Knee joint kinematics, fixation and function related to joint area design in total knee arthroplasty

Comparison of long-term kinematics and wear of total knee arthroplasty implant designs

We sought to evaluate wear and kinematics in well-established implants of posterior stabilized (PS) and cruciate retaining (CR) designs. Ninety-one knees implanted for at least five years were examined. The implants were Genesis II PS (Smith & Nephew, Memphis, TN), Sigma PS (DePuy Synthes, Warsaw, IN), or Sigma CR. Radiostereometric analysis (RSA) images were acquired at multiple flexion angles and the 3D positions of the implant components were determined using model-based RSA software. The location of the center of the contact area between the femoral and polyethylene components was used to obtain contact kinematics, and the magnitude of the virtual intersection between the components indicated linear wear. All three groups had paradoxical anterior motion on both condyles, experienced similar net external rotation, and exhibited instances of internal rotation during flexion. The maximum observed wear rate was significantly greater for the Sigma PS than the Genesis II PS on the medial condyle (mean difference = 0.032 mm/year, p = 0.044), but not the lateral condyle, while there was no difference between the Sigma PS and Sigma CR for either condyle. Knees with lateral condylar separation had greater maximum wear rates on the medial condyle (mean difference = 0.033 mm/year, p = 0.001), while those with medial condylar separation had greater maximum wear rates on the lateral condyle (mean difference = 0.044 mm/year, p = 0.014). At long term follow-up in patients with well-functioning implants, there were differences in kinematics and wear resistance between implants. These results suggest that implant design affects long-term kinematics and wear in well-functioning implants and that condylar separation should be avoided to minimize wear.

Prediction of Knee Kinematics at the Time of Noncontact Anterior Cruciate Ligament Injuries Based on the Bone Bruises

Biomechanical risk factors associated with the alignment and position of the knee for anterior cruciate ligament (ACL) injury are still not conclusive. As bone bruises identified on magnetic resonance imaging (MRI) following acute ACL injury could represent the impact footprint at the time of injury. To improve understanding of the ACL injury mechanism, we aimed to determine the knee kinematics during ACL injury based on the bone bruises. Knee MRI scans of patients who underwent acute noncontact ACL injuries were acquired. Numerical optimization was used to match the bone bruises of the femur and tibia and predict the knee positions during injury. Knee angles were compared between MRI measured position and predicted position. The knee flexion, abduction, and external tibial rotation angles were significantly greater in the predicted position than that in MRI measured position. Relative to MRI measured position, patients had a mean of 34.3 mm of anterior tibial translation, 4.0 mm of lateral tibial translation, and 16.0 mm superior tibial translation in the predicted position. The results suggest that knee valgus and external tibial rotation accompanied by knee flexion are high-risk movement pattern for ACL injury in patients with lateral compartment bone bruising in conjunction with ACL injury.

Risk for hip fracture before and after total knee replacement in Sweden

We studied the risk for hip fracture before and after total knee replacement (TKR) in the entire population in Sweden. Women and men had a low risk for hip fracture before TKR but an increased risk the first year after TKR.

PURPOSE

It is known that osteoarthritis is associated with high bone mass. We therefore studied the risk of hip fracture before and after total knee replacement (TKR), risk of different hip fracture types, and risk subdivided in genders and age groups.

METHODS

We followed the total Swedish population born between 1902 and 1952 (n = 4,258,934) during the period 1987-2002 and identified all patients with TKR due to primary OA (n = 39,291), and all patients with hip fracture (n = 195,860) in the Swedish National Inpatient Register. The risk time analyses were based on Poisson regression models.

RESULTS

The hazard ratio (HR) for hip fracture the last year before TKR was 0.86 (95% CI 0.74 to 1.00) and the first year after 1.26 (95% CI 1.11 to 1.42) compared to individuals without TKR. The HR for femoral neck fracture 0-10 years after TKR was 0.95 (95% CI 0.89 to 1.01) and for trochanteric fracture was 1.13 (95% CI 1.06 to 1.21). The HR for hip fracture in the age group 50-74 was 1.28 (95% CI 1.14 to 1.43) and in the age group 75-90 years was 0.99 (95% CI 0.94 to 1.04) 0-10 years after TKR, compared to individuals without TKR.

CONCLUSION

Individuals had a low risk for hip fracture before TKR but an increased risk the first year after TKR. The risk in individuals below age 75 years and for trochanteric fractures was increased after TKR. Possible explanations include changed knee kinematics after a TKR, physical activity level, fall risk, and other unknown factors.

Different patterns of clonal evolution among different sarcoma subtypes followed for up to 25 years

To compare clonal evolution in tumors arising through different mechanisms, we selected three types of sarcoma-amplicon-driven well-differentiated liposarcoma (WDLS), gene fusion-driven myxoid liposarcoma (MLS), and sarcomas with complex genomes (CXS)-and assessed the dynamics of chromosome and nucleotide level mutations by cytogenetics, SNP array analysis and whole-exome sequencing. Here we show that the extensive single-cell variation in WDLS has minor impact on clonal key amplicons in chromosome 12. In addition, only a few of the single nucleotide variants in WDLS were present in more than one lesion, suggesting that such mutations are of little significance in tumor development. MLS displays few mutations other than the FUS-DDIT3 fusion, and the primary tumor is genetically sometimes much more complex than its relapses, whereas CXS in general shows a gradual increase of both nucleotide- and chromosome-level mutations, similar to what has been described in carcinomas.

Different intraoperative kinematics, stability, and range of motion between cruciate-substituting ultracongruent and posterior-stabilized total knee arthroplasty

PURPOSE

The aim of this study was the comparison of intraoperative kinematics, stability, and range of motion (ROM) between the native osteoarthritic knee and cruciate-substituting fixed-bearing total knee arthroplasty (TKA) using both an ultracongruent (UC) and a posterior-stabilized (PS) insert design in the same patient. We hypothesized less knee flexion and less antero-posterior stability in the UC TKA.

METHODS

Intraoperative measurements of kinematics, stability, and ROM were performed in 40 patients before soft-tissue release and bone cuts, and after implantation of the final femoral and tibial implants with both a UC insert and a PS insert. All measurements were performed using a navigation system.

