Pre-operative 3D glenoid planning improves component placement in terms of version, inclination, offset and orientation. Version and inclination measurements require the position of the inferior angle. As a consequence, current planning tools require a 3D model of the full scapula to accurately determine the glenoid parameters. Statistical shape models (SSMs) can be used to reconstruct the missing anatomy of bones. Therefore, the objective of this study is to develop and validate an SSM for the reconstruction of the inferior scapula, hereby reducing the irradiation exposure for patients. The training dataset for the statistical shape consisted of 110 CT images from patients without observable scapulae pathologies as judged by an experienced shoulder surgeon. 3D scapulae models were constructed from the segmented images. An open-source non-rigid B-spline-based registration algorithm was used to obtain point-to-point correspondences between the models. A statistical shape model was then constructed from the dataset using principal component analysis. Leave-one-out cross-validation was performed to evaluate the accuracy of the predicted glenoid parameters from virtual partial scans. Five types of virtual partial scans were created on each of the training set models, where an increasing amount of scapular body was removed to mimic a partial CT scan. The statistical shape model was reconstructed using the leave-one-out method, so the corresponding training set model is no longer incorporated in the shape model. Reconstruction was performed using a Monte Carlo Markov chain algorithm, random walk proposals included both shape and pose parameters, the closest fitting proposal was selected for the virtual reconstruction. Automatic 3D measurements were performed on both the training and reconstructed 3D models, including glenoid version, inclination, glenoid centre point position and glenoid offset. In terms of inclination and version we found a mean absolute difference between the complete model and the different virtual partial scan models of 0.5° (SD 0.4°). The maximum difference between models was 3° for inclination and 2° for version. For offset and centre point position the mean absolute difference was 0 mm with an absolute maximum of 1 mm. The magnitude of the mean and maximum differences for all anatomic measurements between the partial scan and complete models is smaller than the current surgical accuracy. Considering these findings, we believe a SSM based reconstruction technique can be used to accurately reconstruct the glenoid parameters from partial CT scans.
Aseptic acetabular component failure rates have been reported to be similar or even slightly higher than femoral component failure. Obtaining proper initial stability by press fitting the cementless acetabular cup into an undersized cavity is crucial to allow for secondary osseous integration. However, finding the insertion endpoint that corresponds to an optimal initial stability is challenging. This in vitro study presents an alternative method that allows tracking the insertion progress of acetabular implants in a non-destructive, real-time manner. A simplified acetabular bone model was used for a series of insertion experiments. The bone model consisted of polyurethane solid foam blocks (Sawbones #1522-04 and #1522-05) into which a hemispherical cavity and cylindrical wall, representing the acetabular rim, were machined using a computer numerically controlled (CNC) milling machine (Haas Automation Inc., Oxnard, CA, USA). Fig. 1 depicts the bone model and setup used. A total of 10 insertions were carried out, 5 on a low density block, 5 on a high density block. The acetabular cups were press fitted into the bone models by succeeding hammer hits. The acceleration of the implant-insertor combination was measured using 2 shock accelerometers mounted on the insertor during the insertion process (PCB 350C03, PCB Depew, NY, USA). The force applied to the implant-insertor combination was also measured. 15 hammer hits were applied per insertion experiment. Two features were extracted from the acceleration time signal; total signal energy (E) and signal length (LS). Two features and one correlation measure were extracted from the acceleration frequency spectra; the relative signal power in the low frequency band (PL, from 500–2500Hz) and the signal power in the high frequency band (P Hf, from 4000–4800 Hz). The changes in the low frequency spectra (P Lf, from 500–2500 Hz) between two steps were tracked by calculating the Frequency Response Assurance Criterion (FRAC). Force features similar to the ones proposed by Mathieu et al., 2013 were obtained from the force time data. The convergence behavior of the features was tracked as insertion progressed.Introduction
Materials and Methods
