Obtaining anatomic motion and laxity characteristics in a total knee design

BackgroundSince the introduction of the first total knee designs, a frequent design goal has been to reproduce normal knee motion. However, studies of many currently used total knee designs, have shown that this goal has not been achieved. We proposed that Guided Motion total knee designs, could achieve more anatomic motion than present standard designs.MethodsSeveral Guided Motion knees for application without cruciate ligaments were designed using a computer method where the bearing surfaces were generated by the motion required. A knee testing machine was constructed where physiological forces including compressive, shear and torque were applied during knee flexion. The neutral path of motion and the laxity about the neutral path were measured. This evaluation method was a modification of the ASTM standard Constraint Test.ResultsThe motions of the Guided Motion knees and a standard PS knee were compared with the anatomic motion of knee specimens determined in an earlier study The Guided Motion knees showed motion patterns which were closer to anatomic than the PS knee.ConclusionsThe results provided justification for carrying out further evaluations of functional conditions, using either knee simulators or computer modelling. If anatomic motions could be reproduced in vivo, it is possible that clinical outcomes could be improved.     

Assessment of the antero-posterior and rotational stability of the anterior cruciate ligament analogue in a guided motion bi-cruciate stabilized total knee arthroplasty

Abnormal knee kinematics and sagittal instability after most knee replacements are due in part to deficient anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) function. The guided motion bi-cruciate stabilized knee replacement aspires to stabilize the knee posteriorly and anteriorly by means of a cam-post mechanism. This investigation studies the ACL-stabilizing function of that mechanism in early flexion, and 25 knees that had undergone replacement with this implant were studied. Antero-posterior laxity at 15° flexion was adequately restored for 76% (16/21) of the knees (side-to-side difference <3?mm on KT assessment), and 72% (18/25) knees exhibited a positive pivot shift test. The findings of this study suggest excellent early clinical outcomes for this implant, but the goal of replicating ACL function has only been partially achieved.     

Biomechanics of the knee joint in deep flexion: a prelude to a total knee replacement that allows for maximum flexion.

A two-dimensional anatomically based mathematical model of the human knee joint was developed to understand its biomechanics in deep flexion. The model was used to determine the internal knee loads as it simulates isometric quadriceps and hamstring co-contractions at different flexion angles during deep squat. It was found that in order to achieve deep flexion, large muscle forces are required, resulting in large tibio-femoral contact forces. In deep flexion, the femoral contact point was located on the most proximal point of the posterior condyle, location which was not affected by the level of quad activation. Conversely, the location of the tibial contact point was highly affected by the level of quad activation. Both anterior and posterior fiber bundles of the posterior cruciate ligament were found to carry high loads when the knee is maximally flexed. These results point to the important role of the posterior cruciate ligament in this position, and suggest the necessity of retaining this ligament during total knee replacement (TKR) procedures that allows for maximum flexion angles. Furthermore, the present data provide an explanation why most TKR's do not allow deep flexion: while contact occurs on the most proximal points of the posterior condyles in normal knees, this portion of the condyles is not presently resurfaced when performing a TKR.     

Manipulation under anaesthesia post total knee replacement: long term follow up

A reduced range of motion post total knee replacement (TKR) is a recognised problem. Manipulation under anaesthesia (MUA) is commonly performed in the stiff post-operative TKR. Long-term results are variable in the literature. We retrospectively reviewed, prospectively collected data on 48 patients followed up since 1996 from one centre, over an average of 7.5 years, (range 1 to 10 years) and report on the long-term results. During the study period 2.3% of TKRs underwent MUA. The mean time to MUA post TKR was 12.3 weeks (range 3 to 48). Pre MUA, the mean flexion was 53°. The mean immediate passive flexion post MUA was 97°, an improvement of 44° (Range 10° to 90°, p<0.05). By 1year, the mean flexion was 87°, an improvement of 34°, (range -15° to 70°, p<0.05). At 10 years the mean flexion was 86°, (range 55° to 100°, p<0.05). We found no difference in the gain in range of motion (ROM) between knees manipulated before or after 12 weeks. Additionally, the gain was no different in stiff knees with a pre TKR ROM <90°, compared to a pre TKR ROM >90°. There were no complications as a result of MUA. However, one patient was eventually revised at 2 years secondary to low grade infection. Our findings show that MUA is a safe and effective method at improving the ROM in a stiff post-operative TKR. The improvement is maintained in the long term irrespective of time to MUA and range of motion pre TKR.     

