Function In Total Knee Arthroplasty Research Articles

Posterior Cruciate Ligament Resection and Varus Correction in Total Knee Arthroplasty: A Study Using Computer-Assisted Surgery.

BackgroundAlignment correction is crucial for sustaining longevity and function in total knee arthroplasty (TKA). Although the posterior cruciate ligament (PCL) is a secondary stabilizer in the coronal plane, there have been few reports on the effects of PCL resection on varus correction. The study aim was to assess the effect of PCL resection performed using computer-assisted surgery (CAS) on varus correction in TKA.MethodsFrom April 2019 through January 2021, patients with varus deformity of <20° and grossly intact PCLs were included. We used CAS to measure varus correction and gap change after PCL resection during CAS-TKA.ResultsTwenty-four female and eight male patients (40 operated knees) were included. The mean age was 68.7 ± 9.0 years, and the mean BMI was 26.5 ± 3.7 kg/m2. The mean preoperative mechanical alignment was varus 5.7° ± 2.5°. We found that 1.4° ± 0.6° of varus correction occurred after PCL resection (P < .05). The mean extension and flexion medial-side gap increases were 0.4 mm and 2.0 mm, respectively (P < .05). The mean extension and flexion lateral-side gap increases were 0.4 mm and 1.6 mm, respectively (P < .05).ConclusionPCL resection during TKA resulted in a small degree of varus correction. The flexion gap was larger when the PCL was resected. These effects were predictable, so surgeons should be aware of these findings while performing TKA.

Total Knee Arthroplasty Function at 25 Years Following Proximal Tibial Osteotomy: Paired Outcomes of Bilateral TKAs Following Unilateral Osteotomy.

Proximal tibial osteotomy (PTO) is a well-established treatment for coronal deformity and focal cartilage defects. However, the utility of joint-preserving interventions must be weighed against potential effects on subsequent total knee arthroplasty (TKA). The purpose of this study was to determine the effect of PTO on subsequent TKA by comparing outcomes in patients with bilateral TKAs following unilateral PTO. Patients who underwent bilateral TKAs from 2000 to 2015 at a single institution and had previously undergone a unilateral valgus-producing PTO were reviewed. We evaluated 140 TKAs performed in 70 patients (24 female, 46 male) with a mean age at PTO of 50 ± 8 years. The patients underwent conversion to TKA at a mean of 14 ± 7 years following ipsilateral PTO and were followed for a mean of 25 ± 7 years (range, 6 to 40 years) following PTO. The Knee Society Score (KSS), Forgotten Joint Score-12 (FJS-12), subjective knee preference, and revision were compared between the PTO-TKA and contralateral TKA-only sides. The PTO side demonstrated similar KSS Knee subscores (41 ± 16) compared with the contralateral side (39 ± 16, p = 0.67) immediately prior to arthroplasty. Patients had significant improvements in KSS (p < 0.001) after TKA, with clinically similar KSS values at 2 to 15 years of follow-up when knees were compared in a pairwise fashion (p = 0.10 to 0.83). Five PTO-TKA knees (7%) and 4 control TKA-only knees (6%) underwent revision at a mean of 5 years postoperatively (p = 0.76). The number of all-cause reoperations was approximately twice as high in PTO-TKA knees (13% compared with 6% in TKA-only knees, p = 0.24). At the time of final follow-up, PTO-TKA knees demonstrated similar FJS-12 scores (72 ± 26) compared with the contralateral knees (70 ± 28, p = 0.57). Nineteen percent of patients preferred the PTO-TKA knee, 19% preferred the contralateral TKA-only knee, and 62% stated that their knees were equivalent (p > 0.99). The final Tegner activity score was 2.5 ± 1.4. Long-term clinical function of TKA following PTO was excellent, with patients demonstrating comparable subjective outcomes and equivalent knee preference compared with the contralateral TKA-only knees. Further, well-matched studies are needed to evaluate long-term revision and reoperation rates following PTO-TKA. Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

The Effect of Preoperative Behavioral Intervention on Pain, Anxiety, Opioid Use, and Function in Patients Undergoing Total Knee Arthroplasty: A Randomized Controlled Study.

