Tibial plateau stress fracture: a complication of unicompartmental knee arthroplasty using 4 guide pinholes

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Tibial Lateral Condyle Fracture After Cementless Oxford Unicompartmental Knee Arthroplasty (UKA): A Report of Four Cases

Cementless unicompartmental knee arthroplasty (UKA) has a lower rate of radiolucency in postoperative follow-up than cemented UKA. However, the rate of tibial plateau fracture, one of the complications, has been reported to be higher in cementless UKA than in cemented UKA. We report four cases of postoperative tibial lateral condyle fractures after cementless Oxford UKA. Four patients underwent cementless Oxford UKA. Immediate postoperative radiography and CT showed no fracture lines. At five to six weeks postoperatively, MRI showed a fracture line from the intersection of the longitudinal and transverse tibial osteotomies through the lateral pinhole to the end of the lateral tibial diaphysis. At three months, bone union was observed without surgical treatments. Lateral tibial fracture after cementless Oxford UKA has a good clinical course without the need for surgical intervention. Medial fractures should thus be more actively prevented. MRI is useful for less symptomatic tibial lateral condyle fractures.

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

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

Effect of Tibial Slope on Coronal Alignment in Total Knee Arthroplasty

Malalignment of total knee arthroplasty (TKA) components affects function and survivorship. Common practice is to set coronal alignment prior to adjusting slope. With improper jig placement, adjustment of the slope may alter coronal alignment. The purpose of this study was to quantify the change in coronal alignment with increasing posterior tibial slope while comparing two methods of jig fixation. A prospective consecutive series of 100 patients underwent TKA using computer navigation. Fifty patients had the extramedullary cutting jig secured proximally with one pin and 50 patients had the jig secured proximally with two pins. Coronal alignment (CA) was recorded with each increasing degree of posterior slope (PS) from 0 to 7 degrees. Mean CA and change in CA were compared between cohorts. Utilizing one pin, osteotomies drifted into varus with an average change in CA of 0.34 degrees per degree PS. At 4 degrees PS, patients started to have >3 degrees of varus with 12.0% having >3 degrees of varus at 7 degrees PS. Utilizing two pins, osteotomies drifted into valgus with an average change of 0.04 degrees in CA per degree PS. No patients in the two-pin cohort fell outside 3 degrees varus/valgus CA. CA was significantly different at all degrees of PS between the cohorts. Changes in PS influenced CA making verification of tibial cut intraoperative critical. Use of >1 pin and computer navigation were beneficial to prevent coronal plane malalignment. This relationship may explain why computer navigation has been shown to improve alignment as well as survivorship and outcomes in some patients, especially those <65 years.

Periprosthetic Tibial Plateau Fractures After Unicompartmental Knee Arthroplasty Are Successfully Treated With Open Reduction and Internal Fixation

Periprosthetic tibial fractures after unicompartmental knee arthroplasty (UKA) are rare but devastating events. Given the relative infrequency of these injuries, treatment strategies are not well defined. The goal of this retrospective case series is to report the findings for a series of patients who underwent open reduction and internal fixation (ORIF) of periprosthetic fracture after UKA, including radiographic alignment, Knee Society Score (KSS), and failure rate. Patients were identified by the International Classification of Diseases code for periprosthetic tibial plateau fractures. Electronic medical records and radiographs were retrospectively reviewed. Fracture patterns and coronal and sagittal alignment of UKA components were measured on radiographs. Clinical outcomes, including range of motion assessment, visual analog scale pain score, and KSS, were collected at final follow-up. Eight patients satisfied the inclusion criteria for this study. Fractures occurred at a median of 14 days (range, 5-52 days) after UKA, and all showed a vertical shear pattern that exited at the meta-diaphyseal junction. Of the 8 fractures, 7 (87.5%) healed to radiographic and clinical union after the initial ORIF. One patient required reoperation for hardware failure. Mean visual analog scale pain score and KSS at final follow-up were 3 and 85±14, respectively. Periprosthetic tibial plateau fractures after UKA commonly occur as a vertical shear fracture exiting at the metadiaphyseal junction. The use of ORIF with a 3.5-mm plate in buttress mode is a reliable method for treatment of these fractures. Restoration of alignment and motion is achievable, but residual pain may affect patient-reported outcome scores. [Orthopedics. 2022;45(5):287-292.].

Augmented reality-aided unicompartmental knee arthroplasty

Purpose

To illustrate a surgical technique for augmented reality (AR)-assisted unicompartmental knee arthroplasty (UKA) and report preliminary data.

Methods

We developed an AR-based navigation system that enables the surgeon to see the tibial mechanical axis superimposed on the patient’s leg in addition to the tibial cutting angle. We measured the tibial resection angle in 11 UKAs using postoperative radiographs and calculated the absolute difference between preoperative target angle and postoperative measured angle. The target angle was determined for each patient: mean values were 0.7° ± 1.0° varus in coronal alignment and 5.3° ± 1.4° posterior slope in sagittal alignment.

Results

The angles measured on postoperative radiographs were 2.6° ± 1.2° varus in the coronal plane and 4.8° ± 2.5° posterior slope in the sagittal plane. The absolute differences between the target and measured angles were 1.9° ± 1.5° in coronal alignment and 2.6° ± 1.2° in sagittal alignment. No patients experienced complications, including surgical site infection and periprosthetic fracture.

Conclusion

The AR-based portable navigation system may provide passable accuracy in terms of proximal tibial resection during UKA.

