Comparison of a mobile with a fixed tibial bearing unicompartimental knee prosthesis: a prospective randomized trial using a dedicated outcome score

Unicompartmental knee replacement: controversies and technical considerations

BACKGROUND

Unicompartmental knee replacement (UKR) is one of the effective interventions for the treatment of symptomatic knee osteoarthritis. Moreover, it has multiple advantages over total knee arthroplasty (TKA), including reduced intraoperative blood loss, decreased risk of transfusion, and faster recovery. This study aimed to discuss critical technical considerations regarding UKR and some of the controversies and updates.

METHODS

We conducted a review to provide an overview of the controversies and technical considerations about UKR in several aspects. Only peer-reviewed articles were included, up to December 2023 using PubMed, Google Scholar, ERIC, and Cochrane database for systematic reviews databases.

RESULT

UKR is associated with superior patient-reported clinical and functional outcomes, as well as shorter hospital stays, fewer postoperative complications, and revealed favorable outcomes in patients' return to sport. The choice between mobile- and fixed-bearing prostheses depends, in part, on the surgeon's preference. The mobile-bearing UKR is a less constrained prosthesis and can potentially result in less wear, but it is more technically demanding. While no significant difference between mobile-bearing versus fixed-bearing prostheses, cementless is superior to cemented design. Furthermore, UKR can be a good alternative for high tibial osteotomy (HTO) and still can be considered after a failed HTO. Lastly, recent reviews have shown a revision rate comparable to that of TKA. This is probably influenced by Improved comprehension of the best indications, patient selection criteria, as well as of the design, materials, and technological advances.

CONCLUSION

UKR treatment for unicompartmental knee osteoarthritis is secure and effective. Based on clinical and functional outcomes, decreased morbidity and mortality, and cost-effectiveness, long-term studies suggest that UKR is superior to TKA. Further investigation in this area is warranted.

No difference in mobile and fixed bearing partial knee arthroplasty in octogenarians: a clinical trial

BACKGROUND

A clinical trial comparing MB (mobile-bearing) versus FB (fixed-bearing) in medial partial knee arthroplasty (PKA) in octagenarians has been conducted. The focus of the present study was on PROMs, range of motion (ROM), implant positioning and implants survivorship. The hypothesis of the present study was that MB implants performed better than FB in PKA in octogenarians.

METHODS

The first group received FB PKA-PPK®; the second received MB PKA-Oxford. Patients were not randomly allocated. The following PROMs were administered at T0 (pre-operatively), T1 (1 year after surgery), and T2 (3 years after surgery): visual analogue scale (VAS), Knee Society Score (KSS) and Oxford Knee Score (OKS). Data regarding the implant survivorship and ROM were also collected. Furthermore, the following radiographic parameters were measured: Femoral component varus/valgus; Tibial component varus/valgus; Anteroposterior slope.

RESULTS

At T0, 28 patients were included in the FB and 33 in the MB group. The surgical time was shorter in the FB group (p < 0.001). No difference between FB and MB in ROM, VAS, KSS, and OKS at each follow-up (p > 0.05). No difference was found in implant positioning (p > 0.05). At last follow-up, FB group reported three failures caused by aseptic loosening. Four failures were observed in the MB cohort: two for bearing dislocation and two for aseptic loosening. The Kaplan-Meier Curve found no differences in implant survivorship.

CONCLUSIONS

According to the main findings of the present clinical trial, MB implants performed similar to FB in PKA in octogenarians. The FB group demonstrated shorted surgical time. No difference was found in patient reported outcome measures, ROM, implant positioning, and survivorship.

LEVEL OF EVIDENCE

Level II, prospective study.

Mobile bearing versus fixed bearing medial unicompartmental knee replacement: an independent two center matched-pairs analysis

INTRODUCTION

The aim of the present study was to compare clinical outcome between patients following fixed-bearing (FB) or mobile-bearing (MB) unicompartmental knee replacement (UKR) for antero-medial knee osteoarthrosis (OA) at two independent orthopedic centers.

MATERIALS AND METHODS

Matched-pairs were built between 35 patients receiving FB-UKR and 52 patients following MB-UKR regarding age at time of surgery, body mass index (BMI) and range of motion (ROM) preoperatively. Clinical and functional outcome was measured postoperatively by the American Knee Society Score (AKSS-O/AKSS-F), ROM, Tegner Activity Scale (TAS) as well as the Short Form 36 Health Survey (SF-36).

RESULTS

The average treatment effect of the treated (ATT) after propensity score matching showed a significantly superior ROM in patients following MB-UKR (FB: 118°, MB: 124°). All remaining parameters had no statistically significant differences between both groups involving TAS, AKSS and SF-36.

CONCLUSIONS

The present study suggests that MB-UKR can provide a greater ROM compared to FB-UKR on comparable patients. The authors believe that both designs are suitable for adequate improvement of clinical outcome and ROM for patients suffering from antero-medial osteoarthrosis of the knee joint.

LEVEL OF EVIDENCE

Retrospective cohort study, Level IV.

Mobile Bearing versus Fixed Bearing for Unicompartmental Arthroplasty in Monocompartmental Osteoarthritis of the Knee: A Meta-Analysis

Introduction: Whether mobile-bearing (MB) unicompartmental knee arthroplasty (UKA) performs better than fixed-bearing (FB) implants in patients with monocompartmental osteoarthritis (OA) still remains unclear. Therefore, a meta-analysis comparing MB versus FB for UKA was conducted to investigate the possible advantages of MB versus FB in patient-reported outcome measures (PROMs), range of motion (ROM), and complications. We hypothesised that the MB design performs better than FB. Methods: This systematic review was conducted according to the 2020 PRISMA guidelines. In December 2021, PubMed, Web of Science, Google Scholar, and Embase were accessed, with no time constraints. All the clinical investigations comparing MB versus FB bearing for UKA were accessed. Only studies published in peer-reviewed journals were considered. Studies reporting data on revision settings were excluded, as were those combining unicompartmental and total knee arthroplasty. Results: Data from 25 studies (4696 patients) were collected; 58% (2724 of 4696 patients) were women. The mean length of follow-up was 45.8 ± 43.2. The mean age of the patients was 65.0 ± 5.6 years. No difference was found in range of motion (p = 0.05), Knee Scoring System (p = 0.9), function subscale (p = 0.2), and Oxford Knee Score (p = 0.4). No difference was found in the rate of revision (p = 0.2), aseptic loosening (p = 0.9), deep infections (p = 0.99), fractures (p = 0.6), and further extension of OA to the contralateral joint compartment (p = 0.2). Conclusion: The present meta-analysis failed to identify the possible superiority of the MB implants over the FB for UKA in patients with monocompartmental knee osteoarthritis. Long observational investigations are required to evaluate possible long-term complications and implant survivorship. These results should be interpreted within the limitations of the present study.

St Georg Sled medial unicompartmental arthroplasty: survivorship analysis and function at 20 years follow up

PURPOSE

The peri-operative and short-term benefits of unicompartmental knee arthroplasty (UKA) are well supported in the literature. However, there remains concern regarding the higher revision rate when compared with total knee replacement. This manuscript reports the functional outcome and survivorship of a large series of fixed bearing, medial unicompartmental replacements (St Georg Sled), with a minimum of 20 years follow-up.

METHODS

Between 1974 and 1994, 399 patients (496 knees) underwent a medial fixed-bearing UKA. Prospective data were collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan-Meier survival analysis was used to determine survivorship, with revision or need for revision as end point, and differences assessed using Mantel-Cox log rank test.

RESULTS

Functional knee scores improved post-operatively, but demonstrated a slight decline from 10 years of follow-up onwards. Survivorship is estimated as 86% at 10 years, 80% at 15 years, and 78% at 20 years. Sixty knees were revised, with progression of disease in another compartment the commonest reason. Eighty eight percent were revised using a primary prosthesis. For patients over the age of 65 years at the time of index procedure, 93% died with a functioning prosthesis in situ.

