Objective: Unicompartmental knee arthropasty (UKA) has recently attracted increased popularity and usage, though issues exist regarding tibial component failure. UKA instability may be due to insufficient bony support at the proximal tibia. Pre-operative knowledge of ‘safe’ resurfacing depths offering subchondral bony support could help minimize UKA instability. We recently developed a novel CT imaging tool (CTTOMASD) which assesses subchondral bone mineral density (BMD) in relation to depth from the subchondral surface. The objective of this work was to determine the in-vivo precision of CT-TOMASD safe resurfacing depths in human tibial compartments.

Seven knees from seven donors (2M:5F; age:46+/−11) were scanned three times via QCT (GE Lightspeed; BMD Phantom; 0.625x0.625x0.625mm resolution). CTTOMASD regional analyses were performed for medial and lateral compartments; outputting density versus depth plots fit with polynomial regression equations. As density decreases with increased depth from the subchondral surface, a density threshold of 300mg/ cm3 was arbitrarily set to correspond with the safe resurfacing depth. The 300mg/cm3 density threshold corresponds to the average density of subchondral trabecular bone, and is ~2x the density of weak epiphyseal trabecular bone located beneath stiffer subchondral trabecular bone. Precision was defined using coefficients of variation (CV%).

In-vivo precision errors associated with CT-TOMASD safe resurfacing depths were less than 2.7%. CV% was 2.7% for the medial compartment depth and 2.6% for the lateral compartment depth.

CT-TOMASD demonstrates repeatable measures of safe resurfacing depths invivo.

Safe resurfacing depths are measured in relation to defined density thresholds which can be adjusted according to UKA design and patient specifics (e.g., size, sex). CT induces a low radiation dosage due to the low presence of radiosensitive tissues at the knee (~1/10th of a long-leg standing radiograph). CT-TOMASD has potential to be used as a pre-operative imaging technique for improved UKA stability and longevity.

Introduction: Achieving durable implant–host bone fixation is the major challenge in uncemented revision hip arthroplasty when significant bone stock deficiencies are encountered. The purpose of this study was

to develop an experimental model which would simulate the clinical revision hip scenario and

Methods: Thirty-six porous tantalum plugs were implanted into the distal femur, bilaterally of 18 rabbits for four weeks. There were 3 groups of plugs inserted; control groups of porous tantalum plugs (Ta) with no coating, a 2nd control group of porous tantalum plugs with micro-porous calcium phosphate coating, (Ta-CaP) and porous tantalum plugs coated with alendronate (Ta-CaP-ALN). Subcutaneous fluorochrome labelling was used to track new bone formation. Bone formation was analysed by backscattered electron microscopy and fluorescence microscopy on undecalcified histological sections.

Results: The relative increase in mean volume of gap filling, bone ingrowth and total bone formation was 124 %, 232 % and 170 % respectively in Ta-CaP-ALN compared with the uncoated porous tantalum (Ta) controls, which was statistically significant. The contact length of new bone formation on porous tantalum implants in Ta-CaP-ALN was increased by 700% (8-fold) on average compared with the uncoated porous tantalum (Ta) controls.

Discussion: Alendronate coated porous tantalum significantly modulated implant bioactivity compared with controls. This study has demonstrated the significant enhancement of bone-implant gap filling and bone ingrowth, which can be achieved by coating porous tantalum with alendronate. It is proposed that, when faced with the clinical problem of revision joint replacement in the face of bone loss, the addition of alendronate as a surface coating would enhance biological fixation of the implant and promote the healing of bone defects.

This single incision, anterolateral intermuscular approach (AL-IM) utilises the interval between gluteus medius and tensor fascia lata. The aims of the study were to compare the quality of life, satisfaction and complications of this approach with two of the most commonly used limited incision transmuscular (TM) approaches, namely the mini-posterior (P-TM) and the mini-direct lateral (L-TM).

One hundred and ninety-nine patients receiving MIS THA surgical procedures were evaluated prospectively (63 AL-IM, 68 P-TM and 68 L-TM). The outcome variables were WOMAC function, pain, stiffness, SF-12 (physical & mental), Oxford-12, satisfaction and radiological outcome. Parametric and non-parametric analyses were performed.

