A ligament tensioning device was used during total knee arthroplasty procedures to determine the effective stiffness of the soft tissue envelope around osteoarthritic knees. This information was used to calculate the resting forces on polyethylene components in well balanced knees. Various patient and implant factors were investigated to see if they correlated with the stiffness of the soft tissues around arthritic knees. The effective stiffness of the soft tissues was found to be higher when the posterior cruciate ligament was preserved compared to when it was sacrificed.

The purpose of this study was to determine, in vivo, the effective stiffness of the soft tissue envelope around the knee and to estimate the resting force on the implanted polyethylene component during total knee arthroplasty (TKA). A ligament tensioning device was used to measure displacement between the tibia and the femur versus load during eighty-six consecutive TKA procedures. A maximum of five measurements were made in both flexion and extension. The measurements were taken after bone cuts were made and soft tissue balancing was performed. The effective stiffness of the knee soft tissue envelope was determined in flexion and extension. Post- operative range of motion was measured while the patient was still under anesthetic. There was no significant difference in the average effective stiffness between men and women or between flex-ion and extension. Age did not appear to correlate with effective stiffness. The average effective stiffness was significantly higher in posterior cruciate retaining knees compared to those in which the posterior cruciate was sacrificed. There was no statistical significance between the average resting force on the polyethylene in men versus women, in flexion versus extension, or in posterior cruciate retaining knees versus posterior cruciate sacrificing knees. The immediate post-operative range of motion did not correlate with the resting force on the implanted polyethylene

Purpose: The purpose of this study was to determine how to minimize intramedullary femur pressures, and therefore the risk of fat embolus syndrome, during surgical procedures which require preparation and instrumentation of the femoral canal.

Methods: To study intramedullary femur pressures and experimental model and a finite element model were developed. The experimental model ustilized a bone analogue which consisted of a porous plastic cylinder, having similar porosity and pore size to human femoral bone, with bone marrow being represented by a paraffin wax/petroleum jelly mixture. The finite element model consisted of a three dimensional analysis of a cylinder filled with bone marrow with a reamer advancing through it. Variables such as speed of insertion, fluid viscosity and relative diameters of the instrument and the inner diameter of the simulated bone were varied to see how they affected pressures.

Results: The intramedullary pressures increased with increasing speed of instrument insertion, increasing marrow viscosity, and increased diameter of the instrument relative to the inner diameter of the bone. Experimental and finite element results were in reasonable agreement.

Conclusions: We concluded that slower instrument insertion rates and a greater ratio of bone inner diameter to instrument diameter may minimize the intramedullary pressures and therefore minimize the risk of fat embolus syndrome. In addition, two novel techniques to analyze intramedullary femur pressures have been developed.

Funding : Education Grant

Funding Parties : NSERC

We reviewed and discussed the results of one hundred and fifty-five proximal femoral allografts for revision total hip replacement at an average of eleven years (range , five to twenty years).We looked at graft survivorship, functional results, radiographic assessment and complications. We concluded that this is an excellent technique for restoration of bone stock in the multiplied revised hip.

To review the results of revision hip replacement with use of a proximal femoral allograft (PFA) to restore femoral bone stock.

Between 1983 and 1998 a PFA – prosthetic composite was used to revise two hundred and twenty-seven hips in two hundred and ten patients. Of these two hundred and ten revisions involved an allograft longer than 8 cm. The average age of the patients at the time of revision was sixty-six years. The average number of previous total hip replacements was 2.2. Each patient was assigned a SF-12 score and a Short WOMAC Score. Radiographic assessment for trochanteric union, allograft-host union, component stability, graft fracture and resorption was performed.

At an average of 11.2 years ( range, five to twenty years) after the revision, one hundred and eighty-five patients were alive, twenty-five patients had died and thirty were unavailable for follow-up. SF-12 and short WOMAC scores are still being calculated at the time of abstract submission. 4.4% of hips failed due to infection with 50% being successfully revised. Aseptic loosening of the construct occurred in 3.9% and 78% of these were revised at the time of follow-up. Nonunion of the allograft-host junction occurred in 4.8% and dislocation in 8.4%. Success was defined as a stable implant and no need for additional surgery at the time of follow-up. Success was noted in 84% of available cases.