CONCLUSION

Medial UKA demonstrates good long-term function and survivorship, and represents an excellent surgical option for patients aged over 65 years of age, where few patients will require a revision procedure.

LEVEL OF EVIDENCE

IV.

Comparable incidence of periprosthetic tibial fractures in cementless and cemented unicompartmental knee arthroplasty: a systematic review and meta-analysis

PURPOSE

(I) To determine the incidence of periprosthetic tibial fractures in cemented and cementless unicompartmental knee arthroplasty (UKA) and (II) to summarize the existing evidence on characteristics and risk factors of periprosthetic fractures in UKA.

METHODS

Pubmed, Cochrane and Embase databases were comprehensively searched. Any clinical, laboratory or case report study describing information on proportion, characteristics or risk factors of periprosthetic tibial fractures in UKA was included. Proportion meta-analysis was performed to estimate the incidence of fractures only using data from clinical studies. Information on characteristics and risk factors was evaluated and summarized.

RESULTS

A total of 81 studies were considered to be eligible for inclusion. Based on 41 clinical studies, incidences of fractures were 1.24% (95%CI 0.64-2.41) for cementless and 1.58% (95%CI 1.06-2.36) for cemented UKAs (9451 UKAs). The majority of fractures in the current literature occurred during surgery or presented within 3 months postoperatively (91 of 127; 72%) and were non-traumatic (95 of 113; 84%). Six different fracture types were observed in 21 available radiographs. Laboratory studies revealed that an excessive interference fit (press fit), excessive tibial bone resection, a sagittal cut too deep posteriorly and low bone mineral density (BMD) reduce the force required for a periprosthetic tibial fracture to occur. Clinical studies showed that periprosthetic tibial fractures were associated with increased body mass index and postoperative alignment angles, advanced age, decreased BMD, female gender, and a very overhanging medial tibial condyle.

CONCLUSION

Comparable low incidences of periprosthetic tibial fractures in cementless and cemented UKA can be achieved. However, surgeons should be aware that an excessive interference fit in cementless UKAs in combination with an impaction technique may introduce an additional risk, and could therefore be less forgiving to surgical errors and patients who are at higher risk of periprosthetic tibial fractures.

LEVEL OF EVIDENCE

V.

A structured evaluation of the symptomatic medial Oxford unicompartmental knee arthroplasty (UKA)

Unicompartmental knee arthroplasty (UKA) has several advantages over total knee arthroplasty; however, in many reports, the risk of revision remains higher after UKA.Many reasons for failure of UKA exist.Successful treatment starts with accurate assessment of the symptomatic UKA as a specific mode of failure requires a specific solution.A structured and comprehensive evaluation aids assessment of the symptomatic UKA.This review provides an overview of the causes for a symptomatic medial UKA, its risk factors, diagnostic modalities that can be used, and briefly discusses treatment options. Cite this article: EFORT Open Rev 2021;6:850-860. DOI: 10.1302/2058-5241.6.200105.

A Comparison of Mobile- and Fixed-Bearing Unicompartmental Knee Arthroplasties in the Treatment of Medial Knee Osteoarthritis: A Systematic Review and Meta-analysis of 1,861 Patients

Many studies have compared mobile-bearing (MB) and fixed-bearing (FB) unicompartmental knee arthroplasties (UKAs) in patients with unicompartmental knee osteoarthritis (OA). The present systematic review and meta-analysis examined the differences in the clinical and radiological outcomes of MB UKA and FB UKA. PubMed, EMBASE, and Cochrane databases, as well as Google Scholar were searched for relevant studies. Randomized controlled trials (RCTs) and cohort studies that compared MB UKA and FB UKA were included. The weighted mean difference in the knee scores and range of motion (ROM) as well as the summary odds ratio of postoperative mechanical axis alignment, radiolucency, revision rate, and complications were calculated in the MB UKA and FB UKA groups. Finally, 2 RCTs and 11 cohort studies that involved 1,861 patients (1,996 knees) were included. The FB UKA group showed better postoperative Knee Society score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and ROM than the MB UKA group. However, the MB UKA group had more knees with a neutral limb alignment and a lower incidence of polyethylene wear than the FB UKA group. No significant differences were observed between the groups with respect to radiolucency, revision rate, and complications, such as arthritis progression, aseptic loosening, and postoperative pain. This meta-analysis has demonstrated that both prostheses provided excellent clinical outcomes and survivorship in patients with unicompartmental knee OA. The MB UKA group achieved the expected postoperative neutral limb alignment as compared with the FB UKA group, while the FB UKA group showed higher knee scores and superior ROM than the MB UKA group. Limited evidence is currently available; therefore, the results of our meta-analysis should be interpreted with caution.

[Recommendations for unicondylar knee replacement in the course of time : A current inventory]

BACKGROUND

A higher patient satisfaction stands in contrast to higher revision rates of unicondylar knee joint endoprosthetics (UKE) compared to total knee joint endoprosthetics (TKE). Furthermore, old "dogmas" regarding indications and contraindications persist, which is still reflected in the significantly different case numbers.

AIM

The aim of this article is to provide an overview of the current literature regarding 1. indication and contraindication (BMI, age, sport, arthrosis of other compartments, ligament status) and 2. the "eternal rival" fixed or mobile bearing for UKE.

RESULTS

The choice of the right patient remains essential, even if all the old "dogmas" of contraindications have been relativized or even outdated. Arthroses of the contralateral (in medial UKE correspondingly lateral) compartment and advanced arthroses of the lateral patella facet remain the only persistent contraindications. In contrast, a high BMI, age, chondrocalcinosis, medial patella facet and a defective (but particularly functionally stable) ACL are not contraindications; however, severe obesity is responsible for a significantly higher complication rate and probably a higher rate of loosening. Rather, the experience and thus the number of UKEs of the individual surgeon is decisive for the outcome, to which the discussion about mobile or fixed inlays must also be completely subordinated.

CONCLUSION

The indications for UKE can, therefore, be extended with a clear conscience on the basis of literature, and the current 1:10 UKE:TKE ratio in Germany can be shifted significantly.

Fixed- versus mobile-bearing unicompartmental knee arthroplasty: a meta-analysis

Unicompartmental knee arthroplasty (UKA) can be either a fixed bearing (FB) or a mobile bearing (MB) construct with controversy as to which design is superior. This question is addressed with a systematic review and meta-analysis. A literature search was performed using PubMed, Embase and the Cochrane Library. Studies were reviewed according to the inclusion and exclusion criteria developed in advance. We compared the differences in clinical and radiological outcomes between the FB and MB UKAs. Analyses were performed with the Review Manager and STATA software. A total of 17 studies involving 2612 knees were included. No significant differences were presented between the FB and MB prostheses in clinical and radiological outcomes. However, it was evident that there were differences in the modes and timing of the failures, bearing dislocation led to earlier failures in the MB prosthesis, while the FB prosthesis failed later due to polyethylene wear. There was no evidence of publication bias using the incidence of revisions. There is no significant difference between the FB and MB UKAs; however, there are differences in the modes and timing of failures.

Clinical outcome of bi-unicompartmental knee arthroplasty for both medial and lateral femorotibial arthritis: a systematic review-is there proof of concept?

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) is a well-accepted treatment for isolated unicompartmental osteoarthritis (OA) of the knee. In previous literature, it has been suggested that bi-unicompartmental knee arthroplasty (bi-UKA) which uses two UKA implants in both the medial and lateral compartments of the same knee is a feasible and viable option for the treatment of knee OA. Given the advantages of UKA treatment, it is warranted to review the literature of bi-UKA and discuss the evidence in terms of implant selection, indications, surgical techniques, and outcomes, respectively.

