Fully constrained liners are used to treat recurrent dislocations or patients at high risk after total hip replacements. However, they can cause significant morbidities including recurrent dislocations, infections, aseptic loosening and fractures. We examine long term results of 111 patients with tripolar constrained components to assess their redislocation and failure rate.

The purpose of this study was to assess survivorship, complications and functional outcomes at a minimum 10 years after the constrained tripolar liners used in our institute.

We retrospectively identified 111 patients who had 113 revision tripolar constrained liners between 1998 and 2008. Eighty-nine were revised due to recurrent dislocations, 11 for pseudotumor with dysfunctional abductors, and 13 for periprosthetic infection with loss of soft tissue stabilizers. All patients had revision hip arthroplasty before the constrained liner was used: 13 after the first revision, 17 after the second, 38 after the third, and 45 had more than 3 revisions. We extracted demographics, implant data, rate of dislocations and incidence of other complications. Kaplan Meier curves were used to assess dislocation and failure for any reason. WOMAC was used to assess quality of life.

At 10 years, the survival free of dislocation was 95.6% (95%CI 90- 98), and at 20 years to 90.6% (95% CI 81- 95.5). Eight patients (7.1%) had dislocations of their constrained liners: 1 patient had simultaneous periprosthetic infection identified at the time of open reduction, and 1 patient sustained stem fracture 3 months prior to the liner dislocation. At 10 years, the survival to any further surgery was 89.4% (95% CI 82–93.8), and at 20 years, this was 82.5 (95% CI 71.9–89.3). Five patients (4.4%) had deep infection: 4 of these had excision arthroplasty due to failure to control infection, while 1 patient was treated successfully with debridement, exchange of mobile components and intravenous antibiotics. Two patients (1.8%) had dissociated rings that required change of liner, ring and head. Two patients (1.8%) had periprosthetic femoral fractures that were treated by revision stems and exchange of constrained liners. The mean WOMAC functional and pain scores were 66.2 and 75.9 of 100, respectively.

Constrained tripolar liners in our institute provided favourable results in the long term for recurrent dislocation hip arthroplasty with dysfunctional hip stabilizers. Infection in these patients can prove to be difficult to treat due to their poor soft tissue conditions from repeated surgeries. Comparing long terms results from other types of constrained liners is essential to evaluate these salvage liners.

Aims

We investigated the long-term performance of the Tripolar Trident acetabular component used for recurrent dislocation in revision total hip arthroplasty. We assessed: 1) rate of re-dislocation; 2) incidence of complications requiring re-operation; and 3) Western Ontario and McMaster Universities osteoarthritis index (WOMAC) pain and functional scores.

Trunnionosis, due to mechanical wear and/or corrosion at the head stem taper junction, can occur in metal on polyethylene (MOP) hip implants. In some patients this results in severe soft tissue destruction or Adverse Reaction to Metal Debris (ARMD). The amount of material required to cause ARMD is unknown but analyses of retrieved hips may provide the answer to this clinically important question.

We collected implants from 20 patients with failed hips with MOP bearings, revised due to ARMD. We collected clinical, imaging and blood test data. We graded the severity of taper corrosion (1 to 4), and quantified the volume of material loss from this junction. We compared our results with previous data collected for metal-on-metal (MOM) hips.

The median time to revision of the MOP hips was 51.3 (23.1–56.4) months. All head tapers were moderately to severely corroded with a median corrosion score of 4. The median (range) of total material loss at the taper of the MOP hips was 3.9 mm³ (2.96 – 7.85 mm³) and the material loss rate was 1.4 mm³ / year (0.56 – 1.82).

Comparison with MOM hips revealed no significant difference in taper material loss (p=0.7344) with a median rate of 0.81 mm³ / year (0.01–3.45).

We are the first to quantify the volume of material loss at the head taper of hip implants with MOP bearings that were revised due to trunnionosis. This data indicates that a clinically significant dose of cobalt and chromium to induce ARMD is approximately 1.4 mm³ / year.

We have identified a clinically significant volume of taper material loss in MOP hips.

There has been a reluctance, until relatively recently, to consider replacement of the hip in patients with substantial neuromuscular imbalance. This relates to many factors, including the young age of many (such as cerebral palsy in the older teen and young adult), developmental anatomic abnormality, oft-present poor bone health, neuromuscular imbalance, and the risk of complication; especially dislocation. Mental retardation also introduces challenges with rehabilitation and an increased burden on the family and societal support systems if the outcome is to be maximised. With the development of newer techniques and technology, and the emergence of encouraging outcome studies, these patients can be more easily offered predictable relief of pain, a reasonable chance of improved function, longevity of the reconstruction, and an acceptable risk of complication.

