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Background: A recent development in valgus-producing knee braces has been the adjustable “unloader” brace. The purpose of this study was to compare the effectiveness of off-the-shelf and custom-made patient-adjustable, valgus-producing knee unloader braces in relieving pain, reducing stiffness, and improving function and in reducing varus angulation and the peak adduction moments about the knee during gait and stair-stepping in patients with painful varus gonarthrosis of the knee. Methods: Ten adult patients served as their own controls for the measurement of baseline values and then wore each of the two braces, one after the other, for four to five weeks in a random order. Pain, stiffness, and function were assessed with the Western Ontario and McMaster Universities Osteoarthritis Index. Gait and stair-stepping were evaluated with a three-dimensional motion analysis system and multicomponent force platform. Full-length (hip, knee, and ankle) standing anteroposterior radiographs were used to determine alignment of the knee. Results: Both braces significantly reduced pain and stiffness (p < 0.05), with the custom brace reducing stiffness significantly more than the off-the-shelf brace (p = 0.030). The custom brace significantly improved function (p = 0.010) and reduced the peak knee adduction moments during gait (p = 0.033) and stair-stepping (p = 0.002) compared with baseline values and compared with the off-the-shelf brace (p = 0.029 and p = 0.027, respectively). The custom brace significantly reduced varus angulation of the knee by 1.5° compared with baseline (p = 0.001) and by 1.3° compared with the off-the-shelf brace (p = 0.009). The off-the-shelf brace did not significantly reduce the varus angle. Conclusions: We investigated only the short-term effects of custom and off-the-shelf patient-adjustable valgus-producing knee “unloader” braces and found that patients with varus gonarthrosis of the knee may benefit significantly with respect to pain relief and reduced stiffness from use of either brace. However, such patients may experience additional significant benefit in improved function and reduced stiffness, varus angulation, and medial compartment loading of the knee from use of the custom-made patient-adjustable brace. Level of Evidence: Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.

Seven cadaveric knees were used to investigate the effects of removal and reconstruction of the anterior cruciate ligament with a bone-patellar tendon-bone graft on contact characteristics of the patellofemoral joint during physiologic levels of quadriceps muscle loads at 30 degrees, 60 degrees, and 90 degrees of knee flexion. Loads were applied to the quadriceps tendon to equilibrate externally applied flexion moments equivalent to one-third of values for maximum isometric extension moments. Patellofemoral contact areas and pressures were measured using pressure-sensitive film. Excision of the anterior cruciate ligament resulted in significant decreases in the total patellofemoral contact area by as much as 94 mm2 (68%), the medial facet contact area by as much as 55 mm2 (93%), the combined average contact pressure by 0.7 MPa (21%), the medial facet average contact pressure by 2.3 MPa (70%), the combined peak contact pressure by 3.0 MPa (38%), and the medial facet peak contact pressure by 5.4 MPa (76%), all at 30 degrees of knee flexion. Excision of the anterior cruciate ligament also resulted in significant decreases in total, medial facet, and lateral facet patellofemoral contact areas at 60 degrees and 90 degrees of knee flexion. Intraarticular reconstruction returned these to levels not significantly different from those of the intact knee.

Changes in the tibiotalar contact characteristics were investigated using eight fresh frozen cadaver ankle specimens to further develop an established model of the acquired flatfoot deformity. The deformity was simulated by sectioning the tendons and ligaments of the ankle and foot that normally support the longitudinal arch. Axial loads of 1,350 N were applied to the foot in a neutral position in both the intact specimen and flatfoot model. The flatfoot condition resulted in significant lateral shifts of 5.28 mm in global contact area and 11.26 mm in the location of peak pressure, and in a small but significant posterior shift of 1.14 mm in global contact area. The flatfoot condition also resulted in a significant, 35%, reduction in contact area. Significant increases in mean pressure, 14%, and peak pressure, 13%, were also found, but were not in proportion to the relatively large decrease in contact area. This suggests a transfer of load off of the talar dome. Increased loading of the lateral facet and fibula are suspected. The lateral shift in the contact region created a local increase in mean contact pressure that may be responsible for long term degenerative changes in patients with this deformity.

