The April 2023 Foot & Ankle Roundup³⁶⁰ looks at: Outcomes following a two-stage revision total ankle arthroplasty for periprosthetic joint infection; Temporary bridge plate fixation and joint motion after an unstable Lisfranc injury; Outcomes of fusion in type II os naviculare; Total ankle arthroplasty versus arthrodesis for end-stage ankle osteoarthritis; Normal saline for plantar fasciitis: placebo or therapeutic?; Distraction arthroplasty for ankle osteoarthritis: does it work?; Let there be movement: ankle arthroplasty after previous fusion; Morbidity and mortality after diabetic Charcot foot arthropathy.

The December 2022 Foot & Ankle Roundup³⁶⁰ looks at: Evans calcaneal osteotomy and multiplanar correction in flat foot deformity; Inflammatory biomarkers in tibialis posterior tendon dysfunction; Takedown of ankle fusions and conversion to total ankle arthroplasty; Surgical incision closure with three different materials; Absorbable sutures are not inferior to nonabsorbable sutures for tendo Achilles repair; Zadek’s osteotomy is a reliable technique for treating Haglund’s syndrome; How to best assess patient limitations after acute Achilles tendon injury; Advances in the management of infected nonunion of the foot and ankle.

Abstract. Objectives. Hip instability following total hip arthroplasty in treatment of intracapsular neck of femur fractures is reported at 8–11%. Utilising the principle of a small articulation to minimize the problems of wear coupled with a large articulation, dual-mobility total hip arthroplasty prostheses stabilise the hip further than conventional fixed-bearing designs. The aim of this study is to compare the rate of dislocation and complication between standard fixed-bearing and dual-mobility prostheses for the treatment of intracapsular neck of femur fractures. Methods. A four-year retrospective review in a large district general hospital was completed. All cases of intracapsular neck of femur fractures treated with total hip arthroplasty were identified through the theatre logbooks. Patient's operative and clinical notes were retrospectively reviewed to collect data. Results. A total of 91 patients underwent total hip arthroplasty for intracapsular neck of femur fracture in the four-year period. 61.5% were dual-mobility design versus 28.5% had fixed-bearing implants. There were no statistical differences between patient group characteristics. Choice of implant was dependent on surgeon preference. There was a 0.0% dislocation rate in the dual-mobility group versus 8.6% in the fixed-bearing prosthesis group. All dislocations occurred in patients who underwent total hip arthroplasty with 36.0mm fixed-bearing prosthesis via posterior surgical approach. There was no statistical difference in mortality between both groups. Conclusion. There was an increasing trend of towards the use of dual-mobility prosthesis for fractured neck of femur within this department with excellent outcomes. Dual-mobility designs provide reduced dislocation rates in total hip arthroplasty in intracapsular neck of femur fractures compared to standard fixed-bearing designs at this institution. The authors recommend that all orthopaedic staff consider the use of dual-mobility prostheses in suitable patients and ensure trainees are suitably trained in use of dual-mobility designs. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Objectives

Unicompartmental knee arthroplasty (UKA) is one surgical option for treating symptomatic medial osteoarthritis. Clinical studies have shown the functional benefits of UKA; however, the optimal alignment of the tibial component is still debated. The purpose of this study was to evaluate the effects of tibial coronal and sagittal plane alignment in UKA on knee kinematics and cruciate ligament tension, using a musculoskeletal computer simulation.

