Valgus subsidence of the tibial component in cementless Oxford unicompartmental knee replacement

Advantages and limitations of mobile-bearing unicompartmental knee arthroplasty: an overview of the literature

INTRODUCTION

Interest in unicompartmental knee arthroplasty (UKA) has recently grown. Mobile bearing UKA, in which the bearing is not fixed but rather perfectly conforms with femoral and tibial components and moves completely passively between the femoral and tibial implant, has now been used for approximately half a century.

AREAS COVERED

Alongside the recognized advantages of UKA, the mobile-bearing variant benefits from an extremely low rate of polyethylene wear and tolerable minor malalignment. Revision rates for UKA have been reported to exceed those of total knee arthroplasty, but long-term survival rates and outcomes from mobile-bearing UKA have been found to be satisfactory. In addition to the lateral osteoarthritis and loosening, which are main complications of UKA, bearing dislocation is a specific complication of mobile bearing UKA. Fractures and valgus subsidence are more prevalent than in the cementless UKA. While these continue to be features to be addressed, they have been partially solved.

EXPERT OPINION

Given the manifold benefits of UKA, its application could be extended to a larger patient population. Successful outcomes rely on careful patient selection and the surgeon's extensive familiarity with the procedure. Looking ahead, the incorporation of robotic surgery, already a feature of some fixed-bearing UKAs, might shape the future trajectory of mobile-bearing UKA.

Safe bearing region for avoiding meniscal bearing impingement and overhang in mobile-bearing unicompartmental knee arthroplasty

The purposes of this study were to propose a quantitative method of bearing overhang to minimize the effect of bearing spinning on mobile-bearing unicompartmental knee arthroplasty (MB UKA), suggest and apply safe bearing regions in daily activities. The overhang distance and area were calculated for neutral and spinning positions. The safe bearing regions were based on the relationship between bearing overhang and linear wear rate. Eleven patients were included in an in-vivo experiment under dual fluoroscopic imaging following medial MB UKA. The bearing position was tracked by minimal joint space width, and the bearing overhang was calculated accordingly. Due to an equal contribution of 1 mm increase in medial overhang and 30 mm2 overhang areato wear rate, the maximum effect of potential bearing spinning on medial overhang distance was approximately three times as large as the overhang area. The safe bearing distance and area regions were rectangles and arches with different scales for different size combinations of bearing, femoral and tibial components. The maximum bearing overhang area during lunge (R = 0.76, p = 0.006) and open-chain exercise (R = 0.68, p = 0.02) significantly correlated with the overhang area in standing. The overhang area can be an appropriate parameter for evaluating dislocation degree less affected by potential bearing spinning than the overhang distance in clinical practice. The corresponding safe overhang area regions were proposed for surgical planning and postoperative dislocation degree evaluation. The bearing overhang area in static standing posture can be a valuable reference to estimate the dynamic overhang area and dislocation degree during motion.

Polyethylene bearing wear is comparable for cemented and cementless Oxford unicompartmental knee replacements: Ten-year results of a randomized controlled trial

PURPOSE

There is concern that using cementless components may increase polyethylene wear of the Oxford unicompartmental knee replacement (OUKR). Therefore, this study aimed to measure bearing wear at 10 years in patients from a randomized trial comparing Phase 3 cemented and cementless OUKRs and to investigate factors that may affect wear. It was hypothesized that there would be no difference in wear rate between cemented and cementless OUKRs.

METHODS

Bearing thickness was determined using radiostereometric analysis at postoperative, 3-month, 6-month, 1-year, 2-year, 5-year and 10-year timepoints. As creep occurs early, wear rate was calculated using linear regression between 6 months and 10 years for 39 knees (20 cemented, 19 cementless). Associations between wear and implant, surgical and patient factors were analysed.

RESULTS

The linear wear rate of the Phase 3 OUKR was 0.06 mm/year with no significant difference (p = 0.18) between cemented (0.054 mm/year) and cementless (0.063 mm/year) implants. Age, Oxford Knee Score, component size and bearing thickness had no correlation with wear. A body mass index ≥ 30 was associated with a significantly lower wear rate (p = 0.007) as was having ≥80% femoral component contact area on the bearing (p = 0.003). Bearings positioned ≥1.5 mm from the tibial wall had a significantly higher wear rate (p = 0.002).

CONCLUSIONS

At 10 years, the Phase 3 OUKR linear wear rate is low and not associated with the fixation method. To minimize the risk of wear-related bearing fracture in the very long-term surgeons should consider using 4 mm bearings in very young active patients and ensure that components are appropriately positioned, which is facilitated by the current instrumentation.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Comparison of cementless twin-peg, cemented twin-peg and cemented single-peg femoral component migration after medial unicompartmental knee replacement: a 5-year randomized RSA study

BACKGROUND

The component design and fixation method of joint arthroplasty may affect component migration and survival. The aim of this study was to compare fixation of cementless twin-peg (CLTP), cemented twin-peg (CTP) and cemented single-peg (CSP) femoral components of medial unicompartmental knee replacement (UKR).

