[Revision total knee arthroplasty after unicompartmental femorotibial prosthesis: 54 cases]

Clinical outcomes of various types of revision surgeries after unicompartmental knee arthroplasty failure

PURPOSE

The advantages of unicompartmental knee arthroplasty (UKA) have led to the procedure being increasingly performed worldwide. However, revision surgery is required after UKA failure. According to the literature review, the choice of implant in revision surgery remains a debatable concern. This study analyzed the clinical results of different types of prostheses used in treating failed UKA.

MATERIALS AND METHODS

This is a retrospective review of 33 failed medial UKAs between 2006 and 2017. Demographic data, failure reason, types of revision prostheses, and the severity of bone defects were analyzed. The patients were classified into three groups: primary prosthesis, primary prosthesis with a tibial stem, and revision prosthesis. The implant survival rate and medical cost of the procedures were compared.

RESULTS

A total of 17 primary prostheses, 7 primary prostheses with tibial stems, and 9 revision prostheses were used. After a mean follow-up of 30.8 months, the survival outcomes of the three groups were 88.2%, 100%, and 88.9%, respectively (P = 0.640). The common bone defect in tibia site is Anderson Orthopedic Research Institute [AORI] grade 1 and 2a (16 versus 17). In patients with tibial bone defects AORI grade 2a, the failure rates of primary prostheses and primary prostheses with tibial stems were 25% and 0%, respectively.

CONCLUSIONS

The most common cause for UKA failure was aseptic loosening. The adoption of a standardized surgical technique makes it easier to perform revision surgeries. Primary prostheses with tibial stems provided higher stability, leading to a lower failure rate due to less risk of aseptic loosening in patients with tibial AORI grade 2a. In our experience, we advise surgeons may try using primary prostheses in patients with tibial AORI grade 1 and primary prostheses with tibial stems in patients with tibial AORI grade 2a.

Lateral unicompartmental knee arthroplasty: A review

Isolated lateral compartment osteoarthritis of the knee is a rare condition affecting approximately 1% of the population, which is ten times less common than osteoarthritis affecting only the medial compartment. Unicompartmental knee arthroplasty (UKA) has many potential advantages over total knee arthroplasty. The benefits of UKA include a smaller incision, preservation of more native tissue (including cruciate ligaments and bone), decreased blood loss, and better overall proprioception. When UKA was first introduced in the 1970s, the outcomes of medial UKA (MUKA) were poor, but the few cases of lateral UKA (LUKA) showed promise. Since that time, there has been a relative paucity of literature focused specifically on LUKA given it is a rare procedure. Refinements in patient selection criteria, implant design, and surgical technique have been made leading to increased popularity. A review of the recent literature reveals that LUKA is associated with excellent long-term clinical outcomes and implant survivorship when performed in properly selected patients. Implant design options include fixed vs mobile bearing as well as metal backed vs all polyethylene tibial component, with improved outcomes noted with fixed bearing designs. Three reasons cited for revision (i.e., fracture of the femoral component, fracture of the tibial component, and valgus malalignment) had been reported in past literature but not recently. Presently, while rare, the most common cause of failure and need for revision are osteoarthritis progression and aseptic loosening. Despite the need for an occasional revision procedure, the survivorship of LUKA is comparable to MUKA, although it should be noted that outcomes of MUKA have been notably varied. Continued pursuit of improved techniques and implant designs will continue to show LUKA to be an excellent procedure for appropriately indicated patients.

Comparison of the clinical outcomes of revision of failed UKAs to TKAs with primary TKAs: A systematic review and meta-analysis

Unicompartmental knee arthroplasty (UKA) is one of the effective surgical methods for the treatment of unicompartmental knee arthritis. When UKA fails, a revised surgery to total knee arthroplasty (TKA) is often necessary. The purpose of this study was to compare the clinical outcomes of revision of failed UKAs to TKAs with primary TKAs. The hypothesis was that the TKAs revised from UKAs had inferior clinical outcomes compared with primary TKAs.This meta-analysis was conducted in accordance with the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines. Newcastle-Ottawa Scale (NOS) proposed by the Cochrane Collaboration was used for evaluating the methodological quality of the studies. PubMed, Medline, Embase, Web of Science, and the Cochrane Library were searched to identify studies that compared the revision of UKA to TKA with primary TKA. Primary outcomes included Range of motion (ROM); Knee society score (KSS); (re-)revision rate and complications. Secondary outcomes were blood loss and length of hospital stay.A total of 8 eligible retrospective comparative studies were identified from a keyword search. Results revealed that the primary TKAs group has a better ROM (MD = -7.29, 95% CI:-14.03-0.56, P < .05), higher Knee Society Knee scores (MD = -0.54, 95% CI:-1.12-0.04, P < .05), higher Knee Society function score (MD = -0.65,95% CI:-1.25-0.06, P < .05), lower (re-)revision rate (MD = 4.15, 95% CI:2.37-7.25, P < .05) than rUKAs. There was no significant difference in postoperative complications, blood loss and length of stay between the 2 groups.Our meta-analysis revealed that compared with primary TKAs, TKAs revised from UKAs had inferior clinical outcomes.