There were no significant differences between groups in baseline characteristics including age, sex, BMI, co-morbidity, or pre-op WOMAC, SF-12, Oxford-12 (p> 0.05). However, the AL-IM group was associated with superior outcomes (p< 0.05) in WOMAC function, WOMAC pain, global WOMAC, Oxford-12 and SF-12 physical component.

In the short term the AL-IM approach provides significant improvements in quality of life scores over other limited incision approaches. It provides minimal soft tissue disruption and maintains the abductor musculature and posterior soft tissue envelope, with similar complications and radiological outcomes.

We report the outcomes ten to fifteen years after two stage revision for hip infection in one hundred and three patients.

All patients or their next of kin were contacted to determine their current functional status and whether they had required repeat surgery or had recurrent infection. The Oxford-12, SF-12, and WOMAC questionnaires were administered. A comprehensive chart review was undertaken to review the infective organisms, surgery, approach, complications, and need for further revision surgery.

Ten patients had re-infection, six of whom responded to repeat surgery with no further sequelae. Two patients required resection arthroplasty, one patient underwent hip disarticulation after eventual failure of treatment and bone loss, and one immunocompromised patient developed osteomyelitis and was subsequently lost to follow-up. Long-term success rate for two stage- revision is thus 90.3%, or 96.1% with additional surgery. Since then, three patients required revisions for aseptic loosening, one for recurrent dislocation. We were able to follow up forty-one patients, 85 % of whom provided health-related quality of life outcome scores. Thirty-nine patients were deceased, with their outcome confirmed via their last follow-up or with family members, for a total follow-up rate of 78 %. Twenty-three patients were lost to follow-up, but did not undergo further surgery or have reinfections treated at our centre.

Two-stage revision for hip infection, which includes an interim prosthesis of antibiotic loaded cement, offers a predictable and lasting solution for patients with this difficult problem.

Purpose of the study: Hip resurfacing with a metal-on-metal bearing gives good mid-term clinical results. The design of the femoral piece has an effect on implant longevity, as does the vitality of the underlying cephalic bone. Computer-assisted surgery has been helpful in position the implant but the choice of the best position is still empirical. Prosthesis designers recommend valgus, but with too much there is a risk of a superolaterl notch which would weaken the neck. This leads the surgeon to use a larger femoral implant, and consequently to resect more acetabular bone. Anteversion is not evaluated. The purpose of this study was test mechanically different valgus/varus, anteversion/retroversion positions of the femoral implant.

Material and methods: We implanted 15 femurs made of resin which were geometrically and mechanically identical. The following angles were tested: varus/valgus (−10°, neutral, +10°, +20°) and ante/retroversion (−10°, neutram, +10). A valgus notch (+20° and +10°) and a varus notch (−10°) were simulated. The femurs thus prepared were tested with Instron 8874. Load at failure was noted as well as the type of fracture: distance from the fracture line to the greater trochanter (FGT). Student’s t test was applied.

Results: All of the femurs fractured at the neck. The fracture was closer to the implant (FGT: 11.0 mm) for the 20° valgus implantation (p< 0.05). The displacement was lesser with a valgus notch (mean 2.2 mm) then without a notch (mean 3.3 mm (p< 0.05). The varus notch had no effect. The failure load was lower for 20° valgus (1236 N, range 1117–1356N) then for the other angles (1664N, range 1142–2113 N) with near statistical significance (p=0.08). Retroversion had no effect. Anteversion allowed greater displacement (4.1 mm) and supported greater loading (1879 N) before failure.

Discussion: This study, unlike clinical studies, did not demonstrate any static mechanical superiority of the valgus position for the femoral piece. Another study on cadaver bones is planned for confirmation. Clinical studies reflect the vitality of the trabecular bone supporting the implant, a vitality which could be stimulated by the valgus position.

Impaction allografting is increasingly used for the treatment of failed total hip replacements. In six human cadaveric femurs the impaction allografting procedure was performed to comprehensively describe the postoperative morphology of impaction allografting. After the procedure, the specimens were sectioned and prepared for histomorphometric analysis. The graft porosity was lowest in Gruen zone four (52%) and highest in Gruen zone one (76%). At the level of Gruen zone six and two, virtually the entire cross-section was filled with bone cement. The presented data will serve as a baseline for future investigations of the impaction allografting.

