St. Georg sledge for medial compartment knee replacement. 461 arthroplasties followed for 4 (1-17) years

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.

Bilateral Femoral Component Fractures After Primary Total Knee Arthroplasty With Cruciate-Retaining Femoral Component

A 69-year-old male presented with atraumatic bilateral femoral component fractures at different time intervals after simultaneous bilateral total knee arthroplasty using the cemented Biomet Ascent Knee System. The right and left knee implant fractures occurred 12 and 17 years after primary arthroplasty, respectively. This patient was notably tall (190.5 cm, 98th percentile) and maintained an active lifestyle before implant fractures. Sequential, bilateral knee implant fractures in a system with a previously acceptable track record suggest that biomechanics, patient characteristics, and surgical factors can significantly influence the risks for fracture of an implant.

Evaluation of implant fit and frontal plane alignment after bi-compartmental knee arthroplasty using patient-specific instruments and implants

INTRODUCTION

The goals of successful bi-compartmental knee arthroplasty are to achieve correct fit and positioning of the implant, while appropriately correcting the mechanical alignment of the leg after surgery. As these requirements are not always reliably fulfilled using off-the-shelf implant systems, newer approaches for bi-compartmental resurfacing have been explored.

MATERIAL AND METHODS

In this article we report the radiographic results of 30 patients with anteromedial osteoarthritis (OA) who were treated with a novel patient-specific fixed-bearing bi-compartmental knee resurfacing system using custom-made implants and instruments. Utilizing standardized pre- and postoperative radiographic analyses (based on anterior-posterior and lateral, anterior-posterior weight-bearing full-length radiographs, patella skyline views and preoperative computed tomography (CT) scanning) implant fit and positioning as well as correction of the mechanical axis (hip-knee-ankle angle, HKA) were determined.

RESULTS

On average, HKA was corrected from 173.4 ±3.47° preoperatively to 179.4 ±2.85° postoperatively. The coronal femoro-tibial angle was corrected on average 5.61°. The preoperative tibial slope measured on lateral views was 6.38 ±2.4°, while the average slope in the CT-based planning protocol (iView) was 6.14 ±2.40°. Postoperative lateral tibial slope was determined to be 5.77 ±1.97°. The thickness of the posterior femoral cuts was measured intraoperatively and, in all cases, corresponded well to the targeted thickness of the cuts provided by the iView. The joint line was preserved in all cases and the average Insall-Salvati index was 1.078 ±0.11 pre- and 1.072 ±0.11 postoperatively. The fit of the implant components measured by over- or underhang was excellent throughout (< 1.01 mm).

CONCLUSIONS

Custom-made bicompartmental knee arthroplasty can ensure optimized fitting and positioning of the implant with restoration of the leg axis. These implants could be considered as an alternative primary solution for knee surgeons treating bi-compartmental disease.

The incidence of implant fractures after knee arthroplasty

PURPOSE

This study aimed to evaluate the incidence of "implant" fractures after knee arthroplasty using clinical literature and worldwide arthroplasty registers. The hypothesis was that register datasets report higher rates of these rare complications than clinical studies.

METHODS

Calculations were based on the pooled incidence of revision operations after fractures of knee arthroplasties, comparing clinical studies published in MEDLINE-listed journals and annual reports from worldwide arthroplasty registers in a structured literature analysis based on a standardized methodology.

RESULTS

Twelve clinical studies and datasets from six worldwide registers were included. Rates of fractures of knee arthroplasties were reported from 0.2 to 2.5 % in clinical studies versus 0.02-0.17 % in worldwide arthroplasty registers.

CONCLUSIONS

Fractures of knee arthroplasty systems are rare complications, with clinical studies showing higher incidence rates than worldwide arthroplasty registries. Unicompartmental knee arthroplasty (UKA) implanted before 2000, constrained primary or revision constrained total knee arthroplasties, and patellar replacements showed the highest incidence of implant fracture. The results of this analysis can help clinicians to counsel patients on potential complications following knee arthroplasty.

LEVEL OF EVIDENCE

III.

Systematic review of medial versus lateral survivorship in unicompartmental knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty (UKA) has gained popularity in patients with isolated unicompartmental osteoarthritis. To our knowledge no systematic review has assessed and compared survivorship of medial and lateral UKA. We performed a systematic review assessing medial and lateral UKA survivorship and comparing survivorship in cohort studies and registry-based studies.

METHODS

A search was performed using PubMed, Embase and Cochrane systems. Ninety-six eligible studies reported survivorship, of which fifty-eight reported medial and sixteen reported lateral UKA survivorship. Nineteen cohort studies and seven registry-based studies reported combined medial and lateral survivorship.

RESULTS

The five-year, ten-year and fifteen-year medial UKA survivorship was 93.9%, 91.7% and 88.9%, respectively. Lateral UKA survivorship was 93.2%, 91.4% and 89.4% at five-year, ten-year and fifteen-year, respectively. No statistical difference between both compartments was found. At twenty years and twenty-five years survivorship of medial UKA was 84.7% and 80%, respectively, but no studies reported lateral UKA survivorship at these follow-up intervals. Survivorship of cohort studies was not significantly higher compared to registry-based studies at five years (94.3 vs. 91.7, respectively, p=0.133) but was significantly higher at ten years (90.5 vs. 84.1, p=0.015).

CONCLUSION

This is the first systematic review that shows no difference in the five-, ten- and fifteen-year survivorship of medial and lateral UKA. We found a lower survivorship in the registry-based studies compared to cohort studies.

Ten year survivorship after cemented and uncemented medial Uniglide® unicompartmental knee arthroplasties

BACKGROUND

Results of knee replacement registries have shown that unicompartmental knee arthroplasty (UKA) has a significantly higher revision and failure rate than current state-of-the-art TKA. The aim of this prospective study is to evaluate the long-term outcomes and to calculate the 10 year survival of knees with medial osteoarthritis treated with Uniglide® UKA.

