Revisionsendoprothetik

Microarchitectural properties of compacted cancellous bone allografts: A morphology micro-computed tomography analysis

Massive bone loss poses a significant challenge in defect reconstruction. The use of compacted allografts is a valuable technique to reconstruct bone stock. This study aimed to assess the impact of compression on the microstructure of native cancellous bone chips with a micro-CT analysis. Bone samples were harvested from 15 femoral heads donated by patients who underwent total hip arthroplasty. Bone chips were prepared using a bone mill. All samples with the same weight were compressed by 25% and 50% of their original volume and subsequently scanned with a micro-CT scanner to determine the microarchitectural morphology of the bone chips. Uniaxial compression test was carried out before and after a standardized compaction procedure. Comparing the samples without compaction to 50%, the number of trabeculae doubled, the volume ratio doubled, and the trabeculae spacing was reduced, showing voids of 800 μm on average. The number of interlocking possibilities tripled, while no differences were seen in the trabeculae morphology. Uniaxial compression test showed a yield limit after compaction of 0.125 MPa. Interlocking might occur three times more with a denser material than in a non-compacted sample. The increase in density comparable to manual intraoperative compaction did not lead to significant fragmentation of the allograft material. The assessed microarchitecture should, therefore, reassemble the intraoperative situation during a manual bone impaction procedure.

Acetabular Revision With Intramedullary and Extramedullary Iliac Fixation for Pelvic Discontinuity

BACKGROUND

Parallel to the increase in revision hip procedures surgeons face more and more complex anatomical challenges with pelvic discontinuity (PD) being one of the worst-case scenarios. Here we report on our clinical results using an asymmetric acetabular component for the treatment of PD. The implant is armed in a monoblock fashion with an extramedullary iliac flange and provides the possibility to augment it with an intramedullary iliac press-fit stem.

METHODS

In a single-center retrospective cohort study we analyzed prospectively collected data of 49 patients (35 female, 14 male) suffering from unilateral periprosthetic PD treated with an asymmetric acetabular component between 2009 and 2017. The mean follow-up was 71 months (21-114). Complications were documented and radiographic and functional outcomes were assessed.

RESULTS

Kaplan-Meier analysis revealed a 5-year implant survival of 91% (confidence interval 77%-96%). The 5-year survival with revision for any cause was 87% (CI 74%-94%). The overall revision rate was 16% (n = 8). Two patients required acetabular component revision due to aseptic loosening. Four patients (8%) suffered from periprosthetic infection: one patient was treated with a 2-stage revision, and another one with resection arthroplasty. The other 2 patients were treated with debridement, irrigation, and exchange of the mobile parts. Of 6 patients (12%) suffering from hip dislocation, 2 required implantation of a dual mobility acetabular component. The mean Harris Hip Score improved from 41 preoperatively to 79 at the latest follow-up (P < .001).

CONCLUSION

Our findings demonstrate that an asymmetric acetabular component with extramedullary and optional intramedullary iliac fixation is a reliable and safe treatment method for periprosthetic PD resulting in good clinical and radiographic mid-term results.

Acetabular defect classification and management : Revision arthroplasty of the acetabular cup based on 3-point fixation

BACKGROUND

The purpose of this study was to provide a practicable and contemporary classification system that is reliable and pragmatic with respect to perioperative evaluation, planning, scientific comparison and analysis.

MATERIAL AND METHODS

This was a retrospective study of 160 patients who underwent acetabular revision surgery after THR due to loosening of the acetabular cup. The assessment of the acetabular defect was based on intraoperative description of the bony configuration of the acetabulum as well as on standardized preoperative planning images (pelvic overview and axial view of the hip joint). Preoperative computed tomography (CT) was carried out in individual cases.

RESULTS

Acetabular bone defects were classified into 4 types based on whether or not a 3-point fixation of the acetabular cup within the boundaries of the acetabular cavity was possible. Minor segmental defects or cup loosening without bone loss can be treated with standard hemispherical acetabular components. Bone loss can be filled with bone grafts and/or treated by the appropriate acetabular component in order to ensure stable anchorage. When conventional revision cups are no longer suitable a custom made partial pelvic replacement can be used.

