Buckle Transducer Research Articles

The effect of surgical approaches and tourniquet application on patellofemoral tracking in total knee arthroplasty

The purpose of this study was to assess the influences of surgical approaches and tourniquet application on the lateral retinacular tension (LRT). Single-setting bilateral total knee arthroplasty was performed in 10 patients, and the medial parapatellar and midvastus approaches were randomly performed on each knee using tourniquet application. The LRT was measured using the buckle transducer before and after each approach. Next, the tourniquet was deflated and the measurement was repeated. After the parapatellar approach, LRT was significantly decreased. Conversely, no significant change was seen after the midvastus approach with the tourniquet inflated. However, in the midvastus approach, LRT was significantly decreased after tourniquet deflation. We concluded that both the parapatellar and midvastus approaches influence patellar tracking and LRT. © 2003 Elsevier Inc. All rights reserved.

Lateral patellar retinaculum tension in patellar instability.

The patellar retinaculum is important in patellar tracking. However, little attention has been paid to the biomechanics of the retinaculum. This study assessed the change in tension of the lateral patellofemoral ligament before and after anteromedial tibial tubercle transfer for patellar instability. Twenty-seven knees in 21 patients were studied and the mean age of the patients at surgery was 19 years. A buckle transducer was clamped on the lateral patellofemoral ligament and the transducer was calibrated to zero with the knee at full extension. The knee then was flexed 30 degrees, 60 degrees, 90 degrees, and 120 degrees, and the transducer recorded changes in tension within the lateral patellofemoral ligament. After anteromedial tibial tubercle transfer, lateral patellofemoral ligament tension was measured in the same manner. Although average lateral patellofemoral ligament tension increased with knee flexion with the maximum at 120 degrees flexion, these changes showed four different patterns measuring variability of patellar instability. An increase of lateral patellofemoral ligament tension after anteromedial tibial tubercle transfer meant that lateral retinacular release should be done concurrently to balance patellar tracking. This information may be useful in deciding the appropriate surgical procedure for each patient.

Dynamics of mallard (Anas platyrynchos) gastrocnemius function during swimming versus terrestrial locomotion.

This study investigates how the contractile function of a muscle may be modulated to accommodate changes in locomotor mode and differences in the physical environment. In vivo recordings of lateral gastrocnemius (LG) activation, force development (measured using tendon buckle transducers) and length change (measured using sonomicrometry) were obtained from mallard ducks (Anas platyrhynchos) as they swam at steady speeds in a water tank and walked or ran on land. LG force recordings were compared with combined lateral and medial gastrocnemius (MG) muscle-tendon force recordings obtained from the contralateral limb, allowing force development by the MG to be estimated relative to that of the LG. Although similar stresses were calculated to act in the LG and MG muscles during terrestrial locomotion (126 and 115 kPa, respectively), stresses were considerably greater in the LG compared with the MG during swimming (62 versus 34 kPa, respectively). During both steady swimming and terrestrial locomotion, the LG developed force while shortening over a considerable range of its length (swimming 23.6 % versus terrestrial 37.4 %). Activation of the muscle occurred near the end of passive lengthening during the recovery stroke, just prior to muscle shortening. As a result, the muscle generated broad positive work loops during both locomotor modes. LG work during swimming (4.8 J x kg(-1)) averaged 37 % of the work performed during terrestrial locomotion (13.1 J x kg(-1)), consistent with the twofold greater force and 58 % greater strain of the muscle during walking and running. Because limb cycle frequency was similar for the two locomotor modes (swimming 2.65 versus terrestrial 2.61 Hz), differences in power output (swimming 12.6 W x kg(-1 )versus terrestrial 32.4 W x kg(-1)) largely reflected difference in work per cycle. Tendon elastic energy savings was a small fraction (<5 %) of the work performed by the muscle, consistent with a fiber-tendon design of these two muscles that favors muscle work to produce limb movement with little tendon strain. These results are consistent with a higher cost of terrestrial locomotion in ducks compared with other, more cursorial birds that may operate their muscles more economically and achieve greater tendon elastic savings.