METHODS

Two hundred thirty-four patients were assessed by an independent clinical observer using the American Knee Society Clinical Rating System, a validated outcome measure. Kaplan-Meier analysis was used to calculate the 10 year survival rates using revision surgery for any cause as the end point.

RESULTS

There were no revisions due to progression of lateral osteoarthritis or polyethylene failure. There were one traumatic and three non-traumatic bearing dislocations and two revisions due to aseptic loosening of the tibial component. One joint was revised for traumatic ligament rupture, one for synovitis from bearing impingement, one due to femoral component mal-positioning and one for infection. A total of 10 cases were revised due to failures for any cause in the 61 patients withdrawn because they had died, thus giving a cumulative survival rate at 10 years of 95.57%. The knee (function) score showed an increase from 33.4 (54.7) pre-operatively to 94 (83.4) points post-operatively. The average range of motion increased from 107 to 122° (p<0.01).

CONCLUSION

Based on our findings we believe that the Uniglide® unicompartmental knee prosthesis offers a safe and effective solution for the treatment of medial compartment osteoarthritis.

Fixed bearing lateral unicompartmental knee arthroplasty--short to midterm survivorship and knee scores for 101 prostheses

BACKGROUND

Isolated unicompartmental knee arthritis is less common laterally than medially. Lateral unicompartmental knee arthroplasty (UKA) constitutes only 1% of all knee arthroplasty performed. Use of medial UKA is supported by several published series showing good long-term survivorship and patient satisfaction, in large patient cohorts. Results of lateral UKA however have been mixed. We present the short and mid-term survivorship and 5-year clinical outcome of 101 lateral UKAs using a single prosthesis.

METHODS

Over a 9 year period, 100 patients who satisfied inclusion criteria underwent a lateral fixed-bearing unicompartmental arthroplasty. American Knee Society (AKSS), Oxford Knee (OKS) and modified Western Ontario McMaster Universities Arthritis Index (WOMAC) scores were completed preoperatively and at 1, 2 and 5 years postoperatively. Kaplan-Meier survival analysis was used to determine the 2-year and 5-year survivorship, using revision for any cause as end point.

RESULTS

Survivorship was 98.7% and 95.5% at 2 and 5 years respectively. 1 knee was revised for subsidence of the tibial component and 1 knee for progression of medial compartment osteoarthritis. Of a possible 35 knees in situ at 5 year follow-up, 33 knees were fully scored. Median AKSS, OKS and modified WOMAC scores were 182, 41, and 16 respectively.

CONCLUSIONS

The mid-term survivorship and outcome scores at 5-years suggest that lateral unicompartmental knee arthroplasty provides a valuable alternative to total joint replacement in selected patients with isolated lateral tibio-femoral arthritis at mid-term follow-up. Level II evidence.

Management of Periprosthetic Fracture in Unicompartmental Knee Arthroplasty Patients: A Case Series

Unicompartmental knee arthroplasty (UKA) has been one of the treatment modality specifically for unicompartmental osteoarthritis of the knee. The advantages of UKA are faster recovery period, shorter length of hospital stay, reduced morbidity, and good functional outcome. However, one of the complications in UKA is periprosthetic fracture where most papers suggested a surgical intervention such as revision to total knee replacement. In our six years of experience with UKA surgery from 2005 to 2010, we encountered six periprosthetic fractures out of 966 knees that were operated on among 901 patients. Five patients were treated conservatively by casting and were advised not to bear weight on the affected side. One patient was revised to total knee replacement immediately. Each patient underwent a series of scoring system such as Knee Society Clinical Rating and Oxford Questionnaire to evaluate the outcome of treatment. The results were variable with only one patient showing reasonable improvement by conservative management alone. Another three patients did not show significant functional improvements despite the fractures healing. One patient developed non-union and had to undergo internal fixation to correct the deformity. The patient who underwent a revision to total knee replacement showed significant improvement. We conclude that surgical intervention produced better outcome. Revision to total knee replacement was the preferred treatment.

Long-term survivorship and failure modes of unicompartmental knee arthroplasty

BACKGROUND

In a previously reported series of 51 patients with 62 cemented, fixed-bearing unicompartmental knee arthroplasties, we reported a 10-year, 98% survival rate with an average knee score of 92 points. The survivorship and modes of failure past 10 years are incompletely understood.

QUESTIONS/PURPOSES

At 15-year followup we sought to determine (1) the overall durability and survivorship of this design; (2) modes of failure; and (3) the progression of arthritis in the nonresurfaced compartments.

METHODS

Nineteen knees in 16 patients were available for study with 34 patients lost to death and one lost to followup. At 15 years, we analyzed the Kaplan-Meier survivorship as well as durability with regard to radiographic loosening and knee scores, determined modes of failure, and assessed radiographs for degeneration in the nonresurfaced compartments.

RESULTS

Fifteen-year survivorship was 93% and 20-year survivorship was 90%. Four of 62 knees were revised to total knee arthroplasty at a mean of 144 months. One knee was revised for patellofemoral and lateral compartment degeneration, one for lateral compartment degeneration, one for polyethylene disengagement and metallosis, and one for pain of unclear etiology. No patients had aseptic loosening or osteolysis. The mean knee score was 78 at latest followup. Arthritic progression in the nonresurfaced compartments was common although symptomatic in only two patients.

CONCLUSIONS

With this cemented, fixed-bearing design, the failure rates were low, there were no cases of failure secondary to wear or loosening, and the survivorship was similar to that reported for total knee arthroplasty.

