Midterm clinical and radiographic results of the medial pivot total knee system

No difference in clinical outcomes when retaining or sacrificing the posterior cruciate ligament in medial congruent total knee replacement. A retrospective study

PURPOSE

The aim of this study is to evaluate the effect of retaining or sacrificing the posterior cruciate ligament (PCL) in patients who undergo primary total knee replacement (TKR) with the medial congruent (MC) implant.

METHODS

This retrospective study looks at patients who underwent TKR with the MC implant. Comparison was made between the group with the PCL sacrificed (MC-PCLS) and the group with the PCL retained (MC-PCLR). Range of motion (ROM), Oxford knee score (OKS), Knee society knee score (KS-KS) and Knee society function score (KS-FS) were recorded.

RESULTS

The study identified 76 patients. 50 in the MC-PCLS group and 26 in the MC-PCLR group. Both groups had similar patient demographics. Three months postoperatively, OKS and KS-KS had significant improvement. However, there was significant improvement in KS-FS score in the MC-PCLS group but not the MC-PCLR group (MC-PCLR: 33 ± 17, p = 0.07; MC-PCLS: 19 ± 24, p = 0.01). Twelve months postoperatively, the OKS continued to improve significantly for both groups, while the KS-FS and KS-KS scores appeared to stagnate. The ROM continued to improve significantly for the MC-PCLR group but not the MC-PCLS group (MC-PCLR: 7 ± 9, p = 0.03; MC-PCLS: 4 ± 9, p = 0.30). Both groups were similar in ROM, OKS and KSS scores at both the 3 and 12 month post-operative period.

CONCLUSION

There is no difference in post-operative outcomes with the PCL retained or sacrificed. As such, surgeons can consider routinely sacrificing the PCL for easier balancing of the knee and shorter surgical time.

Good Short-Term Survivorship of Constrained Condylar Revision Knee Implants With Medial Pivot Kinematics: A Level IV Retrospective Study

BACKGROUND

The need for revision total knee arthroplasty surgery is increasing worldwide, and, in many cases, a constrained implant is required to provide joint stability. The purpose of this study was to examine the early loosening and functional outcome of a novel constrained condylar (CCK) revision total knee system designed to have medial pivot (MP) kinematics.

METHODS

A retrospective cohort study was performed, collecting clinical data from all patients who underwent revision total knee arthroplasty using a novel MP CCK system with a minimum four-year clinical follow-up. Patient demographics, survivorship, complications, and Forgotten Joint Score were analyzed based upon chart review.

RESULTS

There were 49 patients available for follow-up, who had a 100% survivorship free of aseptic loosening. All-cause revision survivorship was 92%. There were 4 patients who subsequently underwent rerevision. The causes for rerevision included periprosthetic joint infection in 2 patients, coronal plane instability in one patient, and a traumatic knee dislocation in one patient. There were 45 patients who completed the Forgotten Joint Score, who had an average of 49.8 (± 32.8, range 6.25 to 100).

CONCLUSIONS

At 4 years, mid-term follow-up, this novel CCK revision total knee system designed to have MP kinematics had good patient-reported outcomes with no revision for aseptic loosening. Future studies should evaluate the mid- and long-term survivorship of this innovative implant.

Improved Clinical Outcomes With Dynamic, Force-Controlled, Gap-Balancing in Posterior-Stabilized Total Knee Arthroplasty

BACKGROUND

Optimal soft-tissue management in total knee arthroplasty (TKA) may reduce symptomatic instability. We hypothesized that TKA outcomes using a computer-assisted dynamic ligament balancer that acquires medial and lateral gap sizes throughout the motion arc would show improved Knee Society Scores (KSS) compared to TKAs done with a traditional tensioner at 0 and 90°. We also sought to quantify the degree to which the planned femoral rotation chosen to optimize medio-lateral balance throughout the arc of motion deviated from the femoral rotation needed to achieve a rectangular flexion gap at 90° alone.

METHODS

Baseline demographics, clinical outcomes, KSSs, and femoral rotations were compared in 100 consecutive, computer-assisted TKAs done with the balancer (balancer group) to the immediately prior 100 consecutive computer-assisted TKAs done without the balancer (control group). Minimum follow-up was 13 months and all patients had osteoarthritis. Mean knee motion did not differ preoperatively (110.1 ± 13.6° balancer, 110.4 ± 12.5° control, P = .44) or postoperatively (119.1 ± 10.3° balancer, 118.8 ± 10.9° control, P = .42). Tourniquet times did not differ (93.1 ± 13.0 minutes balancer, 90.7 ± 13.0 minutes control, P = .13). Postoperative length of stay differed (40.2 ± 20.9 hours balancer, 49.0 ± 18.3 hours control, P = .0009). There were 14 readmissions (7 balancer, 7 control), 11 adverse events (4 balancer, 7 control), and 3 manipulations (1 balancer, 2 control). The cohorts were compared using Student's t-tests, Shapiro-Wilk normalities, Wilcoxon rank-sums, and multivariable logistic regression analyses.

RESULTS

Postoperative KSS improvements were higher in the balancer group (P < .0001). In multivariable regression analyses, the balancer group experienced 7 ± 2 point improvement in KSS Knee scores (P < .0001) and 4 ± 2 point improvement in KSS Function scores (P = .040) compared to the control group.

CONCLUSIONS

The statistically and clinically significant improvements in postoperative KSS demonstrated in the balancer cohort are likely driven by improved stability throughout the motion arc. Further study is warranted to evaluate replicability by non-design surgeons.

Biomechanical improvements in gait following medial pivot knee implant surgery

BACKGROUND

Total knee replacements are used to improve function and reduce pain in patients with advanced osteoarthritis. The medially stabilising implant is designed to mimic a healthy knee. This study aims to provide a comprehensive analysis of the kinematics and kinetics of a medially stabilising knee implant, comparing it to a healthy control group, as well as to its pre-operative state and the contralateral limb.

METHODS

Sixteen total knee replacement patients and ten healthy participants were recruited. Patients underwent testing 4-6 weeks before surgery and repeated the same tests 12 months after surgery. Healthy participants completed the same tests at a single time point. All participants completed three walking trials: kinematics was captured with eight cameras; kinetics with in-ground force plates. Subject-specific musculoskeletal models were developed in OpenSim. Inverse kinematics and inverse dynamics were used to determine gait parameters. Joint angles and joint moments were evaluated using Statistical Parametric Mapping. Patient-reported outcome measures were also collected at both time points.