Impaction allografting is an attractive procedure for the treatment of failed total hip replacements. The purpose of this study was to comprehensively describe the morphology of impaction allografting post operatively to form a baseline for further investigations.

Three experienced surgeons performed the impaction allografting procedure on six cadaveric femurs. After the procedure, the femurs were cut in 6mm thick transverse sections and processed for histomorphometric analysis.

The porosity of the impacted graft was highest proximally in Gruen zone one (76%) and lowest in Gruen zone four (52%). Below the tip of the stem (Gruen zone four), the mean cement penetration was significantly lower compared to the proximal part of the femur. The averaged residual impacted graft layer in Gruen zone six and two was (0.5mm SD 0.4mm) significantly thinner compared with Gruen zone’s one, 7/1, and four.

In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer (Figure). Even the simulated lytic defects in this region were filled with the graft cement composite which may not be remodelled by the host bone.

The graft porosity was found to be highest proximally and lowest distally. In the region of Gruen zone six and two the entire cross-section was penetrated with bone cement with almost no residual graft layer.

This investigation will serve as a baseline for future studies of the mechanical and biological processes that make the impaction allografting a successful procedure.

Funding: Stryker Howmedica and DePuy for provided implants and instruments.

Please contact author for figures and/or diagrams.

We have evaluated the function of a trabecular metal augmentation patella to restore knee kinetics and kinematics after revision total knee arthroplasty. An “Oxford type” rig was used with fresh frozen cadaveric knees, for an active model that maximally retained the soft tissue envelope.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

The purpose of this study is to evaluate the kinetic and kinematic function of a new trabecular metal augmentation patella.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

This study demonstrates that the augmentation patella restorers the abnormal tracking and higher extensor mechanism forces seen after patelloplasty in revision TKA to those normal after a TKA.

The mean, maximum extensor mechanism force in extension for the TKA group as compared to the patelloplasty group (p=0.0000032), reduced to near normal with the augmentation patella (p=0.198).

The mean, maximum patella maltracking in extension for the TKA group as compared to the patelloplasty group (p=0.025), reduced to near normal with the augmentation patella (p=0.301).

Eight frozen human cadaveric knees (mean age sixty-eight years) were prepared for an “Oxford type” knee rig. Alignment ands offset were addressed and the soft tissue envelope kept as intact as possible. A load cell was introduced into the extensor mechanism. Femoral, patella and tibial motion were assessed using the Optotrak system.

Patella bone loss at revision TKA remains an unsolved problem, with the patella often too thin to accept a new prosthesis. Leaving the patella shell to articulate against the femoral component can lead to disappointing results.

Funding - Zimmer

We compare two applications of minimally invasive hip arthroplasty (MISTHA) with regards to early complication rate and consumption of health care resources. Complications are associated with both manifestations of MIS surgical technique. Two- incision MIS THA is associated with fewer days in hospital in comparison with one incision MIS THA, however requires a greater amount of operating room resources. This paper is among the first to compare two- incision with one incision MISTHA. Two- incision MISTHA may benefit efforts to reduce health resource utilization associated with hip arthroplasty procedures providing that operating room resource consumption and complication rates are not excessive.

A comparative cohort study to evaluate two-incision versus single-incision minimally invasive hip arthroplasty: assessment of early complication rate and health care resource utilization

To evaluate and compare two applications of minimally invasive hip arthroplasty (MISTHA) with regards to early complication rate and consumption of health care resources

One hundred and sixty-five patients received MISTHA from 2002–2004 at a tertiary referral hospital. Patients received two incision (sixty-six patients) or one incision surgery (ninety-nine patients) which was performed according to standard technique. T-test, chi square, fisher’s exact test were used to compare cohorts of MISTHA patients with regards to early complications and consumption of health care resources while in hospital.

At baseline the two cohorts were not different with regards to age, gender, comorbid status, BMI, and pre-operative WOMAC, Oxford-12, SF-12 (p> .05). Major and minor complication rates were similar in the two cohorts (p> .05). Utilization of operating room resources was greater with the two incision group (mean twentyfive minutes more OR time) however length of stay (mean two days less in hospital) and post-operative analgesic use was significantly reduced (p< .05). Complications and operating room resource consumption were highest early in the surgeons’ experience with these procedures.

Complications are associated with both manifestations of MIS surgical technique. Two- incision MISTHA is associated with fewer days in hospital, however requires a greater amount of operating room resources.