Tripping over obstacles and imbalance during gait were reported as two of the most common causes of falls in the elderly. Imbalance of the whole body during obstacle crossing may cause inappropriate movement of the lower extremities and result in foot-obstacle contact. Thus, this study was performed to investigate the effect of obstacle height on the motion of the whole body's center of mass (COM) and its interaction with the center of pressure (COP) of the stance foot while negotiating obstacles. Six healthy young adults were instructed to perform unobstructed level walking and to step over obstacles of heights corresponding to 2.5, 5, 10, and 15% of the subject's height, all at a comfortable self-selected speed while walking barefoot. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole body's COM. Stepping over the higher obstacles resulted in significantly greater ranges of motion of the COM in the anterior-posterior and vertical directions, a greater velocity of the COM in the vertical direction, and a greater anterior-posterior distance between the COM and COP. In contrast, the motion of the COM in the medial-lateral direction was less likely to be affected when negotiating obstacles of different heights.

Twenty fresh frozen hand specimens from cadavers were studied. Physiologic levels of extrinsic muscle loads were applied to the extrinsic flexor tendons of the index finger to simulate tip pinch of the finger on a fixed plate. The acute effects of transection of the radial collateral ligament and accessory radial collateral ligament (radial collateral ligament complex) with and without transection of the dorsal capsule and volar plate on the position of the proximal phalanx with respect to the metacarpal bone of the index finger were investigated. The acute effects of reconstruction of the radial collateral ligament, for each of two different surgical techniques, on the position of the proximal phalanx also were investigated. The spatial positions of the metacarpal bone and proximal phalanx were measured with a six-degree-of-freedom digitizing system for flexion angles from 0 degrees to 90 degrees in increments of 15 degrees. Transection of the radial collateral ligament complex resulted in significant increases in ulnar deviation (adduction) of the proximal phalanx and in volar translation. Additional transection of the dorsal capsule and volar plate caused significant increases in ulnar deviation, pronation, volar translation, and ulnar shift. The first surgical technique, one traditionally used to reconstruct the metacarpophalangeal joint of the thumb, failed to return the three-dimensional position of the proximal phalanx on the metacarpal head of the index finger to normal. The second surgical technique, based on anatomy, returned the position of the proximal phalanx to levels not statistically different from normal for most flexion angles.

We studied 7 younger and 5 older patients who had rotating-hinge total knee replacements, 10 patients who had semiconstrained total knee replacements, and 8 younger and 11 older healthy control subjects to determine the effects of the rotating-hinge device on gait and stair stepping. The younger patients with the rotating-hinge device had few significant differences from the younger control subjects during gait or stair stepping. The older patients with the rotating-hinge device had several significant differences from both the older control subjects and subjects with the semiconstrained device during gait and stair stepping. Nevertheless, the proportions of older patients with the 2 devices who were able to perform the step-on activity for the highest step were the same.

Patellofemoral pain may be associated with anterior cruciate ligament deficiency or may occur after anterior cruciate ligament reconstruction. We investigated the effects of the removal and reconstruction of the anterior cruciate ligament on the kinematics of the tibiofemoral and patellofemoral joints during physiologic levels of quadriceps muscle loads in seven cadaveric knees. A bone-patellar tendon-bone graft was used for intraarticular reconstruction of the anterior cruciate ligament. The spatial positions of the tibiofemoral and patellofemoral joints were measured between 0 degrees and 90 degrees of knee flexion in 15 degrees increments with a six degree-of-freedom digitizing system. Excision of the anterior cruciate ligament resulted in statistically significant increases in anterior tibial translation between 0 degrees and 90 degrees and valgus tibial rotation between 30 degrees and 90 degrees; intraarticular reconstruction returned these to levels not significantly different from those of the intact knee. Excision of the anterior cruciate ligament resulted in significant increases in lateral patellar tilt, ranging from 6.3 degrees to 9.0 degrees between full extension and 90 degrees of knee flexion, and in lateral patellar shift, ranging from 2.9 mm at 15 degrees of knee flexion to 5.9 mm at 90 degrees; intraarticular reconstruction returned these to levels not significantly different from those of the intact knee. Neither removal nor reconstruction of the anterior cruciate ligament significantly affected tibial internal-external rotation, patellar flexion, patellar mediolateral rotation, patellar anteroposterior translation, or patellar proximodistal translation.