Each year, a large number of total hip arthroplasties (THA) are performed, of which 60 % use cementless fixation. The initial fixation is one of the most important factors for a long lasting fixation [Gheduzzi 2007]. The point of optimal initial fixation, the endpoint of insertion, is not easy to achieve, as the margin between optimal fixation and a femoral fracture is small. Femoral fractures are caused by peak stresses induced during broaching or by the hammer blows when the implant is excessively press-fitted in the femur. In order to reduce the peak stresses during broaching, IMT Integral Medizintechnik (Luzern, Switzerland) designed the Woodpecker, a pneumatic broach that generates impulses at a frequency of 70 Hz. This study explores the feasibility of using the Woodpecker for implant insertion by measuring both the strain in the cortical bone and the vibrational response. An in vitro study is presented. A Profemur Gladiator modular stem (MicroPort Orthopedics Inc. Arlington, TN, USA) and two artificial femora (composite bone 4th generation #3403, Sawbones Europe AB, Malmö, Sweden) were used. One artificial femur was instrumented with three rectangular strain gauge rosettes (Micro-Measurements, Raleigh, NC, USA). The rosettes were placed medially, posteriorly and anteriorly proximally on the cortical bone. Five paired implant insertions were repeated on both artificial bones, alternating between standard hammering and Woodpecker insertions. During the insertion processes the vibrational response was measured at the implant and Woodpecker side (fig. 1) using two shock accelerometers (PCB Piezotronics, Depew, NY, USA). Frequency spectra were derived from the vibrational responses. The endpoint of insertion was defined as the point when the static strain stopped increasing during the insertion.Introduction
Material and Methods
A large number of total hip arthroplasties (THA) are performed each year, of which 60 % use cementless femoral fixation. This means that the implant is press-fitted in the bone by hammer blows. The initial fixation is one of the most important factors for a long lasting fixation [Gheduzzi 2007]. It is not easy to obtain the point of optimal initial fixation, because excessively press-fitting the implant by the hammer blows can cause peak stresses resulting in femoral fracture. In order to reduce these peak stresses during reaming, IMT Integral Medizintechnik (Luzern, Switzerland) designed the Woodpecker, a pneumatic reaming device using a vibrating tool. This study explores the feasibility of using this Woodpecker for implant insertion and detection of optimal fixation by analyzing the vibrational response of the implant and Woodpecker. The press-fit of the implant is quantified by measuring the strain in the cortical bone surrounding the implant. An in vitro study is presented. Two replica femur models (Sawbones Europe AB, Malmo Sweden) were used in this study. One of the femur models was instrumented with three rectangular strain gauge rosettes (Micro-Measurements, Raleigh, USA). The rosettes were placed medially, posteriorly and anteriorly on the proximal femur. Five paired implant insertions were performed on both bone models, alternating between standard hammer blow insertions and using the Woodpecker. The vibrational response was measured during the insertion process, at the implant and Woodpecker side using two shock accelerometers (PCB Piezotronics, Depew, NY, USA). The endpoint of insertion was defined as the point when the static strain stopped increasing. Significant trends were observed in the bandpower feature that was calculated from the vibrational spectrum at the implant side during the Woodpecker insertion. The bandpower is defined as the percentage power of the spectrum in the band 0–1000 Hz. Peak stress values calculated from the strain measurement during the insertion showed to be significantly (p < 0.05) lower at two locations using the Woodpecker compared to the hammer blows at the same level of static strain. However, the final static strain at the endpoint of insertion was approximately a factor two lower using the Woodpecker compared to the hammer. A decreasing trend was observed in the bandpower feature, followed by a stagnation. This point of stagnation was correlated with the stagnation of the periprosthetic stress in the bone measured by the strain gages. The behavior of this bandpower feature shows the possibility of using vibrational measurements during insertion to assess the endpoint of insertion. However it needs to be taken into account that it was not possible to reach the same level of static strain using the Woodpecker as with the hammer insertion. This could mean that either extra hammer blows or a more powerful pneumatic device could be needed for proper implant insertion.
