A biomechanical evaluation of the Lenox Hill knee brace

This study was conducted to determine the effectiveness of the Lenox Hill knee brace in limiting anterior translation and external rotation of the tibia in reference to the femur in normal and ligament-deficient knees. Four fresh cadaver knees were fitted with Lenox Hill knee braces according to the manufacturer's guidelines. A computer-assisted testing apparatus was constructed that allowed each knee to be tested as a function of knee flexion angle, joint load, and soft tissue integrity. Each knee served as its own control. While 45 kg of anterior force was applied to the tibia of the anterior cruciate ligament deficient knees, the Lenox Hill knee brace was able to decrease anterior translation from an average of 10 mm, to 5.7 mm, at 30 degrees of flexion when no vertical load was present. This limiting effect was lost when the medial collateral ligament was sectioned in addition to the anterior cruciate ligament or when both the medial and the lateral collateral ligaments were sectioned along with the anterior cruciate ligament. When 20 Newton-meters (Nm) of torque was applied to the femurs at 30 degrees of flexion without vertical load, the Lenox Hill knee brace limited external rotation of the tibia in all tested categories. For intact knees at 30 degrees of flexion and no vertical load, the Lenox Hill knee brace decreased external rotation from 18 degrees to 10 degrees. In the anterior cruciate ligament-sectioned knees, external rotation was decreased from an average of 20.2 degrees to 16.1 degrees. In the knees with sectioned anterior cruciate and medial collateral ligaments, the average reduction was from 21.2 degrees to 15.4 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)     

Importance of the medial meniscus in the anterior cruciate ligament-deficient knee.

The incidence of meniscal tears in the chronically anterior cruciate ligament-deficient knee is increased, particularly in the medial meniscus because it performs an important function in limiting knee motion. We evaluated the role of the medial meniscus in stabilizing the anterior cruciate ligament-deficient knee and hypothesized that the resultant force in the meniscus is significantly elevated in the anterior cruciate ligament-deficient knee. To test this hypothesis, we employed a robotic/universal force-moment sensor testing system to determine the increase in the resultant force in the human medial meniscus in response to an anterior tibial load following transection of the anterior cruciate ligament. We also measured changes in the kinematics of the knee in multiple degrees of freedom following medial meniscectomy in the anterior cruciate ligament-deficient knee. In response to a 134-N anterior tibial load, the resultant force in the medial meniscus of the anterior cruciate ligament-deficient knee increased significantly compared with that in the meniscus of the intact knee; it increased by a minimum of 10.1 N (52%) at full knee extension to a maximum of 50.2 N (197%) at 60 degrees of flexion. Medial meniscectomy in the anterior cruciate ligament-deficient knee also caused a significant increase in anterior tibial translation in response to the anterior tibial load, ranging from an increase of 2.2 mm at full knee extension to 5.8 mm at 60 degrees of flexion. Conversely, coupled internal tibial rotation in response to the load decreased significantly, ranging from a decrease of 2.5 degrees at 15 degrees of knee flexion to 4.7 degrees at 60 degrees of flexion. Our data confirm the hypothesis that the resultant force in the medial meniscus is significantly greater in the anterior cruciate ligament-deficient knee than in the intact knee when the knee is subjected to anterior tibial loads. This indicates that the demand on the medial meniscus in resisting anterior tibial loads is increased in the anterior cruciate ligament-deficient knee compared with in the intact knee, suggesting a mechanism for the increased incidence of medial meniscal tears observed in chronically anterior cruciate ligament-deficient patients. The large changes in kinematics due to medial meniscectomy in the anterior cruciate ligament-deficient knee confirm the important role of the medial meniscus in controlling knee stability. These findings suggest that the reduction of resultant force in the meniscus may be a further motive for reconstructing the anterior cruciate ligament, with the goal of preserving meniscal integrity.     

Significance of changes in the reference position for measurements of tibial translation and diagnosis of cruciate ligament deficiency.