Introduction. The mobile-bearings were introduced in total knee arthroplasty (TKA) to improve the knee performance by simulating more closely ‘normal’ knee kinematics, and to increase the longevity of TKA by reducing the polyethylene wear and periprosthetic osteolysis. However, the superiority between posterior-stabilized mobile-bearing and fixed-bearing designs still remains controversial. The objective of the present study was to compare the mid-term results of Scorpio + Single Axis system (Stryker Howmedica Osteonics, Allendale, New Jersey) for the mobile-bearing knees and Duracon system (Stryker Howmedica Osteonics, Allendale, New Jersey) for the fixed bearing design with regard to clinical and roentgenographic outcome with special reference to any complications and survivorship. Methods. Prospective, randomized, double-blinded controlled study was carried out on 56 patients undergoing primary, unilateral total knee arthroplasty for osteoarthritis, who were divided into two groups. Group I received mobile-bearing knee prosthesis (29 patients) and Group 2 received fixed-bearing prosthesis (27 patients). The patients were assessed by a physical examination and knee scoring systems preoperatively, at a follow-up of three months, six months, and one year after surgery by independent researcher who was not part of the operating team, and was blinded as to the type of implant inserted. We used the Oxford knee score (OKS) and Knee society score (KSS), with Knee Society Knee Score (KSKS) and Knee Society Functional Score (KSFS) being the subsets. The questionnaire for OKS was printed in our national language, and handed over to the patient at each visit. Results. The Knee Society knee scores, pain scores, functional scores and Oxford knee scores were not statistically different (P > 0.05) between the two groups. Mean postoperative range-of-motion of mobile-bearing knees was significantly greater than that of fixed-bearing knees (127º versus 111º, P = 0.011). 72% of patients could sit cross legged, 48% could sit on the floor, and 17% could squat. Kaplan–Meier survival rate was 100%. No spin-out of mobile bearing was observed. The radiological analysis showed no osteolysis or implant loosening. Conclusion. Mobile-bearing, and fixed-bearing knees demonstrated no statistically significant difference in the Oxford knee score, Knee society score, and radiological outcome with 100% survivorship, at 4 to 6.5 years (mean: 5.5 years) follow up. However, the post-operative range-of-motion of mobile-bearing knees was significantly higher than the fixed-bearing designs (mean, 127° versus 111°; range, 95° to 145° versus 80° to 125°)

In total knee replacement (TKR), neutral mechanical alignment (NMA) is targeted in prosthetic component implantation. A novel implantation approach, referred to as kinematic alignment (KA), has been recently proposed (Eckhoff et al. 2005). This is based on the pre-arthritic lower limb alignment which is reconstructed using suitable image-based techniques, and is claimed to allow better soft-tissue balance (Eckhoff et al. 2005) and restoration of physiological joint function. Patient-specific instrumentation (PSI) introduced in TKR to execute personalized prosthesis component implantation are used for KA. The aim of this study was to report knee kinematics and electromyography (EMG) for a number lower limb muscles from two TKR patient groups, i.e. operated according to NMA via conventional instrumentation, or according to KA via PSI. 20 patients affected by primary gonarthrosis were implanted with a cruciate-retaining fixed-bearing prosthesis with patella resurfacing (Triathlon® by Stryker®, Kalamazoo, MI-USA). 17 of these patients, i.e. 11 operated targeting NMA (group A) via convention instrumentation and 6 targeting KA (group B) via PSI (ShapeMatch® by Stryker®, Kalamazoo, MI-USA), were assessed clinically using the International Knee Society Scoring (IKSS) System and biomechanically at 6-month follow-up. Knee kinematics during stair-climbing, chair-rising and extension-against-gravity was analysed by means of 3D video-fluoroscopy (CAT® Medical System, Monterotondo, Italy) synchronized with 4-channel EMG analysis (EMG Mate, Cometa®, Milan, Italy) of the main knee ad/abductor and flexor/extensor muscles. Knee joint motion was calculated in terms of flex/extension (FE), ad/abduction (AA), and internal/external rotation (IE), together with axial rotation of condyle contact point line (CLR). Postoperative knee and functional IKSS scores in group A were 78±20 and 80±23, worse than in group B, respectively 91±12 and 90±15. Knee motion patterns were much more consistent over patients in group B than A. In both groups, normal ranges were found for FE, IE and AA, the latter being generally smaller than 3°. Average IE ranges in the three motor tasks were respectively 8.2°±3.2°, 10.1°±3.9° and 7.9°±4.0° in group A, and 6.6°±4.0°, 10.5°±2.5° and 11.0°±3.9° in group B. Relevant CLRs were 8.2°±3.2°, 10.2°±3.7° and 8.8°±5.3° in group A, and 7.3°±3.5°, 12.6°±2.6° and 12.5°±4.2° in group B. EMG analysis revealed prolonged activation of the medial/lateral vasti muscles in group A. Such muscle co-contraction was not generally observed in all patients in group B, this perhaps proving more stability in the knee replaced following the KA approach. These results reveal that KA results in better function than NMA in TKR. Though small differences were observed between groups, the higher data consistency and the less prolonged muscle activations detected using KA support indirectly the claim of a more natural knee soft tissue balance. References