全膝关节置换后关节后方复合松解的可行性评价

背景：临床对于膝骨关节炎患者可以实施全膝关节置换治疗,为提高修复效果,促进功能恢复,要采取有效措施改善置换过程中的关节间隙以及置换后的关节活动度。 目的：探讨全膝关节置换后行关节后方复合松解的有效性及可行性。 方法：从两家三甲医院2009年12月至2013年12月收治的行单侧全膝关节置换的膝骨关节炎患者中选择118例进行研究,随机分为对照组和观察组,每组59例。在患者全膝关节置换过程中完成截骨之后,对照组行常规后髁增生骨清理,观察组行关节后方复合松解。观察两组患者置换后伸、屈膝间隙情况和主动屈膝90°和120°所需时间,记录3个月随访时的膝关节功能美国纽约特种外科医院评分以及最大屈膝角度,并进行比较。 结果与结论：经统计和比较,两组患者在屈膝间隙方面差异无显著性意义(P > 0.05);但在伸膝间隙、主动屈膝90°、120°所需时间以及最大屈膝角度方面,两组差异均有显著性意义,观察组优于对照组(P均< 0.05)。比较置换后3个月两组患者的膝关节功能美国纽约特种外科医院评分,可得观察组的各项指标得分以及总分均显著高于对照组,差异均有显著性意义(P均 < 0.05)。表明全膝关节置换后行关节后方复合松解具有一定的有效性和可行性,可以有效改善置换过程中伸膝间隙以及置换后膝关节活动度,但对置换过程中屈膝间隙方面无明显影响。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

Recognizing knee pathologies by classifying instantaneous screws of the six degrees-of-freedom knee motion

We address the problem of knee pathology assessment by using screw theory to describe the knee motion and by using the screw representation of the motion as an input to a machine learning classifier. The flexions of knees with different pathologies are tracked using an optical tracking system. The instantaneous screw parameters which describe the transformation of the tibia with respect to the femur in each two successive observation is represented as the instantaneous screw axis of the motion given in its Plücker line coordinates along with its corresponding pitch. The set of instantaneous screw parameters associated with a particular knee with a given pathology is then identified and clustered in R ⁶ to form a “signature” of the motion for the given pathology. Sawbones model and two cadaver knees with different pathologies were tracked, and the resulting screws were used to train a classifier system. The system was then tested successfully with new, never-trained-before data. The classifier demonstrated a very high success rate in identifying the knee pathology.

Influence of posterior condylar offset on knee flexion after cruciate-sacrificing mobile-bearing total knee replacement: A prospective analysis of 410 consecutive cases

The range of motion of the knee joint after Total Knee Replacement (TKR) is a factor of great importance that determines the postoperative function of patients. Much enthusiasm has been recently directed towards the posterior condylar offset with some authors reporting increasing postoperative knee flexion with increasing posterior condylar offset and others who did not report any significant association. Patients undergoing primary total knee replacement were included in a prospective multicentre study and the effect of the posterior condylar offset on the postoperative knee flexion was assessed after adjusting for known influential factors. All knees were implanted by three senior orthopedist surgeons with the same cemented cruciate-sacrificing mobile-bearing implant and with identical surgical technique. Clinical data, active knee flexion and posterior condylar offset were recorded preoperatively and postoperatively at a minimal one year follow-up for all patients. Univariate and multivariate linear models were fitted to select independent predictors of the postoperative knee flexion.Four hundred and ten consecutive total knee replacements (379 patients) were included in the study. The mean preoperative knee flexion was 112°. The mean condylar offset was 28.3 mm preoperatively and 29.4 mm postoperatively. The mean postoperative knee flexion was 108°. No correlation was found between the posterior condylar offset or the tibial slope and the postoperative knee flexion. The most significant predictive factor for postoperative flexion after posterior-stabilized TKR without PCL retention was the preoperative range of flexion, with a linear effect.     