Evaluation of implant position and knee alignment after patient-specific unicompartmental knee arthroplasty

Implant positioning and knee alignment are two primary goals of successful unicompartmental knee arthroplasty. This prospective study outlines the radiographic results following 32 patient-specific unicompartmental medial resurfacing knee arthroplasties. By means of standardized pre- and postoperative radiographs of the knee in strictly AP and lateral view, AP weight bearing long leg images as well as preoperative CT-based planning drawings an analysis of implant positioning and leg axis correction was performed.The mean preoperative coronal femoro-tibial angle was corrected from 7° to 1° (p<0.001). The preoperative medial proximal tibial angle of 87° was corrected to 89° (p<0.001). The preoperative tibial slope of 5° could be maintained. The extent of the dorsal femoral cut was equivalent to the desired value of 5mm given by the CT-based planning guide. The mean accuracy of the tibial component fit was 0mm in antero-posterior and +1mm in medio-lateral projection. Patient-specific fixed bearing unicompartmental knee arthroplasty can restore leg axis reliably, obtain a medial proximal tibial angle of 90°, avoid an implant mal-positioning and ensure maximal tibial coverage.

The practice of unicompartmental knee arthroplasty in the United Kingdom

PURPOSE

To survey the current practice of unicompartmental knee arthroplasty (UKA) in the United Kingdom.

METHODS

Questionnaires were sent to all 341 local members of the British Association for Surgery of the Knee to inquire into their practice of UKA, including clinical indications, preoperative investigations, surgical approach, preferences in implant design, and the role of UKA in relation to high tibial osteotomy.

RESULTS

56% of respondents performed less than 16 UKAs per year, whereas 16.5% performed over 30 per year. 89.5% of the respondents used anteroposterior radiographs as their main investigation tool. Only 30% and 16.5% used posteroanterior 30 degrees flexion and varus/valgus stress radiographs, respectively, despite being better investigation tools. 57% considered arthroscopy, despite its invasive nature. The main contra-indications to UKA were anterior cruciate ligament deficiency with instability (95%), focal grade-III osteoarthritis in the contralateral compartment (87%), and osteoporosis with rheumatoid arthritis (80.5%), but only 59% of respondents considered an inability to passively correct a pre-existing varus or valgus deformity as a contra-indication. 51.5% of respondents preferred minimally invasive approach, 96% preferred cemented fixation, and over two thirds used the mobile bearing design. 72% of respondents expressed preference for total knee arthroplasty over UKA in localised lateral compartment osteoarthritis.

CONCLUSION

Modern UKA has gained popularity in properly selected patients with localised medial compartment osteoarthritis, provided the knee is not anterior cruciate ligament deficient and any deformity is passively correctable.

Unicompartmental knee replacements with Miller-Galante prosthesis: two to 16-year follow-up of a single surgeon series

We report the outcome of 94 Miller-Galante unicompartmental knee replacements done by a single surgeon over 16 years in a district general hospital in the UK. Patellofemoral arthritis was considered a contraindication only if symptomatic and confirmed on radiography and surgery. Deformity when present was correctable. The mean age at surgery was 66.54 years. The mean follow-up was 10.8 years (2-16 years). The mean Bristol knee score was 43.1 (28-50); 86% of the patients had good or excellent scores. The average range of flexion was 110.6° (80-130°); 89% of the knees had an appropriate alignment. Using revision as the endpoint, outcome for every knee was established. The survival rate for medial unicompartmental knee replacements was 94% at ten years and 87% at 15 years. Although the survival rate for the lateral unicompartmental knee replacement was 97% at five years, it dropped to 41% at eight years. Lateral unicompartmental knee replacements formed only 9.6% of all the replacements in this series. The results for medial unicompartmental knee replacements are similar to reports by other authors for similar and mobile bearing designs. Unicompartmental knee replacement results in a more kinematic knee and produces good functional results.

The implications of damage to the lateral femoral condyle on medial unicompartmental knee replacement

With medial unicompartmental osteoarthritis (OA) there is occasionally a full-thickness ulcer of the cartilage on the medial side of the lateral femoral condyle. It is not clear whether this should be considered a contraindication to unicompartmental knee replacement (UKR). The aim of this study was to determine why these ulcers occur, and whether they compromise the outcome of UKR.

Case studies of knees with medial OA suggest that cartilage lesions on the medial side of the lateral condyle are caused by impingement on the lateral tibial spine as a result of the varus deformity and tibial subluxation. Following UKR the varus and the subluxation are corrected, so that impingement is prevented and the damaged part of the lateral femoral condyle is not transmitting load. An illustrative case report is presented.

Out of 769 knees with OA of the medial compartment treated with the Oxford UKR, 59 (7.7%) had partial-thickness cartilage loss and 20 (2.6%) had a full-thickness cartilage deficit on the medial side of the lateral condyle. The mean Oxford Knee Score (OKS) at the last follow-up at a mean of four years was 41.9 (13 to 48) in those with partial-thickness cartilage loss and 41.0 (20 to 48) in those with full-thickness loss. In those with normal or superficially damaged cartilage the mean was 39.5 (5 to 48) and 39.7 (8 to 48), respectively. There were no statistically significant differences between the pre-operative OKS, the final review OKS or of change in the score in the various groups.

We conclude that in medial compartment OA, damage to the medial side of the lateral femoral condyle is caused by impingement on the tibial spine and should not be considered a contraindication to an Oxford UKR, even if there is extensive full-thickness ulceration of the cartilage.

