[Early assessment of the risk of later implantloosening using Roentgen Sterophotogrammetric Analysis (RSA)]. / Früherkennung des Risikos der späteren Implantatlockerung mittels der Röntgen Stereophotogrammetrischen Analyse (RSA).

BACKGROUND: Aseptic implant loosening is the most common cause of implant revisions in total hip and total knee arthroplasty. Roentgen Stereophotogrammetric Analysis (RSA) represents the current gold standard for the in-vivo assessment of implant fixation. PRESENT SITUATION: Long-term clinical trials have shown that continuous implant migration within the first two postoperative years correlates strongly with a later aseptic loosening. Thus, the implant migration measured with RSA can be regarded as a reliable surrogate marker for later implant loosening. Over the past 40 years, RSA has been continuously further developed, and the model-based RSA approach has reduced the effort involved since markers attached to implant are no longer needed. PERSPECTIVES: The RSA method is gaining importance in the certification process of new orthopaedic implants-for example, the Dutch Orthopedic Society has recommended phased-introduction and RSA studies for new hip implants. Furthermore, in the context of the new EU Medical Device Regulation (MDR), which took effect in May 2017, RSA gained relevance for investigating clinically unproven implants. Critics who associate MDR with hindering innovation can be countered in that the RSA method provides a predictive assessment of implant fixation after only two years of follow-up, which is significantly shorter than standard long-term clinical trials.

Modular tumor prostheses: are current stem designs suitable for distal femoral reconstruction? A biomechanical implant stability analysis in Sawbones.

INTRODUCTION: High loosening rates after distal femoral replacement may be due to implant design not adapted to specific anatomic and biomechanical conditions. MATERIALS AND METHODS: A modular tumor system (MUTARS®, Implantcast GmbH) was implanted with either a curved hexagonal or a straight tapered stems in eight Sawbones® in two consecutively generated bone defect (10 cm and 20 cm proximal to knee joint level). Implant-bone-interface micromotions were measured to analyze main fixation areas and to characterize the fixation pattern. RESULTS: Although areas of highest relative micromotions were measured distally in all groups, areas and lengths of main fixation differed with respect to stem design and bone defect size. Regardless of these changes, overall micromotions could only be reduced with extending bone defects in case of tapered stems. CONCLUSIONS: The tapered design may be favorable in larger defects whereas the hexagonal may be advantageous in defects located more distally.

[Functional electrostimulation for drop foot treatment : Clinical outcome]. / Funktionelle Elektrostimulation zur Therapie des neurogenen Fallfußes : Klinisches Outcome.

INTRODUCTION: Neurologic paralysis of the foot due to damage to the central nervous system is primarily caused by a cerebral insult. The ankle-foot orthosis (AFO), which is the classical conservative treatment option, is associated with drawbacks, e.g., increased contractures, limited mobilization from the sitting position, and cosmetic aspects. METHODS: Functional external electrostimulation (FES) is an suitable treatment method for patients with a central lesion and intact peroneal nerve. Based on this method, the neuroprosthesis is a dynamic therapy option in the form of an implantable nerve stimulator (ActiGait® system, Otto Bock, Duderstadt, Germany) which is placed directly on the motor branch of the peroneus nerve and results in active foot lifting. The aim of the present study is to evaluate the clinical effect of the ActiGait® system with regard to its suitability for everyday use by means of gait tests with an emphasis on time-distance parameters and to compare it with the current literature. RESULTS AND CONCLUSION: In this retrospective study, the clinical results after implantation of the ActiGait® system are presented and evaluated. In summary, the implantation of a neuroprosthesis in patients with stroke-related drop foot represents a sensible and promising therapy option.

[Alloarthroplasty versus above-knee amputation]. / Alloarthroplastik kontra transfemorale Amputation.

BACKGROUND: We report an unusual case of a 38-year-old physically active patient, who suffered a Ewing sarcoma during adolescence and was therefore treated with a tumor endoprostheses ex domo (replacement of distal femur and proximal tibia). Since then he had undergone a couple of surgical interventions for revision and is currently suffering from persistent pain in the leg concerned. An aseptic loosening of the tibial component was evident after radiologic examinations. Because he had suffered for so long our patient refused further surgery to retain the affected limb and he preferred amputation. OBJECTIVES: We would have taken the risk of a femoral residual limb that is much too short compared with a classical above-knee amputation. In this regard we saw difficulties in exoprosthetic treatment with functional limitations that could easily have influenced the outcome negatively. METHOD: Consequently, we decoupled the tibial component from the femoral one within the knee joint and thus performed a knee disarticulation leaving the femoral component. RESULTS: Postoperatively, we found a mostly harmonious gait pattern with a pure mechanical interim prosthesis regarding time-distance parameters, which may be even further improved with the final prosthesis. Sagittal joint angles are comparable to conventionally knee exarticulated ones. DISCUSSION: To date, no comparable case of such an alloarthroplasty, which could regain mobility with an exoprosthetic treatment has been highlighted in the literature. In the result, a knee disarticulation within the area of a knee arthroplasty leaving the femoral component is not inferior to"ordinary" knee disarticulation.