RESULTS

Kinematics changed significantly from a constant posterior femoral rollback before surgery to a paradoxical anterior translation during initial knee flexion with both inserts, but less pronounced with the PS insert (p < 0.001). There was significantly more posterior femoral rollback with the PS insert compared to the UC insert (p < 0.01). Stability measurements demonstrated no differences at full extension and 30° of knee flexion but significantly increased antero-posterior translation in 60° and 90° of knee flexion with the UC insert compared to the PS insert (p < 0.001). ROM measurements demonstrated improvement of knee flexion from 118° at the beginning of the surgery to 123° with the UC insert and 128° with the PS insert (p < 0.001).

CONCLUSION

The use of a UC insert intraoperatively resulted in less antero-posterior stability and slightly less knee flexion compared to a PS insert. Surgeons should be aware of these differences when deciding for one of these options to substitute the posterior cruciate ligament (PCL). The impact of these findings on clinical outcome needs further investigation.

LEVEL OF EVIDENCE

II.

Recombinant Adenovirus-p53 Gene Therapy for Advanced Unresectable Soft-Tissue Sarcomas

Patients with unresectable advanced soft-tissue sarcomas (STS) receiving radiotherapy or/and chemotherapy still have a poor prognosis. This study aimed to evaluate retrospectively the efficacy and safety of recombinant adenovirus-p53 (rAd-p53) gene therapy combined with radiotherapy and hyperthermia for advanced STS. A total of 71 patients with advanced unresectable STS treated at the authors' center from April 2007 to November 2014 were included. Of these 71 patients, 36 cases received rAd-p53 therapy combined with radiotherapy and hyperthermia (p53 group), while 35 cases received radiotherapy and hyperthermia alone (control group). Short-term therapeutic efficacies, long-term survival outcomes, and adverse events were evaluated and compared between groups. Compared to the control group, the p53 group had a significantly higher disease control rate (83.33% vs. 54.29%; p = 0.008) and a lower progressive disease rate (16.67% vs. 45.71%; p = 0.018). In addition, rAd-p53 treatment significantly improved the progression-free survival and overall survival of STS patients. Cox regression indicated that rAd-p53 treatment significantly reduced the risks for disease progression or death event for STS patients. Furthermore, there was no significant difference in all adverse events, except for transient fever, which occurred in 89% of patients with rAd-p53 therapy. rAd-p53 combined with radiotherapy and hyperthermia can effectively improve the therapeutic efficacy and survival outcomes in patients with advanced unresectable STS, providing a new therapeutic strategy.

Interactive effect of femoral posterior condylar offset and tibial posterior slope on knee flexion in posterior cruciate ligament-substituting total knee arthroplasty

BACKGROUND

This work aimed to evaluate the changes in the femoral posterior condylar offset (PCO) and tibial slope after posterior cruciate ligament (PCL)-substituting total knee arthroplasty (TKA), and to address the presence of any interactive effect between the two on knee flexion.

METHODS

Fifty-two PCL-substituting TKAs were performed using a posterior referencing system. Three-dimensional reconstructed computed tomographic (CT) images were used to evaluate PCO and tibial slope before and after arthroplasty. Range of motion and clinical scores were evaluated at a mean of 3.1years postoperatively. Multivariate linear model with interaction terms was used to evaluate and compare the relationships among changes in PCO, tibial slope, and postoperative knee flexion angles.

RESULTS

The degree of change in PCO was greater in the lateral condyle than in the medial condyle (3.1±2.5mm and -0.5±2.8mm, respectively). Postoperative medial and lateral tibial slopes were 1.4°±1.8 and 1.4°±2.0, respectively. The mean degree of postoperative knee flexion was 125°. Analysis with interaction terms and covariate adjustment demonstrated that medial PCO and tibial slope were significantly related to knee flexion with interactive effect (P=0.011). In cases with <3° posterior tibial slope, the postoperative PCO was positively correlated to the degree of knee flexion angle. However, in cases with >3° tibial slope, PCO was negatively correlated to knee flexion.

CONCLUSION

Medial femoral PCO and tibial slope showed interactive effect on knee flexion after PCL-substituting TKAs. Reconstitution of the proper PCO and avoiding excessive tibial slope may be necessary.

Contact Kinematics Correlates to Tibial Component Migration Following Single Radius Posterior Stabilized Knee Replacement

BACKGROUND

Contact kinematics between total knee arthroplasty components is thought to affect implant migration; however, the interaction between kinematics and tibial component migration has not been thoroughly examined in a modern implant system.

METHODS

A total of 24 knees from 23 patients undergoing total knee arthroplasty with a single radius, posterior stabilized implant were examined. Patients underwent radiostereometric analysis at 2 and 6 weeks, 3 and 6 months, and 1 and 2 years to measure migration of the tibial component in all planes. At 1 year, patients also had standing radiostereometric analysis examinations acquired in 0°, 20°, 40°, and 60° of flexion, and the location of contact and magnitude of any condylar liftoff was measured for each flexion angle. Regression analysis was performed between kinematic variables and migration at 1 year.

RESULTS

The average magnitude of maximum total point motion across all patients was 0.671 ± 0.270 mm at 1 year and 0.608 ± 0.359 mm at 2 years (P = .327). Four implants demonstrated continuous migration of >0.2 mm between the first and second year of implantation. There were correlations between the location of contact and tibial component anterior-posterior tilt, varus-valgus tilt, and anterior-posterior translation. The patients with continuous migration demonstrated atypical kinematics and condylar liftoff in some instances.

CONCLUSION

Kinematics can influence tibial component migration, likely through alterations of force transmission. Abnormal kinematics may play a role in long-term implant loosening.

Reduced Bearing Excursion After Mobile-Bearing Unicompartmental Knee Arthroplasty is Associated With Poor Functional Outcomes

BACKGROUND

A small proportion of patients with mobile unicompartmental knee arthroplasty (UKA) report poor functional outcomes in spite of optimal component alignment on postoperative radiographs. The purpose of this study is to assess whether there is a correlation between functional outcome and knee kinematics.