Measurements of tibial translation in response to an external load are used in clinical and laboratory settings to diagnose and characterize knee-ligament injuries. Before these measurements can be quantified, a reference position of the knee must be established (defined as the position of the knee with no external forces or moments applied). The objective of this study was to determine the effects of cruciate ligament deficiency on this reference position and on subsequent measurements of tibial translation and, in so doing, to establish a standard of kinematic measurement for future biomechanical studies. Thirty-six human cadaveric knees were studied with a robotic/universal force-moment sensor testing system. The reference positions of the intact and posterior cruciate ligament-deficient knees of 18 specimens were determined at full extension and at 30, 60, 90, and 120 degrees of flexion, and the remaining five-degree-of-freedom knee motion was unrestricted. Subsequently, under a 134-N anterior-posterior load, the resulting knee kinematics were measured with respect to the reference positions of the intact and posterior cruciate ligament-deficient knees. With posterior cruciate ligament deficiency, the reference position of the knee moved significantly in the posterior direction, reaching a maximal shift of 9.3 +/- 3.8 mm at 90 degrees of flexion. For the posterior cruciate ligament-deficient knee, posterior tibial translation ranged from 13.0 +/- 3.4 to 17.7 +/- 3.6 mm at 30 and 90 degrees, respectively, when measured with respect to the reference positions of the intact knee. When measured with respect to the reference positions of the posterior cruciate ligament-deficient knee, these values were significantly lower, ranging from 11.7 +/- 4.3 mm at 30 degrees of knee flexion to 8.4 +/- 4.8 mm at 90 degrees. A similar protocol was performed to study the effects of anterior cruciate ligament deficiency on 18 additional knees. With anterior cruciate ligament deficiency, only a very small anterior shift in the reference position was observed. Overall, this shift did not significantly affect measurements of tibial translation in the anterior cruciate ligament-deficient knee. Thus, when the tibial translation in the posterior cruciate ligament-injured knee is measured when the reference position of the intact knee is not available, errors can occur and the measurement may not completely reflect the significance of posterior cruciate ligament deficiency. However, there should be less corresponding error when measuring the tibial translation of the anterior cruciate ligament-injured knee because the shift in reference position with anterior cruciate ligament deficiency is too small to be significant. We therefore recommend that in the clinical setting, where the reference position of the knee changes with injury, comparison of total anterior-posterior translation with that of the uninjured knee can be a more reproducible and accurate measurement for assessing cruciate-ligament injury, especially in posterior cruciate ligament-injured knees. Similarly, in biomechanical testing where tibial translations are often reported for the ligament-deficient and reconstructed knees, a fixed reference position should be chosen when measuring knee kinematics. If such a standard is set, measurements of knee kinematics will more accurately reflect the altered condition of the knee and allow valid comparisons between studies.     

The effect of section of the medial collateral ligament on force generated in the anterior cruciate ligament

Ten fresh-frozen knees from cadavera were instrumented with a specially designed transducer that measures the force that the anterior cruciate ligament exerts on its tibial attachment. Specimens were subjected to tibial torque, anterior tibial force, and varus-valgus bending moment at selected angles of flexion of the knee ranging from 0 to 45 degrees. Section of the medial collateral ligament did not change the force generated in the anterior cruciate ligament by applied varus moment. When valgus moment was applied to the knee, force increased dramatically after section of the medial collateral ligament; the increases were greatest at 45 degrees of flexion. Section of the medial collateral ligament had variable effects on the force generated in the anterior cruciate ligament during internal rotation but dramatically increased that generated during external rotation; these increases were greatest at 45 degrees. Section of the medial collateral ligament increased mean total torsional laxity by 13 degrees (at 0 degrees of flexion) to 20 degrees (at 45 degrees of flexion). Application of an anteriorly directed force to the tibia of an intact knee increased the force generated in the anterior cruciate ligament; this increase was maximum near the mid-part of the range of tibial rotation and minimum with external rotation of the tibia. Section of the medial collateral ligament did not change the force generated in the anterior cruciate ligament by straight anterior tibial pull near the mid-part of the range of tibial rotation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Incidence and mechanism of the pivot shift. An in vitro study.