Level of Evidence

IV

Periprosthetic fractures after medial unicompartmental knee arthroplasty: a narrative review

INTRODUCTION

On rare occasions, fractures of the tibial plateau may occur after uni-compartmental knee arthroplasty (UKA) and account for 2% of total UKA failures. The purpose of this narrative review is to identify and discuss potential risk factors that might lead to prevention of this invalidating complication.

MATERIALS AND METHODS

Electronic database of Pubmed, Scopus, Cochrane and Google Scholar were searched. A total of 457 articles related to the topic were found. Of those, 86 references were included in this narrative review.

RESULTS

UKA implantation acts as a stress riser in the medial compartment. To avoid fractures, surgeons need to balance load and bone stock. Post-operative lower limb alignment, implant positioning, level of resection and sizing of the tibial tray have a strong influence on load distribution of the tibial bone. Pain on weight-bearing signals bone-load imbalance and acts as an indicator of bone remodeling and should be a trigger for unloading. The first three months after surgery are critical because of transient post-operative osteoporosis and local biomechanical changes. Acquired osteoporosis is a growing concern in the arthroplasty population. Split fractures require internal fixation, while subsidence fractures differ in their management depending of the amount of bone impaction. Loose implants require revision knee arthroplasty.

CONCLUSION

Peri-prosthetic fracture is a rare, but troublesome event, which can lead to implant failure and revision surgery. Better knowledge of the multifactorial risk factors in association with a thorough surgical technique is key for prevention.

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.

Proximal tibial bone loss in the first 2 years after unicondylar knee arthroplasty: Anatomical pattern, predictors and clinical correlation

BACKGROUND

Tibial stress fracture, anteromedial bone pain, and early subsidence could occur after unicondylar knee arthroplasty (UKA). The change in metaphyseal tibial bone density (MTBD) in the coronal and sagittal planes after UKA might be a contributing factor, but this has rarely been investigated. The aim of this study was to assess the regional and temporal change in MTBD in the coronal and sagittal planes in the first 2 years after UKA.

METHODS

Patients with fixed-bearing medial UKA were recruited. The change in MTBD in the first 24 months after UKA using digital radiological densitometry (DRD) was measured. Potential predictors and clinical correlations were analyzed.

RESULTS

Eighty-four cases (female 60%) were selected for review. The follow up time was 63 (±17) months. Anterior and medial regions had the largest proportion of cases with MTBD reduction (90-97%, P < 0.05). Reduction was largest at anterior and medial regions (21-29%, P < 0.05) and smallest at posterior and lateral regions (5-15%, P < 0.05). Maximal reduction occurred at 12 months for the medial region and 24 months for the anterior region. MTBDs of both regions were not significantly influenced by any confounding factors. Significant correlation was found between medial MTBD and Function Score at 6 months.

CONCLUSIONS

Bone loss in a zonal pattern occurs in the first 2 years after UKA with the largest loss in the anterior region below the tibial tray. It is not affected by body mass index, perioperative alignment, or angle of correction. This suggests a physiological response to trauma other than a mechanical response to the change in bone strain.

Medial Tibial Plateau Stress Fracture Following Navigated Total Knee Arthroplasty: Two Case Reports

Case series

Patients: Female, 47-year-old • Female, 58-year-old

Final Diagnosis: Periprosthetic fracture

Symptoms: Medial knee pain • varus deformity

Medication: —

Clinical Procedure: —

Specialty: Orthopedics and Traumatology

Anterior cruciate ligament avulsion fracture following medial unicompartmental knee arthroplasty: A case report

Introduction

Anterior cruciate ligament (ACL) avulsion fracture after unicompartmental knee arthroplasty (UKA) has not been reported until recently. We describe a case of ACL avulsion fracture that developed after medial UKA.

Case presentation

A 57-year-old woman underwent UKA for right medial compartment osteoarthritis. She developed knee pain and swelling at 2 weeks after UKA, and radiographs showed an ACL avulsion fracture at 3 weeks after UKA. After conservative treatment failed, the fracture was fixed using screws. After 5 months from internal fixation, bone union was confirmed, and the screws were removed. At 16 months after removing screws, there was no further complication.

Discussion

The patient did not exhibit a fracture on the radiograph taken immediately after UKA. We carefully re-examined the radiographs and observed a 5-mm horizontal cement shadow on the lateral side of the tibial component. It is thought that excessive lateral resection of the proximal tibia during UKA may have resulted in a micro fracture and this outcome. In the present case, the posterior slope angle of the tibial component measured postoperatively was 11.5 degrees. The angle of more than 7 degrees along with excessive horizontal resection of the proximal tibia probably increased load on the ACL.

Conclusion

If patients exhibit a horizontal cement shadow near the tibial component and a higher posterior slope angle of the tibial component on the radiograph after UKA, surgeons should be aware of possible ACL avulsion fracture and perform additional radiological examinations in patients with continuous knee pain and swelling.

An Early Periprosthetic Fracture of a Cementless Oxford Unicompartmental Knee Arthroplasty: Risk Factors and Mitigation Strategies

Introduction:

The cementless Oxford partial knee arthroplasty is associated with low perioperative complications and good long-term survival rates. However, perioperative fractures remain a serious morbidity for patients.

Case Report:

This case report describes an early post-operative tibial periprosthetic fracture through the keel slot, which we believe may be contributed by the deep implant keel design and the presence of a narrow metaphysis in the Asian knee. The patient subsequently underwent a revision total knee replacement and fixation of the periprosthetic fracture.

Conclusion:

This paper discusses the ways to identify patients at high risk of developing periprosthetic fractures and to minimize such occurrences, including adopting a modified tibial preparation, doing precise saw cuts, and considering a cemented tibial implant.