The success of cementless total hip arthroplasty (THA), primary as well as for revision, largely depends on the initial stability of the femoral implant. In this respect, several studies have estimated that the micromotion at the bone-implant interface should not exceed 150µm (Jasty 1997, Viceconti 2000) in order to ensure optimal bonding between bone and implant. Therefore, evaluating the initial stability through micromotion measurements serves as a valid method towards reviewing implant design and its potential for uncemented THAs. In general, the methods used to measure the micromotion assume that the implant behaves as a rigid body. While this could be valid for some primary stems (Østbyhaug 2010), studies that support the same assumption related to revision implants were not found. The aim of this study is to assess the initial stability of a femoral revision stem, taking into account possible non-rigid behaviour of the implant. A new in vitro measuring method to determine the micromotion of femoral revision implants is presented. Both implant and bone induced displacements under cyclic load are measured locally. A Profemur R modular revision stem (MicroPort Orthopedics Inc. Arlington, TN, United States of America) and artificial femora (composite bone 4th generation #3403, Sawbones Europe AB, Malmö, Sweden) prepared by a surgeon were used. The micromotions were measured in proximal-distal, medial-lateral or anterior-posterior directions at four locations situated in two transverse planes, using pin and bushing combinations. At each measuring location an Ø8mm bushing was attached to the bone, and a concentric Ø3mm pin was attached to the implant [Fig.1 and 2]. A supporting structure used to hold either guiding bushings or linear variable displacement transducers (LVDT) is attached to the proximal part of the implant. The whole system was installed on a hydraulic force bench (PC160N, Schenck GmbH, Darmstadt, Germany) and 250 physiological loading cycles were applied [Fig.3].Introduction
Methods
Cementless femoral hip stems crucially depend on the initial stability to ensure a long survival of the prosthesis. There is only a small margin between obtaining the optimal press fit and a femoral fracture. The incidence of an intraoperative fracture is reported to be as high as 30% for revision surgery. The aim of this study is to assess what information is contained in the acoustic sound produced by the insertion hammer blows and explore whether this information can be used to assess optimal seating and warn for impeding fractures. Acoustic measurements of the stem insertion hammer blows were taken intra-operatively during 7 cementless primary (Wright Profemur Primary) and 2 cementless revision surgeries (Wright Profemur R Revision). All surgeries were carried out by the same experienced surgeon. The sound was recorded using 6 microphones (PCB 130E2), mounted at a distance of approximately 1 meter from the surgical theater. The 7 primary implants were inserted without complication, 1 revision stem induced a fracture distally during the insertion process. Two surgeons were asked to listen independently to the acoustic sounds post-surgery and to label the hits in the signal they would associate with either a fully fixated implant or with a fracture sound. For 3 out of 7 primary measurements the data was labeled the same by the two surgeons, 4 were labeled differently or undecided and both indicated several hits that would be associated with fracture for the fractured revision case. The acquired time signals were processed using a number of time and frequency domain processing techniques.Introduction
Materials and Methods
Treatment of Paprosky type 3A and 3B defects in revision surgery of a hip arthroplasty is challenging. In previous cases such acetabular defects were treated with massive structural allograft bone reconstructions using cemented all-polyethylene cups. In our department we started using custom made triflanged cups to restore the articulation of the hip. The triflanged cups were designed on the basis of CT-image analysis. We are using a new type of implant construction technique with additive technology. This is a production process consisting of ion beam sintering joining metal powder particles layer upon layer on the basis of a 3D model data. The production technique is similar to rapid prototyping manufacturing. 7 Patients have been treated with this new technique. The case studies will be presented with their clinical and radiographic follow-up. We think that additive technology is a breakthrough in treating this kind of severe acetabular defects.