METHODS

Eighty patients (mean age = 63 years, 48 males) with medial knee osteoarthritis were randomized in three ways to CLTP (n = 25), CTP (n = 26) or CSP (n = 29) femoral UKR components. The patients were followed 5 years postoperatively with RSA, bone mineral density (BMD), PROMs and radiological evaluation of radiolucent lines (RLL), femoral component flexion angle and complications.

RESULTS

At the 5-year follow-up, femoral component total translation was comparable between the three groups (p = 0.60). Femoral component internal rotation was 0.50° (95% CI 0.3; 0.69) for the CLTP group, 0.58° (95% CI 0.38; 0.77) for the CTP group and 0.25° (95% CI 0.07; 0.43) for the CSP group (p = 0.01). BMD decreased peri-prosthetically (range - 11.5%; - 14.0%) until 6-month follow-up and increased toward the 5-year follow-up (range - 3.6%; - 5.8%). BMD change did not correlate with component migration. Lower flexion angle was correlated with higher 5-year subsidence, total translation, varus rotation and maximum total point motion (p = 0.01). Two patients (1 CLTP, 1 CTP) had RLL in the posterior zone. There were two revisions.

CONCLUSION

At 5-year follow-up, fixation of UKA femoral components with twin-peg was not superior to the single-peg design. Cementless and cemented twin-peg femoral components had similar fixation. A lower flexion angle was correlated with higher component migration.

Cementless versus cemented unicompartmental knee arthroplasty: a systematic review of comparative studies

There are still some controversies regarding the clinical use of cementless UKAs. The aim of this systematic review was to determine whether cementless medial UKA leads to similar outcomes compared to cemented medial UKA. This search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews guidelines (PRISMA). The random effects model with 95% confidence interval (CI) was applied to the analysis. The I2 statistic was used to assess study heterogeneity. Six studies were eligible for inclusion (4784 UKAs, 4776 patients): 2947 cemented UKAs (61.6%) and 1837 cementless UKAs (38.4%). The overall mean follow-up was 4.9 years. The all-cause reoperation rate was 11.3% (80 of 706) at mean 5.7-year follow-up for cemented UKA and 6.9% (57 of 824) at mean 4.1-year follow-up for the cementless. The overall revision rate was 10.2% (303 of 2947) for the cemented and 5.8% (108 of 1837) for the cementless. Aseptic loosening was the most frequent reason of revision (2.3% cemented vs 0.5% cementless). The overall rate of radiolucent lines (RLL) was 28.3% (63 of 223) in the cemented cohort and 11.1% in the cementless (26 of 234). All the studies reported improved functional outcomes. Cementless UKA provides at least equivalent if not better results compared to cemented UKA. Despite the use of cemented UKA outnumber cementless fixation, available data shows that cementless UKA had a reduced midterm revision rate, while providing similar functional outcomes.

Hybrid fixation of unicompartmental knee arthroplasty shows equivalent short-term implant survivorship and clinical scores compared to standard fixation techniques

INTRODUCTION

There is a paucity of data regarding hybrid-fixated unicompartmental knee arthroplasty (UKA), and no study directly compared all three available fixation techniques (cementless, cemented, and hybrid). The hypothesis was that hybrid fixation might have a lower incidence of radiolucent lines (RLL) than cemented UKA, with equivalent outcomes to uncemented UKA.

MATERIALS AND METHODS

A total of 104 UKA with a minimal follow-up of 1 year were retrospectively included, of which 40 were cemented, 41 cementless, and 23 hybrid prostheses. The functional outcomes scores included the Oxford Knee (OKS), Subjective Knee (SKS), and Forgotten Joint scores (FJS). RLLs, subsidence, and component positioning were assessed on radiographs.

RESULTS

At a mean follow-up of 28 months, the survival rate was 95% for cemented UKA and 100% for the cementless and hybrid UKA (n.s.), respectively. Postoperative FJS (93 vs. 82 points, p = 0.007) and SKS (4.7 vs. 4.1 points, p = 0.001) were better in cementless than cemented UKA, with hybrid-fixated UKA in between the two (90 and 4.4 points, n.s.). Improvement of OKS preoperatively to postoperatively did not differ between the groups (n.s.). RLLs were more frequent in cemented (23%) compared to cementless (5%, p = 0.021) and hybrid UKA (9%, n.s.). With an incidence of 12%, subsidence occurred more commonly in cementless UKA compared to cemented (5%) and hybrid (0%) (n.s.) UKA.