Tibial cutting guide (resector) holding pins position and subsequent risks of periprosthetic fracture in unicompartmental knee arthroplasty: a finite element analysis study

BACKGROUND

Periprosthetic fracture of the tibia after unicompartmental knee arthroplasty has been reported to be associated with excessive pin holes created for stabilization of the cutting guide. However, fractures have also been reported in cases using two pins as in the method suggested by the manufacturer. It is currently unclear whether variations in pinhole positions make a difference in proximal tibial fracture risk.

METHODS

Finite element models were constructed using Chinese female bone computed tomography images, with bone cuts made according to the surgical steps of implanting a fixed bearing unicompartmental arthroplasty. Four combinations of pinholes (pins placed more closely to the medial tibial cortex or centrally along the mechanical axis as allowed by the tibial cutting guide) created for tibial cutting guide placement were tested by finite element analyses. Testing loads were applied for simulating standing postures. The maximum von Mises stress on the tibial plateau was evaluated.

RESULTS

Pinhole placed close to the medial edge of the proximal tibial plateau is associated with the highest stress (27.67 Mpa) and is more likely to result in medial tibial fracture. On the contrary, pinhole placed along the central axis near the tibial tuberosity has the lowest stress (1.71 Mpa) and reflects lower risk of fracture.

CONCLUSION

The present study revealed that placing tibial cutting guide holding pins centrally would lower the risks of periprosthetic fracture of the medial tibial plateau by analyzing the associated stress in various pin hole positions using finite element analysis.

A Novel Technique for Varus Tibial Cutting for Oxford Unicompartmental Knee Arthroplasty

To reduce the stress on the medial tibial cortex and to decrease the risk of fracture, a varus cut of the tibia appears to be a reasonable alternative to the orthogonal cut by conventional methods. We present a new instrument and procedure, which enables a varus tibial cut for Oxford unicompartmental knee arthroplasty. We used a custom-made, slidable fixator instead of the standard fixator to set the extramedullary rod on the leg. We also made a numeric formula and a chart to arrange the varus cutting angle using the length of the mediolateral shift of the distal end and the longitudinal extension length of the extramedullary tibial rod. A varus cut up to 4.5° can be controlled. This technique is a simple and useful means of obtaining a varus tibial cut for Oxford unicompartmental knee arthroplasty.

Dependence of knee range of motion on the alignment of femoral and tibial components after medial unicompartmental knee arthroplasty

INTRODUCTION

This study evaluated the relationship between postoperative knee flexion angles and the position of femoral and tibial components in unicompartmental knee arthroplasty (UKA).

MATERIALS AND METHODS

Eighteen patients (a total of 22 knees: three men, four knees; 15 females, 18 knees) who underwent navigation-assisted UKA were included. Pre- and postoperative computed tomography images were applied on 3D software, which were matched and used to calculate the position of femoral and tibial components. Correspondingly, we investigated the relationship between the knee range of motion (ROM) at 1-year postoperative follow-up and the position of femoral and tibial components.

RESULTS

At 1-year post-UKA, the knee flexion angle was associated with the posterior flexion angle of tibial components. This particular angle was significantly greater in the group with equal or greater postoperative knee ROM compared to preoperative ROM (5.2 ± 2.1°) than in the group with less postoperative knee ROM compared to preoperative ROM (2.6 ± 1.6°, p < 0.01). There was no significant difference between both groups in the femoral component position, preoperative posterior slope of the medial tibial plateau, change in the pre- to postoperative posterior tibial slope, and postoperative knee society score.

CONCLUSION

The posterior flexion angle of the tibial component affected the improvement/deterioration of the postsurgery knee flexion angle in navigation-assisted UKA. For improved outcomes after UKA using navigation systems, surgeons should aim to achieve a 5° to 8° posterior flexion angle of the tibial component.

What Is the Critical Tibial Resection Depth During Unicompartmental Knee Arthroplasty? A Biomechanical Study of Fracture Risk

BACKGROUND

Fracture after medial unicompartmental knee arthroplasty (UKA) is a rare complication. Biomechanical studies evaluating association between depth of resection and maximum load to failure are lacking. The purpose of this study is to establish the relationship between depth of resection of the medial tibial plateau and mean maximum load to failure.

METHODS

Medial tibial resections were performed from 2 to 10 mm in 25 standardized fourth-generation Sawbones composite tibias (Sawbones, Vashon Island, Washington). A metal-backed tibial component with a 9-mm polyethylene bearing was used (Stryker PKR). Tibias were mounted on a biomechanical testing apparatus (MTESTQuattro) and axially loaded cyclically 10 times per cycle and incrementally increased until failure occurred.

RESULTS

Load to failure was recorded in 25 proximal tibia model samples after medial UKA using sequential resections from 2 to 10 mm. Analysis of variance testing identified significant differences in mean maximum load to failure between groups (P = .0003). Analysis of regression models revealed a statistically significant fit of a quadratic model (R² = 0.59, P = .0001). The inflection point of this quadratic curve was identified at 5.82 mm, indicating that the maximum load to failure across experimental models in this study began to decline beyond a resection depth of 5.82 mm.

CONCLUSION

In this biomechanical model, medial tibial resections beyond 5.82 mm produced a significantly lower mean load to failure using a quadratic curve model. Resections from 2 to 6 mm showed no significant differences in mean load to failure. Identification of the tibial resection depth at which the mean load to failure significantly decreases is clinically relevant as this depth may increase the risk of periprosthetic fracture after a medial UKA.