CONCLUSION

The proposed classification mainly relies on intraoperative findings which were confirmed by preoperative imaging in 154 cases out of 160 (96.25%); however, meticulous preoperative planning based on X‑ray radiographs must be carried out. In addition, a CT scan must be performed whenever type III or type IV defects are anticipated. Compared to the existing classification systems, we can state that our classification system is practicable and pragmatic and simplifies the assessment of bone defects.

Management of pelvic discontinuity in revision arthroplasty : Cementless acetabular cup with iliac stem and cranial strap

BACKGROUND

Pelvic discontinuity causes severe destruction of the acetabular bony walls and is particularly difficult to manage. This article reports the short-term results and complications encountered in the management of loosening of the acetabular cup with pelvic discontinuity using an acetabular cup with an intramedullary iliac stem combined with an extramedullary iliac plate.

MATERIAL AND METHODS

As part of this monocentric retrospective case analysis all patients who underwent acetabular revision surgery after THR due to loosening of the acetabular cup with pelvic discontinuity in this clinic from January 2016 to June 2017 were identified (n = 16). All patients underwent routine clinical and radiological follow-up. In addition, the Harris hip score (HHS) and the Western Ontario and McMaster Universities osteoarthritis index (WOMAC) were evaluated as part of a 1-year follow-up.

RESULTS

All patients were treated with an acetabular revision cup of appropriate size with intramedullary iliac stem combined with an anatomical extramedullary iliac plate. On clinical follow-up at 1 year (median follow-up time 14.5 ± 3.3 months), the average HHS was 69.3 ± 14.1 and the average WOMAC was 79.3 ± 11.7. Complications were registered in 7 out of the 16 patients whereby 1 showed aseptic loosening of the revision cup, dislocations were reported in 4 cases and infections in 2 cases. In the case of the two patients with infections a Girdlestone resection arthroplasty had to be performed.

CONCLUSION

The overall complications and postoperative outcome in revision surgery after THR reported in the literature were compared to the results of this study. Compared to the results of salvage procedures using large or bipolar heads and Girdlestone resection arthroplasty, satisfactory results were obtained using the acetabular cup with an intramedullary iliac stem combined with an extramedullary iliac plate.

Primary Total Hip Arthroplasty in Severe Dysplastic Hip Osteoarthritis With a Far Proximal Cup Position

BACKGROUND

Developmental hip dysplasia is the most common cause of secondary hip osteoarthritis. Due to severe acetabular bone deficiency, cup positioning in total hip arthroplasty (THA) of dysplastic hips remains a surgical challenge. The aim was to analyze the functional outcome of far proximal cup positions in primary THA.

METHODS

Fifty patients (61 hips) with THA for severe dysplastic osteoarthritis and a far proximal cup position were included. Patients were divided according to the heights of the implanted cups with increasing vertical distance from the interteardrop line (group A: 55-65 mm, group B: 65-75 mm, group C: >75 mm). Functional outcome was assessed at latest follow-up (38 ± 16 months) by Lower Extremity Functional Score, Tegner Activity Score, and Harris Hip Score (HHS). Patients answered a Patient Satisfaction Questionnaire. Leg length discrepancy was estimated radiographically.

RESULTS

The Lower Extremity Functional Score significantly decreased in C (45.3 ± 25) compared to A (66.7 ± 15.3) and B (67.9 ± 9.9). The Tegner Activity Score significantly increased in all subgroups from preoperative to postoperative (2.2 ± 1.3 to 4.1 ± 1.4; P < .05). The mean overall HHS was 89.3 ± 14.7 (A: 89.5 ± 14.3, B: 94.3 ± 6.5, C: 78.3 ± 22.1). The HHS domains of activity of daily life and gait were significantly reduced in C (P < .05). Patients described a high satisfaction level with the surgery. No significant differences were found with regard to preoperative and postoperative leg lengthening (P = .881). Neither dislocations, impingement problems nor neurologic complications were observed.