CONCLUSION

Hybrid fixation achieves equivalent results to standard UKA fixation techniques regarding implant survival and functional and radiological outcomes. Therefore, the hybrid fixation technique seems to be a valuable alternative as it combines the advantages of cemented tibial components with those of uncemented femoral components.

LEVEL OF EVIDENCE

III.

Intramedullary rod insertion places the femoral component more laterally during Oxford medial unicompartmental knee arthroplasty

Background

This study aims to assess the influence of intramedullary rods on the implantation positions of femoral components using Microplasty instrumentation in Oxford unicompartmental knee arthroplasty. We hypothesized that femoral components can be laterally implanted incorrectly when using intramedullary rods.

Methods

This prospective study included all 45 consecutive patients (53 knees) who underwent Oxford unicompartmental knee arthroplasty surgery for anteromedial osteoarthritis or spontaneous osteonecrosis of the knee at our hospital during the study period. A custom-made toolset comprising a triangular caliper and circular trial bearings was used to evaluate the distance between the bearing and the vertical wall of the tibia implant (wall-bearing space) using the caliper at 90° flexion both with and without intramedullary rods.

Results

The wall-bearing space was significantly larger when the intramedullary rod was used than when intramedullary rod was not used (1.8 ± 1.1 mm versus 3.4 ± 1.2 mm, P < 0.001). The mean difference of wall-bearing space with and without intramedullary rod was 1.6 ± 0.7 mm.

Conclusions

Femoral components can be laterally implanted incorrectly by an average of 1.6 mm when using intramedullary rods. The wall-bearing space should be evaluated using trial components, and if the relationship is improper, it should be corrected before keel slot preparation.

Bearing Separation From the Lateral Wall of the Tibial Component Is a Risk of Anterior Dislocation of the Mobile Bearing in Oxford Unicompartmental Knee Arthroplasty

BACKGROUND

Bearing dislocation is a serious complication after Oxford unicompartmental knee arthroplasty. Bearing separation from the lateral wall can cause it to spin (90° horizontal rotation) and eventually dislocate because there is just a 2 mm difference in height in both the lateral and medial sides from the bottom of the bearing, compared with the anterior (5 mm) and posterior (3 mm) sides. The details of this problem have not been previously examined.

METHODS

Twenty-one dislocations in 12 patients were retrospectively analyzed. Bearing separation was defined as the bearing position being sufficiently distant from the lateral wall of the tibial component to allow spinning. We analyzed the incidence of separation, the direction and the recurrence of the dislocations, and their causes and treatments.

RESULTS

Five of the 12 patients had separation. Of the total of 21 dislocations, 11 occurred in cases of separation (52%). Seven of 11 anterior dislocations were found to have separation, whereas nine of 13 posterior dislocations occurred without separation (P = .0237). Three of 5 patients with separation had recurrence of dislocation, and eventually 2 underwent revision to fixed-bearing unicompartmental knee arthroplasty.

CONCLUSION

Bearing separation from the lateral wall of the tibial component can cause bearing dislocation, especially in an anterior direction. To prevent separation, the wall-bearing distance should be evaluated before the keel slot preparation, with manipulation as necessary. Conversely, posterior dislocation was predominant in our nonseparation cases.

Prosthetic Alignment and Clinical Outcomes of Navigation-Assisted Unicompartmental Knee Arthroplasty by an Experienced Surgeon Compared With Inexperienced Surgeons

BACKGROUND

To improve the accuracy of tibial cut during unicompartmental knee arthroplasty (UKA), navigation-assisted UKA has been implemented. It has been reported that inexperienced surgeons who use a navigation system achieve better alignment than experienced surgeons who do not use a navigation system. However, there have been no reports comparing the alignments and clinical outcomes of navigation-assisted UKA performed by experienced surgeons in comparison with that by inexperienced surgeons. This study aims to compare these parameters of navigation-assisted UKA performed by experienced and inexperienced surgeons.

METHODS

A total of 209 UKA procedures using an image-free navigation system were included. One experienced surgeon performed 128 UKAs (E group), and six inexperienced surgeons performed 81 UKAs (I group). The target value in the coronal tibial plane was set at 2.0° in varus. Prosthetic alignments and clinical results were compared between the two groups.

RESULTS

No significant differences were found between the two groups for prosthetic alignments and clinical outcomes, except for range of motion. The operation time of the I group was statistically longer than that of the E group (P < .001). The ratio of tibial prosthetic fracture was significantly higher in the I group than that in the E group (P = .022).

CONCLUSION

Using a navigation system during UKA, inexperienced surgeons achieved accurate alignments and excellent clinical results similar to an experienced surgeon. However, tibial periprosthetic fractures occurred more often in patients of inexperienced surgeons. Even when using a navigation system, inexperienced surgeons need to demonstrate careful and cautious surgical techniques.

