Custom-fit versus premanufactured braces

Custom-made and off-the-shelf functional knee orthoses from four manufacturers were evaluated. Anterior tibial translation testing was performed using a pneumatic mechanical surrogated knee. The mechanical surrogate was interfaced with a servohydraulic materials testing system, which applied all anterior/posterior displacements to an ultimate anterior load of 400 N. Comparison of the individual custom versus premanufactured braces showed that the custom braces demonstrated a statistically significant difference for restraining anterior displacement (P=.0001 to P=.0005). Pooled data from all tests showed that the custom brace measurements as a group restrained anterior displacement better than the premanufactured brace group by a mean difference of 0.84 mm (P=.0001). The authors question whether such small, sub-millimeter findings between custom and off-the-shelf functional derotation braces represent any clinically significant differences.     

The effectiveness of self-adjustable custom and off-the-shelf bracing in the treatment of varus gonarthrosis

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 degrees compared with baseline (p=0.001) and by 1.3 degrees 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.     

The effect of functional knee-braces on strain on the anterior cruciate ligament in vivo.

Functional knee-braces are widely used to protect injured or reconstructed anterior cruciate ligaments, despite the fact that few scientific data support their efficacy. We studied seven functional braces, representative of both the typical custom-fit and off-the-shelf designs. The braces were tested on subjects who had a normal anterior cruciate ligament and were scheduled for arthroscopic meniscectomy or exploration of the knee under local anesthesia. After the operative procedure, a Hall-effect strain-transducer was applied to the anterior cruciate ligament. Under low anterior shear loads, two braces provided some protective strain-shielding effect compared with no brace, but this strain-shielding effect did not occur at the higher anterior shear loads expected during the high-stress activities common to athletic events. The DonJoy, Townsend, C.Ti., and Lenox Hill braces demonstrated a strain-shielding effect on the anterior cruciate ligament with an internal torque of five newton-meters applied to the tibia. None of the braces had any effect on strain on the anterior cruciate ligament during active range of motion of the knee from 10 to 120 degrees or during isometric contraction of the quadriceps. Wearing of a brace did not produce an increase in the value for strain on the anterior cruciate ligament. For the activities that were evaluated in this study, none of the braces produced adverse effects on the anterior cruciate ligament, and there were no significant differences in the strain on the anterior cruciate ligament between the use of a custom-fit or an off-the-shelf brace design. There were no apparent advantages of the more expensive custom-made braces compared with the off-the-shelf designs.     

The use of functional knee braces in the control of pathologic anterior knee laxity

Four designs of knee braces, Don-Joy 4 Point, RKS, Lenox Hill, and CTi, were evaluated in 42 patients with a unilateral knee brace. Brace migration was the predominant complaint, as noted in patient questionnaires. All braces tested reduced giving-way episodes (34 of 42 patients reported no giving way during brace usage). All four brands of braces reduced the grade of pivot shift (mean reduction = 0.8 grade). Instrumented laxity testing with the KT-1000 arthrometer was performed with an 89-N passive anterior displacement, high load passive anterior displacement, and a quadriceps contraction active displacement. Brace use decreased the measured pathologic anterior displacement on all tests. During functional testing with one-legged hop and 40-yard shuttle run, the mean values were not significantly changed by brace usage.     

Comparing 2-year outcomes of anterior cruciate ligament reconstruction using either patella-tendon or semitendinosus-tendon autografts: a non-randomised prospective study