FINDINGS

Spatiotemporal results indicate significant differences in velocity and step length between pre-operative patients and control participants. Differences are observed in the adduction angles between the contralateral and ipsilateral limbs pre-operatively. Postoperatively, there was an increase in the 1st peak flexion moment, reduced adduction moment and reduced internal rotation moment. In PROMs, patients all report improvements in pain levels and high satisfaction levels following surgery.

INTERPRETATIONS

Following medial stabilising total knee arthroplasty, patients displayed improved clinical parameters and joint moments reflecting a shift towards more normal, healthy gait.

Sitting Sideways Causes Different Femoral-Tibial Rotations in Each Knee

Purpose According to a previous study, asymmetrical kneeling, such as sitting sideways, does not exhibit asymmetrical movements. Rotational analyses of each femur and tibia help explain why rotational knee kinematics while sitting sideways do not exhibit asymmetrical movement. We aimed to assess the rotation of the femur and tibia in normal knees while sitting sideways. Methods Each volunteer sat sideways under fluoroscopy. Two-dimensional and three-dimensional registration techniques were used. After evaluating the femoral rotation angle relative to the tibia at each flexion angle, the femoral and tibial sole rotation angles at each flexion angle were compared between the ipsilateral and contralateral knees. Results While sitting sideways, both knees showed femoral external rotation relative to the tibia with flexion. In the ipsilateral knees, the femurs exhibited an external rotation of 26.3 ± 8.0°, from 110° to 150° of flexion. Conversely, the tibia exhibited an external rotation of 12.2 ± 7.8°, from 110° to 150° of flexion. From 110° to 150° of flexion, femoral external rotation was significantly larger than tibial external rotation. In the contralateral knees, the femurs exhibited an internal rotation of 23.8 ± 6.3°, from 110° to 150° of flexion (110°, p < 0.001; 120°, p < 0.001; 130°, p < 0.001; 140°, p < 0.001; and 150°, p < 0.001). Contrastingly, the tibia exhibited an internal rotation of 30.4 ± 8.8°, from 110° to 150° of flexion, which was significantly larger than femoral internal rotation (110°, p = 0.002; 120°, p < 0.001; 130°, p < 0.001; 140°, p < 0.001; and 150°, p < 0.001). Conclusions Although bilateral knees exhibited femoral external rotation relative to the tibia while sitting sideways, the ipsilateral and contralateral knees showed femoral and tibial sole rotations in opposite directions. In particular, the contralateral knees might show a strained movement because both femurs and tibias exhibited internal rotation with flexion. Patients who have undergone guided-motion total knee arthroplasty (TKA) or medial-pivot TKAs might be advised to avoid sitting sideways.

Mobile medial pivot (lateral slide)-type total knee arthroplasty exhibited different motion patterns between under anaesthesia and weight-bearing condition

PURPOSE

Total knee arthroplasty (TKA), which has medial pivot and mobile-bearing mechanisms, has been developed and clinically used. However, the in vivo dynamic kinematics of the mobile medial pivot-type TKA (MMPTKA) is unclear. This study analysed the in vivo kinematics of MMPTKA in weight-bearing and nonweight-bearing conditions.

METHODS

The study included 10 knees that underwent primary TKA using MMPTKA. After TKA, lateral view radiographs of the knee in full extension, 90° of flexion and passive full flexion were taken under general anaesthesia in the nonweight-bearing condition. At least 6 months postoperatively, knee motion during squatting from a weight-bearing standing position was observed using a flat-panel detector and analysed using the three-dimensional-to-two-dimensional image registration technique.

RESULTS

Under anaesthesia: in passive full flexion, the anteroposterior (AP) locations of the femoral component's medial and lateral distal points were 10.2 and 16.0 mm posterior, and the rotational angles of the femoral component's X-axis (FCX) and insert were 8.1° external rotation and 18.5° internal rotation to full extension, respectively. Squatting: the AP translations of the femoral component's medial and lateral most distal points were 2.2 and 6.4 mm, and the rotational angles of the FCX and insert were 5.7° and 1.6° external rotation, respectively. Significant differences were observed in the AP translation of the femoral component's medial and lateral most distal points and changes in the insert's rotational angle when comparing under anaesthesia and squatting.

CONCLUSIONS

The kinematics of the insert in MMPTKA was significantly influenced by loading and muscle contraction. The femoral component exhibited substantial external rotation and posterior translation under anaesthesia, which may contribute to achieving an optimal range of motion. The insert remained relatively stable during squatting and minimal rotation was observed, indicating good stability. MMPTKA was expected to demonstrate rational kinematics by incorporating mobile and medial pivot mechanisms.

LEVEL OF EVIDENCE

Level IV, prospective biomechanical case series study.

Cementless medial pivot design demonstrates equal or better outcomes compared to cementless cruciate-retaining design following total knee arthroplasty

Introduction

Traditional total knee arthroplasty (TKA) designs fail to reproduce physiologic knee kinematics, which can contribute to patient dissatisfaction. In an attempt to restore more normal knee kinematics, the medial pivot (MP) design may improve knee function and stability as well as patient satisfaction. A limited number of studies have compared postoperative outcomes of exclusively cementless Cruciate-Retaining (CR) TKAs to cementless MP TKAs. We aimed to compare: (1) 90-day, 1-year, and 2-year complications and revisions, (2) preoperative and postoperative range of motion (ROM), (3) Knee Injury and Osteoarthritis Outcome (KOOS-JR), and (4) visual analog scale (VAS) pain scores at 3-month, 6-month, 1-year, and 2-years.

Methods

A retrospective analysis was performed to identify all patients who had previously undergone a TKA at our institution and compare a cementless CR system to a cementless MP design. Categorical variables, including demographics, comorbidities, and complications utilized Chi-square tests in bivariable analysis. Continuous variables, such as age, were compared using Student's t-tests. Significance was defined as p < 0.05.

Results

Cementless CR and cementless MP cohorts showed low profiles of postoperative complications and favorable patient-reported outcome measures (PROMs). The MP cohort had lower VAS pain at 1-year (1.70 vs. 3.76, p < 0.001) and 2-years (1.43 vs. 2.60, p < 0.001) and higher ROM at 3-months (118 vs. 100, p < 0.001), 6-months (113 vs. 103, p < 0.0001), and 1-year (117 vs. 110, p = 0.02), respectively.

Conclusion

This study is the first comparison of postoperative outcomes between a cementless CR TKA and cementless MP TKA designs. Implant design and fixation type are vital components influencing patient satisfaction after TKA. Pain scores and range of motion favored the cementless MP cohort in comparison to the cementless CR cohort.