This paper is among the first to compare two- incision with one incision MISTHA. Two- incision MISTHA may benefit efforts to reduce health resource utilization associated with hip arthroplasty procedures providing that operating room resource consumption and complication rates are not excessive.

In impaction allografting, the host bone interface consists of morsellized allograft alone or as a composite with bone cement. The objective of this study was to investigate the host bone temporal changes in the interface for these two materials in a rat bone chamber model. The composite-host bone interface strength was significantly higher at three weeks and was higher than the allograft construct. Limited allograft, but extensive periosteal remodelling, was observed at three weeks. At six weeks a new medullary canal was formed and the endosteal cortex was partially absorbed. Endosteal absorption resulting in medullary canal widening may be responsible for clinically unstable stems after impaction allografting.

The host bone interface after impaction allografting consists of morsellized allograft alone or as a composite with cement and it may be important for the clinical success of this procedure. The purpose of this study was to investigate the temporal changes of these interfaces in a rat bone chamber model.

Bone chambers were inserted in both tibiae of thirty-three rats and tightened to the endosteal surface to create a microenvironment. One chamber was filled with allograft bone and the other with an allograft/ cement composite. After zero, three, and six weeks, the rats were euthanized, the interfaces mechanically tested and processed for histomorphometric analysis.

The composite-host bone interface strength was significantly higher at three weeks and was higher than the allograft construct. Extensive periosteal remodelling was observed at three weeks. At six weeks a new medullary canal was formed and the endosteal cortex was partially absorbed.

The increased interface strength of the composite-host bone interface was due to fibrous tissue attachment rather than direct bonding of the bone particles. Cortical porosity and cancellisation is known to be caused by a damaged endosteal circulation resulting in medullary canal widening and may cause clinically unstable implants.

Interface strength of the composite-host bone interface was increased at three weeks through fibrous tissue attachment. A damaged endosteal circulation caused cortical porosis and cancellisation.

With this rat bone chamber model a potential cause of stem subsidence after impacting allografting was identified.

Funding: The George W. Bagby Research Fund.

The Canadian Institutse of Health Research.

The Maurice E. Müller Foundation.

The Swiss Academy of Engineering Science.

The Robert Mathys Foundation.

This study evaluated the effect of prosthetic patellar resurfacing on outcome of revision total knee arthroplasty. One hundred and twenty-six patients who underwent consecutive revision of total knee arthroplasty were identified. The status of the patella was ascertained post revision as to the presence or absence of patellar prosthesis. WOMAC, Oxford-12, SF-12 and patient satisfaction data were obtained at a minimum of two years follow-up. Follow-up was obtained in one hundred and ten patients. There was no significant difference between the two cohorts with regards to outcomes. A patellar prosthesis does not appear to significantly affect pain, function, or satisfaction outcomes following revision total knee arthroplasty.

The purpose of this study is to evaluate the effect of prosthetic patellar resurfacing on outcome of revision total knee arthroplasty in a matched cohort study.

The presence or absence of a patellar prosthesis does not appear to significantly affect pain, function, or satisfaction outcomes following revision total knee arthroplasty.

Attempting to resurface the patella in revision cases may not be worthwhile.

Follow-up was obtained in one hundred and ten patients (fifty-two with patellar component, fifty-eight bony shell), matched for age, sex and co-morbidity scores and followed for a minimum of two years. There was no significant difference between the two cohorts with regards to outcomes of WOMAC pain (mean seventy-two and sixty-five, p=0.17), WOMAC function (mean sixty-four and fifty-nine, p=0.26) scores, Oxford −12 (mean sixty-three and sixty-seven, p=0.2), SF-12 (mean forty and thirty-six, p=0.27) and satisfaction outcomes (mean eight and nine, p=0.07), (power of 0.8, beta=0.2).

From January 1997 to December 1999 one hundred and twenty-six patients who underwent consecutive revision total knee arthroplasty were identified. The status of the patella was ascertained post revision as to the presence or absence of patellar prosthesis. At a minimum of two years follow-up, pain and function were assessed by questionnaire for WOMAC, Oxford-12, SF-12 and patient satisfaction data. Co-morbidity, surgical exposure, HSS knee scores and ROM were also collected. Univariate and multivariate analyses were performed.