Tibial shape and size predicts the risk of tibial plateau fracture after cementless unicompartmental knee arthroplasty in Japanese patients

AIMS

Cementless unicompartmental knee arthroplasty (UKA) has advantages over cemented UKA, including improved fixation, but has a higher risk of tibial plateau fracture, particularly in Japanese patients. The aim of this multicentre study was to determine when cementless tibial components could safely be used in Japanese patients based on the size and shape of the tibia.

METHODS

The study involved 212 cementless Oxford UKAs which were undertaken in 174 patients in six hospitals. The medial eminence line (MEL), which is a line parallel to the tibial axis passing through the tip of medial intercondylar eminence, was drawn on preoperative radiographs. Knees were classified as having a very overhanging medial tibial condyle if this line passed medial to the medial tibial cortex. They were also classified as very small if a size A/AA tibial component was used.

RESULTS

The overall rate of fracture was 8% (17 out of 212 knees). The rate was higher in knees with very overhanging condyles (Odds ratio (OR) 13; p < 0.001) and with very small components (OR 7; p < 0.001). The OR was 21 (p < 0.001) in those with both very overhanging condyles and very small components. In all, 69% of knees (147) had neither very overhanging nor very small components, and the fracture rate in these patients was 1.4% (2 out of 147 knees). Males had a significantly reduced risk of fracture (OR 0.13; p = 0.002), probably because no males required very small components and females were more likely to have very overhanging condyles (OR 3; p = 0.013). 31% of knees (66) were in males and in these the rate of fracture was 1.5% (1 out of 66 knees).

CONCLUSION

The rate of tibial plateau fracture in Japanese patients undergoing cementless UKA is high. We recommend that cemented tibial fixation should be used in Japanese patients who require very small components or have very overhanging condyles, as identified from preoperative radiographs. In the remaining 69% of knees cementless fixation can be used. This approach should result in a low rate of fracture. Cite this article: Bone Joint J 2020;102-B(7):861-867.

The Medial Eminence Line for Predicting Tibial Fracture Risk after Unicompartmental Knee Arthroplasty

Backgroud

Tibial fracture after cementless Oxford unicompartmental knee arthroplasty (OUKA) is a rare but serious complication. It is reported more frequently in Asian countries. The aim of this retrospective study was to assess the morphological characteristics of the tibia by using a simple novel measurement method in patients with tibial fractures after OUKA.

Methods

Six knees (all women) with tibial fractures after cementless OUKA (fracture group) and 150 knees without an obvious complication after cementless OUKA (control group) were examined retrospectively at our institution between January 2016 and April 2017. We drew a medial eminence line (ME line) defined as a line extending from the tip of the medial intercondylar eminence parallel to the tibial axis. The ME line was classified into two types (intramedullary type [type I] and extramedullary type [type E]), and the proportion of each type was compared between fracture patients and controls.

Results

In the fracture group, there were four (66.7%) type E cases and two (33.3%) type I cases; in the control group, there were 18 (12%) type E cases and 132 (88%) type I cases. Fisher exact tests showed that the proportion of type E was higher in the fracture group than in the control group (p < 0.01).

Conclusions

Measurement of the ME line can be recommended as a useful method to assess the risk of postoperative fracture after cementless OUKA.

Iatrogenic Tibia Fracture from an "Errant" Traction Pin Placement Resulting in a Cortical Defect: A Case Study

CASE

A 78-year-old women presented with a closed left midshaft femur fracture after sustaining a fall from standing height and underwent proximal tibial traction pin placement. After subsequent intramedullary nailing of femur fracture, the patient returned 2 months later with a proximal tibia fracture through the unicortical defect left from the traction pin site and underwent successful intramedullary nailing of the tibia.

CONCLUSION

Errant anteriorly placed proximal tibial traction pins pass tangentially across the vertex of the tibia and create residual unicortical defects that may increase the risk for late iatrogenic pin site fractures.

Minimising tibial fracture after unicompartmental knee replacement: A probabilistic finite element study

BACKGROUND

Periprosthetic tibial fracture after unicompartmental knee replacement is a challenging post-operative complication. Patients have an increased risk of mortality after fracture, the majority undergo further surgery, and the revision operations are less successful. Inappropriate surgical technique increases the risk of fracture, but it is unclear which technical aspects of the surgery are most problematic and no research has been performed on how surgical factors interact.

METHODS

Firstly, this study quantified the typical variance in surgical cuts made during unicompartmental knee replacement (determined from bones prepared by surgeons during an instructional course). Secondly, these measured distributions were used to create a probabilistic finite element model of the tibia after replacement. A thousand finite element models were created using the Monte Carlo method, representing 1000 virtual operations, and the risk of tibial fracture was assessed.

FINDINGS

Multivariate linear regression of the results showed that excessive resection depth and making the vertical cut too deep posteriorly increased the risk of fracture. These two parameters also had high variability in the prepared synthetic bones. The regression equation calculated the risk of fracture from three cut parameters (resection depth, vertical and horizonal posterior cuts) and fit the model results with 90% correlation.

INTERPRETATION

This study introduces for the first time the application of a probabilistic approach to predict the aetiology of fracture after unicompartmental knee replacement, providing unique insight into the relative importance of surgical saw cut variations. Targeted changes to operative technique can now be considered to seek to reduce the risk of periprosthetic fracture.