At an average of eleven years revision hip arthroplasties with a PFA are performing very well. This technique remains an excellent alternative when confronted with femoral bone loss in the revision hip setting.

This is a retrospective study of fifty nine hips in fourty nine patients with a previous total hip replacement for developmental dysplasia of the hip who underwent a revision arthroplasty of the hip. Fifty three patients were available for follow up. Radiographs and charts were reviewed and functional outcome scores were obtained in order to determine if a correlation existed between cup position and functional outcome and survivorship. Cup height was found to be a statistically significant predictor for functional outcome and cup survivorship.

To determine if cup height, lateralization or angle are correlated with functional outcome or survivorship in revision total hip replacement (THR) in patients with a previous THR for developmental dysplasia of the hip (DDH).

There is a paucity of literature correlating functional outcome with cup position in revision THR.

Cup height was found to have a statistically significant (p< 0.05) correlation with Harris Hip, SF36, and WOMAC functional scores. High hip centers correlated with worse scores. In addition, patients with hip centers less than 3.5 cm above the radiographic tear drop had a statistically significant improvement in cup survivorship compared to those with higher hip centers.

A retrospective investigation of forty-nine sequential patients (fifty-nine hips) previously diagnosed with DDH who underwent revision THR at our center between 1984 and 2000 was performed. Forty-three patients (fifty-three hips) were available for survivorship analysis and thirty-five patients (forty-five hips) were available for functional analysis. The mean follow up was one hundred and eighteen months (range 36–230). Three independent variables identified apriori as possible correlates were cup height, lateralization and angle as measured on the AP radiographs. Functional outcome measurement consisted of the Harris Hip, SF36 and WOMAC questionnaires. Linear regression analysis and Kaplan-Meier curves were used to determine if any of the variables correlated with functional outcome or survivorship.

Restoration of hip center height to as close to the radiographic tear drop as possible improves functional outcome. Placement of the cup to within 3.5 cm of the tear drop improves cup survivorship.

We reviewed and discussed the results of thirteen distal femoral allografts in conjunction with revision total knee arthroplasty for the treatment of periprosthetic femoral supracondylar fractures associated with poor bone stock. The mean follow up time was six years. We looked at graft survivorship, functional outcome, radiographic assessment, and complications. We concluded that this is a viable salvage procedure for this type of injury.

The incidence of periprosthetic supracondylar fractures of the femur is rising due to the aging population, and the increased number of total knee arthroplasties (TKA) being performed. One option for the treatment of severe fractures, associated with poor bone stock, is the use of a distal femoral allograft (DFA) in conjunction with revision TKA. The purpose of this study was to review and discuss the results of thirteen consecutive patients who were treated at our center between 1990 and 2001.

Data was obtained from a prospective database. Ten of the thirteen patients were available for follow up. The average age was sixty-five years (range twenty-four to ninety-three) and the mean length of follow up was six years (range one to twelve). A chart review was performed to identify complications and graft survivorship. Functional assessment was made on the basis of the modified Hospital for Special Surgery knee score (HSS) and the MOS 36-ITEM Short Form Health Survey (SF-36). Patients were evaluated radiographically by two independent observers (kappa = 0.75, P = 0.02) in an attempt to determine union between the graft and host bone, graft resorption, and component loosening. The average postoperative HSS score and SF-36 were seventy-five and eighty-eight respectively. Mean flexion was 100°. One had an amputation due to the recurrence of infection. X-rays showed no migration, no loosening, good interface union in nine cases and mild to moderate resorption in three cases. We concluded that this is a viable salvage procedure for this type of injury.

A novel, validated three dimensional finite element model of the femur was used to characterize the stress concentration in the bone at the proximal end of a fracture fixation plate. A supracondylar fracture of the distal femur fixed with a plate was modeled utilizing physiologic load patterns simulating several phases of a cycle of gait. The relative maginitude and length of the zone of increased stress was characterized. The effects of varying plate geometry and material in the attempt to decrease stress concentration at the end of the plated were investigated.