Introduction. Total knee arthroplasty (TKA) is a consolidated orthopaedic procedure and success of such operation depends on the prosthetic design [1]. Unfortunately, as there is a good survival rate of primary TKA, failures occur for factors concerning the polyethylene composition of the implants, secondary osteolysis, and ultimately loosening of the implants are the usual causes of failure after normal use [2]. Dynamic in vitro testing of the human knee continues to be an area of interest to the orthopaedic biomechanics community. The scope of this work was to assess pre-clinically the wear behaviour of polyethylene knee insert under a realistic stair climbing activity using a displacement knee simulator. Materials & Methods. Four commercial posterior-stabilized fixed-bearing component prosthesis for TKA were tested in this study (Stryker®-Orthopaedics, Mahwah, NJ-USA). These were new and delivered in sterilized packages. Particularly, corresponding UHMWPE tibial inserts (size #7) were made of conventional surgical grade polyethylene resin (GURâ�¨1020), consolidated by compression moulding (accordingly to ISO 5834/1-2), and EtO sterilized. These were tested in conjunction with corresponding CoCrMo alloy femoral components. For the implementation of realistic loading scenarios during in vitro wear testing for human joint prostheses, an in vitro protocol was designed to simulate the flexion/extension angle, intra/extra rotation angle, and antero/posterior translation. These movements were obtained in patients by three- dimensional video-fluoroscopy. Axial load data were collected by gait analysis [3]. Results. The components run under stair climbing simulation completed the planned two million cycles under bovine calf serum as lubricant. The volumetric wear trend is schematised in Figure 1. The wear patterns observed on the contact surfaces were similar over the three tested inserts. A few pitting phenomena were observed on the insert contact surfaces. In addition, unidirectional scratches were observed in both condyles along the AP direction. Conclusion. The knee wear simulator executed the imposed physiological gait condition, under stair climbing waveforms. This new approach opens the way to more scenarios able to give comprehensive answers to the wear behaviour of knee components. Hence, further development will be the definition of a global protocol, with the implementation of various motor tasks (chair sitting and rising, squatting), using the same approach

Ankle replacements have improved significantly since the first reported attempt at resurfacing of the talar dome in 1962. We are now at a stage where ankle replacement offers a viable option in the treatment of end-stage ankle arthritis. As the procedure becomes more successful, it is important to reflect and review the current surgical outcomes. This allows us to guide our patients in the treatment of end-stage ankle arthritis. What is the better surgical treatment – arthrodesis or replacement?

The February 2015 Foot & Ankle Roundup³⁶⁰ looks at: Syndesmosis screw removal in randomised controlled trial; Diagnostic value of Hawkins sign; Chevron rules supreme?; Diabetes and ankle replacement; Fixed-bearing ankle replacement; Fusion for osteomyelitis of the ankle; ‘Reformed’ fallers.

Introduction

Wear of polyethylene inserts plays an important role in failure of total knee replacement and can be monitored in vivo by measuring the minimum joint space width in anteroposterior radiographs. The objective of this retrospective cross-sectional study was to compare the accuracy and precision of a new model-based method with the conventional method by analysing the difference between the minimum joint space width measurements and the actual thickness of retrieved polyethylene tibial inserts.