PURPOSE: To compare the results of anterior cruciate ligament (ACL) reconstructions using either a patella-tendon autograft or a semitendinosus-tendon autograft. METHODS: Based on surgeon experience and preference, 68 patients underwent ACL reconstruction using either a quadruple-strand semitendinosus autograft (n = 34) or a central one-third bone-patella tendon-bone autograft (n = 34). Each patient was assessed preoperatively and postoperatively at 3, 6, and 24 months using the International Knee Documentation Committee (IKDC) knee score, Biodex muscle strength and endurance testing, and the KT1000 instrumented arthrometer test of knee laxity to anterior translation. All assessments at the 2-year follow-up were performed by the same physician and physiotherapist. RESULTS: While ACL reconstruction improved knee stability and IKDC knee scores significantly, there was no statistically significant difference between semitendinosus- and patella-tendon autograft reconstructions in terms of long-term knee score or laxity to anterior translation. Semitendinosus graft reconstruction was associated with less donor-site morbidity and hamstring weakness. Meniscectomy was associated with poorer long-term knee scores. CONCLUSION: ACL reconstruction is associated with a significantly better IKDC knee score and laxity measurement at 2-year follow-up. However, we were unable to demonstrate a significantly better long-term outcome in knee score or laxity to anterior translation with either a patella-tendon autograft or a semitendinosus-tendon autograft.     

Anterior laxity and MR signals of the knee after exercise: A comparison of 9 normal knees and 6 anterior cruciate ligament reconstructed knees

9 healthy volunteers and 6 patients with anterior cruciate ligament (ACL) grafts underwent anterior knee laxity measurements and MRI examinations of their knees before and after intensive physical exercise. In the volunteer group, anterior displacement of the knee at 89 and 133 newtons of loading, measured with a KT-2000 knee arthrometer, increased after exercise, compared to before it. In addition, anterior terminal stiffness decreased at 133 newtons of anterior loading. In the ACL group, anterior displacement at 89 and 133 newtons of loading also increased, while no difference was found in anterior terminal stiffness before versus after exercise. On MRI, the signal intensity of normal ACLs after exercise was higher than before it. In contrast, the signals from the grafts showed no differences before versus after exercise. Our findings suggest that the ACL grafts are biomechanically and biochemically different from normal ACLs, even 15 months after ACL reconstruction.     

Can suture repair of ACL transection restore normal anteroposterior laxity of the knee? An ex vivo study

Recent work has suggested the transected anterior cruciate ligament (ACL) can heal and support reasonable loads if repaired with sutures and a bioactive scaffold; however, use of a traditional suture configuration results in knees with increased anterior–posterior (AP) laxity. The objective was to determine whether one of five different suture repair constructs when performed at two different joint positions would restore normal AP knee laxity. AP laxity of the porcine knee at 60° of flexion was evaluated for five suture repair techniques. Femoral fixation for all repair techniques utilized a suture anchor. Primary repair was to either the tibial stump, one of three bony locations in the ACL footprint, or a hybrid bony fixation. All five repairs were tied with the knee in first 30° and then 60° of flexion for a total of 10 repair constructs. Suture repair to bony fixation points within the anterior half of the normal ACL footprint resulted in knee laxity values within 0.5 mm of the ACL‐intact joint when the sutures were tied with the knee at 60° flexion. Suture repair to the tibial stump, or with the knee at 30° of flexion, did not restore normal AP laxity of the knee. Three specific suture repair techniques for the transected porcine ACL restored the normal AP laxity of the knee at the time of surgery. Additional studies defining the changes in laxity with cyclic loading and in vivo healing are indicated. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1500–1505, 2008     

A new tibial coordinate system improves the precision of anterior-posterior knee laxity measurements: a cadaveric study using Roentgen stereophotogrammetric analysis.