To evaluate the efficacy of preoperative cognitive-behavioral psychoeducation (CBE) for improved pain, anxiety, opioid use, and postoperative function in total knee arthroplasty (TKA) patients. A randomized controlled trial was conducted among 36 military health system beneficiaries attending preoperative education for TKA. The standard of care (SOC) group (n = 18) received information on home safety, rehabilitation, postoperative precautions, and pain management. In addition, the occupational therapy led CBE group (n = 16) received information on principles of holistic wellness (healing process, effects of stress on healing, heart-rate control through diaphragmatic breathing, anti-inflammatory nutrition, goal setting, and mental imagery). Outcomes of interest: knee active range of motion, pain (Defense and Veterans Pain Rating Scale), opioid medication use, heart-rate coherence (emwave2), anxiety (Generalized Anxiety Disorder Scale), and function (Knee Outcome Survey Activities of Daily Living [KOS-ADL], modified Functional Independence Measure, and Global Rate of Change). The CBE group demonstrated significantly greater decline in pain overall, with activity, and during sleep in relation to the SOC group when comparing visit 1 to visit 5. Opioid medication use was significantly lower for CBE versus SOC. Postoperative General Anxiety Disorder-7 scores decreased significantly among CBE participants with similar increase in high heart rate coherence. Function significantly improved postoperatively based on KOS-ADL and Global Rate of Change scores. Twice as many CBE participants had same-day discharge compared to SOC participants and most CBE participants continued with healthy lifestyle recommendations at the 3-month follow-up. A cognitive-behavioral approach to preoperative education may improve postoperative pain, anxiety, and function while decreasing opioid use among TKA patients. Findings from this pilot study support further research to examine similar interventions among distinct surgical populations and encourage further evaluation on the effects of CBE to enhance health and healthcare delivery.

Arthroplasty of the Knee: Current Techniques for Implant Alignment.

When a total knee arthroplasty (TKA) is implanted using the traditional mechanical alignment technique, this typically results in a straight leg, independently of pre-operative or even pre-arthrotic varus or valgus alignment. With mechanical alignment, we distinguish between 2 different alignment techniques: ligament balancing and bony referencing according to bony skeletal landmarks. In ligament balanced technique beside the straight mechanical axis, the prosthesis is implanted at 90° to the latter. The rotational alignment of the femur is set according to the ligament tension. In the skeletal referenced technique, the rotation of the femur is also set according to bony skeletal landmarks. As a variation of this technique, the prosthesis can be implanted with anatomical alignment. In this technique, the medial slope of the joint line of 3° in the frontal plane is respected during the implantation of TKA. Both techniques result in comparable long-term results with survival rates of almost 80% after 25 years. On the other hand, 15 – 20% of TKA patients report dissatisfaction with their clinical result. For more than 10 years now, the kinematic TKA alignment concept has been developed with the goal to achieve implantation that is adapted to the individual anatomy of the patient. The advocates of this technique expect better function of TKA. This strategy aims to reconstruct the pre-arthrotic anatomy of a given patient while preserving the existing joint line and the mechanical axis without performing ligamentary release. Studies have shown that the function of the prothesis is at least that good as in the conventional techniques. Long-term results are still sparse, but initial studies show that TKA implanted using the kinematic alignment technique exhibit comparable 10-year-survival rates to those implanted using the traditional mechanical alignment technique. Future studies need to show the limitations of this new technique and to identify patients who will or will not significantly benefit from this technique.

Frailty, Race/Ethnicity, Functional Status, and Adverse Outcomes After Total Hip/Knee Arthroplasty: A Moderation Analysis