It is questionable whether patient’s pain, function and satisfaction are affected in revision total knee arthroplasty by patellar prosthetic resurfacing.

Funding: One or more of the authors has received funding from a commercial party. This was DePuy, Inc, Warsaw, IN.

A concern with diaphyseal-fitting cementless stems in revision total hip arthroplasty is intra-operative fractures. Two hundred and eleven patients consecutively underwent revision hip arthroplasty using Solution stems (DePuy, Warsaw, IN). Intra-operative fractures or perforations occurred in sixty-four patients (30% prevalence), with diaphyseal splits in thirty-nine patients (18% prevalence). Risk factors were pre-operative osteolysis, cortex to canal ratio, under-reaming the cortex and large diameter stems. The majority of diaphyseal linear cracks occurred at the distal end of extended trochanteric osteotomies during stem insertion. Intra-operative fracture is associated with an average two days longer length of stay (p< 0.05).

The purpose of this study was to determine the identification of the risk factors and outcomes of intra-operative fractures using a diaphyseal fitting revision stem.

There is an association of intra-operative fracture associated using a diaphyseal-fitting stem in revision total hip arthroplasty with a longer length of stay in hospital.

Identifying preoperative risk factors will allow avoidance of such fractures and prolonged hospital stay.

Intra-operative fractures or perforations occurred in sixty-four patients (30% prevalence) and thirty-nine patients (18% prevalence) sustained diaphyseal splits. Risk factors associated with intra-operative fracture were pre-operative osteolysis, a low cortex to canal ratio, under-reaming the cortex and the use of a large diameter stem. Surgical approach was not directly related to fracture occurrence but the majority of diaphyseal undisplaced linear cracks occurred at the distal end of extended trochanteric osteotomies during stem insertion. Cortical perforation occurred most often with cement removal. Duration of stay was on average two days longer (p< 0.05) for patients with an intraoperative fracture.

Two hundred and eleven patients who had undergone revision hip arthroplasty using the Solution stem (DePuy, Warsaw, IN) between December 1998 and March 2002 were identified. Patients who sustained an intra-operative fracture were compared to controls patients who underwent hip revision at the same time frame but with no fracture. Multiple factors were analyzed to see which were risk factors for intra-operative fractures.

There is a surprisingly high incidence of intra-operative fracture associated with using a diaphyseal-fitting stem in revision total hip arthroplasty. This was associated with a longer length of stay

The prospective evaluation of two hundred and seven symptomatic total knee arthroplasties presenting for revision total knee arthroplasty is reported. On univariate analysis patients who had infection differed significantly (p< .001) from those without infection with regards to: elevated ESR, CRP, positive aspiration, and history of; revision procedure less than two years since last surgery, early wound problems, ongoing pain since index procedure, and discharging wound. On multivariate analysis elevated ESR or CRP, positive aspiration, pain since index procedure and early wound complications were significant predictors of infection (p< .05). These variables were then used to formulate an evidence-based multivariate predictive algorithm to assist the clinician in decision making prior to surgery.

Differentiating septic from aseptic failure of total knee arthroplasty on the basis of clinical features and diagnostic tests can be troublesome for the clinician. The purpose of this paper is to describe significant differences between cases of septic and aseptic failure of total knee arthroplasty. The incorporation of these variables into a practical multivariate clinical prediction algorithm can provide assistance in establishing the diagnosis of infection prior to revision knee arthroplasty.

A simple clinical prediction algorithm can assist in the diagnosis of infection in patients with painful total knee arthroplasty. Patients with five of five criteria have a 99% probability of infection whereas patients with zero of five criteria have a 1% probability of infection.

This is the first multivariate evidence-based clinical prediction algorithm presented for use in decision making prior to revision total knee arthroplasty. The surgeon can use the information derived from clinical and laboratory assessment to compute an approximate pre-operative probability of infection prior to surgery (see table).

On multivariate analysis elevated ESR or CRP, positive aspiration, pain since index procedure and early wound complications were significant predictors of infection (p< .05). These variables were then used to formulate an evidence-based multivariate predictive algorithm to assist in clinical decision making.

Prospective data was collected on two hundred and seven symptomatic knee arthroplasties presenting for revision arthroplasty. A multivariate logistic regression model was used to determine the probability of infection using five significant variables. Combinations of these five variables can provide the clinician with an estimate of the probability of infection prior to revision knee arthroplasty.