CONCLUSION

Primary THA without any concomitant surgical interventions with a far proximal cup position offers a safe and effective treatment option in severe dysplastic hip osteoarthritis.

[Treatment of acetabular bone defects in revision hip arthroplasty using the Revisio-System]

BACKGROUND

Many different systems for the management of primary and secondary acetabular defects are available, each with its inherent advantages and disadvantages. The Revisio-System is a press-fit oval mono-block implant that makes a defect-oriented reconstruction and restoration of the center of rotation possible.

MATERIAL AND METHODS

In this study, we retrospectively reviewed the outcome of 92 consecutive patients treated with this oval press-fit cup due to periacetabular bone loss. The average follow-up was 58.2 months. Defects were classified according to D'Antonio. There were 39 type II, 38 Type III, and 15 type IV defects. After an average of 4.9 years, the implant survival rate was 94.6% with cup revision as the end point and 89.1% with revision for any reason as the end point. The Harris Hip Score increased from 41.1 preoperatively to 62.3 postoperatively. The mean level of pain measured with the Visual Analogue Scale (VSA) was reduced from 6.9 preoperatively to 3.8 postoperatively.

RESULTS

The Revisio-System represents a promising toolbox for defect-orientated reconstruction of acetabular bone loss in revision hip arthroplasty. Our results demonstrate that the implantation of the Revisio-System can result in a good mid-term clinical outcome.

Acetabular defect classification in times of 3D imaging and patient-specific treatment protocols

Parallel to the rising number of revision hip procedures, an increasing number of complex periprosthetic osseous defects can be expected. Stable long-term fixation of the revision implant remains the ultimate goal of the surgical protocol. Within this context, an elaborate preoperative planning process including anticipation of the periacetabular defect form and size and analysis of the remaining supporting osseous elements are essential. However, detection and evaluation of periacetabular bone defects using an unsystematic analysis of plain anteroposterior radiographs of the pelvis is in many cases difficult. Therefore, periacetabular bone defect classification schemes such as the Paprosky system have been introduced that use standardized radiographic criteria to better anticipate the intraoperative reality. Recent studies were able to demonstrate that larger defects are often underestimated when using the Paprosky classification and that the intra- and interobserver reliability of the system is low. This makes it hard to compare results in terms of defects being studied. Novel software tools that are based on the analysis of CT data may provide an opportunity to overcome the limitations of native radiographic defect analysis. In the following article we discuss potential benefits of these novel instruments against the background of the obvious limitations of the currently used native radiographic defect analysis.

Effects of various anchoring components and loading conditions on primary stability of acetabular revision implant

PURPOSE

In revision total hip arthroplasty, until today, orthopaedic surgeons are missing evidence-based guidelines on cementless acetabular cup fixation.

METHODS

5 finite element models were generated featuring the following anchorage strategies: 1 short peg, 1 long peg, 2 long screws, 3 short screws and zero anchoring components for reference. The micromotions at the implant-bone interface were analyzed for 3 different loadcases, "Seated leg-crossing" (joint force 940 N, impingement force 750 N), "Normal gait" (joint force 1820 N), and "Stumbling" (joint force 4520 N).

RESULTS

Within the same loadcase, percentages of interface area below 28 µm are nearly identical in all anchorage strategies. The average percentage of interface area below 28 µm is 31% for "Seated leg-crossing", 17% for "Normal gait", and 11% for "Stumbling". Maximal von Mises stresses in "Normal gait", for example, reach 12 MPa in the short peg, 48 MPa in the long peg, 15 MPa in 1 of the 2 long screws, and 85 MPa in 1 of the 3 short screws.