BackgroundAlthough frailty has been shown to be associated with adverse outcomes in patients undergoing total hip arthroplasty (THA) and total knee arthroplasty (TKA), prior studies have not examined how race/ethnicity might moderate these associations. We aimed to assess race/ethnicity as a potential moderator of the associations of frailty and functional status with arthroplasty outcomes. MethodsThe National Surgical Quality Improvement Program was queried for patients who underwent THA or TKA from 2011 to 2017. Frailty was assessed using the modified frailty index. Regression analyses were conducted to examine associations connecting frailty/functional status with 30-day readmission, adverse discharge, and length of stay (LOS). Further analyses were conducted to investigate race/ethnicity as a potential moderator of these relationships. ResultsWe identified 219,143 TKA and 130,022 THA patients. Frailty and nonindependent functional status were positively associated with all outcomes (P < .001). Compared to White non-Hispanic patients, Black non-Hispanic patients had higher odds for all outcomes after TKA (P < .001) and for adverse discharge/longer LOS after THA (P < .001). Similar associations were observed for Hispanics for the adverse discharge/LOS outcomes. Race/ethnicity moderated the effects of frailty in TKA for all outcomes and in THA for adverse discharge/LOS. Race/ethnicity moderated the effects of nonindependent function in TKA for adverse discharge/LOS and on LOS alone for THA. ConclusionDisparities for Black non-Hispanic and Hispanic patients persist for readmission, adverse discharge, and LOS. However, the effects of increasing frailty and nonindependent functional status on these outcomes were the most pronounced among White non-Hispanic patients.

Effect of Patellar Denervation on Anterior Knee Pain and Knee Function in Total Knee Arthroplasty without Patellar Resurfacing: A Meta-Analysis of Randomized Controlled Trials.

ObjectiveThe aim of the present study was to evaluate the effect of patellar denervation (PD) in preventing anterior knee pain (AKP) and improving knee function after total knee arthroplasty (TKA) without patellar resurfacing, and to help surgeons decide whether or not to use PD in TKA.MethodsThe electronic databases of Pubmed, Embase, Cochrane, Web of Science, and Scopus were searched for all randomized controlled trials (RCT) comparing the outcomes of PD and no patellar denervation (NPD) in TKA without patellar resurfacing. Primary outcomes were incidence of AKP, visual analogue scale for pain (VAS), and patellar score (PS). Secondary outcomes were Knee Society Score (KSS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the Oxford Knee Score (OKS), knee range of motion (ROM), and complications.ResultsA total of nine RCT met the inclusion criteria. On meta‐analysis, PD significantly reduced the incidence of AKP (odds ratio 0.49; 95% confidence interval [CI] 0.26 to 0.92), reduced the VAS (weighted mean difference [WMD] −0.57; 95% CI −1.02 to −0.11), and improved the WOMAC (WMD −4.63; 95% CI −6.49 to −2.77) and the ROM (WMD 9.60; 95% CI 0.39 to 18.81) during the follow‐up within 12 months. In addition, PD improved the PS (WMD 1.01; 95% CI 0.65 to 1.38), KSS (WMD 1.12; 95% CI 0.10 to 2.14), and the WOMAC (WMD −1.41; 95% CI −2.74 to −0.08) during the follow‐up after 12 months.ConclusionPatellar denervation could significantly reduce the VAS and the incidence of AKP in the early stages after TKA as well as improve the clinical outcomes in terms of the PS, the WOMAC, the KSS, and the ROM. This study demonstrates that PD is a safe and recommendable technique that could be routinely performed in TKA.

Predictors of chronic pain and level of physical function in total knee arthroplasty: a protocol for a systematic review and meta-analysis

IntroductionOne in five patients undergoing total knee arthroplasty (TKA) experience unchanged or worse pain and physical function 1 year after surgery. Identifying risk factors for unfavourable outcomes is necessary to...

Isokinetic Strength Test of Muscle Strength and Motor Function in Total Knee Arthroplasty.