Stretch-shortening cycle: a powerful model to study normal and fatigued muscle

Stretch-shortening cycle (SSC) in human skeletal muscle gives unique possibilities to study normal and fatigued muscle function. The in vivo force measurement systems, buckle transducer technique and optic fiber technique, have revealed that, as compared to a pure concentric action, a non-fatiguing SSC exercise demonstrates considerable performance enhancement with increased force at a given shortening velocity. Characteristic to this phenomenon is very low EMG-activity in the concentric phase of the cycle, but a very pronounced contribution of the short-latency stretch-reflex component. This reflex contributes significantly to force generation during the transition (stretch-shortening) phase in SSC action such as hopping and running. The amplitude of the stretch reflex component — and the subsequent force enhancement — may vary according to the increased stretch-load but also to the level of fatigue. While moderate SSC fatigue may result in slight potentiation, the exhaustive SSC fatigue can dramatically reduce the same reflex contribution. SSC fatigue is a useful model to study the processes of reversible muscle damage and how they interact with muscle mechanics, joint and muscle stiffness. All these parameters and their reduction during SSC fatigue changes stiffness regulation through direct influences on muscle spindle (disfacilitation), and by activating III and IV afferent nerve endings (proprioseptic inhibition). The resulting reduced stretch reflex sensitivity and muscle stiffness deteriorate the force potentiation mechanisms. Recovery of these processes is long lasting and follows the bimodal trend of recovery. Direct mechanical disturbances in the sarcomere structural proteins, such as titin, may also occur as a result of an exhaustive SSC exercise bout.

Quantification of Achilles Tendon Force Enhancement by Passively Induced Dorsiflexion Stretches

Magnitude of the reflex contribution to force enhancement was investigated in vivo during passive stretches of the Achilles tendon (AT) of one female subject. Thirty passive (5 × 6) dorsiflexions were induced by a motorized ankle ergometer. Achilles tendon force (ATF) was sensed by a buckle transducer applied surgically around the right AT. Single passive stretches resulted in a low but rather linear ATF increase in the absence of EMG (surface electrodes) activity. In the presence of reflexes, a clear ATF enhancement occurred 13–15 ms after the beginning of the EMG reflex responses. In double dorsiflexions at either 1.2 or 1.9 rad · s-1, which were separated by a maintained stretched position of either 40 or 90 ms, the first stretch resulted in initial linear ATF increase, followed by an additional force enhancement during the plateau phase. This reflexly induced increase represented 94 ± 4 N and 184 ± 1 N, respectively, for the 40 and the 90 ms plateaus, corresponding to 210 ± 85% and 486 ± 177% enhancements as compared to the first passive stretch effect. The results suggest further that timing of the stretch during the twitch response influences the magnitude and rate of force potentiation.

Effect of ankle and knee position on tension in the Achilles tendon.

The purpose of this study was to evaluate the relative contributions of ankle and knee position to tension in the Achilles tendon and to determine whether there exists a position of plantarflexion at which the passive tensioning effect of knee extension is eliminated. Seven matched pairs of fresh-frozen cadaver lower extremities were tested. A buckle transducer was used to measure forces in the tendon throughout the full range of knee motion, with the hindfoot fixed. Positioning the hindfoot in 20 degrees to 25 degrees of plantarflexion effectively eliminates tension in the Achilles tendon, regardless of knee position. This information is directly applicable both to the nonoperative treatment of ruptures of the Achilles tendon employing a short leg cast and to surgical repairs, in which tension must be controlled precisely.

Ligament force and joint motion in the intact ankle: a cadaveric study.

