Background

Cementless Total Knee Arthroplasty has been developed to reduce the incidence of failure secondary to aseptic loosening, osteolysis and stress-induced osteopenia, especially in younger and more active patients. However, failures are still more common compared to cemented components, especially those involving the tibia. It is hypothesized that this is caused by incomplete contact between the tibial tray and the underlying bony surface due to: (i) inadequate flatness of the tibial osteotomy, or (ii) failure of implantation to spread the area of contact over the exposed cancellous surface. In the present study we compare the contact area developed during implantation of a cementless tray as a function of the initial flatness of the tibial osteotomy.

Introduction

The association between CoCr joint replacements and adverse tissue reactions has led to increased interest in alternative materials that are both biocompatible and wear-resistant. One approach is to manufacture components from titanium alloys with a hardened articulating surface to increase resistance to scratching and surface damage caused by third-body particles. In this study we investigate methods for characterizing the performance of retrieved TiAlV components with nitrogen-hardened bearing surfaces.

Introduction

The Vancouver Classification System presents a systematic approach to classification of periprosthetic fractures of the proximal femur (PFPFs) that has been validated in previous studies. However, with the introduction of tapered fluted stems and cable plates since the introduction of the Vancouver System, the connection between fracture class and the preferred method of treatment is often unclear. The present study was undertaken to identify fracture patterns surrounding contemporary femoral stems and the relationship between the current method of treatment and the Vancouver Class of the periprosthetic fracture.

Introduction

The demands placed upon joint surgeons are perhaps greatest when treating the revision arthroplasty patient, who present with complications demanding skill in diagnosis and evaluation, interpersonal communication and the technical aspects of the revision procedure. However, little information exists identifying which specific tasks in revision arthroplasty are most difficult for surgeons to master, and whether the greatest challenges arise from clinical, cognitive or technical facets of patient treatment. This study was undertaken to identify which tasks associated with revision total knee replacement (TKR) are perceived as most challenging to young surgeons and trainees to guide future efforts in surgical training and curriculum development.

Objectives

A lack of connection between surgeons and patients in evaluating the outcome of total knee arthroplasty (TKA) has led to the search for the ideal patient-reported outcome measure (PROM) to evaluate these procedures. We hypothesised that the desired psychometric properties of the ideal outcome tool have not been uniformly addressed in studies describing TKA PROMS.

Introduction: Although Hip Resurfacing Arthroplasty (HRA) has become a popular alternative to THR, the outcome of these procedures varies extensively between centres. This has been attributed to variations in patient selection, surgical experience, and patient volume. In this study we examine the effect of hospital volume on the outcome of hip resurfacing using a national database.

Methods: We examined data collected by the Australian Joint Registry between September 1999 and December 2006 relating to 8945 hip resurfacing procedures performed in 196 hospitals. Survivorship of the implanted components was calculated with revision as the end-point. The cumulative rate of revision at 4 years was compared between hospitals as a function of the number of cases performed during the study period (< 25, 25–49, 50–100, > 100 procedures). Using the log-rank test, differences in the risk of revision, corrected for age and sex of patients, were compared for low (< 25 cases) vs. higher volume centres (> 25 cases). We also estimated the number of cases/year of each centre and examined its apparent impact on revision rate.

Results: The majority (74%) of hospitals reporting performed less than 30 resurfacing procedures over the 7 year study period, with 64% of procedures performed at 16 “high volume” hospitals (> 100 cases), Overall, 249 of the 8945 resurfacing procedures (2.9%) were performed for revision of the original components. At 4 years, the cumulative revision rate dropped from 5.8% for hospitals performing less than 50 cases to 4.7% (50–99 cases) and 2.7% (> 100 cases) for larger volume centres. When adjusted for differences in patient age and sex, the risk of revision was 66% higher in hospitals performing < 25 cases. Based on the available data, the gap in revision rate between high and low volume centres is reduced by 50% once a surgeon’s operative volume exceeds 6 cases per year. On average, this corresponds to a learning curve of approximately 5 cases.

Conclusions: In this study, hospital volume is primarily a reflection of the operative experience of individual surgeons. Our results show that the outcome of hip resurfacing is strongly dependent on the experience of the surgeon and hospital performing the procedure. Even when adjusted for age and sex of the patients, the risk of revision increased by 66% when cases were performed at low volume centres. This supports the need for increased training of surgeons before undertaking hip resurfacing.

Introduction: It is generally agreed that the function of the knee after total knee arthroplasty needs to be improved to meet the expectations of younger and more active patients. However, little objective information consists to quantify the frequency and importance of activities that place increased biomechanical demand on the knee. This study was performed to asses which specific “high-demand” activities are actually performed by patients after knee replacement, and which activities are of greatest personal importance to the patient.

