Tibiofemoral Kinematics Research Articles

Post-cam mechanics and tibiofemoral kinematics: a dynamic in vitro analysis of eight posterior-stabilized total knee designs.

Posterior cruciate ligament (PCL)-substituting total knee arthroplasty (TKA) designs were introduced to avoid paradoxical roll forward of the femur and to optimize knee kinematics. The aim of this in vitro study was to investigate post-cam function and contact mechanics and relate it to knee kinematics during squatting in eight contemporary posterior-stabilized TKA designs. All prostheses were fixed on custom-designed metal fixtures and mounted in a knee rig and five sequential-loaded squats were performed between 30° and 130° of flexion. Contact pressure and contact area were measured using pressure-sensitive Tekscan sensors on the posterior face of the post. Kinematics was recorded with reflective markers and infrared light-capturing cameras. The post-cam mechanisms analyzed in this study are very variable in terms of design features. This leads to large variations in terms of the flexion angle at which the post and cam engage maximal contact force, contact pressure and contact area. We found that more functional post-cam mechanisms, which engage at lower flexion angle and have a similar behavior as normal PCL function, generally show more normal rollback and tibial rotation at the expense of higher contact forces and pressures. All designs show high contact forces. A positive correlation was found between contact force and initial contact angle. Post-cam contact mechanics and kinematics were documented in a standardized setting. Post-cam contact mechanics are correlated with post-cam function. Outcomes of this study can help to develop more functional designs in future. Nevertheless, a compromise will always be made between functional requirements and risk of failure. We assume that more normal knee kinematics leads to more patient satisfaction because of better mobility. Understanding of the post-cam mechanism, and knowing how this system really works, is maybe the clue in further development of new total knee designs.

ACL Reconstruction: Is There A Difference In Graft Motion For Bone-patellar Tendon-bone Vs Hamstring Autograft At 6 Weeks Post-operatively?

Objectives:Graft-tunnel healing following ACL reconstruction (ACLR) is a complex process influenced by multiple surgical variables, one of which is graft type. Clinical outcomes of bone-patellar tendon-bone (BTB) and hamstring (HS) autografts are similar, yet animal studies suggest that the healing processes may differ between the two autografts. Moreover, little is known about the relationship between graft-tunnel motion and the healing process in vivo in humans. This study was designed to compare BTB and HS graft motion within the femoral and tibial tunnels and the intra-articular graft post-operatively. We hypothesized that tunnel motion and mid-substance stretch would be greater for HS than BTB at 6 weeks following surgery.Methods:After IRB approval, 16 subjects (8 BTB, 8 HS) with an average age of 20 (range 16 to 37) underwent anatomic single-bundle ACLR by the same surgeon. Tunnel location, drilling and fixation were identical for all patients. Six 0.8 mm tantalum beads were embedded into ACL grafts prior to implantation using a custom injector. Pairs of beads were located within each bone tunnel and in the graft mid-substance (See image of graft constructs). Six weeks after surgery, CT scans were obtained and used to create 3D femur and tibia bone models. Cylindrical coordinate systems were fit to the bone tunnels to assess motion along tunnel axes. Dynamic stereo x-ray (DSX) images were collected at 100 frames/s while subjects performed treadmill walking and stair descent. Tibiofemoral kinematics were analyzed by combining the 3D models with DSX data. Graft-tunnel motion was defined as the maximum displacement of the implanted beads along the direction of the bone tunnel axis following footstrike. BTB and HS graft tunnel motions were compared using t-tests, with a significance level of p < 0.05.Results:Data are currently available for 6 BTB and 6 HS patients (N=12). Graft motion was seen in both groups within the femoral and tibial tunnels (range: 0.39 - 3.97 mm). Contrary to our hypothesis there was a trend towards greater femoral tunnel graft motion in the BTB relative to HS grafts during walking and stair descent (P=0.14 and 0.12, Table 1A-1B). There was more BTB graft motion in the femoral tunnel than in the tibial tunnel (significantly different for gait), and conversely more HS graft motion in the tibial tunnel than in the femoral tunnel (significantly different for stair descent). There was no detectable mid-substance stretch across all subjects.Conclusion:Six weeks following ACLR, less tunnel motion was expected for the BTB group compared to HS, due to the perceived advantages of bone-on-bone healing. However, more motion was observed for the BTB group within the femoral tunnel compared to HS, challenging the assumption that at 6 weeks after surgery there is greater graft-tunnel healing with BTB grafts. Based on previous studies, the native ACL elongates around 1-4% (0.3-1.2 mm) during loaded knee extension. At 6 weeks post surgery, it appears that the ACL grafts are moving in the tunnels rather than stretching in the mid-substance portion. This pattern may reverse over time, as graft-tunnel healing progresses (1-year followup testing is planned). Additionally, graft type appeared to affect the relative amount of motion between the tibial and femoral tunnels, though the cause and clinical significance of this finding is unclear. Results of this study could have important implications for graft selection, rehabilitation progression and return to sports.