Roentgen stereophotogrammetric analysis (RSA) can be used to measure changes in anterior-posterior (A-P) knee laxity after anterior cruciate ligament (ACL) reconstruction. Previous measurements of A-P knee laxity using RSA have employed a tibial coordinate system with the origin placed midway between the tips of the tibial-eminences. However, the precision in measuring A-P knee laxity might be improved if the origin was placed on the flexion-extension axis of rotation of the knee. The purpose of this study was to determine whether a center-of-rotation tibial coordinate system with the origin placed midway between the centers of the posterior femoral condyles, which closely approximates the flexion-extension center-of-rotation of the knee, improves the precision in measuring A-P knee laxity compared to the tibial-eminence-based coordinate system. A-P knee laxity was measured using each coordinate system six times in three human cadaveric knees implanted with 0.8-mm diameter tantalum markers. For each laxity measurement, the knee was placed in a custom loading apparatus and biplanar radiographs were obtained while the knee resisted a 44 N posterior shear force and 136 N anterior shear force. A-P knee laxity was determined from the change in position of the tibia, with respect to the femur, resulting from the posterior and anterior shear forces. The precision for each coordinate system was calculated as the pooled standard deviation of A-P knee laxity measurements. The precision of the center-of-rotation coordinate system was 0.33 mm, which was about a factor of 2 better than the 0.62 mm precision of the tibial-eminence coordinate system (p=0.006). The 0.33 mm precision with the center-of-rotation coordinate system suggests that an observed change of either 0.56 mm (i.e. 1.7 standard deviations) or greater in A-P knee laxity over time is a real change and not due to measurement error when the new tibial coordinate system is used and other factors contributing to variability are controlled as was done in this study. Accordingly, clinicians and researchers should consider the use of this alternate tibial coordinate system when making serial measurements of A-P knee laxity using RSA because the improved precision allows for the observation of smaller differences.     

Objective anterior cruciate ligament testing

We examined subjects with the Stryker knee laxity tester as part of the clinical examination to determine its usefulness in evaluating the anterior cruciate ligament. We measured 123 athletes with no history of knee injury, as well as 30 patients with ACL injury proven by arthroscopy, and 11 injured patients with intact ACL at arthroscopy. We recorded anterior and posterior tibial displacement at 20 degrees of knee flexion and 20 lbs force in each direction. Anterior laxity and side to side difference correlated with ACL injury; posterior and total AP laxity did not. In normal subjects, mean anterior laxity was 2.5 mm. Only 8% of normal knees had anterior laxity of 5 mm or more. Ten percent of normal subjects had a side to side difference of 2 mm or more. In ACL tears, mean laxity was 8.1 mm, with 94% measuring 5 mm or more. Of the subjects, 89% with unilateral ACL injury had an increase of 2 mm or more on the injured side. Ten of ten acute ACL tears were detected by these criteria, with no false positives. In injured knees with intact ACL, measurements did not differ significantly from normal. We found the objective knee laxity measurement to be a useful complement to clinical knee examination.     

Rotational instability of the knee: internal tibial rotation under a simulated pivot shift test

Introduction  Recently, several publications investigated the rotational instability of the human knee joint under pivot shift examinations and reported the internal tibial rotation as measurement for instrumented knee laxity measurements. We hypothesize that ACL deficiency leads to increased internal tibial rotation under a simulated pivot shift test. Furthermore, it was hypothesized that anatomic single bundle ACL reconstruction significantly reduces the internal tibial rotation under a simulated pivot shift test when compared to the ACL-deficient knee. Methods  In seven human cadaveric knees, the kinematics of the intact knee, ACL-deficient knee, and anatomic single bundle ACL reconstructed knee were determined in response to a 134 N anterior tibial load and a combined rotatory load of 10 N m valgus and 4 N m internal tibial rotation using a robotic/UFS testing system. Statistical analyses were performed using a two-way ANOVA test. Results  Single bundle ACL reconstruction reduced the anterior tibial translation under a simulated KT-1000 test significantly compared to the ACL-deficient knee (P < 0.05). After reconstruction, there was a statistical significant difference to the intact knee at 30° of knee flexion. Under a simulated pivot shift test, anatomic single bundle ACL reconstruction could restore the intact knee kinematics. Internal tibial rotation under a simulated pivot shift showed no significant difference in the ACL-intact, ACL-deficient and ACL-reconstructed knee. Conclusion  In conclusion, ACL deficiency does not increase the internal tibial rotation under a simulated pivot shift test. For objective measurements of the rotational instability of the knee using instrumented knee laxity devices under pivot shift mechanisms, the anterior tibial translation should be rather evaluated than the internal tibial rotation. This study was supported in part by a grant of the German Speaking Association of Arthroscopy (AGA).     