METHODS

From a cohort of consecutive cases of 150 Oxford medial UKA, patients with fair/poor functional outcome at 1-year postsurgery (Oxford Knee Score [OKS] < 34, n = 15) were identified and matched for age, gender, preoperative clinical scores, and follow-up period with a cohort of patients with good/excellent outcome (OKS ≥ 34, n = 15). In vivo kinematic assessment was performed using step-up and deep knee bend exercises under fluoroscopic imaging. The fluoroscopic videos were analyzed using MATLAB software to measure the variation in time taken to complete the exercises, patellar tendon angle, and bearing position with knee flexion angle.

RESULTS

Mean OKS in the fair/poor group was 29.9 and the mean OKS in the good/excellent group was 41.1. The tibial slope, time taken to complete the exercises, and patellar tendon angle trend over the flexion range were similar in both the groups; however, bearing position and the extent of bearing excursion differed significantly. The total bearing excursion in the OKS < 34 group was significantly smaller than the OKS ≥ 34 group (35%). Furthermore, on average, the bearing was positioned 1.7 mm more posterior on the tibia in the OKS < 34 group.

CONCLUSION

This study provides evidence that abnormal knee kinematics, in particular bearing excursion and positioning, are associated with worse functional outcomes after mobile UKA.

A computational simulation study to determine the biomechanical influence of posterior condylar offset and tibial slope in cruciate retaining total knee arthroplasty

Objectives

Posterior condylar offset (PCO) and posterior tibial slope (PTS) are critical factors in total knee arthroplasty (TKA). A computational simulation was performed to evaluate the biomechanical effect of PCO and PTS on cruciate retaining TKA.

Methods

We generated a subject-specific computational model followed by the development of ± 1 mm, ± 2 mm and ± 3 mm PCO models in the posterior direction, and -3°, 0°, 3° and 6° PTS models with each of the PCO models. Using a validated finite element (FE) model, we investigated the influence of the changes in PCO and PTS on the contact stress in the patellar button and the forces on the posterior cruciate ligament (PCL), patellar tendon and quadriceps muscles under the deep knee-bend loading conditions.

Results

Contact stress on the patellar button increased and decreased as PCO translated to the anterior and posterior directions, respectively. In addition, contact stress on the patellar button decreased as PTS increased. These trends were consistent in the FE models with altered PCO. Higher quadriceps muscle and patellar tendon force are required as PCO translated in the anterior direction with an equivalent flexion angle. However, as PTS increased, quadriceps muscle and patellar tendon force reduced in each PCO condition. The forces exerted on the PCL increased as PCO translated to the posterior direction and decreased as PTS increased.

Conclusion

The change in PCO alternatively provided positive and negative biomechanical effects, but it led to a reduction in a negative biomechanical effect as PTS increased.

Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, J-S. Lee, S. K. Kwon. A computational simulation study to determine the biomechanical influence of posterior condylar offset and tibial slope in cruciate retaining total knee arthroplasty. Bone Joint Res 2018;7:69–78. DOI: 10.1302/2046-3758.71.BJR-2017-0143.R1.

Amputation for Extremity Sarcoma: Contemporary Indications and Outcomes

INTRODUCTION

Amputation for localized extremity sarcoma (ES), once the primary therapy, is now rarely performed. We reviewed our experience to determine why patients with sarcoma still undergo immediate or delayed amputation, identify differences based on amputation timing, and evaluate outcomes.

METHODS

Records of patients with primary, nonmetastatic ES who underwent amputation at our institution from 2001 to 2011 were reviewed. Univariate analysis was performed, and survival outcomes were calculated.

RESULTS

We categorized 54 patients into three cohorts: primary amputation (A1, n = 18, 33%), secondary amputation after prior limb-sparing surgery (A2, n = 22, 41%), and hand and foot sarcomas (HF, n = 14, 26%). Median age at amputation was 54 years (range 18-88 years). Common indications for amputation (> 40%) were loss of function, bone involvement, multiple compartment involvement, and large tumor size (A1); proximal location, joint involvement, neurovascular compromise, multiple compartment involvement, multifocal or fungating tumor, loss of function, and large tumor size (A2); and joint involvement and prior unplanned surgery (HF). There was no difference in disease-specific survival (DSS) (p = 0.19) or metastasis-free survival (MFS) (p = 0.31) between early (A1) and delayed (A2) amputation. Compared with cohorts A1/A2, HF patients had longer overall survival (OS) (p = 0.04).

CONCLUSIONS

Indications for amputation for extremity sarcoma vary between those who undergo primary amputation, delayed amputation, and amputation for hand or foot sarcoma. Amputations chosen judiciously are associated with excellent disease control and survival. For patients who ultimately need amputation, timing (early vs. delayed) does not affect survival.

Dynamic RSA for the evaluation of inducible micromotion of Oxford UKA during step-up and step-down motion

Background and purpose - Implant inducible micromotions have been suggested to reflect the quality of the fixation interface. We investigated the usability of dynamic RSA for evaluation of inducible micromotions of the Oxford Unicompartmental Knee Arthroplasty (UKA) tibial component, and evaluated factors that have been suggested to compromise the fixation, such as fixation method, component alignment, and radiolucent lines (RLLs). Patients and methods - 15 patients (12 men) with a mean age of 69 (55-86) years, with an Oxford UKA (7 cemented), were studied after a mean time in situ of 4.4 (3.6-5.1) years. 4 had tibial RLLs. Each patient was recorded with dynamic RSA (10 frames/second) during a step-up/step-down motion. Inducible micromotions were calculated for the tibial component with respect to the tibia bone. Postoperative component alignment was measured with model-based RSA and RLLs were measured on screened radiographs. Results - All tibial components showed inducible micromotions as a function of the step-cycle motion with a mean subsidence of up to -0.06 mm (95% CI: -0.10 to -0.03). Tibial component inducible micromotions were similar for cemented fixation and cementless fixation. Patients with tibial RLLs had 0.5° (95% CI: 0.18-0.81) greater inducible medio-lateral tilt of the tibial component. There was a correlation between postoperative posterior slope of the tibial plateau and inducible anterior-posterior tilt. Interpretation - All patients had inducible micromotions of the tibial component during step-cycle motion. RLLs and a high posterior slope increased the magnitude of inducible micromotions. This suggests that dynamic RSA is a valuable clinical tool for the evaluation of functional implant fixation.