The aim of this study was to determine the incidence and mechanism of the pivot shift phenomenon in the normal and anterior cruciate ligament transected knee in vitro. Fifteen knees were tested under a range of valgus moments and iliotibial tract tensions when intact and after anterior cruciate ligament transection. Knee kinematics were measured and described in terms of tibial rotation as the knee flexed. Eight knees pivoted after anterior cruciate ligament transection. The mean pivot shift motion was an external tibial rotation of 17 degrees (+/- 11 degrees standard deviation) over a range of 27 degrees (+/- 24 degrees) knee flexion, at a mean flexion angle of 56 degrees (+/- 27 degrees). Clinically, this corresponds to a reduction of an anteriorly subluxed lateral tibial plateau as the knee flexes. When intact, pivoting and nonpivoting knees had similar anteroposterior laxity, but after anterior cruciate ligament transection, the pivoting group had significantly greater laxity. The loading required to elicit the pivot shift was critical and variable between knees, which raises questions about comparing clinicians' techniques and results in assessing the buckling instability attributable to anterior cruciate ligament injury.     

Three-dimensional instability of the anterior cruciate deficient knee

Using roentgen stereophotogrammetry we have recorded the three-dimensional movements of the knee during an anteroposterior laxity test in 36 patients with torn anterior cruciate ligaments and in three cadaver knees. At 30 degrees of knee flexion and before loads were applied the tibia occupied a more laterally rotated position if the anterior cruciate ligament had been injured. When the tibia was pulled anteriorly knees with cruciate deficiency rotated more laterally and were more abducted than normal knees. Posterior traction induced lateral rotation in the injured knee and medial rotation in the intact one. Precise knowledge of the three-dimensional instability of the anterior cruciate deficient knee may be important when the laxity is evaluated only in relation to one of the three cardinal axes.     

Three-dimensional tibiofemoral articular contact kinematics of a cruciate-retaining total knee arthroplasty

BACKGROUND: Accurate knowledge of the location of tibiofemoral articular contact following total knee arthroplasty is important in order to understand polyethylene wear and the mechanisms of component failure. The present study was performed to determine the three-dimensional tibiofemoral articular contact patterns of a posterior cruciate ligament-retaining total knee replacement during in vivo weight-bearing flexion. METHODS: Nine osteoarthritic patients who were managed with a single design of a posterior cruciate ligament-retaining total knee implant were investigated with the use of an innovative dual orthogonal fluoroscopic imaging system. The position of the components during in vivo weight-bearing flexion was measured from full extension to maximum flexion in 15 degrees intervals. Tibiofemoral articular contact was determined by the overlap of the tibiofemoral articular surfaces. The centroid of the surface intersection was used to report the point of contact location. The average tibiofemoral contact points on both the medial and lateral tibial component surfaces were reported as a function of flexion. RESULTS: The average maximum weight-bearing flexion angle was 113.3 degrees +/- 13.1 degrees (range, 96 degrees to 138 degrees ). In the anteroposterior direction, the contact location was relatively constant in the medial compartment and moved posteriorly by 5.6 mm in the lateral compartment as the knee flexed from full extension to 90 degrees of flexion. The range of the contact location in the mediolateral direction was 3.7 mm in the medial compartment and 4.8 mm in the lateral compartment. For both compartments, posterior translation of the contact point was significant from 90 degrees to maximum flexion, but the contact point at maximum flexion was not observed to reach the posterior edge of the polyethylene tibial insert articular surface. CONCLUSIONS: While the minimum anteroposterior translation of the contact point on the medial side might be interpreted as a medial pivot rotation during knee flexion, the contact point did move in the mediolateral direction with flexion. Beyond 90 degrees , both medial and lateral contact points were shown to move posteriorly but stopped before reaching the posterior edge of the polyethylene tibial insert articular surface. It seemed that the current component design did not allow the femoral condyle to roll off the polyethylene edge at high degrees of flexion because of the geometry at the posterior lip.     