The aims of this study were to measure the forces in the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) and the motion in the tibiotalar and subtalar joints during simulated weight-bearing in eight cadaver ankle specimens. An MTS test machine was used to apply compressive loads to specimens held in a specially designed testing apparatus in which the ankle position (dorsiflexion-plantarflexion and supination-pronation) could be varied in a controlled manner. The forces in the ATFL and CFL were measured with buckle transducers. Tibiotalar motion and total ankle joint motion were measured with an instrumented spatial linkage. The specimens were positioned sequentially at 10 degrees dorsiflexion, neutral, and 10 degrees and 20 degrees plantarflexion, and this sequence was repeated at 15 degrees supination, neutral pronation/supination, and 15 degrees pronation. Force and motion measurements were recorded in each of these positions with and without a 375 N compressive load simulating weight-bearing. From 10 degrees dorsiflexion to 20 degrees plantarflexion, all motion occurred in the tibiotalar joint. In contrast, the ratio of subtalar motion to tibiotalar motion was 3:1 for supination-pronation and 4:1 for internal-external rotation. Inverse loading patterns were observed for the ATFL and CFL from plantarflexion to dorsiflexion. Compressive loading did not affect CFL tension, but it magnified the pattern of increasing ATFL tension with plantarflexion. The largest increase in ATFL force was observed in supination and plantarflexion with a compressive load (76 +/- 23 N), whereas CFL tension mainly increased in supination and dorsiflexion with a compressive load (109 +/- 28 N). In conclusion, the results showed that the ATFL acted as a primary restraint in inversion, where injuries typically occur (combined plantarflexion, supination and internal rotation). Also, the subtalar joint was of primary importance for normal supination-pronation and internal-external rotation.

In vivo forces during remodeling of a two-segment anterior cruciate ligament graft in a goat model.

An existing goat model was used to measure in vivo graft forces during walking, to determine if the forces set at surgery change over time under the same external load and if the forces in the graft during in vivo function can be dictated by the forces set at surgery. The anterior cruciate ligament was reconstructed in 12 goats with use of a composite graft consisting of a bone-patellar tendon-bone autograft and a synthetic augmentation segment. The forces in the graft segments were established intraoperatively by a force-setting technique. In five animals, the tendon segment was set to carry 90% of the total graft force, and in the seven other animals, the augmentation segment was set to carry 90% of the total force. The total graft force was the same in all animals. Graft forces due to anterior tibial loads of 67 N were measured before and after fixation and 6 weeks after surgery with the use of buckle transducers mounted extra-articularly over the anterior tibia. They were also measured during straight, level walking at 6 weeks. The forces changed significantly from just after surgery to 6 weeks later, such that the initially set load-sharing was eliminated by 6 weeks. At 6 weeks, a relatively smooth gait had been achieved, and the maximum total graft force in each animal during walking averaged 35 N and was of similar magnitude to forces generated by the anterior tibial loads of 67 N with the animal anesthetized. After fixation, forces in the tendon graft segments were significantly different between the group with high set forces and that with low set forces. At 6 weeks, when functional joint loads were approaching normal levels, the graft segment forces for the two groups were not significantly different. Load-sharing between tendon and augmentation segment and load in the tendon segment at 6 weeks could not be dictated at surgery.

Mechanics of the anterior drawer and talar tilt tests. A cadaveric study of lateral ligament injuries of the ankle.

We analyzed the changes in lateral ligament forces during anterior drawer and talar tilt testing and examined ankle joint motion during testing, following an isolated lesion of the anterior talofibular ligament (ATFL) or a combined lesion of the ATFL and calcaneofibular ligament (CFL). 8 cadaver specimens were held in a specially designed testing apparatus in which the ankle position (dorsiflexion-plantarflexion and supination-pronation) could be varied in a controlled manner. Ligament forces were measured with buckle transducers, and joint motion was measured with an instrumented spatial linkage. An anterior drawer test was performed using an 80 N anterior translating force, and a talar tilt test was performed using a 5.7 Nm supination torque with intact ligaments, after sectioning of the ATFL, and again after sectioning of the CFL. The tests were repeated at 10 degrees dorsiflexion, neutral, and 10 degrees and 20 degrees plantarflexion. In the intact ankle, the largest increases in ATFL force were observed during testing in plantarflexion, whereas the largest increases in CFL force were observed in dorsiflexion. Isolated ATFL injury caused only small laxity changes, but a pronounced increase in laxity was observed after a combined CFL and ATFL injury.