ObjectiveTo use isokinetic strength testing system to test and analyze the relationship between changes in muscle strength before and after knee replacement in patients undergoing total knee arthroplasty (TKA).MethodsA total of 200 patients with advanced knee osteoarthritis treated from June 2018 to June 2019 were selected for TKA. The patient's isokinetic muscle strength test was performed in the first, third, and the sixth month before and after the operation. The knee hamstring peak torque (PT value), quadriceps peak torque (PT value), and total work were mainly measured. The knee joint was evaluated at the hospital for special surgery score, range of motion and other knee function standards, and then healthy limbs and normal people were tested with the same method. Statistical data was used to analyze and deal with the data, evaluate the muscle strength and motor function changes with time progressing, then compare the differences to the healthy limb. From P < 0.05, we can see that the differences have some statistical significance. The influences that TKA has on motor function changes of lower limbs were also observed.ResultsAmong the 200 subjects, 162 completed all follow‐up tests, and the remaining 38 were lost to follow‐up for various reasons. The rate of loss of follow‐up was approximately 19%. The isokinetic muscle strength test system and the knee joint function scoring standard were used to record the knee joint muscle strength and function changes before and after knee joint replacement. Statistical analysis was performed to show the knee joint hamstring muscle force and quadriceps muscle strength and joint mobility in the first month after the surgery. The knee joint muscle strength and joint mobility were significantly improved after the third month after the surgery, but there were still some differences compared with normal people. The knee function index was significantly improved in the sixth month after operation (P < 0.05), and there were no significant differences compared with normal people.ConclusionsKnee joint strength and knee function after TKA are significantly improved compared with preoperative function, which is of great significance for the treatment of knee osteoarthritis. The constant velocity muscle strength test system has the advantages of safety, accuracy, repeatability and easy operation. It is a good method to evaluate the knee joint's muscle strength and function after the knee joint replacement.

Tibial alignment technique and its influence on clinical and functional outcomes following total knee arthroplasty

BackgroundRestoration of neutral mechanical axis is thought to influence implant survival and function in Total Knee Arthroplasty (TKA). There is no consensus whether Intramedullary (IM) or Extramedullary (EM) tibial alignment technique is superior to achieve this outcome. Study aims to evaluate functional and radiological outcome of TKA using the EM and IM technique. Materials and methodsA retrospective study of 400 primary TKA (314 patients) was performed. 200 knees were studied in each IM and EM group, which were matched. Functional assessment was performed using Oxford Knee Score (OKS) and Tibial component alignment measured in coronal and sagittal radiographs. ResultsThe average coronal and sagittal alignment of the tibial component in IM group was 89.16° and 88°, whereas in EM group, these were 88.1° and 88.5° respectively. The adjusted mean difference change in Pre and Post-operative OKS in IM group compared to EM group was 0.5 (p = 0.52). There was no statistically significant difference in the complications between the two groups. Subgroup analysis of patients with BMI >35 showed predictable coronal tibial alignment with IM technique with fewer outliers. ConclusionIntramedullary tibial alignment is associated with fewer outliers compared to the extramedullary technique particularly in patients with a BMI over 35.

Predictors of Successful Outcomes Following Revision Total Knee Arthroplasty for Flexion Instability

Background and Hypothesis: Flexion instability is a poorly understood cause of total knee arthroplasty (TKA) failure, often referred to as a “wastebasket” diagnosis for unexplained persistent pain. It remains a challenging diagnosis, with unpredictable outcomes following revision surgery. This study identified predictors of successful patient reported outcome measures (PROMS) following revision for flexion instability.&#x0D; Methods: 121 consecutive revision TKAs for flexion instability from 2011-2018 at a single center were retrospectively reviewed. PROMS were prospectively obtained preoperatively and at minimum one-year follow-up. 33 potential predictors of PROMS encompassed: presenting symptoms, demographics/medical covariates, intraoperative observations, and pre/postoperative radiographic measurements. Variables related to outcomes with p≤0.20 in univariate analysis were entered in regression models. Nonsignificant predictors were pruned until only predictors with p&lt;0.05 and the best model statistics were achieved. &#x0D; Results: The sample was 63% female with mean age of 65±11 and BMI of 34±7 kg/m2. Pre- to postoperative changes in three radiographic measurements vital to the stability and function of TKA were related to function (p&lt;0.001), pain (p=0.019), and satisfaction (p=0.030) after surgery. Pain with walking (p≤0.059) and stair climbing (p≤0.048) were almost exclusively related to demographic/medical covariates. Only one of the presenting symptoms commonly associated with flexion instability influenced early revision outcomes (p=0.021).&#x0D; Conclusion and Potential Impact: Instability is one of the most common reasons for TKA failure leading to costly revision surgery. To our knowledge, this is the largest flexion instability cohort studied to date, including substantially more predictors in an attempt to elucidate factors indicative of successful treatment outcomes. With the exception of radiographic parameters reflecting surgical decisions, findings suggest that many factors related to outcomes may be beyond the control of arthroplasty surgeons.