Tibial plateau fracture related to unicompartmental knee arthroplasty: Two case reports and literature review

RATIONALE

Unicompartmental knee arthroplasty (UKA) is an effective method to treat single compartment disease of the knee joint. Report about the complications of UKA, especially tibial plateau fractures, is rare. Given its rarity, its pathogenesis is not well described, and a standard of treatment is still not established. Therefore, relevant studies and analysis of this complication have a significant effect on helping physicians avoid risks and guide clinical diagnosis and treatment.

PATIENT CONCERNS

The 1st case corresponds to a 70-year-old male patient who complained of knee pain, difficulty walking, nocturnal rest pain, and elevated skin temperature at 3 weeks after the left knee arthroplasty. The second case is a 72-year-old female patient who complained of left knee pain and swelling during movement at 2 weeks after the left knee arthroplasty.

DIAGNOSIS

The 1st case showed a fracture of the medial malleolus of the left knee and a secondary depression of the medial tibial plateau in X-rays and the second case showed a fracture of the medial malleolus of the left knee in computed tomography (CT) and X-rays.

INTERVENTIONS

The 1st case was treated with plate and screw fixation and the second case was treated conservatively and immobilized using brace and remained nonweight bearing for 6 weeks.

OUTCOMES

After 1 year, both patients have good joint activity, and there was no pain or loosening of the prosthesis and fragment displacement.

LESSONS

The incidence of tibial plateau fractures (TPF) related to UKA might be low, but fatal and difficult to treat. Its pathogenesis determines procedure-related factors; when fracture develops, treatment should be based on the degree of displacement, stability of implant fixation, etc.

Rotational position of the tibial component can decrease bony coverage of the tibial component in Oxford mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

This study examined how coverage of the tibial component changes when the tibia vertical cut is externally or internally rotated in Oxford mobile-bearing unicompartmental knee arthroplasty.

MATERIALS AND METHODS

Fifty patients scheduled for primary Oxford medial unicompartmental knee arthroplasty (UKA) at the current hospital were included in this study. This study was a computed tomography (CT) simulation study. The anteroposterior (AP) and mediolateral (ML) length as well as the ML/AP ratio of the tibial cut surfaces were calculated when the vertical cut was performed parallel (base line), five degrees externally rotated (ER5), 10° externally rotated (ER10), five degrees internally rotated (IR5), or 10° internally rotated (IR10) relative to the tibial AP line using pre-operative CT. The tibial AP line connecting the middle of the posterior collateral ligament to the medial border of the patellar tendon attachment is a reproducible and reliable line because it is perpendicular to the SEA. These parameters among three lines were compared using a repeated measures ANOVA.

RESULTS

The mean ML/AP ratios were statistically significantly lower in ER5 (0.53 ± 0.04) than base line (0.56 ± 0.04) (P < 0.01). The ER10 (0.48 ± 0.03) also exhibited lower mean ML/AP ratios than ER5 (0.53 ± 0.04) (P < 0.01). The mean ML/AP ratios were higher in IR5 (0.59 ± 0.04) than base line (0.56 ± 0.04) (P < 0.01). The IR10 (0.63 ± 0.06) also showed a higher mean ML/AP ratio than IR5 (0.59 ± 0.04) (P < 0.01).

CONCLUSION

Rotational malalignment of tibial vertical cuts can affect tibial coverage in Oxford mobile-bearing unicompartmental knee arthroplasty.

Management of the Failed Medial Unicompartmental Knee Arthroplasty

With recent design modifications, proper patient selection, and sound surgical technique, medial unicompartmental knee arthroplasty has demonstrated long-term success in the management of degenerative joint disease. Nevertheless, complications do occur, most often aseptic loosening, tibial fracture, polyethylene wear, bearing dislocation, disease progression, infection, and unexplained pain. Some failures can be managed with retention of the implant, whereas others require revision to total knee arthroplasty (TKA), possibly including augments and stems. Although outcomes of unicompartmental knee arthroplasty may not match those of a primary TKA, they tend to exceed results of revision of a previous TKA.

The Valgus Inclination of the Tibial Component Increases the Risk of Medial Tibial Condylar Fractures in Unicompartmental Knee Arthroplasty

BACKGROUND

Medial tibial condylar fractures (MTCFs) are a rare but serious complication after unicompartmental knee arthroplasty. Although some surgical pitfalls have been reported for MTCFs, it is not clear whether the varus/valgus tibial inclination contributes to the risk of MTCFs.

METHODS

We constructed a 3-dimensional finite elemental method model of the tibia with a medial component and assessed stress concentrations by changing the inclination from 6° varus to 6° valgus. Subsequently, we repeated the same procedure adding extended sagittal bone cuts of 2° and 10° in the posterior tibial cortex. Furthermore, we calculated the bone volume that supported the tibial component, which is considered to affect stress distribution in the medial tibial condyle.

RESULTS

Stress concentrations were observed on the medial tibial metaphyseal cortices and on the anterior and posterior tibial cortices in the corner of cut surfaces in all models; moreover, the maximum principal stresses on the posterior cortex were larger than those on the anterior cortex. The extended sagittal bone cuts in the posterior tibial cortex increased the stresses further at these 3 sites. In the models with a 10° extended sagittal bone cut, the maximum principal stress on the posterior cortex increased as the tibial inclination changed from 6° varus to 6° valgus. The bone volume decreased as the inclination changed from varus to valgus.

CONCLUSION

In this finite element method, the risk of MTCFs increases with increasing valgus inclination of the tibial component and with increased extension of the sagittal cut in the posterior tibial cortex.

Bilateral periprosthetic tibial stress fracture after total knee arthroplasty: A case report

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Periprosthetic tibia fractures are rare cases.

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Bilateral tibial stress fracture developed after total knee arthroplasty is the first of its kind in the literature.

