Purpose: To report a series of unexpected femoral neck failures in a series total hip replacement surgeries using a modular femoral component.

Method: A series of 443 hip replacement patients received modular necks as part of a non cemented hip replacement with ceramic articulations at the acetabulum and femoral head interface. The first implant of the device was on June 8, 2004 and the last on June 12, 2009. Ninety-one of those patients were enrolled in a RSA study of component stability within the proximal femur.

Results: The index fracture of a femoral neck occurred on March 8, 2009 when the patient (28 months post hip replacement) reported a fall. Subsequently five patients have had a fracture of the modular neck. There were five fractures within the RSA study group and one within the non study group (all occurred 17 months to 30 months post op). All fractures were long necks (10.5 mm). There was no difference in femoral component micromotion as measured with RSA between the fractured group and the unrevised group.

Conclusion: Initial non-destructive testing of one retrieval revealed fatigue failure of the femoral neck. An independent study of all relevant data was implemented which included destructive testing of the implants and clinical data with respect to patient activity. We report the outcome of all those investigations.

Purpose: Component loosening is a leading cause of joint replacement failure. Modifying titanium surfaces with chemically bound functional proteins, such as bone morphogenetic protein (BMP), can efficiently strengthen the interface between prosthesis and bone. A prototype system was developed by using gold nanoparticles (AuNPs) to bridge lysozyme (compositionally similar to BMP) and titanium.

Method: For reference, lysozyme-conjugated gold nanoparticles (Lys-AuNPs) were prepared in solution via two different pathways:

gold compound was reduced in the presence of lysozyme to form Lys-AuNPs or

Both solutions were characterized with transmission electron microscopy, ultraviolet-visible spectroscopy, circular dichroism spectroscopy (CD), and enzymatic assays. Next, AuNPs were prepared on 99.5% titanium foil discs (n=32) through electroless deposition. Deposition parameters were modified to create two groups of discs with different average diameters of AuNPs, measured by scanning electron microscopy. Some discs from both groups also underwent treatment with MPA. All discs were treated with lysozyme and the adsorbed amounts and activities of lysozyme were examined with micro BCA and enzymatic assays.

Results: Lysozyme and AuNPs can be conjugated in solution via two different pathways. CD results showed a significant change in the secondary structure of the lysozyme and decrease in enzymatic activity when directly conjugated to AuNPs; however, little change in secondary structure and enzymatic activity was observed for the lysozyme with MPA functionalized AuNPs. For the AuNPs on the titanium discs, SEM showed that the two groups had significantly different average AuNP diameters. Bioactive lysozyme was immobilized onto the discs and the results suggested that discs with the largest AuNPs treated with MPA had higher adsorption and activity of lysozyme.

Conclusion: A wet-chemical technique may be used to bind lysozyme to titanium via gold nanoparticles. Additionally, it was possible to control the size of the AuNPs on titanium which provides a good platform for further functionalisation with thiol molecules such as MPA. This technique holds promise for binding more functional molecules to surgical implants, hence creating “smart” implants that react to their local environment.

Purpose: Despite their inclusion within clinical practice, standardized radiographs may not accurately project an individual’s level of function and mobility. The purpose of this study is to examine the potential relationship between established radiographic features and lurch; a functional measure of asymmetric gait, in a group of patients who will receive total hip arthroplasty (THA).

Method: Thirty-two patients (16 females, 16 males) identified as hip replacement candidates were recruited, with a mean age of 57.0 years. Lurch was obtained using the Walkabout Portable Gait Monitor (WPGM); a wireless, triaxial accelerometry device. The independent variables were comprised of the Kellgren-Lawrence Scale, and a collection of standard radiographic features, as adopted by the American Academy of Orthopaedic Surgeons (AAOS), the National Institutes of Health (NIH), and the World Health Organization (WHO). Radiographs were blinded, and the surgeon completing the rating scale was unaware of patient’s lurch values. Age-adjusted regression analyses were used to examine the potential association between each radiographic feature and lurch.