A large number of background neurological diagnoses can lead to hip degeneration, or can introduce increased complexity during management of hip degeneration unrelated to that background. Be that as it may, a short list of fundamental questions is common to all and will help guide management:

Important questions to be addressed include:

1. Did the NV imbalance precede skeletal development? This relates to the dependence of skeletal shape and size on the loads being placed upon it: hence “Form Follows Function”. The shape and size of the hip, and location of the femoral head, will be much different in the young adult with spastic dislocation due to cerebral palsy, when compared with the elderly adult with a late onset CVA-related spasticity superimposed on hip degeneration.

2. Is the muscle tone which will support the hip arthroplasty predominantly spastic or flaccid? In each there is a risk of dislocation, which needs to be addressed at the index procedure, but in spasticity there is the added question as to what tissues need to be released or de-functioned so as to alter the magnitude and direction of the joint reaction forces.

3. Is pain the main reason for consultation? Because pain relief is the most predictable outcome that we can offer, it should guide the indications and timing of intervention. Replacement of the NM hip to improve function, in the absence of pain, should be approached with great caution.

Cementless stem fixation is a widely used method of stem revision in North America and elsewhere in the world. There is abundant literature in its support. Most of the reports from 1985 to 2005 related to proximally or extensively porocoated designs, the former falling into disfavor with time because of unpredictable outcomes. With few exceptions (e.g. S-ROM) the modularity of these designs was limited to the head/neck junction. But this generation of designs was associated with some issues such as insertional fractures, limited control of anteversion (and risk of dislocation), limited applicability in the setting of severe bone loss (Paprosky Type 4 osteolysis or Vancouver Type B3 periprosthetic fracture), as well as ongoing concern relating to severe proximal stress shielding.

In the past decade we have seen the mounting use of a new design concept: tapered fluted titanium stems (TFTS), which incorporate the advantages of titanium (for less flexural rigidity), conical taper (for vertical taper-lock stability), longitudinal ribs or flutes (for rotational stability), and surface preparation which attracts bone ongrowth for long term fixation.

Four consecutive reports from our center have documented the superiority of the TFTS in our hands, with encouraging outcomes even when dealing with severe bone loss or periprosthetic fractures. There is an increasing body of other literature which reports a similar experience.

Furthermore, with increasing experience and confidence in this design concept, we now use a monoblock or non-modular design in the majority of cases in which a TFTS is indicated. This circumvents the potential drawbacks of stem modularity, including taper corrosion and taper junction fracture. Our recent report of this concept in 104 cases with a 2-year minimum follow-up supports the use of this concept in many if not most stem revisions.

The question remains as to which should be favored? Because of equipoise in the outcomes of the two fundamental stem designs, at least in our hands, clearly the surgeon needs to ask other, more practical questions:

Am I familiar enough with the TFTS technique so as to bypass the potential versatility of the modular stem for the simplicity and potential cost savings of the non-modular?

Is this a case in which modularity will offer me distinct advantages (periprosthetic fracture, and severe bone loss as examples)

Should I introduce the nonmodular TFTS to my practice, choosing straightforward cases first; ones in which I would comfortably and with confidence use an extensively porocoated stem?

It is now well recognised that adverse local tissue reaction (so called pseudotumor or ALTR) may follow the use of metal-on-metal arthroplasty, the source of the metal being the primary bearing surface (the articulation itself) or a modular junction within the construct, such as the trunnion. This is more likely seen if a large femoral head has been used. We are aware of this risk and have implemented surveillance systems worldwide to facilitate its early diagnosis and prompt management. Less well known, and silent in its initial development, is adverse local reaction following metal-on-polyethylene hip replacement.

Initially the problem is unknown to the patient and the surgeon. Typically there follows unexplained pain (due to synovitis), loss of motion, sometimes the development of a mass, followed by increasing dysfunction as the inflammatory, destructive process invades the surrounding soft tissues. Radiographic features are late to follow (focal osteolysis), unless cross-sectional imaging is considered (ultrasound and/or metal suppressed MRI) early in the process. Serum metal ions are an important adjunct in its diagnosis, and it is now acknowledged that the previously used level of 7 ppb is much higher than that required to recognise the entity. Typically there is a reverse of the usual CrCo ratio, and a recent study has suggested that a raised serum Co alone is adequate to assist in the diagnosis

Four important lessons have been learned at our center in recent years and will be demonstrated in this case-based presentation designed for surgeons in practice. It is hoped that the cases and supportive literature will prove useful in advancing the early diagnosis of this troublesome and often silent condition.