The Medial Pivot Design in Total Knee Arthroplasty

Medial pivot total knee arthroplasty implants are designed to function in a similar manner to that of the native knee with a relatively fixed medial center of rotation and a less conforming lateral compartment that follows an arcuate path. Medial pivot implants in total knee arthroplasty have increased in popularity with many companies offering medial pivot or retrofitted medial congruent implants, and there are variations between the various medial pivot and medial congruent implants. Existing literature on medial pivot implants have demonstrated high survivorship and patient outcomes. More studies are needed to compare newer medial pivot implants with each other and with retrofitted medial congruent implants.

Medial Ball-in-Socket Posterior Cruciate-Sacrificing Total Knee Arthroplasty: Clinical, Functional and Radiographic Evaluation of 100 Consecutive Implants

The number of performed total knee arthroplasty (TKA) operations is constantly growing. This study proposes an evaluation of a series of patients undergoing medial pivot (MP) TKA surgery from a subjective, clinical and biomechanical point of view. A consecutive series of 100 TKAs implanted in a single centre, by the same surgeon, with a medial parapatellar approach with the sacrifice of the posterior cruciate ligament and cemented components were evaluated. All patients underwent standardized radiographic and functional clinical evaluation, with standing antero-posterior, lateral and patellar axial views; pre-operatively and post-operatively at 1, 3, 6 and 12 months; and then annually. Results were evaluated using three different patient-related outcome measurement scores (PROMs): the Knee Osteoarthritis Outcome Score (KOOS), the new Knee Society Score (nKSS) and the Short Form Health Survey 36 (SF-36). Excellent results in all treated knees were documented using the PROMs: the mean nKSS was 199.8, the mean KOOS was good to excellent in every subscale, and the mean was SF-36 82%. There were no cases of septic or aseptic loosening, vascular damage, neurological damage, or revision surgery for any reason. According to the experience gained, MP implants demonstrated excellent results, being clinically functional in both objective and subjective terms as well as radiographic evaluations, thus resulting in a winning strategy for obtaining a TKA that makes the patient satisfied and able to perform their daily life activities.

Modern Total Knee Arthroplasty Bearing Designs and the Role of the Posterior Cruciate Ligament

The role of the posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) surgery continues to be a source of debate among the adult reconstruction community. In native knee flexion, the PCL is comprised of an anterolateral and posteromedial bundle that work together to limit posterior tibial translation and allow adequate femoral rollback for deep flexion. In the arthritic knee, the PCL can often become dysfunctional and attenuated, which led to the development of posterior stabilized (PS) TKA bearing options. PS TKAs implement a cam-post construct to functionally replace a resected PCL. While PS designs may facilitate balancing knees with significant deformity, they are associated with complications such as postfracture, increased wear, and patellar clunk/crepitus. In recent years, newer designs have been popularized with greater degrees of congruency and incorporation of medial and lateral pivoting to better recreate native knee kinematics. The American Joint Registry has confirmed the recent predilection for ultra-congruent and cruciate-retaining TKA inserts over PS TKAs during the last decade. Studies have failed to identify an overall clinical superiority between the cruciate substituting and sacrificing designs. The literature has also failed to identify clinical consequences from PCL resection with modern, more conforming TKA designs. In this article, we review modern PCL sacrificing designs and discuss the impact of each on the kinematics after TKA. We also will delineate the role of the PCL in modern TKA in the hopes to better understand the recent surge in sacrificing but not substituting knee implants.

Medial pivot total knee arthroplasty: Mid-term results

This study aims to evaluate the mid-term results of patients who underwent medial pivot total knee arthroplasty at a single center. A total of 304 knees of 236 patients (40 males, 196 females; mean operation age and standard deviation : 66,64 ±7,09 years; range, 45 to 82 years) treated with medial pivot total knee prosthesis in our center between January 2010 and December 2014 were retrospectively analyzed. The American Knee Society Score, Oxford Knee Score, and especially flexion angles were recorded during pre- and postoperative follow-up. Of the operated knees, 71.2% were unilateral and 28.8% were bilateral. The mean follow-up was 79.30±14.76 months. The postoperative results with the Functional Score, Knee Score, Oxford Score, Total Knee Society Score, and flexion angles were significantly higher compared to baseline (p<0.01). All postoperative scores were significantly lower inpatients aged ≥65years, compared to those aged <65 years (p<0.01). In patients who underwent resection of anterior and posterior the cruciate ligaments, only the mean flexion angles were found to increase (p<0.01). Our study results suggest that medial pivot knee prostheses are reliable in the mid-term and provide favorable results in terms of function and patient satisfaction. Level of Evidence: Level IV retrospective study.

Medial Pivot Designs Versus Conventional Bearing Types in Primary Total Knee Arthroplasty: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Medial pivot (MP) designs are growing in popularity. They provide increased sagittal plane stability and theoretically replicate some aspects of native joint kinematics, which may improve total knee arthroplasty outcomes.

METHODS

A systematic review was performed of randomized controlled trials (RCTs) that compared MP designs with cruciate-retaining, posterior-stabilized (PS), ultracongruent, or mobile-bearings in primary total knee arthroplasty, according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The primary outcome measures were all clinical function scores, patient-reported outcome measures, and range of motion. The secondary outcome was complications. Two authors independently selected studies, performed data extraction, and risk-of-bias assessment. Studies at high risk of bias were excluded from meta-analysis. Treatment effects were assessed using random-effects meta-analysis and quantified using pooled mean differences or incidence rate differences as appropriate.

RESULTS

Eight RCTs met inclusion criteria. Five compared MP with PS, two with ultracongruent, and one with cruciate-retaining and mobile-bearing. In total, 350 knees were randomized to MP and 375 to conventional bearings. One RCT was excluded from meta-analysis because of high risk of bias. Meta-analysis comparing MP with PS only was possible and found no differences at any time points for any outcome measure, including 2-year follow-up for Oxford Knee Score (MD = 0.35 favoring PS; 95% CI -0.49 to 1.20) and range of motion (MD = 1.58 favoring MP; 95% CI -0.76 to 11.92, P = 0.30) and 12 months for Western Ontario Arthritis Index (MD = 4.42 favoring MP; 95% CI -12.04 to 3.20, P = 0.09).

CONCLUSIONS

There is no difference in clinical outcomes, with contemporary measurement tools, at any time points, between MP and PS. There are insufficient RCTs comparing MP with other bearings.

Clinical radiographic outcomes and survivorship of medial pivot design total knee arthroplasty: a systematic review of the literature

BACKGROUND

Total knee arthroplasty is a reliable procedure able to reduce pain and disability in patients suffering from osteoarthritis. However, a considerable percentage of patients still experiences unsatisfactory results. Medial pivot total knee arthroplasty has been introduced in the clinical practice to overcome problems related with classic design implants and better mimic native knee kinematics. The aim of this study was to analyze survivorship and clinical and radiographic outcomes of medial pivot implants.