Outcomes After Arthroscopic Evaluation of Patients With Painful Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Persistent pain after medial unicompartmental knee arthroplasty (UKA) is a prevailing reason for revision to total knee arthroplasty (TKA). Many of these pathologies can be addressed arthroscopically. The purpose of this study is to examine the outcomes of patients who undergo an arthroscopy for any reason after medial UKA.

METHODS

A query of our practice registry revealed 58 patients who had undergone medial UKA between October 2003 and June 2015 with subsequent arthroscopy. Mean interval from medial UKA to arthroscopy was 22 months (range 1-101 months). Indications for arthroscopy were acute anterior cruciate ligament tear (1), arthrofibrosis (7), synovitis (12), recurrent hemarthrosis (2), lateral compartment degeneration including isolated lateral meniscus tears (11), and loose cement fragments (25).

RESULTS

Mean follow-up after arthroscopy was 49 months (range 1-143 months). Twelve patients have been revised from UKA to TKA. Relative risk of revision after arthroscopy for lateral compartment degeneration was 4.27 (6 of 11; 55%; P = .002) and for retrieval of loose cement fragments was 0.05 (0 of 25; 0%; P = .03). Relative risk for revision after arthroscopy for anterior cruciate ligament tear, arthrofibrosis, synovitis, or recurrent hemarthrosis did not meet clinical significance secondary to the low number of patients in these categories.

CONCLUSION

The results of this study suggest that arthroscopic retrieval of cement fragments does not compromise UKA longevity. However, arthroscopy for lateral compartment degradation after UKA, while not the cause of revision, appears to be an ineffective treatment and predicts a high risk of revision to TKA regardless of its relative radiographic insignificance.

Unicompartmental Knee Arthroplasty: Modes of Failure and Conversion to Total Knee Arthroplasty

Despite the excellent success rates of the modern unicompartmental knee arthroplasty (UKA), results of knee replacement registries still shows a relatively high revision and failure rate for UKA, especially when compared with traditional total knee arthroplasty (TKA). Bearing dislocation continues to be advocated as the predominant mechanism of failure in mobile UKA, whereas polyethylene wear and aseptic loosening remains the main cause of failure of fixed UKA. Degeneration of the unreplaced compartments has been reported in both mobile and fixed designs. When the revision is required, most of failed UKAs are converted to TKAs. Surgical challenges of the UKA revision, and outcomes of UKA converted to TKA are still debated in literature.

Is isolated insert exchange a valuable choice for polyethylene wear in metal-backed unicompartmental knee arthroplasty?

PURPOSE

The aim of this study was to evaluate the clinical outcome and survival rate after isolated liner exchange for polyethylene (PE) wear in well-fixed metal-backed fixed-bearing unicompartmental knee arthroplasty (UKA).

METHODS

Twenty medial UKAs in 19 patients [mean age 68.7 years ± 8.7 (range 48.5-81.5 years)] operated on for a direct PE liner exchange after isolated PE wear between 1996 and 2010 in two institutions were retrospectively reviewed. The mean delay between the index operation and revision was 8.2 years ± 2.6 (range 4.8-12.8 years). A four-level satisfaction questionnaire was used, and clinical outcomes were assessed using Knee Society scores (KSS) and range of motion (ROM) evaluation. Radiological evaluation analysed the position of the implants and progression of the disease. Survival rate of the implants was evaluated using Kaplan-Meier analysis with two different end-points.

RESULTS

At the last follow-up [mean 6.8 years ± 5.2 (range 1.1-15.9 years)], 15 patients (79 %) were enthusiastic or satisfied. KSS improved from 73.4 to 86.4 points (p = 0.01) and function from 58.9 to 89.2 points (p < 0.001). ROM at last FU was 126.5° ± 10.3°. The survival rate at 12 years considering "revision for any reason" as the end-point was 71.3 ± 15.3 %, and the survival rate at 12 years considering "revision of UKA to TKA" as the end-point was 93.3 ± 6.4 %.