MATERIALS AND METHODS

Following the PRISMA guidelines, PubMed, Medline, Embase, CINAHL, Web of Science, and Cochrane Library were searched for studies presenting outcome of bi-UKA. Studies were included if they reported clinical outcomes using two unicompartmental prostheses for both medial and lateral femorotibial arthritis. Studies with the addition of patellofemoral arthroplasty or concomitant soft-tissue reconstruction and those not published in English were excluded.

RESULTS

In the early literature, the procedure of bi-UKA were performed for very severe OA and rheumatoid arthritis, but indications have evolved to reflect a more contemporary case-mix of knee OA patients. Both mobile and fixed bearing implants have been used, with the latter being the most frequent choice. A medial parapatellar approach for incision and arthrotomy has been the most frequently used technique. The present review found a promising clinical outcome of both simultaneous and staged bi-UKA although the number of long-term follow-up studies was limited.

CONCLUSIONS

Both simultaneous and staged bi-UKA has demonstrated good functional outcomes. However, the volume and level of evidence in general is low for studies captured in this review, and the data on long-term outcomes remain limited. The present review indicates that bi-UKA is a feasible and viable surgical option for bicompartmental femorotibial OA in carefully selected patients.

Does Unicondylar Knee Arthroplasty Affect Tibial Bone Strain? A Paired Cadaveric Comparison of Fixed- and Mobile-bearing Designs

BACKGROUND

Unexplained pain in the medial proximal tibia frequently leads to revision after unicondylar knee arthroplasty (UKA). As one of the most important factors for osteogenic adaptive response, increased bone strain following UKA has been suggested as a possible cause.

QUESTIONS/PURPOSES

In this study we: (1) performed a cadaver-based kinematic analysis on paired cadaveric specimens before and after mobile-bearing and fixed-bearing UKA; and (2) simultaneously characterized the strain distribution in the anterior and posterior proximal tibia during squatting.

METHODS

Five pairs of fresh, frozen full-leg cadaver specimens (four male, one female, 64 years to 87 years) were subjected to a dynamic squatting motion on a kinematic rig to simulate joint loading for a large ROM. Forces were applied to the quadriceps and hamstrings during the simulation while an infrared camera system tracked the location of reflective markers attached to the tibia and femur. Tibial cortical bone strain was measured with stacked strain gauge rosettes attached at predefined anterior and posterior positions on the medial cortex. Pairwise implantation of mobile-bearing (UKAMB) and fixed-bearing implants (UKAFB) allowed a direct comparison of right and left knees from the same donor through a linear mixed model.

RESULTS

UKAMB more closely replicated native kinematics in terms of tibial rotation and in AP and mediolateral translation. Maximum principal bone strain values were consistently increased compared with native (anteromedial, mean [± SD] peak strain: 311 µε ± 190 and posterior, mean peak strain: 321 µε ± 147) with both designs in the anteromedial (UKAFB, mean peak strain: 551 µε ± 381, Cohen's d effect size 1.3 and UKAMB, mean peak strain: 596 µε ± 564, Cohen's d effect size 1.5) and posterior (UKAFB, mean peak strain: 505 µε ± 511, Cohen's d effect size 1.3 and UKAMB, mean peak strain: 633 µε ± 424, Cohen's d effect size 2.1) region. However, in the anterolateral region of the medial tibial bone, UKAFB demonstrated the overall largest increase in strain (mean peak strain: 1010 µε ± 787, Cohen's d effect size 1.9), while UKAMB (613 µε ± 395, Cohen's d effect size 0.2) closely replicated values of the native knee (563 µε ± 234).

CONCLUSION

In this in vitro cadaver study both UKAMB and UKAFB led to an increase in bone strain in comparison with the native knee. However, in the anterolateral region of the medial tibial plateau, proximal tibial bone strain was lower after UKAMB and UKAFB. Both UKAMB and UKAFB lead to comparable increases in anteromedial and posterior tibial strain in comparison with the native knee. In the anterolateral region of the medial tibial plateau UKA, proximal tibial bone strain was closer to the native knee after UKAMB than after UKAFB. In an attempt to link kinematics and strain behavior of these designs there seemed to be no obvious relation.

CLINICAL RELEVANCE

Further clinical research may be able to discern whether the observed differences in cortical strain after UKA is associated with unexplained pain in patients and whether the observed differences in cortical bone strain between mobile-bearing and fixed unicondylar designs results in a further difference in unexplained pain.

Comparison of implant position and joint awareness between fixed- and mobile-bearing unicompartmental knee arthroplasty: a minimum of five year follow-up study

PURPOSE

To compare the implant position and patient-reported outcomes (PROs) regarding joint awareness using the Forgotten Joint Score (FJS) following between fixed-bearing (FB) and mobile-bearing (MB) unicompartmental knee arthroplasty (UKA) with a minimum of five years' follow-up.

METHODS

One hundred fifteen consecutive UKAs (58 FB UKAs and 57 MB UKAs) performed were retrospectively evaluated. We compared the radiographic parameters including component positions and relationships as well as lower extremity alignment. Post-operative clinical outcomes were assessed using Knee Society Score (KSS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, Tegner activity score, and FJS.

RESULTS

The MB UKA group showed more convergent componentry relationship between femoral and tibial components (p < 0.001). The joint line of the MB UKA group was restored significantly better (p < 0.05). In addition, the positioning of femoral and tibial components of the MB UKA group showed less deviation from the weight-bearing line (WBL) (p < 0.05). Although there were no differences in KSS, WOMAC, and Tegner activity scores between the groups, the MB UKA group showed significantly better FJS than did the FB UKA group at five years post-operatively (p < 0.05).

CONCLUSION

The MB UKA group had a more convergent componentry relationship, less deviation from WBL, better joint-line restoration, and reduced joint awareness than did the FB UKA group at five years follow-up.

Finite Element Study on the Preservation of Normal Knee Kinematics with Respect to the Prosthetic Design in Patient-Specific Medial Unicompartmental Knee Arthroplasty

Alterations in native knee kinematics in medial unicompartmental knee arthroplasty (UKA) are caused by the nonanatomic articular surface of conventional implants. Technology for an anatomy mimetic patient-specific (PS) UKA has been introduced. However, there have been no studies on evaluating the preservation of native knee kinematics with respect to different prosthetic designs in PS UKA. The purpose of this study was to evaluate the preservation of native knee kinematics with respect to different UKA designs using a computational simulation. We evaluated three different UKA designs: a nonconforming design, an anatomy mimetic design, and a conforming design for use under gait and squat loading conditions. The results show that the anatomy mimetic UKA design achieves closer kinematics to those of a native knee compared to the other two UKA designs under such conditions. The anatomy memetic UKA design exhibited a 0.39 mm and 0.36° decrease in the translation and rotation, respectively, in the swing phase compared with those of the natural knee. In addition, under the gait and squat loading conditions, the conforming UKA design shows limited kinematics compared to the nonconforming UKA design. Our results show that the conformity of each component in PS UKA is an important factor in knee joint kinematics; however, the anatomy mimetic UKA design cannot restore perfect native kinematics.

[Research progress in unicompartmental knee arthroplasty]

OBJECTIVE

To summarize the clinical application and research progress in unicompartmental knee arthroplasty (UKA).

METHODS

The literature related to UKA in recent years was reviewed and the emerging indications, implant options, comparisons between other surgical techniques, and recent advances were summarized.

RESULTS

Clinical studies show that UKA has many advantages, such as less trauma, faster recovery, and fewer postoperative complications. At present, the operative indication has been expanded. The body mass index more than 25 kg/m 2, less than 60 years old, patellofemoral arthritis, and anterior cruciate ligament dysfunction are no longer considered as contraindications. The prosthesis type in UKA should be selected according to the patient's condition. In recent years, the robot-assisted UKA can effectively improve the effectiveness, improve patient satisfaction, and reduce postoperative complications.