CT Morphometric Analysis of Medial Tibial Condyles: Are the Currently Available Designs of Unicompartmental Knee Arthroplasty Suitable for Indian Knees?

BACKGROUND

The main purpose of this study is to assess the compatibility of medial tibial condyle (MTC) morphometry of Indian population with that of six contemporary UKA prostheses tibial components. We hypothesized that from the currently available UKA designs at least one would fit the MTC morphometry optimally as per the manufacturer's recommendation.

METHODS

We used CT morphometric data of 100 (66 males and 34 females) consecutive nonarthritic adult knees with reference to the MTC to assess the compatibility of currently available (in India) UKA prostheses. Each MTC was measured in the anteroposterior dimension, mediolateral at pre-defined points and the MTC aspect ratio calculated. Proportion of knees which could be optimally fitted with the existing UKA tibial components was calculated.

RESULTS

The mean age was 39.6 (SD 15.9) years. Anteroposterior and mediolateral dimensions in males were higher as compared to females (p < 0.001). As the anteroposterior dimension increased, the MTC aspect ratio decreased. There was asymmetry of anteroposterior halves with maximum mediolateral width being posterior to the central mediolateral width by 5.5 (SD 2.8) mm. Optimal anteroposterior fit ranged from 66 to 93%. However, optimal mediolateral fit as well, ranged from 5 to 37% with underhang present in 17-61% and > 2 mm medial overhang present in 0-35% cases. In 23% of cases, not a single implant could be fitted optimally.

CONCLUSION

Currently available UKA implants do not provide optimal tibial fit in nearly 25% of Indian patients. A surgeon needs to be aware of these limitations of existing implants when considering UKA.

Cementless knee arthroplasty: a review of recent performance

Cementless knee arthroplasty has seen a recent resurgence in popularity due to conceptual advantages, including improved osseointegration providing biological fixation, increased surgical efficiency, and reduced systemic complications associated with cement impaction and wear from cement debris. Increasingly younger and higher demand patients are requiring knee arthroplasty, and as such, there is optimism cementless fixation may improve implant survivorship and functional outcomes.

Compared to cemented implants, the National Joint Registry (NJR) currently reports higher revision rates in cementless total knee arthroplasty (TKA), but lower in unicompartmental knee arthroplasty (UKA). However, recent studies are beginning to show excellent outcomes with cementless implants, particularly with UKA which has shown superior performance to cemented varieties. Cementless TKA has yet to show long-term benefit, and currently performs equivalently to cemented in short- to medium-term cohort studies. However, with novel concepts including 3D-printed coatings, robotic-assisted surgery, radiostereometric analysis, and kinematic or functional knee alignment principles, it is hoped they may help improve the outcomes of cementless TKA in the long-term. In addition, though cementless implant costs remain higher due to novel implant coatings, it is speculated cost-effectiveness can be achieved through greater surgical efficiency and potential reduction in revision costs. There is paucity of level one data on long-term outcomes between fixation methods and the cost-effectiveness of modern cementless knee arthroplasty.

This review explores recent literature on cementless knee arthroplasty, with regards to clinical outcomes, implant survivorship, complications, and cost-effectiveness; providing a concise update to assist clinicians on implant choice.

Cite this article: Bone Jt Open 2021;2(1):48–57.

Cementless medial Oxford unicompartmental knee replacement. Five-year results from an independent series

BACKGROUND

Unicompartmental knee replacement (UKR) is a common treatment option for patients with advanced medial compartment knee arthritis. The Oxford UKR (OUKR) is the most commonly used implant for partial knee replacement. A cementless Oxford prosthesis was introduced in 2004 aiming to reduce the revision rate by potentially reducing radiolucencies as well as errors of cementation associated with the cemented prosthesis. Whilst results from the designer centre have been reported, there is little independent clinical evidence of outcomes. The aim of this study was to evaluate the survival of the cementless OUKR in a single surgeon series at an independent centre and to assess clinical and radiographic outcomes.

METHODS

All patients who received a cementless medial OUKR and had a minimum of five-year follow-up were included in the series. The Oxford knee score was used to evaluate patient outcomes at five years postoperatively. Survival rates, complications and evidence of radiolucencies on plain radiographs were also reviewed.

RESULTS

One hundred and fifty-eight cementless medial OUKR were implanted in 126 patients. Three patients died and four knees were revised. The five-year survival was 97.4% and the median Oxford knee score was 43 at five years postoperatively. No Complete radiolucent lines were observed on radiographs at one year. Four tibial components subsided.

CONCLUSIONS

This independent series shows that low revision rates and excellent results can be achieved with the use of the cementless OUKR at five years. Early subsidence of the tibial component, which is specific to the cementless prosthesis, warrants further investigation.