Early failure of a unicompartmental knee arthroplasty design with an all-polyethylene tibial component

Refined prosthetic designs and surgical techniques for unicompartmental knee arthroplasty have recently been associated with improved outcomes. The purpose of the present study was to evaluate the clinical and radiographic outcomes of the EIUS unicompartmental design, which has an all-polyethylene tibial component, and to compare these outcomes with published reports of other unicompartmental prostheses. Between February 2002 and March 2005, 113 patients (144 knees) underwent a medial unicompartmental knee arthroplasty, all performed by a single surgeon who used the EIUS prosthesis. At a mean follow-up of 36 months (range, 24-54 months), the mean Knee Society objective and functional scores improved from 55 points (range, 31-77 points) and 49 points (range, 35-60 points) to 92 points (range, 45-100 points) and 89 points (range, 10-100 points), respectively. The implant survival rate was 89%, with 16 knees either revised or scheduled for revision. The reasons for revision included aseptic loosening of the tibial component (eight knees), progressive symptomatic patellofemoral disease (four knees), and tibial component subsidence (four knees). Multiple regression analysis revealed that age, gender, and body mass index were not significantly correlated with success or failure of this design, although nine of the 16 patients who required revision were obese. This prosthesis was associated with higher revision rates than components which utilize metal-backed implants. Further modifications in the design, indications, or technique may be necessary to improve outcomes of this unicompartmental knee arthroplasty system.

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.

Finite element analysis of unicompartmental knee arthroplasty

Concerns over accelerated damage to the untreated compartment of the knee following unicompartmental knee arthroplasty (UKA), as well as the relatively poor success rates observed for lateral as opposed to the medial arthroplasty, remain issues for attention. Finite element analysis (FEA) was used to assess changes to the kinematics and potential for cartilage damage across the knee joint in response to the implantation of the Oxford Mobile Bearing UKA. FE models of lateral and medial compartment arthroplasty were developed, in addition to a healthy natural knee model, to gauge changes incurred through the arthroplasty. Varus-valgus misalignments were introduced to the femoral components to simulate surgical inaccuracy or over-correction. Boundary conditions from the Stanmore knee simulator during the stance phase of level gait were used. AP translations of the tibia in the medial UKA models were comparable to the behaviour of the natural knee models (+/-0.6mm deviation from pre-operative motion). Following lateral UKA, 4.1mm additional posterior translation of the tibia was recorded than predicted for the natural knee. IE rotations of the medial UKA models were less consistent with the pre-operative knee model than the lateral UKA models (7.7 degrees vs. 3.6 degrees deviation). Varus misalignment of the femoral prosthesis was more influential than valgus for medial UKA kinematics, whereas in lateral UKA, a valgus misalignment of the femoral prosthesis was most influential on the kinematics. Resection of the cartilage in the medial compartment reduced the overall risk of progressive OA in the knee, whereas removing the cartilage from the lateral compartment, and in particular introducing a valgus femoral misalignment, increased the overall risk of progressive OA in the knee. Based on these results, under the conditions tested herein, both medial and lateral UKA can be said to induce kinematics of the knee which could be considered broadly comparable to those of the natural knee, and that even a 10 degrees varus-valgus misalignment of the femoral component may not induce highly irregular kinematics. However, elevated posterior translation of the tibia in lateral UKA and large excursions of the insert may explain the higher incidence of bearing dislocation observed in some clinical studies.

Minimal-resection arthroplasty to treat meniscal tears with associated condyle lesions: finite element analysis

An early intervention prosthesis which minimizes the extent of resected healthy bone would be advantageous to patients for whom a total or unicompartmental replacement would sacrifice extensive healthy tissue. In this study the use of a device to treat osteoarthritis localized upon a single condyle of the femur with an associated irreparable meniscal tear is considered. The effects of implant alignment are considered from the standpoint of kinematics and potential for cartilage damage. The results suggest that alterations in implant position influence joint kinematics during stance. Anteroposterior (AP) adjustment of the medial prosthesis minimizes the capability of the knee to rotate internally, placing higher demands on the cruciate ligaments. AP adjustments of the lateral prosthesis induces greater posterior drawback, reducing internal-external rotation. Natural knee kinematics are best reproduced by the medial condyle rather than the lateral condyle. Stress exposure of the cartilage increased with the introduction of the femoral condyle prosthesis, which may progress eventually to osteoarthritis, although the results indicate that the medial condyle device is less likely to lead to cartilage damage than is lateral condyle replacement. This study demonstrates that a minimal-resection femoral condyle device may provide sufficient knee joint function to serve as an interim treatment prior to total or unicompartmental knee arthroplasty.

Medial unicompartimental knee arthroplasty for osteonecrosis or osteoarthritis

We report a prospective series of 33 unicompartmental knee arthroplasties (UKAs) operated for a spontaneous osteonecrosis of the knee (SPONK) compared with 35 UKAs operated for osteoarthritis (OA). The mean follow-up was 5 years. Preoperative functional score in the SPONK group was significantly lower than that in the OA group. The results were comparable in terms of pain, knee score and function. At the last follow-up, the survival rate was 92.8% for the SPONK group and 95.4% for the OA group. We found a higher rate of radiolucencies in the SPONK group, however, without any clinical symptoms. The UKA is a good option in the treatment of SPONK.

Minimally invasive surgery of the knee

Minimally invasive knee replacement surgery has been developed in an attempt to lessen the impact of operations on the patient's quality of life, in the same way as arthroscopy, the forefather of minimally invasive surgery (MIS), revolutionised cartilage and ligament surgery three decades earlier. The technique is based on minimising soft tissue and muscle trauma, skin incision length, and capsular disruption while trying to maintain the ultimate goal of a well-aligned, well-fixed knee replacement. Short-term advantages including accelerated recovery and reduction in blood loss have been demonstrated, but it remains to be investigated whether MIS is able to provide sustainable benefits and long-term outcome equivalent to conventional surgery. Successful application of MIS techniques have been confirmed in conjunction with unicompartmental knee arthroplasty (UKR) implantation, while its use with total knee arthroplasty remains experimental. Critics have expressed concern that reduced visibility may compromise implant positioning and leg alignment which could have a negative effect on prosthetic long-term survival. MIS clearly represents a unique and more technically demanding procedure, but the learning curve may perhaps overshadow the benefits. Computer navigation may help to avoid such problems but so far scientific evidence regarding definitive outcomes is lacking, and some of the MIS techniques are still in the early phases of development.