Results: Increased amounts of lurch (i.e. functional impairment) were independently associated with higher Kellgren-Lawrence Scale scores (p=.047), increased Joint Space Narrowing in the mid-portion of the joint (zone 2; p=.004), the presence of acetabular wear (p=.045), an increased severity of subchondral femoral head cysts (p=.004), and higher surgeon-rated Visual Analog Scale scores for overall severity of joint degeneration (p=.008). Lurch was not significantly associated with the remaining 10 features which were examined. Further analyses revealed that lurch was not significantly associated with certain demographic factors, including sex, Body Mass Index, and co-morbid health conditions.

Conclusion: Although the Kellgren-Lawrence scale was associated with an objective measure of gait, our results indicate that other radiographic features may provide a more accurate prediction of gait performance among this patient population. As lurch appears to be a robust objective measure of physical impairment, which is unaffected by BMI and co-morbidities, we believe that portable triaxial accelerometers can likely be used to conveniently collect objective gait data. This functional data may be used to supplement clinical efforts to screen and prioritize appropriate hip arthroplasty patients.

Purpose: Radiostereometric Analysis (RSA) is used to measure migration and inducible displacement (ID) of orthopedic implant devices to allow early prediction of implant failure (eg. Aseptic loosening). Total Ankle Arthroplasty (TAA) is used for the treatment of end-stage ankle arthritis. First generation TAA implant have meet with widespread failures while some second generation TAA implants are showing improved results. In this study RSA is used to evaluate the biomechanical properties of a new third generation TAA implant in an attempt to set a standard for the biomechanical evaluation on TAA implants in-vivo.

Method: Patients undergoing TAA were enrolled consecutively (n=12; 7 males; mean age=59 years; mean BMI=29) and had 8 markers (0.08mm) inserted in both the tibia and talus during surgery. Standing, weight-bearing RSA exams were performed at 3 and 6 months and compared to concurrent supine exams to determine component ID.

Results: For tibial components: at six months the components had translated posteriorly (0.3mm±0.5) and proximally (0.5mm±0.2), tilted into varus (0.5°±1.3), and tilted posteriorly (0.4°±0.8). The magnitudes of ID for the tibial components were moderate (mean < 0.2mm and 0.5°, standard deviation < 0.3mm and 2.2° in each direction). For talar components: at six months the components had translated distally (0.28mm±0.35), rotated internally (0.21°±1.32) and tilted posteriorly (0.15°±0.90). There was varus/valgus tilt measured in the talar components but there was no consistent direction of migration (0.03°±1.4). At six months the magnitudes of ID for the talar components were small (mean < 0.1mm and 0.25°, standard deviation < 0.2mm and 0.6° in each direction).

Conclusion: An RSA methodology has been established to predict stability.

Purpose: Resurfacing arthroplasty (RA) is becoming popular as an alternative to total hip arthroplasty (THA). Direct to consumer advertising reports good to excellent outcomes and patients sometimes seek RA on the assumption that it provides increased survivorship over THA. We report the 5 year survivorship of 25 RA procedures done at one institution.

Method: 25 patients were prospectively followed after receiving a Conserve Plus RA through a direct lateral approach between 2002 and 2005. There were 22 males and 3 females with an mean age at surgery of 42 years. The average length of follow-up was 40 months. Failure was defined as revision of the components or a pending revision.

Results: At a mean of 2 years follow-up, 3 patients had been revised and 2 more were scheduled for revision surgery for a failure rate of 20%. Reasons for revision included 1 neck fracture and 2 aseptically loose acetabular components. The 2 patients waiting for revision also had aseptically loose acetabular components. Patients receiving or requiring revision were operated on throughout the series and were not necessarily part of the surgical learning curve.

Conclusion: RA of the hip done through a direct lateral approach in this series had an unacceptably high failure rate for aseptic loosening of the acetabular component.

Purpose: To meet the increasing demand for arthroplasty in Canada healthcare providers are investigating efficiency improvements to maximize utilization of limited surgical resources. One target is routine annual arthroplasty follow-up for which there are no established guidelines. A previous study by the authors revealed that 52% of arthroplasty patients could be followed with standardized questionnaires and x-rays resulting in a 30% savings to the healthcare system. In this study we report the patient time, travel and financial burdens for annual follow-up at a tertiary care centre versus a hypothetical model using standardized assessment at community hospitals and a web-enabled PACS.