Knee kinematics during walking at different speeds in people who have undergone total knee replacement

People who have undergone total knee replacement (TKR) experience difficulties in some daily activities including walking. Walking at faster speeds requires more knee flexion and may therefore present a greater challenge following TKR. The aim of this study was to compare the knee kinematics of patients following TKR and unimpaired controls during comfortable and fast walking speeds. Forty patients (22 women, 18 men) 12 months following TKR and 40 control participants (matched for age and sex) were assessed during walking at self-selected comfortable and fast speeds using three dimensional motion analysis. The group averages of spatiotemporal and peak kinematic characteristics in the sagittal, coronal and transverse movement planes were compared using univariate analysis of variance with walking speed as a co-variate. The TKR group walked with significantly reduced cadence (p < 0.001 at both speeds) and reduced stride length (p < 0.001 at both speeds), less knee flexion during stance and swing phases (p < 0.001 for both speeds) and less knee extension during stance phase (p < 0.024 for comfortable speed; p < 0.042 for fast speed). The TKR group also walked with less peak knee external rotation than controls at both speeds (p < 0.001 for both speeds). Both groups increased their velocity, cadence and stride length by a similar proportion when walking at fast speed. When walking at a faster speed, spatiotemporal gait parameters and knee motion are altered in a similar manner for both TKR patients and controls. However, at both walking speeds, TKR patients exhibit residual deficits 12 months following surgery.     

Intra-operative navigation of knee kinematics and the influence of osteoarthritis

Intra-operative assessment of knee kinematics should optimise implantation of total knee arthroplasties. The purpose of this work was to validate the data delivered by an adapted navigation system in 10 healthy cadaver knees and to investigate the kinematics of 10 osteoarthritic (OA) knees in patients undergoing total knee replacement. The system displayed the magnitude of axial rotation, the position of the instantaneous centre of axial rotation and the displacements of the condyles. Successive cycles from full extension to 140° of flexion in the same knee produced a mean external rotation of 20° ± 10°, which was correlated to knee flexion (r=0.6 ± 0.2 in healthy knees, r=0.8 ± 0.2 in OA knees). The centre of axial rotation migrated posteriorly an average of 8.2mm in both groups. The posterior displacements were 4 mm ± 5 mm in healthy and 5 mm ± 6 mm in OA knees for the medial condyle, and 21 mm ± 9 mm in healthy and 21 mm ± 10 mm in OA knees for the lateral condyle. The medial condyle lifted off beyond 110° of flexion. Results in healthy knees were consistent with those reported in the current literature. The kinematics of healthy and of OA knees with an intact anterior cruciate ligament did not differ significantly.     

Gait analysis of patients following total knee replacement: a systematic review

Gait analysis has been used to objectively measure patients' function following total knee replacement (TKR). Whilst the findings of this research may have important implications for the understanding of the outcomes of TKR, the methodology of existing research appears to be diverse and many of the results inconsistent. The objective of this systematic review was to synthesise reported findings and to summarise the methods used by researchers in this field. Eleven articles published in the medical literature that used gait analysis to compare patients following TKR with controls were identified for inclusion in this review. Each article was assessed for methodologic quality and data was compared across studies through the calculation of effect sizes. Consistently large effect sizes showed that patients following TKR walk with less total knee motion during gait and with less knee flexion during swing than controls. Kinetic discrepancies between patients and controls were also identified. The substantial methodologic differences between studies may contribute to the inconsistencies in reported findings for many gait outcomes. Future research is needed to determine the clinical relevance of these findings.     

Quantifying the kinematics of natural and prosthetic knee flexion

A new method has been developed for quantifying knee kinematics during flexion. This method was used to measure knee kinematics from lateral radiographs taken at different angles of flexion with the two femoral condyles superimposed in each image, thus standardizing the plane of flexion-extension. When applied to the radiographs of five healthy male volunteers (age range 21–26 years), it showed that flexion was accompanied by translation between the articular surfaces. Knee kinematics were also measured in five patients after total knee replacement (TKR) surgery with a Kinemax^TM Modular Total Knee prosthesis (Howmedica, Warsaw, Indiana). In the TKR patients, a translation was detected in three out of the five patients. This indicates that the prosthesis is capable of restoring normal kinematics, but does not always do so.     