Effect of Posterior Horn Medial Meniscus Root Tear on In Vivo Knee Kinematics.

Background:Medial meniscus root tear (MMRT) is a recently recognized yet frequently missed meniscal tear pattern that biomechanically creates an environment approaching meniscal deficiency.Hypothesis/Purpose:The purpose of this study was to assess the effect of MMRT on tibiofemoral kinematics and arthrokinematics during daily activities by comparing the injured knees of subjects with isolated MMRT to their uninjured contralateral knees. The hypothesis was that the injured knee will demonstrate significantly more lateral tibial translation and adduction than the uninjured knee, and that the medial compartment will exhibit significantly different arthrokinematics than the lateral compartment in the affected limb.Study Design:Cross-sectional study; Level of evidence, 3.Methods:Seven subjects with isolated MMRT were recruited and volumetric, density-based 3-dimensional models of their distal femurs and proximal tibia were created from computed tomography scans. High-speed, biplane radiographs were obtained of both their affected and unaffected knees. Moving 3-dimensional models of tibiofemoral kinematics were calculated using model-based tracking to assess overall kinematic variables and specific measures of tibiofemoral joint contact. The affected knees of the subjects were then compared to their unaffected contralateral knees.Results:Affected knees demonstrated significantly more lateral tibial translation than the uninjured contralateral limb in all dynamic activities. Additionally, the medial compartment displayed greater amounts of mobility than the lateral compartment in the injured limbs.Conclusion:This study suggests that MMRT causes significant changes in in vivo knee kinematics and arthrokinematics and that the magnitude of these changes is influenced by dynamic task difficulty.Clinical Relevance:Medial meniscus root tears lead to significant changes in joint arthrokinematics, with increased lateral tibial translation and greater medial compartment excursion. With complete root tears, essentially 100% of circumferential fibers are lost. This study will further our knowledge of meniscal deficiency and osteoarthritis and provide a baseline for more common forms of medial meniscal injuries (vertical, horizontal, radial), with various degrees of circumferential fiber function remaining.

Cartilage MRI relaxation times after arthroscopic partial medial meniscectomy reveal localized degeneration.

Little is known about the early changes in cartilage composition and tibiofemoral kinematics following partial meniscectomy. The purpose of this study was to determine the effects of partial meniscectomy on cartilage compositional properties using T1ρ and T2 relaxation time mapping and to assess changes in tibiofemoral kinematics. It is hypothesize that abnormal tibiofemoral kinematics and relaxation time elevation (a reflection of changes in cartilage biochemical composition) in the weight-bearing regions of the knees following meniscectomy will be observed. Nine patients (7 males and 2 females; mean age, 48.6 ± 10.8 years; BMI = 27.3 ± 3.8 kg/m(2)) with tears of the posterior horn of the medial meniscus underwent arthroscopic partial meniscectomy. Pre-surgical and 6 months post-surgical MRIs were obtained in all subjects to evaluate cartilage relaxation times and tibiofemoral kinematics. Paired t tests were performed to determine significant changes in cartilage relaxation times from baseline. T1ρ relaxation time in the region of the medial femoral condyle directly adjacent to the resection showed an increase of 7.4% at 6 months (p = 0.02). T2 relaxation times in both the medial and lateral tibial plateaus showed significant elevation at 6 months. Consistent kinematic trends were not found in post-meniscectomized knees. These results suggest that arthroscopic partial meniscectomy affects the biochemical composition of articular cartilage in the knee in as early as 6 months. The largest responses were observed in the weight-bearing regions and the cartilage immediately adjacent to the resection. This suggests that the loading environment has been altered enough to result in cartilage compositional changes in a very brief period of time following meniscectomy. IV.

Biotribology of a mobile bearing posterior stabilised knee design - Effect of motion restraint on wear, tibio-femoral kinematics and particles

The objective of our study was to evaluate the impact of a biphaseal anterior–posterior (AP) and internal–external (IE) motion restraint system on the wear behaviour, tibio-femoral kinematics and particle release of a mobile bearing posterior stabilised knee design in comparison to the widely used linear restraint.in vitro wear simulation was performed using a posterior stabilised total knee replacement with a mobile rotating platform gliding surface design to compare the standard ISO 14243-1:2002 (E) protocol with a linear AP and IE motion restraint and the new ISO 14243-1:2009 (E) protocol with a biphaseal AP and IE motion restraint.For the mobile gliding surfaces, an increase in wear rate by more than a magnitude was measured applying the biphaseal protocol (8.5±1.6mg/million cycles) in a direct comparison to the linear protocol (0.33±0.07mg/million cycles), with statistically significant difference. The amplitudes of AP displacement were 3.22±0.47mm for the biphaseal test, compared to 1.97±0.22mm in the linear test and the amplitudes of the IE rotation angle had mean values of 7.32°±0.91° under the biphaseal setup, compared to 1.97°±0.14° under linear motion restraint test conditions.From our observations, we conclude that the changes in AP translation and IE rotation motion restraints from ISO linear to ISO biphaseal test conditions highly impact the knee joint kinematics and wear behaviour of a mobile bearing posterior stabilised knee design.