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A stress fracture should be kept in mind in the persistent pain in the upper end of the tibia that occurs after surgery.

Introduction

Periprosthetic fractures around the knee after total knee arthroplasty can be seen in the femur, tibia and patella. The tibial fractures are rare cases. Our case with bilateral tibial stress fracture developed after total knee arthroplasty (TKA) is the first of its kind in the literature.

Presentation of case

75-year-old male patient with bilateral knee osteoarthritis had not benefited from conservative treatment methods previously applied. Left TKA was applied. In the second month postoperatively, periprosthetic tibial fracture was identified and osteosynthesis was implemented with locked tibia proximal plate-screw. Bone union in 12 weeks was observed in his follow-ups.

After 15 months of his first operation, TKA was applied to the right knee. Postoperatively in the second month, as in the first operation, periprosthetic tibial fracture was detected. Osteosynthesis with locking plate-screw was applied and union in 12 weeks was observed in his follow-up.

He was seen mobilized independently and without support in the last control of the case made in the 24th month after the second operation.

Discussion

The number of TKA applications is expected to increase in the future. The incidence of periprosthetic fractures should also be expected to increase in these cases. Periprosthetic tibial fractures after TKA are rarely seen. The treatment of periprosthetic fractures around the knee after TKA can be difficult.

Conclusion

In the case of persistent pain in the upper end of the tibia after the surgery, stress fracture should be considered.

Post-Traumatic Periprosthetic Tibial and Fibular Fracture After Total Ankle Arthroplasty: A Case Report

Periprosthetic fractures after total ankle arthroplasty are uncommon, with most cases occurring intraoperatively. We describe a post-traumatic periprosthetic fracture of the distal tibia and fibula after total ankle arthroplasty that was treated with minimally invasive plate osteosynthesis. It is important for orthopedic surgeons not only to recognize the risk factors for postoperative periprosthetic total ankle arthroplasty fractures, but also to be familiar with the treatment options available to maximize function and minimize complications. The design of the tibial prosthesis and surgical techniques required to prepare the ankle joint for implantation are important areas of future research to limit the risk of periprosthetic fractures.

[Modern unicondylar knee arthroplasty. Tips and tricks]

BACKGROUND

Unicondylar knee arthroplasty (UKA) is an established therapeutic option for advanced medial or lateral gonarthrosis.

OBJECTIVES

The cornerstones of a successful UKA, careful patient selection, preoperative planning and precise operation technique, are discussed in this overview article.

IMPORTANCE

In contrast to total knee arthroplasty, UKA allows preservation of the contralateral and patellofemoral compartments as well as the cruciate ligaments and is often associated with rapid postoperative recovery, improved knee kinematics and knee function. However, UKA is technically very demanding. High revision rates have been reported in particular with widespread application, according to national joint replacement registries.

CONCLUSION

Successful UKA relies on meticulous patient selection, preoperative planning and surgical technique. It is justified to broaden classic UKA indications. In medial and lateral UKA three types of mechanical varus-valgus deformity can be encountered: type 1 (isolated intraarticular deformity), type 2 (pronounced deformity due to extraarticular varus deformity in medial UKA or valgus deformity in lateral UKA), type 3 (reduced deformity due to extraarticular valgus deformity in medial UKA or varus deformity in lateral UKA). We believe these deformities should be addressed accordingly with surgical technique.

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.

Comparison of high tibial osteotomy and unicompartmental knee arthroplasty at a minimum follow-up of 3 years

The purpose of this study was to compare clinical outcomes including return to recreational activities (cycling, swimming, exercise walking, dancing, jogging, and mountain climbing) after opening-wedge high tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA). Clinical outcomes were assessed using Tegner activity scores, ranges of motion, and Lysholm knee scores. In both groups, the number of patients participating in recreational activities was significantly reduced after surgery, but without a significant intergroup difference (1.3 activities in HTO group and in 1.6 activities in UKA group). Average Tegner activity scale scores, ranges of motion, and Lysholm knee scores did not show significant differences between the 2 groups. This study identified no significant differences between HTO and UKA for medial unicompartmental osteoarthritis in terms of return to recreational activity and short-term clinical outcomes.

Two Year Follow-up of the Preservation Unicompartmental Knee Implant

Reported results of unicondylar knee arthroplasty (UKA) have mixed reviews in comparison with results of tri-compartmental knee arthroplasty (TKA). We prospectively evaluated the short-term results (2 years) of a newer design of a UKA implant (Preservation UKA) with a cobalt-chromium femoral component and an all polyethylene tibial component. Seventy-two patients with intact ligaments and loss of only medial articular cartilage received the Preservation prosthesis. Data were obtained using WOMAC, Knee Society score (KSS), and standard radiographs. WOMAC scores improved by 24 points and KSS improved by 33 points at 2-year follow-up. Mean flexion increased by 4° to126° at 2 years. On X-ray, only one patient had a radiolucency. No fractures occurred. Two knees were revised due to clinical symptoms of medial compartment pain. This 2-year follow-up study of the Preservation UKA shows promising early results. Long-term data would be necessary to compare results with TKA or other unicompartmental replacements.

Early complications after minimally invasive mobile-bearing medial unicompartmental knee arthroplasty

The purpose of this article is to review the early complications of minimally invasive mobile-bearing unicompartmental knee arthroplasty by analyzing the first 100 consecutive cases. All cases were medial unicompartmental arthroplasties with a follow-up of at least 24 months (range, 24-51 months). Seven revision procedures were performed due to 2 fractures of the medial tibial plateau, 1 loosening of the femoral component, and 4 dislocations of the meniscal bearing. The early results as determined by The Knee Society scores, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores and postoperative range of motion were satisfactory. However, there exists a high rate of early failures, which occurred during the initial learning curve. Therefore, surgeons must be aware that in order to minimize these complications, attention to detail is mandatory.