METHODS

A systematic research was conducted in eight different databases. Thirty-four studies met the inclusion criteria and were included in the analysis. Data on objective and patients-reported outcomes, radiographic alignment, and survivorship were collected and analyzed. Revision rate was expressed as revision per 100 components years.

RESULT

A total of 3377 procedures were included. Mean follow-up was 85.7 months (range, 12-182). The revision per 100 components years was 0.19, which corresponds to a revision rate of 1.9% after 10 years. Mean post-operative range of motion was 117.3 ± 0.4°. Mean clinical and functional Knee Society Score were, respectively, 85.9 ± 1.1 and 84.7 ± 3.5 at final follow-up. Post-operative femorotibial alignment was 177.1 ± 0.5°. Alfa and beta angles were 95.7 ± 0.1° and 89.2 ± 0.1°, respectively. Gamma and delta angles were 2.3 ± 0.6° and 86.7 ± 0.4°.

CONCLUSION

Medial pivoting implants provided excellent survivorship and low revision rate, as well as good-to-excellent results in term of objective and patient-reported clinical outcomes, and reliable correction of radiographic parameters. More high-quality studies with long-term follow-up are needed to clarify the role of medial pivoting implants.

Early migration of a medially stabilized total knee arthroplasty : a radiostereometric analysis study up to two years

Aims

Medial pivot (MP) total knee arthroplasties (TKAs) were designed to mimic native knee kinematics with their deep medial congruent fitting of the tibia to the femur almost like a ball-on-socket, and a flat lateral part. GMK Sphere is a novel MP implant. Our primary aim was to study the migration pattern of the tibial tray of this TKA.

Methods

A total of 31 patients were recruited to this single-group radiostereometric analysis (RSA) study and received a medial pivot GMK Sphere TKA. The distributions of male patients versus female patients and right versus left knees were 21:10 and 17:14, respectively. Mean BMI was 29 kg/m² (95% confidence interval (CI) 27 to 30) and mean age at surgery was 63 years (95% CI 61 to 66). Maximum total point motions (MTPMs), medial, proximal, and anterior translations and transversal, internal, and varus rotations were calculated at three, 12, and 24 months. Patient-reported outcome measure data were also retrieved.

Results

MTPMs at three, 12, and 24 months were 1.0 mm (95% CI 0.8 to 1.2), 1.3 mm (95% CI 0.9 to 1.7), and 1.4 mm (0.8 to 2.0), respectively. The Forgotten Joint Score was 79 (95% CI 39 to 95) and Knee Injury and Osteoarthritis Outcome Score obtained at two years was 94 (95% CI 81 to 100), 86 (95% CI 75 to 93), 94 (95% CI 88 to 100), 69 (95% CI 48 to 88), and 81 (95% CI59 to 100) for Pain, Symptoms, Activities of Daily Living, Sport & Recreation, and Quality of Life, respectively.

Conclusion

In conclusion, we found that the mean increase in MTPM was lower than 0.2 mm between 12 and 24 months and thus apparently stable. Yet the GMK Sphere had higher migration at one and two years than anticipated. Based on current RSA data, we therefore cannot conclude on the long-term performance of the implant, pending further assessment.

Cite this article: Bone Jt Open 2021;2(9):737–744.

Clinical and Radiological Outcomes Following Medial Pivot Total Knee Arthroplasty: A Retrospective Chart Review Study

Medial pivot total knee arthroplasty (MP-TKA) is a relatively new design that simulates normal knee mechanics with the aim of enhancing postoperative recovery. Furthermore, it reduces postoperative complications in patients with end-stage osteoarthritis of the knee. No study has been done regarding this topic in Saudi Arabia yet, so we aimed to study the post-operative clinical and radiological outcomes of MP-TKA, as well as the postoperative complications. A retrospective cohort chart review study was conducted on 46 patients and 70 knees after applying our inclusion/exclusion criteria. The patients were followed up for an average period of two years. Clinical outcomes were assessed pre- and postoperatively by the validated Saudi Arabian version of the Knee Injury and Osteoarthritis Outcome Score (KOOS), as well as radiological outcomes and postoperative complications gathered from patients’ charts. The postoperative KOOS score showed a statistically significant improvement in pain, symptoms, and activities of daily living in comparison with the preoperative score (P-value < 0.0001). The mean time until ambulation and length of hospital stay were five and 14 days, respectively. Four patients (8.7%) showed radiological complications. Deep vein thrombosis was observed in only two knees (4.3%), and there were no revision cases. Thus, MP-TKA has been shown to improve pain, symptoms, and activities of daily living with a relatively short time until ambulation and length of hospital stay, in addition to a low incidence of postoperative and radiological complications.

A Prospective Randomized Controlled Trial Comparing Medial-Pivot versus Posterior-Stabilized Total Knee Arthroplasty

BACKGROUND

The medial-pivot (MP) design for total knee arthroplasty (TKA) aims to restore more natural "ball-and-socket" knee kinematics compared to the traditional posterior-stabilized (PS) implants for TKA. The objective of this study is to determine if there was any difference in functional outcomes between patients undergoing MP-TKA vs PS-TKA.

METHODS

This prospective randomized controlled trial consisted of 43 patients undergoing MP-TKA vs 45 patients receiving a single-radius PS-TKA design. The primary outcome was postoperative range of motion (ROM). Secondary outcomes included the Western Ontario and McMaster Universities Arthritis Index, Oxford Knee Score, Knee Society Score (KSS), and radiological outcomes. All study patients were followed-up for 2 years after surgery.

RESULTS

Patients undergoing MP-TKA had comparable ROM at 1 year (114.6° ± 16.3° vs 111.3° ± 17.8° respectively, P = .88) and 2 years after surgery (114.9° ± 15.5° vs 114.9° ± 16.4° respectively, P = .92) compared to PS-TKA. There were also no differences in Western Ontario and McMaster Universities Arthritis Index (26.8 ± 19.84 vs 22.0 ± 12.03 respectively, P = .14), Oxford Knee Score (42.7 ± 8.1 vs 42.3 ± 6.7 respectively, P = .18), KSS clinical scores (82.9 ± 16.96 vs 81.42 ± 10.45 respectively, P = .12) and KSS functional scores (76.2 ± 18.81 vs 73.93 ± 8.53 respectively, P = .62) at 2-year follow-up. There was no difference in postoperative limb alignment or complications.

CONCLUSION

This study demonstrated excellent results in both the single-radius PS-TKA design and MP-TKA design. No differences were identified at 2-year follow-up with respect to postoperative ROM and patient-reported outcome measures.