Method: A consecutive sample survey of elective THA and TKA patients (n=158; 99 females; 94 THA; 64 TKA; mean age=69 years) who were at least twelve months postoperative. Patient’s address, work status, mode of travel and times required for travel, physician consult, x-ray, and clinic wait were recorded. A web-based mapping application was used to determine distances from patients’ homes to the tertiary care centre and nearest community hospital. Financial burden was calculated using Statistics Canada figures for average Canadian wage and private vehicle travel costs.

Results: Sixteen patients were working at the time of the study and 149 travelled in a private vehicle. For the tertiary care centre: round-trip distance was 168 km, total time burden was 194 minutes (travel=129 minutes, clinic wait=54 minutes, time with physician=6 minutes, x-ray=5 minutes), and total financial burden per patient was $58. For the community hospital: round-trip distance was 19 km, total time burden was 39 minutes (travel=14 minutes, clinic wait=20 minutes, x-ray=5 minutes), and total financial burden was $7.

Conclusion: Utilizing community hospital resources for arthroplasty follow-up could reduce patients’ travel by 89%, financial burden by 88%, and time burden by 81%. This approach has the potential to enable the focusing of arthroplasty clinic follow-up resources only on patients reporting problems or with symptomatic x-rays thus freeing up surgeon time for surgeries. There are also the broader societal implications of reducing ‘health miles’ and the resulting carbon dioxide emissions related to health care delivery by leveraging new technologies to move information rather than people.

Purpose: Porous metal technology may have significant impacts on implant fixation and long-term survival due to their high co-efficient of friction and similarity to trabecular bone in morphology and mechanical behaviour. While promising, the in vivo mechanical behaviour and micromotion at the interface has not previously been reported on. We report on the 2-year results of an RCT using radiosterometric analysis (RSA) to asses a porous metal (PM) monoblock tibial component.

Method: Patients undergoing TKA were randomized to receive a either the PM (n=34) or the cemented tibial component (n=33). A standardized protocol was used for intra and post-operative factors. RSA exams were obtained postoperatively within 4 days of surgery and at 6, 12 and 24 months. One patient was excluded due to an intraoperative complication, and four others were lost to follow-up due to poor bead visibility or morbidity. Standard subjective outcome measures were applied.

Results: There were no revisions in either group. The PM group exhibited two distinct migration patterns. One group stabilized immediately with similar migration to the cemented cases (0.38 vs. 0.46 p=0.4). A subset of 6 PM cases demonstrated significantly higher initial migration (mean=2.01mm, p< 0.01) but appeared stable at 2 years. In addition, 3 of the 6 high migration cases manifested independent bead subsidence. This was determined to be due to PM plate deformation. Two cemented cases were considered at risk for early failure due to aseptic loosening because of RSA migration pattern. There were no differences between groups in the subjective health outcome measures.

Conclusion: A subset of PM components demonstrated high early migration followed by stabilization. It appears that some of these PM components deformed under load, most often in the posteromedial corner, perhaps as a result of malalignment or ligament imbalance. The implications of this finding are yet to be determined.

Purpose: To test for a decrease in knee musculature co-activation at one- and two-year post total knee replacement (TKR) compared to pre-TKR values.

Method Thirty men and 35 women with knee osteoarthritis (OA), after providing informed consent, participated in this study. Surface electromyograms (EMG) recorded the activation of seven muscle sites (rectus femoris, vastus lateralis and medialis, lateral and medial hamstrings, lateral and medial gastrocnemius) while subjects ambulated, at a self-selected velocity, along a six-meter walkway; one week prior to TKR surgery, and one- and two-years post-TKR. Linear enveloped EMG waveforms, amplitude normalized to 100%MVIC and time normalized to 100% of the gait cycle, were entered into a principal component analysis model [1]. A two-factor (pre-post, muscle) repeated measures ANOVA was applied to test statistically significant main effects (pre-post, muscle) and interactions (alpha = 0.05).