CONCLUSION

With the development of surgical techniques, designs of prosthesis, and the robotic technology, UKA would be further applicated. As more long-term data on UKA become available, it will further guide clinicians in counseling patients on whether UKA should be performed.

Comparison of Fixed-Bearing and Mobile-Bearing Unicompartmental Knee Arthroplasty: A Systematic Review and Meta-Analysis

BACKGROUND

Prior studies have compared fixed-bearing unicompartmental knee arthroplasty (FB-UKA) with mobile-bearing UKA (MB-UKA), suggesting that both procedures have good clinical outcomes. However, which treatment is more beneficial for patients is controversial. The purpose of our study is to evaluate the postoperative outcomes, including the revision rate, complications, functional results, range of motion, and femoral-tibial angle, between the 2 procedures.

METHODS

We searched the MEDLINE, EMBASE, Cochrane Library, and Web of Science databases starting from August 2017 to May 2018. The publication date of articles was not restricted. Before we submit our contribution, we have re-searched it again. Articles that directly compared the postoperative outcomes of the 2 prosthesis type were included.

RESULTS

A total of 15 comparative studies were included in our meta-analysis. The pooled data indicated no differences between the 2 operation modes in terms of revision rates, complications, and knee function, but earlier failure occurred more frequently with the MB design.

CONCLUSION

Both the arthroplasty types provided satisfactory clinical results for patients with classic indications. However, MB-UKA tended to fail in early postoperative years whereas fixed-bearing UKA in later postoperative years. Therefore treatment options should be carefully considered for each patient, and surgeons should still use their personal experience when deciding between these options.

Medial Unicompartmental Knee Arthroplasty with a Fixed Bearing Implant

Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty in isolated medial arthritis. UKA restores native tibial and femoral joint surfaces and corrects pre-disease limb alignment, by which natural knee biomechanics are restored, ensuring effective functional recovery. Proper patient selection and accurate surgical technique contribute to good functional outcome and long-term survival. The key steps of the procedure (as well as multiple tips and tricks) are demonstrated in the video article: (1) preoperative assessment and planning; (2) patient positioning and setup; (3) exposure; (4) instrument options and surgical technique; (5) distal femoral resection; (6) proximal tibial resection; (7) assessment of alignment and gaps; (8) finishing the femur—sizing, position, and posterior resection; (9) finishing the tibia—sizing and position; (10) trialing the implant; (11) implanting final components—cementing technique; (12) closure; and (13) rehabilitation. Following these surgical steps and principles will lead to excellent functional long-term results with a low revision rate and a minimum of complications.

Medial Unicompartmental Arthroplasty of the Knee

Indications for medial unicompartmental knee arthroplasty (UKA) have expanded over the past two decades. Proposed advantages include faster recovery, improved kinematics, and better functional outcomes compared with total knee arthroplasty (TKA) in age-matched control subjects. A focused preoperative examination and imaging is essential to identify appropriate surgical candidates. No difference has been demonstrated between fixed- and mobile-bearing implants for implant survivorship or patient-reported outcomes. The most common reasons for conversion to a TKA are aseptic loosening and progression of osteoarthritis. Ten-year survival for UKA in cohort studies has shown to be >90% with outcomes after conversion to TKA being similar to outcomes for revision TKA. Registries have consistently shown lower implant survival for UKA compared with that for TKA, which is likely secondary to use of several different implants by surgeons of varying levels of experience. UKA has the potential to be a cost-effective alternative to TKA in certain patient populations when performed at high-volume centers with advanced surgical techniques.

Outcomes of a Fixed-Bearing, Medial, Cemented Unicondylar Knee Arthroplasty Design: Survival Analysis and Functional Score of 460 Cases

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty in isolated medial osteoarthritis (OA). However, despite satisfactory reports on the clinical performance, UKA revision rates are still concerning. This retrospective study reports on the long-term survivorship, functional outcomes, and reasons for revision in fixed-bearing UKA implant.

METHODS

Between 2005 and 2013, 460 consecutive patients were treated with medial UKA in one center using a fixed-bearing UKA system. All patients were evaluated clinically and radiographically before surgery, and postoperatively at 6 weeks and 1 year. Between February and April 2016, all patients were reevaluated using the Oxford Knee Score.

RESULTS

Mean follow-up was 5.5 (range, 2-11) years. The mean Oxford Knee Score was 43.3 (7-48), with 94.6% patients showing excellent or good outcomes. Eleven revisions (2.4%) occurred. The survivorship was 97.2% (95% confidence interval, 96.2%-99.2%) and 94.2% (95% confidence interval, 86.8%-97.5%) at 5 and 10 years, respectively, with revision of any implant component for any reason as the end point. The causes for revision were infection (4 cases, 0.9%); lateral pain due to overload (2 cases, 0.4%); progression of OA in the lateral compartment (2 cases, 0.4%); patellar pain with patellar chondropathy (2 cases, 0.4%); and severe synovitis (1 cases, 0.2%). There were no reoperations or revisions for component loosening, instability, component wear, or periprosthetic fracture.

CONCLUSION

A fixed-bearing UKA system is a good treatment option for medial end-stage OA. Satisfactory functional results were achieved with low incidence of complications and revisions.

A Comparison of Mobile and Fixed-Bearing Unicompartmental Knee Arthroplasty at a Minimum 10-Year Follow-up

BACKGROUND

The long-term survivorship and functional outcomes of the mobile-bearing (MB) compared to the fixed-bearing (FB) unicompartmental knee arthroplasty (UKA) implant design remain a topic of debate. The aim of the current study was to compare the survivorship and functional outcomes of MB and FB UKA at a minimum 10-year follow-up.

METHODS

We retrospectively reviewed 106 consecutive medial UKAs (89 patients) from our institution with a minimum 10-year follow-up. The 38 MB and 68 FB knees had follow-up of 14.2 years (12.9-15.5) and 11.5 years (10.2-15.1), respectively. Validated patient-reported outcomes and radiographs were evaluated as were etiology, timing, and complexity of revision. Kaplan-Meier 10-year survival was calculated with revision to total knee arthroplasty as the end point.

RESULTS

The 10-year survival was 82.9% (95% confidence interval [CI] 65.8-91.9) for MB and 90.9% (95% CI 79.4-96.2) for FB UKA (P = .102), and 88.0% (95% CI 79.3-93.2) for the entire cohort. Patient outcomes were similar between groups, as were timing and etiologies for revision to total knee arthroplasty. One-third of revisions required either stems or tibial augments, and of these, all were of MB design.

CONCLUSION

Survival and functional outcomes were similar between MB and FB designs. One-third of revisions required either stems or augments, all were of MB design.

Obesity has no effect on outcomes following unicompartmental knee arthroplasty

PURPOSE

Although obesity has historically been described as a contraindication to UKA, improved outcomes with modern UKA implant designs have challenged this perception. The purpose of this study was to assess the influence of obesity on the outcomes of UKA with a robotic-assisted system at a minimum follow-up of 24 months with the hypothesis that obesity has no effect on robotic-assisted UKA outcomes.

METHODS

There were 746 medial robotic-assisted UKAs (672 patients) with a mean age of 64 years (SD 11) and a mean follow-up time of 34.6 months (SD 7.8). Mean overall body mass index (BMI) was 32.1 kg/m² (SD 6.5), and patients were stratified into seven weight categories according to the World Health Organization classification.

RESULTS

Patient BMI did not influence the rate of revision surgery to TKA (5.8 %) or conversion from InLay to OnLay design (1.7 %, n.s.). Mean postoperative Oxford knee score was 37 (SD 11) without correlation with BMI (n.s.). The type of prosthesis (InLay/OnLay) regardless of BMI had no influence on revision rate (n.s.). BMI did not influence 90-day readmissions (4.4 %, n.s.), but showed significant correlation with higher opioid medication requirements and a higher number of physical therapy session needed to reach discharge goals (p = 0.031).