The exact nature and distribution of stresses around femoral fracture fixation plates remains unclear making it difficult to determine how close to existing hardware a distal femoral plate can be implanted. Our objective was to use a novel, validated finite element (FE) model to examine the stress distribution at the proximal end of the plate.

The von Mises element stresses in the bone without the implant were compared to those with the implant. Additionally, we determined the effect of metal (titanium versus stainless steel), and plate taper (ten, thirty and forty-five degrees) on stresses at the proximal end of the plate.

The peak von Mises stress in the plated bone occurred below the corners of the plate, and was approximately four times that in the un-plated case (thirty-eight MPa versus nine MPa). We identified a distance of 34 mm (approximately one bone diameter) beyond the edge of the plate before stresses returned to within 1% of the un-plated control. The choice of metal did not affect the state of stress distribution in the bone beyond the proximal edge of the plate. In addition, the stress concentrations decreased proportionally as the taper angle decreased from forty-five to ten.

Utilizing this FE model we report the following:

Stresses are concentrated at the end of plates and return to within normal limits approximately one bone diameter beyond the edge of the plate.

Funding: The authors gratefully acknowledge the financial support of Materials and Manufacturing Ontario (MMO) and the Dean’s New Faculty Seed Grant at Ryerson University.

Femoral nails are thought to be load sharing devices. However, the specific load sharing characteristics and associated stress concentrations have not yet been reported in the literature. The purpose of this study was to use a validated, three dimensional finite element model of a nailed femur subjected to gait loads in order to determine the resulting stresses in the femur and the nail. The results showed that load was shared between the nail and the bone throughout the gait cycle. In addition, high stress concentrations were noted in the bone around the screw holes, and dynamization was of minimal benefit.

To determine the stresses in the bone and nail in a femur with a locked, retrograde, intramedullary nail.

The retrograde femoral nail is a load sharing device. High stress concentrations occur in the bone around locking screw holes. When only one locking screw is used proximally and distally, stresses in the implant are excessive and may lead to failure. Dynamization was of minimal benefit.

This is the first study to use a validated three dimensional finite element model to provide a detailed biomechanical analysis of stress patterns in a retrograde nailed femur under gait loads. The results can help resolve issues of stress shielding, implant removal, number of locking screws and dynamization.

In the fully locked condition, loads in the femur were significantly higher than those in the nail for most of the gait cycle. Removal of locking screws to obtain dynamization only increased axial load in the femur by 17 %. However, stresses in the locking screws increased by as much as 250% when fewer than 4 screws were used. Maximum stresses in the bone were found around screw holes.

A three dimensional finite element model of the femur and nail was developed. The model was validated by comparing results to a physical saw bone model instrumented with strain gages and subjected to a simple a compressive load. Once good correlation with simple loading patterns was demonstrated, gait loading patterns obtained from literature were incorporated and simulations were run for various conditions.

Notching of the anterior femoral cortex during total knee arthroplasty is thought to be a possible risk factor for subsequent periprosthetic femoral fracture. Understanding the stress pattern caused by notching may help the orthopedic surgeon reduce the risk of fracture. A validated, three dimensional, finite element model of the femur using gait loads has been used to analyze the stress concentrations caused by anterior femoral cortex notching. Three factors that increase these stresses were identified. The notch depth, radius of curvature, and its proximity to the end of the femoral prosthesis influence the state of stress in the surrounding bone.

The purpose of this study was to characterize the stress concentration caused by anterior femoral notching during total knee replacement (TKR) in order to determine when a patient is at risk for a periprosthetic fracture of the femur.

We concluded that notches greater than 3 mm with sharp corners located directly at the proximal end of the femoral implant produced the highest stress concentrations and may lead to a significant risk of periprosthetic femur fracture.

One complication that can occur during TKR is notching of the anterior femoral cortex which results in a stress concentration. It is important to characterize this stress riser in order to determine when a stemmed femoral component should be used to minimize the risk of fracture.