Introduction. The SAIPH™ (MatOrtho, UK) total knee replacement is a new fixed-bearing prosthesis design having attributes of a mobile bearing and the posterior stabilised categories for knee arthroplasties. The implant design goal is an articulation that provides definitive anteroposterior stability to beneficially control tibiofemoral translation, the ability for the tibia to axially rotate to accommodate various lifestyle activities, and to maintain a relatively posterior femoral position on the tibia to facilitate range of motion. This study aims to analyze knee kinematics of the SAIPH™ total knee arthroplasty (TKA) by videofluroscopy during four different weightbearing activities. Method. Fourteen consecutive patients operated on by a single surgeon, with a minimum follow up of 24 months were included in this IRB-approved study. A medially conforming knee was implanted in all cases. Participants in the study were asked to perform weightbearing kneeling, lunging, step-up/down and pivoting activities while their knee motions were recorded by videofluoroscopy. Three-dimensional (3D) joint kinematics were determined using model-image registration. The 3D orientation of each TKA component was expressed using standard joint angle conventions, and the anterior/posterior location of each condyle was expressed relative to the deepest part of the tibial sulcus. Results. Maximum knee flexion during the kneeling activity averaged 127 ° (100°–155°). Condylar contact was posterior on the tibia during kneeling (Figure 1). The medial femoral condyle (MFC) translated an average of 4 mm (SD 3 mm) posteriorly at 127 ° of kneeling flexion. The lateral femoral condyle (LFC) translated posteriorly 8 mm (SD 3 mm). None of these knees demonstrated paradoxical forward slide of the femur during this activity. The tibia rotated internally an average of 5° during flexion. During the lunge activity mean knee flexion was 121°. There was a similar asymmetric posterior translation of the femoral condyles, 5 mm for the MFC, and 8 mm for the LFC, and an average internal rotation of the tibia of 3°. During the step-up/down activity the MFC translated posteriorly 2 mm, and the LFC 3 mm (Figure 2). The tibia internally rotated 4° from extension to 85° flexion during stepping. During the pivot activity, the MFC remain stable in the tibial sulcus and the LFC translated posteriorly while the tibia rotated externally to internally (Figure 3). Conclusion. The SAIPH™ knee shows a medial pivot motion with tibial internal rotation of the tibia during active weightbearing flexion and deep knee flexion, as seen in previous studies. The kinematics are similar in pattern to normal knees showing an asymmetric posterior translation of the lateral femoral condyle and tibial internal rotation with knee flexion. A medially conforming implant design provides intrinsic anteroposterior stability to control femoral translation across the entire range of flexion, allows tibial rotation, and provides functional flexion comparable to specialized posterior-stabilised implant designs

The outcome of high tibial osteotomy (HTO) deteriorates with time, and additional procedures may be required. The aim of this study was to compare the clinical and radiological outcomes between unicompartmental knee replacement (UKR) and total knee replacement (TKR) after HTO as well as after primary UKR. A total of 63 patients (63 knees) were studied retrospectively and divided into three groups: UKR after HTO (group A; n = 22), TKR after HTO (group B; n = 18) and primary UKR (group C; n = 22). The Oxford knee score (OKS), Knee Society score (KSS), hip–knee–ankle angles, mechanical axis and patellar height were evaluated pre- and post-operatively. At a mean of 64 months (19 to 180) post-operatively the mean OKS was 43.8 (33 to 49), 43.3 (30 to 48) and 42.5 (29 to 48) for groups A, B and C, respectively (p = 0.73). The mean KSS knee score was 88.8 (54 to 100), 88.11 (51 to 100) and 85.3 (45 to 100) for groups A, B and C, respectively (p = 0.65), and the mean KSS function score was 85.0 (50 to 100) in group A, 85.8 (20 to 100) in group B and 79.3 (50 to 100) in group C (p = 0.48). Radiologically the results were comparable for all groups except for patellar height, with a higher incidence of patella infra following a previous HTO (p = 0.02).

Cite this article: Bone Joint J 2013;95-B:1348–53.