Tibial rotation kinematics subsequent to knee arthroplasty

BACKGROUND

The use of computer assisted joint replacement has facilitated precise intraoperative measurement of knee kinematics. The changes in "screw home mechanism" (SHM) resulting from Total Knee Arthroplasty (TKA) with different prostheses and constraints has not yet been accurately described.

METHODS

A pilot study was first completed. Intraoperative kinematic data was collected two groups of 15 patients receiving different prostheses.

RESULTS

On average, patients lost 5.3° of ER (SD = 6.1°). There was no significant difference between the prostheses or different prosthetic constraints.

CONCLUSIONS

There significant loss of SHM after TKA. Further research is required to understand its impact on patient function.

Comparison of cemented and uncemented fixation in total knee arthroplasty

As a result of reading this article, physicians should be able to :1. Understand the rationale behind using uncemented fixation in total knee arthroplasty.2.Discuss the current literature comparing cemented and uncemented total knee arthroplasty3. Describe the value of radiostereographic analysis in assessing implant stability.4. Appreciate the limitations in the available literature advocating 1 mode of fixation in total knee arthroplasty. Total knee arthroplasty performed worldwide uses either cemented, cementless, or hybrid (cementless femur with a cemented tibia) fixation of the components. No recent literature review concerning the outcomes of cemented vs noncemented components has been performed. Noncemented components offer the potential advantage of a biologic interface between the bone and implants, which could demonstrate the greatest advantage in long-term durable fixation in the follow-up of young patients undergoing arthroplasty. Several advances have been made in the backing of the tibial components that have not been available long enough to yield long-term comparative follow-up studies. Short-term radiostereographic analysis studies have yielded differing results. Although long-term, high-quality studies are still needed, material advances in biologic fixation surfaces, such as trabecular metal and hydroxyapatite, may offer promising results for young and active patients undergoing total knee arthroplasty when compared with traditional cemented options.

Posterior cruciate substituting versus posterior cruciate retaining total knee arthroplasty prostheses: a meta-analysis

PURPOSE

The arguments about whether posterior-substituting prostheses or cruciate-retaining prostheses are superior to the other after total knee arthroplasty never stop. This meta-analysis was conducted to evaluate the clinical effects of these two different designs.

METHODS

The study was performed according to the guidelines described in the Cochrane handbook for systematic reviews of interventions. Methodological features were collected and extracted by two reviewers independently.

RESULTS

Nine randomized controlled trials with 1261 knees were eligible for pooled analysis. The meta-analysis demonstrated there were no statistical differences in the Knee Society Score, Hospital for Special Surgery, Western Ontario and McMaster Universities index, tibial component alignment, femoral component alignment, tibial posterior slope, joint line, and incidence of complications with short-to medium-term follow-up (p>0.01). Statistically difference in postoperative range of motion (WMD: 4.34°, 95% CI: 3.18° to 5.50°) in favor of PS prostheses was found between groups (p<0.01).

CONCLUSION

The findings indicate there were no significant statistical differences in knee scores, radiological outcomes, and complications between the two types of implants. Statistically significant difference in postoperative ROM was found between the two groups, but no clinical difference.

Fixation of pathological humeral fractures by the cemented plate technique

Pathological fractures of the humerus are associated with pain, morbidity, loss of function and a diminished quality of life. We report our experience of stabilising these fractures using polymethylmethacrylate and non-locking plates. We undertook a retrospective review over 20 years of patients treated at a tertiary musculoskeletal oncology centre. Those who had undergone surgery for an impending or completed pathological humeral fracture with a diagnosis of metastatic disease or myeloma were identified from our database. There were 63 patients (43 men, 20 women) in the series with a mean age of 63 years (39 to 87). All had undergone intralesional curettage of the tumour followed by fixation with intramedullary polymethylmethacrylate and plating. Complications occurred in 14 patients (22.2%) and seven (11.1%) required re-operation. At the latest follow-up, 47 patients (74.6%) were deceased and 16 (25.4%) were living with a mean follow-up of 75 months (1 to 184). A total of 54 (86%) patients had no or mild pain and 50 (80%) required no or minimal assistance with activities of daily living. Of the 16 living patients none had pain and all could perform activities of daily living without assistance. Intralesional resection of the tumour, filling of the cavity with cement, and plate stabilisation of the pathological fracture gives immediate rigidity and allows an early return of function without the need for bony union. The patient's local disease burden is reduced, which may alleviate tumour-related pain and slow the progression of the disease. The cemented-plate technique provides a reliable option for the treatment of pathological fractures of the humerus.

Simultaneous measurements of knee motion using an optical tracking system and radiostereometric analysis (RSA)

BACKGROUND AND PURPOSE

Invasive methods are more reproducible and accurate than non-invasive ones when it comes to recording knee kinematics, but they are usually less accessible and less safe, mainly due to risk of infection. For this reason, non-invasive methods with passive markers are widely used. With these methods, varying marker sets based on a number of single markers, or sets of markers, known as clusters, are used to track body segments. We compared one invasive method--radiostereometric analysis--with a non-invasive method, an optical tracking system with 15 skin-mounted markers.

METHODS

9 subjects (10 knees) were investigated simultaneously with a dynamic RSA system and a motion-capture system while performing an active knee extension.

RESULTS

For flexion/extension, there was good agreement on an individual basis and at the group level. For internal/external rotation, the group mean was fairly similar, up to 25 degrees of flexion. Recordings of abductions and/or adductions revealed a systematic mean difference of 2-4 degrees during the range of flexion measured. The correlation between the 2 methods in the horizontal and frontal planes was poor.

INTERPRETATION

Our skin-marker model provided reliable data for flexion/extension. Recordings of internal/external rotation and abduction/adduction were less accurate on an individual basis than at the group level, most probably due to soft-tissue motion and the presence of small true motion in these planes.