Femoral migration of the cementless Oxford which caused the bearing dislocation: a report of two cases

BACKGROUND

There are no previous reports on the complications around the femoral component of cementless Oxford unicompartmental knee arthroplasty (UKA). However, we experienced two cases of femoral migration to the proximal side, which caused bearing dislocations after cementless Oxford UKA.

CASE PRESENTATION

Case1. In an 82-year-old woman, bearing dislocation occurred 13 months postoperatively because of femoral migration that was resolved with an revision surgery to cemented component and thicker mobile insert. Case2. In a 52-year-old man, first bearing dislocation occurred 7 months postoperatively. Five months after revising the insert to a thicker one, another dislocation occurred mainly because of the femoral migration. Eventually, a revision to total knee arthroplasty was necessary.

CONCLUSIONS

The inferred main reasons of femoral migration of cementless Oxford were osteoporosis for the first case and early return to high performance sports activity for the second case. Although several merits of using cementless prosthesis, particularly better fixation and lesser radiolucency than cemented prosthesis, have been reported, surgeons should pay attention to the patient's bone quality and advise a slow return to high-level physical activity.

Cementless Oxford Medial Unicompartmental Knee Replacement-Clinical and Radiological Results of 228 Knees with a Minimum 2-Year Follow-Up

(1) Background: Studies show several advantages of unicompartmental knee replacement (UKR) over total knee replacements (TKR), whereas registry based revision rates of UKR are significantly higher than for TKA. Registry data report lower revision rates for cementless UKR compared to cemented UKR. The aim of this study was to assess clinical and radiological results of cementless Oxford UKR (OUKR) in an independent cohort. (2) Methods: This retrospective cohort study examines a consecutive series of 228 cementless OUKR. Clinical outcome was measured using functional scores (Oxford Knee Score (OKS), American Knee Society Score (AKSS), Hannover Functional Ability Questionnaire for Osteoarthritis (FFbH-OA), range of motion (ROM)), pain and satisfaction. Radiographs were analyzed regarding the incidence of radiolucent lines (RL), implant positioning, and their possible impact on clinical outcome. (3) Results: At a mean follow-up of 37.1 months, the two and three year revision free survival-rates were 97.5% and 96.9%. Reasons for revision surgery were progression of osteoarthritis, inlay dislocation and pain. All clinical outcome scores showed a significant improvement from pre- to postoperative. The incidence of RL around the implant was highest within the first year postoperatively (36%), and decreased (5%) within the second year. Their presence was not correlated with inferior clinical outcome. Implant positioning showed no influence on clinical outcome. (4) Conclusion: Cementless OUKR showed excellent clinical outcome and survival rates, with reliable osteointegration. Neither the incidence of radiolucent lines nor implant positioning were associated with inferior clinical outcome.

Unicompartmental Knee Arthroplasty: US and Global Perspectives

Unicompartmental knee arthroplasty (UKA) is a treatment option for anteromedial osteoarthritis. Compared with total knee arthroplasty (TKA), UKA offers improved knee range of motion, functional recovery and decreased medical complications. Revision rates continue to be higher with UKA compared with TKA. With current UKA implants, there is no significant difference in mobile bearing or fixed bearing, or between cemented and cementless implants. Enabling technology, such as robotic-assisted surgery, has demonstrated improvements in component positioning, but no long-term difference in survival compared with traditional manual instruments.

Valgus Subsidence of the Tibial Component Caused by Tibial Component Malpositioning in Cementless Oxford Mobile-Bearing Unicompartmental Knee Arthroplasty

BACKGROUND

Valgus subsidence (VS) of the tibial component is a rare complication of unicompartmental knee arthroplasty (UKA), and surgeons might consider revision surgery. The present study aimed to identify the factors related to VS of the tibial component after cementless Oxford mobile-bearing UKA.

METHODS

The study included 120 patients who underwent Oxford mobile-bearing UKA using a cementless tibial component in our center between September 2015 and September 2016. Six showed VS of >2° after surgery. Patients were stratified into 2 groups according to the occurrence of VS of the tibial component (VS group, n = 6; no-subsidence group, n = 114). Postoperative radiographic evaluations were conducted to assess the varus/valgus alignment, rotation, and mediolateral position of the tibial and femoral components. The Oxford Knee Score (OKS) was assessed at 3, 6, and 12 months postoperatively. Positional parameters and sequential change in OKS were compared between the two groups using unpaired t-test (P < .05, statistically significant).

RESULTS

At 3 months postoperatively, an average VS of 3.4° in the VS group was observed, with a significant decrease in OKS. VS was associated with a significantly more medial position and external rotation of the tibial component. After 3 months, VS stopped, and the OKS gradually improved without revision surgery.