In revision total hip arthroplasty (THA), acetabular reconstruction while dealing with severe bone loss is a challenge. The porous tantalum revision acetabular shells have been in use for the past decade. Several reports have documented successful use at early to mid-term follow up. There is, however, very little literature around the long-term survival and quality of life outcome with the use of these shells.

We reviewed the results of 46 acetabular revisions with Paprosky 2 and 3 acetabular bone defects reconstructed with a hemispheric, tantalum acetabular shell and multiple supplementary screws. There were 31 females. Average age at revision was 64 years (range 23–85 years). The mean and median follow up was 11 years (range 10–12 years, SD 1). Morselised femoral allograft was used in 34 hips to fill contained cavitary defectes. Bulk femoral allografting was performed in 2 hips.

At a minimum follow-up of 10 (range 10–12) years, the survivorship of the porous tantalum acetabular shell, with revision of the shell as end point was 96%. The minimum 10-year survivorship with hip revision for any reason as end point was 92%. We noted excellent pain relief (mean WOMAC pain 92.6) and good functional outcome (mean WOMAC function 90.3, mean UCLA 5); and generic quality of life measures (mean SF-12 physical component 48.3; mean SF-12 mental component 56.7). Patient satisfaction with pain relief, function and return to recreational activities were noted to be excellent.

Cementless acetabular revision with the tantalum acetabular shell demonstrated excellent clinical and quality of life outcomes at minimum 10-year follow-up. As far as we are aware this is the first report of minimum 10-year follow up of use of this technique for revision hip arthroplasty.

Revision surgery for pelvic discontinuity in the presence of bone loss is challenging. The cup-cage reconstruction option has become popular for the management of pelvic discontinuity in the recent years. The aim of this study was to review the clinical, radiological and patient reported outcomes with the use of cup cage construct for pelvic discontinuity at our institution.

Twenty-seven patients (27 cup-cage reconstructions) were identified at median 6-year (minimum 2 year, maximum 10 years) follow up. Eight were female patients. The median age was 77 years [mean 72, range 37–90, SD 13.6]. There were 5 deaths and 2 were lost to follow up.

Two patients were converted to excision arthroplasty; one for infection and one for failure of the construct. A further 3 patients required revision for instability but the cup cage construct was not revised (2 revisions of cemented cups to a constrained cup and one revision of proximal modular component of the femoral prosthesis). Revision of the cup cage construct was not necessary in any of these cases. We noted excellent pain relief (mean WOMAC pain 85.6) and good functional outcome (mean WOMAC function 78.2, mean UCLA 5, mean OHS 78.6). Patient satisfaction with regards pain relief; function and return to activities were noted to be excellent. Radiological changes were noted in further 4 patients (cup migration in one case; fracture of ischial spike in one case and breakage of the cage screws in 2 patients). No migration of the construct was noted in any of the cases.

In conclusion, the cup cage construct is an excellent method of dealing with complex pelvic discontinuity. Our study suggests a low failure rate; high patient satisfaction and pain relief and moderate functional outcome at median 6 year follow up.

The practice at most centers in North America for the investigation and management of non-acute infection after hip replacement has been relatively standard for some time. Diagnosis has depended on a thorough history, physical examination, plain radiographs, straightforward laboratory inflammatory markers, joint aspiration for bacteriologic study, intraoperative frozen section in selected cases, and intraoperative synovial biopsies for confirmatory bacteriologic evaluation. The cornerstone of treatment on this continent has revolved around two-stage revision hip replacement, with increasing popularity for the use of interval articulating antibiotic loaded spacers, and increasing use of cementless fixation at the second stage. But this standard approach has been under increasing scrutiny in recent years, for good reason.

The use of more precise “best evidence” paradigms on which to base the diagnosis have been developed. There is encouraging work on the application of more specific synovial and serum markers. The need to remove all implant material in all cases has been challenged. And there is evidence that the two stage approach is associated with greater morbidity, mortality and cost. The latter has led to a re-examination of the role and results of single-stage exchange revision, at least in selected cases, where the patient is immune competent, the soft tissue and bone anatomy is not badly deficient, the organism is known, and the antibiotic sensitivity is favorable.

The most encouraging of the recent developments is the increasing consensus that multicenter collaborative study is required if we are to make genuine progress in the one-stage/two-stage debate. At least one multicenter prospective randomised study is scheduled to commence in 2015.

Cementless stem fixation is a widely used method of stem revision in North America and elsewhere in the world. There is abundant literature in its support. Most of the reports from 1985 to 2005 related to proximally or extensively porocoated designs, the former falling into disfavor with time because of unpredictable outcomes. With few exceptions (eg S-ROM) the modularity of these designs was limited to the head/neck junction. But this generation of designs was associated with some issues such as insertional fractures, limited control of anteversion (and risk of dislocation), limited applicability in the setting of severe bone loss (Paprosky Type 4 osteolysis or Vancouver Type B3 periprosthetic fracture), as well as ongoing concern relating to severe proximal stress shielding.