Results: The mean age, mass and height pre-TKR were 63.4 years, 91.4 kg and 1.69 m, respectively. Forty seven and 25 subjects completed the one- and two-year follow up, respectively. Walking velocity increased from 0.9 m/s pre-TKR to 1.1 m/s for both one- and two-year post TKR. Four principal components explained 89% of the variance in the waveform data. PC1 (60% of the variance), associated with co-activation throughout the entire stance phase, was found to be statistically significant (p< 0.05). The post hoc analysis revealed no significant differences between one- and two-year post-TKR PC1 scores, but the two vasti muscles and lateral hamstring had significantly lower PC1 scores post-TKR compared to pre-TKR values. There were significant differences among muscles with the two vasti muscles higher pre-TKR compared to all other muscles, and lateral hamstring higher pre-TKR than the remaining four muscles.

Conclusion: PC1 captured a co-activation pattern illustrating muscle activation during the majority of the stance phase of gait for the vasti and lateral hamstring muscles. This pattern, previously shown in severe OA gait [1], is considered an adapted response to the pain and joint instability associated with latter stages of OA progression. These findings support that the neuromuscular control strategies are altered within one year with no additional change for the two year post-TKR measures. These results support a more efficient neuromuscular control strategy post-TKR and perhaps an associated decrease in metabolic cost and an improvement in function.

Purpose: To investigate the effect that gender may have on the RSA defined migration pattern of cemented and uncemented tibial components in total knee arthroplasty (TKA).

Method: 70 patients with primary osteoarthritis of the knee were randomized to receive a Nexgen uncemented Trabecular Metal (TM) monoblock tibial component (n=37; 20 female; mean age=66 years; mean BMI=32) or cemented cobalt chrome modular tibial cmponent (n=33; 19 female; mean age=65 years; mean BMI=33). The same design of posterior stabilized tibial component was used in all cases. Four experienced knee surgeons followed a standardized surgical technique (PCL resection, patella resurfacing, RSA bead placement in poly-ethylene and tibia) and post-operative protocol (CPM as tolerated, no drains, WBAT). Within 4 days of surgery and at 6, 12 and 24 months post-operatively patients underwent bi-planar x-rays. RSA analysis was performed with MB-RSA (MEDIS, Leiden). Results were reported as maximum total point motion, and 6 degrees of freedom translations and rotations. A repeated measure ANOVA was used to test for differences and all statistical analysis was performed using Minitab V.14 (Minitab Inc, State College, PA, USA).

Results: Highly significant differences were seen in the migration patterns in females between the TM and cemented tibial components. Females with the TM implant tended to rotate internally (0.29° vs. −0.16°, p< 0.0001), tilt posteriorly (−0.49° vs. 0.01°, p< 0.0001) and subside (−0.357mm vs. 0.00mm, p< 0.0001) compared with the female subjects with the cemented implant. In the male group, only subsidence was different between the TM and cemented groups (−0.344mm vs. −0.01mm, p< 0.0001).

Conclusion: Uncemented TM implants in females tended to tilt posteriorly, rotate internally and subside. Uncemented implants in males tended only to subside. The increased tilting and rotation detected in females could be due to lower BMD or to mismatching between the shape of the female proximal tibial and the tibial component. These results may have implications for the current use of uncemented implants in females and for future design of uncemented implants for the female population.

Purpose: To investigate the association between pre-operative gait patterns and the RSA defined migration migration pattern of cemented and uncemented tibial components post total knee arthroplasty (TKA).