Mid-term survivorship and clinical outcomes of the medial stabilized systems in primary total knee arthroplasty: A systematic review

Introduction

Medial Pivot Total Knee Arthroplasty was introduced in clinical practice in 1990s to reproduce the in vivo-natural knee kinematics. This design is characterized by an asymmetric constraint profile, with aa highly congruent medial compartment, and a less congruent lateral compartment. Short-term outcomes of the medial pivot systems in primary knee arthroplasty have been widely reported in the current literature, however, only few studies have described results beyond 5-year follow-up.

Objectives

The primary objectives of this systematic review of the literature is to analyze the mid-term studies on medial pivot total knee arthroplasty focusing on the reoperation rate, survivorship and clinical outcome scores.

Methods

The US National Library of Medicine (PubMed/MEDLINE), EMBASE, and the Cochrane Database of Systematic Reviews were queried for publications from January 1980 to December 2019 utilizing the following keywords: "medial pivot", "medial stabilized", "medial rotating", "medial congruent", medial ball and socket", "arthroplasty", "TKA", "TKR", and "knee surgery".

Results

18 articles met the inclusion criteria for the present study. The average quality was 11.4 for non-comparative studies and 21.7 for comparative studies based on MINORS criteria. A total 2832 knee arthroplasties were included for the final analysis with an average age of 69 years, and an average follow-up of 8.1 years (minimum 5 years). The overall reoperation rate was 2.4%, with periprosthetic joint infection as the leading cause of revision in 0.9% of cases, followed by aseptic loosening in 0.4% of cases. The average Knee Society Score improved to a mean preoperative score of 40.1 to a mean postoperative score of 89.2. The functional knee society score improved from a mean preoperative score of 44.8 to an average postoperative score of 82.9. The global range of motion improved from 104.8° preoperatively to 115.6° postoperatively.

Conclusion

We found that medial pivot system in primary total knee arthroplasty provide overall mid-term survivorship comparable to other standard implasnts. In addition, medial pivot system is associated with better high-end function compared to standard implants.

Comparative study on mid- and long-term clinical effects of medial pivot prosthesis and posterior-stabilized prosthesis after total knee arthroplasty

Objective

The purpose of this study was to explore the mid-and long-term clinical effects of Chinese patients with medial pivot (MP) prosthesis and posterior-stabilized (PS) prosthesis after total knee arthroplasty (TKA), to provide a reference for the recommendation of clinical prostheses.

Methods

A retrospective analysis of 802 patients who received TKA was performed from June 2010 to December 2013. A total of 432 patients received a MP prosthesis (MP group) and 375 patients received a PS prosthesis (PS group). Postoperative range of motion (ROM), clinical scores including the knee scoring system (KSS), the Western Ontario and McMaster Universities osteoarthritis index (WOMAC), the forgotten joint score (FJS), and postoperative complications were compared between the two groups.

Results

A total of 527 patients were followed up, including 290 in the MP group and 237 in the PS group. Both groups achieved satisfactory results in terms of KSS score, WOMAC score, and postoperative ROM, which were significantly improved compared with those before surgery, but the difference between the groups was not statistically significant (P > 0.05). The FJS scores of the MP group and the PS group were satisfactory and no significant difference was observed (P = 0.426). Postoperative complications occurred in 5 and 11 patients in the MP group and PS group, respectively.

Conclusion

The clinical results of TKA with MP or PS in Chinese patients at mid- and long-term are encouraging, and no significant differences were observed between the two types of prostheses. Studies have also shown that both prostheses are safe for Chinese patients.

Decreased Survival of Medial Pivot Designs Compared with Cruciate-retaining Designs in TKA Without Patellar Resurfacing

BACKGROUND

The medial pivot TKA design was introduced in the 1990s. These are fixed-bearing, medial-conforming implants with virtually no translation in the medial part of the knee, in contrast to the flat lateral part of the insert allowing for translation similar to the native knee during flexion and extension. Most primary TKAs performed in Norway and Australia are cruciate-retaining. All of the medial pivot implants in our study are cruciate-sacrificing but without a post-cam mechanism. The medial pivot implant design was developed to more closely mimic native knee motion, in the hope of improving function, and not primarily as a more constrained knee for difficult cases. In the past 10 to 12 years, a second-generation medial-pivot design has emerged, but there are no larger registry studies on the survival of these implants. Both cruciate-retaining and medial pivot designs are reported in the Australian and Norwegian registries, allowing for large-scale, comparative survivorship studies.

QUESTIONS/PURPOSES

(1) Is there any difference in survival between the medial pivot design and the three most commonly used cruciate-retaining TKA designs? (2) Is there any difference in survival among the different medial pivot implant designs? (3) What are the main indications for revision of medial pivot TKAs?

METHODS

Registry data from the Australian Orthopaedic Association National Joint Replacement Registry and Norwegian Arthroplasty Register from 2005 until the end of 2017 were used to compare the five different brands of medial pivot TKA designs (total primary TKAs assessed: 6310). In Australia, the study group of medial pivot implants represented 9% (6012 of 72,477) of the total number of cemented/hybrid TKAs without patellar resurfacing; 345 had cementless femoral components. In Norway, the study group represented 1% (298 of 47,820) of the total number of TKAs with cemented tibias without patellar resurfacing; all had cemented femoral components. The control group consisted of the three most commonly used cruciate-retaining TKA designs (n = 70,870; Australia n = 54,554; Norway n = 16,316). All TKAs used a fixed-bearing, cemented tibial component and did not involve patella resurfacing. Kaplan-Meier survival analysis was assessed to estimate survivorship. We compared the groups by calculating the hazard ratios (HR) using Cox regression adjusted for age, gender and preoperative diagnosis with 95% CI. To answer our third question, we calculated the percentage of each revision indication from the total number of revisions in each group, and used a Cox regression analysis to compare revision causes and HRs. Analyses were performed separately by each registry. Accounting for competing risks (Fine and Gray) did not alter our findings [].

RESULTS

After controlling for potential confounding variables such as gender, age and preoperative diagnosis, we found an increased revision risk for the medial pivot compared with cruciate-retaining TKA designs in Australia (HR 1.4 [95% CI 1.2 to 1.7]; p < 0.001), but not in Norway (HR 1.5 [95% CI 0.9 to 2.4]; p = 0.1). Two brands of the medial pivot design reported to the AOANJRR showed an increased risk of revision compared with cruciate-retaining designs: the Advance® II MP (HR 1.7 [95% CI 1.2 to 2.6]; p = 0.004) and the GMK® Sphere (HR 2.0 [95% CI 1.5 to 2.6]; p < 0.001), whereas the MRK (HR 0.7 [95% CI 0.4 to 1.5]; p = 0.4), the Evolution® MP (HR 1.4 [95% CI 1.0 to 1.9]; p = 0.06) and the SAIPH® (HR 0.9 [95% CI 0.5 to 1.5]; p = 0.7) showed no difference. The most common reasons for revision of medial pivot implants in Australia were infection (27%), pain alone (19%), patellar erosion (13%), loosening/lysis (12%); in Norway the primary indications were loosening/lysis (28%), instability (28%), malalignment (11%) and pain alone (11%).