Subject-Specific Finite Element Modeling of the Tibiofemoral Joint Based on CT, Magnetic Resonance Imaging and Dynamic Stereo-Radiography Data in Vivo

In this paper, we present a new methodology for subject-specific finite element modeling of the tibiofemoral joint based on in vivo computed tomography (CT), magnetic resonance imaging (MRI), and dynamic stereo-radiography (DSX) data. We implemented and compared two techniques to incorporate in vivo skeletal kinematics as boundary conditions: one used MRI-measured tibiofemoral kinematics in a nonweight-bearing supine position and allowed five degrees of freedom (excluding flexion-extension) at the joint in response to an axially applied force; the other used DSX-measured tibiofemoral kinematics in a weight-bearing standing position and permitted only axial translation in response to the same force. Verification and comparison of the model predictions employed data from a meniscus transplantation study subject with a meniscectomized and an intact knee. The model-predicted cartilage-cartilage contact areas were examined against "benchmarks" from a novel in situ contact area analysis (ISCAA) in which the intersection volume between nondeformed femoral and tibial cartilage was characterized to determine the contact. The results showed that the DSX-based model predicted contact areas in close alignment with the benchmarks, and outperformed the MRI-based model: the contact centroid predicted by the former was on average 85% closer to the benchmark location. The DSX-based FE model predictions also indicated that the (lateral) meniscectomy increased the contact area in the lateral compartment and increased the maximum contact pressure and maximum compressive stress in both compartments. We discuss the importance of accurate, task-specific skeletal kinematics in subject-specific FE modeling, along with the effects of simplifying assumptions and limitations.

Kinematic behaviour and soft tissue management in guided motion total knee replacement

Dissatisfaction after total knee arthroplasty (TKA) may be caused by abnormal knee kinematics, and there is concern that 'guided motion' TKAs, designed to replicate normal knee kinematics, cause anterolateral knee pain due to stretching of soft tissues. It was hypothesised that excessive tibial internal rotation and femoral rollback during flexion were to blame. Eighteen fresh-frozen specimens were used in two studies. The first study used a knee extension rig and transducers to measure ligament length changes during flexion. The second study used a knee flexion rig and optical trackers to measure tibiofemoral kinematics. Both experiments used the intact knee and were repeated with three TKAs: two guidedmotion (Journey and Journey II) and a conventional Genesis II PS TKA. TKA did not cause significant elongation of any of the ligaments examined. The medial patellofemoral ligament and the medial collateral ligament tended to be slacker post-TKA, and all three TKAs caused some tightening of the superficial iliotibial band, but these changes were not significant. Normal knee kinematics was not restored by any of the devices. The screw-home mechanism was absent in all three TKAs; anterior laxity was increased in all three devices up to 90° flexion, but tibial internal rotation was not increased. The conventional TKA allowed significantly greater anterior laxity than normal, while the Journey I caused greater tibial anterior translation in flexion. The hypothesis that over-internal rotation and rollback in the original guidedmotion knee caused excessive tightening in the soft tissues around the knee was supported; the updated design reduced that tendency. If similar changes occur during real-life activities, these results imply a potential reduction in the incidence of anterolateral knee pain clinically in patients with a guided motion TKA.

Biomechanical Analysis of Knee Laxity With Isolated Anteromedial or Posterolateral Bundle–Deficient Anterior Cruciate Ligament

The purpose of this study was to clarify the changes in the kinematics of the knee that result from isolated deficiency of the anteromedial (AM) or posterolateral (PL) bundle. Fourteen cadaveric knees were mounted in a 6-df rig and tested using the following 5 loading conditions: 90-N anterior and posterior tibial loads, 5-Nm internal and external tibial torques, and a simulated pivot-shift test. Tibiofemoral kinematics during flexion-extension was recorded with an optical tracking system for (1) intact knees, (2) knees in which the isolated AM bundle was cut, (3) knees in which the isolated PL bundle was cut, and (4) anterior cruciate ligament (ACL)-deficient knees. The distances between the femoral and tibial attachments of the AM and PL bundles of the ACL were also calculated. Anterior translation laxity under an anterior tibial load, rotational laxity under an internal tibial torque, and anterior translation laxity under pivot-shift loading were significantly different between the knees with AM and PL bundle deficiencies (P < .024), but the changes were small: less than 3 mm or 1.5°. The AM bundle distance increased significantly more after an AM bundle tear (P = .004) than after a PL bundle tear in flexion. Cutting the PL bundle did not have a significant effect on the lengths between the bundle attachments. An isolated AM or PL bundle tear caused a small increase in laxity (<3 mm or <1.5°). If there is a clinically identifiable increase in laxity, then--in addition to the isolated tear of the AM or PL bundle--there must also be a tear of the other bundle of the ACL, or at least a partial tear.