CONCLUSION

These findings suggest that BMI does not influence clinical outcomes and readmission rates of robotic-assisted UKA at mid-term. The classic contraindication of BMI >30 kg/m² may not be justified with the use of modern UKA designs or techniques.

LEVEL OF EVIDENCE

IV.

A cost comparison of unicompartmental and total knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty (TKA) in appropriately selected patients. There is a paucity of data comparing hospital resource utilization and costs for UKA versus TKA.

METHODS

We retrospectively reviewed 128 patients who underwent UKA or TKA for osteoarthritis by a single surgeon in the 2011 Fiscal Year. Sixty-four patients in each group were matched based on sex, age, race, body mass index, Charlson Comorbidity Index, and insurance type. Clinical data were obtained from medical records while costs were obtained from hospital billing. Bivariate analyses were used to compare outcomes.

RESULTS

Both anesthesia and operative time (minutes) were significantly shorter for patients undergoing UKA (125.7 vs. 156.4; p<0.001, and 81.4 vs. 112.2; p<0.001). UKA patients required fewer transfusions (0% vs. 11.0%; p=0.007) and had a shorter hospital stay (2.2 vs. 3.8days; p<0.001). 96% of UKAs were discharged home compared with 75% of TKAs (p<0.001). Hospital direct costs were lower for UKA ($7893 vs. $11,156; p<0.001) as were total costs (hospital direct costs plus overhead; $11,397 vs. $16,243; p<0.001). Supply costs and implant costs were similarly lower for UKA ($701 vs. $781; p<0.001, and $3448 vs. $5006; p<0.001).

CONCLUSION

Our data suggest that UKA provides a cost-effective alternative to TKA in appropriately selected patients. As the number of patients with end-stage arthritis of the knee requiring surgical care continues to rise, the costs of caring for these patients must be considered.

LEVEL OF EVIDENCE

Level III, case control study.

Development and clinical application of meniscal unicompartmental arthroplasty

About one-third of osteoarthritic patients requiring knee replacement have focal lesions limited mainly to the medial compartment and can achieve excellent postoperative function after medial unicompartmental replacement. However, late failures of many unicompartmental prostheses require revision at a rate about twice that of total knee replacement. The use of a fully conforming mobile-bearing meniscal unicompartmental prosthesis in the hands of experienced surgeons can reduce revision rates to levels equivalent to the best results achieved with total knee replacement. The paper argues the case for such a prosthesis and demonstrates that the usual modes of failure of unicompartmental arthroplasty, most of them biomechanical, can thereby be avoided.

Comparison of Alignment Correction Angles Between Fixed-Bearing and Mobile-Bearing UKA

Good outcomes have been reported with both fixed-bearing and mobile-bearing unicompartmental knee arthroplasty (UKA). However, overcorrected alignment could induce the progression of arthritis on the non-arthroplasty side. Changes of limb alignment after UKA with both types of bearings (fixed bearing: 24 knees, mobile bearing: 28 knees) were investigated. The mean difference between the preoperative standing femoral-tibial angle (FTA) and postoperative standing FTA was significantly larger in mobile bearing UKA group. In fixed-bearing UKA, there must be some laxity in MCL tension so that a 2-mm tension gauge can be inserted. In mobile-bearing UKA, appropriate MCL tension is needed to prevent bearing dislocation. This difference in MCL tension may have caused the difference in the correction angle between the groups.

Fixed- versus mobile-bearing UKA: a systematic review and meta-analysis

PURPOSE

Two design concepts are currently used for unicondylar knee arthroplasty (UKA) prostheses: fixed bearing (FB) and mobile bearing (MB). While MB prostheses have theoretical advantages over their FB counterparts, it is not clear whether they are associated with better outcomes. A systematic review was conducted to examine survivorship differences and differences in failure modes of between FB and MB designs.

METHODS

PubMed, Scirus and Cochrane library databases were searched for medial UKA outcome studies. A total of 44 papers, involving 9,463 knees, were eligible. Outcomes examined included knee function, survivorship and the reasons for, and incidence of, revision for FB and MB prostheses. Random effects meta-analysis was employed to obtain pooled revision rate estimates. Where available, cause-specific time to revision was extracted.

RESULTS

Mean follow-up was 8.7 years for FB and 5.9 years for MB prostheses. There were no other relevant baseline differences. The overall crude revision rate for FB and for MB prostheses was 0.90 (95 % confidence interval (CI) 0.65-1.21) and 1.51 (95 % CI 1.11-1.93) per 100 component years, respectively. After stratification on follow-up time and age, the revision rates were not substantially different, aside for younger patients in short term from studies with short-term follow-up.

CONCLUSION

No essential differences between the two designs were observed. MB and FB UKA designs have comparable revision rates. As our study is based on predominantly observational data, with large variations in reporting standards, inferences should be drawn with caution.

LEVEL OF EVIDENCE

IV.

Long-term results of compartmental arthroplasties of the knee

Partial knee arthroplasty (PKA), either medial or lateral unicompartmental knee artroplasty (UKA) or patellofemoral arthroplasty (PFA) are a good option in suitable patients and have the advantages of reduced operative trauma, preservation of both cruciate ligaments and bone stock, and restoration of normal kinematics within the knee joint. However, questions remain concerning long-term survival. The goal of this review article was to present the long-term results of medial and lateral UKA, PFA and combined compartmental arthroplasty for multicompartmental disease. Medium- and long-term studies suggest reasonable outcomes at ten years with survival greater than 95% in UKA performed for medial osteoarthritis or osteonecrosis, and similarly for lateral UKA, particularly when fixed-bearing implants are used. Disappointing long-term outcomes have been observed with the first generation of patellofemoral implants, as well as early Bi-Uni (ie, combined medial and lateral UKA) or Bicompartmental (combined UKA and PFA) implants due to design and fixation issues. Promising short- and med-term results with the newer generations of PFAs and bicompartmental arthroplasties will require long-term confirmation.

Cite this article: Bone Joint J 2015;97-B(10 Suppl A):9–15.

Outcome of Unicompartmental Knee Arthroplasty: A Systematic Review of Comparative Studies between Fixed and Mobile Bearings Focusing on Complications

The purpose of this systematic review is to collate results of studies comparing fixed and mobile bearing unicompartmental knee arthroplasty (UKA), focusing on complications and timing for reoperations. Out of 723 results derived from PubMed, EMBASE and Cochrane database search engines on bearings in arthroplasty, 10 studies comparing clinical results of fixed bearings to mobile bearings in UKA were found eligible for analysis. The reoperation rate was calculated using a novel method such as reoperations per hundred component years, and the causes of specific reoperations were investigated. The overall reoperation rate per hundred component years was similar between the mobile bearings (1.392) and fixed bearings (1.377); however, mobile bearings were more susceptible to reoperations in cases with aseptic loosening (0.393>0.255), progression of arthritis (0.428>0.357) and implant dislocation (0.286>0). The overall incidence of complications is similar for fixed and mobile bearing designs in UKA. The discussion on complications presented above may assist surgeons in their choice of bearing design.

Biomechanical comparison of fixed- and mobile-bearing for unicomparmental knee arthroplasty using finite element analysis

Unicomparmental knee arthroplasty (UKA) is a popular alternative to total knee arthroplasty (TKA) and high tibial osteotomy for unicompartmental knee conditions, especially in young patients. However, failure of UKA occurs due to either progressive osteoarthritis (OA) in the other compartment or wear on the polyethylene (PE) insert. This study used finite element (FE) analysis to investigate the effects of PE insert contact pressure and stress in opposite compartments for fixed- and mobile-bearing UKA. Analysis was performed using high kinematics displacement and rotation inputs, which were based on the kinematics of the natural knee. ISO standards were used for axial load and flexion. The mobile-bearing PE insert had lower contact pressure than the fixed-bearing PE insert. With the mobile-bearing UKA, lower stress on the opposite compartment reduces the overall risk of progressive OA in the knee. The fixed-bearing UKA increases the overall risk of progressive OA in the knee due to higher stress on the opposite compartment. However, the PE insert of mobile-bearing showed pronounced backside stress at the inferior surface.