Methods: An initial group of 243 patients (47% male; 53% female, average age: 70 years; range: (45–91 yrs)) were enrolled in this study with Institutional approval. All were at least 1 year post knee replacement and resided in the Houston area. All participants completed a validated, self-administered knee function questionnaire consisting of 55 scaled multiple choice questions regarding each respondent’s physical activities, limitations, and level of importance for those activities. Participants were also asked to assess the personal importance of each activity and the severity of any symptoms experienced when each activity was performed. An expanded version of the Knee Function Questionnaire was completed by a second group of 101 patients from 5 centres in the United States and Canada. This instrument addressed 120 physical, vocational and recreational activities involving the knee. Fifty-four of these activities were considered “highly demanding” and were drawn from a wide variety of water and team sports, martial arts, running/biking, exercise, weight-lifting and fitness training.

Results: The initial study demonstrated that TKR patients participate in a wide range of “high demand” activities. Most commonly, activities requiring increased knee flexion were gardening (58% participation), kneeling (64%), and squatting (39%). Moderate to severe difficulty was reported by 39% (squatting) to 64% (kneeling) of respondents performing these activities. The most common activity which placed increased loads on the affected joint was carrying loaded shopping bags (47% participation), which provoked Significant symptoms in 23% of patients. The expanded nation-wide study showed that after TKR, few patients actually perform high impact competitive sports although many patients perform individual exercise routines which potentially place Significant demands on the knee. The most common of these “high demand” activities were still squatting and kneeling, but also included participation in gym and exercise activities, typically leg extensions (59%), leg curls (35%) and leg press exercises (33%).

Conclusions:

Kneeling and squatting are the most common “high-demand” activities actually performed on a routine basis by patients after TKR

Summary: Intraoperative assessment of knee kinematics during passive flexion and extension of the unloaded knee fails to adequately replicate the kinematics of the loaded knee during a functional activity.

Introduction: Intraoperatively, the alignment and stability of the prosthetic knee are assessed by observing the motion of the articular surfaces during passive flexion/extension. However, this examination is performed via a medial arthrotomy with limited visibility of the articular surfaces and with the joint unloaded. In view of these limitations of the intraoperative exam, this study was conducted to determine whether unloaded knee motion observed on the operating table is predictive of the motion of the knee during a loaded functional activity.

Methods: Six cadaveric knees were tested:

in a simulator which reproduced the manual intraoperative manipulation of the knee during unloaded passive range of motion (PROM), and

Standard 14cm midvastus medial arthrotomies were performed on each knee, and the PROM and squatting simulations were repeated. A laser scanner was used in conjunction with CT models to recreate the three-dimensional position of the knee and allow calculation of medial and lateral femoral rollback and tibial rotation.

Results: With PROM, the femoral condyles translated posteriorly (medial: 6.8±2.2mm, lateral: 15.2±1.3mm) and the tibia rotated internally (13.8±2.0°). A similar motion pattern was observed during squatting with slightly less medial (5.2±0.7mm; p=0.57), and lateral (12.8±0.9mm; p=0.06) rollback and rotation (10.7±1.54°; p=0.30). Interestingly, paradoxical anterior translation of the femur (> 2mm) and external rotation of the tibia (> 2°) were observed in 30% of knees during a loaded squat; however, this motion was not predicted by the PROM test.

Discussion: Similar knee kinematics are observed during unloaded flexion/extension and a physiologic squatting activity. However, the unloaded intraoperative test was unable to predict the occurrence of paradoxical motion during functional loading. Therefore, passive intraoperative testing of the knee is of limited value as a predictor of functional knee biomechanics.

Introduction: There is an increasing appreciation of the potential impact of ethnic and gender diversity on access to healthcare. Previous studies have shown that both race and gender are important confounding factors. In this study we isolate the influence of ethnicity on the functional outcome of total knee replacement by examining outcomes in female patients.

Materials and Methods: We reviewed a data-base of 412 female patients (518 knees) who had undergone primary TKA performed by a single surgeon between 1990 and 2008. Eighty-seven of these patients (25 African-American, 23 Hispanic and 26 Caucasian patients) were case-matched for age and BMI at the time of surgery. The average patient age was 67.0 years with a BMI of 32.0. The groups showed no statistical different in age (p=0.99) or BMI (p=0.90). Preoperative and postoperative Knee Society scores were available on all patients in addition to marital status. Outcome measures of all three groups were compared using ANOVA statistical methods with post hoc analysis.

Results: Post-op Knee Society Scores were Significantly lower in the African-American patients (76.2, p=0.02) than the Hispanic (85.1) and Caucasian (87.9) groups. There was also a Significant difference in post-op pain scores for African-American, Hispanic, and Caucasian patients were 32.2, 40.3, and 42.8 respectively, (p=0.02) showing a statistically Significant difference between groups. The average Function Score was also lower in both African-American (61.1) and Hispanic (63.3) groups when compared to Caucasian (72.1) but this difference was not statistically Significant (p=0.09, p=0.25). There was no Significant difference in preoperative knee scores, post-op ROM or stability, or marital status among the three groups (p > .05).