Effect of increased quadriceps tensile stiffness on peak anterior cruciate ligament strain during a simulated pivot landing

ACL injury prevention programs often involve strengthening the knee muscles. We posit that an unrecognized benefit of such training is the associated increase in the tensile stiffness of the hypertrophied muscle. We tested the hypothesis that an increased quadriceps tensile stiffness would reduce peak anteromedial bundle (AM-)ACL relative strain in female knees. Twelve female cadaver knees were subjected to compound impulsive two-times body weight loads in compression, flexion, and internal tibial torque beginning at 15° flexion. Knees were equipped with modifiable custom springs to represent the nonlinear rapid stretch behavior of a normal and increased stiffness female quadriceps (i.e., 33% greater stiffness). Peak AM-ACL relative strain was measured using an in situ transducer while muscle forces and tibiofemoral kinematics and kinetics were recorded. A 3D ADAMS™ dynamic biomechanical knee model was used in silico to interpret the experimental results which were analyzed using a repeated-measures Wilcoxon test. Female knees exhibited a 16% reduction in peak AM-ACL relative strain and 21% reduction in change in flexion when quadriceps tensile stiffness was increased by 33% (mean (SD) difference: 0.97% (0.65%), p = 0.003). We conclude that increased quadriceps tensile stiffness reduces peak ACL strain during a controlled study simulating a pivot landing.

Timing sequence of multi-planar knee kinematics revealed by physiologic cadaveric simulation of landing: Implications for ACL injury mechanism

BackgroundChallenges in accurate, in vivo quantification of multi-planar knee kinematics and relevant timing sequence during high-risk injurious tasks pose challenges in understanding the relative contributions of joint loads in non-contact injury mechanisms. Biomechanical testing on human cadaveric tissue, if properly designed, offers a practical means to evaluate joint biomechanics and injury mechanisms. This study seeks to investigate the detailed interactions between tibiofemoral joint multi-planar kinematics and anterior cruciate ligament strain in a cadaveric model of landing using a validated physiologic drop-stand apparatus. MethodsSixteen instrumented cadaveric legs, mean 45(SD 7) years (8 female and 8 male) were tested. Event timing sequence, change in tibiofemoral kinematics (position, angular velocity and linear acceleration) and change in anterior cruciate ligament strain were quantified. FindingsThe proposed cadaveric model demonstrated similar tibiofemoral kinematics/kinetics as reported measurements obtained from in vivo studies. While knee flexion, anterior tibial translation, knee abduction and increased anterior cruciate ligament strain initiated and reached maximum values almost simultaneously, internal tibial rotation initiated and peaked significantly later (P<0.015 for all comparisons). Further, internal tibial rotation reached mean 1.8(SD 2.5)°, almost 63% of its maximum value, at the time that peak anterior cruciate ligament strain occurred, while both anterior tibial translation and knee abduction had already reached their peaks. InterpretationTogether, these findings indicate that although internal tibial rotation contributes to increased anterior cruciate ligament strain, it is secondary to knee abduction and anterior tibial translation in its effect on anterior cruciate ligament strain and potential risk of injury.

A new spacer-guided, PCL balancing technique for cruciate-retaining total knee replacement

The goal of this study was to investigate whether a new posterior cruciate ligament (PCL) balancing approach with a spacer technique during total knee arthroplasty (TKA) reproduced the correct tibiofemoral contact point (CP) location. It was hypothesized that it should be possible to adequately balance the PCL with this geometrical technique, obtaining correct position and stability of the medial femoral condyle, independent of insert shape. Nine fresh-frozen full-leg cadaver specimens were used. After native testing, prototype components of a new PCL-retaining implant were implanted using navigation and a bone-referencing technique. After finishing the bone cuts, the spacer technique was used to ascertain balancing of the PCL and the tibial cut was corrected if necessary. Passive and squat motions were performed before and after TKA using a dynamic knee simulator while tibiofemoral kinematics were recorded using six infrared cameras. CPs (native and implant) were calculated as the projections of the femoral condylar centres on the horizontal plane of the tibia. The spacer technique resulted in correct PCL balancing in all specimens. The kinematic patterns of native and replaced knees showed no statistically significant differences in passive and squat motions. The medial CP after TKA was at the same position as in the native knee. No paradoxical sliding forward was seen after TKA, supporting our hypothesis. The spacer technique can be applied by surgeons during PCL-retaining TKA and will lead to good PCL balancing, indicated by a correct CP, no lift-off in flexion and no posterior sag.