As population grows older, and patients receive primary joint replacements at younger age, more and more patients receive a total hip prosthesis nowadays. Ten-year failure rates of revision hip replacements are estimated at 25.6%. The acetabular component is involved in over 58% of those failures. From the second revision on, the pelvic bone stock is significantly reduced and any standard device proves inadequate in the long term [Villanueva et al. 2008]. To deal with these challenges, a custom approach could prove valuable [Deboer et al. 2007]. A new and innovative CT-based methodology allows creating a biomechanically justified and defect-filling personalized implant for acetabular revision surgery [Figure 1]. Bone defects are filled with patient-specific porous structures, while thin porous layers at the implant-bone interface facilitate long-term fixation. Pre-operative planning of screw positions and lengths according to patient-specific bone quality allow for optimal fixation and accurate transfer to surgery using jigs. Implant cup orientation is anatomically analyzed for required inclination and anteversion angles. The implant is patient-specifically analyzed for mechanical integrity and interaction with the bone based upon fully individualized muscle modeling and finite element simulation.Introduction
Materials and methods
The number of joint revision surgeries is rising, and the complexity of the cases is increasing. In 58% of the revision cases, the acetabular component has to be revised. For these indications, literature decision schemes [Paprosky 2005] point at custom pre-shaped implants. Any standard device would prove either unfeasible during surgery or inadequate in the short term. Studies show that custom-made triflanged implants can be a durable solution with good clinical results. However, the number of cases reported is few confirming that the device is not in widespread use. A patient, female 50 yrs old, diagnosed having a pseudotumor after Resurfacing Arthroplasty for osteo-arthritis of the left hip joint. The revision also failed after 1 y and she developed a pelvic discontinuity. X-ray and Ct scans were taken and sent to a specialized implant manufacturer [Mobelife, Leuven, Belgium]. The novel process of patient-specific implant design comprises three highly automated steps. In the first step, advanced 3D image processing presented the bony structures and implant components. Analysis showed that anterior column was missing, while the posterior column was degraded and fractured. The acetabular defect was diagnosed being Paprosky 3B. The former acetabular component migrated in posterolateral direction resulting in luxation of the joint. The reconstruction proposal showed the missing bone stock and anatomical joint location. In the second step, a triflanged custom acetabular metal backing implant was proposed. The bone defect (35ml) is filled with a patient-specific porous structure which is rigidly connected to a solid patient-specific plate. The proposed implant shape is determined taking into account surgical window and surrounding soft tissues. Cup orientation is anatomically analyzed for inclination and anteversion. A cemented liner fixation was preferred (Biomet Advantage 48mm). Screw positions and lengths are pre-operatively planned depending on bone quality, and transferred into surgery using jig guiding technology (Materialise NV, Leuven, Belgium). In the third step, the implant design was evaluated in a fully patient-specific manner in dedicated engineering (FEA) software. Using the novel automated CT-based methodology, patient-specific bone quality and thickness, as well as individualised muscle attachments and muscle and joint forces were included in the evaluation. Implants and jig were produced with Additive Manufacturing techniques under ISO 13485 certification, using respectively Selective Laser Melting (SLM) techniques [Kruth 2005] in medical grade Ti6Al4V material, and the Selective Laser Sintering technique using medical grade epoxy monomer. The parts were cleaned ultrasonically, and quality control was performed by optical scanning [Atos2 scanning device, GOM Intl. AG, Wilden, Switzerland]. Sterilization is performed in the hospital. A unique combination of advanced 3D planning, patient-specific designed and evaluated implants and drill guides is presented. This paper illustrates, by means of a clinical case, the novel tools and devices that are able to turn reconstruction of complex acetabular deficiencies into a reliable procedure.Case Report
CONCLUSION
The operation technique and prosthetic materials for total hip replacement (THR) have continuously improved. Still, defining the end-point of the prosthetic stem insertion into the femur canal relies on the feeling of the orthopaedic surgeon. This consists of a sense of mechanical stability when exerting torque forces on the prosthesis as well as a feeling of the prosthesis being well fixed and not displaceable along the axis of the femur. Stability and survival of the implant is directly related to the long term fixation stability of the prosthesis stem. But, excessive press-fitting of a THR femoral component can cause intra-operative fractures. In our centre custom made stem prostheses are commonly used to increase the optimal fit in the femoral canal. We report the first per-operative use of a non invasive vibration analysis technique for the mechanical characterization of the primary bone-prosthesis stability. From in vitro studies a protocol has been derived for per-operative use. The prosthesis neck is attached to a shaker using a stinger provided with a clamping system. The excitation is realized through white noise in the range 0–12.5 kHz, introducing a power of approximately 0.5W into the femur-prosthesis