Please contact author for tables and/or charts.

Purpose: Hip resurfacing techniques utilize mechanical jigs to align a femoral guide-pin that directs implant placement. Errors in alignment may lead to premature failure. The purpose of this study was to compare femoral guide-pin placement using a computer-assisted surgical (CAS) navigation system to a currently available manual alignment device.

Methods: A computer-assisted navigation system was developed by our group. Target guide-pin position was determined for each cadaveric hip from radiographs. A guide-pin was driven into each hip using either the CAS method or a manual alignment jig (Durom; Zimmer) by a novice or expert surgeon respectively. Radiographic pin position was compared to the target and accuracy was compared between the two techniques.

Results: Guide-pin insertion trajectory using the CAS system was significantly less variable in varus/valgus alignment than the mechanical jig (2.0° SD vs. 5.5° SD; p < 0.05). Ante/retroversion variability was also lower using CAS (4.4° SD vs. 7.7° SD) as was alignment error (CAS: 2.0° ± 2.2° SD valgus vs. Durom: 3.3° ± 5.5° SD varus, p=0.17; CAS: 0.1° ± 4.6° SD anteverted; Durom 3.2° ± 7.7° SD retroverted, p=0.48) but not significantly. Both methods proved accurate in placing the pin within 2 mm from the centre of the neck axis. Procedure time was similar between the two methods

Conclusions: Computer-assisted surgical navigation significantly improves reliability of guide-pin placement. This technique may help achieve better femoral implant alignment regardless of experience and contribute to improving hip resurfacing outcomes.

Funding : Other Education Grant

Funding Parties : Zimmer/UBC Research Fund

Patient satisfaction is not uniform or consistent following revision total knee arthroplasty. This study evaluates ninety-nine patients with a self-administered patient satisfaction questionnaire at a minimum of two years following the revision procedure (1997–99) to determine differences between satisfied (sixty-six patients) and dissatisfied patients (thirty-three patients). Univariate analysis revealed that patients satisfied with their results were significantly different (p< .05) than dissatisfied patients with regards to post op scores including those of the WOMAC pain and function, oxford, and SF-12. Patients were not different with regards to (p> .05) age, comorbidity score, surgical approach, or sepsis as a reason for the revision procedure. Regression analysis demonstrated that gender, post-op WOMAC score, and pre-op arc of motion were significant determinants of satisfaction.

The purpose of this study is to evaluate determinants of patient satisfaction following revision total knee arthroplasty.

Patient satisfaction with revision knee surgery is most strongly associated with both pre and post-operative descriptors of knee function as well as gender.

Understanding the variables associated with satisfaction/dissatisfaction following revision knee arthroplasty may further assist ongoing research efforts to improve the outcomes of this procedure.

Univariate analysis revealed that patients satisfied with their results were significantly different (p< .05) than dissatisfied patients with regards to WOMAC pain and function score, oxford knee score, and SF-12. Patients were not different with regards to (p> .05) age, comorbidity score, surgical approach, or presence of sepsis as a reason for the revision procedure. Regression analysis demonstrated that gender, post-op WOMAC score, and pre-op arc of motion were significant determinants of satisfaction (p< .05).

A self-administered patient satisfaction survey was completed by ninety-nine patients at a minimum of two years following revision total knee arthroplasty. Fifty-nine patients were females and forty were males. Sixty-six patients were satisfied and thirty-three patients were dissatisfied with the outcome of their surgery at two years post-op. Univariate analysis and multivariate regression suggest that pre and post-operative joint function and gender are the most significant determinants of patient satisfaction

Purpose: To examine whether neutral or valgus placement results in greater fracture strength ex vivo, when the femoral neck is notched superolaterally as sometimes occurs during hip resurfacing arthroplasty.

Methods: We loaded 10 paired fresh-frozen notched proximal cadaveric femora (8F/2M, 66 to 80 years) to failure. In each case, the right femur was implanted, using bone cement, with a machined resurfacing component aligned neutrally with respect to the femoral neck whereas the left femur was implanted at 10° valgus. The superolateral notch was 3 mm wide by 2 mm deep directly beside the component. Potted femurs were loaded to failure using an Instron materials testing machine. All 20 femora were scanned using Dual-Energy X-Ray Absorptiometry.