The effects of primary implant bearing design on the complexity of revision unicondylar knee arthroplasty

Comparisons of fixed- (FB) and mobile-bearing (MB) implants have failed to demonstrate a superiority of one design over the other. Despite showing equally successful outcomes, the wear patterns and small particulate debris associated with MB implants have been linked to an increased prevalence of osteolysis. This study compared the complexity of revision surgery for both bearing types. Operative time, use of augmentation and/or bone grafts, and the level of constraint required during revision were used to assess complexity. It was found that MB knees more frequently required tibial augmentation in our sample population (P=0.020), but overall surgical complexity was equivalent for revisions of both implant designs. These data suggest that additional research pertaining to the potential differences between implants be investigated.

Fixed- versus mobile-bearing unicondylar knee arthroplasty: are failure modes different?

PURPOSE

An ongoing controversy exists on whether mobile-bearing design is superior over fixed-bearing design in unicondylar knee arthroplasties (UKAs). The present study conducted a systematic review to ascertain differences in performance between fixed- and mobile-bearing designs in UKAs.

METHODS

A literature search was performed in PubMed, Embase, Scopus and the Cochrane Library. A total of 9 comparative studies involving 915 knees comparing outcomes of mobile-bearing UKAs with fixed-bearing UKAs were included in the current analysis. Outcomes of interest included knee function, quality of life, radiographic outcomes, reasons and incidence of reoperation, timing of failures, and survivorship.

RESULTS

The results presented no significant differences between the two designs in terms of knee scores, range of motion, limb alignment, implant positioning, incidence of radiolucent lines and overall reoperation rates. However, their differences have been noted in their modes and timing of failures. Early failures are related to the risk of bearing dislocation in the mobile-bearing design. In contrast, later failures are related to the risk of polyethylene wear in the fixed-bearing design.

CONCLUSIONS

The available evidence has not confirmed the advantage of mobile-bearing UKAs over fixed-bearing UKAs but pointed out specific modes of failure.

Results and outcomes of unicompartmental knee arthroplasty

Precise outcome evaluation is mandatory to improve analysis of the results of knee replacement procedures. Patients' expectations toward surgery and activity levels have increased with changes in patient populations and improvement of surgical results. It is difficult, however, to accurately assess outcomes because objective evaluation of patient function performed only by a surgeon remains highly inaccurate. New methods of objective evaluation after unicompartmental knee arthroplasty have been developed. These devices provide information about range of motion and patient function during daily activities. This article provides up-to-date information concerning the different tools of function evaluation after unicompartmental knee arthroplasty.

Clinical and technical factors influencing outcomes of unicompartmental knee arthroplasty: Retrospective multicentre study of 944 knees

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) is reserved for osteoarthritis confined to a single femoro-tibial compartment with an intact anterior cruciate ligament. UKA remains controversial. The objective of this retrospective multicentre study in a large sample was to assess the influence of age, sex, body mass index (BMI), patellofemoral involvement, and implant design on functional outcomes and prosthesis survival rates.

MATERIAL AND METHODS

Nine hundred and forty-four patients who underwent UKA at centres located in western France between 1988 and 2008 were re-evaluated. The IKS scores and KOOS were determined. Prosthesis survival according to various factors was assessed using the Kaplan-Meier method.

RESULTS

A clinical evaluation was performed in 720 cases after a mean follow-up of 62 months. The IKS function score improved by 23.6 points in men and 17.3 points in women (P=0.007). Ten-year prosthesis survival was 83.7% overall; 79% in women versus 87% in men (P<0.01); and 76.7% in patients younger than 70 years versus 88.3% in those 70 years or over (P<0.01). BMI had no significant influence on prosthesis survival. No significant differences between clinical outcomes or prosthesis survival were found across implant design categories.

DISCUSSION

The retrospective design and large number of centres and surgeons mandate caution when interpreting our results. Subgroup sizes were too small for an analysis of factors such as anterior cruciate ligament deficiency, BMI>40 kg/m(2), or cementless implant.

LEVEL OF EVIDENCE

Level IV, retrospective study.

A safe overhang limit for unicompartmental knee arthroplasties based on medial collateral ligament strains: an in vitro study

Excessive tibial component overhang during unicompartmental knee arthroplasty (UKA) may cause medial collateral ligament (MCL) impingement, which, in turn, may lead to medial knee pain [Chau et al. Tibial component overhang 226 following unicompartmental knee replacement-does it matter? The Knee. 2009;16(5):310-3]. This study examines MCL loads in 6 human cadaveric knees for different levels of overhang using a robotic testing system. The results indicated no statistically significant difference between the baseline MCL load (no overhang) and the 2-mm overhang (P = .261). However, there were significant differences in MCL load between 2- vs 4-mm (P = .012) and 2- vs 6-mm overhang (P = .022). The loads were almost doubled from 2 to 4 mm of overhang. We conclude that, to minimize pain from excessive MCL loading, surgeons should avoid tibial component overhang greater than 2 mm in unicompartmental knee arthroplasties.

No difference in quality-of-life outcomes after mobile and fixed-bearing medial unicompartmental knee replacement

This is a retrospective study comparing the clinical outcomes of mobile vs fixed medial unicompartmental knee replacements. Patients were identified from a prospectively collected database. Demographic data and pre- and postoperative outcomes (Oxford, Western Ontario and McMaster Universities Osteoarthritis Index, Short Form Health Survey-12, and satisfaction) were collected-104 knees (90 patients) with minimum 2-years of follow-up: 37 mobile and 67 fixed-bearing. At baseline, the median age was 60 years (mobile) and 66 (fixed); body mass index was significantly higher (32) for the mobile group than for the fixed (28). At follow-up, the groups differed only in the Oxford score: median 83 (mobile) and 90 (fixed). There is no difference in outcomes between mobile and fixed unicompartmental knee replacements.

Revision after total knee arthroplasty and unicompartmental knee arthroplasty in the Medicare population

This study compares the relative risk of revision and associated risk factors after total or unicompartmental knee arthroplasty (TKA or UKA) in the Medicare population. A total of 61 767 TKA and 2848 UKA patients were identified. Reviewed data included type of treatment, gender, age, race, Charlson Index for comorbidity, length of stay, Medicare buy-in for socioeconomic status, region, and year. Unicompartmental knee arthroplasty patients were at increased risk for revision at 2 and 5 years. Those patients undergoing UKA were significantly more likely to require revision in the first 5 years as compared with those undergoing TKA. Risk factors contributing to TKA revision included younger male patients with higher comorbidities and lower socioeconomic status. About UKA, lower revision rates tend to favor those surgeons with higher volume.

Revision of medial Oxford unicompartmental knee replacement to a total knee replacement: similar to a primary?

Unicompartmental knee replacement (UKR) is an option for the treatment of isolated medial compartment osteoarthritis. A commonly perceived potential advantage is that revision of a UKR is straightforward. The purpose of this study was to determine the early outcomes and the level of complexity of revisions of Oxford UKRs performed at our hospital. A retrospective review of a prospective database of all phase III Oxford UKRs was undertaken. This identified 89 Oxford UKRs which were revised at our institution between 2002 and 2008. The median time from the primary procedure to revision was 19 months (interquartile range 2-73 months). Nine were revised to another UKR. Eighty were revised to a total knee replacement (TKR). Fifty-three were revised with primary TKR components. Twenty-seven were revised using stems and/or augments. The median overall tibial component thickness (including augments) was 15 mm. Forty-five knees had an overall tibial component thickness greater than 15 mm. A primary Oxford UKR bearing thickness of greater than 6mm was associated with an increased likelihood of requiring revision components. On the basis of this review, tibial bone defects were commonly encountered when revising UKRs. Reconstruction with either an augment and a stem, or thick polyethylene component was often required. We recommend that the potential complexity of revision for UKR failure should be borne in mind when considering a primary Oxford UKR.