CONCLUSION

Isolated liner exchange for PE wear in well-fixed metal-backed fixed-bearing UKA represents a valuable treatment option in selective patients with durable improvement of clinical outcomes without compromising any future revision.

LEVEL OF EVIDENCE

Retrospective therapeutic study, Level IV.

Outcomes of Unicompartmental Knee Arthroplasty After Aseptic Revision to Total Knee Arthroplasty: A Comparative Study of 768 TKAs and 578 UKAs Revised to TKAs from the Norwegian Arthroplasty Register (1994 to 2011)

BACKGROUND

The general recommendation for a failed primary unicompartmental knee arthroplasty (UKA) is revision to a total knee arthroplasty (TKA). The purpose of the present study was to compare the outcomes, intraoperative data, and mode of failure of primary UKAs and primary TKAs revised to TKAs.

METHODS

The study was based on 768 failed primary TKAs revised to TKAs (TKA→TKA) and 578 failed primary UKAs revised to TKAs (UKA→TKA) reported to the Norwegian Arthroplasty Register between 1994 and 2011. Patient-reported outcome measures (PROMs) including the EuroQol EQ-5D, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and visual analog scales assessing satisfaction and pain were used. We performed Kaplan-Meier and Cox regression analyses adjusting for propensity score to assess the survival rate and the risk of re-revision and multiple linear regression analyses to estimate the differences between the two groups in mean PROM scores.

RESULTS

Overall, 12% in the UKA→TKA group and 13% in the TKA→TKA group underwent re-revision between 1994 and 2011. The ten-year survival percentage of UKA→TKA versus TKA→TKA was 82% versus 81%, respectively (p = 0.63). There was no difference in the overall risk of re-revision for UKA→TKA versus TKA→TKA (relative risk [RR] = 1.2; p = 0.19), or in the PROM scores. However, the risk of re-revision was two times higher for TKA→TKA patients who were greater than seventy years of age at the time of revision (RR = 2.1; p = 0.05). A loose tibial component (28% versus 17%), pain alone (22% versus 12%), instability (19% versus 19%), and deep infection (16% versus 31%) were major causes of re-revision for UKA→TKA versus TKA→TKA, respectively, but the observed differences were not significant, with the exception of deep infection, which was significantly greater in the TKA→TKA group (RR = 2.2; p = 0.03). The surgical procedure of TKA→TKA took a longer time (mean of 150 versus 114 minutes) and more of the procedures required stems (58% versus 19%) and stabilization (27% versus 9%) compared with UKA→TKA.

CONCLUSIONS

Despite TKA→TKA seeming to be a technically more difficult surgical procedure, with a higher percentage of re-revisions due to deep infection compared with UKA→TKA, the overall outcomes of UKA→TKA and TKA→TKA were similar.

Bicompartmental knee arthroplasty

Total knee arthroplasty (TKA) is the most worldwide practiced surgery for knee osteoarthritis and its efficacy is mightily described by literature. Concerns about the invasiveness of TKA let the introduction of segmental resurfacing of the joint for younger patients with localized osteoarthritis. Bone stock sparing and ligaments preservation are the essence of both unicompartmental knee arthroplasty (UKA) and bicompartmental knee arthroplasty (BKA). Advantages related to BKA are the respect of knee biomechanics, lower complications rates, shorter hospital stay, faster rehabilitation. Moreover, in case of failure of the first implant the conversion to TKA is undemanding and can be compared to a standard prosthesis. Our experience suggest that BKA is a reliable technique in selected cases and especially younger people with higher functional requests can favourably profit from it. Although those results are encouraging, we still need further prospective, randomized, long-term studies to finally assess BKA indications and outcomes.

Are Revisions of Unicompartmental Knee Arthroplasties More Like a Primary or Revision TKA?

If revision is required, most unicompartmental arhroplasties (UKAs) are converted to total knee arthroplasties (TKAs) and conflicting results regarding surgical complexity and outcome have been reported in publications. 48 UKAs converted to a TKA between 1998 and 2009 were matched based on age, gender, and body mass index, pre-operative Knee Society Score, length of follow-up, and date of the index surgery to 48 primary TKAs and 48 revision TKAs. Surgical characteristics, clinical outcomes, and complications were compared at a mean follow-up of 7 ± 4 years. Even if a revision of UKA is technically less demanding than a revision TKA, functional scores, quality of life, complications and survival rate after revision UKA are more comparable to a revision than primary TKA.