CONCLUSIONS

Common orthopaedic practice, to use peg or screw fixation alternatively according to bone availability or other clinical aspects, can be confirmed. The short peg may be a good alternative to the long peg with regard to the preservation of bone stock. However, the current study implies that the extent of potential osseointegration depends less on the chosen anchorage strategy but strongly on postoperative loading conditions. Total hip patients should be instructed on adequate postoperative activities.

Bipolar hip arthroplasty as salvage treatment for loosening of the acetabular cup with significant bone defects

Introduction: Revision arthroplasty of the hip is becoming increasingly important in recent years. Early primary arthroplasty and longer life expectancy of the patients increases the number of revision surgery. Revision surgery of hip arthroplasty is major surgery for the patients, especially the elderly, with significant risks concerning the general condition of the patient. The aim of this work is to evaluate the outcome of bipolar hip arthroplasty as a salvage procedure for treatment of loosening of the acetabular cup with significant acetabular bone defects after total hip replacement (THR) in multi-morbid patients.

Patients and methods: During the period from January 1^st 2007 to December 31^st 2011 19 revision hip surgeries were performed in 19 patients, in which the loosened acetabular cup was replaced by a bipolar head. The examined patient group consisted exclusively of female patients with an average of 75 years. The predominant diagnosis was “aseptic loosening” (84.2%). All patients in our study were multi-morbid. We decided to resort to bipolar hip arthroplasty due to the compromised general condition of patients and the major acetabular bone defects, which were confirmed intraoperatively. The postoperative follow-up ranged from 0.5 to 67 months (average 19.1 months).

Results: Evaluation of the modified Harris Hip Score showed an overall improvement of the function of the hip joint after surgery of approximately 45%.

Surgery was less time consuming and thus adequate for patients with significantly poor general health condition. We noticed different complications in a significant amount of patients (68.4%). The most common complication encountered was the proximal migration of the bipolar head.

The rate of revision following the use of bipolar hip arthroplasty in revision surgery of the hip in our patients was high (21%). Despite the high number of complications reported in our study, we have noticed significant improvement of hip joint function as well as subjective pain relief in the majority of patients. We clearly achieved clinically satisfactory results in 14 patients.

Conclusion: Bipolar hip arthroplasty is by no means to be regarded as standard procedure in revision surgery of THR. It provides an option or salvage procedure for patients with poor general condition in whom the quickest possible surgical intervention preserving mobility is required. This is particularly true for multi-morbid patients in whom sufficient acetabular fixation is not possible.

[Bone defect adjusted strategy in revision arthroplasty of the hip : Wich implant in wich situation? Innovations and approved methods]

BACKGROUND

Revision total hip arthroplasty is of rising importance, with 35,000 procedures a year in Germany.

OBJECTIVES

Primary stability of the revision implant, reconstruction of the anatomical hip center, reconstruction of bone stock, and permanent secondary integration are the main priorities.

METHODS

Current literature and examples from our own experience are presented.

RESULTS AND CONCLUSIONS

Novel developments from basic research and industrial partners extend the possibilities for treating affected patients. For an integrated therapy concept in implant selection criteria, such as situation and structure of the defect, combination with any remaining implants, causes of loosening and failure, implant allergy, and patient-specific parameters should be taken into consideration.

[Partial pelvic resection (internal hemipelvectomy) and endoprosthetic replacement in periacetabular tumors]

OBJECTIVE

Treatment of tumors of the pelvic girdle by resection of part or all of the innominate bone with preservation of the extremity. Implantation and stable fixation using a custom-made megaprosthesis to restore painless joint function and loading capacity. The surgical goal is to obtain a wide surgical margin and local tumor control.

INDICATIONS

Primary bone and soft tissue sarcomas, benign or semi-malignant aggressive lesions, metastatic disease (radiation resistance and/or good prognosis).

CONTRAINDICATIONS

Limited life expectancy and poor physical status, extensive metastatic disease, persistent deep infection or recalcitrant osteomyelitis, poor therapeutic compliance, local recurrence following a previous limb-sparing resection, extensive infiltration of the neurovascular structures and the intra- and extrapelvic soft tissues.