Results: The effect of neutral versus valgus placement was complex. (1) Two pairs slowly crushed; the remaining femurs exhibited a clear fracture. When only the fracture-type failures were analyzed, valgus placement resulted in fracture loads on average 22% higher than for neutral placement (paired t-test, p< 0.05). All femurs failed within the notch, as occurs clinically. (2) Femurs with high bone density (BMD> 0.65 g/cm2) showed a significant increase in fracture load (p< 0.05) whereas femurs with low BMD (< 0.65 g/cm2) were unaffected by component placement. BMD was highly correlated with fracture load (Pearson r=0.87, p=0.0003). (3) The greatest improvements occurred when the neck-shaft angle was relatively low, 128°–132°. (4) Two of ten femurs required larger head sizes at 10° valgus.

Conclusions: (1) Fracture load was primarily controlled by bone quality (BMD); (2) nevertheless, varus/valgus placement did affect the fracture load; (3) the magnitude and direction of this effect depended on fracture type, bone mineral density and the original neck-shaft angle; (4) for the level of bone quality typical of patients undergoing hip resurfacing, and for low-to-average neck-shaft angles (up to 132°), the fracture load for 10° valgus placement was significantly higher than for neutral placement. Funding: Other Education Grant

The purpose of this study is to evaluate the effect of prosthetic patellar resurfacing on outcome of revision total knee arthroplasty in a matched cohort study.

From January 1997 to December 1999 126 patients who underwent revision of total knee arthroplasty were identified. The status of the patella was ascertained post revision as to the presence or absence of patellar prosthesis. At a minimum of two years follow-up, pain and function were assessed by questionnaire for WOMAC, Oxford-12, SF-12 and patient satisfaction data. Co-morbidity, surgical exposure, HSS knee scores and ROM were also collected. Univariate and multivariate analysis were performed. Follow-up was obtained in 110 patients (52 with patellar component, 58 bony shell), matched for age (mean 70 and 67 years), sex and co-morbidity scores and followed for a minimum of two years. There was no significant difference between the two cohorts with regards to outcomes of WOMAC pain scores (mean 66 and 74, p=0.14), WOMAC function scores (mean 59 and 65, p=0.22), Oxford- 12 scores (mean 57 and 64, p=0.17), and satisfaction score outcomes (57 and 68, p=0.14). It remains controversial whether the patient’s pain, function and satisfaction are affected in revision total knee arthroplasty by patellar prosthetic resurfacing. Insufficient patellar bone stock may preclude prosthetic resurfacing in which case patel-loplasty is performed. From this series, the presence or absence of a patellar prosthesis does not appear to sig-nificantly affect pain, function, or satisfaction outcomes following revision total knee arthroplasty.

We have evaluated the function of a trabecular metal augmentation patella to restore knee kinetics and kinematics after revision total knee arthroplasty. An “Oxford type” rig was used with fresh frozen cadaveric knees, for an active model that maximally retained the soft tissue envelope.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

The purpose of this study is to evaluate the kinetic and kinematic function of a new trabecular metal augmentation patella.

Investigating the force through the extensor mechanism, we found a statistically significant difference between the TKA before and after patelloplasty, which was abolished by the insertion of the augmentation patella.

Investigation patella tracking, we found a statistically significant difference between the TKA before and after patelloplasty, that was rectified by the insertion of the augmentation patella.

This study demonstrates that the augmentation patella restorers the abnormal tracking and higher extensor mechanism forces seen after patelloplasty in revision TKA to those normal after a TKA.

The mean, maximum extensor mechanism force in extension for the TKA group as compared to the patelloplasty group (p=0.0000032), reduced to near normal with the augmentation patella (p=0.198).

The mean, maximum patella maltracking in extension for the TKA group as compared to the patelloplasty group (p=0.025), reduced to near normal with the augmentation patella (p=0.301).

Eight frozen human cadaveric knees (mean age sixty-eight years) were prepared for an “Oxford type” knee rig. Alignment ands offset were addressed and the soft tissue envelope kept as intact as possible. A load cell was introduced into the extensor mechanism. Femoral, patella and tibial motion were assessed using the Optotrak system.

Patella bone loss at revision TKA remains an unsolved problem, with the patella often too thin to accept a new prosthesis. Leaving the patella shell to articulate against the femoral component can lead to disappointing results.