[Medial unicondylar knee replacement]

BACKGROUND

Unicondylar knee replacement (UKA) is a viable alternative to high tibial osteotomy (HTO) and total knee replacement in the treatment of medial osteoarthritis of the knee. With the correct indication, the results of UKA and HTO are comparable.

RESULTS

In comparison with the results of total knee replacements, UKA leads to faster rehabilitation, superior postoperative range of motion, and higher postoperative activity levels. Despite the excellent long-term results, the survival rate is inferior to the results of total knee replacement. The major causes for failure are progression of osteoarthritis in the lateral and patellofemoral joint as well as the loosening of the tibial component.

CONCLUSION

The conversion to total knee replacement can mostly be performed without problems. However, the expected results are inferior to primary total knee replacement and the reported revision rates are higher.

Chronic infection of unicompartmental knee arthroplasty: one-stage conversion to total knee arthroplasty

BACKGROUND

The main reasons for revision of unicompartmental knee arthroplasty (UKA) are loosening, wear, extension of osteoarthritis to another compartment, and infection. There have been no studies of the management of infected UKA, whose incidence varies from 0.2% to 1%. Our objective was to describe infection-related and mechanical outcomes of chronic UKA infection managed by one-stage conversion to total knee arthroplasty (TKA).

PATIENTS AND METHODS

Consecutive patients with chronic UKA infection managed by one-stage conversion to TKA between January 2003 and December 2010 were included in a retrospective single-center study. All patients also received appropriate dual antibiotic therapy intravenously for 6 weeks then orally for 6 additional weeks.

RESULTS

During the study period, among 233 cases of infected knee arthroplasty managed at our center, 9 met the study inclusion criteria. The UKA was medial in 6 patients, lateral in 2, and patellofemoral in 1. Median age was 67 years (range, 36-83 years) and median infection duration was 9months. In 5 patients, previous treatment with synovectomy, joint lavage, and antibiotics had failed. The following bacteria were identified: oxacillin-susceptible Staphylococci, n=6 (S. epidermidis, n=4; S. capitis, n=1; and S. lugdunensis, n=1); nutritionally deficient Streptococcus, n=1; Enterococcus durans, n=1; and Escherichia coli, n=1. Median follow-up was 60 months (range, 36-96 months). No patient experienced recurrent infection or required revision surgery for infection. No medical complications limiting the use of appropriate antibiotic therapy were recorded. The mean preoperative knee and function scores were 60 and 50, respectively; corresponding mean postoperative values were 75 and 65, respectively.

DISCUSSION

UKA infection involves both the prosthesis and the native cartilage, neither of which can be treated conservatively in chronic forms. After identification of the causative organism, synovectomy and joint excision followed by same-stage TKA and combined with appropriate antibiotic therapy for 3 months is effective.

LEVEL OF EVIDENCE

IV, retrospective cohort study.

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.

Assessing patient-oriented results after revision total knee arthroplasty

BACKGROUND

Revision total knee arthroplasties (TKA) have been performed with increasing frequency over the last 25 years.

METHODS

In this study, we retrospectively analyzed 78 patients who underwent 78 revision TKAs during the years 2003–2007 with an average follow-up of 81 months (range 60–108 months). All patients were treated with a standard rotating hinge prosthesis (TC3, DePuy, Warsaw, IN, USA) due to significant instability. We evaluated the postoperative results using the Knee Society clinical rating system and the WOMAC rating system.

RESULTS

Clinical results revealed significant improvements in both scores. Complications occurred in almost one-third of the cases, with a reoperation rate of 26 %.

CONCLUSION

Our mid-term findings show that revision TKAs lead to an improvement in patient-perceived outcomes of physical variables. While revision TKA is a useful option for patients, procedure-associated complications should not be neglected. During the course of the procedure, it is important to collect patient-oriented data and focus on responsive and valid scores.