Comparison of kinematic analysis by mapping tibiofemoral contact with movement of the femoral condylar centres in healthy and anterior cruciate ligament injured knees.

Two methods of analysis of knee kinematics from magnetic resonance images (MRI) in vivo have been developed independently: mapping the tibiofemoral contact, and tracking the femoral condylar centre. These two methods are compared for the assessment of kinematics in the healthy and the anterior cruciate ligament injured knee. Sagittal images of both knees of 20 subjects with unilateral anterior cruciate ligament injury were analysed. The subjects had performed a supine leg press against a 150 N load. Images were generated at 15 degrees intervals from 0 degrees to 90 degrees knee flexion. The tibiofemoral contact, and the centre of the femoral condyle (defined by the flexion facet centre (FFC)), were measured from the posterior tibial cortex. The pattern of contact in the healthy knee showed the femoral roll back from 0 degrees to 30 degrees, then from 30 degrees to 90 degrees the medial condyle rolled back little, while the lateral condyle continued to roll back on the tibial plateau. The contact pattern was more posterior in the injured knee (p=0.012), particularly in the lateral compartment. The medial FFC moved back very little during knee flexion, while the lateral FFC moved back throughout the flexion arc. The FFC was not significantly different in the injured knee (p=0.17). The contact and movement of the FFC both demonstrated kinematic events at the knee, such as longitudinal rotation. Both methods are relevant to design of total knee arthroplasty: movement of the FFC for consideration of axis alignment, and contact pattern for issues of interface wear and arthritic change in ligament injury.     

Effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on tension of an anterior cruciate ligament graft: an in vitro study

BACKGROUND: High tension in an anterior cruciate ligament graft adversely affects both the graft and the knee; however, it is unknown why high graft tension in flexion occurs in association with a posterior femoral tunnel. The purpose of the present study was to determine the effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on the tension of an anterior cruciate ligament graft during passive flexion. METHODS: Eight cadaveric knees were tested. The angle of the tibial tunnel was varied to 60 degrees, 70 degrees, and 80 degrees in the coronal plane with use of three interchangeable, low-friction bushings. The femoral tunnel, with a 1-mm-thick posterior wall, was drilled through the tibial tunnel bushing with use of the transtibial technique. After the graft had been tested in all three tibial bushings with one femoral tunnel, the femoral tunnel was filled with bone cement and the tunnel combinations were tested. Lastly, the graft was replaced in the 80 degrees femoral and tibial tunnels, and the tests were repeated with excision of the lateral edge of the posterior cruciate ligament in 2-mm increments. Graft tension, the flexion angle, and anteroposterior laxity were recorded in a six-degrees-of-freedom load-application system that passively moved the knee from 0 degrees to 120 degrees of flexion. RESULTS: The graft tension at 120 degrees of flexion was affected by the angle of the femoral tunnel and by incremental excision of the posterior cruciate ligament. The highest graft tension at 120 degrees of flexion was 169 +/- 9 N, which was detected with the graft in the 80 degrees femoral and 80 degrees tibial tunnels. The lowest graft tension at 120 degrees of flexion was 76 +/- 8 N, which was detected with the graft in the 60 degrees femoral and 60 degrees tibial tunnels. The graft tension of 76 N at 120 degrees of flexion with the graft in the 60 degrees femoral and 60 degrees tibial tunnels was closer to the tension in the intact anterior cruciate ligament. Excision of the lateral edge of the posterior cruciate ligament in 2 and 4-mm increments significantly lowered the graft tension at 120 degrees of flexion without changing the anteroposterior position of the tibia. CONCLUSIONS: Placing the femoral tunnel at 60 degrees in the coronal plane lowers graft tension in flexion. Our results suggest that high graft tension in flexion is caused by impingement of the graft against the posterior cruciate ligament, which results from placing the femoral tunnel medially at the apex of the notch in the coronal plane.     