Relative positions of the contacts on the cartilage surfaces of the knee joint

The goal of this project was to determine the centers of contacts (points of closest approach of the articular surfaces) for the tibio-femoral and patello-femoral joints throughout the flexion range, with a focus on high flexion where there is potential overlap between the contacts. The purpose was to determine the implications to the design of joint replacements and tissue engineered implants. Eight cadaveric knees were mounted in a rig with different loading combinations applied to the femur, including axial load, anterior/posterior shear, and internal/external torque. The range of flexion was 0 degrees to 155 degrees . Reference points on the bones measured during the experiments were used to later reconstruct an accurate 3D computer model of the multiple joint positions and determine the centers of contact between the opposing bearing surfaces. The tibio-femoral contact at 0 degrees flexion was displaced 5 mm anterior to the notch (the end point of the articular cartilage on the mid-line of the femoral sulcus) on the medial side, while remaining level with the notch on the lateral side. The patella contacts on the femur extended 15 mm posterior to the intercondylar notch with a centerline between the lateral and medial paths being several millimeters lateral to the center of the femur. The centers of the patella contacts were close to the inner margin of the medial condyle and did not directly overlap with the centers of the tibial contacts. On the lateral side the patella contacts ended where the tibial contacts began. For applications to medial unicondylar knee replacement design it was shown that patellar impingement on the anterior of the femoral component would occur at 110 degrees flexion. For TKR design, a continuous patella contact up to high flexion could be obtained by extending the trochlea 15 mm posterior to the intercondylar notch.     

Laxity and contact forces of total knee designed for anatomic motion: A cadaveric study

Background

Total knee designs that attempt to reproduce more physiological knee kinematics are gaining attention given their possible improvement in functional outcomes. This study examined if a total knee designed for anatomic motion, where the soft tissue balancing was intended to replicate anatomical tibiofemoral contact forces, can more closely reproduce the laxity of the native knee.

Bilateral non-union of high tibial osteotomies treated by total knee arthroplasty: a case report

Non-union following high tibial osteotomy (HTO) is very uncommon. We present a case of bilateral non-union of HTOs with end-stage knee arthritis treated with staged, bilateral, posterior stabilized knee replacements. A 77-year-old female presented to our clinic with complaints of debilitating knee pain. She used a frame to get about in her home, she was unable to get up stairs, and she rarely went outside. Simple radiographs revealed bilateral non-unions of her osteotomies, subluxation of the tibial plateauxs and severe knee osteoarthritis. At the time of surgery, the non-unions were found to be fibrous stable. We took a minimal tibial plateaux resection and used long stem tibial stems with offset couplers to bypass the non-unions. At minimum 1 year follow-up, she was walking pain free with full knee range of motion. We found that primary total knee replacement (TKR) using tibial stems and without treating the tibial non-union gave satisfactory results.     

A randomised controlled trial investigating the effect of posterior capsular stripping on knee flexion and range of motion in patients undergoing primary knee arthroplasty

Increasing knee flexion following total knee arthroplasty (TKA) has become an important outcome measure. Surgical technique is one factor that can influence knee motion.In this study, it was hypothesised that stripping of the posterior knee capsule could improve flexion and range of motion (ROM) following TKA.Patients who were undergoing TKA were prospectively randomised into two groups — one group (62 patients) were allocated stripping of the posterior knee capsule (PCS), the other group (66 patients) no stripping (no-PCS).The primary outcome was change in flexion and ROM compared to pre-operative measurements at three time points; after wound closure, 3 months and 1 year post-operatively. Secondary outcomes were absolute measurements of flexion, extension, ROM and complications. All operations were performed by a single surgeon using the same implant and technique. All patients received identical post-operative rehabilitation.There was a significant gain in flexion after wound closure in the PCS group (p = 0.022), however there was no significant difference at 3 months or 1 year post-operatively. Absolute values of extension (p = 0.008) and flexion (p = 0.001) 3 months post-operatively were significantly reduced for the PCS group. The absolute value of ROM was significantly higher for the no-PCS group at 3 months (p = 0.0002) and 1 year (p = 0.005).There were no significant difference in the rate of complications.Posterior capsular stripping causes a transient increase in flexion that does not persist post-operatively. We do not recommend routine stripping of the posterior knee capsule in patients undergoing TKA.     

