion of regression and SVM classification techniques diagnosed ACL deficiency. RESULTS: The clinically determined PS grades of all 122 knees were as follows: 0 (n = 69), +1 (n = 23), +2 (n = 27), and +3 (n = 3). The SVM classification analysis was 77% accurate in correctly classifying these grades, with 98% of computed PS grades falling within ±1 grade of the clinically determined value. The system fusion algorithm diagnosed ACL deficiency in an individual with an overall accuracy of 97%. This method yielded 6% false negatives and 0% false positives. CONCLUSION: This study used inertial sensor technology with SVM algorithms to accurately determine clinically assigned PS grades in ACL-intact and ACL-deficient knees. By extending the assessment to a separate group of patients without ACL injury, the inertial sensor data demonstrated highly accurate diagnosis of ACL deficiency.

Measurements of tibial rotation during a simulated pivot shift manoeuvre using a gyroscopic sensor.

PURPOSE: The pivot shift has been correlated with patient-reported outcomes and knee function following ACL injury and reconstruction. Tibial rotation has been recognized as an important component to the pivot shift motion path. However, few methodologies exist to quantify tibial rotation in the clinical setting. The purpose of this study was to validate the use of a wireless gyroscopic sensor to measure axial rotation of the tibia during a manually simulated pivot shift manoeuvre in cadaveric specimens. We hypothesized that integrated gyroscopic measurements of tibial rotation velocity (tibial rotation) would be highly correlated with tibial rotations simultaneously recorded with a rotary potentiometer during a simulated pivot shift motion under intact and ACL-deficient conditions. METHODS: Gyroscopic measurements of rotational velocity were integrated and calibrated to a known arc of rotation. The gyroscope was mounted on the distal tibia with its axis aligned to the tibial shaft. Ten simulations of a pivot shift motion pathway were performed on nine cadaveric knees under intact and ACL-deficient conditions. Logistic regression was used to compare gyroscopic and potentiometer measurements of tibial rotation for both test conditions. RESULTS: Gyroscopic measurements of maximum external tibial rotation during the simulated pivot shift motion pathway were strongly correlated with potentiometer measurements of external tibial rotation in both the intact and ACL-deficient states (R (2) = 0.984). CONCLUSION: The gyroscope evaluated in this cadaveric study was capable of accurately recording tibial rotation during a simulated pivot shift motion pathway.

ACL forces and knee kinematics produced by axial tibial compression during a passive flexion-extension cycle.

Application of axial tibial force to the knee at a fixed flexion angle has been shown to generate ACL force. However, direct measurements of ACL force under an applied axial tibial force have not been reported during a passive flexion-extension cycle. We hypothesized that ACL forces and knee kinematics during knee extension would be significantly different than those during knee flexion, and that ACL removal would significantly increase all kinematic measurements. A 500 N axial tibial force was applied to intact knees during knee flexion-extension between 0° and 50°. Contact force on the sloping lateral tibial plateau produced a coupled internal + valgus rotation of the tibia, anterior tibial displacement, and elevated ACL forces. ACL forces during knee extension were significantly greater than those during knee flexion between 5° and 50°. During knee extension, ACL removal significantly increased anterior tibial displacement between 0° and 50°, valgus rotation between 5° and 50°, and internal tibial rotation between 5° and 15°. With the ACL removed, kinematic measurements during knee extension were significantly greater than those during knee flexion between 5° and 45°. The direction of knee flexion-extension movement is an important variable in determining ACL forces and knee kinematics produced by axial tibial force.

Use of a gyroscope sensor to quantify tibial motions during a pivot shift test.

PURPOSE: The purpose of this preliminary study was to evaluate the use of a gyroscope sensor to record rotations of the tibia about its long axis during a clinical pivot shift examination. METHODS: Ten patients with a unilateral ACL injury were tested under anaesthesia prior to surgery. Each ankle was placed in neutral position, wrapped and stabilized with athletic tape, and a small aluminium plate was taped to the bottom of the foot. A data recovery module was attached to the bottom of each plate using a swivel bracket that allowed alignment of the gyro axis with the long axis of the tibia. The module contained a triaxial gyroscope, battery and circuitry for wireless data broadcast to a laptop computer. Ten pivot shift tests were performed on both knees, and the surgeon's clinical grading of the pivot shift was noted for each limb. Mean values (10 trials) of peak tibial rotational velocity and integrated tibial rotation were compared between knees for each patient during the pivot shift reduction event (external tibial rotation during knee flexion). RESULTS: Five patients (50%) had significantly greater tibial rotation in their injured knee, four showed no difference between knees, and one had significantly greater rotation in the normal knee (p < 0.05). Seven patients (70%) showed greater peak rotational velocity in their injured knee, and three had no difference between the knees (p < 0.05). Correlations of rotation and rotational velocity with clinical pivot shift grade were weak (r2 = 0.09 and 0.19, respectively). CONCLUSIONS: Foot gyroscope measurements did not correctly identify the injured limb in all patients. Peak rotational velocity during the reduction event was a better indicator of ACL deficiency than the integrated rotation. If this technology is to be more useful clinically, gyroscope data may have to be combined with accelerometer data, perhaps with sensors mounted on both the tibia and femur. LEVEL OF EVIDENCE: Diagnostic case-control study, Level III.

Syndesmosis fixation using dual 3.5 mm and 4.5 mm screws with tricortical and quadricortical purchase: a biomechanical study.

BACKGROUND: Grade 3 syndesmosis (high ankle) sprains of the ankle are frequently treated using screws that fix the distal fibula to the tibia. We hypothesized that forces acting on the distal fibula and displacements of the distal fibula relative to the tibia recorded during simulated ankle loading tests would be significantly affected by syndesmosis screw size and the number of engaged tibial cortices. METHODS: Distal fibular forces and displacements were measured after cutting the distal inferior tibiofibular ligaments and fixing the distal fibula to the distal fibula with 2 syndesmosis screws. Screws of 3.5 mm and 4.5 mm were applied with tricortical and quadricortical purchase. RESULTS: There were no significant differences in distal fibular forces or displacements between any combination of screw size and cortical purchase tested. The highest mean fibular force recorded in the study (110.2 N) occurred when 10 N-m of external foot torque was applied to a dorsiflexed ankle loaded with 1000 N axial weight-bearing force. For ankle dorsiflexion and external foot torque tests, the distal fibula always displaced posteriorly with respect to the tibia. Mean displacements of the fibula from 1000 N applied axial weight-bearing force (maximum 0.15 mm) and from 10 N-m of forced foot dorsiflexion (maximum 0.43 mm) were considerably less than those from 10 N-m external foot torque (1.7 mm to 2.7 mm). CONCLUSIONS: Screw size and the number of engaged tibial cortices had no significant effect on mechanical stability of the distal fibula during these tests. Application of external foot torque (internal tibial torque) to a weight-bearing ankle produced the greatest bending displacements of the screws, and should be avoided during rehabilitation to reduce the possibility of screw breakage. CLINICAL RELEVANCE: In terms of mechanical stability, surgeons may have considerable flexibility with regard to screw fixation of high ankle sprains.