Funding - Zimmer

This prospective cohort study examined the relationship between waiting time for elective total hip arthroplasty (THA) and changes in pre- to post-operative quality of life. It included one hundred and forty-seven patients who entered the waiting list for primary THA with osteoarthritis. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire was used to assess patients at surgical consultation time (baseline) and one year post-operation. Baseline WOMAC score was a significant predictor for follow-up WOMAC score. Expedited access to THA results in a larger proportion of patients showing “better than expected” function at twelve months after the operation.

This study examined the relationship between waiting time for elective total hip arthroplasty (THA) and changes in pre- to post-operative quality of life.

Expedited access to THA results in a larger proportion of patients showing “better than expected” function at twelve months after the operation. The odds of a “better than expected” functional outcome decreased by 8% for each additional month on the wait list.

The study provides the estimates of decreased probability of “better than expected” outcome given a prolonged waiting time. Our study indicates that timely access to THA is needed for optimal post-operative outcome.

Baseline WOMAC score was a significant predictor for the follow-up WOMAC score in function (p=0.0005), pain (p=0.0036), and stiffness (p= 0.0004). Waiting for six months or less doubled the odds of achieving a “better than expected” functional outcome compared to longer waits (p= 0.05).

This prospective cohort study included one hundred and forty-seven patients who entered the waiting list for primary THA with osteoarthritis. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire was used to assess patients at the surgical consultation time (baseline) and one year post operation. Regression models were used to determine the “expected” outcome for a certain individual baseline score. By using expected HRQOL outcome, we identified patients whose benefit from THA is better than expected. Logistic regression models were used to assess the relationship between waiting time and the probability of “better than expected” outcome.

Purpose: There is little information in the literature regarding outcomes of unicompartmental knee arthroplasty (UKA) in patients receiving worker’s compensation (WC). The purpose of the present study is to compare the outcomes of UKA in patients receiving WC compared to patients without WC.

Methods: Nineteen patients with a WC claim treated by UKA for medial compartment arthritis were compared to twenty patients who underwent similar procedure but had no WC claim. Average follow up period was 37 months (range 30–60 months). Outcomes were evaluated using Knee Society Score (KSS) data. T test was used for statistical analysis. Comparisons were also made with respect to conversion in to total knee arthroplasty (TKA).

Results: WC patients improved from a mean preoperative KSS of 47.4 (range 30–70) to 76.9 (range 55–99), while non-WC patients improved from 43.3 (range 35–63) to 90.7 (range 74–100). The difference in improvement between the two groups was statistically significant (p=0.004). Furthermore, the postoperative KSS in the non-WC patients was significantly higher than that of the WC group (p=0.007). There was no significant difference between the incidences of conversion to TKA between the two groups.

Conclusions: These findings suggest that patients with WC claims have poorer outcomes after UKA in comparison to non-WC patients.

Purpose: To evaluate and compare patient reported quality of life and satisfaction following metal on metal hip resurfacing and total hip arthroplasty procedures.

Methods: Patients receiving metal-on-metal hip resurfacing and primary total hip arthroplasty were assessed at baseline and followed prospectively with regards to outcomes of quality of life (WOMAC, Oxford-12, SF-12) and satisfaction. Patients receiving resurfacing were matched (1:3) to a cohort of THA on characteristics of age, gender, and comorbidity status. Sample size was selected to evaluate superiority using WOMAC function score with effect size of 0.5, alpha .05, power 80%. Univariate and multivariate analyses were performed.

Results: 222 patients were evaluated with regards to baseline socio-demographic characteristics and quality of life scores(56 resurfacing, 166 THR). Patient cohorts were not different at baseline pre-operatively with regards to age, gender, comorbidity status, WOMAC, Oxford-12, and SF-12 (p> .05). At minimum one year post-op both cohorts reported excellent outcomes. Patients receiving hip resurfacing had superior outcomes with regards to WOMAC function, WOMAC pain, and Oxford-12 hip scores (p< .05). However patients were similar with regards to outcomes of SF-12 mental status and patient-reported satisfaction.

Conclusions: Hip resurfacing and THA patients report excellent outcomes, however, patients receiving hip resurfacing report superior quality of life compared to a matched cohort of THA.