In Vivo Tension and Mechanical Properties of the Patellar Tendon in Growing Rabbits.

Changes in the morphology and mechanical properties of the patellar tendon with maturation were studied in rabbits aged 1, 2, and 6 months. The length, cross-sectional area, tensile strength, and tangent modulus of the tendon significantly increased with age. The rate of increase in the maximum load which was estimated by multiplying tensile strength by the cross-sectional area was similar to that in body weight. Tension in the patellar tendon was measured in vivo with a buckle transducer. The rate of age-related increase in the peak tension measured during normal locomotion was almost equal to that in body weight. These results indicate that the pateliar tendon responds well to increases of in vivo tension which occurs as part of the maturation process and exhibits corresponding increases in mechanical strength.

The function of the long dorsal sacroiliac ligament: its implication for understanding low back pain.

In embalmed human bodies the tension of the long dorsal sacroiliac ligament was measured during incremental loading of anatomical structures that are biomechanically relevant. To assess the function of the long dorsal sacroiliac ligament. In many patients with aspecific low back pain or peripartum pelvic pain, pain is experienced in the region in which the long dorsal sacroiliac ligament is located. It is not well known that the ligament can be easily palpated in the area directly caudal to the posterior superior iliac spine. Data on the functional and clinical importance of this ligament are lacking. A dissection study was performed on the sacral and lumbar regions. The tension of the long dorsal sacroiliac ligament (n = 12) was tested under loading. Tension was measured with a buckle transducer. Several structures, including the erector spinae muscle, the posterior layer of the thoracolumbar fascia, the sarcotuberous ligament, and the sacrum, were incrementally loaded (with forces of 0-50 newtons). The sacrum was loaded in two directions, causing nutation (ventral rotation of the sacrum relative to the iliac bones) and counternutation (the reverse). Forced nutation in the sacroiliac joints diminished the tension and forced counternutation increased the tension. Tension in the long dorsal sacroiliac ligament increased during loading of the ipsilateral sacrotuberous ligament and erector spinae muscle. The tension decreased during traction to the gluteus maximus muscle. Tension also decreased during traction to the ipsilateral and contralateral posterior layer of the thoracolumbar fascia in a direction simulating contraction of the latissimus dorsi muscle. The long dorsal sacroiliac ligament has close anatomical relations with the erector spinae muscle, the posterior layer of the thoracolumbar fascia, and a specific part of the sacrotuberous ligament (tuberoiliac ligament). Functionally, it is an important link between legs, spine, and arms. The ligament is tensed when the sacroiliac joints are counternutated and slackened when nutated. The reverse holds for the sacrotuberous ligament. Slackening of the long dorsal sacroiliac ligament can be counterbalanced by both the sacrotuberous ligament and the erector muscle. Pain localized within the boundaries of the long ligament could indicate among other things a spinal condition with sustained counternutation of the sacroiliac joints. In diagnosing patients with aspecific low back pain or peripartum pelvic pain, the long dorsal sacroiliac ligament should not be neglected. Even in cases of arthrodesis of the sacroiliac joints, tension in the long ligament can still be altered by different structures.

In vivo muscle force and elastic energy storage during steady-speed hopping of tammar wallabies (Macropus eugenii)