Three factors that affected the stress concentration were identified. First, increasing the notch depth lead to significant increased stress concentrations. When the depth was greater than 3 mm, local stresses increased markedly. Second, the radius of curvature was found to be inversely related to stress concentration. As the radius decreased, the local stress increased. Third, the proximity of the notch to the prostheses affected the stress concentration. Notches that were 1 mm proximal to the implant resulted in much larger stresses than those that were 10 mm away.

A validated, three dimensional finite element model of a femur subjected to a gait loading pattern was used to characterize the stress concentration caused by anterior femoral notching. The results compared well to previous work reported in the literature.

Periprosthetic fracture management after hip arthroplasty is complicated by poor bone stock and loose femoral components. Using a prospective database, thirty-five fractures treated by proximal femoral allograft reconstruction were identified. Patients treated between 1989–2000 with minimum two- year results, were reviewed at a mean of 3.8 years. Twenty-six fractures were acute, and nine had failed previous treatment. Union of the PFA was achieved in all but five cases (83%). In twenty-eight cases (78%) no further surgery was required and patient ambulation was pain free. When conventional treatment is not possible, the use of a PFA provides encouraging results.

Periprosthetic femoral fracture treatment is complicated by comminution, bone loss, and potentially loose femoral components. Treatment can include cast-braces, internal fixation, revision arthroplasty or the use of proximal femoral allograft composites (PFA). This study reports on thirty-five fractures treated with a PFA between 1989–2000. Five patients were lost and twelve patients (33%) were deceased. Follow-up averaged 3.8 years (range 0.1–11.3) with minimum two-year results in surviving patients. Six patients had either Rheumatoid arthritis or DDH with very narrow femoral canals.

There were twenty-three acute fractures, five failures of non-operative management, four failures of ORIF and two fractured femoral stems. Fractures were classified by the Vancouver system with: B1–7%, B2–30%, B3–43% and C-20%. Prefracture functional scores revealed that 30% of patients had significant functional impairment and were awaiting revision arthroplasty. Patients had had an average of two previous surgical procedures (range 1–4).

The mean length of the PFA was 14cm and union between graft and host bone was achieved in all but five cases (83%). Resorption of the graft was seen in eight cases (27%), lucent lines in six cases (20%) and implant migration in four cases (13%). Post revision arthroplasty Harris Hip and SF-36 scores revealed substantial disability in this patient group.

Twenty-eight cases (73%) were deemed successful with patients not requiring further surgery and enjoying pain free ambulation. In fractures with unstable femoral components and inadequate bone stock or very narrow femoral canals few options are available. This technique provides encouraging results and a viable option when conventional treatment is not possible.

Notching of the anterior femoral cortex during total knee arthroplasty is thought to be a possible risk factor for subsequent periprosthetic femoral fracture. Understanding the stress pattern caused by notching may help the orthopedic surgeon reduce the risk of fracture. A validated, three dimensional, finite element model of the femur using gait loads has been used to analyze the stress concentrations caused by anterior femoral cortex notching. Three factors that increase these stresses were identified. The notch depth, radius of curvature, and its proximity to the end of the femoral prosthesis influence the state of stress in the surrounding bone.

The purpose of this study was to characterize the stress concentration caused by anterior femoral notching during total knee replacement (TKR) in order to determine when a patient is at risk for a periprosthetic fracture of the femur.

We concluded that notches greater than 3 mm with sharp corners located directly at the proximal end of the femoral implant produced the highest stress concentrations and may lead to a significant risk of periprosthetic femur fracture.

One complication that can occur during TKR is notching of the anterior femoral cortex which results in a stress concentration. It is important to characterize this stress riser in order to determine when a stemmed femoral component should be used to minimize the risk of fracture.

Three factors that affected the stress concentration were identified. First, increasing the notch depth lead to significant increased stress concentrations. When the depth was greater than 3 mm, local stresses increased markedly. Second, the radius of curvature was found to be inversely related to stress concentration. As the radius decreased, the local stress increased. Third, the proximity of the notch to the prostheses affected the stress concentration. Notches that were 1 mm proximal to the implant resulted in much larger stresses than those that were 10 mm away.

A validated, three dimensional finite element model of a femur subjected to a gait loading pattern was used to characterize the stress concentration caused by anterior femoral notching. The results compared well to previous work reported in the literature.