Hip joint function and reconstruction of the anterior femoral offset in patients with short stem vs. conventional THA.

In cases where mobility and joint function are impaired after implantation of a THA, weakening of hip movement in both extension/flexion and adduction/abduction may play a role due to shortening of the physiological lever arm of the hip muscles. Mechanical factors of influence include the lateral femoral offset, which affects the lever arm, and the antetorsion angle of the hip prosthesis, which affects the anterior femoral offset. This study aimed to investigate the effect of an altered antetorsion angle of the implant on the hip moments and gait patterns of the patient. For this study, 13 patients with a conventional stem on one side and a calcar-guided short stem implanted on the contralateral side were included. To determine the maximum hip moment, tests were performed on a dynamometer in extension/flexion and adduction/abduction in addition to gait analysis. As a control, a comparison was made with data from a reference group of 30 healthy subjects. Both implants showed similar symmetry indices. There was a significant difference between the implants for adduction moments (p < 0.001). The ratios between the directions of moments showed no significant differences. The joint function measured by isokinetic measurements and gait analysis remains comparable to the healthy control group after short stem arthroplasty, but shows slight changes after conventional stem arthroplasty.

Medium to long-term results after reconstruction of bone defects at the knee with tumor endoprostheses.

BACKGROUND AND OBJECTIVES: Limb salvage and reconstruction with tumor endoprostheses is considered as therapeutic standard in the treatment of bone defects at the knee. Few studies report long-term results so far. METHODS: Seventy-seven patients who had a cementless or cemented MUTARS endoprosthesis implanted were followed-up for a mean period of 46 months (3-128 months). The defects were due to primary tumor lesions in 69 cases or metastases in 8 cases. The distal femur (n = 49) or the proximal tibia (n = 28) was reconstructed predominantly with cementless implants (femur: 69%, tibia: 92%). The resection of the tumor was intraarticular in 46 and extraarticular in 31 patients. RESULTS: After 10 years probability of limb salvage was 92% with a recurrence rate of 3%. Complications were frequent with a revision rate of 58% and lead to a cumulative probability of survival of the initially implanted prosthesis of 57% after 5 years. Locking mechanism failure (n = 15) and aseptic loosening (n = 13) were the most frequent failure modes. CONCLUSIONS: Regardless of achieving a low recurrence rate and satisfactory functional results, we found a high complication rate after implantation of a megaprosthesis. This was particularly evident for extraarticular resections and cemented fixation, which should be avoided when possible.

[Revision hip stems: an analysis of the fixation]. / Femorale Revisionsprothesen : Eine Analyse der Verankerung.

BACKGROUND: Revision hip replacements are complicated surgeries because the femoral quality is often reduced by large substance losses. Stem fixation in terms of sufficient primary stability is therefore a great challenge for the orthopaedic surgeon. AIM: The aim of the present study was to examine two currently used prostheses in Germany (MHP and MRP) concerning their ability to securely bridge femoral defects. RESULTS: Up to a segmental metaphyseal defect, both stems showed sufficient fixation in our experimental setup. However, because of its predominantly distal fixation, the MRP stem would unnecessarily bridge proximal bone areas still capable of load bearing. In the presence of a transfemoral approach, the surgeon should favour the distal fixation mode because in this situation the proximal fixation option is absent. Therefore, the isthmus takes a key role for both stem designs.

[Foot drop treatment by implantation of a neuroprosthesis (ActiGait®)]. / Behandlung des Fallfußes durch Implantation einer Neuroprothese (ActiGait®).