Effects of femoral tunnel placement on knee laxity and forces in an anterior cruciate ligament graft.

The purpose of this study was to measure the effects of variation in placement of the femoral tunnel upon knee laxity, graft pretension required to restore normal anterior-posterior (AP) laxity and graft forces following anterior cruciate ligament (ACL) reconstruction. Two variants in tunnel position were studied: (1) AP position along the medial border of the lateral femoral condyle (at a standard 11 o'clock notch orientation) and (2) orientation along the arc of the femoral notch (o'clock position) at a fixed distance of 6-7 mm anterior to the posterior wall. AP laxity and forces in the native ACL were measured in fresh frozen cadaveric knee specimens during passive knee flexion-extension under the following modes of tibial loading: no external tibial force, anterior tibial force, varus-valgus moment, and internal-external tibial torque. One group (15 specimens) was used to determine effects of AP tunnel placement, while a second group (14 specimens) was used to study variations in o'clock position of the femoral tunnel within the femoral notch. A bone-patellar tendon-bone graft was placed into a femoral tunnel centered at a point 6-7 mm anterior to the posterior wall at the 11 o'clock position in the femoral notch. A graft pretension was determined such that AP laxity of the knee at 30 deg of flexion was restored to within 1 mm of normal; this was termed the laxity match pretension. All tests were repeated with a graft in the standard 11 o'clock tunnel, and then with a graft in tunnels placed at other selected positions. Varying placement of the femoral tunnel 1 h clockwise or counterclockwise from the 11 o'clock position did not significantly affect any biomechanical parameter measured in this study, nor did placing the graft 2.5 mm posteriorly within the standard 11 o'clock femoral tunnel. Placing the graft in a tunnel 5.0 mm anterior to the standard 11 o'clock tunnel increased the mean laxity match pretension by 16.8 N (62%) and produced a knee which was on average 1.7 mm more lax than normal at 10 deg of flexion and 4.2 mm less lax at 90 deg. During passive knee flexion-extension testing, mean graft forces with the 5.0 mm anterior tunnel were significantly higher than corresponding means with the standard 11 o'clock tunnel between 40 and 90 deg of flexion for all modes of constant tibial loading. These results indicate that AP positioning of the femoral tunnel at the 11 o'clock position is more critical than o'clock positioning in terms of restoring normal levels of graft force and knee laxity profiles at the time of ACL reconstruction.     

Biomechanical characteristics of the anatomic rectangular tunnel anterior cruciate ligament reconstruction with a bone-patellar tendon-bone graft

Purpose

To clarify 1) the force sharing between two portions of BTB graft in anatomic rectangular tunnel (ART) reconstruction and 2) the knee stability in ART technique under anterior tibial load.

Arthrometric Evaluation of Stabilizing Effect of Knee Functional Bracing at Different Flexion Angles

Previous in-vivo investigations on the stabilizing efficacy of knee bracing for ACL reconstructed patients have been often limited to 20-30 degrees of knee flexion. In this study, the effectiveness of a uniaxial hinged functional brace to improve the knee stability was assessed at 30, 60 and 90 degrees of knee flexion. Arthrometry tests were conducted on 15 healthy subjects before and following wearing the brace and the tibial displacements were measured at up to 150 N anterior forces. Results indicated that functional bracing has a significant stabilizing effect throughout the range of knee flexion examined (p < 0.05). The rate of effectiveness, however, was not consistent across the flexion range, e.g., 50% at 30 degrees and only 4% at 90 degrees. It was suggested that accurate sizing and fitting as well as attention to correct hinge placement relative to the femoral condyles can limit brace migration and improve its effectiveness in mid and deep knee flexion. With using adaptive limb fittings, through flexible pads, and a polycentric joint a more significant improvement of the overall brace performance and efficacy might be obtained.