SURGICAL TECHNIQUE

Levels of osteotomy are defined preoperatively by a CT-controlled manufactured three-dimensional 1:1 model of the pelvis. Using these data, the custom-made prosthesis and osteotomy templates are then constructed by the manufacturer. The anterior (internal, retroperitoneal) and posterior (extrapelvic, retrogluteal) aspects of the pelvis are exposed using the utilitarian incision surgical approach. The external iliac and femoral vessels are mobilized as they cross the superior pubic ramus. The adductor muscles, the rectus femoris and sartorius muscle are released from their insertions on the pelvis and the obturator vessels and nerve are transected. If the tumor extends to the hip joint, the femur is transected at a level distal to the intertrochanteric line to ensure hip joint integrity and to prevent tumor contamination. A large myocutaneous flap with the gluteus maximus muscle is retracted posteriorly. The pelvitrochanteric and small gluteal muscles are divided near their insertion in the upper border of the femur. To release the hamstrings and the attachment of the sacrotuberous ligament, the ischial tuberosity is exposed. After osteotomy using the prefabricated templates, the pelvis is released and the specimen is removed en bloc. The custom made prosthesis can either be fixed to the remaining iliac bone or to the massa lateralis of the sacrum. The released muscles are refixated on the remaining bone or the implant.

POSTOPERATIVE MANAGEMENT

Time of mobilization and degree of weight-bearing depends on the extent of muscle resection. Usually partial loading of the operated limb with 10 kg for a period of 6-12 weeks, then increased loading with 10 kg per week. Thrombosis prophylaxis until full weight bearing. Physiotherapy and gait training. At follow-up, patients are monitored for local recurrence and metastases using history, physical examination, and radiographic studies.

RESULTS

Between 1994 and 2008, 38 consecutive patients with periacetabular tumors were treated by resection and reconstruction with a custom-made pelvic megaprosthesis. The overall survival of the patients was 58% at 5 years and 30% at 10 years. One or more operative revisions were performed in 52.6% of the patients. The rate of local recurrence was 15.8%. Deep infection (21%) was the most common reason for revision. In two of these cases (5.3%), a secondary external hemipelvectomy had to be performed. There were four cases of aseptic loosening (10.5%) in which the prosthesis had to be revised. Six patients had recurrent hip dislocation (15.8%). In four of them a modification of the inserted inlay and an implantation of a trevira tube had to be performed respectively. Peroneal palsy occurred in 6 patients (15.8%) with recovery in only two. There were 4 operative interventions because of postoperative bleeding (10.5%). The mean MSTS score for 12 of the 18 living patients was 43.7%. In particular, gait was classified as poor and almost all patients were reliant on walking aids. However, most patients showed good emotional acceptance.

[Total hip replacement in developmental dysplasia: anatomical features and technical pitfalls]

Total hip arthroplasty is the procedure of choice for most patients with advanced, symptomatic osteoarthritis due to congenital dysplasia of the hip. However, the complexity of arthroplasty is significantly increased because of anatomic abnormalities associated with dysplasia of the hip. In addition the relatively young age of patients may affect survival of the implant. From a biomechanical standpoint the primary surgical objective is reconstruction of the anatomical center of rotation. Independent of the pelvic bone stock the socket should be located as near as possible to the anatomical acetabular location. There are various operative strategies to ascertain sufficient stability of the socket. The anterolateral deficiency of the acetabulum can be reconstructed by bulk femoral autografting or bone impaction grafting. Furthermore controlled perforation of the medial wall or implantation of reinforcement rings and oval sockets have been described. Cementless, biological socket fixation shows superior long-term results compared to cemented cups, especially in these young patients. The location of the reconstructed acetabulum and the desired leg length influence the type of femoral reconstruction and in some cases femoral shortening is required. In this article endoprosthetic reconstructive options for developmental dysplasia of the hip are discussed depending on the femoral and acetabular deformity.