system. The input force and the response acceleration are measured in the same point with an impedance head mounted between the shaker and the stinger. The Frequency Response Function (FRF) is measured and recorded by a Pimento vibration analyzer connected to a portable computer provided with the appropriate software. All equipment is installed in the surgical theatre but outside the so-called laminar flow area. The surgeon inserts the implant in the femoral canal through repetitive controlled hammer blows. After each blow, the FRF of the implant-bone structure is measured directly on the prosthesis neck. The hammering is stopped when the FRF graph does not change noticeably anymore. The amount of FRF change between insertion steps is quantified by the Pearson’s correlation coefficient R between successive FRFs. A correlation between the FRFs of successive stages of R=(0.99 +/− 0.01) over the range 0–10000 Hz is proposed as an endpoint criterion. Non-cemented custom made stem insertion was studied in 30 patients. In 26/30 cases (86.7%), the correlation coefficient between the last two FRFs was >
0.99 when the surgeon stopped the insertion. In 4 cases, the surgeon decided to stop the insertion because of suspected bone fragility, the final correlation coefficient was lower. In one case an abnormal change in the FRF graph triggered inspection of the femur bone. A small fracture was observed and insertion was stopped. In a second case FRF graph showed an oscillating behaviour, while the stem was visibly not completely inserted. After withdrawal of the stem and readjustment of the femoral canal, the stem could be reinserted and the Pearson’s correlation index at end of insertion was 0.998. The use of custom made stem prosthesis, made exactly to fit into the femoral canal increases the risk of excessive press fit and intra-operative fractures. Vibration analysis showed to be a useful tool to define end of the stem insertion.
In total hip replacement (THR), the initial fixation of the femoral stem has a critical influence on its long term stability. Objective intra-operative assessment of primary stability is a challenge, surgeons having to rely mainly on their clinical experience. Excessive press-fitting of the stem can cause intra-operative fractures in up to 30% of revision cases. In a previous study we demonstrated the feasibility and validity of a vibrational technique for the assessment of the femur-stem fixation in vitro. In this in vivo study the vibration analysis was applied for the per-operative assessment of stem fixation in 30 THR patients who obtained an intra-operatively manufactured, hydroxyapatite coated, cementless prosthesis. The surgeon inserted the stem through repetitive controlled hammer blows. After each blow, the frequency response function (FRF) of the stem-bone structure was measured directly on the prosthesis neck in the range 0–10 kHz. The hammering was stopped when the FRF graph did not change anymore. Extra blows would not improve the stability but would increase the fracture risk. In 26 out of 30 cases (86.7%), the correlation coefficient between the last two FRFs was above 0.99 when the insertion was stopped. In four cases, when the surgeon decided to stop the insertion because of suspected bone fragility, the final correlation coefficient attained lower values. During the insertion of a cementless prosthesis, the changes of boundary conditions and implant stability between subsequent stages are reflected by the FRF evolution. The higher resonance frequencies are more sensitive to the stability change. The correlation between successive FRFs can be used as a criterion for the detection of the insertion endpoint. Moreover, the FRF analysis can be used to detect dangerous situations during surgery like stem blockage and fracture risk. This study should be completed and validated by a post-operative follow-up of the patients.
We report the follow-up of a cohort of 86 patients who underwent total hip replacement (THR) with custom-made stem prosthesis. Fixation mode, cemented (group 1) or uncemented (group 2) is based on the bone quality. Aspects of physical health and changes in mental health are documented using 3 patient-administered questionnaires, pre-operatively and 6 weeks, 3, 6 and 12 months post-operatively. Harris Hip Score (HHS), Hip disability and osteoarthritis outcome score (HOOS) and SF-36, multi-purpose, short-form health survey were used. Globally HHS increases significantly (p<
0.01). In group 1 up to 3 months post-operatively and in group 2 up to 1 year. (p <
0.05). In group 2 HHS is significantly higher 6 months and 1 year postoperatively (p<
0.05). No significant differences in HOOS subscores between subjects of group 1 and 2 for subsequent time points were found. The scores related to Pain and Symptoms increased significantly 6 weeks after THR (p<
0.01). Sports and recreation scores increased significantly up to 3 months after THR (p<
0.01). Activities of daily living, and Quality of Life (QoL) improved up to 6 months after surgery (p<
0.01). No significant difference between the 2 groups in QoL was observed. The physical component summary increased up to 3 months after surgery (p<
0.01). The mental component summary did not change significantly after THR. The difference noted in HHS between group 1 and 2 may be due to the selection of the fixation technique which is often directly related to the patient’s age. The results of the HOOS score confirm the findings of the HHS. Not all patients responded to the questions relative to recreation and sport of the HOOS score. QoL is an important indicator for success as perceived by the patient. In this study a rapid improvement of QoL is observed (3 months) and there is little change at 6 and 12 months.