Key points

• Functional bracing improves the knee joint stability mostly in extension posture.
• Unlike the non-braced condition, the least knee joint stability appears in mid and deep flexion angles when using a hinged brace.
• Accurate sizing and fitting and attention to correct hinge placement relative to the femoral condyles can limit brace migration and improve its effectiveness in mid and deep knee flexion.
• The overall brace performance and efficacy might be improved significantly using adaptive limb fittings through flexible pads and/or polycentric joints.

Key words: Functional brace, knee, ACL injury, instability, arthrometery     

Anterior laxity and MR signals of the knee after exercise. A comparison of 9 normal knees and 6 anterior cruciate ligament reconstructed knees.

9 healthy volunteers and 6 patients with anterior cruciate ligament (ACL) grafts underwent anterior knee laxity measurements and MRI examinations of their knees before and after intensive physical exercise. In the volunteer group, anterior displacement of the knee at 89 and 133 newtons of loading, measured with a KT-2000 knee arthrometer, increased after exercise, compared to before it. In addition, anterior terminal stiffness decreased at 133 newtons of anterior loading. In the ACL group, anterior displacement at 89 and 133 newtons of loading also increased, while no difference was found in anterior terminal stiffness before versus after exercise. On MRI, the signal intensity of normal ACLs after exercise was higher than before it. In contrast, the signals from the grafts showed no differences before versus after exercise. Our findings suggest that the ACL grafts are biomechanically and biochemically different from normal ACLs, even 15 months after ACL reconstruction.     

Can rotatory knee laxity be predicted in isolated anterior cruciate ligament surgery?

Purpose

Despite the overall success of the surgical anterior cruciate ligament (ACL) reconstruction, some patients still present with instability symptoms even after the surgery, mainly due to the presence of associated lesions. At present, the pivot shift test has been reported to be the benchmark to assess rotatory knee laxity. The purpose of this study was to quantitatively evaluate rotatory knee laxity at time-zero in order to determine whether detected post-reconstruction laxity was predictable by its value measured before the reconstruction, which was hypothized to be influenced by the presence of associated lesions.

Methods

Rotatory knee laxity was retrospectively analysed in 42 patients, including two different ACL reconstructions. The maximal anterior displacement and the absolute value of the posterior acceleration reached during the reduction of the tibial lateral compartment were intra-operatively acquired by using a navigation system and identified as discriminating parameters. For each parameter, statistical linear regression analysis (line slope and intercept) was performed between pre- and post-reconstruction values.

Results

No statistically significant influence of the initial posterior acceleration on the post-reconstruction outcome was found (line slope, p > 0.05), although a statistically significant line intercept was indeed identified (p < 0.001). A statistically significant influence on the surgery outcome was instead found for the initial value of the anterior tibial displacement (line slope = 0.39, p = 0.004), meaning that, on average, about 40 % of the post-reconstruction lateral compartment displacement could be explained by the corresponding pre-reconstruction value. Both of these findings highlighted the importance of intra-operative quantification of rotatory knee laxity to identify correct indications for the surgery.

Conclusions

This study provided important implications for the future possibility of defining a quantifying tool able to assess rotatory knee laxity during ACL reconstruction. This could allow detection of additional injuries to secondary restraints by easily performing rotatory knee laxity tests, which in turn could reduce post-surgical recurrence of knee instability.     