[Implant with a mobile or a fixed bearing in unicompartmental knee joint replacemen]

Although the goal of anatomical and functional joint reconstruction in unicompartmental knee replacement is well defined, no uniform implant design has become established. In particular, the differential indications for implantation of an implant with a mobile or a fixed bearing are still not clear. The long-term results of mobile and with fixed bearings are comparable, but there are significant differences in resulting knee joint kinematics, tribological properties and implant-associated complications. In unicompartmental knee replacement mobile bearings restore the physiological joint kinematics better than fixed implants, although the differences to total knee arthroplasty seem minor. The decoupling of mobile bearings from the tibia implant allows a high level of congruence with the femoral implant, resulting in larger contact areas than with fixed bearings. This fact in combination with the more physiological joint kinematics leads to less wear and a lower incidence of osteolyses with mobile bearings. Disadvantages of mobile bearings are the higher complication and early revision rates resulting from bearing dislocation and impingement syndromes caused by suboptimal implantation technique or instability. Especially in cases with ligamentous pathology fixed bearings involve a lower complication rate. It seems their use can also be beneficial in patients with a low level of activity, as problems related to wear are of minor importance for this subgroup. The data currently available allow differentiations between various indications for implants with mobile or fixed bearings, so that the implants can be matched to the patient and the joint pathology in unicompartmental knee joint replacement.

Lateral unicompartmental knee replacement: fixed or mobile bearing?

Between May 2001 and May 2003, 233 consecutive Preservation unicompartmental knee replacements (UKR) were performed. Of these, 30 were lateral UKRs (13%) performed in 12 men and 16 women (2 bilateral cases) with a mean age of 67 years (range 36-93 years). A metal-backed mobile bearing tibial component was used in 13 knees and an all-polyethylene fixed bearing tibial component in 17 knees. The patients were reviewed prospectively at 1 and 2 years. The 2 year results show no difference in range of motion or function between the mobile and fixed bearing versions of the Preservation knee when used on the lateral side. There were three early revisions, all in the mobile bearing group.

The survivorship and results of total knee replacements converted from unicompartmental knee replacements

Unicompartmental knee replacements (UKR) converted to total knee replacements (TKR) have often been viewed with scepticism because of the perceived difficulty of revising a UKR to a TKR. We present the survivorship analysis of a 77 patient cohort as well as the current results of a 35 patient cohort. There were a total of 77 patients in the survivorship study with an average follow-up of 6.9 years and an average Bristol Knee Score of 78.5. Using Kaplan-Meier survivorship analysis, a 91% survivorship at 10 years was demonstrated. The average age at revision to TKR was 66.1 years. The average follow-up period was 10.5 years and a recent clinical and radiological review of the 35 living patients showed an average Bristol Knee Score of 78.2 with 16 excellent, 11 good, five fair and three failed.

CONCLUSION

The results of the UKRs have already shown it to be safe, reliable and repeatable. We believe that this study shows that revision of UKR to TKR is not technically difficult and that the results are comparable to the results of primary TKRs.

ADAPTIVE BONE REMODELLING OF ALL POLYETHYLENE UNICOMPARTMENTAL TIBIAL BEARINGS

BACKGROUND

Failure of unicompartmental knees is either by progressive osteoarthritis or by failure of the prosthesis. Prosthesis failure can be because of either the actual component itself or its fixation method. Specifically, the tibial component may wear, loosen or subside into the tibial metaphyseal bone. We modelled all polyethylene tibial components and investigated the periprosthetic adaptive remodelling of the bone.

METHODS

Computed tomography scans were used to reconstruct the tibial geometry and a 3-D finite element mesh was created. The tibia loading was set at 45% of the gait cycle. The distal end of the tibia set as fixed. Implant orientations were in accordance with the manufacturer specifications. The bone mineral density changes at three regions of interest under the component were measured and plotted.

RESULTS

All regions of interest became stable at the 12-month time-point. Predictive bone mineral changes were minimal in both resorption and deposition. Zones 1-3 for the St Georg Sled (Waldermar Link, Hamburg, Germany) presented evidence of stress shielding and a maximum loss of approximately 6% bone mineral density. The Eius (Stryker Orthopaedics, Mahwah, NJ, USA) showed increased loading and caused an increase in bone mineral density for all regions of interests; the maximum being approximately 10%.

CONCLUSION

These findings are consistent with the clinical experience of unicompartmental knee replacements, where the changes are small and have little effect on the outcome of the prosthesis. From a mechanical perspective, the results are also consistent when a compliant material is used to distribute loads. They do, however, support the biomechanical theory that a change in geometry influences the loading environment and as a consequence the adaptive response of the bone is also influenced.

Survivorship of the St Georg Sled medial unicompartmental knee replacement beyond ten years

There have been several reports of good survivorship and excellent function at ten years with fixed-bearing unicompartmental knee replacement. However, little is known about survival beyond ten years. From the Bristol database of over 4000 knee replacements, we identified 203 St Georg Sled unicompartmental knee replacements (174 patients) which had already survived ten years. The mean age of the patients at surgery was 67.1 years (35.7 to 85) with 67 (38.5%) being under 65 years at the time of surgery. They were reviewed at a mean of 14.8 years (10 to 29.4) from surgery to determine survivorship and function. There were 99 knees followed up for 15 years, 21 for 20 years and four for 25 years. The remainder failed, were withdrawn, or the patient had died. In 58 patients (69 knees) the implant was in situ at the time of death. Revision was undertaken in 16 knees (7.9%) at a mean of 13 years (10.2 to 21.6) after operation. In seven knees (3.4%) this was for progression of arthritis, in three (1.5%) for wear of polyethylene, in four (2%) for tibial loosening, in two (1%) for fracture of the femoral component and in two (1%) for infection. Two knees (1%) were revised for more than one reason. The mean Bristol knee score of the surviving knees fell from 86 (34 to 100) to 79 (42 to 100) during the second decade. Survivorship to 20 years was 85.9% (95% CI 82.9% to 88.9%) and at 25 years was 80% (95% CI 70.2% to 89.8%). Satisfactory survival of a fixed-bearing unicompartmental knee replacement can be achieved into the second decade and beyond.