This study was performed to test the hypothesis that the motion of the lower extremities when stepping over obstacles is governed by the criterion of minimum mechanical energy. The trajectories of the swing ankle during level walking and when stepping over obstacles of 51, 102, 153, and 204 mm heights were predicted and measured for eight healthy young adults. The predictions were made with a planar, seven-link linkage model based on the criterion of minimum mechanical energy using the method of dynamic programming. When stepping over obstacles, the predicted trajectories of the swing ankle were just high enough for the swing toe to clear the obstacles. The clearances measured between the obstacle and toe were significantly larger than those predicted. When stepping over obstacles the levels of work required to generate the measured trajectories were significantly larger (p < or = 0.002) than those required to produce the predicted trajectories. The amount of work necessary to generate the measured or predicted trajectories increased linearly (significant at p < or = 0.022) with obstacle height and, except when predicting the trajectory for the lowest obstacle, was significantly greater than that required when walking on level ground (p < 0.02). Thus, conservation of energy was found to become a less dominant criterion for governing the motion of the body when crossing obstacles than when walking on level ground.

We modeled an intraarticular anterior cruciate ligament graft and investigated the effects of attachment orientation and twist of the graft on its isometry during quadriceps muscle loading. Physiologic levels of quadriceps muscle loads were applied to 15 intact cadaveric knees. We measured the changes in distance between points on the tibia and femur for knee flexion angles between 0 degree and 120 degrees using a three-dimensional digitizer. Selected points on the tibia and femur, representing graft attachment sites, allowed us to model the graft as a broad band. Distance was used to approximate graft fiber length. A 180 degrees twist in the graft significantly reduced the maximal range of changes in distance when the graft was attached in the anteroposterior direction. Range is defined as the difference between the largest and smallest changes in distance among the fibers of the graft for a given angle of flexion. This reduction enhanced isometry among the fibers of the graft. Enhanced isometry would be expected to enhance load sharing among these fibers, thereby increasing the overall strength of the graft. For a graft 10 mm wide and 4 mm thick, the dimensions of a typical patellar tendon graft, the best overall isometry was found when the breadth of the graft was attached to the tibia in the mediolateral direction, to the femur along the most isometric line, and with a 180 degrees twist in the graft.

We report the effects of femoral tunnel position and graft tensioning technique on posterior laxity of the posterior cruciate ligament-reconstructed knee. An isometric femoral tunnel site was located using a specially designed alignment jig. Additional femoral tunnel positions were located 5 mm proximal and distal to the isometric femoral tunnel. With the graft in the proximal femoral tunnel, graft tension decreased as the knee flexed; with the graft in the distal femoral tunnel, graft tension increased as the knee flexed. When the graft was placed in the isometric femoral tunnel, a nearly isometric graft tension was maintained between 0 degrees and 90 degrees of knee flexion. One technique tested was tensioning the graft at 90 degrees of knee flexion while applying an anterior drawer force of 156 N to the tibia. This technique restored statistically normal posterior stability to the posterior cruciate ligament-deficient knee between 0 degrees and 90 degrees for the distal femoral tunnel position, between 0 degrees and 75 degrees for the isometric tunnel position, and between 0 degrees and 45 degrees for the proximal tunnel position. When the graft was tensioned with the knee in full extension and without the application of an anterior drawer force, posterior translation of the reconstructed knee was significantly different from that of the intact knee between 15 degrees and 90 degrees for all femoral tunnel positions.