Effect of Increased Iliotibial Band Load on Tibiofemoral Kinematics and Force Distributions: A Direct Measurement in Cadaveric Knees

Controlled laboratory study using cadaveric knee specimens and a repeated-measures design. To investigate the effect of increased iliotibial band load (assumed to represent increased tensor fascia latae and gluteus maximus strength) on tibiofemoral kinematics and force distribution on the tibiofemoral articulation. Owing to the difficulty in measuring in vivo joint loading, there is limited evidence on the direct relationship between increased iliotibial band load and force distribution in the tibiofemoral articulation. Eight fresh-frozen cadaveric knee specimens were used in this study. A robotic testing system assessed tibiofemoral kinematics under 3 simulated loading conditions: (1) 300-N quadriceps load, 100-N hamstrings load, 0-N iliotibial band load; (2) 300-N quadriceps load, 100-N hamstrings load, 50-N iliotibial band load; and (3) 300-N quadriceps load, 100-N hamstrings load, 100-N iliotibial band load. The load distribution in the medial and lateral tibiofemoral articulation was also measured under these loading conditions by using piezoelectric pressure sensors. Data were collected and analyzed at full extension and at 5°, 10°, 15°, 20°, 25°, and 30° of knee flexion. The loads transmitted through the medial tibiofemoral articulation significantly decreased when the load on the iliotibial band was increased, with a concomitant significant increase in lateral tibiofemoral articulation load. Greater iliotibial band load also increased anterior tibial translation and valgus tibial rotation, and decreased the amount of internal tibial rotation and medial tibial translation. The present study demonstrated that an increase in iliotibial band load, when tested in a non-weight-bearing condition in a cadaveric model, can significantly decrease the loads transmitted through the medial tibiofemoral articulation.

Anterior Cruciate Ligament–Deficient Patients With Passive Knee Joint Laxity Have a Decreased Range of Anterior-Posterior Motion During Active Movements

Background: Although instability of the knee joint is known to modify gait patterns, the amount that patients compensate for joint laxity during active movements remains unknown. Purpose: By developing a novel technique to allow the assessment of tibiofemoral kinematics, this study aimed to elucidate the role of passive joint laxity on active tibiofemoral kinematics during walking. Study Design: Controlled laboratory study. Methods: Using motion capture, together with combinations of advanced techniques for assessing skeletal kinematics (including the symmetrical axis of rotation approach [SARA], symmetrical center of rotation estimation [SCoRE], and optimal common shape technique [OCST]), a novel noninvasive approach to evaluate dynamic tibiofemoral motion was demonstrated as both reproducible and repeatable. Passive and active anterior-posterior translations of the tibiofemoral joint were then examined in 13 patients with anterior cruciate ligament (ACL) ruptures that were confirmed by magnetic resonance imaging and compared with those in their healthy contralateral limbs. Results: Passive tibial anterior translation was significantly greater in the ACL-ruptured knees than in the contralateral healthy controls. However, the femora of the ACL-ruptured knees generally remained more posterior (~3 mm) relative to the tibia within a gait cycle of walking compared with the healthy limbs. Surprisingly, the mean range of tibiofemoral anterior-posterior translation over an entire gait cycle was significantly lower in ACL-ruptured knees than in the healthy joints (P = .026). A positive correlation was detected between passive laxity and active joint mobility, but with a consistent reduction in the range of tibiofemoral anterior-posterior translation of approximately 3 mm in the ACL-deficient knees. Conclusion: It seems that either active stabilization of tibiofemoral kinematics or anterior subluxation of the tibia reduces joint translation in lax knees. This implies that either a muscular overcompensation mechanism or a physical limitation due to secondary passive stabilizers occurs within the joint and thus produces a situation that has a reduced range of active motion compared with knees with physiological stability. Clinical Relevance: The reduced range of active tibiofemoral translation suggests overloading of the passive structures in passively lax knees, either through excessive muscular action or joint subluxation, and could provide a plausible mechanism for explaining posttraumatic degeneration of cartilage in the joint.