CONCLUSIONS

The medial pivot TKA design as a group had a higher revision rate than cruciate-retaining fixed-bearing controls in TKA performed without patellar component resurfacing. By brand, the Advance II MP and the GMK Sphere had inferior survivorship, whereas the MRK, the SAIPH and the Evolution MP had no differences in survivorship compared with cruciate-retaining controls. In Australia, TKAs with the medial pivot design without patella resurfacing had a higher rate of revisions for instability, malalignment, and patella erosion. In Norway, there was an increased risk of revision for lysis and loosening compared with the cruciate-retaining design. Several of these implants had short follow-up in this study. Further registry studies with longer follow up are therefore necessary.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Comparison of Patient Satisfaction Between Medial Pivot Prostheses and Posterior-Stabilized Prostheses in Total Knee Arthroplasty

OBJECTIVE

To compare medial pivot (MP) prostheses to two types of posterior-stabilized (PS) prostheses (NexGen and NRG) in terms of patient satisfaction, causes of dissatisfaction, and risk factors for dissatisfaction after total knee arthroplasty (TKA).

METHODS

A total of 453 patients who underwent primary TKA by one senior surgeon from August 2016 to August 2018 were investigated in a retrospective study, including 121, 219, and 113 patients in the MP, NexGen, and NRG groups, respectively. The mean age and follow-up time of patients were 70.82 ± 7.06 years and 20.64 ± 3.88 months. A survey was designed and responses were collected by telephone, WeChat, and outpatient follow up. Patient satisfaction, causes of dissatisfaction, post-TKA pain on a numeric rating scale (NRS), and range of motion (ROM) were compared among groups, and risk factors were investigated. Patient satisfaction included a five-level satisfaction rating (very satisfied, satisfied, neutral, dissatisfied, or very dissatisfied), with five options for causes of dissatisfaction (persistent pain, limited ROM, knee instability, asthenia, and/or other factors).

RESULTS

Overall, 89.84% of patients were satisfied with the results of primary TKA. There were no significant differences among the three groups regarding the side of the operation, the length of hospitalization in days, or the average follow-up time. Patient satisfaction was similar among the MP (87.38%), NexGen (89.89%), and NRG groups (90.32%). Persistent pain after TKA was the major cause of dissatisfaction (32/40), but no difference in the frequency of this complaint was found among the groups (P = 0.663). The NRS score (P = 0.598) and the ROM (P = 0.959) of the MP group were not significantly different from those of the NexGen and NRG groups. Gender, length of hospitalization, and follow-up time were all uncorrelated with patient satisfaction, but age showed a very weak correlation with patient satisfaction (r = 0.110, P = 0.033). Moreover, the NRS score (r = 0.459, P < 0.000) and the ROM (r = -0.175, P = 0.001) were significantly correlated with patient dissatisfaction. The odds ratio of dissatisfaction was 6.37 (P < 0.000) in patients with moderate to severe pain (NRS ≥ 3) compared to patients with mild pain (NRS < 3).

CONCLUSION

Patient satisfaction and function were not found to be higher in the MP group than in the two PS groups, and persistent pain was the major cause of and an important risk factor for patient dissatisfaction.

Does the medial pivot knee improve the clinical and radiographic outcome of total knee arthroplasty? A single centre study on two hundred and ninety seven patients

PURPOSE

Total knee arthroplasty (TKA) is a cost-effective surgery with a survival rate higher than 90% after 15 years. Nevertheless, patients are unsatisfied in more than 15% of cases. Medial pivot (MP) prosthetic designs were introduced in late 90's with the aim to reproduce natural knee kinematics. The purpose of this study is to evaluate the survivorship and clinical outcomes of a novel design of MP knee with a minimum follow-up of five years.

METHODS

This is a retrospective review of all patients who underwent primary TKA using the K-Mod dynamic congruence implant (Gruppo Bioimpianti, Peschiera Borromeo, Milan, Italy) between 2012 and 2013 at a single institution. A total of 339 patients (351 knees) were included with a mean age of 74 years (range 41-89). The Knee Society score, the global range of movement, the Western Ontario and McMaster Universities Osteoarthritis score, Forgotten Joint score, and the short-term form 12 health survey were collected. FJS and SF-12 were collected only post-operatively. Radiographic outcomes were evaluated according to the Knee Society's roentgenographic evaluation system. Kaplan-Meyer (KM) curves were performed to evaluate implant survivorship. A two-tailed paired t test was performed to evaluate the differences between pre-operative and post-operative score.

RESULTS

A total 297 patients (315 knees) were available for clinical and radiographic analysis, and the mean follow-up was 66.4 months. A total of 17 patients (17 knees 5.4%) experienced a post-operative complication, and a reoperation was performed in five patients (5 knees 1.6%). Four patients had a periprosthetic joint infection, and two patients had a post-traumatic periprosthetic femoral fracture. The KM survivorship at five years was 98.2% (95% CI 0.96 to 0.99) for revision for any reason. There was a statistically significant improvement (p < 0.05) in all the objective and subjective outcomes measured.

CONCLUSION

The K-Mod dynamic congruence design has shown an excellent clinical, radiographic, and patient-reported outcome in primary TKAs.

Medial ball and socket total knee arthroplasty: five-year clinical results

AIMS

Between 15% and 20% of patients remain dissatisfied following total knee arthroplasty (TKA). The SAIPH knee system (MatOrtho, Surrey, United Kingdom) is a medial ball and socket TKA that has been designed to replicate native knee kinematics in order to maximize the range of movement, stability, and function. This system is being progressively introduced in a stepwise fashion, with this study reporting the mid-term clinical and radiological outcomes.

PATIENTS AND METHODS

A retrospective review was undertaken of the first 100 consecutive patients with five-year follow-up following SAIPH TKA performed by the senior authors. The data that were collected included the demographics of the patients, clinical findings, the rate of intraoperative ligamentous release, patient-reported outcome measures (PROMS), radiological assessment, complications, and all-cause revision. Revision data were cross-checked with a national registry.