The use of a femoral revision stem in the treatment of primary or secondary bone tumours of the proximal femur

Endoprosthetic reconstruction following resection of 31 tumours of the proximal femur in 30 patients was performed using a Wagner SL femoral revision stem. The mean follow-up was 25.6 months (0.6 to 130.0). Of the 28 patients with a metastasis, 27 died within a mean follow-up period of 18.1 months (0.6 to 56.3) after the operation, and the remaining patient was excluded from the study 44.4 months post-operatively when the stem was removed. The two patients with primary bone tumours were still alive at the latest follow-up of 81.0 and 130.0 months, respectively. One stem only was removed for suspected low-grade infection 44.4 months post-operatively. The worst-case survival rate with removal of the stem for any cause and/or loss to follow-up was 80.0% (95% confidence interval 44.9 to 100) at 130.0 months. The mean Karnofsky index increased from 44.2% (20% to 70%) pre-operatively to 59.7% (0% to 100%) post-operatively, and the mean Merle d’Aubigné score improved from 4.5 (0 to 15) to 12.0 (0 to 18). The mean post-operative Musculoskeletal Tumour Society score was 62.4% (3.3% to 100%).

The Wagner SL femoral revision stem offers an alternative to special tumour prostheses for the treatment of primary and secondary tumours of the proximal femur. The mid-term results are very promising, but long-term experience is necessary.

Clinical and radiological outcomes of fixed- versus mobile-bearing total knee replacement: a meta-analysis

Controversy exists regarding the clinical and radiological differences in outcomes between fixed- and mobile-bearing total knee replacements (TKR). The aim of this study was to compare these two TKR designs using a meta-analysis of the electronic databases MEDLINE, EMBASE, CINAHL and AMED in addition to a review of unpublished material. All included papers were critically appraised using a modified PEDro critical appraisal tool. Thirty-three studies were eligible, assessing the outcomes of 3532 TKRs. Analysis suggested that there was no significant difference in clinical or radiological outcomes and complication rates between fixed- and mobile-bearing TKRs.

Predicting range of movement after knee replacement: the importance of posterior condylar offset and tibial slope

We have attempted to quantify the influence of clinical, radiological and prosthetic design factors upon flexion following knee replacement. Our study examined the outcome following 101 knee replacements performed in two prospective randomized trials using similar cruciate retaining implants. Multivariate analyses, after adjusting for age, sex, diagnosis and the type of prosthesis revealed that the only significant correlates for range of movement at 12 months were the difference in posterior condylar offset ratio (p < 0.001), tibial slope (p < 0.001) and preoperative range of movement (p = 0.025). We found a moderate correlation between 12-month range of movement and posterior tibial slope (R = 0.58) and the difference of post femoral condylar offset (i.e, post-operative minus preoperative posterior condylar offset, R = 0.65). Posterior condylar offset had the greatest impact upon final range of movement highlighting this as an important consideration for the operating surgeon at pre-operative templating when choosing both the design and size of the femoral component.

The effect of an unplanned excision of a soft-tissue sarcoma on prognosis

We investigated whether our policy of routine re-excision of the tumour bed after an unplanned excision of a soft-tissue sarcoma was justified. Between April 1982 and December 2005, 2201 patients were referred to our hospital with the diagnosis of soft-tissue sarcoma, of whom 402 (18%) had undergone an unplanned excision elsewhere. A total of 363 (16.5%) were included in this study. Each patient was routinely restaged and the original histology was reviewed. Re-excision was undertaken in 316 (87%). We analysed the patient, tumour and treatment factors in relation to local control, metastasis and overall survival. Residual tumour was found in 188 patients (59%). There was thus no residual disease in 128 patients of whom 10% (13) went on to develop a local recurrence. In 149 patients (47%), the re-excision specimen contained residual tumour, but it had been widely excised. Local recurrence occurred in 30 of these patients (20%). In 39 patients (12%), residual tumour was present in a marginal resection specimen. Of these, 46% (18) developed a local recurrence. A final positive margin in a high-grade tumour had a 60% risk of local recurrence even with post-operative radiotherapy. Metastases developed in 24% (86). The overall survival was 77% at five years. Survival was related to the grade of the tumour and the finding of residual tumour at the time of re-excision. We concluded that our policy of routine re-excision after unplanned excision of soft-tissue sarcoma was justified in view of the high risk of finding residual tumour.

Clinical course of nonvisceral soft tissue leiomyosarcoma in 225 patients from the Scandinavian Sarcoma Group

BACKGROUND

Leiomyosarcoma of nonvisceral soft tissues is an uncommon malignant tumor; thus, only small numbers of cases have been reported. This study was based on a large series of patients from the Scandinavian Sarcoma Group Register acquired during a 15-year period (from 1986 to 2001). Follow-up information was available for all patients.

METHODS

The authors analyzed the clinical features of 225 patients with cutaneous, subcutaneous, or deep-seated leiomyosarcoma of the extremities, trunk wall, and superficial parts of the head and neck region to determine the natural course of the disease. Only patients who received their treatment at a specialist sarcoma center were included. Re-evaluation of histopathology was performed.

RESULTS

The age of the patients (121 women and 104 men) ranged from 20 years to 98 years (median, 70 years), and the tumors ranged in size from 0.6 cm to 35 cm (median, 4.0 cm). Eighty-two percent of the tumors were classified as high grade. The median follow-up for survivors was 5.5 years. The local treatment was adequate in 154 of 206 patients (75%) who were without metastasis at presentation. At 10 years, 84% of the 206 patients with localized disease at presentation were free from local recurrence, 66% remained metastasis free, and 49% were alive. Multivariate analysis showed that higher malignancy grade (P = .006), larger tumor size (P = .003), and deeper tumor location (P = .002) were correlated significantly with decreased metastasis-free survival, inadequate local treatment was correlated with local recurrence (P = .007), and high malignancy grade was correlated with decreased overall survival (P = .007).

CONCLUSIONS

The long-term prognosis for patients with subcutaneous and deep-seated soft tissue leiomyosarcoma remains poor despite the ability to achieve adequate local control through nonmutilating surgery with or without radiotherapy.

Cemented versus hydroxyapatite fixation of the femoral component of the Freeman-Samuelson total knee replacement

We have carried out a radiostereometric study of 50 patients (54 knees) with osteoarthritis of the knee who were randomly allocated to receive a cemented or a hydroxyapatite-coated femoral component for total knee replacement. The patients were also stratified to receive one of three types of articulating surface (standard, rotating platform, Freeman-Samuelson (FS)1000) all based on the Freeman-Samuelson design. The tibial components were cemented in all cases. Radiostereometry was performed post-operatively and at 3, 12 and 24 months. The analysis was restricted to rotation of the femoral component over time.