INTRODUCTION. Mobile-bearing knee prostheses have been designed in order to provide less constrained knee kinematics compared to fixed-bearing prosthesis. Currently, there is no evidence to confirm the superiority of either of the two implants with regard to walking performances. It has been shown that subjective outcome scores correlate poorly with real walking performance and it has been recommended to obtain an additional assessment of walking ability with objective gait analysis. OBJECTIVES. We assessed recovery after total knee arthroplasty (TKA) with mobile- and fixed-bearing between patients during the first postoperative year, and at 5 years follow-up, using a new objective method to measure gait parameters in real life conditions. METHODS. 56 patients with mobile- and fixed-bearing of the same design were included in this randomised controlled double-blinded study and evaluated pre- and post-operatively at 6 weeks, 3 months, 6 months 1 year and 5 years. At each visit a WOMAC and Knee Society Score were calculated and each participant completed an EQ-5D questionnaire. To assess the patients' gait five miniature angular rate sensors mounted respectively on the sacrum and each shank and thigh measured lower limb movement and rotation. The patients walked 30 metres on a flat surface and gait parameters were recorded with a small ambulatory device in order to carry out an objective gait analysis. RESULTS. Objective recovery was strongly correlated with patients' age. When the whole population was considered, there was no significant difference between groups at any time in objective gait parameters. After separating the population according to their age (less than 71 years old, compared to those of more than 71 years old) a secondary analysis showed that the bearing type can lead to opposite results in different age groups. At five years follow-up, most of the recorded gait parameters (stride length, knee max rotation speed, shank and thigh range of motion, and limp) showed better results for mobile bearing in younger patients, while better gait performances were found systematically with fixed-bearing TKA in older patients. CONCLUSION. To our knowledge, this is the first study where similarly designed posterior-stabilised knee replacements with fixed- and mobile-bearing have been compared with gait analysis in real-life conditions. We observed systematically differences between mobile and fixed bearing groups, which are confirmed by multivariate analysis. Our results suggest that older patients might not benefit from a mobile bearing TKA and that extended age controlled study should be performed to identify an age, above which fixed bearing should not be the recommended choice. Before choosing the bearing type, surgeons should take into account the age of the patient

To evaluate prospectively the mid-term results of the Zimmer Unicondylar Knee arthoplasty (UKA). Between 2005 and 2012, 187 unicompartmental knee arthroplasties (UKA) were performed by a single surgeon using a fixed-bearing prosthesis (Zimmer). 37 cases were excluded as either were lost to follow-up or had less than six months follow-up. The study included 150 UKAs. Deformity, if present, was correctable. Patellofemoral joint (PFJ) disease was not considered as an absolute contraindication. The average patient age at the time of surgery was 66 years (range 42–88 years); 78 of which were male. Mean follow-up time was 3.6 years (range 7–81 months). Mean Body Mass Index (BMI) was 29 (range 21–41). Clinical and conventional radiological evaluations were carried out at six months, one, two and five years postoperatively. 147 cases were medial compartment replacement and three were lateral. 86 patients had grade III OA and 64 had grade IV (Kellgren and Lawrence). 113 patients had an element of PFJ disease. The mean Knee Society knee and function scores had an improvement from 55 and 54 points pre-operatively to 95 and 94 points respectively at time of most recent evaluation. The average flexion improved from 116 degrees pre-operatively to 127 degrees. Two cases were revised, one due to progression of osteoarthritis in the lateral compartment of the knee and the other was due to arthrofibrosis. The Zimmer unicompartmental knee arthroplasty provided excellent pain relief and restoration of function in carefully selected patients. However, long-term studies are necessary to investigate the survival rate for this prothesis

Unicompartmental knee replacement (UKR) is technically challenging, but has the advantage over total knee replacement (TKR) of conserving bone and ligaments, preserving knee range of movement and stability. Computer navigation allows for accurate placement of the components, important for preventing failures secondary to mal-alignment. Evidence suggests an increase in failure rates beyond 3 degrees of coronal mal-alignment. Our previous work has shown superior functional scores in those patients having undergone UKR, when compared with those having had TKR. However, to a certain extent, this is likely to be due to differences in the two cohorts. Those selected for UKRs are likely to be younger, with less advanced and less widespread degenerative disease. It is almost inevitable, therefore, that functional outcomes will be superior. We aimed to compare the functional and radiological outcomes of UKR vs TKR in a more matched population. Ninety-two patients having had one hundred consecutive computer navigated UKRs were reviewed both clinically and radiographically. The Smith & Nephew Accuris fixed-bearing modular prosthesis was used in all cases, with the ‘Brainlab’ navigation system. For our comparative group we identified patients who had actually undergone navigated TKR several years ago, but who, in retrospect, would have now been offered a UKR in line with our current practice. These patients were identified following review of pre-operative radiographs and operation notes, confirming degenerative disease confined mainly to one compartment of the knee, in the absence of any concern as to the integrity of the anterior cruciate ligament. This sub-group of patients were also assessed clinically and radiographically. Mean follow-up for the UKR group was 25 months, (range 8–45.) For our TKR sub-group, nineteen patients were identified. Average length of stay for the UKR group was 3.7 days, (range 2 to 7,) and for the TKR group this was 5.2 days, (range 3 to 10.). Functional scores (Oxford Knee Score) were good to excellent for the majority of patients in both groups, although they were significantly better in the UKR group. Mean Oxford Knee Score in the UKR group was 7.5, (0–48, with 0 being best.) Mean score in the TKR sub-group was 12.1. (p = 0.02). Reliably comparing TKR with UKR is difficult, due to the fundamental differences in the two groups. We have endeavoured to match these two cohorts as best possible, in order to compare the outcomes of both. Our use of computer navigation in both groups allows for accurate prosthesis placement. When measuring component position, there were no ‘outliers,’ outside of the widely accepted three degrees of deviation. We propose that, with the correct patient selection, UKR gives a better functional outcome than TKR. Longer-term follow-up of our UKR group is required to monitor the onset of progressive arthrosis in other joint compartments, although our early results are very encouraging. Furthermore, we advocate the use of computer navigation to firstly allow for more accurate component positioning, and secondly to make challenging UKR surgery less technically demanding