We investigated the changes in distance between Gerdy's tubercle on the tibia and points on the posterior two thirds of the lateral surface of the lateral femoral condyle and adjacent lateral femoral shaft in 15 cadav eric knees. A three-dimensional digitizer was used to quantify motion of the knee during flexion ranging from full extension to 120° of flexion. Four load states were applied: internal, external, and neutral rotation, and quadriceps muscles loads based on one third of values in the literature for maximal isometric quadriceps muscles moments. The femoral location most isometric to Gerdy's tubercle was found to be strongly influenced by the load state. A 1.0 cm wide iliotibial band tenodesis was mod elled by five straight lines arising from Gerdy's tu bercle and attaching to a simulated washer at the junction of the lateral femoral condyle and shaft. Using this model and the motion data obtained from the cadavers, we investigated the effects of quadri ceps muscles loading and external rotation of the knee on changes in the distances between these tibial and femoral attachments for each of the five lines. A 180° twist modelled into the tenodesis sig nificantly reduced the range of changes in distance (difference between the largest and smallest changes in distance among the lines for a given angle of flex ion) for both of these load states. Therefore, a 180° twist in the tenodesis can enhance isometry among the fibers of the tenodesis. This implies that a 180° twist can enhance load sharing among the fibers of the tenodesis and, therefore, enhance the overall strength of the tenodesis.

Strain in the anteromedial fibers of the anterior cruciate ligament [ACL(am)] was studied in six cadaver knees. ACL(am) strain was measured in five knees during the application of isometric quadriceps forces alone and simultaneously applied isometric quadriceps and hamstrings forces at 10 degrees increments from 0 degrees to 90 degrees of knee flexion. ACL(am) strain during muscle loading was measured with respect to the ACL(am) strain measured with the knee in its resting position (neutral or near neutral position). A sixth knee was used to investigate the reproducibility of the resting position and quadriceps-induced ACL(am) strains. The strains induced in the ACL(am) by the quadriceps were significantly greater than 0 at knee flexion angles from 0 to 40 degrees and not significantly different from 0 for 50 to 90 degrees. The ACL(am) strains induced by simultaneously applied hamstrings and quadriceps forces were not significantly different from 0 at any of the knee flexion angles tested. Simultaneously applied hamstrings and quadriceps forces significantly reduced ACL(am) strain at 10, 20, and 90 degrees of knee flexion compared to the ACL(am) strain induced by quadriceps forces alone. The hamstrings are potentially capable of both significantly reducing and negating quadriceps-induced ACL(am) strain at 10 and 20 degrees of knee flexion.

Injuries to the ulnar collateral ligament (UCL) of the metacarpophalangeal joint of the thumb are common and may result in functional instability of the joint. Eight cadaveric hands were studied. Physiologic levels of muscle loads were applied to the extrinsic flexor tendon of the thumb to simulate tip pinch of the thumb. We investigated the effects of transection of the UCL and accessory UCL (UCL complex) with and without transection of the dorsal capsule and volar plate and of reconstruction of the UCL, for 2 surgical techniques, on the position of the proximal phalanx with respect to the thumb metacarpal. The spatial positions of the metacarpal and proximal phalanx were measured with a 6 degrees of freedom digitizing system for flexion angles from 0 degrees to 60 degrees in 15 degrees increments. Transection of the UCL complex, dorsal capsule, and volar plate (ulnar capsuloligamentous structures) of the metacarpophalangeal joint did not affect radioulnar deviation or radioulnar shift, but did produce significant increases in supination by 8 degrees and volar translation by 2 mm at 45 degrees and 60 degrees compared with those found for the intact joint. The UCL was reconstructed with a tendon graft using the autogenous extensor digiti quinti. The first surgical technique, a traditional technique, and the second surgical technique, a technique based on anatomy, returned the position of the proximal phalanx on the metacarpal head to normal, with the exceptions of volar translation of the proximal phalanx at 60 degrees and trends toward abnormal supination of the proximal phalanx for flexion angels of 45 degrees and 60 degrees.