OBJECTIVE: Gait improvement by restoring dorsiflexion using a neuroprosthesis implant. INDICATIONS: Foot drop with damage to the 1st motor neuron; passive mobility in ankle is possible; adult patients. CONTRAINDICATIONS: Foot drop with peripheral damage and injury to the peroneal nerve; already implanted stimulators (e.g., defibrillator, pacemaker, or pain stimulator); severe anesthesia risks in multimorbid patients. SURGICAL TECHNIQUE: Surgery in lateral position. Searching for the peroneal nerve after dorsal incision in the popliteal fossa, using the medial edge of the biceps femoris as anatomic landmark. After identification of the motor branch of the peroneal nerve by positive dorsiflexion after using electrostimulation apply the electrode cuff on the nerve. Epifascial implantation of stimulation body lateral at the middle third of the thigh over the tractus iliotibialis. POSTOPERATIVE MANAGEMENT: Pain-adapted full weight bearing, no knee flexion more than 90° for 4-6 weeks, activation of neuroprosthesis 3 weeks after surgery, physiotherapy with gait training is required. RESULTS: Between 2013 and 2015, implantation of the neuroprosthesis was performed in 21 patients (13 men/8 women) with chronic foot drop due to a central lesion. Significant improvement in walking speed measured with the 10 meter walk test (11.8 ± 5.4 s to 7.9 s ± 3.4; p = 0.007), in gait endurance with 6 min walk test (212.2 ± 75.5 m to 306.4 ± 96.4 m; p ≤ 0.001), and in gait performance using the Emory Functional Ambulation Profile (105.9 ± 49.7 s to 63.2 ± 31. 3 s; p ≤ 0.001). No patient required surgical revision. Postoperative bleeding was recorded in one case (4%). Patient satisfaction and improvement in mobility and quality of life could be achieved (95% and 90%, respectively).

Restoring mobility after stroke: first kinematic results from a pilot study with a hybrid drop foot stimulator.

OBJECTIVE: The objective was to obtain first insights into the kinematic and kinetic walking patterns resulting from an implanted functional electrical stimulation system in subjects with a drop foot caused by stroke. METHODS: Four subjects who experienced a stroke were chosen due to a comparatively long/short time after surgery and young/old at the stroke event were examined retrospectively with gait analysis. Kinematics and kinetics of normal walking were assessed in comparison with and without activated drop foot stimulation. RESULTS: In general, an improvement regarding spatiotemporal parameters as a result of the stimulation could be observed. Walking speed was increased by 45 % and stride length by 22 % after a mean usage of 7 (2-14) months, whereas both younger subjects improved significantly more. Dorsiflexion increased in all subjects on average from 1.3° to 11.6° during initial contact as well as from 11.3° to 17.0° during mid-swing and therefore implies an advantage of around 5.5 inch foot clearance. Pathologic elements like knee hyperextension during loading response and mid-stance, leg circumduction during swing or the increased hip flexion of the contralateral leg during mid-stance could be in general adjusted with stimulation. CONCLUSION: An implantable functional electrical stimulation system seems to be a promising treatment of drop feet following strokes. Further clinical investigations are necessary to confirm these first insights.

[Anatomic reconstruction of hip joint biomechanics: conventional vs. short-stem prosthesis]. / Die anatomische Rekonstruktion des Hüftgelenks: ein Vergleich von Kurz- und Standardschaft.

BACKGROUND: Currently, short cementless femoral stems are alternative implants to treat osteoarthritis in young patients with sufficient bone quality in order to get a more proximal load transfer. The purpose of the present study was to biomechanically compare joint reconstructions resulting from implantations of a short-stemmed and a conventional hip replacement. METHODS: 100 patients (50 short-stemmed and 50 conventional) were retrospectively examined. For evaluation of biomechanical parameters standardised pre- and postoperative X-rays (pelvic AP views) were used and digitally analysed. RESULTS: The horizontal femoral off-set increased within both groups (short: 2.0 mm and conventional: 3.3 mm), with a significant increase in the conventional group. The hip centre of rotation was significantly medialised after both procedures (short: 6.0 mm and conventional: 4.2 mm). Limb length was shorter preoperatively at the arthroplasty side, but increased thereafter (short: 2.1 mm and conventional: 2.6 mm). Compared to the native contralateral side the limb length was almost equal after THA (short: 0.7 mm and conventional: 0.8 mm). CONCLUSIONS: Our study shows that an almost anatomic reconstruction of hip joint biomechanics is possible with a short-stemmed prosthesis compared to a conventional stem, regarding limb length, centre of rotation and offset.

[Anatomic reconstruction of hip joint biomechanics with the bone preserving Silent Micro Hip™ prosthesis]. / Anatomische Rekonstruktion des Hüftgelenks mit der schenkelhalserhaltenden Silent Micro Hip™.

BACKGROUND: The design and the surgical technique of the Silent Micro Hip™ are different compared to other hip stems due to a conical shape for fixation within the metaphyseal femur. The purpose of the present study was to evaluate hip joint biomechanics of the Silent Micro Hip™ in comparison to other implants. Implant-specific differences are highlighted. MATERIAL AND METHOD: 150 consecutive patients (each group 50 Silent Micro Hip™, Nanos™ and SL-Plus™ MIA) were analysed retrospectively. For evaluation of biomechanical parameters pre- and postoperative X-rays (pelvic AP views) were used. RESULTS: The horizontal femoral offset and the limb length showed no significant difference between the Silent Micro Hip™ and the Nanos™ or SL-Plus™ MIA stem at the reconstructed hip. An almost anatomic reconstruction of hip joint biomechanics was reached with all three types of implants. CONCLUSIONS: The Silent Micro Hip™ allows for almost anatomic reconstruction of hip joint biomechanics. Short-term results support the bone-preserving reconstruction with a proximal femoral load transfer. Further studies on the mid- and long-term outcomes are ongoing.