The success of total knee replacement (TKR) depends on optimal soft-tissue balancing, among many other factors. The objective of this study is to correlate post-operative anteroposterior (AP) translation of a posterior cruciate ligament-retaining TKR with clinical outcome at two years. In total 100 patients were divided into three groups based on their AP translation as measured by the KT-1000 arthrometer. Group 1 patients had AP translation < 5 mm, Group 2 had AP translation from 5 mm to 10 mm, and Group 3 had AP translation >  10 mm. Outcome assessment included range of movement of the knee, the presence of flexion contractures, hyperextension, knee mechanical axes and functional outcome using the Knee Society score, Oxford knee score and the Short-Form 36 questionnaire.

At two years, patients in Group 2 reported significantly better Oxford knee scores than the other groups (p = 0.045). A positive correlation between range of movement and AP translation was noted, with patients in group 3 having the greatest range of movement (mean flexion: 117.9° (106° to 130°)) (p < 0.001). However, significantly more patients in Group 3 developed hyperextension > 10° (p = 0.01).

In this study, the best outcome for cruciate-ligament retaining TKR was achieved in patients with an AP translation of 5 mm to 10 mm.

Computer navigation has the potential to revolutionise orthopaedic surgery, although according to the latest 7. th. Annual NJR Report, only 2% of the 5 800 unicompartmental knee replacements (UKRs) performed in 2009 were carried out using ‘image guidance.’ The report also states an average 3-year revision rate for UKRs of 6.5%. Previous NJR data has shown that this figure rises up to 12% for certain types of prosthesis. We suspect that a significant proportion of these revisions are due to failure secondary to component malpositioning. We therefore propose that the use of computer navigation enables a more accurate prosthesis placement, leading to a reduction in the revision rate for early failure secondary to component malpositioning. Our early results of one hundred consecutive computer navigated UKRs are presented and discussed. Ninety-two patients having had one hundred consecutive computer navigated UKRs were reviewed both clinically and radiographically. The Smith & Nephew Accuris fixed-bearing modular prosthesis was used in all cases, with the ‘Brainlab’ navigation system. Pre-operative aim was neutral tibial cut with three degrees posterior slope. Post-operative component alignment was measured with PACs web measuring tools. Patients were scored clinically using the Oxford Knee Score. Our patient cohort includes 54 male knees and 46 female knees. Average age is 66.6yrs. Average length of stay was 3.7 days, (range 2–7.) With respect to the tibial component, average alignment was 0.7° varus, and 2.32° posterior slope. All components were within the acceptable 3 degrees deviation. Functional scores are very satisfactory, with an overall patient satisfaction rate of 97%. To date, only one UKR has required revision. This was due to ongoing medial pain due to medial overhang, not related to computer navigation. There was one superficial infection, with full resolution following a superficial surgical washout, debridement and antibiotics. Unlike complications reported in the NJR, we report no peri-prosthetic fractures or patella tendon injuries. Our results demonstrate accurate prosthesis placement with the use of computer navigation. Furthermore, clinical scores are highly satisfactory. Our current revision rate is 1% at a mean of 27 months post-op. Although longer-term follow-up of our group is required, our results compare very favourably to statistics published in the NJR, (average 3-year revision rate 6.5%.) The only major differences appear to be the type of prosthesis used and the use of computer navigation. It is our proposal that computer navigation reduces the number of revisions required due to component malpositioning and subsequent failure. Furthermore, we believe that this challenging surgery is made easier with the use of computer navigation. We expect our longer-term results to show significant benefits of computer navigation over conventional techniques