Influence of the Tourniquet on Pain and Function in Total Knee Arthroplasty: a Systematic Review and Meta-Analysis.

The use of the tourniquet in total knee arthroplasty is still a subject of controversial discussion. Previous studies mainly focus on parameters like blood loss and operation time. The aim of this systematic review is to evaluate the postoperative outcome involving parameters such as pain intensity, analgesic consumption, knee function and complication rate with and without tourniquet use, to find a recommendation for future application in total knee arthroplasty. This review is based on the PRISMA Checklists. A systematic research was performed in PubMed using the key words "tourniquet", "total knee arthroplasty", "TKA" and "knee endoprosthesis" up to and including January 2018. The initial search revealed 686 Papers which were extracted by the parameters intensity of pain, analgesic consumption, function (range of motion, Hospital for Special Surgery Score, Knee Society Score) and complications (deep vein thrombosis, surgical side infection, pulmonary embolism). The program Review Manager Version 5.3 was used for statistical analysis. A significance level of p < 0,05 was defined. 18 studies were included in this review with 1279 total knee arthroplasties overall (646 with the use of tourniquet and 633 without). The analysis shows a significant lower pain intensity until the fifth postoperative day (p = 0,03) and also after one to three months (p = 0,04) without using the tourniquet. Range of motion is significantly higher in two to three days postoperatively (p < 0,00 001) when the surgery was performed without tourniquet. Knee Society Score shows no difference between the two groups. A deep vein thrombosis appears significantly more often when using a tourniquet (p = 0,04). There was no higher occurrence in pulmonary embolism and surgical side infections. The use of a pneumatic tourniquet in total knee arthroplasty affects especially the early postoperative pain and functional recovery.

Effect of Adductor Canal Block on Acute Perioperative Pain and Function in Total Knee Arthroplasty

BackgroundMultimodal pain management strategies are commonplace in perioperative management of total knee arthroplasty (TKA), although controversy remains regarding the role of adductor canal blocks (ACB) in this algorithm. The purpose of this study is to independently evaluate the effect of ACB on short-term postoperative outcomes including (1) length of stay (LOS), (2) postoperative narcotic utilization, and (3) function with physical therapy in the era of modern TKA. MethodsWe retrospectively identified a cohort of consecutive patients from January 2014 to January 2018 who had undergone unilateral primary TKA using a single-shot ACB in addition to a standardized multimodal pain regimen vs those who only received a multimodal pain regimen. These 2 groups were compared using independent sample t-tests with primary end points of interest being LOS, distance ambulated with therapy, and inpatient narcotic use. ResultsThere were 624 patients in the ACB group, with a mean age of 64.5 years. The group without ACB consisted of 69 patients, with a mean age of 67.2 years. We observed no significant difference in narcotic utilization postoperatively (2.361 vs 2.097, P = .088). The ACB group ambulated significantly further with therapy (75.8 vs 59.9 ft, P = .008) and had a shorter LOS in both total hours and percentage of postoperative day 1 (%POD1) discharges (34.8 vs 40.6 hours, P = .01, 83% vs 66.6%, P = .01). ConclusionACB did not decrease postoperative pain medication utilization. The modest improvement in distance ambulated with therapy on POD1 (16 ft) and LOS (16% greater POD1 discharges) may not support the cost-effectiveness of this intervention. Level of EvidenceIII, Retrospective Cohort.

Kinematic Alignment in Cruciate Retaining Implants Improves the Biomechanical Function in Total Knee Arthroplasty during Gait and Deep Knee Bend.