RESULTS

A total of 100 TKAs in 92 patients were included. Three patients died (three TKAs) and a further two TKAs were revised. Of the remaining 95 TKAs, five-year follow-up data were available for 81 TKAs (85%) in 87 patients. There were significant improvements in all PROMs and high satisfaction. The mean ROM at final follow-up was from 0° (full extension) to 124° flexion. There were seven major complications (7%): one infection, two deep vein thromboses, one cerebrovascular event, and two patients with stiffness requiring a manipulation under anaesthesia. Two patients required a lateral retinacular release to optimize patellar tracking in valgus knees; no additional ligament releases were performed in any patient. Radiological analysis demonstrated no evidence of implant-related complications.

CONCLUSION

These results demonstrate satisfactory clinical and radiological outcomes at five years following a medial ball and socket TKA. The complication and revision rates are consistent with those previously reported for patients undergoing TKA. These results demonstrate the safety and efficacy of the SAIPH Knee TKA system and support its wider use.

A Systematic Review of Clinical Functional Outcomes After Medial Stabilized Versus Non-Medial Stabilized Total Knee Joint Replacement

BACKGROUND

Medial stabilized total knee joint replacement (TKJR) construct is designed to closely replicate the kinematics of the knee. Little is known regarding comparison of clinical functional outcomes of patients utilising validated patient reported outcome measures (PROM) after medial stabilized TKJR and other construct designs.

PURPOSE

To perform a systematic review of the available literature related to the assessment of clinical functional outcomes following a TKJR employing a medial stabilized construct design.

METHODS

The review was performed with a Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) algorithm. The literature search was performed using variouscombinations of keywords. The statistical analysis was completed using Review Manager (RevMan), Version 5.3.

RESULTS

In the nineteen unique studies identified, there were 2,448 medial stabilized TKJRs implanted in 2,195 participants, there were 1,777 TKJRs with non-medial stabilized design constructs implanted in 1,734 subjects. The final mean Knee Society Score (KSS) value in the medial stabilized group was 89.92 compared to 90.76 in the non-medial stabilized group, with the final KSS mean value difference between the two groups was statistically significant and favored the non-medial stabilized group (SMD 0.21; 95% CI: 0.01 to 0.41; p = 004). The mean difference in the final WOMAC values between the two groups was also statistically significant and favored the medial stabilized group (SMD: -0.27; 95% CI: -0.47 to -0.07; p = 0.009). Moderate to high values (I2 ) of heterogeneity were observed during the statistical comparison of these functional outcomes.

CONCLUSION

Based on the small number of studies with appropriate statistical analysis, we are unable to reach a clear conclusion in the clinical performance of medial stabilized knee replacement construct.

LEVEL OF EVIDENCE

Level II.

Total knee arthroplasty with the Medial-Pivot knee system: Clinical and radiological outcomes at 9.5 years' mean follow-up

INTRODUCTION

The "ball-in-socket" design of the Medial-Pivot knee system (MicroPort Orthopedics, Arlington, Tennessee, USA) aims to reproduce normal knee kinematics by medializing its rotational axis. The goal of this study was to measure knee range of motion (ROM) with this implant after a mean follow-up of 10 years and to report the survivorship and long-term clinical and radiological outcomes. We hypothesized the prosthetic knee would have at least 120° flexion at 10 years.

MATERIAL AND METHODS

This was retrospective, single-centre study of 74 Medial-Pivot knees implanted in 71 patients (average age of 69 years) between May 2005 and November 2007. All patients who received a Medial-Pivot knee were included consecutively. The mean follow-up was 10 years. Clinical and radiological assessments were performed using the Knee Society Score (KSS) and Ewald's score. Kaplan-Meir survival analysis was used to calculate survivorship.

RESULTS

Seven percent of cases were lost to follow-up. The knee ROM was 110° at 10 years. The survivorship was 93% for all revision causes and 95.9% when revisions due to trauma or infection were excluded. The mean KSS score was 195. Stable radiolucent lines were found in 14% of cases. No aseptic loosening was observed.

CONCLUSION

Our hypothesis was not confirmed. Knee flexion at the final follow-up was comparable to other semi-constrained implant designs but was not as large as expected. The survival of the Medial-Pivot knee at 10 years is good. Its radiological and clinical outcomes are satisfactory.

LEVEL OF EVIDENCE

IV (retrospective cohort study).

Analysis of in-vivo articular cartilage contact surface of the knee during a step-up motion

BACKGROUND

Numerous studies have reported on the tibiofemoral articular cartilage contact kinematics, however, no data has been reported on the articular cartilage geometry at the contact area. This study investigated the in-vivo tibiofemoral articular cartilage contact biomechanics during a dynamic step-up motion.

METHODS

Ten healthy subjects were imaged using a validated magnetic resonance and dual fluoroscopic imaging technique during a step-up motion. Three-dimensional bone and cartilage models were constructed from the magnetic resonance images. The cartilage contact along the motion path was analyzed, including cartilage contact location and the cartilage surface geometry at the contact area.

FINDINGS

The cartilage contact excursions were similar in anteroposterior and mediolateral directions in the medial and lateral compartments of the tibia plateau (P>0.05). Both medial and lateral compartments were under convex (femur) to convex (tibia) contact in the sagittal plane, and under convex (femur) to concave (tibia) contact in the coronal plane. The medial tibial articular contact radius was larger than the lateral side in the sagittal plane along the motion path (P<0.001).

INTERPRETATIONS

These data revealed that both the medial and lateral compartments of the knee experienced convex (femur) to convex (tibia) contact in sagittal plane (or anteroposterior direction) during the dynamic step-up motion. These data could provide new insight into the in-vivo cartilage contact biomechanics research, and may provide guidelines for development of anatomical total knee arthroplasties that are aimed to reproduce normal knee joint kinematics.

Redefining Knee Balance in a Medially Stabilized Prosthesis: An In-Vitro Study

BACKGROUND

To date, there is still no consensus on what soft tissues must be preserved and what structures can be safely released during total knee arthroplasty (TKA) with a medially stabilized implant.

OBJECTIVE

The aim of this study was to analyze the effect of a progressive selective release of the medial and lateral soft tissues in a knee implanted with a medially stabilized prosthesis.

METHOD

Six cadaveric fresh-frozen full leg specimens were tested. In each case, kinematic pattern and mediolateral laxity were measured in three stages: firstly, prior to implantation; secondly, after the implantation of the trial components, but before any soft tissue release; and thirdly, progressively as soft tissue was released with the trial implant in place. The incremental impact of each selective release on knee balance was then analyzed.

RESULTS

In all cases sagittal stability was not affected by the progressive release of the lateral soft tissue envelope. It was possible to perform progressive lateral release provided the anterior one-third of the iliotibial band (ITB) remained intact. Progressive medial release could be performed on the medial side provided the anterior fibers of the superficial medial collateral ligament (sMCL) remained intact.