Periprosthetic fracture management after hip arthroplasty is complicated by poor bone stock and loose femoral components. Using a prospective database, thirty-five fractures treated by proximal femoral allograft reconstruction were identified. Patients treated between 1989–2000 with minimum two- year results, were reviewed at a mean of 3.8 years. Twenty-six fractures were acute, and nine had failed previous treatment. Union of the PFA was achieved in all but five cases (83%). In twenty-eight cases (78%) no further surgery was required and patient ambulation was pain free. When conventional treatment is not possible, the use of a PFA provides encouraging results.

Periprosthetic femoral fracture treatment is complicated by comminution, bone loss, and potentially loose femoral components. Treatment can include cast-braces, internal fixation, revision arthroplasty or the use of proximal femoral allograft composites (PFA). This study reports on thirty-five fractures treated with a PFA between 1989–2000. Five patients were lost and twelve patients (33%) were deceased. Follow-up averaged 3.8 years (range 0.1–11.3) with minimum two-year results in surviving patients. Six patients had either Rheumatoid arthritis or DDH with very narrow femoral canals.

There were twenty-three acute fractures, five failures of non-operative management, four failures of ORIF and two fractured femoral stems. Fractures were classified by the Vancouver system with: B1–7%, B2–30%, B3–43% and C-20%. Prefracture functional scores revealed that 30% of patients had significant functional impairment and were awaiting revision arthroplasty. Patients had had an average of two previous surgical procedures (range 1–4).

The mean length of the PFA was 14cm and union between graft and host bone was achieved in all but five cases (83%). Resorption of the graft was seen in eight cases (27%), lucent lines in six cases (20%) and implant migration in four cases (13%). Post revision arthroplasty Harris Hip and SF-36 scores revealed substantial disability in this patient group.

Twenty-eight cases (73%) were deemed successful with patients not requiring further surgery and enjoying pain free ambulation. In fractures with unstable femoral components and inadequate bone stock or very narrow femoral canals few options are available. This technique provides encouraging results and a viable option when conventional treatment is not possible.

A retrospective study of one hundred and nineteen unicompartmental knee arthroplasties was performed. Outcome measures were the Oxford twelve-item knee questionnaire, the Short Musculoskeletal Functional Assessment (SMFA) and the WOMAC. Regression analysis was performed in order to determine predictors of outcome. After an average follow up period of four years, the mean scores indicated a good to excellent functional outcome. The only predictor of outcome identified was gender, with women obtaining a better functional outcome than men. Other variables that did not influence functional outcome included age, weight, stage of disease, previous HTO and bilateral procedures.

The purpose of this study was to determine

the functional outcome of unicompartmental knee arthroplasty and

Although unicompartmental knee arthroplasty is becoming more widely accepted as a treatment option for degenerative osteoarthritis, there are very few studies in the literature that systematically investigate the predictors of outcome for this procedure.

This is a retrospective study of one hundred and nineteen unicompartmental knee arthroplasties perfomed at a university hospital by a single surgeon. The outcome measures used were the Oxford twelve-item knee questionnaire, the Short Musculoskeletal Function Assessment (SMFA) and the Western Ontario and McMaster (WOMAC) functional indices. Multiple regression analysis was performed to determine predictors of outcome from chart derived variables.

After a mean follow-up of four years the mean Oxford Knee Score was thirty-nine and the mean SMFA and WOMAC functional scores were eight and seven respectively, indicating a good to excellent functional outcome. Regression analysis revealed gender as a predictor of outcome however other variables including age (range 49–84 yrs), weight (range 55–225 kgs), previous ORIF, preoperative varus/valgus (range 0–16 degrees), joint subluxation (range 0–13mm), radiographic stage of disease (Kellgren and Lawrence), as well as previous HTO and bilateral (simultaneous or staged) unicompartmental knee arthroplasty were found to not correlate with functional outcome.

Good to excellent functional outcome scores can be achieved with unicompartmental knee replacement. Previous HTO or bilateral procedures as well as weight, pre-operative varus/valgus < sixteen degrees or radiographic stage of disease were not predictive of outcome.