Limited knee extension during gait after total knee arthroplasty is related to a low Oxford Knee Score

BackgroundAfter total knee replacement (TKR) some patients report low self-perceived function, which is clinically measured using patient reported outcome measures (PROMs). However, PROMs, e.g. the Oxford Knee Score (OKS), inherently lack objective parameters of knee function. Biomechanical gait analysis is an objective and reliable measurement to quantitatively assess joint function. Therefore, the aim of this study was to explore the relationship between biomechanical gait parameters and the OKS.MethodsGait analyses were recorded in 37 patients at least one year after primary TKR and in 24 healthy controls. Parameters from this analysis were calculated for hip, knee and ankle joint angles and joint moments in the sagittal and frontal plane including initial contact, early, late stance and swing. For the patients these parameters were expressed as its difference to control values at matched walking speed. Linear regression analyses were performed between the parameters from gait analysis and the OKS, with speed as covariate.ResultsThe difference in knee extension angle at initial contact and late stance between patients and controls was significantly related to the OKS. Per one degree knee extension difference increase, the OKS reduced with 1.0 to 1.6 points. Overall, patients extended their knee less than controls. Neither ankle and hip gait parameters, nor joint moments showed a relation with OKS.ConclusionsAll patients with a submaximal score on the OKS showed limited knee extension during gait, even without a mechanical constraint in knee extension. This could be related to motor control limitations in this patient group.     

Patellar resurfacing has minimal impact on in vitro tibiofemoral kinematics during deep knee flexion in total knee arthroplasty

BackgroundWhile patellar resurfacing can affect patellofemoral kinematics, the effect on tibiofemoral kinematics is unknown. We hypothesized that patellar resurfacing would affect tibiofemoral kinematics during deep knee flexion due to biomechanical alteration of the extensor mechanism.MethodsWe performed cruciate-retaining TKA in fresh-frozen human cadaveric knees (N = 5) and recorded fluoroscopic kinematics during deep knee flexion before and after the patellar resurfacing. To simulate deep knee flexion, cadaver knees were tested on a dynamic, quadriceps-driven, closed-kinetic chain simulator based on the Oxford knee rig design under loads equivalent to stair climbing. To measure knee kinematics, a 2-dimensional to 3-dimensional fluoroscopic registration technique was used. Component rotation, varus-valgus angle, and anteroposterior translation of medial and lateral contact points of the femoral component relative to the tibial component were calculated over the range of flexion.ResultsThere were no significant differences in femoral component external rotation (before patellar resurfacing: 6.6 ± 2.3°, after patellar resurfacing: 7.2 ± 1.8°, p = 0.36), and less than 1° difference in femorotibial varus-valgus angle between patellar resurfacing and non-resurfacing (p = 0.01). For both conditions, the medial and lateral femorotibial contact points moved posteriorly from 0° to 30° of flexion, but not beyond 30° of flexion. At 10° of flexion, after patellar resurfacing, the medial contact point was more anteriorly located than before patellar resurfacing.ConclusionDespite the potential for alteration of the knee extensor biomechanics, patellar resurfacing had minimal effect on tibiofemoral kinematics. Patellar resurfacing, if performed adequately, is unlikely to affect postoperative knee function.     