Muscle activity around the knee and gait performance in unicompartmental knee arthroplasty patients: a comparative study on fixed- and mobile-bearing designs

PURPOSE

Unicompartmental knee arthroplasty (UKA) offers clinical and functional advantages over total knee arthroplasty. The aim of this study was to compare the functional recovery of patients with mobile UKA versus fixed-bearing designs by state-of-the-art gait analysis and, in particular, by assessing muscular activity.

METHODS

Ten patients with the Oxford (mobile bearing) and ten patients with Optetrak (fixed bearing) UKA were evaluated at a minimum follow-up of 1 year post-operatively by gait analysis, which includes the main time-distance parameters, kinematics and kinetics of the replaced knee, and muscular activity of the main relevant muscles. Twenty healthy young subjects were used as controls.

RESULTS

The mean International Knee Society score was 92.7 ± 11.2 for all 20 UKA knees; for the Oxford UKA, it was 94.1 ± 9.5; and for the Optetrak UKA, it was 91.5 ± 12.9, although follow-up was significantly lower for the latter. Time-distance parameters showed a slower gait in both groups compared with that of controls, and the Oxford group had values closer to the controls. Knee joint flexion was similar to that of controls at initial contact and loading response with no differences between groups. In all patients, the joint moments were smaller to that of controls. Residual abnormalities such as the prolonged rectus femoris activity were present in both designs, and the only difference distinguishing the Optetrak group from the others was the combined co-contraction of the hamstrings.

CONCLUSIONS

A good restoration of gait was achieved by most unicompartmental knee patients independently of the UKA design, although some abnormalities persisted in muscle activity around the knee.

LEVEL OF EVIDENCE

Retrospective comparative study, Level III.

No long-term difference between fixed and mobile medial unicompartmental arthroplasty

BACKGROUND

Early studies in the literature reported relatively high early minor reintervention rate for the mobile-bearing unilateral knee arthroplasty (UKA) compared with short- and midterm survivorship after fixed- or mobile-bearing UKA. However, whether the long-term function and survivorship are similar is unclear.

QUESTIONS/PURPOSES

We therefore asked whether (1) mobile- or fixed-bearing UKAs have comparable function (as measured by the Knee Society scores); (2) mobile- and fixed-bearing UKA have comparable Knee Society radiographic scores; and (3) the long-term survivorship is comparable.

METHODS

We retrospectively reviewed 75 patients (79 knees) with a fixed-bearing UKA and 72 patients (77 knees) with a mobile-bearing UKA operated on between 1989 and 1992. Mean age of the patients was 63 years; gender and body mass index (26 kg/m(2)) were comparable in the two groups. We obtained Knee Society function and radiographic scores and determined survival. The minimum followup was 15 years (mean, 17.2 ± 4.8 years; range, 15-21.2 years).

RESULTS

The mean Knee Society function and knee scores were comparable in the two groups. Radiographically, the number of overcorrections and the number of radiolucencies were statistically higher in the mobile-bearing group (69% versus 24%). At final followup, considering revision for any reason, 12 of 77 (15%) UKAs were revised (for aseptic loosening, dislocation, and arthritis progression) in the mobile-bearing group and 10 of 79 (12%) in the fixed-bearing group (for wear and arthritis progression).

CONCLUSIONS

This long-term study did not demonstrate any difference in survivorship between fixed and mobile-bearing but pointed out specific modes of failure.

Innovations in total knee replacement: new trends in operative treatment and changes in peri-operative management

The human knee joint can sustain damage due to injury, or more usually osteoarthritis, to one, two or all three of the knee compartments: the medial femorotibial, the lateral femorotibial and the patellofemoral compartments. When pain associated with this damage is unmanageable using nonsurgical techniques, knee replacement surgery might be the most appropriate course of action. This procedure aims to restore a pain-free, fully functional and durable knee joint. Total knee replacement is a well-established treatment modality, and more recently, partial knee replacement-more commonly known as bi- or unicompartmental knee replacement-has seen resurgence in interest and popularity. Combined with the use of minimally invasive surgery (MIS) techniques, gender-specific prosthetics and computer-assisted navigation systems, orthopaedic surgeons are now able to offer patients knee replacement procedures that are associated with (1) minimal risks during and after surgery by avoiding fat embolism, reducing blood loss and minimising soft tissue disruption; (2) smaller incisions; (3) faster and less painful rehabilitation; (4) reduced hospital stay and faster return to normal activities of daily living; (5) an improved range of motion; (6) less requirement for analgesics; and (7) a durable, well-aligned, highly functional knee. With the ongoing advancements in surgical technique, medical technology and prosthesis design, knee replacement surgery is constantly evolving. This review provides a personal account of the recent innovations that have been made, with a particular emphasis on the potential use of MIS techniques combined with computer-assisted navigation systems to treat younger, more physically active patients with resurfacing partial/total implant knee arthroplasty.

Mobile or fixed unicompartmental knee prostheses? In-vitro wear assessments to solve this dilemma

The unicompartmental knee prosthesis is an attractive alternative to total knee arthroplasty. Current UKP devices can be subdivided into two groups based on different design principles: fixed bearing knees, where the ultra-high molecular weight polyethylene meniscal component snap or press fits into the tibial tray, and mobile bearing designs which facilitate movement of the insert relative to the tray. The present study was aimed at comparing the in-vitro wear behaviour of fixed and mobile unicompartmental knee menisci under two configurations: the femoral components were cemented into a custom-made metallic block or, as a novelty of the present study, into a synthetic femur (i.e. under conditions which should better reproduce the in-vivo behaviour). Analyses were performed using a displacement-control knee wear simulator with "three-plus-one" stations. All the kinematics tests were set in accordance with the ISO 14243-1,2,3. Fixed and mobile polyethylene menisci showed a different wear behaviour: the fixation-frame influenced directional load transfer through each component in a qualitative and quantitative way. In fact, gravimetric results showed that under the metal block holder fixation, mobile components worn more than fixed components (weight losses of 8.7±2.0 mg and 2.6±1.09 mg, respectively); on the other hand, under the synthetic femur configuration, differences in wear behaviour were less pronounced and mobile menisci underwent a slightly lower weight loss than fixed components (4.5±2.2 mg vs. 6.7±1.4 mg). This different trend was explained in relation to the kinematic schemes of the two fixation methods. Raman spectroscopy, used to evaluate the UHMWPE crystallinity changes induced by mechanical stress, showed that mobile menisci specimens were more affected than the fixed components in both their superior and inferior surfaces, independent of the fixation-frame. In conclusion, if tested under conditions which should better reproduce the in-vivo behaviour, mobile UKPs did not show a worse wear behaviour than fixed components in terms of weight losses, although UHMWPE changes at the molecular scale could be detrimental.

Contact stresses in a patient-specific unicompartmental knee replacement

BACKGROUND

Unicompartmental knee replacement has gained popularity in recent times, showing improved success rates. The main reasons for the failure of unicompartmental knee replacement are the wear of the polyethylene bearing, aseptic loosening and wear in the opposite compartment. The contact stresses involved are significant contributing factors to these causes of failure.

METHODS

In this study, a patient-specific unicompartmental knee replacement is proposed using a methodology based on neural network modeling of a database of healthy knee geometries. This custom implant was then compared to two conventional implant designs in terms of contact stress in a validated finite element model.

FINDINGS

The custom implant experienced lower contact stresses at the tibio-femoral joint compared to a fixed-bearing design and also displayed more uniform stress distribution at the bone-implant interface than any of the other implant designs.