The relationships between the lengths of the ligaments and kinematics of the knee and quadriceps load, for low to physiologic levels of quadriceps loads, have not previously been studied. We investigated the effects of increasing levels of quadriceps force, necessary to balance increasing levels of externally applied flexion moments, on the kinematics of the tibiofemoral joint and on the separation distances between insertions of selected fibers of the major ligaments of the knee in twelve cadavera. Static measurements were made using a six-degree-of-freedom digitizer for flexion angles ranging from 0 to 120 deg in 15 deg increments. Quadriceps generated extension of the knee was performed by applying loads to the quadriceps tendon to equilibrate each of four magnitudes of external flexion moments equivalent to 8.33, 16.67, 25.00, and 33.33 percent of values previously reported for maximum isometric extension moments. The magnitude of quadriceps force increased linearly (p < 0.0001) as external flexion moment increased throughout the entire range of flexion. Anterior translation, internal rotation, and abduction of the tibia increased linearly (p < 0.0001, p < 0.001, p < 0.001) as external flexion moment and, hence, quadriceps load increased. For the fibers studied, the anterior cruciate ligament (p < 0.0076), posterior cruciate ligament (p < 0.0001), and medial collateral ligament (p < 0.0383) lengthened linearly while the lateral collateral ligament (p < 0.0124) shortened linearly as quadriceps load increased. Based on these results for low to physiologic levels of quadriceps loads, it is reasonable to assume that the ligament lengths or knee kinematics expected with higher quadriceps loads can be extrapolated.

This study was performed to test the hypothesis that reducing the horizontal distance between the trailing foot (foot crossing the obstacle last) and obstacle, during stance just prior to stepping over the obstacle, would reduce flexion of the hip, knee, and ankle joints of the trailing limb when the toe is over the obstacle to reduce the vertical toe-obstacle clearance and increase the risk of tripping. Fourteen healthy young adults stepped over an obstacle of 51, 102, 153, and 204 mm height in a self-selected manner (i.e., toe-obstacle distance was not controlled) and for toe-obstacle distance targets of 10, 20, 30, and 40% of their step lengths measured during unobstructed gait. The reductions in toe-obstacle distance resulted in linear decreases in flexion of the hip, knee, and ankle when the toe was over the obstacle. Toe-obstacle clearance of the trailing limb decreased significantly as toe-obstacle distance decreased. The reductions in toe-obstacle distance led to contact of the trailing (but not the leading) foot with the obstacle, the closer the obstacle the greater the number of contacts. The reductions also resulted in linear decreases in swing time of the trailing limb from toe-off to when the toe was over the obstacle. The height of the hip was not affected by toe-obstacle distance. Angular velocity of knee flexion was found to increase linearly as toe-obstacle distance decreased and appears to be of primary importance in avoiding obstacle contact.

We tested the effect of intraarticular reconstructions of the anterior cruciate ligament alone and in combination with extraarticular reconstructions in 10 cadaveric knees. These knees had anterior cruciate ligament deficiency alone or in combination with anterolateral capsuloligamentous deficiencies. In the knees with combined injury, intraarticular reconstruction returned anterior stability to levels not significantly different from levels found for the knees deficient in the anterior cruciate ligament alone and treated with this procedure. After intraarticular reconstruction, rotational stability of the knee with combined injuries failed to return to the levels seen in the knee with isolated anterior cruciate ligament deficiencies that underwent the same treatment. When a tenodesis with either 0 N or 22 N of tension was added to the intraarticular reconstruction in the knee with combined injuries, we found that excessive internal rotation significantly decreased at all angles of flexion, except at full extension with 0 N of tension. In addition, the extraarticular reconstruction with 22 N of tension in the tenodesis overconstrained the knee in internal rotation between 30 degrees and 90 degrees of knee flexion. The tenodesis with 0 N of tension overconstrained the knee at only 60 degrees and 90 degrees of flexion. These results suggest extraarticular reconstruction as an adjunct to the intraarticular operation for the knee with anterior cruciate ligament and anterolateral structural injuries. The results also suggest that the surgeon can affect anterior and rotational laxity by adjusting the tension in the tenodesis.