全膝关节置换修复膝内翻畸形：胫股角及膝关节活动度随访评价

背景：膝关节内翻畸形施行人工全膝关节置换难度大,涉及面多,包括手术入路、术中截骨、软组织松解顺序、方法及程度、软组织平衡等,目前意见不统一,争议较多。 目的：观察全膝关节置换修复成人膝关节内翻畸形胫股角及膝关节活动度的1年以上随访结果。 方法：2006年6月至2013年6月对31例(35膝)膝内翻畸形采用后稳定型假体进行全膝关节置换,髌骨内侧入路,正确截骨,选择性软组织松解,以恢复膝关节正常力线和软组织平衡,获得膝关节的稳定,置换后采取针对性的康复训练。全膝关节置换前后拍X射线片测量胫股角,置换后定期随访检查膝关节活动度,并进行美国特种外科医院(HSS)评分、美国西部Ontario和McMaster大学骨关节炎指数(WOMAC)评估。 结果与结论：所有患者均获得随访,随访时间为12-96个月,随访方式为门诊复查随访。胫股角由置换前平均内翻17.69°(5°-30°)纠正至置换后的5.66°(2°-8°),膝关节活动度由置换前的74.29°(60°-95°)提高到置换后119.46° (105°-130°);HSS评分由置换前的26.60分(14-42分)提高到置换后89.03分(82-95分),优28膝,良7膝;WOMAC评分由42.83分(28-54分)提高到置换后90.17分(85-95分)。结果经统计学分析提示,所有病例置换后胫股角、膝关节活动度、HSS及WOMAC评分均较置换前显著改善(P < 0.01)。置换后X射线片检查未见假体周围透亮区,关节力线正常,无髌骨低位、髌骨骨折。提示成人膝关节内翻畸形患者全膝关节置换后1年以上随访畸形均得到纠正,功能明显改善,修复效果满意。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程全文链接：     

Does joint line elevation after revision knee arthroplasty affect tibio-femoral kinematics,contact pressure or collateral ligament lengths? An in vitro analysis

Introduction

Correct restoration of the joint line is generally considered as crucial when performing total knee arthroplasty (TKA). During revision knee arthroplasty however, elevation of the joint line occurs frequently. The general belief is that this negatively affects the clinical outcome, but the reasons are still not well understood.

Material and methods

In this cadaveric in vitro study the biomechanical consequences of joint line elevation were investigated using a previously validated cadaver model simulating active deep knee squats and passive flexion-extension cycles. Knee specimens were sequentially tested after total knee arthroplasty with joint line restoration and after 4 mm joint line elevation.

Results

The tibia rotated internally with increasing knee flexion during both passive and squatting motion (range: 17° and 7° respectively). Joint line elevation of 4 mm did not make a statistically significant difference. During passive motion, the tibia tended to become slightly more adducted with increasing knee flexion (range: 2°), while it went into slighlty less adduction during squatting (range: –2°). Neither of both trends was influenced by joint line elevation. Also anteroposterior translation of the femoral condyle centres was not affected by joint line elevation, although there was a tendency for a small posterior shift (of about 3 mm) during squatting after joint line elevation. In terms of kinetics, ligaments lengths and length changes, tibiofemoral contact pressures and quadriceps forces all showed the same patterns before and joint line elevation. No statistically significant changes could be detected.

Conclusions

Our study suggests that joint line elevation by 4 mm in revision total knee arthroplasty does not cause significant kinematic and kinetic differences during passive flexion/extension movement and squatting in the tibio-femoral joint, nor does it affect the elongation patterns of collateral ligaments. Therefore, clinical problems after joint line elevation are probably situated in the patello-femoral joint or caused by joint line elevation of more than 4 mm.     

Sensitivity of knee soft-tissues to surgical technique in total knee arthroplasty

Restricted range of motion and excessive laxity are both potential complications of total knee arthroplasty (TKA). During TKA surgery, the surgeon is frequently faced with the question of how tightly to implant the prosthesis. The most common method of altering implantation tightness is to vary the thickness of the polyethylene inlay after the bone cuts have been made and the trial components inserted. We have sought to quantify how altering the polyethylene thickness may affect post-operative soft tissue tension for a range of prosthetic designs.Four different prosthetic designs were implanted into fresh-frozen cadaveric knee joints. All four designs were implanted in the standard manner, with a 100 Newton distraction force used to set soft tissue balance. The tibiofemoral force was then recorded at 15° intervals throughout the passive flexion range. After the standard implantation of each prosthesis, the tibial component was raised or lowered to mimic increasing and decreasing the polyethylene thickness by 2 mm and the force measurements repeated.Tibiofemoral force in extension correlated with implantation tightness for all prosthesis designs. Between 15° and 90°of knee flexion, all four designs were insensitive to changes in implantation tightness. Beyond 90° the effect was more notable in rotating platform mobile-bearing and cruciate-retaining prostheses than in posterior-stabilised mobile-bearing designs.The findings of this research may be useful in assisting surgical decision-making during the implantation of TKA prostheses.