Unicompartmental or total knee arthroplasty?: Results from a matched study

There are few direct comparative studies evaluating results after unicompartmental knee arthroplasty and total knee arthroplasty. We determined the active range of motion, Knee Society score, and 5-year survivorship rate after 54 consecutive unilateral unicompartmental knee arthroplasties compared with a matched group of 54 unilateral total knee arthroplasties. The two groups of patients were matched for age, gender, body mass index, preoperative active range of movement, and preoperative Knee Society scores. All patients had osteoarthritis of the knee. Patients were assessed prospectively at 6, 18, 36, and 60 months postoperatively, and the mean followup was 59 months in both groups. The mean postoperative active range of motion was greater after unicompartmental knee arthroplasty, but there were no differences in the overall Knee Society knee and function scores. The 5-year survivorship rate based on revision for any reason was 88% for unicompartmental knee arthroplasty and 100% for total knee arthroplasty. The worst case 5-year survivorship rate, assuming all patients lost to followup had revision surgery, was 85% for unicompartmental knee arthroplasty and 98% for total knee arthroplasty. Total knee arthroplasty was a more reliable procedure. Midterm clinical outcomes were similar for both procedures, but the complication rate may be greater for unicompartmental knee arthroplasty.

Influence de la malposition rotatoire de l’implant condylien dans les échecs de prothèse unicompartimentale médiale du genou

PURPOSE OF THE STUDY

Rotatory malposition of the femoral component of a unicompartmental knee arthroplasty (UKA) is a key element of mechanical failure despite proper alignment and position of the tibial implant. The purpose of this study was to describe a method for measuring femoral implant rotation on the anteroposterior x-ray using an original geometric model.

MATERIAL AND METHODS

276 medial UKA (227 non-cemented Uni Goeland, Depuy; Uni, AMP) and 49 cemented (Miller-Galante, Zimmer) were reviewed and analyzed at a mean 11 years (range 7 - 15) using the Knee Society Score. Mean objective and functional scores were 43 and 47 points preoperatively. Postoperative alignment and position of the femorotibial contact point were determined. The frontal and sagittal position of the tibial plateau was noted by the angle formed with the mechanical axis. Angles alpha and B of the femoral implant formed between the mechanical axis and the greater condylar axis and the inferior condylar line passing through the apex of the condylar convexity respectively were measured on the AP view. Frontal rotation (angle B) of the femoral implant reflected the orientation of the distal condylar cut. The frontal measurement (angle alpha) was validated using simple geometric formulas: knowing angles alpha and B and the size of the implant and the displacement of the point of contact was measured together with the true rotation of the femoral implant or anteroposterior divergence, function of the difference alpha-B which is its frontal projection and reflects the orientation of the posterior condylar cut.

RESULTS

Mean alignment was 3 degrees varus. At last follow-up, outcome was satisfactory in 81.2% of the knees (224 UKA). Mean objective and functional scores were 90 and 87 points. Angles alpha and B were parallel and orthogonal to the mechanical axis or off by less than 4 degrees external rotation (+6 degrees to -4 degrees). The mean difference alpha-B (frontal projection of the femoral implant transverse rotation) was 1 degrees. The point of contact was 4 mm or less from the middle of the tibia. Failures were observed in 18.8% of knees (52 UKA): 4 for diverse reasons and 48 for mechanical failure, including 3 with polyethylene wear without loosening (two by eccentric point of contact and neutral position and one by inverted misalignments). 45 UKA (16.3%) presented loosening of the tibial plateau alone with rotatory femoral malposition: mean a angle off 13% from the mechanical axis (+16 degrees to -9 degrees ), mean B angle off 8 degrees (+12 degrees to -8 degrees), mean alpha-B difference 5 degrees , femoral implant in square position on polyethylene with a peripheral point of contact > or 5 mm from the middle of the tibial plateau. The tibial implant exhibited mean varus of 1.5 degrees.

DISCUSSION

The main cause of failure was rotatory malposition of the condylar implant often associating frontal with transversal rotation. This increased mediolateral translation of the point of contact during knee motion causing abrasion and excessive pressure on the medial portion of the plateau. Frontal malrotation externalizes the posterior cut on the condyle tilted by the varus position, without correcting the varus of the mechanical axis in flexion. To avoid such prosthetic malrotations, three corrections must be made before making the bone cuts: cancel the external rotation of the condyles in flexion by positioning the distal cut guide in extension; re-establish the mechanical axis by reducing the internal tilt of the condyles resulting from the varus position both in extension (distal cut) and flexion (posterior cut). Improved instrumentations and reproducible techniques are needed to re-establish the 3D anatomic orientation of the femoral component, a key element for longer life of unicompartmental prostheses. This method for measuring the rotation of the femoral implant and the displacement of the point of contact using a geometric model applied to the AP view is useful for better understanding UKA failures.

Early failure of minimally invasive unicompartmental knee arthroplasty is associated with obesity

There has been increasing use of and expanding indications for unicompartmental knee arthroplasty using minimally invasive techniques. We sought to define contraindications by examining failures. We retrospectively reviewed the early results of a consecutive series of minimally invasive medial unicompartmental knee arthroplasty using two implant designs. Seventy-nine consecutive unicompartmental knee arthroplasty cases (48 instrumented and 31 noninstrumented) with minimum 2-year followup were reviewed. Patients with radiographic involvement with or without pain referable to the lateral compartment or to the patellofemoral joint were not considered candidates. Failure was defined as revision or pending revision. The average followup was 40.2 months. There were 16 failures (six tibial loosening, three plateau fracture, four persistent medial pain, one progressive arthritis, and two sepsis). Age, gender, disease severity and implant design did not predict failure. Body mass index greater than 32 did predict failure and was associated with a reduction in survivorship by log-rank and Wilcoxon analyses. These results show reliable success if obesity is considered a contraindication and technical errors resulting in fracture are eliminated. Better defining the ideal candidate for unicompartmental knee arthroplasty, with obesity remaining a contraindication, will make this a more predictable and reliable procedure.