After two years, rotation of the femoral components in the transverse, longitudinal and sagittal planes did not differ between the cemented and the hydroxyapatite-coated implants (p = 0.2 to 0.9).

In total knee replacements with a rotating platform, the femoral component tended to tilt more posteriorly than in the other two designs, regardless of the choice of fixation (cemented or hydroxyapatite-coated, p = 0.04). The standard version of the femoral component, whether cemented or hydroxyapatite-coated, rotated more into valgus than was observed with the rotating-platform and FS1000 designs (p = 0.005). The increased constraint provided by the FS1000 component did not appear to have any adverse effect on fixation of the femoral component.

The effect of coordinate system choice and segment reference on RSA-based knee translation measures

Roentgen stereophotogrammetric analysis (RSA) can be utilized to accurately describe joint kinematics, but even when measuring small displacements within radiographically discernible structures, standardized reference frames are imperative for useful comparison across patients and across studies. In the current paper, accurately controlled laboratory models demonstrated the considerable influence that a mere 1.9-cm offset of the origin of the coordinate system from the rotation axes could exert on translation measures when rotations were occurring. In addition, the use of two different coordinate systems to gauge translation on a radiographic anterior-posterior (A-P) knee laxity exam resulted in a significant correlation (R(2)=0.562) between the two systems; however, differences of up 9.28 mm were found between corresponding measurements. This implies that clinical conclusions can potentially be upheld or refuted, based on the same data set, subject to coordinate system definition. Although the data analyzed presently involved the knee joint, similar issues surround the RSA motion analysis of other joints as well.

Posterior stabilized component increased femoral bone loss after total knee replacement. 5-year follow-up of 47 knees using dual energy X-ray absorptiometry

After total knee replacement (TKR) bone mineral density (BMD) commonly decreases behind the anterior flange of the femoral component, which may increase the risk for supracondylar fracture. Our aim was to evaluate if changes in femoral design and joint area constraint had any effect on the postoperative bone remodeling in the distal femur. We used dual-energy X-ray absorptiometry in 47 knees up to 5 years after operation with the AMK (DePuy, Johnson and Johnson Leeds, UK) TKR. The knees had been randomly allocated to receive a flat or a concave tibial insert with retention of the posterior cruciate ligament when preoperative deformity was less severe, and either a concave or a posterior-stabilized (PS) insert with resection of the posterior cruciate ligament when deformity was more pronounced. The most pronounced relative reduction (15-38%) in bone mineral density (BMD) was seen posterior to the anterior flange. There were no significant differences in relative change in BMD between flat and concave inserts. Knees operated with PS inserts had more reduction posterior to the flange than knees with concave inserts in the subgroup with more advanced preoperative deformity (23% and 38% respectively). Use of posterior stabilized insert may increase the risk of supracondylar fracture compared to concave insert in knees with advanced preoperative deformity.

Fractures of the shaft of the humerus

We studied the epidemiology of 401 fractures of the shaft of the humerus in 397 patients aged 16 years or older. The incidence was 14.5 per 100 000 per year with a gradually increasing age-specific incidence from the fifth decade, reaching almost 60 per 100 000 per year in the ninth decade. Most were closed fractures in elderly patients which had been sustained as the result of a simple fall. The age distribution in women was characterised by a peak in the eighth decade while that in men was more even. Simple fractures were by far the most common and most were located in the middle or proximal shaft. The incidence of palsy of the radial nerve was 8% and fractures in the middle and distal shaft were most likely to be responsible. Only 2% of the fractures were open and 8% were pathological. These figures are representative of a population with a low incidence of high-energy and penetrating trauma, which probably reflects the situation in most European countries.

Mobile vs. fixed bearing unicondylar knee arthroplasty: A randomized study on short term clinical outcomes and knee kinematics

The literature contains limited yet controversial information regarding whether a fixed or a mobile bearing implant should be used in unicompartmental knee arthroplasty (UKA). This randomized study was to further document the performance and comparison of the two designs. Fifty-six knees in 48 patients (mean age of 72 years) undergoing medial UKA were randomized into a fixed bearing (Miller/Galante) or a mobile bearing (Oxford) UKA. The 2 year clinical outcomes (clinical scores), radiographic findings, and weight bearing knee kinematics (assessed using RSA) were compared between the two groups. The mobile bearing knees displayed a larger and an incrementally increased tibial internal rotation (4.3 degrees, 7.6 degrees, 9.5 degrees vs. 3.0 degrees, 3.0 degrees, 4.2 degrees respectively at 30 degrees, 60 degrees, 90 degrees of knee flexion) compared to the fixed ones. The medial femoral condyle in the mobile bearing knees remained 2 mm from the initial position vs. a 4.2 mm anterior translation in the fixed bearing knees during knee flexion. The contact point in the mobile bearing implant moved 2 mm posteriorly vs. a 6 mm anterior movement in the other group. The mobile bearing knees had a lower incidence of radiolucency at the bone implant interface (8% vs. 37%, p < 0.05). The incidence of lateral compartment OA and progression of OA at patello-femoral joint were equal. No differences were found regarding Knee Society Scores, WOMAC, and SF-36 scores (p > 0.05). This study indicates that mobile bearing knees had a better kinematics, a lower incidence of radiolucency but not yet a better knee function at 2 years.

Malrotation in total knee arthroplasty: effect on tibial cortex strain captured by laser-based strain acquisition

BACKGROUND

Malrotation of the tibial and femoral components has been recognized to be a clinical complication affecting the performance and durability of total knee arthroplasty. This study used a novel strain acquisition technique to determine the effect of tibio-femoral component malrotation on tibial torque and strain distribution of the proximal tibial cortex with a cemented fixed-bearing posterior-stabilized knee.

METHODS

Using electronic speckle pattern interferometry, strain on the proximal tibia of human cadaveric knees was obtained in response to 1500N axial loading for neutrally aligned tibial and femoral components, and for 10 degrees internal and external malrotation between the tibial and femoral components. Local strain gage measurements were combined with full-field optical strain measurements to quantify effects on tibial cortex strain and strain distributions caused by the 10 degrees malrotations. In addition, tibial torque was measured for incremental degrees of tibio-femoral malrotation.