In order to evaluate the role of elastic energy recovery in the hopping of macropodids, in vivo measurements of muscle&shy;tendon forces using buckle force transducers attached to the tendons of the gastrocnemius (G), plantaris (PL) and flexor digitorum longus (FDL) of tammar wallabies were made as the animals hopped on a treadmill at speeds ranging from 2.1 to 6.3 m s-1. These muscles and tendons constitute the main structures that are most important in energy storage and recovery. Electromyographic recordings from the lateral gastrocnemius and plantaris muscles, together with high-speed films (200 frames s-1) and video (60 fields s-1), were also used to correlate muscle activation and kinematic patterns of limb movement with force development. On the basis of in situ calibrations of the buckle transducers, we found that muscle forces and elastic energy storage increased with increased hopping speed in all three muscle&shy;tendon units. Elastic energy recovery reached a maximum of 25 % of metabolic energy expenditure at 6.3 m s-1 and is probably greater than this at higher speeds. Force sharing among the three muscles was consistently maintained over this range of speeds in terms of recruitment. Although forces and stresses were generally comparable within the gastrocnemius and plantaris muscles, maximal tendon stresses were considerably greater in the gastrocnemius, because of its smaller cross-sectional area (peak muscle stress: 227 versus 262 kPa; peak tendon stress: 36 versus 32 MPa, G versus PL). As a result, energy storage was greatest in the gastrocnemius tendon despite its much shorter length, which limits its volume and, hence, energy storage capacity, compared with PL and FDL tendons. Forces and stresses (17 MPa maximum) developed within the FDL tendon were consistently much lower than those for the other two tendons. Peak stresses in these three tendons indicated safety factors of 3.0 for G, 3.3 for PL and 6.0 for FDL. The lower stresses developed within the tendons of the plantaris and, especially, the flexor digitorum longus may indicate the need to maintain sufficient stiffness for phalangeal control of foot placement, at the expense of reduced strain energy recovery.

Experimental measurement of ligament force, facet force, and segment motion in the human lumbar spine

Facet forces, longitudinal ligament loads, and vertebral body motion were experimentally measured in five fresh human lumbar spine segments, L1–L2. Strain gages on the bone surface were used to quantify facet loads. Buckle transducers were used to measure anterior and posterior longitudinal ligament loads. The three-dimensional motion of the motion segment was measured with an instrumented spatial linkage. The facets were found to carry no load in flexion, large loads during extension (205 N at a 10 Nm moment and a 190 N axial load), torsion (65 N at a 10 Nm moment and a 150 N axial load), and lateral bending (78 N at a 3 Nm moment and a 160 N axial load). The facet contact site on the inferior articular process of L1 was found to move inferiorly to a position of tip impingement near the lamina as extension moments increased. Impingement occurred in the range of 4–6 Nm extension. The posterior and anterior longitudinal ligaments were predominatly loaded in flexion and extension, respectively. No ligament loads occurred in lateral bending and torsion. A 1 cm strip of the anterior longitudinal ligament carried loads up to 130 N at the largest extension moment of 11.4 Nm. The posterior longitudinal ligament had a 60 N load at the largest flexion moment of 7.1 Nm. There was no pre-load in the ligament detectable with the buckle transducers (>4 N). The facets and ligaments began carrying load immediately with applied load, without a lax region. The experimental technique developed and used provides a good tool for obtaining simultaneous facet joint loads, ligament loads, and vertebral body motion without altering the motion segment.

Relationship between changes in length and force in in vitro reconstructed anterior cruciate ligament.

The effect of tibial and femoral attachment site on the length change and force of an anterior cruciate ligament graft during unloaded flexion in eight cadaver specimens was examined. Two tibial sites (anteromedial and central portion of the anterior cruciate ligament attachment) and three femoral sites (anterior and central portions of the anterior cruciate ligament attachment, and over-the-top) were evaluated. Graft length changes between all combinations of attachment sites were measured from full extension to 150 degrees of passive flexion at 15 degrees intervals using the displacement of a 2-mm inextensible cord. The anterior cruciate ligament was then reconstructed using a Kennedy Ligament Augmentation Device, and graft forces at the same angles of passive flexion were measured with a buckle transducer. Graft length change and force were more affected by the femoral attachment site than the tibial site. There was a close correlation between length change and force measurements in flexion, but not near extension. The pattern of force and length change versus flexion angle for a given combination of attachment sites sometimes varied over the knees tested. Our results suggest that intraoperative isometry measurements are worthwhile for indicating an overloaded graft in flexion; however, length changes near extension may not adequately reflect graft force, creating the possibility that a graft may be more highly loaded than realized.