Radiostereometric analysis (RSA) is a technique that can be used to measure in-vivo micro-motion of the components of hip arthroplasty. 86 patients received a titanium custom-made prosthesis. The average age was 64 year (20y –84y). During the study 30 patients out of 86 received a cementless femoral stem. The choice of stem fixation is determined by the quality of the bone. In all cases a 36 mm cobalt chromium head is used. Spherical tantalum markers, chosen because of the proven biocompatibility, were inserted into stable locations in the femoral bone during surgery using a specialized insertion tool, according to the protocol. Evaluation was done 1, 6, 12, 24, 52 weeks after surgery. Overall subsidence follows a parallel pattern for the cemented and uncemented prosthesis that is slightly stronger in for the uncemented prosthesis. Over the 6 months evaluation period the prosthesis migrates towards the lateral side with 0.25 mm in both groups. An anteroversion of 0.5° to 1° is noted at 6 months follow-up. The varus valgus movement of the prosthesis is similar for both groups at 6 months. At 6 weeks a slight valgus flexion is noted, this is reversed at 3 months. At this point in time the effect is more pronounced in the group with a cemented prosthesis. Micro motion is difficult to assess on plain radiography. In this study more subsidence is noted in the uncemented prosthesis compared to the cemented. The degree of rotation of the stem measured in our study is comparable with those reported by others. In our primary THR we observe a bi-modal micromotion except for the subsidence the initial movement up till 6 weeks is reversed at 3 months follow-up and at 6 months the prosthesis seems stabilized, though longer follow-up is required to confirm stabilization.
Success of a total hip replacement is commonly assessed by the Haris Hip Score (HHS), which provides information on pain reduction and regained mobility. Radiographic images provide information relative to the stability of the prosthesis. We use the intraoperatively manufactured prosthesis since 1989; the initially performed THR were done with uncoated prostheses. After introduction of the hydroxyapatite coating our prosthesis stems were coated. We retrospectively evaluated the clinical and radiographic outcome of 3 patient cohorts who received intra-operatively custom made stem prosthesis.
Group 1: Uncoated stem prosthesis fixated with tro-chanteric osteotomy. Group 2: Uncoated stem cementless implant Group 3: Cementless hydroxyapatite coated stem prosthesis Clinical assessment and radiographic assessment is performed using pre-operatively and at each follow-up visit. Baseline data are the pre-operative HHS and first radiography postoperatively. These data are compared with the data of the latest follow-up visit. RX’s are scored according to the ARA score. Records were analysed for 83 patients in group 1, with a mean follow-up period of 93 months. In group 2, 35 patients were followed for 105 months and 54 patients from group 3 were followed for 41 months. In the 3 groups the HHS at follow-up was >
75, this means an improvement of minimum 25 points for group 1 and 2 (baseline HHS for group 2 was not available) The mean ARA scores at follow-up were 1.6; 1.7 and 5.3 for respectively group 1; 2 and 3. Clinical outcome is comparable in the three studied cohorts. The ARA score is indicating poor outcome for the uncoated prosthesis, regardless of the type of fixation, while the coated prosthesis group has a good to excellent ARA score. These findings tend to confirm the superiority of the hydroxyapatite coated prosthesis.