FINDINGS

Tibio-femoral malrotations as small as 2 degrees caused tibial torque in excess of 4 Nm. At 10 degrees malrotation, tibial torque significantly increased to over 8 Nm (P<0.001) as compared to neutrally aligned components. Local strain gage results significantly increased from 500 muepsilon to 632 muepsilon compressive strain in response to 10 degrees external malrotation, and to 1000 muepsilon compressive strain in response to 10 degrees internal malrotation. Full-field optical strain reports yielded the highest strain of 2153 muepsilon for 10 degrees internal malrotation 30 mm below the joint line.

INTERPRETATION

Laser-based strain measurement technology provides novel capabilities to capture cortex strain fields. The sensitivity of cortex strain and torsion to small amounts of tibio-femoral malrotation may explain factors contributing to aseptic implant loosening of the tibial component.

A mobile-bearing knee prosthesis can reduce strain at the proximal tibia

Mobile and fixed-bearing knee prostheses are likely to generate distinct strain gradients in the proximal tibia. The resulting strain distribution in the proximal tibia governs bone remodeling and affects implant integration and stability. We determined the effects of fixed and mobile-bearing total knee prostheses on strain distribution at the proximal tibia. This mobile-bearing prosthesis was evaluated in cadaveric specimens under axial and torsional loading. Strain on the proximal tibial cortex was measured with rosette strain gages and an optical full-field strain acquisition system. Tibial torsion in response to combined axial and torsional loading was documented. There was no difference in cortex strain between the fixed and the mobile-bearing prostheses under 1.5 kN axial loading. Superimposing 10 degrees tibial internal rotation induced 22% less compressive strain in the mobile-bearing prosthesis compared with the fixed-bearing prosthesis. Under 10 degrees tibial external rotation, the mobile-bearing prosthesis induced 33% less compressive strain than the fixed-bearing prosthesis. Optically acquired strain fields showed peak compressive strain at the anteromedial aspect 30 mm below the joint line. The mobile-bearing prosthesis reduced torque in the proximal tibia during knee rotation by 68-73% compared with the fixed-bearing prosthesis. Our data suggest that the particular mobile-bearing prosthesis tested potentially reduces elevated strain levels in the proximal tibia.

Mid-term wear characteristics of an uncemented acetabular component

We investigated the rate of polyethylene wear of a cementless acetabular component at different periods of follow-up in order to test the hypothesis than an irrecoverable deformation process (creep) was followed by an initially low, but gradually increasing wear rate. We studied prospectively 93 uncemented total hip arthroplasties in 83 patients (mean age 50 years (22 to 63)) with a mean follow-up of 8.2 years (3 to 12). We measured the penetration of the femoral head from radiographs taken immediately after surgery at three, six and nine years, or at the latest follow-up. The median wear rate was 0.17 mm per year in the first three years, a finding which we considered to be caused by creep. Thereafter, the rate of wear declined to 0.07 mm per year (four- to six-year period) and then increased to 0.17 mm per year (seven to nine years) and 0.27 mm per year (more than nine years), which we considered to be a reflection of genuine polyethylene wear. After the nine-year follow-up the wear rates were higher in patients with marked osteolysis. We found no relationship between the inclination angle of the acetabular component or femoral head orientation and the rate of wear. No acetabular component required revision.

Survival in patients operated on for pathologic fracture: implications for end-of-life orthopedic care

PURPOSE

Life expectancy is routinely used as part of the decision-making process in deciding the value of surgery for the treatment of bone metastases. We sought to investigate the validity of frequently used indices in the prognostication of survival in patients with metastatic bone disease.

METHODS

The study prospectively assessed 191 patients who underwent surgery for metastatic bone disease. Diagnostic, staging, nutritional, and hematologic parameters cited to be related to life expectancy were evaluated. Preoperatively, the surgeon recorded an estimate of projected life expectancy for each patient. The time until death was recorded.

RESULTS

Kaplan-Meier survival analyses indicated that the survival estimate, primary diagnosis, use of systemic therapy, Eastern Cooperative Oncology Group (ECOG) performance status, number of bone metastases, presence of visceral metastases, and serum hemoglobin, albumin, and lymphocyte counts were significant for predicting survival (P < .004). Cox regression analysis indicated that the independently significant predictors of survival were diagnosis (P < .006), ECOG performance status (P < .04), number of bone metastases (P < .008), presence of visceral metastases (P < .03), hemoglobin count (P < .009), and survival estimate (P < .00005). Diagnosis, ECOG performance status, and visceral metastases covaried with surgeon survival estimate. Linear regression and receiver-operator characteristic assessment confirmed that clinician estimation was the most accurate predictor of survival, followed by hemoglobin count, number of visceral metastases, ECOG performance status, primary diagnosis, and number of bone metastases. Nevertheless, survival estimate was accurate in predicting actual survival in only 33 (18%) of 181 patients.

CONCLUSION

A better means of prognostication is needed. In this article, we present a sliding scale for this purpose.

Fixation of total knee arthroplasty improved by mobile-bearing design

We examined the in vivo displacement of mobile-bearing polyethylene and its effect on prosthesis-bone fixation. Thirty-five patients with the Interax ISA mobile platform total knee arthroplasties were examined by roentgen stereophotogrammetric analysis. Our protocol included weightbearing to measure the range of motion of the mobile platform in relation to the tibial component. We also studied the micromotions of the tibial component in relation to the tibia during a 2-year followup. The analysis of micromotion (maximum total motion mean, 0.5 mm; subsidence mean, 0.15 mm) showed this mobile platform design is stable and improves fixation at the prosthesis-bone interface. Longitudinal rotations of the mobile platform occurred in all patients and followed a homogeneous pattern of motion, depending on the examination. However, anteroposterior translations did not show any patterns with specific examination. This suggests the meniscal movement adapts itself to different weightbearing conditions. We measured the in vivo mobile-bearing displacement under static loading conditions. We also observed improved fixation at the bone-prosthesis interface.