Biomechanical effect of a two-segment anterior cruciate ligament graft with separate femoral attachments and differing levels of prescribed load sharing.

The objective of this study was to analyze the biomechanical effect of varying the level of prescribed load sharing between two segments of an anterior cruciate ligament (ACL) graft, and of separating the femoral attachments of these segments. Total anterior-posterior (AP) laxity was measured using an instrumented spatial linkage. Forces in graft segments were measured using buckle transducers. The two-segment graft was formed using the middle third of the patellar tendon with bone blocks and a synthetic augmentation device. Proximal fixation was obtained using a fixture which allowed changing the individual locations of the femoral attachments of the tendon and augmentation segments. Distal fixation was achieved using a force-setting device which allowed the loads in each segment to be set to prescribed levels. Total graft force, load sharing, and total AP laxity were recorded during the application of 100-N AP tibial loads at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 110 degrees flexion, for various combinations of load sharing set at extension and locations of femoral attachment sites. The load sharing, total graft force, and AP laxity during AP loading at the five test flexion angles were not significantly affected by changing the prescribed level of load sharing set at extension for a given femoral attachment configuration. However, varying the separate hole locations of the graft segments for a given level of load sharing significantly affected load sharing, total graft force, and AP laxity. If the tendon graft was located posteriorly (on the medial surface of the lateral femoral condyle) and the augmentation segment proximally, the augmentation carried a greater portion of the total force in flexion. If the augmentation segment was changed to a more posterosuperior location and the tendon posteroinferior, the tendon carried a higher percentage of the total force in flexion. AP laxity in most reconstruction states was significantly greater than in the normal joint with an intact ACL. The nature of the load sharing between the graft segments under AP tibial load over the flexion range can be controlled by the appropriate choice of the segments' femoral attachment locations.

Ligament tension pattern in the flexed knee in combined passive anterior translation and axial rotation

Twenty-two fresh-frozen specimens were used to measure tensions generated in selected bands of the major ligaments of the flexed knee (40-90 degrees) when an axially prerotated tibia is subjected to passive anterior shear and when an anteriorly pretranslated tibia is subjected to passive axial torque. The tensions were measured using the buckle transducer attached to the anteromedial band of the anterior cruciate ligament [ACL (am)], the posterior fibers of the posterior cruciate ligament [PCL (pf)], the long fibers of the medial collateral ligament [MCL (lf)], and in the total lateral collateral ligament [LCL]. The knee specimens were subjected to the combined motions in a 6-df passive loading apparatus. The results indicated that the joint resistance to anterior translation increased markedly with internal prerotation and only marginally with external prerotation. This increase in joint resistance, however, was associated with a decrease in ACL function. It has been inferred that the posterior structures, capsular and meniscal, contribute significantly to joint resistance when the tibia is prerotated in either sense. For internal prerotation, the interference between the medial femoral condyle and the central tibial eminence was found to be an additional mechanism of resistance to anterior translation. Also, it has been found that although the ACL (am) tension increased with internal rotation in the normal case, it decreased with internal rotation in the presence of an anterior pretranslation. It is concluded that ACL response to combined joint motion cannot be ascertained by a simple summation of its responses to individual motions.

In Vivo Measurement of Tension in the Rabbit Patellar Tendon.

Tension developing in the right and left patellar tendon was measured in vivo with a buckle transducer in six rabbits. Peak tension measured during normal running was quite large and ranged from 44 N to 123 N, which is from 130% to 380% of body weight. Maximum load of the whole patellar tendon, which is the failure load determined from tensile testing, was 799±40 N (Mean±S. E.) : it is 7 to 18 times as much as the in vivo peak tension. Right patellar tendons of the other eight rabbits were over. stressed by decreasing the cross-sectional area by about 50% by partial cut-removal of both sides of the tendon. After this surgical treatment, these rabbits were allowed their daily activities in cages for 3 or 6 weeks. Tension developed in the patellar tendon was measured in vivo using the buckle transducer. There were no significant differences in the tension developed in the tendon inside the body between the treated and intact knees, which indicated that the stress applied to the tendon was increased to about 200% by the treatment of partial cut-removal.