Saw cuts in unicompartmental knee arthroplasty: an analysis of Sawbone preparations

Unicompartmental knee arthroplasty (UKA) has become a frequently used treatment option for anteromedial osteoarthritis (OA) of the knee due to good clinical and functional results. However, serious complications like tibial plateau fractures have been reported. These can be associated with saw cuts during surgery. The purpose of this study was to analyse saw cuts during Sawbone preparations at instructional unicompartmental knee courses and to identify potential sources of surgical error. One hundred Sawbone preparations were performed by knee surgeons inexperienced with UKA. Sawing errors during preparation were analysed and quantified. Tibial and femoral errors can occur during preparation. At the proximal tibia three errors can be found: extended vertical cuts (A), extended horizontal cuts (B) and perforation of the posterior cortex. An ascending cut at the posterior femoral condyle (C) is possible during femoral preparation. Errors type A were found at a mean length of 2.4 mm+/-2.3 mm with a maximum value of 10.1 mm. In 18% errors of more than 4.0 mm were found. Type B errors showed an average value of 2.0 mm+/-1.7 mm with maximum values of 7.4 mm. Type C errors were found at a mean of 1.3 mm+/-1.0 mm (maximum value 5.1 mm). Our data showed that in 18% of the cases, vertical cutting errors of more than 4.0 mm occurred in inexperienced surgeons.

Pseudomeniscal synovial impingement after unicondylar knee arthroplasty

Unicondylar knee arthroplasty (UKA) is a well-established treatment option for unicompartmental knee arthrosis. Although UKA achieves high success rates, surgeons should be aware of many potential sources of persistent postoperative pain. Common causes include septic or aseptic loosening, a loose body, implant failure, and chronic regional pain syndrome. Tibial plateau stress fracture, meniscus rupture, and cement extrusion have also been reported as infrequent causes of persistent pain. We encountered 2 patients in whom persistent pain after UKA was attributed to synovial impingement mimicking a meniscus tear, and we refer to this as pseudomeniscal synovial impingement. This article presents the clinical histories and histologic findings of 2 patients fitted with a mobile-bearing UKA system and a fixed-bearing UKA system, respectively. These patients were successfully treated by arthroscopic excision.

Patellar height before and after unicompartmental knee arthroplasty: association with early clinical outcome?

INTRODUCTION

There is paucity of information available concerning the role of patellar height in unicompartmental knee arthroplasty (UKA). The present study was conducted to determine the patellar height before and after UKA and to assess possible effects on the early clinical outcome.

MATERIALS AND METHODS

We measured the patellar height before and after UKA in 83 consecutive knees using the Blackburne-Peel (BP) index and Insall-Salvati (IS) ratio and investigated the impact of the patellar height on the clinical outcome 2 years after surgery.

RESULTS

BP values significantly decreased from 0.81 before surgery to 0.76 postoperatively (P < 0.001). IS ratios did not significantly decrease from 1.02 to 1.01 (P = 0.108). Lower preoperative BP values were negatively correlated with the postoperative knee extension (r = -0.357, P = 0.026), while higher preoperative BP values were negatively associated with the postoperative Knee Society Score (r = -0.302, P = 0.046). Lower preoperative IS values were negatively correlated with postoperative Knee Scores (r = -0.394, P = 0.019).

CONCLUSION

After UKA, the patellar height decreased significantly according to the BP index, but not significantly according to the IS ratio. We found only weak and inconsistent correlations between the patellar height and clinical outcome parameters. Hence, based on the present results, the patellar height seems not to be a strict separate patient-selection criterion for UKA.

Lateral meniscus and lateral femoral condyle cartilage injury by retained cement after medial unicondylar knee arthroplasty

The authors experienced an unusual case of a patient with a complex tear of the lateral meniscus and adjacent lateral femoral condyle cartilage injury in the contralateral compartment by retained cement, possibly located at the posteromedial side of the medial tibial component after unicondylar knee arthroplasty. Arthroscopic partial meniscectomy and cartilage microfracture were successfully performed. Two small cement fragments were removed from the posterolateral compartment. A sharp pain in the lateral side disappeared postoperatively and posterior knee pain was much reduced.

Periprosthetic fracture of the proximal tibia after lateral unicompartmental knee arthroplasty

We report a case of periprosthetic fracture of the proximal tibia after lateral unicompartmental knee arthroplasty following a trivial fall. At the time of surgery, the components were found to be loose; and there was a large uncontained tibial defect with bone loss and communition at the fracture site. The patient was treated by revision total knee arthroplasty and proximal structural tibial allograft, with a satisfactory result at 5-year follow up. Our case illustrates that a bone-conserving unicompartmental knee arthroplasty, if complicated by a periprosthetic fracture, can also present with a difficult surgical problem. Attention to preoperative planning and to availability of structural allograft for such difficult cases is recommended.