Background. Mobile-bearing (MB) total knee prostheses have been developed to achieve lower contact stress and higher conformity compared to fixed-bearing total knee prostheses. However, little is known about the in vivo kinematics of MB prostheses especially about the kinematics of polyethylene insert (PE). In vivo motion of PE during squatting still remains unclear. The objective of this study is to investigate the in vivo motion of MB total knee arthroplasty including PE during squatting. Patients and methods. We investigated the in vivo knee kinematics of 11 knees (10 patients) implanted with Vanguard Rotationg Platform High Flex (Biomet. (r). ). Under fluoroscopic surveillance, each patient did a wight-bearing deep knee bending motion. Motion between each component was analyzed using two- to three-dimensional registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components, and PE (implanted with five tantalum beads intra-operatively) from single-view fluoroscopic images. We evaluated the range of motion between the femoral and tibial components, axial rotation between the femoral component and PE, the femoral and tibial component, and the PE and tibial component, and AP translation of the nearest point between the femoral and tibial component and between the femoral component and PE. Results. The mean range of hyper-extension was 0.5±3.2° (range:-4.0 to 4.7°) and the mean range of flexion of 119.0±11.3°(range:98 to 137°). The external rotating femoral component relative to the tibial component demonstrated 8.6±3.2°(range:5.5 to 14.7°) for 0-120 degrees flexion. The PE rotated 9.6±4.5°(range:2.5 to 18.0°) externally relative to the tibial component, the femoral component rotated little relative to the PE. In upright standing position, the femoral component already rotated 1.2±9.8°(range:-16.5 to 15.9°) externally relative to the tibial component and the PE also rotated 0.8±9.8°(range:-16.1 to 16.0°) externally on the tibial tray. From 0°to 120°of flexion there was almost little A-P translation of the medial femoral condyle within 2 mm. The lateral condyle translated posteriorly with knee flexion. The average amount of posterior translation was 5.7±1.6 mm (range:2.5 to 7.5 mm). The femoral component relative to the tibial component exhibited a medial pivot pattern external rotation for 0-120 degrees flexion. Discussion and conclusion. In this study, we evaluated the in vivo motion of MB total knee arthroplasty including PE during squatting. About this total knee prosthesis, the mobile-bearing mechanism which advantages over fixed-bearing prosthesis to keep high comformity might work well, and arc of range of motion was maintained. Furthermore, in upright standing position, the femoral component and PE already rotated externally relative to the tibial component in almost equal measure. This indicated that, self-aligning mechanism, another characteristic of the MB prosthesis might also work well

Background

Currently there are various knee prosthesis designs available each with its plus and minus points; there is no general consensus on whether mobile-bearing knees are functionally better than fixed-bearing ones. This study is designed to compare outcomes after total knee arthroplasty with both of the above prostheses.

This study compared the outcome of total knee replacement (TKR) in adult patients with fixed- and mobile-bearing prostheses during the first post-operative year and at five years’ follow-up, using gait parameters as a new objective measure. This double-blind randomised controlled clinical trial included 55 patients with mobile-bearing (n = 26) and fixed-bearing (n = 29) prostheses of the same design, evaluated pre-operatively and post-operatively at six weeks, three months, six months, one year and five years. Each participant undertook two walking trials of 30 m and completed the EuroQol questionnaire, Western Ontario and McMaster Universities osteoarthritis index, Knee Society score, and visual analogue scales for pain and stiffness. Gait analysis was performed using five miniature angular rate sensors mounted on the trunk (sacrum), each thigh and calf. The study population was divided into two groups according to age (≤ 70 years versus > 70 years).

Improvements in most gait parameters at five years’ follow-up were greater for fixed-bearing TKRs in older patients (> 70 years), and greater for mobile-bearing TKRs in younger patients (≤ 70 years). These findings should be confirmed by an extended age controlled study, as the ideal choice of prosthesis might depend on the age of the patient at the time of surgery.