CONCLUSIONS

VS might be caused by the malpositioning of the tibial component. VS of the tibial component after UKA appears to stop, with simultaneous pain relief, even without revision after 3 months postoperatively.

Adequate Positioning of the Tibial Component Is Key to Avoiding Bearing Impingement in Oxford Unicompartmental Knee Arthroplasty

BACKGROUND

Bearing dislocation is a serious complication of unicompartmental knee arthroplasty (UKA) with the Oxford knee prosthesis equipped with a mobile bearing. We aimed to clarify the extent of intraoperative movement of the mobile bearing and its relationship with the positioning of prosthesis components in patients undergoing Oxford UKA.

METHODS

This retrospective study included 50 patients (50 knees) who underwent Oxford UKA for anteromedial osteoarthritis or osteonecrosis of the knee. Intraoperative bearing movement was assessed at various angles of knee flexion (0°, 30°, 60°, 90°, and 120°). We stratified patients according to the extent of bearing movement posteriorly during intraoperative knee flexion, with or without contacting the lateral wall of the tibial component (with contact, 20 knees; without contact, 30 knees). Postoperative radiographic evaluations were conducted at 1 week postoperatively to assess the positional parameters of the tibial and femoral components (varus/valgus alignment, rotation, mediolateral position). Clinical evaluations were conducted at 1 year postoperatively (maximum flexion angle, Oxford Knee Score).

RESULTS

Abnormal intraoperative movement of the mobile bearing resulting in contact with the lateral wall of the tibial component was associated with a significantly more medial position and external rotation of the tibial component, as well as poorer improvement in knee flexion angle at 1 year postoperatively.

CONCLUSION

In Oxford UKA recipients, the bearing may impinge on the lateral wall of the tibial component during flexion above 60° if the tibial component is placed too medially or exhibits pronounced external rotation, which may limit knee function improvement postoperatively.

Ten-year survival and seven-year functional results of cementless Oxford unicompartmental knee replacement: A prospective consecutive series of our first 1000 cases

BACKGROUND

Cementless fixation is an alternative to cemented unicompartmental knee replacement (UKR), with several advantages over cementation. This study reports the ten-year survival and seven-year clinical outcome of cementless Oxford unicompartmental knee replacement (OUKR).

METHODS

This prospective study describes the clinical outcome and survival of the first 1000 consecutive cementless medial OUKRs implanted at two centres for recommended indications.

RESULTS

The 10-year survival was 97% (CI 95%: 92-100%), with 25 knees being revised. The commonest reason for revision was progression of arthritis laterally, which occurred in nine knees, followed by primary dislocation of the bearing, which occurred in six knees. There were two dislocations secondary to trauma and a ruptured ACL, and two tibial plateau fractures. Although there were no definite cases of aseptic loosening, two early revisions were related to tibial fixation: one for pain and a radiolucent line and one for incomplete seating of the component with a radiolucent line. There were four revisions for pain, but the cause of the pain was uncertain: in one there was tibial overhang and in two there was patellofemoral degeneration, which possibly contributed to the pain. There were no deep infections. The mean OKS improved from 23 (SD 8) to 42 (SD 7) at a mean follow-up of 7.0 years (p < 0.001). There was no significant difference in survival or clinical outcome between the designer and independent centre.

CONCLUSIONS

The cementless OUKR is a safe and reproducible procedure with excellent 10-year survival and clinical results in the hands of both designer and independent surgeons.

The Oxford Medial Unicompartmental Knee Arthroplasty: The South African Experience

BACKGROUND

The Oxford unicompartmental knee arthroplasty (OUKA) is a successful treatment for endstage, symptomatic anteromedial osteoarthritis. This study reports the results of a cohort of consecutive cemented and cementless medial OUKAs from an independent center and aims to answer the following questions: what is the survival of OUKA in the hands of a nondesigner surgeon? Are there any differences in the survival of cementless and cemented OUKA? Are the failure modes any different with the cementless and cemented OUKA?

METHODS

One thousand one hundred twenty consecutive OUKAs were implanted in a single center for the recommended indications. Patients were prospectively identified and followed up. Survival was calculated with revision as the end point.

RESULTS

There were 522 cemented and 598 cementless implants. The mean follow-up was 8.3 years for cemented implants (range 0.5-17, standard deviation [SD] 2.9) and 2.7 years (range 0.5-7, SD 1.8) for cementless implants. The Oxford knee score improved from a preoperative mean of 22 (SD 8.1) to 40 (SD 7.9) at the last follow-up (P < .001). There were 59 failures requiring revision surgery, with a 5.3% cumulative revision rate. The most common reason for failure was progression of osteoarthritis in the lateral compartment, occurred in 26 cases (2.3%). The cumulative 10-year survival was 91% (95% confidence interval 87.3-95.2).