Anterior Cruciate Ligament Fatigue Failures in Knees Subjected to Repeated Simulated Pivot Landings

Background: It is not known whether the human anterior cruciate ligament (ACL) is susceptible to fatigue failure as a result of repetitive loading or whether certain knee morphologic characteristics increase that risk. Hypotheses: The number of knee loading cycles required to fail an ACL by fatigue failure is unaffected by the magnitude of the external load delivered to the knee joint. Furthermore, sex, ACL cross-sectional area, and lateral tibial slope will not affect the number of loading cycles to ACL failure. Study Design: Controlled laboratory study. Methods: Knee pairs from 10 cadaveric donors (5 female) of similar age, height, and weight were imaged with 3-T magnetic resonance imaging to measure lateral tibial slope and ACL cross-sectional area. One knee from each pair was then subjected to repeated application of a load of 3 times body weight (3*BW), while the other knee was subjected to a 4*BW load, both involving impulsive compression force, knee flexion moment, and internal tibial torque combined with realistic trans-knee muscle forces. The resulting 3-dimensional tibiofemoral kinematics and kinetics were recorded, along with ACL relative strain and quadriceps, hamstring, and gastrocnemius muscle forces. The loading cycle was repeated until the ACL ruptured, a 3-mm increase in cumulative anterior tibial translation occurred, or a minimum of 50 trials was reached. Results: Eight of 10 knees failed under the 4*BW load (mean ± SD cycles to failure, 21 ± 18), while 5 of 10 knees failed under the 3*BW load (mean ± SD cycles to failure, 52 ± 10). Four knees exhibited a 3-mm increase in anterior tibial translation, 7 knees developed partial or complete visible ACL tears, and 2 knees developed complete ACL tibial avulsions. A Cox regression showed that the number of cycles to ACL failure was influenced by the simulated landing force (P = .012) and ACL cross-sectional area (P = .022). Donor sex and lateral tibial slope did not influence the number of cycles to ACL failure. Conclusion: The human ACL is susceptible to fatigue failure when pivot landings of 3*BW or more load the knee repeatedly within a short time span. An ACL with a smaller cross-sectional area is at greater risk for this type of failure. Clinical Relevance: The results show that the human knee can only withstand a certain number of 3*BW or greater jump loading cycles within a short time period before the ACL will fail. Therefore, limiting the increase in the number and severity of pivot landing maneuvers performed over a week of training would make sense from an injury prevention viewpoint.

Optimized Design of an Instrumented Spatial Linkage that Minimizes Errors in Locating the Rotational Axes of the Tibiofemoral Joint: A Computational Analysis

An accurate method to locate of the flexion-extension (F-E) axis and longitudinal rotation (LR) axis of the tibiofemoral joint is required to accurately characterize tibiofemoral kinematics. A method was recently developed to locate these axes using an instrumented spatial linkage (ISL) (2012, "On the Estimate of the Two Dominant Axes of the Knee Using an Instrumented Spatial Linkage," J. Appl. Biomech., 28(2), pp. 200-209). However, a more comprehensive error analysis is needed to optimize the design and characterize the limitations of the device before using it experimentally. To better understand the errors in the use of an ISL in finding the F-E and LR axes, our objectives were to (1) develop a method to computationally determine the orientation and position errors in locating the F-E and LR axes due to transducer nonlinearity and hysteresis, ISL size and attachment position, and the pattern of applied tibiofemoral motion, (2) determine the optimal size and attachment position of an ISL to minimize these errors, (3) determine the best pattern of pattern of applied motion to minimize these errors, and (4) examine the sensitivity of the errors to range of flexion and internal-external (I-E) rotation. A mathematical model was created that consisted of a virtual "elbow-type" ISL that measured motion across a virtual tibiofemoral joint. Two orientation and two position errors were computed for each axis by simulating the axis-finding method for 200 iterations while adding transducer errors to the revolute joints of the virtual ISL. The ISL size and position that minimized these errors were determined from 1080 different combinations. The errors in locating the axes using the optimal ISL were calculated for each of three patterns of motion applied to the tibiofemoral joint, consisting of a sequential pattern of discrete tibiofemoral positions, a random pattern of discrete tibiofemoral positions, and a sequential pattern of continuous tibiofemoral positions. Finally, errors as a function of range of flexion and I-E rotation were determined using the optimal pattern of applied motion. An ISL that was attached to the anterior aspect of the knee with 300-mm link lengths had the lowest maximum error without colliding with the anatomy of the joint. A sequential pattern of discrete tibiofemoral positions limited the largest orientation or position error without displaying large bias error. Finally, the minimum range of applied motion that ensured all errors were below 1 deg or 1 mm was 30 deg flexion with ±15 deg I-E rotation. Thus a method for comprehensive analysis of error when using this axis-finding method has been established, and was used to determine the optimal ISL and range of applied motion; this method of analysis could be used to determine the errors for any ISL size and position, any applied motion, and potentially any anatomical joint.

Is there a gold standard for TKA tibial component rotational alignment?