CONCLUSION

The medially conforming implant remains stable provided the anterior fibers of sMCL and the anterior fibers of the ITB remain intact. The implant's sagittal stability is mainly dependent on its medial ball-in-socket design.

Are Midterm Patient-Reported Outcome Measures Between Rotating-Platform Mobile-Bearing Prosthesis and Medial-Pivot Prosthesis Different? A Minimum of 5-Year Follow-Up Study

BACKGROUND

Both rotating-platform (RP) mobile-bearing and medial-pivot (MP) fixed-bearing prostheses allow axial femorotibial rotation using a highly conforming polyethylene insert. However, limited comparative data are available between the 2 designs. This study was performed to compare the midterm clinical outcomes and patient-reported outcome measures (PROMs) of RP and MP prostheses.

METHODS

We retrospectively reviewed the records of 52 total knee arthroplasties using RP mobile-bearing prosthesis and 49 total knee arthroplasties using MP fixed prosthesis with a minimum follow-up period of 5 years. Clinical and radiological outcomes, failure rates, and PROMs, including the Western Ontario and McMaster Universities Osteoarthritis Index score and satisfaction, were compared.

RESULTS

There was no difference in clinical or radiographic outcomes (P > .1 for all comparisons), with the exception of the larger flexion contracture (FC) in the MP group (0.3° in RP vs 2.3° in MP, P < .01). No failure in either group was recorded during the study period. PROMs were comparable (P > .1 in all comparisons), with the exception of higher satisfactions in the RP group while performing light household duties (P < .01) and leisure or recreational activities (P = .014) in patients without FC.

CONCLUSION

The midterm clinical results with both the RP mobile-bearing and MP fixed-bearing prostheses were satisfactory. Although both prostheses provided comparable PROMs, patients with an RP prosthesis were more satisfied than those with an MP prosthesis for highly demanding activities that are strongly associated with the presence of postoperative FC.

Patient satisfaction at 2 months following total knee replacement using a second generation medial-pivot system: follow-up of 250 consecutive cases

BACKGROUND

Patient dissatisfaction following total knee replacement (TKR) has been reported as high as 24%. Most previous studies have focused on satisfaction for TKR overall, with few reporting satisfaction for specific implant designs. The purpose of this study was to assess patient satisfaction for TKRs performed using a second generation medial-pivot system (EVOLUTION^®, MicroPort Orthopedics Inc., Arlington, TN, USA).

METHODS

Of a single surgeon's first 250 consecutive TKRs performed using the subject system, 224 completed a patient satisfaction assessment, the Knee Injury and Osteoarthritis Outcome Score (KOOS), range of motion, and radiographs at 2 months follow-up.

RESULTS

The overall very satisfied/satisfied rate was 94.6% at 2 months. Following the first 50 TKRs, the satisfied rate improved to 99.4% suggesting a bias towards the initial cases potentially due to learning the system and instrumentation. Overall KOOS, range of motion, and radiographic outcomes were satisfactory at final follow-up.

CONCLUSIONS

In conclusion, more subjects implanted with a second generation medial-pivot system were satisfied compared to previous reports for TKR.

An 11- to 15-year clinical outcome study of the Advance Medial Pivot total knee arthroplasty

Aims

The Advance Medial-Pivot total knee arthroplasty (TKA) was designed to reflect contemporary data regarding the kinematics of the knee. We wished to examine the long-term results obtained with this prosthesis by extending a previous evaluation.

Patients and Methods

We retrospectively evaluated prospectively collected data from 225 consecutive patients (41 men and 184 women; mean age at surgery 71 years, 52 to 84) who underwent 284 TKAs with a mean follow-up of 13.4 years (11 to 15). Implant failure, complication rate, clinical (both subjective and objective) and radiological outcome were assessed. Pre- and post-operative clinical and radiographic data were available at regular intervals for all patients. A total of ten patients (4.4%; ten TKAs) were lost to follow-up.

Results

Survival analysis at 15 years showed a cumulative success rate of 97.3% (95% confidence interval (CI) 96.7 to 97.9) for revision for any reason, of 96.4% (95% CI 95.2 to 97.6) for all operations, and 98.8% (95% CI 98.2 to 99.4) for aseptic loosening as an end point. Three TKAs (1.06%) were revised due to aseptic loosening, two (0.7%) due to infection, one (0.35%) due to instability and one (0.35%) due to a traumatic dislocation. All patients showed a statistically significant improvement on the Knee Society Score (p = 0.001), Western Ontario and McMaster University Osteoarthritis Index (p = 0.001), Short Form-12 (p = 0.01), and Oxford Knee Score (p = 0.01). A total of 207 patients (92%) were able to perform age appropriate activities with a mean flexion of the knee of 117° (85° to 135°) at final follow-up.

Conclusion

This study demonstrates satisfactory functional and radiographic long-term results for this implant. Cite this article: Bone Joint J 2016;98-B:1050–5.

Early radiographic and functional outcomes of a cancellous titanium-coated tibial component for total knee arthroplasty

BACKGROUND

Various surface coatings have been developed over the past decades to enhance fixation of cementless total knee arthroplasty (TKA). BIOFOAM(®) (MicroPort Orthopedics Inc., Arlington, TN, USA) is a novel cancellous titanium surface coating intended to increase both initial and long-term fixation. The purpose of this study was to investigate the early functional and radiographic outcomes of this coating used in a TKA application.

MATERIALS AND METHODS

One hundred and four (104) primary TKAs in 85 subjects using BIOFOAM-coated tibial components were prospectively enrolled at four centers. Subjects were evaluated using Knee Society Scores and radiographic analysis at a minimum follow-up of 24 months.

RESULTS

Knee Society Scores and flexion were all significantly improved at final follow-up compared to baseline. Radiographic analyses were satisfactory, with no progressive radiolucencies and only a single subject presenting with a radiolucency surrounding a tibial component. There were two revisions in the cohort: one for instability following a ruptured lateral collateral ligament and one for recurrent tibial insert dislocation.

CONCLUSIONS

This is the first study to report clinical outcomes associated with the BIOFOAM coating used in a cementless TKA application. Early functional scores and radiographic analyses are promising, but further investigations are needed to confirm long-term clinical success with these components.

Medial pivot knee in primary total knee arthroplasty

Total knee arthroplasty (TKA) with a medial pivot design was developed in order to mimic normal knee kinematics; the highly congruent medial compartment implant should improve clinical results and decrease contact stresses. Clinical and radiographic mid-term outcomes are satisfactory, but we need other studies to evaluate long-term results and indications for unusual cases.