CONCLUSION

The results of this prospective, consecutive case series from the African continent demonstrated that excellent results are achievable with the OUKA in independent centers if the correct indications and surgical technique are used.

Cementless unicompartmental knee replacement allows early return to normal activity

Background

Physical activity and regular participation in recreational sports gain importance in patients’ lifestyle after knee arthroplasty. Cementless unicompartimental Knee replacement with the Oxford System has been introduced into clinical routine. Currently there is no data reporting on the physical activity, return to sports rate and quality of live after medial cementless Oxford Unicompartimental Knee Replacement (OUKR).

Methods

This retrospective cohort study reports on the functional outcome of the first 27 consecutive patients (30 knees) that were consecutively treated with a cementless medial OUKR between 2007 and 2009 in our hospital. Physical activity and quality of life were measured using the Tegner-Score, the UCLA-Activity Score, the Schulthess Clinical Activity Questionnaire and the SF-36 Score. The patients’ satisfaction with the outcome was measured using a visual analogue scale.

Results

Mean age at surgery was 62.5 years. Patients showed a rapid recovery with 17 out of 27 patients returning to sports within 3 months, 24 within 6 months after surgery. The Return-to-activity-rate was 100%. 10 out of 27 patients showed a high activity level (UCLA ≥7 points) with a mean postoperative UCLA-Score of 6.1 points.

Conclusions

Patients recover rapidly after cementless OUKR with a return to sports rate of 100% and patients are able to participate in high impact sports disciplines.

Cementless Oxford medial unicompartimental knee replacement: an independent series with a 5-year-follow-up

PURPOSE

Cemented unicompartmental knee replacement (UKR) has proven excellent long-term survival rates and functional scores in Price et al. (Clin Orthop Relat Res 435:171-180, 2005), Price and Svard (Clin Orthop Relat Res 469(1):174-179, 2011) and Murray et al. (Bone Joint Surg Br 80(6):983-989, 1998). The main causes for revision, aseptic loosening and pain of unknown origin might be addressed by cementless UKR in Liddle et al. (Bone Joint J 95-B(2):181-187, 2013), Pandit et al. (J Bone Joint Surg Am 95(15):1365-1372, 2013), National Joint Registry for England, Wales and Northern Ireland: 10th Annual Report 2013 ( http://www.njrcentre.org.uk/njrcentre/Portals/0/Documents/England/Reports/10th_annual_report/NJR%2010th%20Annual%20Report%202013%20B.pdf , 2013), Swedish Knee Arthroplasty Register: Annual Report 2013 ( http://www.myknee.se/pdf/SKAR2013_Eng.pdf , 2013).

METHODS

This single-centre retrospective cohort study reports the 5-year follow-up results of our first 30 consecutively implanted cementless Oxford UKR (OUKR). Clinical outcome was measured using the OKS, AKSS, range of movement and level of pain (visual analogue scale). The results were compared to cemented OUKR in a matched-pair analysis.

RESULTS

Implant survival was 89.7%. One revision each was performed due to tibial fracture, progression of osteoarthritis (OA) and inlay dislocation. The 5-year survival rate of the cementless group was 89.7% and of the cemented group 94.1%. Both groups showed excellent postoperative clinical scores.

CONCLUSIONS

Cementless fixation shows good survival rates and clinical outcome compared to cemented fixation.

Comparative Fixation and Subsidence Profiles of Cementless Unicompartmental Knee Arthroplasty Implants

BACKGROUND

Aseptic loosening is the primary cause of failure for both cemented and cementless unicondylar knee replacements (UKRs). Micromotion and subsidence of tibial baseplate are two causes of failure, due to poor fixation and misalignment, respectively.

METHODS

Stair ascent activity profiles from Bergmann et al and Li et al were used. Biphasic Sawbones models were prepared according to the surgical techniques of traditional and novel cementless UKRs. Implants were tested for 10,000 cycles representing post-operative bone interdigitation period, and micromotion was observed using speckle pattern measurements, which demonstrated sufficient resolution. Additionally, the test method proposed by Liddle et al was used to measure subsidence with pressure sensors under increasingly lateralized loading.

RESULTS

Mean displacement due to micromotion for mediolateral and anteroposterior plane was consistently greater for traditional cementless UKR. Mean displacement for axial micromotion was significantly higher for traditional UKR at the anterior aspect of the implant; however, values were lower for the medial periphery of the implant. Subsidence was significantly lower for the novel design with increasingly lateralized loading, and indentation was not observed on the test substrate, when compared to the traditional design.

CONCLUSION

Our findings demonstrate that the novel cementless design is capable of fixation and elimination of subsidence in laboratory test settings. Both designs limit micromotion to below the established loosening micromotion value of 150 μm. The L-shaped keel design resists both micromotion and subsidence and may prevent failure modes that can lead to aseptic loosening for UKRs. These findings are highly relevant for clinical application.