We present the results of a prospective longitudinal follow-up study of Dual X-ray Absorptiometry (DXA) measurements of the evolution of bone mineral density (BMD) of acetabulum and femur in 86 patients who underwent total hip arthroplasty (THA). A standard uncemented cup and intra-operatively manufactured stem prosthesis was used in all patients. Stem fixation was determided by the bone quality Thirthy patients received cementless and 56 patients received cemented stem prosthesis. Post-operative DXA scans were obtained in peri-prosthetic bone at 10 days, 6 weeks, 3, 6 and 12 months after THA. Peri-prosthetic BMD values in the proximal femur were obtained in the 7 Gruen zones. In the acetabulum a 4 region of interest model (ROI) was used. Bimodal significant femoral BMD changes are found in all Gruen zones except for zone 1 of the cemented group where an immediate recovery is observed. The recovery mostly starts after 6 months of follow-up and the highest remodelling is found in the calcar region reaching even values of −16% at 6 months but no statistical significance was observed between the two groups. Significant linear losses (p<
0.0001) are observed in the pelvis region independent of type of fixation except the opposite change (p<
0.01) in the inferior region observing an immediate recovery in the uncemented group. We compared the impact of a cemented stem with a non cemented stem on the bone remodelling of the cup and found that there was a correlation between the type of fixation and the mode of remodelling at the acetabular level. This suggest that a parameter such as the flexibility my have an influence on the bone remodelling at the acetabulum level. The pattern of bone remodelling observed on the different Gruen zones reflects the local load transfer to peri-prosthetic bone.
We want to prove that you cannot make a good fitting stem of a THP before surgery because the resulting shape of the femoral cavity is set after all the tools have been introduced in the femur. We are fully aware that fit and fill alone is not enough to obtain good fixation therefor all the investigated implants were plasma spray coated with HA. We have investigated two groups of patients:
Pre – operative group: custommade implant based on CT scans and manufactured before surgery. The proximal part was size for size and coated with HA; the distal part is cylindrical (44 cases, followup from 2.6 years to 6.2 years). Per – operative group: custommade implants based on a mould of the femoral cavity in the proximal femur and manufactured during surgery. The prosthesis was size for size and the HA coating was applied on the proximal 1/3 of the implant. (13 cases with a minimum follow-up of two years). The manufacturing procedures and coating specifications for both groups were exactly the same. We’ve compared the Harris hip score for both groups and we’ve performed a radiolographical analysis. Of the preoperative group 6 protheses had to be revised. This results in a revision rate of 13 % which is not acceptable. In the peroperative group however, no revisions have been performed. Radiografically the peroperative group showed much better results than the preoperative group. The obtained results suggest that it is not only important to have a good bone growth initiator such as HA but the implant needs to be in close contact with the bone.
We want to prove that you cannot make a good fitting stem of a THP before surgery because the resulting shape of the femoral cavity is set after all the tools have been introduced in the femur. We are fully aware that fit and fill alone is not enough to obtain good fixation therefor all the investigated implants were plasma spray coated with HA. We’ve investigated two groups of patients:
Pre-operative group: custommade implant based on CT scans and manufactured before surgery The proximal part was size for size and coated with HA; the distal part is cylindrical (44 cases, followup from 1.6 years to 5.2 years) Per-operative group: custommade implants based on a mould of the femoral cavity in the proximal femur and manufactured during surgery. The prosthesis was size for size and the HA coating was applied on the proximal 1/3 of the implant. (13 cases, with a minimum followup 1 year). The coating specifications for both groups were exactly the same.We’ve compared the Harris hip score for both groups and we’ve performed a radiolographical analysis. Of the pre- operative group 6 protheses had to be revised.This results in a revision rate of 25 % which is not acceptable.In the peroperative group however, no revisions have been performed. Radiografically the per-operative group showed much better results than then the pre-operative group. The obtained results suggest that it is not only important to have a good bone growth initiator such as HA but the implant needs to be in close contact with the bone.This confirms the limited gap bridging capacity of HA which has been reported by several authors in the past. A close fit can only be obtained by designing and manufacturing the implant during surgery based on the actual size of the femoral cavity.