Method for setting total graft force and load sharing in augmented ACL grafts

The objective of this study was to develop a method for obtaining a controllable and reproducible immediate postoperative mechanical state in a knee with an anterior cruciate ligament (ACL) reconstruction. This method, called the force-setting technique, was demonstrated using a composite graft consisting of the middle third of the patellar tendon with bone blocks (PT) and the ligament augmentation device (LAD). The total graft force was set to match the force in the intact ACL at 30 degrees flexion with the knee under the same standardized external load, while at the same time the load sharing between the biologic and augmentation components was controlled. The total graft force was set to match the ACL force three separate times in each knee, with ratios of load sharing set at the following levels: 50% PT-50% LAD, 25% PT-75% LAD, and 75% PT-25% LAD. ACL, PT, LAD, and collateral forces were measured using buckle transducers, and three-dimensional knee motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to eight specimens at 0 degree, 30 degrees, 60 degrees, and 90 degrees flexion with an intact ACL, an excised ACL, and the three load-sharing reconstruction states. The total graft force could be consistently set to within an average of 2% of the intact ACL force at 30 degrees flexion, and load sharing between the graft segments could be set to within an average of 5.1% of the desired ratio at 30 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting graft force in surgical reconstruction of the anterior cruciate ligament

The effect of the maximum unloaded graft length (Lo) and femoral fixation hole location on graft force with the knee under anteriorly directed tibial loads was measured in five fresh cadaver knees with a reconstruction of the anterior cruciate ligament (ACL). The reconstruction was performed using a composite graft consisting of the semitendinosus and gracilis tendons augmented with the Kennedy ligament augmentation device (LAD). Buckle transducers were used to measure ligament and graft forces. The total graft force was adjusted to match the intact ACL at 30 degrees flexion using a force-setting method so that a standardized reference configuration could be repeatedly obtained. The graft force was highly sensitive to Lo, typically changing by 50% with a change in Lo of 3 mm. Variation in femoral hole location of 5 mm anterior, posterior, proximal, and distal to the anatomic position produced changes in graft force, particularly at 60 degrees and 90 degrees flexion; however, these changes were not statistically significant. The effect of femoral hole location varied considerably between knees. This variability makes predicting proper hole placement difficult, and suggests the need to adjust each knee at surgery to account for this variable femoral hole position sensitivity.

The effect of an iliotibial tenodesis on intraarticular graft forces and knee joint motion

Lateral extraarticular reconstructions are used as isolated procedures in knees with moderate rotatory instability and as "backups" in knees requiring primary repair or intraarticular reconstruction for major rotatory instability. We used an experimental knee testing system to analyze the immediate postoperative mechanical effect of an iliotibial band tenodesis on an intraarticular reconstruction of the ACL in fresh cadaver knees using a composite graft consisting of a bone-patellar tendonbone segment augmented with the Kennedy Ligament Augmentation Device (LAD, 3M Co., St. Paul, MN). The intraarticular graft was standardized by using a forcesetting technique. Ligament and graft forces were measured using buckle transducers, and joint motion was measured using an instrumented spatial linkage as 90 N anteriorly directed tibial loads were applied to seven fresh knee specimens at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. The following knee states were tested in each specimen: intact ACL, excised ACL, intraarticular reconstruction, intraarticular reconstruction with the tenodesis added, and tenodesis with the intraarticular reconstruction added. Adding the iliotibial band tenodesis to an existing standardized intraarticular reconstruction significantly decreased the force in the ACL composite graft by an average of 43%. When the standardized intraarticular reconstruction was added to an existing tenodesis, the graft forces were an average of 15% below the level of when the reconstruction was performed alone. The force in the tenodesis was significantly less than the composite graft force at extension; however, the differences between the tenodesis and total graft force were not significant from 30 degrees to 90 degrees of flexion.(ABSTRACT TRUNCATED AT 250 WORDS)