Joint function and durability after TKA depends on many factors, but component alignment is particularly important. Although the transepicondylar axis is regarded as the gold standard for rotationally aligning the femoral component, various techniques exist for tibial component rotational alignment. The impact of this variability on joint kinematics and stability is unknown. We determined how rotationally aligning the tibial component to four different axes changes knee stability and passive tibiofemoral kinematics in a knee after TKA. Using a custom surgical navigation system and stability device to measure stability and passive tibiofemoral motion, we tested 10 cadaveric knees from five hemicorpses before TKA and then with the tibial component aligned to four axes using a modified tibial tray. No changes in knee stability or passive kinematics occurred as a result of the four techniques of tibial rotational alignment. TKA produces a 'looser' knee over the native condition by increasing mean laxity by 5.2°, decreasing mean maximum stiffness by 4.5 N·m/°, increasing mean anterior femoral translation during passive flexion by 5.4 mm, and increasing mean internal-external tibial rotation during passive flexion by 4.8°. However, no statistically or clinically important differences occurred between the four TKA conditions. For all tibial rotations, TKA increased laxity, decreased stiffness, and increased tibiofemoral motion during passive flexion but showed little change based on the tibial alignment. Our observations suggest surgeons who align the tibial component to any of the axes we examined are expected to have results consistent with those who may use a different axis.

Tibial Tuberosity Realignment Alters in Vivo Patellar Tracking

Objectives:For patients with recurrent patellofemoral instability, tibial tuberosity medialization is commonly performed to reduce the lateral force applied to the patella by the patellar tendon. Medialization also alters the force acting on the tibia, which could alter tibiofemoral kinematics. Several other procedures are advocated to treat patellar instability, some of which are combined with medialization. The current study uses computational reconstruction of in vivo function to evaluate the influence of tibial tuberosity medialization on patellofemoral and tibiofemoral motion.Methods:Six patients preparing to undergo tuberosity medialization for recurrent instability were evaluated pre-operatively and one year post-operatively. Procedures performed in combination with medialization included tuberosity anteriorization in five patients, medial patellofemoral ligament (MPFL) reconstruction in five patients, tuberosity distalization in two patients, and lateral retinacular release in two patients. Each patient performed a knee extension exercise without external resistance while lying on the bed of a dynamic CT scanner (Aquilion ONE scanner, Toshiba Medical Systems). Models of the femur, tibia and patella were reconstructed from 5 or 6 volumes of 320 axial images separated by 0.5 mm spanning the extension range. Local coordinate systems were created for each pre-operative bone in the most extended position based on anatomical landmarks. Every other reconstruction of the knee was aligned to the most extended knee by shape-matching the distal femurs. The patella and tibia with the embedded reference axes were copied and individually shape-matched to replace all other pre-operative and post-operative bones. Tibiofemoral and patellofemoral kinematics were quantified at each position of knee flexion. The patellar lateral shift and tilt and the external rotation of the tibia were interpolated to 5°, 10°, 20°, 30°, and 40° of flexion and compared between the pre-operative and post-operative conditions at each flexion angle with a paired t-test.Results:Surgical realignment altered patellofemoral (Fig. 1) and tibiofemoral kinematics. Realignment decreased the average patellar lateral shift and tilt by more than 3 mm and 3°, respectively, at all flexion angles, with the change greatest at the lowest flexion angles (Table 1). Both changes were significant at 5° and 10° of flexion. The average tibial external rotation increased by approximately 2° following surgery, with the change most consistent with the knee flexed. The change was significant at 30° and 40° of flexion.Conclusion: The study indicates that tuberosity medialization reduces patellar lateral shift and tilt in patients with recurrent instability. The change is greatest when the patella is superior to the trochlear groove near full extension. The altered kinematics should reduce the risk of instability. The procedures performed in addition to medialization complicate the analysis. Simultaneous MPFL reconstruction performed for five knees could have contributed to altered tracking, although the MPFL was reconstructed to act as only a checkrein against dislocation. Increased tibial external rotation due to the change in orientation of the patellar tendon is an unintended consequence of tuberosity medialization. The long term influence of this change on the tibiofemoral joint is currently unknown.