Tibiofemoral cartilage contact biomechanics in patients after reconstruction of a ruptured anterior cruciate ligament

We investigated the in vivo cartilage contact biomechanics of the tibiofemoral joint in patients after reconstruction of a ruptured anterior cruciate ligament (ACL). A dual fluoroscopic and MR imaging technique was used to investigate the cartilage contact biomechanics of the tibiofemoral joint during in vivo weight‐bearing flexion of the knee in eight patients 6 months following clinically successful reconstruction of an acute isolated ACL rupture. The location of tibiofemoral cartilage contact, size of the contact area, cartilage thickness at the contact area, and magnitude of the cartilage contact deformation of the ACL‐reconstructed knees were compared with those previously measured in intact (contralateral) knees and ACL‐deficient knees of the same subjects. Contact biomechanics of the tibiofemoral cartilage after ACL reconstruction were similar to those measured in intact knees. However, at lower flexion, the abnormal posterior and lateral shift of cartilage contact location to smaller regions of thinner tibial cartilage that has been described in ACL‐deficient knees persisted in ACL‐reconstructed knees, resulting in an increase of the magnitude of cartilage contact deformation at those flexion angles. Reconstruction of the ACL restored some of the in vivo cartilage contact biomechanics of the tibiofemoral joint to normal. Clinically, recovering anterior knee stability might be insufficient to prevent post‐operative cartilage degeneration due to lack of restoration of in vivo cartilage contact biomechanics. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1781–1788, 2012     

Fixed‐bearing medial unicompartmental knee arthroplasty restores neither the medial pivoting behavior nor the ligament forces of the intact knee in passive flexion

Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces. Therefore, a computational model of the tibiofemoral joint was used to determine how non‐conforming, fixed bearing medial UKA affects tibiofemoral kinematics, and tension in the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) during passive knee flexion. Fixed bearing medial UKA could not maintain the medial pivoting that occurred in the intact knee from 0° to 30° of passive flexion. Abnormal anterior–posterior (AP) translations of the femoral condyles relative to the tibia delayed coupled internal tibial rotation, which occurred in the intact knee from 0° to 30° of flexion, but occurred from 30° to 90° of flexion following UKA. Increasing or decreasing tibial insert thickness following medial UKA also failed to restore the medial pivoting behavior of the intact knee despite modulating MCL and ACL forces. Reduced AP constraint in non‐conforming medial UKA relative to the intact knee leads to abnormal condylar translations regardless of insert thickness even with intact cruciate and collateral ligaments. This finding suggests that the conformity of the medial compartment as driven by the medial meniscus and articular morphology plays an important role in controlling AP condylar translations in the intact tibiofemoral joint during passive flexion. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1868–1875, 2018.

     

Three-dimensional motion analysis of clinical stress tests for anterior knee subluxations

The three rotations and three translations that comprise total knee motion were simultaneously measured in cadaveric knees during the commonly employed clinical tests for anterior cruciate injury. A second study determined the three-dimensional motions that occurred when known forces and moments were applied. A total of eight whole lower limbs were studied. A 6 degree-of-freedom instrumented linkage (3-D electrogoniometer), rigidly mounted to the tibia and femur, was used. The ligaments sectioned included the lateral extraarticular restraints (iliotibial band, lateral capsule) and the anterior cruciate ligament, both separately and in combination. After sectioning the anterior cruciate ligament alone, anterior displacement of both the medial and lateral tibial condyles increased markedly during the flexion rotation drawer and pivot shift tests. At 30 degrees knee flexion, total anterior-posterior displacement increased 100 percent, but internal-external tibial rotation increased only 15 percent. In all the anterior displacement type of clinical tests (including Lachman's test), there was not a true rigid coupling of knee motions because the examiner controlled the amount of internal tibial rotation and anterior tibial translation. After anterior cruciate sectioning alone, both the lateral and medial tibial condyles displaced anteriorly. Sectioning the medial structures caused additional anterior translation of the medial and lateral tibial condyles. We measured many different combinations of motions that depend on the ligament and capsular structures injured, the clinical test used, and how the clinician performed the test. Differing types of anterior subluxation require that the separate subluxations of the medial and lateral tibial condyles be determined during each stress test.     