In the past decade we have seen the mounting use of a new design concept: tapered fluted titanium stems (TFTS), which incorporate the advantages of titanium (for less flexural rigidity), conical taper (for vertical taper-lock stability), longitudinal ribs and flutes (for rotational stability), and surface preparation which attracts bone on growth for long term fixation.

Four consecutive reports from our center have documented the superiority of the TFTS in our hands, with encouraging outcomes even when dealing with severe bone loss or periprosthetic fractures. There is an increasing body of other literature which reports a similar experience. Furthermore, with increasing experience and confidence in this design, we now use a monoblock or non-modular design in greater than 95% of cases in which a TFTS is indicated at our center. This circumvents the potential drawbacks of stem modularity, including taper corrosion and taper junction fracture.

Much is made of the role of good judgment in the reduction of error, although it is undeniable that error has a role in the development of such judgment. Hence retrospectives from those with experience have merit if we can assume they have introspection and insight as well.

In this panel discussion we will explore the experience of a group of renowned surgeons in the field of hip and knee reconstruction, and we will seek their wisdom on new techniques and technology, honed over a few decades of exciting discovery and oft-times unexpected disappointment.

In addition, as the session title suggests, these revered colleagues will be invited to reflect on those they encountered, in person or otherwise, by happenstance or design, who profoundly influenced their careers and how that influence shaped their lives and the lives of those entrusted to their care.

“If I have seen further than others, it is by standing upon the shoulders of giants” Sir Isaac Newton.

Cementless stem fixation is a widely used method of stem revision in North America and elsewhere in the World. There is abundant literature in its support. Most of the reports from 1985 to 2005 related to proximally or extensively porocoated designs, the former falling into disfavor with time because of unpredictable outcomes. With few exceptions (eg S-ROM) the modularity of these designs was limited to the head/neck junction. But this generation of designs was associated with some issues such as insertional fractures, limited control of anteversion (and risk of dislocation), limited applicability in the setting of severe bone loss (Paprosky Type 4 osteolysis or Vancouver Type B3 periprosthetic fracture), as well as ongoing concern relating to severe proximal stress shielding.

In the past decade we have seen the mounting use of a new design concept: tapered fluted titanium stems (TFTS), which incorporate the advantages of titanium (for less flexural rigidity), conical taper (for vertical taper-lock stability), longitudinal ribs and flutes (for rotational stability), and surface preparation which attracts bone on growth for long term fixation.

Four consecutive reports from our center have documented the superiority of the TFTS in our hands, with encouraging outcomes even when dealing with severe bone loss or periprosthetic fractures. There is an increasing body of other literature which reports a similar experience.

Furthermore, with increasing experience and confidence in this design, we now use a monoblock or non-modular design in greater than 95% of cases in which a TFTS is indicated at our center. This circumvents the potential drawbacks of stem modularity, including taper corrosion and taper junction fracture.

A large number of classification systems exist to assist in the evaluation and treatment of periprosthetic fractures following joint replacement. They vary in the language or categorisation they employ, the joints to which they are differently applied, the factors they assess, and the hierarchy or importance assigned to those factors. Not all incorporate the three most important variables which should govern treatment (fracture location, implant fixation, bone quality), nor the factors which have been demonstrated to most prominently influence outcomes. To a greater or lesser extent they attempt to include the principles of the Vancouver Classification System, and yet they differ in ways that lead to awkwardness in their application within the clinical setting. As an example, for fractures of the patella alone, three different systems have been proposed.

As the result of an international effort endorsed by the AO/OTA, the Universal Classification System, or UCS, has been developed. It incorporates the most important factors that should influence evaluation, treatment, and outcomes evaluation. It applies the system to the musculoskeletal system as a whole, regardless of the joint involved or the bone that is broken. And it uses a single common language to describe the injury and prescribe the logical principles of treatment.

It is hoped the UCS will appeal to our colleagues worldwide and will assist all of us in the care of our patients who suffer a periprosthetic fracture after joint replacement; be that the hip, knee, ankle, shoulder, elbow or wrist. The UCS can be applied with equal ease and merit to all.

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 to determine the effects of alendronate coating on porous tantalum on gap filling and bone ingrowth in the experimental model.

Introduction

Despite advances in surgical technique and prosthetics there continues to be a number of patients who are dissatisfied with the results of their knee replacement procedure. The outcome after total knee arthroplasty (TKA) has been reported frequently with use of condition-specific measures, but patient satisfaction has not been well studied.

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.