INTERPRETATION

Custom unicompartmental knee replacements therefore have the potential of providing good contact stress distribution, preserve bone stock and could be more anatomically accurate.

Scientific evidence for the use of modern unicompartmental knee arthroplasty

Unicompartmental knee arthroplasty as a surgical treatment for monocompartmental knee arthritis remains a controversial procedure with questions surrounding the benefits and survivorship of the procedure versus osteotomies or total knee arthroplasties. The authors, by examining the complete body of literature for scientific evidence concerning the procedure, will describe the history of usage of these prostheses, their rationale for usage, modern devices and their results, and why they may have advantages as a treatment modality for monocompartmental knee arthritis. Outcomes of current unicompartmental designs will be presented and evaluated to determine which aspects of the design and patient selection technique are associated with success or failure. Commonly asked questions regarding the use of these devices will be addressed. The authors will also describe some potential modifications that might affect the use of these components in the future, including minimally invasive procedures and robotics, and how these devices may change over the next 5 years.

Unicompartmental knee resurfacing: enlarged tibio-femoral contact area and reduced contact stress using novel patient-derived geometries

Advances in imaging technology and computer-assisted design (CAD) have recently enabled the introduction of patient-specific knee implant designs that hold the potential to improve functional performance on the basis of patient-specific geometries, namely a patient-specific sagittal and coronal curvature, as well as enhanced bone preservation. The objective of this study was to investigate the use of a novel implant design utilizing a patient specific sagittal J-curve on the femoral component combined with a novel constant, patient-derived femoral coronal curvature and to assess tibio-femoral contact area and contact stress on a femur matched curved tibial polyethylene insert. Mean contact area and standard deviations were 81+/-5, 96+/-5 and 74+/-4 mm(2) for the heel strike, toe off and mid-stance positions, respectively. Mean contact stress and standard deviations were 23.83+/-1.39, 23.27+/-1.14 and 20.78+/-0.54 MPa for the heel strike, toe off and mid-stance positions, respectively. Standard deviations of the measurements were small, not exceeding 6-7% confirming the consistency of loading conditions across different flexion angles. The results were comparable to those reported for standard, off-the-shelf fixed-bearing implants with paired femoral and tibial geometries. These data show that a constant coronal curvature can be applied to a patient-specific implant by measuring coronal curvatures across the femoral condyle in each patient and by deriving an average curvature. This novel approach combines unique benefits of patient-specific geometry with proven design concepts for minimizing polyethylene wear.

Does bearing design influence midterm survivorship of unicompartmental arthroplasty?

Medial unicompartmental arthroplasties (UKA) are available with mobile- and fixed-bearing designs, with the advantages of one bearing over another unproven. We questioned whether the bearing design influenced clinical outcome, survivorship, the reason for revision, or the timing of failures. We retrospectively reviewed 179 patients (229 knees) who had medial unicompartmental knee arthroplasties between 1990 and 2007; of these 79 knees had a mobile-bearing design and 150 knees a fixed-bearing design. Patients with mobile-bearing UKA had a minimum followup of 1 year (mean, 3.6 years; range, 1-11.3 years); those with fixed-bearing UKA a minimum followup of 1 year (mean, 8.1 years; range, 1-17.8 years). Patients were evaluated with clinical outcome scores and radiographically using the Knee Society rating system. Seven of 79 (9%) mobile-bearing knees underwent revision at a mean of 2.6 years, and 22 of 150 (15%) fixed-bearing knees underwent revision at a mean of 6.9 years. The 5-year cumulative survival rates were 88% (SE +/- 0.47, 95% CI 0.7229-1) and 96% (SE +/- 0.16, 95% CI 0.93-0.9979) for the mobile- and fixed-bearing designs respectively using the endpoint of revision surgery. We observed no differences in the indications or complexity of revision surgery between the groups and none in midterm survivorship.

LEVEL OF EVIDENCE

Level III, comparative study. See Guidelines for Authors for a complete description of levels of evidence.

Fixed versus mobile bearing unicompartmental knee replacement: a meta-analysis

This systematic review compares the clinical, radiological and kinematic outcomes of fixed compared to mobile bearing unicompartmental knee replacements (UKRs). A meta-analysis of pooled mean difference and relative risk data was undertaken following a review of electronic databases. Five studies were identified. Analysis suggested that there was no significant difference in clinical outcome or complication rate between mobile and fixed bearing UKR. However, the evidence reviewed presented with a number of methodological limitations. Areas for further study are recommended.

Bi-unicompartmental versus total knee arthroplasty: a matched paired study with early clinical results

INTRODUCTION

The authors performed a matched paired study between two groups: bi-unicompartmental (Bi-UKR) versus total knee replacements (TKR) for the treatment of isolated bicompartmental tibio-femoral knee arthritis with an asymptomatic patello-femoral joint. The Authors believe that Bi-UKR could achieve comparable outcomes than TKR, but with a real less invasive surgery and maintaining a higher joint function.

MATERIALS AND METHODS

A total of 22 patients with bicompartmental tibio-femoral knee arthritis, who underwent Bi-UKR between January 1999 and March 2003, were included in the study (group A). In all the knees the arthritic changes were graded according to the classification of Alback. All patients had an asymptomatic patello-femoral joint. All patients had a varus deformity lower than 8 degrees , a body-mass index lower than 34, no clinical evidence of ACL laxity or flexion deformity and a preoperative range of motion of a least 110 degrees . At a minimum follow-up of 48 months, every single patient in group A was matched with a patient who had undergone a computer assisted TKR between August 1999 and September 2002 (group B). In the Bi-UKR group, in two cases we registered intraoperatively the avulsion of the treated tibial spines, requiring intra-operative internal fixation and without adverse effects on the final outcome. Statistical analysis of the results was performed.

RESULTS

At a minimum follow-up of 48 months there were no statistical significant differences in the surgical time while the hospital stay was statistically longer in TKR group. No statistically significant difference was seen for the Knee Society, Functional and GIUM scores between the two groups. Statistically significant better WOMAC Function and Stiffness indexes were registered for the Bi-UKR group. TKR implants were statistically better aligned with all the implants positioned within 4 degrees of an ideal hip-knee-ankle (HKA) angle of 180 degrees .

CONCLUSIONS

The results of this 48 months follow-up study suggest that Bi-UKR is a viable option for bicompartmental tibio-femoral arthritis at least as well as TKR but maintaining a higher level of function.

Contemporary unicompartmental knee arthroplasty: fixed vs mobile bearing

Contemporary unicompartmental knee arthroplasty has shown resurgence in use partly because of studies reporting excellent long-term survivorship. Both fixed-bearing as well as mobile-bearing designs have shown comparable results. Fixed-bearing designs, in particular, implants with metal-backed tibial components have shown more consistent long-term survival, whereas fixed bearings with an all-polyethylene tibial component have had mixed results. Similar to the all-polyethylene tibial component designs, mobile-bearing designs have demonstrated mixed results. One concern with mobile bearings is the high rate of complete tibial radiolucent lines. The keys to long-term survival of both fixed and mobile-bearing designs in unicompartmental knee arthroplasty are patient selection, surgical technique, and surgical experience.

Tissue sparing surgery in knee reconstruction: unicompartmental (UKA), patellofemoral (PFA), UKA + PFA, bi-unicompartmental (Bi-UKA) arthroplasties

Recently mini-invasive joint replacement has become one of the hottest topics in the orthopaedic world. However, these terms have been improperly misunderstood as a "key-hole" surgery where traditional components are implanted with shorter surgical approaches, with few benefits and several possible dangers. Small implants as unicompartmental knee prostheses, patellofemoral prostheses and bi-unicompartmental knee prostheses might represent real less invasive procedures: Tissue sparing surgery, the Italian way to minimally invasive surgery (MIS). According to their experience the authors go through this real tissue sparing surgery not limited only to a small incision, but where the surgeons can respect the physiological joint biomechanics.