Background: Revision total hip replacement in patients with a previous diagnosis of developmental dysplasia of the hip (DDH) can be a challenging and technically demanding procedure. Two of the major concerns are deficient acetabular bone stock and the position of the acetabular implant, particularly if the hip centre was not restored during the primary procedure. The purpose of this study was to determine if cup height, lateralization or abduction angle are correlated with functional outcome or survivorship in revision total hip replacement (THR) in patients with a previous diagnosis of DDH.

Methods: A retrospective investigation of 51 sequential patients (63 hips) previously diagnosed with DDH who underwent revision THR at our center between 1984 and 2000 was performed. The mean duration of follow up was 119 months (range 36 to 238 months). Forty-one patients (52 hips) were available for functional outcome and survivorship analysis. The remaining ten patients (11 hips) were available only for survivorship analysis. Three independent variables identified apriori as possible correlates were cup height, lateralization and angle as measured on the AP radiographs. Functional outcome measurement consisted of the Harris Hip, SF36 and WOMAC questionnaires. Linear regression analysis and Kaplan-Meier curves were used to determine if any of the variables correlated with functional outcome or survivorship.

Results: Cup height was found to have a statistically significant (p< 0.05) correlation with Harris Hip, SF36, and WOMAC functional scores. High hip centers correlated with worse scores. In addition, patients with hip centers less than 3.5 cm above the radiographic tear drop had a statistically significant improvement in cup survivorship compared to those with higher hip centers.

Conclusion: Restoration of hip center height to as close to the radiographic teardrop as possible improves functional outcome and cup survivorship.

Our aim was to determine if the height of the cup, lateralisation or the abduction angle correlated with functional outcome or survivorship in revision total hip replacement in patients with a previous diagnosis of developmental dysplasia of the hip. A retrospective investigation of 51 patients (63 hips) who had undergone revision total hip replacement was performed. The mean duration of follow-up was 119 months. Forty-one patients (52 hips) were available for both determination of functional outcome and survivorship analysis. Ten patients (11 hips) were only available for survivorship analysis.

The height of the cup was found to have a statistically significant correlation with functional outcome and a high hip centre correlated with a worse outcome score. Patients with a hip centre of less than 3.5 cm above the anatomical level had a statistically better survivorship of the cup than those with centres higher than this. Restoration of the height of the centre of the hip to as near the anatomical position as possible improved functional outcome and survivorship of the cup.

Purpose: Prevalence of supracondylar fractures above a total knee arthroplasty (TKA) is increasing due to the increasing age of treated patients and the larger number of implants. We report the functional results in a series of thirteen patients treated with a distal femoral graft (DFG) associated with revision TKA.

Material and methods: Between 1990 and 2001, thirteen patients (twelve women and one man), mean age 65 years (24–93) were treated with DFG associated with revision TKA. All fractures were type III using the Lewis classification and involved severe osteoporotic bone associated with loosening of the femoral piece. Before fracture, the patients had had two operations on average (1–4). The fracture occurred as a result of a fall in nine patients, low-energy trauma in three, and during mobilisation under general anaesthesia in one. The functional results were noted prospectively using the modified HSS score and the SF-36 quality-of-life questionnaire. Radiographic assessment of bone healing and implant stability was performed by two independent observers (kappa=0.75, p=0.02).

Results: At mean follow-up of 60 months (12–144), the mean HSS score was 75 (64–86). Mean knee flexion was 100° (50–115°). One patient required subsequent amputation due to infection. Using our classification, functional outcome was good or excellent in seven patients, fair in four and poor in two. For nine patients, x-rays showed no sign of loosening. In three patients, there was minimal to moderate periprosthetic bone resorption.

Discussion: Treatment of periprosthetic fractures of the knee is a therapeutic challenge. Osteoporosis and comminution is a complex association making stable osteo-synthesis difficult with conventional methods. Massive knee prosthesis using a DFG and a standard TKA is an attractive alternative. This technique allows restoration of the bone stock by bone healing and constitutes a less aggressive therapeutic solution.

Conclusion: Despite the risk of infection, we believe that composite prostheses can be an attractive option for the treatment of periprosthetic supracondylar fractures of the knee.