Impingement of the Mobile Bearing on the Lateral Wall of the Tibial Tray in Unicompartmental Knee Arthroplasty

BACKGROUND

Tilting of the mobile bearing relative to the tibial tray in the flexion position may result from the implantation of femoral components more laterally relative to tibial components during unicompartmental knee arthroplasty (UKA) using the Oxford Knee. The purpose of the present study was to compare femoral component positions after UKA using the phase 3 device and a novel device. We further evaluated the placement of the femoral components with the new device in the flexion position to determine the association with short-term prognosis.

METHODS

The location of femoral and tibial components in the flexion position of 38 knees implanted using the phase 3 device and 49 knees using a novel device was assessed at 1 year postoperatively using radiography of the proximal tibia and distal femur in the flexion position.

RESULTS

The femoral component was implanted more laterally using the new device than using the phase 3 device in the flexion position (P = .012), which caused the impingement of the mobile bearing against the lateral wall of the tibial tray. After UKA using the new device, 10% of patients exhibited the tilting phenomenon of the mobile bearing because of the lateral implantation of the femoral implant.

CONCLUSION

To prevent implantation of the femoral component too laterally using the new device during UKA, knee surgeons should set the drill guide more medially such that the center of the drill is aligned with the middle of the medial femoral condyle.

Finite Element Analysis of Mobile-bearing Unicompartmental Knee Arthroplasty: The Influence of Tibial Component Coronal Alignment

Background:

Controversies about the rational positioning of the tibial component in unicompartmental knee arthroplasty (UKA) still exist. Previous finite element (FE) studies were rare, and the results varied. This FE study aimed to analyze the influence of the tibial component coronal alignment on knee biomechanics in mobile-bearing UKA and find a ration range of inclination angles.

Methods:

A three-dimensional FE model of the intact knee was constructed from image data of one normal subject. A 1000 N compressive load was applied to the intact knee model for validating. Then a set of eleven UKA FE models was developed with the coronal inclination angles of the tibial tray ranging from 10° valgus to 10° varus. Tibial bone stresses and strains, contact pressures and load distribution in all UKA models were calculated and analyzed under the unified loading and boundary conditions.

Results:

Load distribution, contact pressures, and contact areas in intact knee model were validated. In UKA models, von Mises stress and compressive strain at proximal medial cortical bone increased significantly as the tibial tray was in valgus inclination >4°, which may increase the risk of residual pain. Compressive strains at tibial keel slot were above the high threshold with varus inclination >4°, which may result in greater risk of component migration. Tibial bone resection corner acted as a strain-raiser regardless of the inclination angles. Compressive strains at the resected surface slightly changed with the varying inclinations and were not supposed to induce bone resorption and component loosening. Contact pressures and load percentage in lateral compartment increased with the more varus inclination, which may lead to osteoarthritis progression.

Conclusions:

Static knee biomechanics after UKA can be greatly affected by tibial component coronal alignment. A range from 4° valgus to 4° varus inclination of tibial component can be recommended in mobile-bearing UKA.

Aetiology of lateral progression of arthritis following Oxford medial unicompartmental knee replacement: a case-control study

Purpose

The aim of this case–control study is to assess for predictive factors that may determine development of lateral compartment progression after Oxford medial unicompartmental knee replacement.

Methods

Twenty-eight patients who were revised as a result of lateral osteoarthritis progression were matched to 52 alive and unrevised patients. Body mass index, intra-operative findings, postoperative leg alignment, meniscal bearing size and histological findings have been analysed. Radiological analysis was carried out on the immediate postoperative radiographs by two blinded observers to assess the severity of arthritis in the lateral compartment. The measurements of the components positions were converted into binary figures as to whether they were inside or outside the recommended limits for analysis. Conditional logistic regression was used to identify important predictors of progression, taking into account the case–control grouping.

Results

The results shows that the condition of the lateral compartment is a significant predictor for developing subsequent lateral compartment arthrosis (OR 2.627, p = 0.019). The study showed no relationship between progression of arthritis and component position (OR [0.5–1.18], p [0.21–1]). Nor have it demonstrated that BMI (OR 1.06, p = 0.61), postoperative leg alignment (OR 1.26, p = 0.636), meniscal bearing size (1.32, p = 0.307) or presence of chondrocalcinosis (OR 0.35, p = 0.36) have any association with lateral osteoarthritis progression.

Conclusions

This study showed the importance of excluding radiographic evidence of lateral compartment osteoarthritis on the preoperative radiograph prior to medial unicompartmental knee replacement. We have not been able to show any relationship between progression of arthritis and component position.

Level of proof Case–control study, level III.