Kinematic alignment (KA), which co-aligns the rotational axes of the components with three kinematic axes of the knee by aligning the components to the prearthritic joint lines, has been a recently introduced surgical technique. However, whether KA and cruciate retaining (CR) implants provide better biomechanical function during activities than mechanical alignment (MA) in posterior stabilized (PS) implants is unclear. We evaluated the biomechanical functions during the stance phase gait and deep knee bend, with a computer simulation and measured forces in the medial and lateral collateral ligaments and medial and lateral contact stresses in the polyethylene insert and patellar button. The forces on the medial collateral ligament in KA were lower than those in MA in both CR and PS TKA in the stance phase gait and deep knee bend conditions, whereas those on the lateral collateral ligament did not show any difference between the two surgical alignment techniques in the stance phase gait condition. The maximum contact stresses on the medial PE inserts in KA were lower than those in MA in both CR and PS TKA in the stance phase gait and deep knee bend conditions. However, the maximum contact stresses on the lateral PE inserts and the patellar button did not differ between MA and KA. The biomechanical function was superior in KA TKA than in MA TKA, and KA was more effective in CR TKA. This comparison could be used as a reference by surgeons to reduce the failure rates by using KA TKA instead of MA TKA.

Effect of geometric variations on tibiofemoral surface and post-cam design of normal knee kinematics restoration

BackgroundRestoration of natural knee kinematics for a designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty (TKA). In different posterior-stabilized TKAs, there are wide variations in tibiofemoral surfaces and post-cam design. However, it is not known whether these design variations preserve natural knee kinematics. The purpose of this study was to determine the most appropriate tibiofemoral surface and post-cam designs to restore natural knee kinematics of the TKA.MethodsA subject-specific finite element knee modal was used to evaluate tibiofemoral surface and post-cam design. Three different posts in convex, straight, and concave geometries were considered with a fixed circular cam design in this study. In addition, this post-cam design was applied to three different surface conformities for conforming, medial pivot, and subject anatomy mimetic tibiofemoral surfaces. We evaluated the femoral rollback, internal-external rotation, and quadriceps muscle force under a deep-knee-bend condition.ResultsThe three different tibiofemoral conformities showed that the convex post provided the most natural-knee-like femoral rollback. This was also observed in internal rotation. In surface conformity, subject anatomy mimetic tibiofemoral surfaces showed the most natural -knee-like kinematics and quadriceps force.ConclusionsThis study confirmed that convex post design and subject anatomy mimetic tibiofemoral surfaces provided the most natural-knee-like kinematics. This study suggested that post-cam design and tibiofemoral surface conformity should be considered in conventional and customized TKA.

Impact of Simulated Knee Injuries on the Patellofemoral and Tibiofemoral Kinematics Investigated with an Electromagnetic Tracking Approach: A Cadaver Study.

Purpose The purpose of this study was to evaluate the approach of using an electromagnetic tracking (EMT) system for measuring the effects of stepwise, simulated knee injuries on patellofemoral (PF) and tibiofemoral (TF) kinematics. Methods Three cadaver knees were placed in a motion rig. EMT sensors were mounted on the patella, the medial/lateral femoral epicondyles, the tibial condyle, and the tibial tuberosity (TT). After determining the motion of an intact knee, three injuries were simulated and the resulting bony motion was tracked. Results Starting with the intact knee fully extended (0° flexion) and bending it to approximately 20°, the patella shifted slightly in the medial direction. Then, while bending the knee to the flexed position (90° flexion), the patella shifted progressively more laterally. After transecting the anterior cruciate ligament (ACL), the base of the medial menisci (MM) at the pars intermedia, and the medial collateral ligament (MCL), individual changes were observed. For example, the medial femoral epicondyle displayed a medial lift-off in all knees. Conclusion We demonstrated that our EMT approach is an acceptable method to accurately measure PF joint motion. This method could also enable visualization and in-depth analysis of in vivo patellar function in total knee arthroplasty, if it is established for routine clinical use.

Do New knee Implant Designs Accelerate Early Motion and Function in Total knee Arthroplasty (TKA) Patients?

Do New knee Implant Designs Accelerate Early Motion and Function in Total knee Arthroplasty (TKA) Patients?