Method: 43 patients with primary osteoarthritis of the knee underwent Optotrack gait analysis in the week before TKA surgery. Three-dimensional net external knee joint moments and angles were calculated with inverse dynamics. The variability in subject gait patterns was captured with a set of discrete scores that represented weightings on objectively-extracted features of the gait waveform data using principal component analysis. The subjects were randomized to receive the uncemented Nexgen Trabecular metal Monoblock tibial component (n=22; mean age=66 years; mean BMI=32) or the modular cemented cobalt chrome tibial component (n=21; mean age=65 years; mean BMI=33). Both groups were posterior-stabilized and used the same design femoral component. Four experienced surgeons followed a standardized surgical technique and postoperative protocol. Within 4 days of surgery and at 6 months post-operatively, patients had bi-planar knee x-rays taken. RSA analysis was performed with MB-RSA (MEDIS, Leiden). RSA results were reported as maximum total point motion, translations and rotations at 6 months. Spearman’s rank correlations were used to examine the relationship between the first three principle component (PC) scores for each gait variable and the RSA metrics (P< 0.05).

Results: There was a highly significant correlation between MTPM and the first principal component (PC) of the knee adduction moment, which represented the overall magnitude of moment during the stance phase of the gait cycle (r=0.459, P=0.005). Higher preoperative knee adduction moment magnitudes were associated with greater MTPM postoperatively. Internal rotation of the components was correlated with the second PC of internal/external rotation moment at the knee, which represented the magnitude of the moment at load acceptance (r=0.341, P=0.042). Greater knee internal rotation moments at load acceptance preoperatively were associated with higher internal rotation postoperatively.

Conclusion: The amount of postoperative migration of the tibial component in TKA was found to be correlated with preoperative gait patterns, particularly to the magnitude of the knee adduction moment.. These results suggest that surgical success and prosthesis survivorship may be dependent on the preoperative mechanical environment of the knee joint (i.e., gait).

Purpose: The purpose of this study was to determine what differences exist in the knee flexion, rotation and adduction moments and periarticular knee muscle activation patterns between subjects with medial compartment knee osteoarthritis (OA) and those with lateral compartment knee OA.

Method: Forty eight individuals with knee OA were studied. The group was divided into those with predominantly medial compartment involvement (38 subjects, age 63 ± 8 years) and those with lateral involvement (10 subjects, age 63 ± 9 years). Three-dimensional motion (Optotrak) and ground reaction force (AMTI) data were collected while the subjects walked at a self-selected velocity. The knee flexion, rotation and adduction moments, time normalized to the percentage of one gait cycle, were calculated using an inverse dynamics approach. Electromyograms (EMG) were also collected from the rectus femoris, vastus lateralis, vastus medialis, medial and lateral hamstrings, and medial and lateral gastrocnemius and normalized to maximum voluntary isometric contractions. Knee moments and waveforms for each muscle for one complete gait cycle were analyzed for group differences using principal component analysis (PCA) followed by Student’s t-tests (alpha-adj = 0.017) for the PCA scores.

Results: The two groups were statistical similar in terms of age, height, weight, and walking velocity (p> 0.05). PCA analysis revealed statistically significant differences (p< 0.017) in patterns for the knee adduction moment, medial gastrocnemius, and lateral hamstrings between the two groups.

Conclusion: As expected, there was a difference in the knee adduction moment between the two groups. What is novel is that the muscle activation patterns from the lateral site group are consistent with an attempt to unload that compartment. The results of this study provide evidence that biomechanical and neuromuscular differences do exist, depending on the OA site. This could have implications for developing site-specific conservative management approaches

To study the association between hip and ankle biomechanics during gait and moderate knee osteoarthritis (OA).

Gait analysis was performed on a group of forty-four patients clinically diagnosed with moderate knee OA, and on a group of sixty asymptomatic subjects. Three-dimensional net joint angles and net joint reaction moments at the hip, knee and ankle joints were calculated. Peak values were extracted from the gait waveform patterns and compared between the two subject groups with Student’s t-tests.

The peak hip extension moment, the peak hip adduction moment, the peak hip internal and external rotation moments, and the peak ankle dorsiflexion and plantarflexion moments were all reduced in the knee osteoarthritis population compared to the asymptomatic population.

Differences in knee joint loading patterns with moderate knee osteoarthritis have been previously reported, but these data suggest that changes in the mechanical environment of all lower extremity joints are associated with early stages of knee osteoarthritis. Other studies have associated reduced peak hip adduction moments with reduced likelihood of OA progression. These data provide a rationale for hip abductor muscle strengthening as a means to lower knee joint loading.