The effect of reconstructing the posterior cruciate ligament on anteroposterior laxity of the knee was evaluated in 7 cadaveric knees. A bone-patellar tendon-bone graft was used. Femoral pilot holes were drilled to locate the most isometric sites for attachment of the graft to the femur using an isometer. A tension of 89 N was set in the graft using a tensiometer with the knee in 90 degree flexion while applying an anterior drawer force of 156 N to the tibia. Posterior displacement of the knee was measured in 15 degree increments from O degree to 90 degrees in the intact knee, in the knee with the posterior cruciate ligament transected, and after reconstruction of the posterior cruciate ligament in response to 100 N of posteriorly applied force. Graft tension was nearly constant between 0 degrees and 90 degrees flexion, indicating the grafts to be isometric. The reconstruction reduced posterior translation of the tibia in the posterior cruciate ligament excised knee at all angles of flexion; the differences were statistically significant. The reconstruction returned posterior translation to levels not significantly different from those of the intact knee between 0 degrees and 45 degrees flexion but not in the greater angles of flexion tested.

An algorithm was developed to predict the minimum energy consumption trajectory of the swing limb. The method of dynamic programming, a multistage optimization method, was applied to generate the optimum trajectory of the swing ankle which minimized the mechanical energy required to generate the moments of the joints of the lower extremities during the single support phase of gait. Predictions and measurements of gait were compared for six healthy subjects. The predicted hip and knee flexion angles of the swing limb were not significantly different from those experimentally measured except for hip flexion at times greater than 75% of the swing period. The predicted ground reaction forces were not significantly different from the measured ground reaction forces. Furthermore, the moments about the joints were not significantly different from those computed using the measured ground reaction forces and kinematics of the limbs. The results of this study support the hypothesis that human gait is energy efficient.

We compared the reproducibility of measurements made with the Genucom knee analysis system using two methods of restraint. The first method was that sug gested by the manufacturer and consisted of clamping the thigh to the examination chair with 70 N of vertical force and 110 N of mediolateral force and used a single elastic strap to secure the electrogoniometer cuff to the leg. In the second, or enhanced, method, the vertical and mediolateral clamping forces were each increased to 156 N, and an additional strap was used to secure the cuff to the leg. Tests performed were the anteroposte rior stress tests at 20° and 90° of knee flexion, and the varus-valgus stress test, the internal-external rotation stress test, and the medial and lateral pivot shift tests at 20°. Five normal subjects were installed and tested on 6 different days with the manufacturer's suggested se curing method and on 12 different days with the en hanced securing method. The enhanced method of re straint resulted in significantly reduced day-to-day variance for all tests performed except the varus-valgus stress test.

Patients have complained of pain after the use of the central one-third patellar tendon for reconstruction of the anterior cruciate ligament-deficient knee. This study investigated the effect on patellofemoral contact areas and pressures of harvesting the central 10 mm of the patellar tendon in five cadaveric knees. Isometric quad riceps forces were applied to produce approximately 30% of reported maximum voluntary extension mo ments at the knee. Using Fuji pressure-sensitive film, measurements were recorded for three states: the normal knee, after the graft removal, and after the tendon was closed. Contact areas and pressures were measured at 20°, 30°, 60°, and 80° of knee flexion in each specimen. Tests of the reproducibility of our meth ods were performed. Average patellofemoral contact areas for three states ranged from 1.6 cm2 at 20° of knee flexion to 3.0 cm2 at 60°. The average patellofemoral contact pressures ranged from 1.9 MPa at 20° of knee flexion to 3.0 MPa at 30°. At each flexion angle there were no significant differences in average patellar contact area or pressure for the three states ( P < 0.05). These results suggest that neither harvesting the central 10 mm of the patellar tendon, nor closing the gap, significantly alters patello femoral contact area or pressure.