LEVEL OF EVIDENCE

Prognostic study, Level IV-2 (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Long-term clinical results of the medial Oxford unicompartmental knee arthroplasty

The medial Oxford unicompartmental knee arthroplasty uses a fully congruent mobile bearing, varying in thickness from 3.5-11.5 mm. Impressive clinical and survival results have been achieved by the designing surgeon, but can they be reproduced by an independent center and does the use of bearings less than 6 mm thick reduce the implant's survival? Between November 1983 and May 2000, 439 medial Oxford prostheses were implanted by three surgeons in Skovde, Sweden. One hundred fourteen knees (89 patients) were reviewed clinically at a minimum of 10 years postoperatively, using the Hospital for Special Surgery knee score. Ninety-one percent of the knees had good or excellent results, with no poor results, and 82% were reported as pain free. The 15-year survival rate for the entire cohort was 93%, and for the 432 knees (344 patients) that met the current indications for using the device, the survival rate was 94%. The 10-year survival rate for bearings less than 6 mm thick was 95%, compared with 94% with bearings greater than 6 mm. The results show that an independent center can achieve excellent long-term clinical and survival results in patients implanted with the Oxford prosthesis. Survival of the implant was not reduced by the use of thin polyethylene bearings.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series--no, or historical, control group). See the Guidelines for Authors for a complete description of levels of evidence.

The use of computer-assisted surgical navigation to prevent malalignment in unicompartmental knee arthroplasty

We reviewed the outcome of 30 consecutive primary unicompartmental knee arthroplasties (UKAs) performed by a single surgeon over a 26-month period. All operations were performed to treat osteoarthritis of the medial compartment of the knee. Fifteen Allegretto (Sulzer, Winterthur, Switzerland) UKAs were implanted without computer navigation whereas 15 EIUS (Stryker-Howmedica, Allendale, NJ) UKAs were implanted using navigation. The patients were assessed clinically using the Oxford knee score and radiologically using long-leg weight-bearing films and non-weight-bearing computed tomography leg alignment films. No patients operated on were lost to follow-up. Unicompartmental knee arthroplasty performed with computer-assisted surgical navigation resulted in a more accurate and reproducible limb alignment than UKA performed without surgical navigation.

Early complications of unicompartmental knee replacement: the Droitwich experience

A total of 185 patients underwent unicompartmental knee replacements (UKR) in 206 knees over a period of 5 years. This is a retrospective look at the early results and a comment on the complications seen within the first year in these patients. Patient selection and technical error were responsible for the bulk of the complications seen within the first year post-operatively.

Fixed or mobile bearing unicompartmental knee replacement? A comparative cohort study

Unicompartmental knee replacement (UKR) for anteromedial osteoarthritis is a well-established technique. Numerous clinical outcome studies demonstrate good medium and long-term results. The aim of this prospective study was to compare the complications and short-term clinical outcome of the St. Georg Sled, a fixed bearing UKR, with the Oxford mobile bearing UKR. Outcome at 2 years was assessed using the Bristol knee score and the Oxford knee score; in addition, complications occurring since formal scoring at 2-year follow-up were recorded. A total of 47 Oxford UKRs and 57 St. Georg Sled UKRs were performed in 91 patients, none of whom were lost to follow-up. At 2 years, both outcome measures were better for the St. Georg Sled Group. The pain component of the Bristol knee score was significantly better for this group (p-value = 0.013). Three patients in the Oxford group had bearing dislocations and a further four patients required revision (mean time to revision 3.0 years). In the St. Georg Sled group, three patients required revisions (mean time to revision 3.4 years). These results demonstrate that in the short-term, the Oxford mobile bearing prosthesis has a higher re-operation rate and that the St. Georg Sled achieves better pain relief. The functional scores of the two groups were similar.

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

Between February 1996 and December 1997, forty consecutive patients with medial compartment knee arthritis were assigned randomly into two groups. All underwent a unicompartimental knee replacement. The tibial prosthesis in group A (20 knees) had a fixed bearing and in group B (20 knees) a mobile bearing. The average age was 69. Five in group A and 71 in group B. Pre-operatively, and at an average follow-up of 5.7 years, all the knees were assessed using both a dedicated UKR score specifically developed and adopted by the Italian Orthopaedic Unicompartimental Knee Replacement Users Group (GIUM) and the Knee Society Score. During surgery in group B we experienced a medial tibial plateau fracture fixed intra-operatively. One prosthesis in group A required an early revision to a TKR because of a continuous pain without any evident sign of loosening. There were no meniscal dislocations in group B. No statistically significant difference in outcome was observed between the two groups at the latest follow-up.

Medial unicompartmental knee arthroplasty with the Miller-Galante prosthesis

BACKGROUND

Unicompartmental knee arthroplasty has become a popular treatment alternative for osteoarthritis that is confined to the medial part of the knee. Excellent intermediate-term results recently have been reported in association with the Miller-Galante unicompartmental implant. The purpose of the present study was to report on our longer-term experience with the Miller-Galante medial unicompartmental knee implant.

METHODS

We evaluated the results of 113 medial unicompartmental knee arthroplasties that had been performed with use of the Miller-Galante implant in eighty-four patients between 1989 and 2000. The mean age of the patients at the time of surgery was sixty-eight years. Forty-five patients were men, and thirty-nine were women. Thirteen patients (sixteen knees) died at a mean of seven years after the index arthroplasty. No patient was lost to follow-up. The remaining seventy-one patients (ninety-seven knees) were followed for a mean of ten years and were evaluated with use of the Knee Society clinical and radiographic rating system.