Revision from unicompartmental to total knee replacement: the clinical outcome depends on reason for revision

Although it has been suggested that the outcome after revision of a unicondylar knee replacement (UKR) to total knee replacement (TKR) is better when the mechanism of failure is understood, a comparative study on this subject has not been undertaken. A total of 30 patients (30 knees) who underwent revision of their unsatisfactory UKR to TKR were included in the study: 15 patients with unexplained pain comprised group A and 15 patients with a defined cause for pain formed group B. The Oxford knee score (OKS), visual analogue scale for pain (VAS) and patient satisfaction were assessed before revision and at one year after revision, and compared between the groups. The mean OKS improved from 19 (10 to 30) to 25 (11 to 41) in group A and from 23 (11 to 45) to 38 (20 to 48) in group B. The mean VAS improved from 7.7 (5 to 10) to 5.4 (1 to 8) in group A and from 7.4 (2 to 9) to 1.7 (0 to 8) in group B. There was a statistically significant difference between the mean improvements in each group for both OKS (p = 0.022) and VAS (p = 0.002). Subgroup analysis in group A, performed in order to define a patient factor that predicts outcome of revision surgery in patients with unexplained pain, showed no pre-operative differences between both subgroups. These results may be used to inform patients about what to expect from revision surgery, highlighting that revision of UKR to TKR for unexplained pain generally results in a less favourable outcome than revision for a known cause of pain.

Results of a French multicentre retrospective experience with four hundred and eighteen failed unicondylar knee arthroplasties

PURPOSE

By means of a multicentre retrospective study based on the failure of 418 aseptic unicondylar knee arthroplasties (UKA) our aims were to present the different types of revision procedure used in failed UKAs, to establish a clear operative strategy for each type of revision and to better define the indications for each type of revision.

METHODS

Aseptic loosening was the principal cause of failure (n = 184, 44%) of which 99 cases were isolated tibial loosening (23.5 % of the whole series and 54% of all loosening), 25 were isolated femoral loosening (six and 13.6%) and 60 were both femoral and tibial loosening (14.3 and 32.6%). The next most common causes of failure were progression of arthritis (n = 56, 13.4%), polyethylene wear (n = 53, 12.7%), implant positioning errors (n = 26), technical difficulties (n = six) and implant failure (n = 16, 3.8% of cases). Data collection was performed online using OrthoWave software (Aria, Bruay Labuissiere, France), which allows collection of all details of the primary and revision surgery to be recorded.

RESULTS

A total of 426 revisions were performed; 371 patients underwent revision to a total knee arthroplasty (TKA) (87%), 33 patients (7.7%) were revised to an ipsilateral UKA, 11 (2.6%) patients underwent contralateral UKA (ten) or patellofemoral arthroplasty (one) and 11 patients (2.6%) underwent revision without any change in implants.

CONCLUSIONS

Before considering a revision procedure it is important to establish a definite cause of failure in order to select the most appropriate revision strategy. Revision to a TKA is by far the most common strategy for revision of failed UKA but by no means the only available option. Partial revisions either to an alternative ipsilateral UKA or contralateral UKA are viable less invasive techniques, which in carefully selected patients and in experienced hands warrant consideration.

Patient-specific guide for revision of medial unicondylar knee arthroplasty to total knee arthroplasty: beneficial first results of a new operating technique performed on 10 patients

BACKGROUND AND PURPOSE

Unicompartmental to total knee arthroplasty revision surgery can be technically demanding. Joint line restoration, rotation, and augmentations can cause difficulties. We describe a new technique in which single-way fitting guides serve to position the knee system cutting blocks.

METHOD

Preoperatively, images of the distal femur and proximal tibia are taken using CT scanning. These images are used to create a patient-specific guide that fits in one single position on the contours of the bone and the prosthesis in situ. The guides are fixed with pins and then removed. The pins determine the position of the cutting blocks. 10 consecutive revisions were performed using this technique.

RESULTS

All guides fitted well. 7 of 10 femoral prostheses were within the desired AP and sagittal angle ± 3°. However, 1 proximal tibia did not have enough bone stock on the medial plateau for adequate fixation of the guide, so conversion to intramedular referencing was performed. This was to be expected after the preoperative planning. All tibial components were within the desired AP angle ± 3° and 7 of 10 were within the desired sagittal angle. Hip-knee-ankle angle was within 0 ± 3° in 8 of 10 cases.

INTERPRETATION

This new technique makes preoperative planning and execution of this plan during surgery less demanding. Problems such as the need for augmentations can be predicted at the preoperative planning. The instrumentation must be redesigned in order to make this technique work in cases where there is minimal bone stock present.