The biomechanical effectiveness of an extraarticular ACL reconstruction, an intraarticular ACL reconstruc tion, and the combination of these on both anterior stability and internal rotational stability of the ACL de ficient knee was investigated in six cadaver knees. The extraarticular reconstruction consisted of the Müller anterolateral femorotibial ligament iliotibial band teno desis, and the intraarticular reconstruction used the middle third of the patellar tendon in the manner of Clancy. The extraarticular reconstruction was found to over- constrain internal tibial rotation of the ACL excised knee between 30° and 90° ( P < 0.05). While the isolated extraarticular reconstruction did not return normal an terior stability to the ACL deficient knee ( P < 0.05), it did significantly reduce the anterior laxity of the ACL deficient knee between 30° and 90° of knee flexion ( P < 0.05). For the combined reconstruction, the intraarticular procedure was performed and then only enough ten sion was applied to the extraarticular reconstruction to take up slack in the tenodesis without shifting the rotatory position of the tibia from that produced by the intraarticular procedure alone. Neither the intraarticular reconstruction nor the combined procedure resulted in any significant shifts from normal ( P < 0.05) in the rotatory position of the unloaded tibia; during loading neither resulted in rotational displacements significantly different from normal; and both of these procedures reduced the increased anterior laxity of the ACL defi cient knee to a level not statistically different from normal. Because the extraarticular reconstruction shared the load when performed with the intraarticular reconstruc tion as part of a combined procedure, we concluded that it would be useful as an adjunctive procedure in appropriate clinical situations.

An automated system to study foot-floor contact weight bearing patterns has been developed. The system includes a contact area transducer with digital signal conditioning, force plate and minicomputer. The system is capable of measuring foot-floor contact areas, average contact pressure, speed of the center of pressure and vertical force in relation to the position of the resultant force under the foot. In addition, the system provides computerized images of the instantaneous foot contact areas and centers of pressure resulting in a composite foot contact area and the pathway of the center of pressure. A preliminary study, using the system, indicated several common features among the weight bearing patterns of normal subjects during gait. The highest contact pressures occurred in the region of the heel and metatarsal heads during heel strike and toe off respectively. The contact area under the foot increased with increasing vertical force producing a nearly constant average contact pressure through the midstance phase of gait. The highest speed of the center of pressure was found to occur in the region of the heel, while a pause in the progression of the center of pressure was observed in the region of the second and third metatarsal heads. In contrast to the other parameters the pathway of the center of pressure was found to have the greatest variations among test subjects. However, for repeated observations of a single subject the pathway was found to be reproducible.

The biomechanical effectiveness of the Müller anterolateral femorotibial ligament (ALFTL) iliotibial band tenodesis on anterior stability and internal rotational stability of the ACL deficient knee was investigated in six cadaver knees. Anterior drawer and internal rotation of the tibia were measured at 15 degrees increments from 0 degrees to 90 degrees in response to 50 N of anteriorly applied tibial force and 3 Nm of internally applied internal torque, respectively, in the intact knee, the ACL excised knee, and following the ALFTL reconstruction. A strain gage was used to measure the resting graft tension and to measure strain in the graft during the load-displacement tests. The Müller ALFTL tenodesis failed to return normal anterior stability to the ACL deficient knee (P less than 0.05). The tenodesis did, however, reduce the anterior laxity of the ACL deficient knee from 30 degrees to 90 degrees of knee flexion (P less than 0.05). The tenodesis overconstrained internal tibial rotation of the ACL excised knee from 30 degrees to 90 degrees (P less than 0.05). Measurements of strain in the tenodesis supported the load-displacement findings that the tenodesis was most effective in constraining anterior drawer and internal tibial rotation from 30 degrees to 90 degrees of knee flexion.