The Role of the Indirect Femoral Insertion of the Anterior Cruciate Ligament in Restraining Tibial Translation and Rotation: Implications for Anatomic Femoral Tunnel Placement

Objectives:Despite a trend toward lowering the femoral tunnel and thus positioning ACL grafts partially within the indirect insertion of the ACL attachment, the biomechanical role of the indirect insertion has not been described. The purpose of this study was to determine the effect of debridement of the indirect femoral ACL insertion on tibiofemoral translation and rotation. It was hypothesized that debridement would have a negligible affect on tibiofemoral kinematics.Methods:Knee kinematics in six degrees of freedom were measured on a robotic device in nine cadaveric knees. Measurements were made with the ACL intact, following debridement of the indirect insertion, and following complete sectioning of the ACL. Three loading conditions were used: (1) a 134 N anterior tibial load, (2) a combined 10 Nm valgus and 5 Nm internal rotation torque, and (3) a simulated, robotic pivot shift. Debridement involved exposing 5-6 mm of bone from the central, inferior aspect of the direct ACL attachment to the inferior cartilage margin. Anterior tibial translation (ATT) was recorded in response to an anterior tibial load and combined rotatory loads at 0°, 15°, 30°, 45°, 60°, and 90° of knee flexion. Additionally, posterior tibial translation and external tibial rotation were recorded during a simulated, robotic pivot shift. Based on pilot data, it was estimated that 9 specimens would be required to detect a 1.4 mm difference in ATT between different experimental conditions with 80% power at an alpha level of 0.05. Data were analyzed using repeated measures ANOVA.Results:For the anterior tibial loading condition, debridement of the indirect insertion increased tibial translation by 0.37±0.24 mm at 0º (P<.01) and by 0.16±0.19 mm at 15º (P<.05; increases were < 1 mm in all specimens). ACL deficiency increased ATT in response to an anterior tibial load (P<.0001) with maximum effect at 15º (11.26±1.15 mm vs. ACL intact; 11.04±1.08 mm vs. indirect insertion debridement). For the combined rotatory loading condition, debridement increased tibial translation by 0.17±0.11 mm at 0º (P<.01; increases were < 0.3 mm in all specimens) with no effect at other flexion angles. ACL deficiency increased ATT in response to a combined rotatory load (P<.01) with maximum effect at 15º (4.45±0.85 mm vs. ACL intact; 4.44±0.84 mm vs. indirect insertion debridement). The contribution of the indirect insertion to restraining ATT in response to an anterior tibial load or a combined rotatory load was ≤ 5.5% in all specimens, at all flexion angles. During the simulated pivot shift, posterior tibial translation (12.79±3.22 mm) and external tibial rotation (17.60±4.30º) were greater in the ACL deficient condition (P<.0001) compared with the ACL intact (1.29±1.34 mm and 1.54±1.61º) and indirect insertion debridement conditions (1.28±1.34 mm and 1.54±1.47º). Posterior translation and external tibial rotation were not significantly different between the ACL intact and debridement conditions (P=.68, P=.99).Conclusion:Debridement of the indirect insertion resulted in a less than 1 mm increase in tibial translation and a less than 0.5º increase in tibial rotation in all specimens and testing conditions. Thus, the indirect femoral insertion of the ACL contributed minimally to restraint of tibial translation and rotation. These results support placement of the soft tissue aspect of a BPTB graft within the area of the direct insertion of the ACL and superior to the biomechanically insignificant indirect insertion.

Tibiofemoral kinematics: the effect of footwear and foot orthoses during running

Background The knee is the most common site of running related injuries (42.1% of all injuries). Orthoses are thought to manage knee pain by reducing internal tibial rotation as the subtalar joint pronates. However, the influence of the footwear that orthoses are placed in is often ignored. This study aimed to determine the immediate effects of footwear and foot orthoses on transverse plane rotation of the tibiofemoral joint during the stance phase of running.

Relationship between Static Anterior Laxity Using the KT-1000 and Dynamic Tibial Rotation during Motion in Patients with Anatomical Anterior Cruciate Ligament Reconstruction

The anterior cruciate ligament (ACL) plays an important role in controlling knee joint stability, not only by limiting tibial anterior translation but also by controlling knee axial rotation. The aim of ACL reconstruction is to reduce excessive anterior joint laxity, hoping to restore normal tibiofemoral kinematics including knee axial rotation. The purpose of this study was to investigate the relationship between static anterior instability and tibial rotation during several activities in an anterior cruciate ligament reconstructed knee. Seven patients with unilateral ACL injury performed plain walking, running, landing and side step cutting tasks after ACL reconstruction with a mean follow-up of 14 months. The kinematic data for the 4 motions was measured using a motion analysis system and the point cluster technique. The evaluation period was defined to be from the first contact to removal of the tested leg from the ground. Maximum tibial internal rotation during tasks was calculated using the point cluster technique (PCT). Passive anterior tibial translation was measured using a KT-1000 arthrometer. Regression analysis was used to determine the correlation of the maximum internal rotation with the side-to-side difference of static anterior tibial translation measured using a KT-1000 arthrometer. During side step cutting maneuvers, maximum tibial internal rotation significantly showed negative correlation with static anterior tibial translation (p<0.05, r=0.83). The anterior laxity contributed to the normal knee rotation kinematics. The normal anterior tibial translation obtained by ACL reconstruction is thought to be the key factor in successful restoration of normal knee kinematics.