Unicompartmental knee arthroplasty: functional recovery and radiographic results with a minimally invasive technique

We prospectively evaluated 100 consecutive unicompartmental knee arthroplasties, performed in minimally invasive quadriceps-sparing fashion, for medial compartment osteoarthritis in patients aged 46 to 79 years, with anteromedial tibial wear, less than 10 degrees of flexion contracture, correctable varus not exceeding 15 degrees , and an intact anterior cruciate ligament. We aimed to determine (1) early functional outcome and (2) radiographic limb alignment and component placement. Mean incision length was 7.2 cm, hospital stay 2.1 days, and blood loss 240 ml. Flexion at 3 months was between 120 degrees and 155 degrees (mean, 139 degrees ). Among the patients, 80% could flex beyond 130 degrees , and 91% could sit cross-legged, kneel, and get up easily from the floor. The mean hip-knee-ankle axis was 177 degrees . Ninety-five percent of femoral components were centered on the tibial component. Tibial component slope was restored in 91%.

Tibial plateau stress fracture after unicondylar knee arthroplasty using a navigation system: two case reports

Satisfactory alignments of components in total knee arthroplasty have been reported since the introduction of navigation systems. And thus, such techniques have been introduced for minimally invasive unicondylar knee arthroplasty (UKA). Several intraoperative fractures of the tibial plateau have been reported in association with minimally invasive UKA and some stress fractures of tibial plateau associated with design of instrument have been reported. Here, we report on two cases of stress fracture of the tibial medial plateau after minimally invasive UKA was performed using a navigation system.

Medial tibial plateau fracture complicating unicompartmental knee arthroplasty

We describe a new cause of a medial tibial plateau fracture complicating the early postoperative rehabilitation following unicompartmental knee arthroplasty. The patient was successfully treated by open reduction and internal fixation by buttress plating the fracture and retaining the prosthesis. The treatment option used proved to be successful, although careful patient selection for unicompartmental knee arthroplasty should be recommended to decrease the risk of this complication.

Incidence and reasons for reoperation after minimally invasive unicompartmental knee arthroplasty

The goal of this report is to review reoperations undertaken on the initial 221 unicompartmental arthroplasties performed using a minimally invasive technique. A comparison was then performed between these cases and the previous 514 open medial unicompartmental arthroplasties performed at our institution. In the minimally invasive group, 9 (4.1%) of 221 knees were revised (8 for component loosening, 1 for deep infection). Of 212 unrevised knees, 16 have required a total of 18 nonrevision reoperations. Overall, 25 of 221 knees required at least 1 reoperation (total reoperation rate, 11.3%). Despite an accelerated recovery and decreased hospital stay in our minimally invasive unicompartmental arthroplasties, the rate of revision due to aseptic loosening (3.7% vs 1.0%) and the overall reoperation rate (11.3% vs 8.6%) compare unfavorably with those performed with an open technique.

Conversion of failed unicompartmental knee arthroplasty to TKA

As the number of unicompartmental knee arthroplasties performed continues to rise, so too will the number of failures. In order to justify its continued use, conversion to total knee arthroplasty must be evaluated. From 1993-2004, 22 consecutive knees from 18 patients with a failed unicondylar knee arthroplasty underwent conversion to total knee arthroplasty. The most common modes of failure were polyethylene wear (12 patients), loosening of the femoral (4 patients) or tibial component (3 patients), and osteoarthritis progression (3 patients). All patients were converted to primary cruciate retaining components. Twenty-seven percent of patients had contained defects on the femoral condyle that required bone graft. No femoral stems or metal augmentation were required. Forty-five percent of patients had contained defects on the tibia that required bone graft. Metal wedge augmentation was required in five knees (23%), and stems were used in two patients. Sixteen of 22 knees (73%) were followed for an average of 64.5 months. Knee Society knee scores and functional scores at latest followup were 93 and 78, respectively. Conversion of a failed unicondylar knee arthroplasty to a total knee arthroplasty is technically demanding, but may be done successfully with careful preoperative planning and possible need for revision techniques.

LEVEL OF EVIDENCE

Therapeutic study, level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Minimally invasive surgery vs conventional exposure using the Miller-Galante unicompartmental knee arthroplasty: a randomized radiostereometric study

Forty-one patients were randomized to a cemented Miller-Galante unicompartmental (Zimmer, Warsaw, Ind) knee arthroplasty inserted with either minimally invasive surgery or with a standard exposure. Clinical data and conventional radiographs were recorded and patients were followed with radiostereometric analysis to measure migration rate of the tibial component. The rehabilitation of patients operated through a small incision was faster, and there was a significant difference in days of hospitalization (P = .03). No statistical significant difference was found between the 2 groups regarding clinical or radiographic data. The Hospital for Special Surgery score was 96 and 92, respectively, for the minimally invasive surgery and conventional group at 2 years. The limb alignment was equal in both groups with a mean femorotibial axis of 182 degrees after surgery. The rate of migration for tibial components was very small, with a maximal total point motion of 0.8 mm for both groups after 2 years follow-up.

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.

Imaging of knee arthroplasty

Knee replacement surgery, either with unicompartmental or total systems, is common. The purpose of this manuscript is to review the appearance of normal knee arthroplasty and the appearances of complications such as infection, polyethylene wear, aseptic loosening and particle-induced osteolysis, patellofemoral abnormalities, axial instability, and periprosthetic and component fracture. Knowledge of the potential complications and their imaging appearances will help the radiologist in the diagnostic evaluation of the patient with a painful knee arthroplasty.

Unicompartmental knee arthroplasty: new indications, more complications?

Despite mixed results with unicompartmental knee arthroplasty (UKA) in the 1970s, the UKA was established as a reliable procedure in the low-demand, elderly patient. Dependable results up to a decade prompted the idea that UKA may work equally well in the younger patient. Expanded indications for UKA are being evaluated: might higher failure rates and difficult revisions emerge from younger, more active patients?