Medical restraints to anterior-posterior motion of the knee

We investigated the motion of cadaver knees before and after section of the medial structures and anterior cruciate ligament. The knees were tested using a 5-degrees-of-freedom in vitro knee-testing apparatus that measured anterior-posterior, medial-lateral, and axial displacement as well as internal-external and valgus-varus rotation. The flexion angle could be varied but was fixed for each individual test. A 125-newton anterior-posterior force was applied perpendicular to the tibial shaft and the resulting motion of the knee was measured. In five knees the anterior cruciate ligament was cut first, followed by progressive cuts of the structures on the medial side (superficial medial collateral ligament, deep medial ligament, oblique fibers of the superficial medial ligament, and the posteromedial part of the capsule). Conversely, in five knees the medial structures were progressively cut first, followed by section of the anterior cruciate ligament. Tests were performed after each cut. With an intact anterior cruciate ligament, progressive cutting of the medial side had no effect on anterior and posterior displacements. When section of the medial structures followed cutting of the anterior cruciate ligament, anterior displacement exceeded that seen after isolated section of the anterior cruciate ligament. The anterior and posterior load-tests were repeated with the tibia fixed in 5 degrees of internal and 5 degrees of external rotation. Fixed external rotation had no effect on anterior and posterior displacements. Fixed internal rotation significantly decreased anterior displacement only when both the anterior cruciate ligament and the medial structures were cut.(ABSTRACT TRUNCATED AT 250 WORDS)     

Three-dimensional knee joint movements during a step-up: Evaluation after anterior cruciate ligament rupture

The three-dimensional motions of the knee were analysed during closed kinetic chain knee extension in 13 patients with unilateral chronic injury of the anterior cruciate ligament. The patients ascended a platform, and serial stereophotogrammetric roentgenograms were exposed from about 100° of flexion to full extension. From a position of about 100° of knee flexion and 20° of internal rotation, the tibia rotated externally during the extension. Almost no tibial adduction or abduction was observed. The tibial intercondylar eminence translated laterally, distally, and anteriorly relative to the femur. In knees with absence of the anterior cruciate ligament, the intercondylar eminence had a more posterior position compared with the contralateral normal knees. The proximal tibia was used as a fixed reference segment to evaluate the anteroposterior translations of a central point in the femoral condyles. The femoral point was more anteriorly displaced in the injured than in the contralateral knees. This difference might reflect increased activity of the hamstrings in the injured knees, because it was most pronounced at 80° of flexion and decreased with increasing extension. In the sagittal plane, the mean helical axis was positioned close to the femoral insertion of the ligament at 80° of flexion and was displaced distally and anteriorly during extension. In the frontal plane, the axis had a transverse direction at 80° of flexion. At close to full extension, the axis was positioned distally in the lateral condyle and proximally in the medial condyle. In the horizontal plane, the helical axes ran slightly more anteriorly in the medial than in the lateral femoral condyle but changed inclination at close to full extension and became almost parallel to the transverse axis.     