Discussion:

Within the female population, ethnicity was shown to have a Significant influence on the outcome of TKA as inferior results were reported by both Hispanic and African-American patients when compared to Caucasians. This effect is particularly marked in African-American women whose Knee Society Scores were 13% lower at follow-up compared to Caucasians.

Introduction: With the development of powerful computing tools, it is now possible to quantify variations in skeletal morphology using standardized analytical protocols. In this presentation, we describe the development of computer-based tools to analyze components of femoral deformity in developmental hip dysplasia (DDH) and femoro-acetabular impingement (FAI).

Methods: Typically, three dimensional surface-splined computer models of bones are generated by reconstructing CT scan data. The models generated are then segmented into discrete objects (e.g. the femoral head, neck, shaft, condyles, sulcus, and apophyses) and a coordinate system is attached to each anatomic object to define its relative position and orientation in space. The size of each object can be described by characteristic parameters (eg height, length, width), and its shape with dimensionless ratios (eg width/length). Other methods include principal component analysis which expresses te principal sources of statistical variation in object dimensions, and correspondence analysis, which describes the variation of each point on the surface of a bone compared to the average specimen in the observed population.

Illustrative Applications:

DDH

These methods have been applied to examine systematic variations in the shape and dimensions of the dysplastic femur through reference to data from 171 dysplastic and 84 skeletally normal patients. Of the 171 dysplastic femora, 74 (43%) were graded as Crowe I, 82 (48%) as Crowe stages II or III, and 15 (9%) as Crowe IV. The change in femoral morphology was quantified as a function of the grade of deformity in comparison with normal controls. The principal sources of deformity were also identified.

Results: The results of these analyses will be presented during the lecture.

Conclusions: Mathematical analysis of the shape of bones allows us to describe the type and severity of skeletal deformities in precise quantitative terms. This leads to new, three-dimensional definitions of skeletal phenotypes, and allows automated screening and classification of imaging data sets for the detection of dysmorphic conditions. This approach also has the potential to provide new insights into the true nature of complex deformities presenting for orthopedic treatment.

Interfacial defects between the cement mantle and a hip implant may arise from constrained shrinkage of the cement or from air introduced during insertion of the stem. Shrinkage-induced interfacial porosity consists of small pores randomly located around the stem, whereas introduced interfacial gaps are large, individual and less uniformly distributed areas of stem-cement separation. Using a validated CT-based technique, we investigated the extent, morphology and distribution of interfacial gaps for two types of stem, the Charnley-Kerboul and the Lubinus SPII, and for two techniques of implantation, line-to-line and undersized.

The interfacial gaps were variable and involved a mean of 6.43% (sd 8.99) of the surface of the stem. Neither the type of implant nor the technique of implantation had a significant effect on the regions of the gaps, which occurred more often over the flat areas of the implant than along the corners of the stems, and were more common proximally than distally for Charnley-Kerboul stems cemented line-to-line. Interfacial defects could have a major effect on the stability and survival of the implant.

Using a modern cementing technique, we implanted 22 stereolithographic polymeric replicas of the Charnley-Kerboul stem in 11 pairs of human cadaver femora. On one side, the replicas were cemented line-to-line with the largest broach. On the other, one-size undersized replicas were used (radial difference, 0.89 mm sd 0.13).

CT analysis showed that the line-to-line stems without distal centralisers were at least as well aligned and centered as undersized stems with a centraliser, but were surrounded by less cement and presented more areas of thin (< 2 mm) or deficient (< 1 mm) cement. These areas were located predominantly at the corners and in the middle and distal thirds of the stem. Nevertheless, in line-to-line stems, penetration of cement into cancellous bone resulted in a mean thickness of cement of 3.1 mm (sd 0.6) and only 6.2% of deficient and 26.4% of thin cement. In over 90% of these areas, the cement was directly supported by cortical bone or cortical bone with less than 1 mm of cancellous bone interposed.

When Charnley-Kerboul stems are cemented line-to-line, good clinical results are observed because cement-deficient areas are limited and are frequently supported by cortical bone.

We studied the morphometry of 35 femora from 31 female patients with developmental dysplasia of the hip (DDH) and another 15 from 15 age- and sex-matched control patients using CT and three-dimensional computer reconstruction models. According to the classification of Crowe et al 15 of the dysplastic hips were graded as class I (less than 50% subluxation), ten as class II/III (50% to 100% subluxation) and ten as class IV (more than 100% subluxation).

The femora with DDH had 10 to 14° more anteversion than the control group independent of the degree of subluxation of the hip. In even the most mildly dysplastic joints, the femur had a smaller and more anteverted canal than the normal control. With increased subluxation, additional abnormalities were observed in the size and position of the femoral head. Femora from dislocated joints had a short, anteverted neck associated with a smaller, narrower, and straighter canal than femora of classes I and II/III or the normal control group.

We suggest that when total hip replacement is performed in the patient with DDH, the femoral prosthesis should be chosen on the basis of the severity of the subluxation and the degree of anteversion of each individual femur.