The stress-inducible displacement detected through RSA in non-migrating UKR

Roentgen stereophotogrammetric analysis (RSA) under stress conditions was used to investigate possible stress-inducible displacement of the tibial component of unicompartmental knee prostheses (UKR) in which the stability was previously assessed by radiographic evaluation and standard supine RSA examinations. Sixteen patients, implanted with Duracon UNI(R) prosthesis, were selected for this study. The RSA protocol included examinations in plain upright standing posture and during execution of stress-inducing tasks in weight-bearing stance. The first follow-up was performed at an average of 14 months, and the second one at 26 months. The results showed non-negligible stress-induced rotations of the prosthetic tibial component in all the patients in most of the stress tasks performed. Rotational stress tasks and squatting turned out to be the stress conditions in which induced displacement reached the most significant values (p<0.05). These micromotions occurred mainly around the transverse axis of the knee joint and in one examination around the sagittal axis. Stress-induced translations were negligible in all the examinations. Moreover, we focused our attention on two patients suffering from inexplicable pain, and we observed a significant difference in the inducible rotation around the x-axis between these patients and the remaining fourteen. Stress-inducible displacement is a common finding in knee prostheses, but we observed that in patients with inexplicable pain, these micromotions reached values greater than the median calculated on patients without any pain. This result suggests the introduction of the stress-inducible displacement as a new parameter to be taken into consideration when analyzing the outcome of patients treated by UKR.

Prognostic factors for survival in patients with locally recurrent extremity soft tissue sarcomas

BACKGROUND

Factors prognostic for survival in patients with locally recurrent extremity soft tissue sarcomas (STS) are poorly defined, thus making it difficult to identify high-risk patients who may benefit from adjuvant therapy.

METHODS

A total of 1421 patients underwent surgical treatment for primary extremity STS at a single institution between 1982 and 2002. Of these, 179 (13%) patients underwent complete surgical resection of an isolated local recurrence and were the subjects of this study. Clinicopathologic factors from both the primary tumor and the local recurrence were analyzed.

RESULTS

The median interval to initial local recurrence was 16 months: 65% developed a local recurrence by 2 years and 90% by 4 years. Only four patients who presented with a low-grade primary tumor progressed to a high-grade local recurrence. Independent prognostic factors for disease-specific survival after local recurrence were a high histological grade (hazard ratio, 5.1; P = .0004), a large local recurrence tumor size (hazard ratio, 1.5; P = .0001), and a short local recurrence-free interval (hazard ratio, 1.6; P = .0001). Patients who developed a local recurrence >5 cm in < or =16 months (n = 44; 0 low grade) had a 4-year disease-specific survival of 18%, compared with 81% for patients who developed a local recurrence < or =5 cm in >16 months (n = 46; 11 low grade).

CONCLUSIONS

Histological grade, local recurrence size, and local recurrence-free interval are independently predictive of survival in patients with locally recurrent extremity STS. A large local recurrence that develops in a short interval indicates a biologically aggressive tumor with a high tumor-specific mortality. Patients who develop such recurrences are ideal subjects for systemic neoadjuvant therapy trials.

Tibiofemoral kinematic analysis of kneeling after total knee arthroplasty

Some surgeons warn against kneeling after total knee arthroplasty (TKA), because limited clinical data exist. We describe the tibiofemoral contact position of TKA components during kneeling in vivo. Ten posterior-substituting (PS) and 10 cruciate-retaining (CR) designs were examined using a radiographic image-matching technique. Movement from standing to kneeling at 90 degrees produced different responses. CR knees translated anteriorly (medial, 4 +/- 4 mm; lateral, 2 +/- 6 mm). PS knees underwent little posterior translation (medial, 0.2 +/- 3 mm; lateral, 1 +/- 4 mm). Movement from 90 degrees to maximum flexion produced femoral posterior translation (CR medial, 5 +/- 4 mm; CR lateral, 5 +/- 4 mm; PS medial, 6 +/- 4 mm; PS lateral, 6 +/- 3 mm). The relationship between tibiofemoral contact position and flexion angle was more variable for CR (r2=.38) than for PS (r2=.64). Knee kinematics was similar to other deep-flexion weight-bearing activities.

The stability of the cemented tibial component of total knee arthroplasty: posterior cruciate-retaining versus posterior-stabilized design

Micromotion of the tibial component in 40 knee arthroplasties for gonarthrosis was studied using Roentgen stereophotogrammetric analysis. The stability of this component was assessed for 2 years' postoperatively. In all arthroplasties, an attempt was made to reconstruct the preoperative posterior slope. Posterior cruciate-retaining (CR) and posterior-stabilized (PS) components showed at 2 years a maximum total point motion of 0.6 +/- 0.4 mm and 0.7 +/- 0.5 mm, respectively. Whereas 92.5% of the implants were determined to be stable, 1 of the CR group and 2 of the PS group displayed migration between the first and the second year of at least 0.2 mm. A negative correlation between subsidence of the tibial component at 2 years of follow-up and the difference between preoperative and postoperative tibial slope was found. Consequently, we suggest that restoring the original posterior slope of the tibial plateau must be a goal of tibial component implantation.

Kinematics of three variations of the Freeman-Samuelson total knee prosthesis

The effect of changes in the articulating surfaces on the kinematics of the Freeman-Samuelson total knee replacement was evaluated. Twenty-two patients (22 knees) (median age, 69 years) were randomized to a standard design with a fixed polyethylene bearing, a design with a mobile bearing, or a new design with a spherical medial femoral condyle with a fixed bearing. The patients were studied with radiostereometry and film-exchangers at 0 degrees nonweightbearing and during active weightbearing extension from 45 degrees to 15 degrees. The center of the tibial tray with a mobile-bearing prosthesis occupied a more anterior position than observed in the designs with a fixed bearing. The medial femoral condyle center had a more posterior position in the standard design than in the design with a spherical medial condyle. From a distally displaced position at 45 degrees, the medial condylar center displaced a mean of 1.8 mm proximally during extension in the standard design and had a constant position in the meniscal design. In the spherical design the medial condyle was displaced proximally at 45 degrees and displaced a mean of 1.6 mm distally during extension. The reduced anteroposterior and proximodistal translations in the meniscal design are compatible with improved congruency between the components. The design with a spherical medial condyle stabilized anteroposterior motions, but showed more pronounced proximodistal displacement medially than did the other two designs.