In Vivo Kinematics of the Anterior Cruciate Ligament Deficient Knee During Wide-Based Squat Using a 2D/3D Registration Technique

Anterior cruciate ligament (ACL) deficiency increases the risk of early osteoarthritis (OA). Studies of ACL deficient knee kinematics would be important to reveal the disease process and therefore to find mechanisms which would potentially slow OA progression. The purpose of this study was to determine if in vivo kinematics of the anterior cruciate ligament deficient (ACLD) knee during a wide-based squat activity differ from kinematics of the contralateral intact knee. Thirty-three patients with a unilateral ACLD knee consented to participate in this institutional review board approved study with the contralateral intact knee serving as the control. In vivo knee kinematics during the wide-based squat were analyzed using a 2D/3D registration technique utilizing CT-based bone models and lateral fluoroscopy. Comparisons were performed using values between 0 and 100° flexion both in flexion and extension phases of the squat activity. Both the ACLD and intact knees demonstrated increasing tibial internal rotation with knee flexion, and no difference was observed in tibial rotation between the groups. The tibia in the ACLD knee was more anterior than that of the contralateral knees at 0 and 5° flexion in both phases (p < 0.05). Tibiofemoral medial contact points of the ACLD knees were more posterior than that of the contralateral knees at 5, 10 and 15° of knee flexion in the extension phase of the squat activity (p < 0.05). Tibiofemoral lateral contact points of the ACLD knees were more posterior than that of the contralateral knees at 0° flexion in the both phases (p < 0.05). The kinematics of the ACLD and contralateral intact knees were similar during the wide-based squat except at the low flexion angles. Therefore, we conclude the wide-based squat may be recommended for the ACLD knee by avoiding terminal extension.

Key points

• In vivo knee kinematics during the wide-based squat was analyzed using a 2D/3D registration technique utilizing CT-based bone models and lateral fluoroscopy.
• Significant differences of in vivo knee kinematics between the ACLD and contralateral knees were detected at low flexion angles.
• The wide-based squat is considered a safe exercise for the ACLD knee.

Key words: 2D/3D registration technique, anterior cruciate ligament deficient knee, in vivo knee kinematics, wide-based squat activity.     

Femoral rollback after cruciate-retaining and stabilizing total knee arthroplasty

Limited data comparing the kinematics of posterior cruciate ligament-retaining or substituting total knee arthroplasty with its own intact knee under identical loadings is available. In the current study, posterior femoral translation of the lateral and medial femoral condyles under unloaded conditions was examined for intact, cruciate-retaining, cruciate ligament-deficient cruciate-retaining and posterior-substituting knee arthroplasties. Cruciate-retaining and substituting total knee arthroplasties behaved similarly to the cruciate-deficient cruciate-retaining total knee arthroplasty between 0 degrees and 30 degrees flexion. Beyond 30 degrees, the posterior cruciate-retaining arthroplasty showed a significant increase in posterior translation of both femoral condyles. The posterior cruciate-substituting arthroplasty only showed a significant increase in posterior femoral translation after 90 degrees. At 120 degrees, both arthroplasties restored approximately 80% of that of the native knee. Posterior translation of the lateral femoral condyle was greater than that observed in the medial condyle for all knees, indicating the presence of internal tibial rotation during knee flexion. The data showed that the posterior cruciate ligament is an important structure in posterior cruciate-retaining total knee arthroplasty and proper balancing is imperative to the success of the implant. The cam-spine engagement is valuable in restoring posterior femoral translation in posterior cruciate-substituting total knee arthroplasty.     

Kinematics of medial osteoarthritic knees before and after posterior cruciate ligament retaining total knee arthroplasty