Decrease in anterior knee laxity by electrical stimulation of normal and reconstructed anterior cruciate ligaments

We have investigated the changes in anterior laxity of the knee in response to direct electrical stimulation of eight normal and 45 reconstructed anterior cruciate ligaments (ACLs). In the latter, the mean time from reconstruction was 26.7 months (24 to 32). The ACL was stimulated electrically using a bipolar electrode probe during arthroscopy. Anterior laxity was examined with the knee flexed at 20 degrees under a force of 134 N applied anteriorly to the tibia using the KT-2000 knee arthrometer before, during and after electrical stimulation. Anterior tibial translation in eight normal and 17 ACL-reconstructed knees was significantly decreased during stimulation, compared with that before stimulation. In 28 knees with reconstruction of the ACL, in 22 of which the grafts were found to have detectable somatosensory evoked potentials during stimulation, anterior tibial translation was not decreased. These findings suggest that the ACL-hamstring reflex arc in normal knees may contribute to the functional stability and that this may not be fully restored after some reconstructions of the ACL.     

Growth influences knee laxity after anterior tibial spine fracture: a study on rabbits

An anterior tibial spine (ATS) fracture, with or without displacement, was created in the right knee of 8-week and 22-23-week-old rabbits. After 4 weeks of cast immobilization and 8 weeks of free cage activities, the animals were killed. A method to measure anterior knee laxity in rabbits was developed using a material testing machine. The laxity of the right knee was compared to the unoperated left knee in each rabbit. The difference was found to have increased in the adult rabbits after the healing of a displaced ATS fracture (median 0.5 mm, range 0.3-0.9), but not in the young rabbits (median 0.2 mm, range 0.0 -0.4). The ultimate load of the anterior cruciate ligament (ACL) was reduced after healing of the ATS fracture. The results support the theory that further growth may compensate for the functional elongation of the ACL caused by healing of a displaced ATS fracture. The study also indicates that an ATS fracture may affect the mechanical properties of the ACL.     

Comparison of Johnson Anti-Shear Accessory and Standard Dynamometer Attachment for Anterior and Posterior Tibial Translation during Isometric Muscle Contractions

The purpose of this study was to compare the effectiveness of the Johnson Anti-Shear Accessory (JASA) and the standard dynamometer accessory (SDA) in controlling tibial translation for isometric knee flexion and extension exercise on the Cybex(R) II. The subject was a 26-year-old male with known anterior cruciate ligament (ACL) deficiency of the left knee. The subject performed maximum isometric muscle contractions for JASA and SDA conditions. Medial-lateral roentgenograms were obtained while the subject maintained isometric knee flexion and extension muscle contractions at three positions of knee flexion. JASA and SDA trials were analyzed for one extension position and one flexion position. The authors compared JASA and SDA conditions for magnitude of contact pad force and for degree of tibial translation evidenced on the roentgenograms. Tibial translation was greater and contact pad force was less for the SDA condition than the JASA condition. The results suggest the JASA is useful in protecting ACL surgical reconstructions, the partially torn ACL, and secondary supporting structures of the knee as patients perform isometric exercise on Cybex instrumentation. J Orthop Sports Phys Ther 1990;11(11):547-553.     

Effect of posterior tibial slope on knee biomechanics during functional activity

Treatment of medial compartment knee osteoarthritis with high tibial osteotomy can produce an unintended change in the slope of the tibial plateau in the sagittal plane. The effect of changing posterior tibial slope (PTS) on cruciate ligament forces has not been quantified for knee loading in activities of daily living. The purpose of this study was to determine how changes in PTS affect tibial shear force, anterior tibial translation (ATT), and knee‐ligament loading during daily physical activity. We hypothesized that tibial shear force, ATT, and ACL force all increase as PTS increases. A previously validated computer model was used to calculate ATT, tibial shear force, and cruciate‐ligament forces for the normal knee during three common load‐bearing tasks: standing, squatting, and walking. The model calculations were repeated with PTS altered in 1° increments up to a maximum change in tibial slope of 10°. Tibial shear force and ATT increased as PTS was increased. For standing and walking, ACL force increased as tibial slope was increased; for squatting, PCL force decreased as tibial slope was increased. The effect of changing PTS on ACL force was greatest for walking. The true effect of changing tibial slope on knee‐joint biomechanics may only be evident under physiologic loading conditions which include muscle forces. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:223–231, 2011