[Transosseous refixation of the common extensor muscle tendons in chronic lateral epicondylitis with and without additional reconstruction of the LUCL--a retrospective evaluation of 101 patients]. / Die transossäre Refixation der Extensoren bei chronischer radialer Epikondylopathie mit und ohne Rekonstruktion des LUCL-Komplexes--eine retrospektive Analyse von 101 Patienten.

INTRODUCTION: The chronic lateral epicondylitis (EHR) as a common pathology of the elbow is often associated with posterolateral rotatory instability of the elbow (PLRI). After evaluation of intra-articular pathology by prior diagnostic arthroscopy, we aimed to build patient groups regarding the stability of the elbow joint. In patients with a stable elbow joint, open surgery with a debridement to the origin of the common extensor tendon and transosseous refixation was performed. Patients with relevant posterolateral rotatory instability, however, underwent an additional LUCL complex stabilisation using triceps tendon graft besides debridement as mentioned above. The purpose of this study was to evaluate and compare the clinical functional outcome between these groups. MATERIAL AND METHODS: 101 patients were included in our study. Arthroscopies were first performed on all patients to identify intra-articular pathological changes. In 26 patients with stable elbows, open surgery with debridement to the origin of the common extensor tendon and transosseous refixation was performed. For the other 75 patients who were found presenting a relevant posterolateral rotatory instability, a stabilisation of the LUCL in addition to the open procedure mentioned above was performed. Examinations and questionnaires were used for retrospective evaluation at follow-up. RESULTS: Both groups of patients revealed significant improvement in pain relief and elbow function. We observed no significant difference between the two methods concerning clinical and functional outcome. CONCLUSION: We recommend diagnostic arthroscopy with assessment of stability prior to the open performance to offer a more reliable evidence for surgical technique selection and therefore to achieve a better clinical outcome.

Periprosthetic tibial fractures in unicompartmental knee arthroplasty as a function of extended sagittal saw cuts: an experimental study.

Periprosthetic tibial plateau fractures (TPF) are rare but represent a serious complication of unicompartmental knee arthroplasty (UKA). As TPFs usually occur perioperatively, these can be associated with extended sagittal saw cuts during surgery. The aim of the study was to evaluate TPF as a function of extended sagittal saw cuts. The hypothesis was that extended sagittal saw cuts reduce the loading capacity of the tibial plateau and increase the risk of periprosthetic TPF. In a randomised study, standardised cemented Oxford UKA tibial component implantation was performed in six matched, paired fresh-frozen tibiae. In group A, a regular preparation of the tibial plateau was performed, whereas in group B a standardised extended sagittal saw cut was made at the dorsal cortex of the tibia. All tibiae were fractured under standardised conditions and fracture patterns and fracture loads were analysed. In group A, tibiae fractured with a mean load of F(max)=3.9 (2.3-8.5) kN, whereas in group B fractures occurred at a mean load of F(max)=2.6 (1.1-5.0) kN. The difference was statistically significant (p<0.05). Extended sagittal saw cuts in UKA weaken the tibial bone structure. Our results show that descendent extended sagittal saw cuts of 10 degrees reduce fracture loads by about 30%. Surgeons should be aware of the potential pitfalls of an extended sagittal saw cut, as this can lead to reduced loading capacity of the tibial plateau and increase the risk of periprosthetic TPF.

[Particle release in metal-on-metal bearings. A risk analysis]. / Partikelfreisetzung bei Metall-Metall-Gleitpaarungen. Eine Risikoanalyse.

Modern metal-on-metal bearings show very low wear rates but release particles and ions from the articulating surfaces into the joint and the whole organism. Especially during the run-in period an increased number of particles is produced. The released metal ions potentially trigger cytotoxic, cancerogenic and allergic reactions, which can impair the patient's health locally or systemically. Many surgeons fear a hypersensitivity reaction to the metal ions of the CoCr alloy in their patients. Today it is assumed that the incidence of these implant-related complications is very low but in some cases it will lead to early failure of the implant. Because the available alternative bearing combinations (ceramic-on-polyethylene and ceramic-on-ceramic) also bear the risk of severe complications, a final statement on the best and safest bearing choice for the patient cannot be made based on the currently existing data.