Lateral unicompartmental knee arthroplasty: a review

Lateral unicondylar knee arthroplasty (UKA) has been utilized as a treatment for isolated lateral tibiofemoral osteoarthritis (OA) since the first description of UKA in the 1970s. To date, there remains some controversy on UKA procedures. As indications for lateral UKA are usually rare, surgeon experience seems to be the key factor for a successful intervention. Better understanding of biomechanics of the knee joint, recent developments in prosthesis design, surgical techniques and indications may add to improved outcomes of lateral UKA. Alternatives that are applied to treat lateral tibiofemoral OA include arthroscopic interventions, osteotomies and total knee arthroplasty (TKA). In comparison with TKA, potential advantages of UKA include a minimally or less invasive approach, less bone resection, preservation of the cruciate ligaments, preservation of the medial tibiofemoral and the patellofemoral compartments, shorter rehabilitation, and physiological knee kinematics. This review aims to summarize the current concepts of implant designs as well as indications and contraindications for lateral UKA. The literature will be presented and discussed as well as results and realistic expectations on both the surgeon's and the patient's side. Alternative treatments and future concepts for lateral UKA will be presented.

UKA in combination with PFR at average 12-year follow-up

INTRODUCTION

Safety and efficacy of unicompartmental knee arthroplasty (UKA) has been shown in large patient series. Patellofemoral replacement (PFR) is known to be a viable solution to end-stage patellofemoral arthritis. Bicompartmental osteoarthritis (OA) affecting the medial tibio-femoral and the patello-femoral compartment (medio-patellofemoral OA) is often treated with total knee arthroplasty (TKA). It was hypothesized that medio-patellofemoral OA can successfully be treated with bicompartmental arthroplasty.

METHOD

In a retrospective approach nine patients who had received UKA in combination with PFR were included into the study. Intact ACL and lateral compartment were conditions for the indication. Patients were clinically examined including clinical scores (KSS and WOMAC) and radiographies were evaluated. Satisfaction of patients was recorded under four categories.

RESULTS

Average follow-up after bicompartmental arthroplasty was 11.8 ± 5.4 years (4-17 years). Among the nine patients there were eight females and one male at an average age at operation of 64 ± 5 years. No surgical revisions were required following bicompartmental arthroplasty. The KSS score increased from a preoperative 68.8 ± 26.2 to 175.5 ± 22.9 at latest follow-up (p = 0.002). WOMAC was 18.3 ± 8.6 at latest follow-up. All patients included were satisfied (n = 3) or very satisfied (n = 6) with the outcome of this surgical procedure.

CONCLUSION

This small case series shows that a bicompartmental arthroplasty can be a successful approach to prevent or postpone TKA. However, this intervention is technically demanding and requires experience in both UKA and PFR.

Revision of 33 unicompartmental knee prostheses using total knee arthroplasty: strategy and results

The purpose of this study was twofold: to evaluate the radiological and clinical results of 33 total knee arthroplasties (TKA) implanted between January 1993 and March 2005, to replace failed medial unicompartmental knee arthroplasty (UKA), and to develop a strategy to deal with bone defects in the tibial plateau. Failure was due to: tibial loosening (15 cases), femoral loosening (five cases), femoral and tibial loosening (two cases), polyethylene wear (five cases), lateral compartment osteoarthritis (two cases), patellofemoral osteoarthritis (two cases), laxity and PE dislocation (one case), and sepsis in one case. In 12 cases the tibial bone defect was filled with a metallic wedge, in seven we used an allograft (femoral head), and in one we used both. We report the results of 27 cases (five patients died and one was lost to follow-up). The mean follow-up was 73+/-41.7 months (range, 8-153) and the global IKS score was 166.72+/-21.3 points (range, 128-200). X-rays of the eight allografts showed osteointegration in all cases and no radiolucency was noted.

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.

[Is computer navigation a useful tool in unicompartmental knee arthroplasty? A pilot cadaver study]

We conducted this pilot cadaver study to investigate whether the use of a navigation system during minimally invasive unicompartmental knee arthroplasty leads to more consistent results than the conventional hand-guided technique. We describe the accuracy of implant positioning in using standard instrumentation and computer navigation. Radiographic assessment showed that accurate component placement was achieved using both methods. These results were not statistically significant. The computer navigated femoral component placement without intramedullary (IM) rod was as accurate as the conventional method with IM rod. The study showed that computer navigation can produce accurate results even without an intramedullary rod. Image guidance can maintain the accuracy of the standard instrumentation and enhance 3D vision and the intraoperative orientation of the surgeon.