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for the treatment of patients with end‐stage osteoarthritis (OA). However, the function of the knee is not always fully recovered after TKA. We used a dual fluoroscopic imaging system to evaluate the in vivo kinematics of the knee with medial compartment OA before and after a posterior cruciate ligament‐retaining TKA (PCR‐TKA) during weight‐bearing knee flexion, and compared the results to those of normal knees. The OA knees displayed similar internal/external tibial rotation to normal knees. However, the OA knees had less overall posterior femoral translation relative to the tibia between 0° and 105° flexion and more varus knee rotation between 0° and 45° flexion, than in the normal knees. Additionally, in the OA knees the femur was located more medially than in the normal knees, particularly between 30° and 60° flexion. After PCR‐TKA, the knee kinematics were not restored to normal. The overall internal tibial rotation and posterior femoral translation between 0° and 105° knee flexion were dramatically reduced. Additionally, PCR‐TKA introduced an abnormal anterior femoral translation during early knee flexion, and the femur was located lateral to the tibia throughout weight‐bearing flexion. The data help understand the biomechanical functions of the knee with medial compartment OA before and after contemporary PCR‐TKA. They may also be useful for improvement of future prostheses designs and surgical techniques in treatment of knees with end‐stage OA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:40–46, 2011     

Active knee motion after cruciate ligament rupture. Stereoradiography

In 10 patients with an old injury of the anterior cruciate ligament, the three-dimensional movements of the knee joint were studied when the patients flexed their knees. Tibial motions were recorded using roentgen stereophotogrammetric analysis. Internal rotation and adduction of the tibia were reduced in the injured knees when compared with the intact knees; during flexion of the knee joint, the tibial intercondylar eminence occupied a more lateral and posterior position on the injured side. Our results may indicate that the knee joint is continuously exposed to abnormal stresses when the anterior cruciate ligament is torn.     

Articular cartilage lesions of the knee

The pathogenesis and clinical significance of articular cartilage lesions of the knee persist as topics of considerable interest among orthopedic surgeons. This study was designed to assess the association of articular cartilage degeneration with concomitant intraarticular abnormalities and to correlate the prevalence and severity of articular cartilage damage with preoperative historical and physical exam findings in patients presenting with knee pain. Twenty-six history and physical exam data points were prospectively collected from 192 patients (200 knees), consecutively undergoing arthroscopic knee surgery. During surgery, all articular cartilage lesions were recorded with respect to size, location, and character and were graded according to Oglivie-Harris et al. All concomitant knee joint abnormalities were simultaneously recorded. Of 200 knees examined arthroscopically, 12 knees revealed no demonstrable etiology for the presenting symptoms, 65 knees revealed assorted intraarticular pathology but no articular cartilage degeneration, and the remaining 123 knees revealed a total of 211 articular cartilage lesions (103 femoral, 72 patellar, 36 tibial); 7 femoral, 6 patellar and 0 tibial lesions were completely isolated (no concomitant knee joint pathology). The concomitance of femoral defects with tibial lesions was highly significant (p = 0.01). Femoral and tibial articular cartilage lesions were strikingly correlated with the presence of an unstable torn meniscus (p less than 0.001). Medial compartment articular cartilage lesions were significantly more common (p = 0.001), more closely associated with meniscal derangement, and appreciably more severe than lateral compartment lesions. In 75% of anterior cruciate ligament-deficient knees with concomitant articular cartilage degeneration, the duration from injury to surgery was greater than 9 months, and in each of these cases, a history of reinjury to the knee was elicited. From these data one can conclude that: (a) in some patients with painful knees, isolated articular cartilage lesions may be the only abnormality noted at arthroscopy; (b) unstable meniscal tears are significantly associated with destruction of articular cartilage; (c) the medial compartment is particularly susceptible to articular cartilage degeneration; and (d) in our series, anterior cruciate ligament tears were increasingly associated with articular cartilage destruction as the elapsed time from injury to arthroscopy increased.     

Active knee motion after cruciate ligament rupture

In 10 patients with an old injury of the anterior cruciate ligament, the three-dimensional movements of the knee joint were studied when the patients flexed their knees. Tibial motions were recorded using roentgen stereopho-togrammetric analysis. Internal rotation and adduction of the tibia were reduced in the injured knees when compared with the intact knees; during flexion of the knee joint, the tibial intercondylar eminence occupied a more lateral and posterior position on the injured side. Our results may indicate that the knee joint is continuously exposed to abnormal stresses when the anterior cruciate ligament is torn.