Effect of tourniquet use on blood loss and post-operative function in total knee arthroplasty

Effect of tourniquet use on blood loss and post-operative function in total knee arthroplasty

Assessment Of Normal Knee Kinematics During Activities Of Daily Living In Older Adults

Accurate measurement of knee motion is necessary for assessment of joint function for diagnosis of pathology. In particular, the high prevalence of knee pain, osteoarthritis, and total knee arthroplasty (TKA) in adults over the age of 55 requires a baseline description of healthy knee function during demanding activities of daily living. However, accurate measurement of in vivo dynamic knee kinematics in six degrees of freedom (DOF) is technically challenging using conventional marker-based motion capture. For this reason, we have developed a high-speed stereo radiography (HSSR) system which makes possible 3D tracking of bone and implants with sub-millimeter accuracy. PURPOSE: Measure knee kinematics during higher demand activities in older adults to establish a useful baseline for the envelope of healthy knee motion. We hypothesized that the amount of motion in DOFs that are primarily constrained by soft tissue (internal/external (IE) rotation and anterior/posterior (AP) translation) would be more activity dependent, as compared with DOFs partially constrained by articular geometry (varus/valgus (VV) rotation). METHODS: In vivo 3D knee kinematics from 2 healthy subjects (1M/1F, 60/56yrs, 171.4±3.6cm,78.7±1.0kg) were measured using the HSSR system while performing 2 tasks: step down and pivot on stance leg during gait. Tracking of bone motion at the knee was performed by optimizing the position of subject bone models reconstructed from CT to the 2D stereo radiographs. Comparisons of total excursion of IE and VV rotation, and AP translation were made across subjects and activities. RESULTS: For both subjects, the pivot activity produced the largest excursion of IE (S1 21.2deg, S2 18.1 deg) and AP (S1 5.1 mm, S2 11.8 mm), compared to step down IE (S1 3.2 deg, S2 13.5 deg) and AP (S1 5.1 mm, S2 7.5 mm). Excursion in VV was less than 5 deg across activities for both subjects. CONCLUSIONS: These early results revealed greater activity dependent excursion in DOFs constrained by soft tissue whereas VV exhibited similar motion across activities. Current work is underway to include additional healthy subjects and activities that will provide a kinematic baseline for assessment of knee pathology and TKA function.

Geometric variable designs of cam/post mechanisms influence the kinematics of knee implants.

Reproducing the femoral rollback through specially designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty. Most contemporary implants use cam/post mechanism to replace the function of Posterior Cruciate Ligament. This study was aimed to determine the most appropriate cam and post designs to produce normal femoral rollback of the knee. Three different cams (triangle, ellipse, and circle) and three different posts (straight, convex, concave) geometries were considered in this study and were analysed using kinematic analyses. Femoral rollback did not occur until reaching 50° of knee flexion. Beyond this angle, two of the nine combinations demonstrate poor knee flexion and were eliminated from the study. The combination of circle cam with concave post, straight post and convex post showed 15.6, 15.9 and 16.1mm posterior translation of the femur, respectively. The use of ellipse cam with convex post and straight post demonstrated a 15.3 and 14.9mm femoral rollback, whilst the combination of triangle cam with convex post and straight post showed 16.1 and 15.8mm femoral rollback, respectively. The present study demonstrates that the use of circle cam and convex post created the best femoral rollback effect which in turn produces the highest amount of knee flexion. The findings of the study suggest that if the design is applied for knee implants, superior knee flexion may be possible for future patients. IV.

Anterior Referencing versus Posterior Referencing in Total Knee Arthroplasty

Appropriate femoral component positioning and sizing is essential for proper kinematic function in total knee arthroplasty (TKA). Anterior or posterior referencing (AR or PR) are two major techniques for setting center of rotation and for balancing the sagittal plane of the arthroplasty. Both techniques have advantages and disadvantages. Minimally invasive surgical (MIS) TKA has added yet another aspect to intraoperative techniques and postoperative outcomes. A total of 100 consecutive patients undergoing unilateral MIS TKA were prospectively randomized to either AR or PR. Knee Society Scores, range of motion, SF-12, and strength testing by Cybex dynamometer were evaluated at standardized intervals postoperatively for 2 years. There were no statistically significant differences in surgical (incision length, surgical release, blood loss, surgical time, and length of stay) or clinical outcomes between two groups at all postoperative intervals (2 and 6 weeks, 3 and 6 months, and 1 and 2 years). Results demonstrate that both AR and PR are effective and can be used successfully during MIS TKA.