RESULTS

Eleven knees were revised at a mean of four years after the index procedure. The mean Knee Society knee and function scores for the sixty-one patients (eighty-six knees) who were living and who had not had a revision improved from 48 and 53 points preoperatively to 93 and 80 points at the time of the most recent evaluation. The five and ten-year rates of survival were 94% and 90%, respectively, with revision to tricompartmental knee arthroplasty as the end point and 93% and 86%, respectively, with revision or radiographic loosening as the end point.

CONCLUSIONS

The Miller-Galante medial unicompartmental knee arthroplasty provided excellent pain relief and restoration of function in carefully selected patients and demonstrated durable implant survival at ten years.

Minimally invasive unicompartmental knee replacement with a nonimage-based navigation system

In a prospective study, two groups of 20 unicompartmental knee replacements (UKR) each were operated either using a CT-free navigation system or the conventional minimal invasive technique. Radiographic assessment of postoperative alignment was performed by long-leg coronal and lateral radiographs. The results revealed a significant difference between the two groups in favor of navigation. In the computer-assisted group, 95% of UKRs were in a range of 4-0 degrees varus (mechanical axis) compared with 70% in the conventional group. The only inconvenience was a prolonged operation time (+19 min). Due to the limited exposure, the navigation system is helpful in achieving a more precise component orientation. The danger of overcorrection is diminished by real-time information about the leg axis at each step during the operation.

Minimally invasive unicondylar knee arthroplasty for the treatment of unicompartmental osteoarthritis: an outpatient arthritic bypass procedure

This review summarizes past studies examining the progression of osteoarthritis (OA) of the knee that have led to the conclusion that the disease is slow, progressive, and typically limited to one tibiofemoral compartment. Treatments such as unicondylar knee arthroplasty (UKA) that address the single diseased compartment, preserving bone and soft tissue, seem appropriate. The senior author's minimally invasive surgical technique for performing UKA also is described.

When should we do knee replacements?

It is not known whether it is better to perform total knee replacements early or late in the course of arthritis. To examine the determinants of patient-related outcomes after knee replacement, we examined 812 patients in the Avon knee registry, in whom pre-operative and 5-year post-operative American Knee Society Scores were available. Ninety percent had a good outcome at 5 years. Women had significantly more severe disease at the time of surgery than men. Older people (>79 years) had the worst disease at the time of surgery, and made the least health gain, although their overall outcomes were still good. Those with the most severe disease at the time of operation made greater gains to those with less disease, but remained in worse health at 5 years, suggesting that earlier surgery may be preferable.

Unicompartmental knee arthroplasty for younger patients: an alternative view

Unicompartmental knee arthroplasty has been a controversial operation for the past 3 decades. Many surgeons in the 1980s and 1990s found little or no indication for the procedure. Others were enthusiastic for its use in selected patients with osteoarthritis who had unicompartmental disease. Initially, unicompartmental knee arthroplasty was thought to be appropriate for the elderly patient who was sedentary. With the advent of minimally invasive techniques, indications have expanded to include its use in younger patients (especially females) as an alternative to osteotomy or tricompartmental knee arthroplasty. Advantages over osteotomy include higher initial success, greater longevity, and fewer early complications. If done conservatively, salvage is not difficult. The extent of safe postoperative activity levels has yet to be established. Failure rates seem to be higher in heavy active males. A metallic interposition hemiarthroplasty in the form of a McKeever or Macintosh prosthesis has been available for 50 years as a unicompartmental arthroplasty, but with limited use. It still may have a role in selected patients as a conservative temporizing procedure.

Revision surgery after failed unicompartmental knee arthroplasty: a study of 35 cases

This retrospective study evaluates the results of 35 revision procedures after failed unicompartmental knee arthroplasty (UKA) in 34 patients, which were done during the period 1986 to 1996. There were 28 women and 6 men with a mean age of 71 years (range, 54-85 years). In all cases, St. Georg and Endo (W. Link, Hamburg, Germany) unicompartmental prostheses were used except 1 PCA unicondylar implant (How medica, Rutherford, NJ) and 1 Böhler unicondylar implant (Allo Pro, Baar, Switzerland). Failures most frequently were due to aseptic loosening followed by polyethylene wear. Two deep infections occurred. Revisions were performed 1 week to 11 years after UKA; 23 were required within the first 5 years. In most cases, revision was to a total knee arthroplasty. Partial component exchange was done in 9 cases. All 34 patients were evaluated clinically after exchange arthroplasty. After a mean follow-up time of 4 years (range, 1-12.2 years), we found 11 excellent, 13 good, 4 fair, and 7 poor results according to the Hospital for Special Surgery score. The fair and poor results were due to aseptic loosening of the knee prosthesis in 6 knees. One of 2 patients with deep infection needed femoral amputation. With correct indication and considerable surgical experience, UKA is still a good alternative, especially in the elderly patient.

The introduction period of unicompartmental knee arthroplasty is critical: a clinical, clinical multicentered, and radiostereometric study of 251 Duracon unicompartmental knee arthroplasties

One hundred twenty-eight consecutive knees were operated on with the Duracon unicompartmental knee arthroplasty. Of 111 knees, followed 3 years (range, 1-6 years), 109 knees were satisfactory. Two knees were revised because of progression of osteoarthritis and inexplicable pain. Radiostereometric analysis in 49 knees showed a migration of 0.6 mm after 2 years. The magnitude of migration was lower in comparison with published series. In a multicenter study comprising 4 other hospitals, there were 8 revisions in 123 operated knees. The reasons were loosening, subsidence, or fracture. These revisions were within 1 year and mostly related to operative technique. Unicompartmental knee arthroplasty is a demanding procedure that needs special experience and includes a risk of early failures during the introduction of a system.